Eric A. Toschlog, Scott G. Sagraves, and Michael F. Rotondo
The Priority of the Airway
In the crucial initial management of the injured patient, securing the airway is quite literally the single most important priority; failure to oxygenate and ventilate represents the difference between life and death as well as functionality and disability. Airway loss initiates a terminal and irreversible cascade of events. Not only are hypoxia and hypoventilation common injury-related causes of mortality, but also they additionally represent one of the most common causes of preventable mortality following injury. The trauma patient represents a unique and exquisite airway challenge, from both anatomic and physiologic perspectives. The multisystem trauma patient represents the culmination of interrelated insults to oxygenation and ventilation, where under extreme duress, clinicians must rapidly recognize compounding injury and prioritize the airway in what may be multiple conflicting priorities.
BASIC AIRWAY EQUIPMENT AND PREPARATION
Preparation for Airway Management
Successful airway management starts with planning and preparation. Planning begins by assembling an airway kit or cart containing the necessary equipment for intubation. The practitioner should take the time to inventory the equipment prior to the intubation, ensuring function and availability.
The airway cart should consist of drugs, endotracheal tubes, airways, laryngoscopes, airway adjuncts, a variety of syringes and needles, and equipment to establish a surgical airway.
The primary components of the airway kit are the endotracheal tube and laryngoscope. The airway cart should have a variety of tubes in both cuffed and uncuffed types, including tubes down to a 2.0 internal diameter size for pediatrics, and a variety of stylet sizes. Both Miller and Macintosh laryngoscope blades should be included. In addition, the airway cart should be stocked with both the oropharyngeal airway (OPA) and nasopharyngeal airway (NPA) in all sizes. In the event of failed intubation, several airway adjuncts should be included in the standard airway cart. An array of adjuncts is now available to assist with difficult intubation and failed airway, including supralaryngeal airways, lighted wand stylets, retrograde intubation kits, a variety of video laryngoscopic devices, and the gum elastic bougie (GEB).
The goal of airway management in the trauma admitting area is to closely simulate the control of the operating room. Key personnel should work as a team to assure a successful intubation (Fig. 11-1). The optimal intubating team should consist of at least three members including the intubator, a respiratory therapist, and an assistant to maintain cervical spine alignment or to provide the Sellick maneuver to prevent aspiration.
FIGURE 11-1 The optimal rapid sequence intubation team is comprised of (1) the intubating provider at the head of the bed, (2) an assistant to the patient’s right to facilitate passage of necessary equipment from the airway cart (to the intubating provider’s right) and to provide cricoid cartilage pressure, (3) a provider to administer drugs to the patient’s left, and (4) a respiratory therapist to assist with airway maneuvers. Note the presence of full barrier precautions, pulse oximetry, telemetry, colorimetry, and two functioning large-bore intravenous catheters.
Monitoring and Troubleshooting
Pulse Oximetry. The pulse oximeter is a portable, noninvasive, and reliable device that measures SpO2. Although very accurate in analysis of peripheral oxygen delivery, the pulse oximeter may display inaccurate readings in the case of carbon monoxide poisoning, high-intensity lighting, hemoglobin abnormalities, and a pulseless extremity or in severe anemia.
Capnography. End-tidal carbon dioxide (ETCO2) detectors measure the partial pressure of carbon dioxide in a sample gas. The patient’s Paco2 is typically 2–5 mm Hg higher than the ETCO2 and a normal reading in a trauma patient is approximately 30–40 mm Hg. ETCO2 reading may be used to confirm placement of an endotracheal tube. The presence of carbon dioxide in the exhaled air strongly suggests correct placement of the endotracheal tube in the trachea in a perfusing patient. The disposable capnometer indicates the presence of carbon dioxide with a color change. The electronic capnometer provides the health care provider with a numerical ETCO2 and plots the CO2 concentration against time. Although the use of capnometry as an adjunct to monitor the patient’s exhaled carbon dioxide has met some success, conditions such as hypotension, increased intrathoracic pressure, and pulmonary embolus resulting in an increased dead space ventilation may decrease the accuracy of the capnometer.
Troubleshooting. The intubating team should have the patient attached to a cardiac monitor, blood pressure cuff, and pulse oximeter (Fig. 11-1). Intravenous access should be established. The patient should receive supplemental oxygen via a nonrebreather mask or a bag valve mask (BVM) depending on the patient’s inherent respiratory drive. The correct size of endotracheal tube should be brought to the bedside and a correctly sized stylet should be inserted. The endotracheal balloon should be checked for leaks. Once the balloon has been checked, a 10-cm3 syringe is left attached to the pilot balloon. A suction device with a large catheter tip should be readily available and be placed near the right side of the patient’s head. The laryngoscope handle/blade connection should be checked for a functional light source. A means to secure the endotracheal tube should be available. Dentures should be removed just before intubation, particularly if the patient is being bagged and his or her dentures allow for a tight mask seal. If cervical spine injury has been excluded, the patient should be positioned with the neck slightly flexed and the head slightly extended on an imaginary axis through the patient’s ears. Placing a pillow or towel under the patient’s occipital region and elevating the head approximately 10 cm may facilitate this position. Due diligence with respect to preparation of both personnel and equipment makes for a less stressful intubation and improves the practitioner’s chances of successfully intubating the patient.1
Manual Airway Maneuvers
Before any airway maneuver is undertaken, a quick visual inspection of the oropharyngeal cavity should be done. Any foreign or loose material should be swept clear with a gloved finger or removed with suction. Blood may be present in the mouth of a trauma patient and adequate suctioning is essential to maintaining an open airway. Administration of oxygen prior to suctioning may prevent hypoxemia due to prolonged suctioning. The tongue can cause airway obstruction in the unresponsive patient as it often lacks tone and falls into the oropharynx. Manual airway maneuvers serve to elevate the tongue out of the hypopharynx.
Jaw Thrust. The cervical spine should be kept in normal alignment. The provider should grasp the sides of the patient’s face with fingers 3-5 along the ramus portion of the mandible. The provider’s thumb is on the patient’s cheek and the index finger on the chin and lower lip. These two fingers can open the patient’s lips or serve to seal the mask on a BVM. The provider’s fingers should form an “E” with the three lower fingers and a “C” with the thumb and index finger. Force is applied to the angle of the mandible forcing the mandible forward and anteriorly, while simultaneously opening the mouth with the index finger on the chin.
Chin Lift. With either a free, gloved hand or another provider’s gloved hand, the provider’s thumb is placed into the patient’s mouth, the patient’s lower incisors and chin are grasped, and the patient’s mandible is lifted anteriorly. This maneuver supplements the jaw thrust and works to lift the mandible anteriorly, elevating the tongue out of the oropharynx.
Sellick Maneuver. The injured patient may have swallowed large amounts of air, or air has been forced into the stomach during BVM ventilation. The use of the Sellick maneuver, particularly during BVM ventilation, aids in preventing aspiration. The maneuver is accomplished by applying gentle posterior pressure with the thumb and index finger to the patient’s cricoid cartilage. This pressure causes the cricoid cartilage to be displaced posteriorly, effectively closing off the esophagus.
Basic Mechanical Airway Devices
Oropharyngeal and nasopharyngeal devices can be inserted into either the mouth or nose of the patient, serving to elevate the tongue out of the oropharynx. The OPA is a curved, plastic or hard rubber device, which comes in various sizes and has channeling for suction catheters. The device is sized by placing the OPA in the space between the patient’s ear and corner of the mouth. A correctly sized OPA will extend from the patient’s mouth to the angle of the jaw.
Indications for the use of the OPA include a patient who is unable to maintain his or her airway or to prevent an intubated patient from biting the endotracheal tube. Advantages for use of the OPA include the following:
1. Prevention of obstruction by the patient’s teeth and lips
2. Maintenance of the airway in a spontaneously breathing unconscious patient
3. Ease of suctioning
4. Use as a bite block in a patient who is having a seizure
The OPA is contraindicated in a conscious patient as it may stimulate a gag reflex. In addition, it does not isolate the trachea, nor can it be inserted through clenched teeth. It may obstruct the airway if it is improperly placed and can be dislodged easily. To place the OPA, the mouth is opened and the OPA is inserted with the curve reversed and the tip pointing toward the roof of the patient’s mouth. Using a twisting motion the OPA is rotated into position behind the base of the patient’s tongue. Alternatively, a tongue blade can be used to depress the tongue with the OPA placed directly into the oropharynx.
The NPA is a soft rubber or latex uncuffed tube that is designed to conform to the patient’s natural nasopharyngeal curvature. It is designed to lift the posterior tongue out of the oropharynx. Like the OPA, it is indicated for patients who cannot maintain their airway. The advantages of the NPA include ease and speed of insertion, patient tolerance and comfort, and effectiveness when the patient’s teeth are clenched. Disadvantages of the NPA include its smaller size, the risk of nasal bleeding during insertion, and lack of utility when a basilar skull fracture is suspected.2
The provider should first size the NPA by selecting an NPA that is slightly smaller than the patient’s nostril. The distance from the patient’s nose to earlobe determines the length. The NPA should be liberally lubricated with lidocaine gel prior to insertion. The right nare is preferentially chosen, as it is typically larger. Gentle pressure should be applied until the flange rests against the patient’s nostril. After a basic mechanical airway has been inserted, the patient should be oxygenated with supplemental oxygen or a BVM.
Bag Valve Mask
The BVM assists the provider with oxygenation and ventilation in the apneic or hypoventilating patient. With an effective mask seal and an open airway, the BVM can deliver tidal volumes approaching 1.5 L and nearly 100% inspired oxygen with an attached oxygen reservoir. The BVM consists of a bag with a volume of 1.6 L and a standard face mask attached via a oneway, nonrebreathing valve. A reservoir bag and oxygen source is attached to the opposite end of the bag. Multiple sizes are available to treat neonatal, infant, children, and adult patients. To effectively use the BVM, a second provider may be required to establish a properly fitted mask seal while the second provider squeezes the bag. Maintenance of oxygenation and ventilation can be improved by utilizing a basic mechanical airway and proper jaw thrust and chin lift techniques while “bagging” the patient.
ASSESSMENT OF THE AIRWAY
A single indicator has not been identified that accurately predicts the inability to intubate. However, an attempt at airway assessment is mandatory to assist with the prediction of difficulty to intubate or ventilate.3
Time permitted, a history should be quickly obtained. The patient should be interrogated as to prosthetic dental devices, any previous difficulty with anesthesia or intubation, sleep apnea, trismus, and the timing of his or her last meal.
A general assessment of the oropharynx, nose, maxilla, mandible, and neck should be rapidly undertaken. An assessment of the patient’s overall level of consciousness (e.g., Glasgow Coma Score) and the ability of the patient to open his or her mouth should also be performed. If possible, have the patient stick out his or her tongue to evaluate the size of the tongue. The vocal quality of the patient should be noted during the physical exam, as well. The presence of stridor usually indicates some degree of injury to the upper airway. Assess for dentures or other prosthetic devices that may need to be removed prior to intubation.
INTUBATION OF THE TRACHEA
The majority of injured patients are able to undergo successful orotracheal intubation (OTI). In compliance with the ATLS course, the preferred definitive airway is tracheal intubation through the mouth using direct laryngosocopy.1
Guidelines for Emergency Tracheal Intubation
Indications for intubation relate to the following three simple questions:
• First, is the patient able to oxygenate and ventilate?
• Second, is the patient able to maintain an airway?
• Third, will the underlying injury and physiology of the patient lead to a failure to maintain the airway, oxygenate or ventilate?
The practice management guidelines of the Eastern Association for the Surgery of Trauma (EAST) for tracheal intubation secondary to trauma reveal no Level I data (evidence from randomized, controlled trials) that predict the need for urgent intubation.4 The guideline calls for emergency tracheal intubation in trauma patients exhibiting the following characteristics:
• Acute airway obstruction
• Severe hypoxemia despite supplemental oxygen
• Severe cognitive impairment (Glasgow Coma Scale score ≤8)
• Cardiac arrest
• Severe hemorrhagic shock
In concordance with ATLS, the EAST guidelines promulgate the concept that OTI utilizing direct laryngoscopy is the procedure of choice for airway control following trauma.4
Anatomy and Technique of Direct Laryngoscopy and Intubation
Success in intubating the injured patient is dependent on thorough knowledge of the anatomy of the upper airway and a meticulous adherence to proper technique. The vocal cords lie posterior and inferior to the pliable epiglottis, which should be visualized as a constant reference point during laryngoscopy. The posterior-most esophagus may be lifted into view with sufficient elevation of the epiglottis. Since the majority of intubations occur prior to cervical spine clearance, head and neck immobilization is of highest priority. In the rare instance that the cervical spine is cleared, the patient should be placed in the sniffing position initially (extension of the head, slight flexion of the lower cervical spine), which optimizes the alignment of the oral, pharyngeal, and laryngeal axes.
Following preparation of equipment and personnel, the laryngoscope is grasped firmly with the left hand. It should be emphasized that the right hand should be kept free, for suctioning, manipulation of oral structures, and placement of the endotracheal tube. Selection of a straight versus curved blade has less to do with proven efficacy in a particular scenario than the comfort and proficiency of the laryngoscopist with a particular blade. In general, the straight blade is utilized to pass beneath, and directly elevate, the epiglottis. The straight blade is inserted into the esophagus, with the blade withdrawn slowly under direct visualization to expose the glottic opening. The same technique can be applied with a curved blade of sufficient size, although the curved blade technique typically utilizes insertion of the tip of the blade into the vallecula, with anterior traction of the epiglottis, exposing the glottic opening. The tongue should be displaced by the blade to the patient’s left for best visualization of the epiglottis.
The motion and direction of the laryngoscope in the left hand during laryngoscopy is of critical importance to safe and successful intubation of the trachea. The proper technique of laryngoscopy employs upward motion of the laryngoscope in the parallel plane of the handle. A “rocking” motion, during which the handle is rotated counterclockwise and posterior, should never be used. This posterior circular motion can impart dangerous extension on the cervical spine or fracture or dislodge teeth. In addition, the left elbow should not be placed on the bed or spine board for stabilization. As the blade is positioned to visualize the glottic opening, the right hand can be utilized to employ the BURP maneuver if the glottic opening is not readily visible. This technique includes Backward, Upward, Rightward, Pressure on the thyroid cartilage and is distinct from the Sellick maneuver.
RAPID SEQUENCE INTUBATION
Intubation by rapid sequence induction (RSI) has become the gold standard for management of the airway in trauma and critical illness. The technique of RSI has been demonstrated to increase intubation success rates and reduce complications compared to pre-RSI techniques in a variety of emergent settings.5–9 RSI benefits include provision of optimal intubating conditions for injured patients, rapid airway control, high success rates, and reduction of pulmonary aspiration. The adaptability of RSI to individual patient conditions renders the technique optimal for airway control in the injured.
First developed to facilitate operating room intubations in patients with full stomachs, thereby minimizing risk of aspiration,10 the technique is now widely utilized by prehospital paramedics,11,12 emergency medicine physicians,13and trauma surgeons, with a high reported intubation success rate by nonanesthesiologists.5,14 Approximately 80% of intubations performed in North American emergency departments utilize RSI, with a 90% success rate by the first intubator.14 In the technique of RSI, laryngoscopy and intubation are facilitated by use of sedating induction agents and short-acting neuromuscular blockade (NMB). Rapid sequence intubation (RSI) can be divided into five phases: (1) patient and equipment preparation, (2) preoxygenation, (3) premedication, (4) paralysis, and (5) placement of the tube. A time line for RSI is demonstrated in Table 11-1.
TABLE 11-1 How We Do It: Steps and Timing of Rapid Sequence Intubation in a 70-kg Adult
Although significant injury with physiologic instability may preclude prolonged preparation for RSI, all efforts should be made to allow for individualized assessment of comorbid conditions, airway status, predictors of difficult intubation, and anticipated pharmacologic regimen. The selection and sequence of pharmacologic agents should be determined, with all agents ready and available in clearly labeled syringes. A horizontal approach to the preparatory phase of RSI is optimal, during which multiple personnel with predetermined responsibilities and positions work simultaneously (Fig. 11-1). In this manner, the preoxygenation phase is initiated during preparation
Although not originally considered an essential component of RSI, preoxygenation is now considered optimal if the oxygenation, ventilation, and hemodynamic status of the patient permit. The purpose of preoxygenation is to replace the nitrogen-dominant room air occupying the pulmonary functional residual capacity with a 100% oxygen reservoir, such that saturation of arterial hemoglobin (SaO2) is prolonged. Preoxygenation can be accomplished by gently assisting spontaneous respirations with 100% oxygen or simply allowing the patient to breathe 100% oxygen. Forceful BVM ventilation should be assiduously avoided during the intubation sequence, as it may produce unnecessary gastric distention, increasing the risk for pulmonary aspiration of gastric contents. Recommendations for the duration of preoxygenation necessary for optimal hemoglobin saturation range from 3 to 5 minutes; however, the effectiveness of preoxygenation is dependent on the physiologic status of the patient as well as age, size, and comorbid conditions. For example, an optimally preoxygenated healthy 70-kg adult will maintain SaO2 over 90% for approximately 8 minutes, an obese adult less than 3 minutes, and a 10-kg child less than 4 minutes.15 More importantly, the desaturation from 90% SaO2 to 0% occurs much more rapidly than the fall from 100% to 90%. The approximate Pao2 at 90% SaO2 is 60 mm Hg, falling to 27 mm Hg at an SaO2 of 50%. An injured patient with little compensatory reserve can decline from 90% to 0% literally in seconds.
PHARMACOLOGY OF RAPID SEQUENCE INTUBATION
It is imperative that providers caring for the injured be facile with all pharmacologic agents utilized for RSI, including both barbiturate and nonbarbiturate hypnotics, neuromuscular blocking agents, benzodiazepines, dissociative agents, and opiates (Table 11-2). A “one method fits all” approach is not always applicable,16 and each patient should be individualized based on type and mechanism of injury, comorbidities, and potential for adverse events. However, the majority of trauma patients can be effectively intubated using a generalized pharmacologic regimen.
TABLE 11-2 Pharmacology of Rapid Sequence Intubation
Clinical predictors of need for sedation and paralysis have been identified. In data from a prospective study of endotracheal intubation, factors associated with drug-facilitated intubation, defined as intubation facilitated by the use of sedatives or paralytics, included clenched jaw or trismus, declining verbal Glasgow Coma Scale score, and use of cervical spine precautions.17 The vast majority of patients currently undergoing RSI received both sedative and paralytic agents. Evidence-based principles identified by the EAST airway workgroup for drugs administered during OTI include the following:4
• Neuromuscular paralysis
• Regimen that maintains hemodynamic stability
• Regimen that minimizes intracranial hypertension
• Regimen that prevents vomiting
• Regimen that prevents intraocular content extrusion
Airway stimulation, including laryngoscopy and endotracheal tube placement, results in the pressor response, an intense autonomic sympathetic discharge producing tachycardia, hypertension, and increased intracranial pressure.10,18The degree of airway stimulation is proportional to the magnitude of the pressor response. Correspondingly, increased intragastric, intrathoracic, and intracranial pressures may result from Valsalva, bronchospasm, or coughing. As the foundation of RSI relates to abrogating the untoward effects of airway stimulation, preinduction agents are routinely utilized to blunt the physiologic response to laryngoscopy and endotracheal tube placement. A common mnemonic for the preinduction regimen is LOAD, which includes Lidocaine, Opiates, Atropine, and a Defasciculating agent, although atropine is typically utilized in pediatric populations only.
Opioids. Depth of sedation may correlate with speed of intubation in RSI.19 The sedative and analgesic effects of opioids may provide benefit to the injured patient prior to induction. A commonly used opioid for RSI in the prehospital and emergency department setting is fentanyl, which at 5.0 mcg/kg has been shown to be hemodynamically neutral compared to midazolam and thiopental during RSI.19 Fentanyl effectively blunts airway reactivity,20 and confers the significant added benefit of analgesia in the injured patient.
Benzodiazepines. Benzodiazepines, a family of gamma aminobutyric acid (GABA) agonists, have been utilized in RSI for sedation. Midazolam is the most widely studied agent, having favorable pharmacokinetics for RSI, including rapid onset and short half-life. Advantages include hemodynamic neutrality and retrograde amnesia, although onset is slower than comparable agents and the intubation reflex is not attenuated,19 rendering it less commonly used in RSI protocols than opioids.
Antiarrhythmics. Despite a great deal of controversy regarding the potential benefits of lidocaine during RSI, it is a preinduction agent common to RSI protocols,21 and is advocated in many emergency airway courses. Lidocaine has a number of theoretical beneficial preintubation effects, including abrogation of airway reactivity following placement of the endotracheal tube, the tachycardic response to intubation, and succinylcholine-induced myalgia and fasciculations.22 The two primary potential benefits of lidocaine use in RSI are to mitigate against reflex bronchospasm and increased intracranial pressure. Although definitive data are lacking regarding effects on intracranial pressure, the potential benefits outweigh the negligible side effects of the RSI dose.
Beta-Adrenergic Blockers. Esmolol has been utilized as a preinduction agent for mitigation of the tachycardic component of the pressor response. In comparison to lidocaine and fentanyl, esmolol has demonstrated superiority in attenuating the pressor response.23 Beneficial pharmacokinetics include rapid onset and short action; however, the bradycardic and negative inotropic effects of esmolol may blunt the compensatory response to hemorrhage. The cardiac effects may produce corresponding reductions in cerebral blood flow. Therefore, esmolol should be considered only in controlled circumstances in which hemorrhage of brain injury have been definitively excluded. The availability of other safer agents that effectively minimize the pressor response relegates beta-blockers to clear second-line status.
Defasciculation Paralytic Agents. Succinylcholine, the standard neuromuscular blocking agent utilized for RSI, produces significant myoclonal fasciculations, prompting a rise in intracranial pressure in patients at risk for intracranial hypertension. Therefore, a defasciculating dose of a competitive neuromuscular blocking is administered during RSI. Common defasciculating agents include vecuronium and rocuronium, and, less commonly, pancuronium. Defasciculating doses are administered as 10% of the paralyzing dose, given 3–5 minutes prior to administration of succinylcholine. It is unusual for defasciculating doses of neuromuscular blockers to cause apnea. However, patient weight is commonly an estimate during RSI following injury, and preparations to assist with ventilation should be made.
The perfect induction agent would possess rapid onset and elimination, render the patient unconscious but also amnestic, possess analgesic properties, and have negligible side effects. In injured and critically ill patients, the ideal agent would produce little cardiovascular effects and maintain cerebral perfusion pressure. Regrettably, such an agent does not yet exist. Because many agents produce side effects, including myocardial depression with the potential for hypoperfusion, careful attention should be dedicated to the selection of individual agents.
Etomidate. Etomidate is a short-acting carboxylated imidazole hypnotic agent frequently utilized for rapid sequence induction. It possesses ideal characteristics for urgent and emergent RSI in trauma patients, including rapid onset and clearance, reduction in cerebral metabolic rate,24 and negligible effects on hemodynamics. This favorable pharmacokinetic profile has led to the widespread use of etomidate for RSI in head injury and hemodynamically labile patients. Accordingly, the American College of Surgeons Committee on Trauma added etomidate to the Advanced Trauma Life Support course as an induction agent for hypotensive trauma patients.1 The most significant side effect of etomidate relates to adrenal insufficiency, as it produces a reversible blockade of adrenal 11-beta-hydroxylase. In patients at risk for adrenal insufficiency, including head-injured, mechanically ventilated, and septic populations, etomidate has been independently correlated with reductions in serum cortisol.25,26 The controversial question relates to whether transient adrenal suppression produces lasting effects on outcome. In a recent large single-center study, a single induction dose of etomidate was independently associated with ARDS and multiple organ dysfunction syndrome.27 Further studies are warranted to determine the long-term safety of etomidate for RSI; however, given the multiple favorable characteristics of the drug, etomidate remains the standard induction agent in most RSI protocols.
Propofol. Propofol is a nonbarbiturate hypnotic agent that rapidly induces deep sedation and significant relaxation of laryngeal musculature.10 When used for induction, propofol produces intubation conditions equal to thiopental and equal to or superior to etomidate.28 Propofol should be used with caution in head-injured or hemodynamically labile patients due to a consistent hypotensive effect and potential reduction of cerebral blood flow.
Barbiturates. Thiopental is the most commonly used barbiturate for RSI. Like other induction agents, thiopental has rapid onset and clearance. In the aeromedical setting, thiopental has been shown equally efficacious to etomidate as an adjunct to RSI.29 Similarly, in an evaluation of 2,380 RSI procedures, patients were more likely to be successfully intubated using thiopental or propofol as compared to etomidate or a benzodiazepine.28 Thiopental reduces cerebral oxygen consumption and exhibits anticonvulsant effects, rendering it useful in closed head injury (CHI). However, the significant limitation of thiopental use in trauma relates to inhibition of central nervous system sympathetic response. Consequently, thiopental produces reduced myocardial contractility and systemic vascular resistance, inducing hypotension. Therefore, it is best reserved for patients who are euvolemic and normotensive, limiting its application in critically ill patients. Methohexital is an additional barbiturate that has been used for RSI. It exhibits similar effects to thiopental, although it is significantly more potent and has shorter onset and duration than thiopental.
Dissociative Agents. Ketamine, a rapid-onset dissociative sedative and anesthetic agent, is frequently used for RSI in the pediatric population and in adults with chronic obstructive pulmonary disease. In addition to its sedative effects, ketamine exhibits the beneficial properties of potent analgesia and a partial amnesia. As a sympathomimetic agent, ketamine may induce tachycardia and increased blood pressure. In addition, ketamine induces cerebral vasodilatation, potentially exacerbating intracranial hypertension. Trauma patients with documented or potential CHI should therefore not undergo induction for RSI with ketamine.
Neuromuscular Blocking Agents
Pharmacologic paralysis represents an integral component of RSI, facilitating emergent intubation for more than three decades.30 Paralysis of facial musculature facilitates visualization during laryngoscopy, confers total control of the patient, and reduces complications during intubation. Prehospital NMB has been demonstrated to be safe,8,9 and to improve intubation success in injured patients undergoing RSI.31,32 Potential adverse effects should be diligently assessed, particularly with use of succinylcholine. In addition, preparations for rescue techniques must be made prior to administration of a paralytic agent, in the event of intubation failure. Because paralytic agents provide no sedative, analgesic, or amnestic effect, it is imperative to combine paralytic use with an appropriate induction agent.
Succinylcholine. Succinylcholine, a depolarizing acetylcholine dimer, acts noncompetitively at the acetylcholine receptor in a biphasic manner to produce muscular paralysis at the motor end plate. Succinylcholine stimulates all muscarinic and nicotinic cholinergic receptors of both parasympathetic and sympathetic systems. Initial brief depolarization results in clinically notable muscular fasciculations, followed by sustained myocyte depolarization. Succinylcholine degradation is dependent on hydrolysis by pseudocholinesterase, and resistant to acetylcholinesterase. Due to rapid onset of action and short half-life, succinylcholine remains the gold standard for RSI in patients not at risk for adverse events. The standard dose of succinylcholine for RSI is 1.0 mg/kg, although recent data suggest a smaller dose of 0.5–0.6 mg/kg is sufficient for RSI,33 facilitating more rapid resumption of spontaneous respiration. Intramuscular injection of succinylcholine has been described, although the required dose, 4 mg/kg, is higher, and onset is slower, than intravenous injection.
A clear understanding of the potential adverse effects of succinylcholine is critical to its appropriate use in RSI. Contraindications are primarily related to conditions that accentuate the hyperkalemic effects of succinylcholine, as it normally produces a 0.5- to 1.0-mEq/L elevation of serum potassium. Contraindications related to hyperkalemia include thermal injury of age exceeding 24 hours, although receptor upregulation likely does not become clinically relevant until postburn day 5. Therefore, it is safe to use succinylcholine for RSI in most acute burns. Contraindications include crush injury or rhabdomyolysis with hyperkalemia, congenital or acquired myopathies, and conditions of subacute and chronic upper and motor neuron denervation including paralysis and polyneuropathy of critical illness.10Contraindications related to known comorbid conditions include history of malignant hyperthermia and pseudocholinesterase deficiency. In addition, succinylcholine is reported to raise intragastric and intracranial pressure due to muscle fasciculations, and may contribute to increased intraocular pressure. It should be used with caution in head injury and penetrating globe injury, although the evidence that succinylcholine raises intraocular pressure is anecdotal at best.34
Nondepolarizing Agents. Nondepolarizing NMBAs, through competitive blockade of acetylcholine transmission at postjunctional, cholinergic nicotinic receptors, provide an alternative for patients not appropriate for succinylcholine. The aminosteroid compounds, including rocuronium, pancuronium, and vecuronium, represent the commonly used NMBAs for RSI. Nondepolarizing agents for RSI are selected based on the ability to best approximate the rapid onset and elimination of succinylcholine. The most intensively studied nondepolarizing agent utilized for RSI is rocuronium, which exhibits short onset and intermediate duration of action. When contraindications to succinylcholine exist, rocuronium produces acceptable intubating conditions and should remain in the RSI armamentarium as an alternative to succinylcholine.
Cricoid Cartilage Pressure (Sellick Maneuver)
The Sellick maneuver is reported to reduce aspiration and improve vocal cord visualization during RSI. The efficacy of Sellick maneuver requires a force of greater than 40 N. When attempting the Sellick maneuver, proper technique is imperative. In a review of videotaped RSI evaluating deviations from RSI protocol in emergency medicine residents, 45% employed improper use of the technique.35
Accurate confirmation of tube placement is critical. The first method to confirm placement is visualization of the endotracheal tube passing through the vocal cords, although this relies on the subjective impression of the operator and is not infallible. Other useful but nonspecific methods include auscultation of breath sounds in both lung fields, and visualization of both rise and fall of the chest and endotracheal tube condensation with exhalation. The standard confirmatory method for RSI is detection of exhaled carbon dioxide, through use of capnography or colorimetric end-tidal devices, which change from purple to yellow in the presence of exhaled carbon dioxide.36 The two primary clinical circumstances that may render the colorimetric device inaccurate include false-positive detection after esophageal intubation when sufficient carbon dioxide is present in the esophagus and false-negative detection during cardiac arrest with undetectable levels of tracheal carbon dioxide. If color change is not noted within two to three breaths, improper placement is likely and the endotracheal tube should be replaced.
Complications and Outcomes after Rapid Sequence Intubation
Success rates for RSI are well established, and a recent international study including a database with over 10,000 intubations noted a success rate exceeding 97% for trauma patients.37 However, complications do occur. Sedative and paralytic agents utilized in RSI place injured patients at risk for cardiovascular collapse, diminution of respiratory effort, pulmonary aspiration, and abrupt loss of airway. The primary complication of RSI involves airway failure, particularly esophageal intubation. The National Emergency Airway Registry (NEAR) classifies adverse events related to intubation as immediate, technical, and physiologic.37 Immediate events include witnessed aspiration, airway trauma, and undetected esophageal intubation. Technical events include recognized esophageal intubation and mainstem intubation. Physiologic events, often difficult to separate from underlying patient conditions related to injury, include pneumothorax, dysrrhythmia, and cardiac arrest.
ALTERNATIVES AND ADJUNCTS TO ENDOTRACHEAL INTUBATION
Nasotracheal intubation (NTI) is identified within the ATLS course as an alternative to OTI under select circumstances.1 Any discussion of NTI should begin by noting two absolute contraindications: apnea and severe midface trauma or suspicion of basilar skull fracture during which NTI could breech the cranial vault. Relative contraindications include coagulopathy, combativeness, intracranial hypertension, and suspected upper airway obstruction. NTI should also be avoided in patients with little oxygenation or ventilatory reserve due to significant delay incurred with the technique. Because of contraindications, failure rate, and complications, NTI has been nearly supplanted by RSI. The primary indication for NTI relates to the difficult airway. In a spontaneously breathing patient with an anticipated difficult airway in whom RSI is predicted to fail, NTI can be considered for tracheal intubation.
Following preparation of all necessary equipment, as well as planning an algorithm for procedure failure, the patient is preoxygenated as in RSI. The nares, nasopharynx, and trachea should be anesthetized. Lidocaine jelly or topical cocaine solution can be instilled into the selected nare, topical anesthetic sprayed into the oropharynx and nasopharynx, and lidocaine solution injected through the cricothyroid membrane. An appropriate size tube should be selected, typically having an internal diameter of 6.0–7.5 mm. The tube should be well lubricated and gently inserted into the nare, with the tip directed toward the occiput. When the tube passes into the posterior nasopharynx, it should be directed caudad, and resistance is commonly encountered. The tube should be rotated approximately one quarter turn toward the opposite nare, and advanced. When the tube advances into the distal nasopharynx, it should be restored to neutral and advanced. When breath sounds are heard through the tube (condensation may be visible), the tube should be advanced carefully but rapidly approximately 3–5 cm. If the tube has entered the trachea, the patient will cough repeatedly, and condensation may be seen. Placement should be confirmed with auscultation of breath sounds and use of an ETCO2 detector.
First described by Butler and Cirillo in 1960 as an alternative to conducting unplanned preoperative tracheostomies,38 retrograde endotracheal intubation (REI) represents another potential adjunctive airway rescue procedure. Conceptually REI involves needle cannulation of the trachea through the cricothyroid membrane, with passage of a flexible guide wire or epidural catheter into the oropharynx (Fig. 11-2). If a catheter is utilized, it can be affixed to the Murphy’s eye of an endotracheal tube, which is pulled in an anterograde fashion into the trachea. When the ET tube is at the cricothyroid membrane, the catheter is cut flush with the skin and removed. More commonly, an ET tube is passed over a flexible guide wire or obturator into the trachea, with the wire removed by transection at the skin and withdrawal through the oropharynx. Current commercial kits include a large-bore needle, a flexible guide wire, and a thicker flexible obturator to guide passage of the ET tube.
FIGURE 11-2 Retrograde intubation. An epidural size 17 Tuohy needle is inserted through the cricothyroid membrane as close to the upper border of the cricoid cartilage as possible and angled cephalad (A). An epidural catheter (B) is advanced through the vocal cords into the oropharynx and pulled out of the mouth. The epidural needle is withdrawn, and the catheter is tied to the Murphy’s eye of a size ID 7- to 8-mm endotracheal tube (C), which is then pulled thorough the vocal cords. Once through or at the vocal cords, the endotracheal tube is pushed into the trachea, and once in position, the epidural catheter can be cut at the skin. Modifications include threading the endotracheal tube or a tube changer over the catheter or a J wire, and railroading the endotracheal tube into the trachea; or feeding the distal end of a J wire through the suction port of a bronchoscope over which an endotracheal tube has been loaded.
The cited mean time to intubation utilizing REI has been reported to be from approximately 1 minute in simulators39 and cadavers40 to approximately 3–5 minutes in actual patient scenarios.41,42 A recent retrospective review of REI over an 8-year period at a Level I trauma center documented use of the technique in only eight patients (0.5% of intubations), with success and complication rates of 50% and 38%, respectively.42
Gum Elastic Bougie
The GEB or Eschmann stylet is a semirigid, malleable endotracheal tube introducer that has been used for airway emergencies in a variety of settings. The 60-cm bougie, which has a diameter of 5 mm, is angled at 40°, 3.5 cm from the distal end. During difficult laryngoscopy, when the vocal cords are not well visualized, the GEB is advanced to the level of the epiglottis, with the angled portion directed anteriorly. With further advancement, the tube may enter the trachea, and if successful, a “washboard” effect is palpated, as the bougie tip passes over tracheal rings. An ETT can then be passed over the GEB into the trachea.
If a smooth unobstructed course is encountered, and the GEB passes greater than 40–45 cm, a presumed esophageal intubation has occurred. In a prospective blinded trial in 20 human cadavers, the accuracy of tracheal ring “clicks” for tracheal intubation was assessed.43 Overall, 93% of tracheal placements were correctly identified, with ring clicks being 95% sensitive for tracheal intubation. In a recent review of 1,442 prehospital intubations, the GEB was utilized in 41 patients.44 Of the 3% requiring GEB use, intubation was successful in 33 cases (78%).
Esophageal Tracheal Combitube (ETC)
The ETC is a relatively new device that is primarily used as a rescue airway in the prehospital arena. Although inserted as a single tube, it is essentially a two-tube system with a divider in the distal tube. The device has two balloons: one proximal to occlude the oropharynx and a second balloon distally to occlude either the esophagus or trachea depending on into which structure the device is placed (Fig. 11-3). The ETC is inserted blindly and commonly is inserted into the esophagus. Both balloons are inflated. The longer, blue tube is ventilated first. If sounds are auscultated in the chest and there are no sounds auscultated over the epigastrium, the ETC is in the esophagus and ventilation should continue through the blue tube. If sounds are heard in the epigastrium, this suggests that the ETC is in the trachea. Ventilation should then be changed to the clear, shorter tube, while not changing the position of the ETC. Indications for its use include the following:
1. Immediate intubation cannot be performed
2. Unsuccessful endotracheal intubation in a patient requiring an airway
3. The patient may be entrapped and access to the patient’s head is poor
4. Direct visualization of the larynx cannot be obtained due to secretions
FIGURE 11-3 (A) Lateral photograph of the combitube double-lumen tube. (B) The combitube in place for emergency airway control. The tube is inserted blindly by lifting the jaw and tongue upward until the two printed rings (R) are at the teeth. The tip of the tube usually enters the esophagus. The pharyngeal cuff (P) is inflated with 100 mL of air and, when correctly placed, seals off the nasopharynx and oral cavity. The distal cuff (E) is inflated with 15 mL of air. Ventilation through the longer (blue) connecting tube (L) will inflate the lungs via the eight side holes in the pharyngeal portion of the combitube (as illustrated). If no breath sounds are heard, ventilation is attempted through the other lumen (the shorter tube) as the distal tube and cuff (E) has probably entered the larynx.
Contraindications for ETC use include age less than 16 years and height less than 5 ft.
Potential advantages include its ease in insertion, the ability to ventilate through either tube, no requirement of visualization during insertion, and prevention of aspiration with inflation of the proximal balloon. Disadvantages to ETC use include: endotracheal intubation becomes more difficult as the ETC obscures the trachea, the trachea cannot be directly suctioned with the ETC in place, and it cannot be used in the conscious patient with a gag reflex.
Laryngeal Mask Airway
The laryngeal mask airway (LMA North America, Inc, San Diego) was introduced over 20 years ago by Dr Archie Brain,45 and has evolved into a viable temporizing rescue maneuver for the difficult airway. The LMA Classic™ consists of a flexible tube attached to an inflatable cuff that is passed into the hypopharynx and advanced over the larynx (Fig. 11-4). When the cuff is inflated, a seal is created around the glottic aperture, permitting selective ventilation of the trachea. Since introduction of the LMA, a number of incarnations have ensued, each with theorized situation-specific advantages.
FIGURE 11-4 (A) Anterior and lateral photograph of the Brain laryngeal mask airway (LMA). (B) The LMA in position. The LMA is inserted blindly with the cuff deflated or partly inflated over the tongue and pushed as far as it will go. The cuff is inflated with 20–30 mL of air. When correctly placed, the cuff lies in the pharynx, its tip obstructing the upper esophageal lumen, and the mask interposed between the base of the tongue and the posterior pharyngeal wall to open the airway. Patients can breathe spontaneously through it (when it is used to reduce upper airway obstruction) or can be ventilated via the LMA if apneic.
The LMA may be utilized in the difficult airway during resuscitation in an unconscious patient, when intubation skills are lacking or intubation has been unsuccessful. Accordingly, the primary clinical indications for use of the LMA include: airway rescue and maintenance in an “unable to intubate, able to ventilate” situation, and as a first-line adjunct in an “unable to intubate, unable to ventilate” situation. Under the latter condition, LMA placement should proceed while preparations for cricothyroidotomy are underway. Under such conditions, the LMA may offer temporizing delivery of supplemental oxygen and assist ventilation. The Classic™ LMA has been successfully placed as an airway adjunct by prehospital personnel,46 Navy SEAL corpsmen under fire,47 emergency medicine physicians, and trauma surgeons.
Placement of an LMA does not constitute a definitive airway. Contraindications to the use of an LMA exist, and complications have been reported. Use of the LMA should never delay cricothyroidotomy when need and expertise exist. The LMA is contraindicated in patients who are not obtunded or deeply sedated, as irritation of the airway may exacerbate cervical spine injury and intracranial hypertension. Under conditions of severe craniofacial or pharyngeal trauma, care should be taken not to worsen injury. Leakage from around the cuff may occur in patients with fixed reductions in pulmonary compliance secondary to thoracic injury. Reported complications include aspiration; although the LMA may prevent aspiration of secretions or blood secondary to nasopharyngeal trauma, it does not effectively separate the respiratory and alimentary tracts.48
Laryngeal Tube Airway
The laryngeal tube airway (LTA), a relatively new supralaryngeal device, is a variation on the form and function of the combitube, although it is reported to exhibit substantially less resistance on insertion. The LTA is primarily intended as an emergency airway device.49 It is a single-lumen silicon tube with low-pressure oropharyngeal and esophageal cuffs, with the esophageal cuff terminating in a rounded tip. Between the two cuffs lies a ventilation outlet for selective ventilation of the trachea. Four variations of the LTA now exist, with addition of distal suction capabilities representing the primary design development. Literature assessing the role of the LTA in trauma patients and the emergent airway is limited. Due to the positive attributes demonstrated in the scant literature to date, the LTA warrants study in the emergent, difficult airway, particularly in comparison to the combitube. A variation of the LTA is the King LT®, approved for use in 2003, which is being utilized with increasing frequency by prehospital providers. In comparisons between the King LT® and the combitube, prehospital providers tested under conditions of simulated emergent airway placed the King LT equally effectively and significantly faster than the combitube.50
The morbidity and mortality associated with the difficult airway, compounded by potential litigation and the burgeoning epidemic of obesity, have fostered rapid growth in video laryngoscopy. A myriad of devices are now available, including the Truphatek Truview EVO2®, Pentax Airway Scope®, GlideScope®, Airway Scope®, and AirTraq Laryngoscope®. All devices have a rigid blade for laryngoscopy combined with videoscopic visualization of the anatomy in proximity to the end of the blade. The visual field is located through an eyepiece in proximity to the blade handle or on a separate portable monitor. The technology provides direct visualization of the glottic opening, facilitating intubation. Video laryngoscopes are being utilized in essentially any scenario in which a difficult airway may be encountered, including the emergency department, operating room, and intensive care unit. Application in the prehospital environment has been limited by financial constraints, lack of comparative data, and need for provider training. In comparisons of the effectiveness of video and conventional laryngoscopy, visualization of the glottis appears to be superior using video devices, but data regarding speed and efficacy of intubation are conflicting.
In this era of constantly evolving gadgetry, the surgical airway remains the mainstay for rapid control of the difficult airway. Cricothyroidotomy is an ancient procedure that, despite having undergone a myriad of incarnations in the past two decades, remains an effective method to secure a compromised airway.
Multiple reviews of surgical cricothyroidotomy in recent years have redemonstrated a success rate of greater than 90% at obtaining an airway,51–53 including performance by prehospital providers.53Cricothyroidotomy may be performed as the first airway control maneuver in cases of craniofacial trauma precluding oral or NTI; however, it is more commonly utilized after translaryngeal intubation attempts have failed. The greatest impediment to cricothyroidotomy is the recognition that it is necessary and subsequent performance of the procedure. Acute complications include procedure failure, pneumothorax, hemorrhage, and misplaced tube, while late complications include tracheal stenosis. In a series of 122 patients undergoing emergency department cricothyroidotomy identified by the EAST workgroup, the complication rate was 28.7%.4 A single contraindication to cricothyroidotomy exists, young age. Traditional recommendations suggest needle cricothyroidotomy for children less than 12 years of age, although body size should be taken into account.
Technique of Cricothyroidotomy
Preparation for a difficult airway should include securing necessary equipment for cricothyroidotomy, and all difficult airway carts should include the necessary instruments. An evaluation of surface anatomy and sterile preparation of the neck may facilitate the procedure in the event of airway failure. The most important instrument for surgical cricothyroidotomy is a scalpel, with many procedures having been performed with little else. Additional instruments may include tissue forceps and a hemostat. Cuffed endotracheal tubes with internal diameters of 5.0–7.0 mm should be at the ready.
The procedure is initiated under universal precautions with a rapid antiseptic preparation of the skin, followed by identification of the position of the cricothyroid membrane just superior to the cricoid cartilage. The trachea and larynx are then stabilized with the nondominant hand, with the thumb, index, and long fingers immobilizing the superior cornua of the larynx. A generous vertical incision is made over the membrane. The pretracheal tissue and fascia anterior to the membrane are rapidly divided with the scalpel, followed by a horizontal incision in the membrane. The index finger of the stabilizing hand may be utilized to palpate the membrane, guiding correct orientation of the incision. Many descriptions of the technique include insertion of the scalpel handle through the incised membrane to dilate the opening; however, given the conditions under which the procedure is typically performed, this technique may lead to inadvertent injury. The cricoid incision can be dilated with artery forceps, a hemostat, and a Trousseau dilator, or digitally. The index finger of the stabilizing hand should be used to maintain control of the cricoidotomy and guide tube insertion. Care should be taken to insert the endotracheal tube in a controlled fashion to a depth of approximately 5 cm. Insertion is facilitated by use of a rigid stylet; otherwise the tube may selectively pass retrograde toward the vocal cords.
It should be emphasized that cricothyroidotomy is a poorly visualized or blind procedure in many instances. The obese neck may render superficial landmarks less than obvious, and transaction of anterior jugular vein branches or thyroid tissue can lead to significant and unnerving hemorrhage. The stabilizing hand on the larynx may prove invaluable under such circumstances, and should not be removed until the airway is secure.
A number of commercial alternatives to traditional surgical cricothyroidotomy have been developed, in an attempt to expedite the procedure and reduce the degree of expertise required. The devices, cricothyrotomes, typically utilize one of two techniques to cannulate the trachea, depending on whether a Seldinger technique is utilized. For Seldinger-type kits, the cricothyroid membrane is punctured with a needle, a flexible guide wire is passed, and a tracheostomy tube is passed over a dilator. Alternatively, other kits utilize a tracheostomy tube placed over a puncture device without the intervening placement of a guide wire.
Percutaneous needle cricothyroidotomy with transtracheal jet ventilation is an alternative to surgical cricothyroidotomy. The neck should be rapidly sterilized and the skin anesthetized. The cricothyroid cartilage and membrane are identified. A 14- to 16-gauge catheter is attached to a syringe half-filled with saline. The cricothyroid membrane is cannulated in an inferior and caudal direction, at an angle of 30–60° from the trachea. The trachea is aspirated, with position confirmed by bubbles in the saline. The needle is removed, and the catheter is attached to a jet ventilation system using a Luer lock. Alternatively, a 5-mL syringe can be cut and attached directly to oxygen tubing or the tubing can be wedged into the open end of the syringe, and connected to high-flow 100% oxygen. An alternative method is to attach a 3-cm3 syringe to a 14-gauge catheter with an endotracheal tube adapter inserted into the open end of the syringe (Fig. 11-5). This technique allows direct attachment of the BVM to the syringe. Whatever system is utilized, an aperture should be created such that when occluded, jet insufflation occurs, and when open, flow may escape. Jet insufflation should proceed at approximately 1 second of flow (inspiration) for every 3 seconds of release (expiration). Because ventilation is not actually occurring, alveolar carbon dioxide rises. A point of emphasis is the temporizing nature of the procedure; life may be sustained for approximately 30 minutes until a definitive airway can be achieved.
FIGURE 11-5 A photograph of a useful setup for needle cricothyroidotomy, consisting of a standard 8-mm diameter endotracheal tube adapter, a 3-cm3 syringe, and a 14-gauge angiocatheter. The endotracheal tube adapter is removed and inserted into the open end of the 3-cm3 syringe (plunger removed). The angiocatheter is affixed to the syringe. A bag valve mask is then able to be attached to the adapter, allowing easy ventilation of the patient.
AIRWAY CHALLENGES IN THE INJURED PATIENT
Craniofacial, maxillofacial, and tracheolaryngeal injuries commonly present with threatened airways. Direct injury to the facial soft tissues and bony skeleton, tongue, and larynx may cause intrinsic and extrinsic airway obstruction from edema, hemorrhage, secretions, or loss of bony architecture. In a recent large review of craniomaxillofacial trauma at a Level I trauma center, 16,465 patients sustained head, neck, or facial injuries over a 12-year period, many of which required advanced airway techniques or cricothyroidotomy.54 In a review of 92 maxillofacial civilian gunshot wounds, 22% presented with a threatened airway, 60% of which required an emergent surgical airway.55Similarly, in a separate 4-year review of 84 maxillofacial gunshots, 21% required urgent tracheostomy.56
Although emergent surgical intervention is often required, many patients with severe bony and soft tissue injury are able to clear blood and secretions. If the cervical spine is cleared, slight forward positioning, suctioning, and calming of the patient frequently allow for forward displacement of a bilateral mandibular fracture or macerated soft tissue and maintenance of a patent airway. Close observation and transport to the operating room may optimize conditions for definitive airway procedures such as an awake tracheostomy or submental intubation. In the context of massive bony and soft tissue injury (Fig. 11-6), such as the catastrophic self-inflicted submental gunshot wound, an urgent need for definitive airway does not necessarily require a surgical airway. Despite the intimidating appearance of such injuries, many can be easily orotracheally intubated due to loss of restrictive anatomy.
FIGURE 11-6 Despite the extreme destructive nature of the maxillofacial injury, orotracheal intubation is the first method to secure a definitive airway. If orotracheal intubation fails and hypoxia ensues, cricothyroidotomy should be performed inferior to the tissue destruction. If the patient is able to oxygenate, an urgent yet controlled tracheostomy in the operating room is an alternative.
The management of laryngotracheal injuries is based foremost on airway status. In the previously mentioned study of craniomaxillofacial trauma, 0.2% of patients with head, neck, or facial injuries over a 12-year period sustained laryngeal fractures, of which 97% sustained concomitant maxillofacial trauma.54 Seventy-four percent of laryngeal fractures required advanced airway maneuvers. In another report, 71 patients with laryngotracheal trauma were identified over an 8-year period.57 Of note, 73% of injuries were penetrating, but blunt mechanism was more likely to require an emergent airway (79% vs. 46%).
Clues to the diagnosis of laryngotracheal injury include marked pain, tenderness and ecchymosis across the anterior neck or larynx, hoarseness or stridor, or the presence of subcutaneous emphysema. Subcutaneous emphysema or crepitance is the chief clinical sign. In a review of 19 patients presenting to a Level I trauma center with upper aerodigestive tract injury, 100% had radiographic evidence of subcutaneous emphysema or palpable crepitance, 21% had dysphagia, and 63% had stridor or hoarseness.58
Treatment options for this constellation of injuries include fiber-optic techniques, OTI, and surgical airway. In patients who are oxygenating, ventilating, and protecting their airway, in which clinical suspicion of tracheolaryngeal injury is present, the procedures of choice are fiber-optic laryngoscopy or bronchoscopy to assess airway integrity under controlled conditions, with performance of a surgical airway if necessary. If tracheolaryngeal injury is visualized, an attempt at endotracheal tube passage over the scope may ensue. Under urgent conditions, unless obvious tracheal or laryngeal disruption is evident, OTI remains the procedure of choice. However, if resistance is met, intubation should be aborted, and a surgical airway performed, corresponding to the suspected level of injury. Temporizing supralaryngeal devices should be avoided in this circumstance, as the potential for worsening subcutaneous emphysema and distortion of anatomy exists. For open wounds in which a tracheal injury is visualized, the trachea may be cannulated directly, with conversion to OTI under controlled conditions.
Cervical Spine Trauma
The critical need to immobilize the cervical spine in virtually all blunt trauma patients is a significant additive element in the difficulty of airway management following injury. Fear of spinal cord injury by cervical manipulation during laryngoscopy led to the purely theoretical practice of blind NTI for all multisystem blunt trauma patients. Accumulating evidence suggests that OTI, with strict cervical spine stabilization, is safe as a standard of care.
A number of studies in the past decade have assessed the effects of various intubation techniques on cervical spine motion. The majority has utilized fluoroscopic images, in cadavers or in the controlled setting of the operating room.59,60 Nearly all studies compare cervical motion incurred during direct laryngoscopy with a Macintosh blade and techniques that utilize either fiber-optic laryngoscopy or devices to facilitate blind intubation. To summarize findings to date, direct laryngoscopy produces more extension at all levels of the cervical spine than fluoroscopic and videoscopic techniques and the intubating LMA.59,60 However, nearly all techniques are significantly more time consuming than direct laryngoscopy, and the degree of extension, depending on the cervical level, ranges from 3.5° to 22.5°.60 If sufficient time, equipment, and expertise exist, alternative techniques to direct laryngoscopy may be considered, particularly with the intubating LMA, which has been reasonably well studied in the prehospital environment. However, given the emergent nature of most field and emergency department intubations and constraints of equipment and expertise, combined with the small degree of extension with proper cervical stabilization during direct laryngoscopy, the tried and true method of airway control in the injured patient remains RSI using direct laryngoscopy.
Multiple scenarios in thermal injury may precipitate airway compromise. Airway edema with obstruction can be multifactorial following thermal injury, and, alone or in combination, may include: major nonfacial burns with shock with requisite large-volume crystalloid resuscitation, circumferential thoracic burns, direct thermal or caustic injury to the lips, tongue, or pharynx, and inhalational injury. The Advanced Burn Life Support course, similar to ATLS, emphasizes the primacy of airway in thermal and inhalational injury.1
The incidence of smoke inhalation, the most common inhalational injury, is approximately 20% in all patients admitted to Level I burn centers and in isolation carries a 5–8% mortality rate.61 Inhalational injury can affect any of three distinct areas of the respiratory tract, including supraglottic, tracheobronchial, and pulmonary parenchymal regions. Inhalation injury is defined as aspiration of superheated gases, steam, hot liquids, or noxious products of incomplete combustion. Inhalational injury causes a number of pulmonary physiologic derangements that ultimately lead to acute respiratory failure. The injuries evolve over time and parenchymal lung dysfunction is often minimal for 24–72 hours.
Normal oxygenation and chest radiographs do not exclude the diagnosis.62 Because the etiology of early death from smoke inhalation is most commonly airway compromise, a high clinical index of suspicion is integral to survivability. Recent consensus recommendations from the American Burn Association (ABA) state: “Inhalation injury is suspected in the presence of one or more specific points of history (closed space exposure to hot gasses, steam or products of combustion), physical examination (singed vibrissae and carbonaceous sputum), or laboratory findings (elevated carboxyhemoglobin or cyanide level).”62
Inhalation injury alone is an ABA criterion for transfer to a burn center. Because the onset of symptoms from inhalational injury is variable and frequently insidious, significant clinical suspicion should prompt establishment of a definitive airway prior to transfer. Currently, bronchoscopic examination is the standard definitive diagnostic measure,62 assessing for the presence of carbonaceous debris and mucosal erythema or ulceration. Although intubation alone is fraught with both early and late sequelae, a window of opportunity may exist for controlled intubation. Subsequent airway edema and rapid pulmonary deterioration can convert a controlled situation into an emergent, difficult airway at an inopportune time during transport. If clinical suspicion is significant or bronchoscopy suggests an inhalational component, clinicians should err on the side of intubation. The EAST Management Guidelines Workgroup completed an extensive review of the literature evaluating the need for intubation following inhalational injury. The committee identified airway obstruction, severe cognitive impairment (Glasgow Coma Scale score <8), cutaneous burn exceeding 40% total body surface area, prolonged transport time, and impending airway obstruction (due to moderate to severe facial burn, oropharyngeal burn, and airway injury visualized on endoscopy) as indications for intubation.4
Due to efficient cooling capabilities of the upper respiratory tract, thermal injury is usually confined to the upper airways, unless smoke with high water content or steam is inhaled.63 Significant oropharyngeal or facial burns with mucosal edema do not preclude oral intubation. Attempts at laryngoscopy are warranted, although failure of OTI should prompt rapid transition to surgical airway. Circumferential third-degree burns of the chest may impair oxygenation and ventilation secondary to reductions in chest wall compliance, pulmonary static compliance, and increased intra-abdominal pressure.64 Under these circumstances, it is imperative for clinicians to address the airway definitively with endotracheal intubation or rescue maneuvers, and to concurrently address the need for chest wall escharotomy as expeditiously as possible.
Closed Head Injury
Perhaps no injury imparts more importance on precise airway management than CHI. Injury to the brain is the most common, single indication for a definitive airway in blunt trauma. Initial goals focus on airway protection and maintenance, while sustained goals focus on secondary brain injury prevention through optimization of oxygenation and regulation of carbon dioxide. Airway management is particularly challenging in head-injured patients with potential for intracranial hypertension. It is well recognized that hypoxia, even a single episode, has deleterious effects on outcome, and uncontrolled hyperventilation, with resultant cerebral vasoconstriction, may worsen outcome as well.65 The Brain Trauma Foundation guidelines state that hypoxia, defined as apnea, cyanosis, oxygen saturations <90%, or partial pressure of arterial oxygen <60 mm Hg, must be scrupulously avoided.66 In addition to prevention of hypoxia, the avoidance of hypercarbia is of critical importance. Hypercarbia results in cerebral vasodilatation, increasing intracranial blood volume, with resultant elevated intracranial pressure. Early definitive airway control is theoretically appealing, and the recommendation that Glasgow Coma Score <8 prompt intubation remains in the Advanced Trauma Life Support course.1 RSI may help to eliminate prolonged awake intubation attempts and therefore the risk of hypercarbia.
Despite the intuitive belief that early intubation may prevent hypoxia or extremes of ventilation, data assessing prehospital intubation in CHI are conflicting. In two recent studies, prehospital use of RSI by paramedics was shown to correlate with poor functional outcome and death in head-injured patients.67,68 Conversely, other recent studies have demonstrated outcome benefit in traumatic brain injury patients undergoing RSI, particularly when neuromuscular blocking agents are utilized.69 In a recent swine model evaluating the effects of various RSI regimens on intracranial pressure, those utilizing paralytic agents produced 3-fold increases in peak intracranial pressure compared to regimens using sedation only.70 The association between RSI and mortality may have little to do with the procedure itself; rather, preintubation hypoxia, and postintubation hyperventilation, may represent the mortality causation. In a study of 291 CHI patients, 144 patients underwent continuous ETCO2 measurement.71 Patients with ETCO2 monitoring had a lower incidence of inadvertent severe hyperventilation (defined as partial pressure carbon dioxide <25 mm Hg), and patients with severe hyperventilation had significantly higher mortality than those without hyperventilation.71 In further work from the San Diego Paramedic RSI trial, 79% of patients were documented to have ETCO2values less than 30 mm Hg during RSI or transport, and 59% of patients had levels less than 25 mm Hg.72
In a study assessing the frequency of hypoxia (defined as oxygen saturation measured by oximetry <90%) during paramedic RSI, 57% of patients demonstrated hypoxia lasting a median duration of 160 seconds.73 The median decrease in oxygen saturation was 22%. In summary, RSI should be undertaken with strict attention to preoxygenation and rate of postintubation ventilation in CHI.
THE PEDIATRIC AIRWAY
Airway management in the critically ill and injured child presents a number of unique challenges rendering emergent management less successful by clinicians primarily trained in the adult airway.74 In general, airway management principles for the pediatric population are similar to the adult population, although anatomy, physiology, and pharmacology may differ.
The pediatric cranium comprises a larger relative percentage of body surface and mass, flexing the cervical spine in the supine position, and emphasizing the requirement for cervical stabilization. Internal airway differences at laryngoscopy that have the potential to render the pediatric airway challenging include a larger amount of distensible soft tissue. Children may have significant tonsilar and adenoid tissue as well as a large tongue that collapses into the posterior pharynx, each having the potential to obstruct laryngoscopy and hemorrhage with instrumentation. Compounded by the fact that the glottic opening of the trachea is at the level of C-1 in infancy, and the larynx is more anterior with decreasing age, the angle between the laryngeal orifice and the glottic opening is more acute. Other anatomic variations from adults include a narrower cricoid ring, narrower and shorter trachea, and smaller cricothyroid membrane. As a rule, children less than 2 years of age have high anterior airways while children greater than 8 years of age approximate adult alignment. Children aged 2–8 have transitional airways with less consistency among individuals.
More rapid onset of hypoxemia in children is related to higher basal oxygen consumption, 6–8 mL/(kg min) in infants versus 3–4 mL/(kg min) in adults. Increased susceptibility to hypoxemia leads to a higher percentage of cardiac arrest due to airway compromise than in the adult population. The higher metabolic rate, compounded by reduced cardiovascular tolerance to hypoxia, accentuates the urgency of airway maintenance necessary in hemorrhagic, obstructive, or neurogenic shock. In addition, rapid desaturation in children is coupled to a relative reduction in functional residual capacity.
Anatomic and physiologic attributes of children mandate alterations in airway equipment and drug preparation, as well as anticipated algorithms for management of the difficult airway. The Broselow™ Pediatric Emergency Tape, although intended as a guide only, is an excellent airway resource for clinicians unfamiliar with standard sizes and doses. The tape includes length-based estimates of kilogram body weight, with corresponding recommendations for drug dosing and equipment sizing. The tape includes recommendations for size of endotracheal tube, insertion length, stylet, suction catheter, laryngoscope, BVM, ETCO2 detector, as well as oral airways, NPAs, and LMAs.
The BVM apparatus should be selected with attention to size of face mask, proper seal, and delivered tidal volume. Although pop-off valves set at 35–45 cm H2O are often recommended, a higher generated airway pressure may be required to ventilate the injured child, and air may escape from the valve unrecognized. Circular masks often provide a better seal in infants and children. Endotracheal tube internal diameter may based on the Broselow™ tape or formulas, including age/4 + 4, or (16 + age)/4. Uncuffed endotracheal tubes are recommended in younger children, with cuffed tubes employed for children requiring a 5.5-mm internal diameter or greater. Given the short tracheal length in children, right mainstem intubation is a potential complication following endotracheal intubation. In addition to Broselow™ tape recommendations, depth of insertion may be calculated as the internal diameter of the tube multiplied by 3. An NPA is selected based on the approximate distance from the tip of the nose to the angle of the tragus. The size of ETCO2 measurement also differs with use in children. The pediatric model should be used for children weighing less than 15 kg.
Although all clinicians caring for the injured should be facile with the pediatric airway, it is frequently difficult to recall specific differences in airway drug doses. Again, the Broselow™ tape may be invaluable when determining appropriate dosing. During RSI, defasciculating doses of nondepolarizing neuromuscular blocking agents are not recommended for children less than 20 kg body weight. In addition, it is imperative to remember that children have a higher percentage of extracellular volume than adults, requiring higher dose of succinylcholine (2 mg/kg). Finally, due to the potential for reflex bradycardia during RSI, all children when receiving succinylcholine and children less than 5 years of age undergoing any form of airway manipulation should receive atropine, although atropine does not always abrogate bradycardia.75
Given the unique impact of hypoxia on pediatric physiology, failure to gain definitive control of the airway can be catastrophic. Conversely, the decision to intubate has unique ramifications in children. BVM offers an excellent means to oxygenate and ventilate children. When definitive airway control is necessary, RSI is the technique of choice for definitive control of the pediatric airway, and is now recommended by pediatric life support courses. Surgical cricothyroidotomy is considered a contraindication in infants76 and small children, due to the size of the cricothyroid membrane, although data are limited. For children less than 8–10 years, needle cricothyroidotomy should be utilized, although limited data exist regarding the efficacy of this technique.
EMERGENCY AIRWAY ALGORITHMS
Airway algorithms provide a reproducible structural framework for recognition and response, guiding management under complex and stressful situations. Once the need for definitive airway protection has been identified, a concise and logical approach to airway control, based on situational and patient characteristics, is imperative.
The failed airway and the difficult airway are distinct. The two entities are not unrelated; the difficult airway frequently leads to the failed airway. To negotiate the sequence of both the failed and difficult airways, an understanding of current definitions is necessary. A failed airway is defined as any clinical scenario in which a patient is unable to oxygenate or ventilate. A failed airway may exist on presentation secondary to a disease process, or after a clinician has initiated any one of a number of airway interventions that have failed to maintain oxygenation or ventilation
The difficult airway refers to any preintubation characteristics, related to injury type or pattern, physiology, anatomy, comorbidities, or skills of the practitioner that predict difficulty with the standard OTI algorithm. In the emergent situation, scant time may be available to plan or enact alternatives to OTI, such as an awake technique or NTI. Alternatively, an identified difficult airway may be followed by an uneventful progression through standard RSI technique. In summary, the difficult airway does not always portend a failed airway, nor does the failed airway universally arise from a predicted difficult airway. In the words of one author, “The difficult airway is something one anticipates, the failed airway is something one experiences.”15
Decision Making in the Failed Airway
When airway control is required, the first assessment relates to the urgency of the airway: determination of airway failure. Patients who are apneic, in extremis, or manifest inability to protect the airway with resultant oxygenation and ventilation failure represent airway failure. The first step in airway failure is BVM ventilation while rapid preparations for tracheal intubation are made (Fig. 11-7). Further management steps are based on success of BVM.
FIGURE 11-7 Algorithm for the failed airway.
Airway Failure: Bag-Valve-Mask Ventilation, SpO2 >90%
The effectiveness of BVM ventilation determines the progression to either OTI or urgent surgical intervention. If BVM results in successful oxygenation and ventilation, OTI should be attempted. If OTI is unsuccessful, further treatment always depends on the ability to oxygenate and ventilate the patient with BVM. If at any point the patient cannot be ventilated or desaturates, an emergent surgical airway should be undertaken. Following an initial failure of OTI, an assessment of reasons for failure should quickly follow. If paralysis is deemed beneficial based on the status of facial musculature on the first attempt at OTI, succinylcholine should be administered followed by a repeat attempt at OTI. If a second failure occurs, a third attempt should only occur if BVM remains effective and a more experienced clinician is available. If a third failure at OTI occurs, two options exist. First, a surgical airway is always acceptable after three OTI failures, and should be the mainstay for a definitive airway at this juncture. If surgical expertise is unavailable, alternative methods of tracheal intubation such as retrograde intubation or the intubating LMA may be considered provided BVM ventilation remains effective. If alternatives fail, temporizing measures to maintain oxygenation and ventilation, including ETC and supralaryngeal airways, should be utilized until surgical expertise is available.
Airway Failure: Bag-Valve-Mask Ventilation, SpO2 <90%
The foundation of this scenario is rapid transition to definitive surgical airway (Fig. 11-7). If SpO2 cannot be maintained >90% using BVM, emergent transition to a rapid single attempt at OTI or a surgical airway should be undertaken. The decision at this point should be based on available equipment and expertise. If a surgical airway is possible, delay for even a single attempt at tracheal intubation may be lethal. The decision to attempt tracheal intubation should be predicated on anticipated ease of placement and lack of surgical expertise. If OTI fails and a surgical airway is not possible, alternative methods of tracheal intubation should be avoided, with progression to attempts at temporizing measures to oxygenate and ventilate.
A number of trauma patients may be alert, breathing spontaneously, yet not adequately oxygenating or ventilating, therefore representing a failed airway. Under these circumstances, vigorous BVM should be avoided, with supplemental oxygen applied to spontaneous breaths. The patient should be assessed for injuries potentially not requiring intubation, such as pneumothorax, with oxygen administered in the highest concentration possible. Emergent RSI should follow. If unable to intubate, a surgical airway should be undertaken. In the event that surgical airway is not possible, temporizing alternatives, including supralaryngeal airway or ETC, should be considered.
The Difficult Airway
For patients who have need for definitive airway but do not present with airway failure, time permits for assessment of, and preparation for, a potentially difficult airway (Fig. 11-8).
FIGURE 11-8 Algorithm for the difficult airway.
The most commonly used predictive scheme used in anesthesiology is the Mallampati airway classification system. The degree of airway difficulty is based on the ability to visualize the structures of the oropharynx, and the tongue’s ability to obscure the oropharynx is a predictor of the difficulty to establish an airway. The “Rule of Threes” was developed to combine the physical characteristics of mouth opening, jaw size, and mandible size (thyromental distance) as a predictor of a difficult airway at the bedside. If three provider finger breaths can be placed between the following distances: the patient’s upper and lower teeth, the hyoid bone and the chin, and the thyroid cartilage and the sternal notch, the provider has a higher success rate in direct laryngoscopy.
Equipment and Technique for the Difficult Airway
In a survey of emergency medicine program directors regarding airway adjunct availability, the frequency of various adjuncts was reported and included: cricothyroidotomy kits (95%), fiber-optic scopes (76%), bougies (70%), LMAs (66%), intubating LMAs (61%), lighted stylets (54%), retrograde intubation kits (49%), combitube (46%), and esophageal obturator airways (15%). Despite the preparedness, 94% of airways consisted of OTI.77
Although difficult airway criteria are common, the majority of difficult airways are managed with RSI, with a low incidence of complications. Therefore, anticipation of a difficult airway, with preparation for alternatives to OTI, is critical. The step in RSI that may prompt airway failure is paralysis. Therefore, the single deviation from a standard RSI approach is laryngoscopy without paralysis (Fig. 11-8). In patients not meeting airway failure criteria, the pharynx and trachea can be topically anesthetized followed by administration of a short-acting sedative. Sedation alone may be sufficient to allow endotracheal intubation. In addition, the process may identify the airway as amenable to RSI with paralysis. If RSI fails to secure the difficult airway, management proceeds according to a failed airway (Fig. 11-7).
COMPLICATIONS ASSOCIATED WITH THE EMERGENCY AIRWAY
Complications associated with emergency airway management are multiple and common, conferring significant morbidity and mortality both during and subsequent to airway procedures. For RSI, morbidity increases concordant to number of attempts at laryngoscopy.78 The most common and ominous immediate complications are failure to intubate, failure to recognize esophageal intubation, and failure to ventilate. Pulmonary aspiration of gastric contents, an immediate complication, imparts both early and late morbidity, secondary to the potential for acute lung injury and pneumonia.
Failure to Intubate
Failure to intubate is the most feared complication of emergent airway intervention, initiating the critical pathway of alternative means of oxygenation and ventilation. Published rates of intubation failure are as varied as the patient populations and environments from which they originate. The majority of recent series, evaluating a range of providers including paramedics, residents, and attending physicians, report emergent intubation failure rates of 2–13%.17,36 In a recent multicenter prospective trial, the endotracheal intubation success rate across providers for out-of-hospital intubation was 86.8%.17 Unrecognized misplaced intubation represents a potentially lethal subset of failed intubation. Rates of prehospital misplaced intubation, primarily esophageal, reported in the multiple studies evaluating this complication range from 0.4% to 25%, with most documenting rates of less than 10%.79
Esophageal intubation, comprising a subset of intubation failure, can represent a minor or catastrophic complication, depending on time of recognition. Early recognition is facilitated by lack of appropriate color change on colorimetry, desaturation, lack of breath sounds over bilateral lung fields, and auscultation of inspired air over the epigastrium. Unrecognized esophageal intubation incidence ranges from 0% in small series to 10% in larger studies.80When esophageal intubation is proven or suspected, it is imperative to rapidly remove the tube and reintubate.
The untoward effects of aspiration range from obscuration of vocal cords during intubation to death secondary to failed intubation, chemical pneumonitis with acute respiratory distress syndrome, and pneumonia. Studies of emergent airway management have reported the incidence of aspiration to range from 1% to 20%, depending on the patient population and environment.81 The few early studies focusing on the prehospital setting have reported an aspiration incidence of 34–39%.82 A recent study, using pepsin assay of tracheal aspirates, identified an aspiration incidence of 22% for urgent intubations in the emergency department compared to 50% in the prehospital environment.81
Emergency intubation has been identified as a risk factor for pneumonia after trauma, likely related to pulmonary aspiration during the procedure. In a review of 99 cases of early onset ventilator-associated pneumonia (VAP), multivariate regression identified emergency intubation and aspiration as factors independently associated with multidrug-resistant infections.83 The incidence of pneumonia is significantly higher after a field versus emergency department airway,84 and has been independently associated with paramedic RSI.85
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