Lynette L. Young
• Respiratory failure is the most common cause of cardiac arrest in pediatric patients.
• It is important to recognize respiratory distress early so that actions can be taken to avoid respiratory failure whenever possible.
• If respiratory failure does occur, prompt intervention will give the patient the best chance for survival with the least neurologic sequelae.
• Young children have less physiologic reserve and can deteriorate very rapidly.
• In a critical situation, the emergency physician has the task of not only making quick resuscitation management decisions but must also consider age-related anatomic differences, appropriate equipment (Table 18-1), and drug-dosage differences when caring for infants and children.
Endotracheal Tube Size and Depth and Laryngoscope Blade Size by Agea,b
ANATOMY AND PHYSIOLOGY
Children have anatomic and physiologic differences that should be considered when evaluating a pediatric patient presenting in respiratory distress. Young infants may be obligate nose breathers, and any degree of obstruction of the nasal passages can produce respiratory difficulty.
The chest wall of children is more flexible and the muscles are less developed compared with adults. The diaphragm is more prone to fatigue. The limitation of diaphragmatic movement by gastric distention, increased residual capacity from air trapping from asthma, bronchiolitis, or foreign body obstruction can result in reduction of tidal volume, which may produce respiratory failure. The relatively smaller lower airways are especially vulnerable to mucous plugging and ventilation–perfusion mismatch associated with common diseases of the lower airways, such as asthma and bronchiolitis.
The actual area available for gas exchange in infants and young children is relatively limited. Alveolar space doubles by 18 months of age and triples by 3 years of age. The limited ability to recruit additional alveoli makes the infant dependent on increasing the respiratory rate to augment minute ventilation and eliminate carbon dioxide. Tachypnea, therefore, is a universal finding in infants and young children in respiratory distress. The combination of increased muscle exertion and the need to sustain a rapid respiratory rate can result in progressive muscle fatigue and respiratory failure. This is especially true in young infants who have a limited metabolic reserve. Children have about twice the oxygen consumption rate compared with adults, and they have proportionally smaller functional residual capacity. With intubation of an infant or child, it is important to remember that they have the potential to desaturate more quickly than adults (see Chapter 17 for airway differences between infants and children).
Most commonly, a patient in respiratory distress will present to the ED with a history of difficulty breathing. Parents may note coughing, rapid noisy breathing, or a change in behavior. Feeding problems are often a sign of respiratory compromise in infants. In older children, wheezing or decreased physical activity may be presenting complaints.
The past medical history is essential in determining the etiology of the acute problem. Infants with a history of significant prematurity may have bronchopulmonary dysplasia, a syndrome characterized by varying degrees of hypoxia, hypercarbia, reactive airway disease, and a heightened susceptibility to respiratory infections. Infants with a history of sweating during bottle-feedings may have undiagnosed congestive heart failure. For patients with a history of asthma, information regarding the frequency and severity of past exacerbations is important in determining both the acute treatment and disposition. A patient with a history of a chronic cough or recurrent pneumonia may have an underlying disorder, such as reactive airway disease, cystic fibrosis, or a retained foreign body. Respiratory symptoms can also be caused by systemic disorders. Effortless tachypnea and hyperpnea accompany disorders such as diabetic ketoacidosis and sepsis, as an attempt to compensate for metabolic acidosis.
Simply observing the patient yields a wealth of information regarding the degree of respiratory distress. Mental status is the first and foremost factor to evaluate. Infants and young children with mild respiratory difficulty will have normal mental status. Patients with more severe disease become irritable or anxious and can appear restless and unable to assume a comfortable position. Older patients in extreme distress are usually unable to lie supine and may exhibit head-bobbing. Young infants in severe distress will appear anxious, will often not make eye contact, and usually will not smile. If feeding is attempted, they will refuse the bottle, since the work of breathing precludes the exertion of sucking. Incipient respiratory failure is heralded by extreme agitation, and finally by lethargy or somnolence. Cyanosis is an ominous finding.
Observing the patient’s chest will add to the assessment of the degree of respiratory distress. Patients with significant respiratory distress will virtually always be tachypneic. However, because respiratory rate is age dependent and can be influenced by underlying medical conditions, it must be viewed in the context of the overall clinical picture. Visual inspection of the chest wall may reveal retractions, which signify the use of accessory muscles of respiration. Retractions are seen in the supraclavicular and subcostal areas. In more severe cases, nasal flaring is seen. Retractions imply a significant degree of respiratory distress and must never be overlooked.
Listening to grossly audible breath sounds will help to localize the pathology. Stridor is generally heard on inspiration, but with severe obstruction, it can be present on both inspiration and exhalation. Stridor suggests upper airway pathology, such as croup, epiglottitis, or foreign-body obstruction. Grossly audible wheezing usually indicates obstruction of the lower airways. Lower airway disease resulting in alveolar collapse can also be associated with grunting, which is caused by premature closure of the glottis during expiration. Grunting increases airway pressure and can help prevent further alveolar collapse and thus preserve functional residual capacity. Grunting is most often seen in infants and always indicates severe respiratory distress, whether from primary lung disease or a systemic illness, such as sepsis.
Auscultation of the chest supplements the information gained from observation of the patient. The first factor to assess is air exchange. Upper airway obstruction predominantly affects the inhalation of air, whereas lower airway obstruction predominantly affects exhalation. Patients who appear to be struggling to breathe and have limited air exchange appreciated on auscultation are in imminent danger of respiratory failure.
Laboratory studies are useful in assessing the degree of respiratory compromise. The advent of a reliable measurement of oxygen saturation via percutaneous pulse oximetry has made it possible to evaluate a patient’s oxygenation (saturation) status quickly and painlessly. Pulse oximetry is especially useful in infants, in whom the physical findings may be difficult to assess and an arterial blood gas difficult to obtain. However, pulse oximetry provides only limited information regarding overall pulmonary physiology. The slope of the oxygen–hemoglobin dissociation curve is such that patients with marginal oxygen saturations may have significant hypoxemia. The pulse oximeter does not measure the arterial carbon dioxide tension (PaCO2) or acid–base status, and therefore careful clinical correlation is necessary in many situations, such as asthma and bronchiolitis, in which CO2 retention and respiratory acidosis are possible. Pulse oximetry is also unreliable for patients with low-perfusion states, carbon monoxide toxicity, and methemoglobinemia.
For patients with moderate to severe respiratory distress, pulse oximetry cannot replace the information obtained by an arterial blood gas. Respiratory failure is often defined as arterial oxygen tension (PaO2) <60 mm Hg despite supplemental inhaled oxygen of 60% or arterial carbon dioxide tension (PaCO2) >60 mm Hg. However, absolute values of arterial oxygen and carbon dioxide tension must be viewed in the context of the clinical situation, as well as the patient’s baseline pulmonary status. A patient may not meet strict criteria for respiratory failure but may develop muscle fatigue such that the work of breathing cannot be sustained despite blood gas values that appear adequate. Conversely, a patient with severe underlying lung disease, such as bronchopulmonary dysplasia or cystic fibrosis, may be well adjusted to chronic hypercarbia; in this case the clinical assessment of the work of breathing supplants the laboratory data. In most children with severe lung disease, parents are aware of baseline information that can aid the physician in interpreting percutaneous oxygen saturation and blood gas values.
INDICATIONS FOR ASSISTED VENTILATION
In the event that respiratory failure occurs, assisted ventilation is indicated. The most common indication for assisted ventilation in a pediatric patient in respiratory distress is progressive muscle fatigue. In this situation, laboratory parameters will often reveal hypoxemia refractory to supplemental oxygen and a rising PaCO2. Other indications for assisted ventilation are apnea, inadequate respiratory effort, and conditions in which it is desirable to reduce the work of breathing, such as refractory shock or increased intracranial pressure that requires controlled ventilation.1 For patients with altered mental status, when the ability to maintain an adequate airway is in question, assisted ventilation is also indicated, although pulmonary function may be normal.
The initial treatment of hypoxemia is administration of oxygen. Supplemental oxygen can be delivered by nasal cannula, simple mask, non-rebreather mask, and bag-mask. Ventilatory assistance begins with establishing a patent airway (see Chapter 17 for airway management).
Effective bag-valve-mask (BVM) ventilation of infants and children is a vital skill (Fig. 17-6 and 17-7). In the out-of-hospital setting, it has been shown that endotracheal intubation by paramedics compared with BVM ventilation did not improve survival or neurologic outcome in the pediatric patient.2 The 2010 American Heart Association (AHA) guidelines recommends BVM ventilation for infants and children in the prehospital setting especially if there is a short transport time.3 A transparent mask should fit snugly from the bridge of the nose to the prominence of the symphysis of the mandible. Circular masks with seals are more effective in infants and in small children than triangular masks that attempt to duplicate the shape of the face (see Chapter 17 for a detailed description of equipment and technique for BVM ventilation of infants and children).
ADVANCED AIRWAY MANAGEMENT
In most situations that require BVM ventilation, insertion of an endotracheal tube is necessary to establish an adequate airway and allow optimal management. Successful intubation of the trachea requires preparation of personnel, medications, and equipment.
Preoxygenation displaces nitrogen from the lungs and provides a physiologic reservoir of oxygen that protects the patient from anoxic injury during the process of intubation. In spontaneously breathing patients, 3 to 5 minutes of 100% O2 delivered by a non-rebreather mask provides the patient with 3 to 4 minutes of adequate oxygenation even in the face of apnea. For patients receiving assisted ventilation, minimizing the time of bagging is important in reducing the possibility of gastric distention and aspiration during intubation. In this situation, several breaths with 100% O2 provides an adequate reservoir of oxygen. Cricoid pressure during intubation is no longer routinely recommended.3 The technique for tracheal intubation can be reviewed in Chapter 17.
The correct endotracheal tube size can be determined by using a length-based system or formula based on age (Table 18-1). The length-based tapes are more accurate than age-based formulas in estimating the endotracheal tube size in young children.4,5 With a well-positioned endotracheal tube of the proper size, an audible air leak is heard when ventilation is applied at a pressure of 15 to 20 cm H2O. If no air leak is audible, the tube is too tight. Conversely, if the air leak is too large, it will impair ventilation since insufficient tidal volume is generated. Cuffed endotracheal tubes have been shown to be safely used in the operating room and intensive care unit in children. Cuffed endotracheal tubes are noted to be as safe as uncuffed tubes and may be used in the hospital for infants past the newborn period and children.3 Using a cuffed endotracheal tube might be beneficial in certain situations such as poor lung compliance, high airway resistance, and large glottic air leak.
Correct endotracheal tube placement is confirmed clinically by observing adequate chest wall expansion and auscultating bilateral breath sounds. Asymmetric breath sounds imply that the tube is too far down the trachea and has lodged in either the right or left mainstem bronchus. The anatomic vectors are such that the right mainstem bronchus is more likely to be intubated, and breath sounds are heard louder on the right side. In young infants, however, the airway vectors are such that intubation of the left mainstem bronchus may occur. This situation is corrected by slowly withdrawing the tube until equal breath sounds are heard. If unilateral breath sounds persist despite withdrawal of the tube, a pneumothorax is possible. The laryngeal mask airway (LMA) is a tube with a deflatable masklike projection at the distal end. The LMA is an alternative to the endotracheal tube for a patient with a difficult airway.6–8 The LMA is passed through the pharynx and advanced until resistance is felt when the mask is over the epiglottis/tracheal opening. The inflation of the cuff occludes the hypopharynx but leaves the distal end open over the glottic opening, providing a clear secure airway. The LMA has been demonstrated as a successful airway management tool in the hospital and in out-of-hospital settings. Numerous studies have shown that the LMA is effective in pediatrics, but proper training and supervision is required to master correct LMA placement. LMA is contraindicated in the infant or child with a gag response or with the potential for excessive patient movement. There is a risk of aspiration that must be considered when using LMA. LMA may be an alternative if endotracheal intubation is not possible in pediatric cardiac arrest, although there is no data about its routine use in this scenario. The Combitube and the laryngeal tube airway (King LT Airway) are two other airway devices. The Combitube comes in two sizes. The smaller size tube is for patients over 4 ft and thus cannot be used in many pediatric patients. The King LT-D (disposable) is available in pediatric sizes (size 2 for height 35–45 in, 90–115 cm, or weight 12–25 kg and size 2.5 for height 41–51 in, 105–130 cm, or weight 25–35 kg). In simulation studies, the pediatric King LT-D may be easier to place than an endotracheal tube.9,10
It is occasionally necessary to provide mechanical ventilation for intubated patients in the ED while awaiting transport or intensive care unit admission. Although a thorough discussion of ventilators is beyond the scope of this chapter, a few facts regarding the use of these machines are important. The two major types of mechanical ventilators are pressure and volume ventilators. Both assist the patient by delivering compressed gases with positive pressure; however, they differ in the method that terminates the inspiratory phase of the breathing cycle.
A volume ventilator delivers a preset volume of gas during each mechanical inspiration. This type of ventilator compensates for all changes in resistance and is therefore useful for patients with decreased lung compliance. The danger of volume ventilators is that they generate high airway pressures that can result in barotrauma. Currently, they are used for children and older infants. The usual tidal volume in an infant or child is 8 to 10 mL/kg. Previously higher volumes were used, but using positive end expiratory pressure (PEEP) to maintain lung volume will reduce the risk of barotrauma associated with higher volumes. The rate depends on the patient’s age and the clinical condition.
Pressure ventilators terminate inspiration when a preset pressure is reached and therefore avoid excessive inflating pressures. With pressure ventilators, it is possible to control the inspiratory time, and exhalation is allowed when the preset pressure is reached. They do not compensate for changes in lung compliance, and they deliver a variable amount of gas with each breath. Currently, pressure ventilators are used mainly in neonates and young infants. The inspiratory pressure used is the lowest pressure that attains adequate chest expansion and ventilation. This is best determined by observing a manometer while the patient is being bagged.
Both volume and pressure ventilators have the ability to provide PEEP, which is added to prevent alveolar collapse during exhalation and to preserve functional residual capacity. This can alleviate ventilation–perfusion mismatch and consequent hypoxemia and is especially important in situations in which there is decreased lung compliance. The major side effect of excessive PEEP is decreased venous return to the right side of the heart and decreased cardiac output. In the ED setting, PEEP is usually set at 3 to 5 cm H2O.
Despite the widespread availability of pulse oximetry and end-tidal CO2 monitoring, most patients on ventilators will require serial blood gases until the optimal parameters for ventilating the patient are determined. Adjusting pH and PCO2 can be done by manipulating minute ventilation, adjusting respiratory rate, and tidal volume. Controlling PO2 is done by adjusting FIO2 and PEEP.
NONINVASIVE MECHANICAL VENTILATION
Noninvasive mechanical ventilation has been used to provide respiratory support without the risks associated with tracheal intubation.11–13 The benefits may include improved oxygenation and ventilation with decreased muscle fatigue. The modalities of aiding the patient’s own spontaneous respiratory efforts includes continuous positive airway pressure (CPAP), bi-level positive airway pressure (BiPAP), and high-flow nasal cannula.
With CPAP, there is continuous pressure delivered through the entire respiratory cycle. Generally, positive airway pressures are delivered at 4 to 10 cm water level. CPAP can be delivered by face mask in children, and with the use of binasal prongs for small infants where it is difficult to fit a mask. Nasal CPAP has been successfully studied in prematures, neonates, and infants with improvement of oxygenation and reduction of respiratory distress.14–16 The infant with bronchiolitis may benefit from this mode of respiratory support.
BiPAP cycles between a higher inspiratory positive airway pressure (IPAP) and the lower expiratory positive airway pressure (EPAP). When initiating BiPAP, start with small initial pressure settings and increase gradually over time. IPAP is usually set at 8 to 10 cm H2O and increased to 16 cm or more to achieve a decrease in the work of breathing, decrease in respiratory rate, and improved oxygenation. The EPAP is used to improve functional residual capacity and is usually started at 4 to 10 cm H2O. Successful use of BiPAP requires a cooperative patient and a good-fitting mask.17 A retrospective study reviewed the use of BiPAP to treat status asthmaticus in a pediatric ED in 83 patients who were refractory to conventional medical therapy.18 It was tolerated by 88% of patients and with an age range of 2 to 17 years. All of these patients had been planned pediatric intensive care unit (PICU) admissions. Sixteen patients (22%) had improved in the ED and were weaned off BiPAP. They were subsequently admitted to the wards. A prospective study of 20 patients investigated BiPAP in addition to standard of care management of children admitted to a PICU with status asthmaticus.19 This pilot study concluded that BiPAP may be helpful in decreasing the work of breathing. Larger studies may be helpful in determining whether early initiation of noninvasive positive pressure ventilation in children with status asthmaticus is beneficial.
Humidified high-flow nasal cannulae were initially used to provide CPAP mainly in newborns.20,21 More recently, warm and humidified gases are delivered by nasal cannula at up to 8 L/min in infants and younger children and up to 40 to 50 L/min in adolescents and adults. Use of high-flow nasal cannula in the ED for pediatric acute respiratory insufficiency may be helpful in reducing the need for intubation.22
Most of the experience using noninvasive positive pressure ventilation (NIPPV) in pediatric patients comes from the PICU.23 These modalities have also been used in the home for children with obstructive sleep apnea and neuromuscular diseases. With newer technology and more experience being obtained, NIPPV may be considered for use in the ED also.18,22,24–26 NIPPV could be beneficial in the acute management of children with asthma, bronchiolitis, near-drowning, cystic fibrosis, and neuromuscular disease presenting in respiratory distress. NIPPV should not be used in patients who are obtunded, vomiting, hypotensive, or have cardiac dysrhythmias. Clinical improvement is usually seen in several hours. Any patient who is receiving NIPPV acutely in the ED is critically ill and must therefore be watched very closely for deterioration. The emergency physicians must be prepared for tracheal intubation of the child if necessary.
Thanks to Thomas J. Abramo and Michael Cowan who authored the first and second editions of this chapter.
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