Thoracic Anesthesia

PART 2

Thoracic Anesthesia Practice


CHAPTERS


 

21
Anesthesia for Pediatric Thoracic Surgery

Laura K. Diaz
Arjunan Ganesh
Katherine Grichnik
John B. Eck


Key Points

1. Infants with unilateral lung disease are best oxygenated with the healthy lung in the nondependent position given the soft, compressible nature of their rib-cage, the relationship of FRC to residual volume, and less significant hydrostatic pressure gradient between the right and left lungs. This is contrary with what is usually seen in the adult population.

2. The choice of induction technique (spontaneous breathing versus positive pressure ventilation) during airway foreign body retrieval should be dictated by the location of the foreign body and by the risk of advancing that object to a location in the respiratory tree that either obstructs ventilation or is not easily retrievable.

3. The anesthetic management for a patient presenting with an anterior mediastinal mass is both complex and hazardous, particularly during induction of anesthesia. Maintenance of spontaneous ventilation is often preferred. The availability of a rigid bronchoscope, the ability to reposition the patient easily, and in some cases circulatory support (ECMO) assistance may be indicated for large and/or very symptomatic mediastinal masses.



Clinical Vignette


A 2-month-old infant was diagnosed prenatally with a right-sided congenital cystic adenomatoid malformation. He is scheduled for a surgical resection via right thoracotomy. He just completed a 14-day course of antibiotics for pulmonary infection.

Vital signs Wt: 3.6 kg, BP 74/42, HR 135, RR 40, SpO2 96% on 0.2 L/min oxygen. CT scan reveals multiple 2 to 3 cm cystic lesions in the right upper lobe, some with air/fluid levels.


Thoracic surgery in the pediatric population presents additional challenges to the routine problems encountered in adult patients presenting with thoracic disease. This chapter will review the key knowledge necessary to care for these patients and will use one condition (congenital cystic adenomatous malformations) as an example of the general issues to consider for intrathoracic surgery in an infant. In addition, the chapter will provide a discussion of two other conditions that may result in a pediatric thoracic surgical procedure: foreign body in the airway and anterior mediastinal mass.

OVERVIEW

Conditions Necessitating Thoracic Surgery

Conditions that present in the first year of life may include lesions of the respiratory tree, lung, vasculature, and diaphragm.1 Examples include tracheal stenosis and malacia (both congenital and secondary to prolonged intubation), pulmonary sequestration, pulmonary hypoplasia (associated with a number of intrauterine problems), congenital diaphragmatic hernia, tracheoesophageal fistula, esophageal atresia, coarctation of the aorta and patent ductus arteriosus. Conditions that more commonly arise after the first year of life include primary or metastatic tumors (especially lymphoblastic lymphoma, Hodgkin lymphoma and neuroblastoma), severe infection (consolidated pneumonia, abscess and empyema), arteriovenous malformation, pectus excavatum and kyphoscoliosis. Finally, a common cause for an emergent thoracic procedure is a foreign body in the airway.

Anatomic Differences

There are several key differences between adult and pediatric airway anatomy.2 The first is the large head relative to the body, with a more prominent occiput in infants and young children (Figure 21–1). Due to this anatomic configuration, the neck may be slightly flexed when supine and can lead to difficulty with airway manipulation and intubation. Secondly, pediatric patients have a relatively large tongue compared to the size of the oropharynx, which can also lead to difficulty with intubation. Further, the laryngeal structures are distinct: the larynx itself is situated in more anterior and cephalad position compared to the adult (C2-3 compared to C4-5). The epiglottis is large, long and can appear U-shaped, often necessitating the use of a straight laryngoscope blade to lift it for vocal cord visualization (Figure 21–2). The narrowest portion of the funnel shaped larynx is below the vocal cords at the level of the cricoid cartilage. Finally, the trachea and neck are proportionally shorter in infants and small children relative to adult anatomy.

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Figure 21–1. A child being positioned for an anesthetic. Note the size of the head relative to the body. A roll under the shoulders may avoid flexion at the neck and maintain a patent airway.(Courtesy of Scott Tolle.)

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Figure 21–2. The glottic opening of an infant. Note the relatively long epiglottis. (Courtesy of A. Inglis, MD.)

Preoperative Assessment

As in adults, an assessment of the presenting problem, a family history, current medications, history of gastroesophageal reflux, drug, food, and/or environmental allergies and a review of systems for coexisting medical problems are necessary. For infants, the birth history along with any significant perinatal medical history, including the existence of coexisting syndromes or chromosomal abnormalities should be reviewed.

Recent or ongoing upper respiratory infections should be reviewed carefully as they are common in children and may increase the risk of perioperative oxygen desaturation, laryngospasm or bronchospasm, and postoperative croup.3 Surgery is often deferred until several weeks after an infectious process has resolved; however, some thoracic surgical conditions may include concurrent, frequent infections (eg, congenital cystic adenomatous malformations [CCAM]) that necessitate proceeding with the surgical intervention in the face of a respiratory illness. Extra vigilance for airway-related complications is important in that circumstance.

Physical examination of the infant or child should emphasize evaluation of the airway, cardiovascular system, state of hydration, and potential sites of vascular access. Difficulties with mouth opening or neck extension should be noted. Vital signs should also include measurement of baseline hemoglobin-oxygen saturation, and pulses should be assessed in all extremities. Laboratory studies, including a complete blood count and platelet count, should be reviewed and any abnormalities should be noted. A chest radiograph should also be obtained and reviewed for any evidence of mediastinal shift, pulmonary herniation, or inferior displacement of the hemidiaphragm.

Imaging

Infants and children presenting for thoracic surgery will most likely have had multiple types of imaging studies, which should be examined prior to an anesthetic. In addition to a chest radiograph, computed tomography (CT), magnetic resonance imaging (MRI) and/or arteriography may have been performed. Echocardiography, ventilation to perfusion scanning, and pulmonary function testing may be indicated for some conditions. The anatomic location of the lesion to be surgically corrected should be understood, along with its blood supply and relationship to nearby key anatomic structures.

One-Lung Ventilation for Pediatrics

Although major pediatric intrathoracic surgery has traditionally been performed using a single-lumen endotracheal tube and manual lung compression by the surgeon, the advent of video-assisted thoracic surgery (VATS) has led to the more widespread use of one-lung ventilation (OLV) for major thoracic procedures. A VATS approach may be preferred as it provides better cosmetic results, probably decreases postoperative pain, and limits future development of scoliosis or musculoskeletal deformity sometimes seen after open thoracotomy.4 Although several techniques for lung isolation have been described in children,5-20 due to the small size of the infant’s trachea and bronchi, only some of these techniques can be used in the smallest patients. Similar to the adult population, there are several important considerations for both the establishment of OLV and management of oxygenation, ventilation, and perfusion during OLV.1

Endobronchial Intubation

The first step is to control the airway in a manner that facilitates OLV. One technique is to use a single-lumen endotracheal tube (ETT) with deliberate mainstem intubation of the bronchus on the contralateral side of the planned surgery.21 Right bronchial intubation is straightforward, but to intubate the left bronchus, the bevel of the tube is rotated 180 degrees while the patient’s head is turned to the patient’s right.22 Selective bronchial intubation may also be accomplished using a fiberoptic bronchoscope or fluoroscopy to guide the ETT into the desired bronchus. Cuffed ETTs may also be used, but care should be taken to ensure that the distance from the proximal cuff to the tip of the ETT is shorter than the length of the bronchus.23 A variation on this technique is the independent intubation of both bronchi.24,25 Problems with endobronchial intubation techniques include possible obstruction of the right upper lobe bronchus, inability to provide an adequate seal with partial inflation of the operative lung, and inability to evacuate secretions from the operative lung. The primary risk related to endobronchial intubation is endobronchial injury resulting from a relatively large endotracheal tube relative to the size of the bronchus.

Endobronchial Blockers

Multiple options also exist for the use of balloon-tipped endobronchial blockers that pass either beside or through the endotracheal tube. The usual limitation is the relative size of the bronchial blocker compared to the endotracheal tube. The Fogarty embolectomy catheter (Edwards Lifesciences, Irvine, CA; Arrow International, Reading, PA) is the most commonly used catheter for bronchial blockade8,26,27 in small infants, but the Arndt blocker (Cook Critical Care, Bloomington, IN) has also been occasionally used in this age group.27,28 The advantages of bronchial blockers include the ability to achieve lung isolation, intermittently ventilate both lungs (by deflating the blocker), and aspirate blood and secretions from the operative side when blockers with end-holes are used.

The Fogarty embolectomy catheter set includes a wire stylet that can be curved at the distal end to help direct the catheter’s tip into the appropriate bronchus. The blocker may be inserted through or beside the ETT. A fiberoptic scope may be used to guide the blocker into the appropriate bronchus. In one case report, an endobronchial blocker was coupled to the fiberoptic scope intratracheally in an interesting approach that helped successfully achieve OLV in a 3-kg infant.28 Fluoroscopy may also be used to assist in blocker placement. In small children, the Arndt blocker has been placed successfully using fluoroscopy with the ETT then being placed beside the blocker.27

Dislodgment is the most common problem associated with bronchial blockers. This can be corrected intraoperatively using either fiberoptic or fluoroscopic guidance. Another problem associated with blockers is the potential for bronchial rupture or injury.29 Thus, lung isolation in small infants requires the services of a team experienced in these techniques.

Dual-Lumen Endotracheal Tubes

Dual-lumen endotracheal tubes (DLT) offer the advantage of superb airway control but have a large cross-sectional area and are therefore mostly useful in larger children. The smallest cuffed DLT is size 26 French, which may be used in children as young as 8 years old. 28 French and 32 French DLTs are usually suitable for children aged 10 and older1 (Table 21-1). With DLT use, one must be aware of the increased resistance to airflow with OLV. Excessive positive-pressure ventilation may cause barotrauma resulting in pneumothorax, pneumomediastinum, or interstitial emphysema. This usually occurs in the ventilated, dependent lung but occasionally occurs in the non-dependent lung upon re-expansion.

Table 21–1. Endotracheal Tube Selection for One-Lung Ventilation in Children

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Principles of OLV

The general principles of OLV in adults apply to pediatrics as well. General anesthesia, muscle relaxants, lateral position, and dependent lung compression often cause a decrease in functional residual capacity of both lungs and atelectasis in the dependent lung. Hypoxic pulmonary vasoconstriction that normally minimizes V/Q mismatch may be limited by inhaled anesthetics and other vasodilating drugs.1

The approach to OLV in infants requires an understanding of the physiological differences between adults and very small children. Positioning these patients in the lateral decubitus position can significantly worsen V/Q matching compared to an adult. In adults with unilateral lung disease, oxygenation is better with the healthy lung dependent and the diseased lung nondependent due to a relative increase in perfusion of the dependent lung.30 However, in infants the situation is reversed: oxygenation is improved when the healthy lung is nondependent and the diseased lung is dependent.31 Several variables may account for this problem. The rib cage is soft and compressible, FRC is close to residual volume (leading to airway closure), abdominal hydrostatic pressure is proportionally less, and there is a reduced hydrostatic pressure gradient between the nondependent and dependent lungs. Airway closure may also occur with tidal volume ventilation.1,32 Further, pediatric patients have relatively higher oxygen requirements (6-8 mL/kg/min of oxygen in an infant vs 2-3 mL/kg/min in an adult) and are thus at high risk of hypoxemia during lateral positioning and OLV. OLV techniques used in children should therefore ideally include the option of providing oxygen to the operative lung.33

Pain Management for Thoracic Surgery

The amount of pain that an infant or child may experience is dependent on the surgical incision, the location and extent of the operation, and concurrent disease states. In general, as in adults, pain management may be achieved with intravenous medications (opiates and non-opioids), regional or peripheral nerve infiltration with local anesthetic, and neuraxial blockade.

The use of intravenous opioids will be influenced both by the surgical approach and adjunctive use of regional anesthesia techniques. In neonates and infants, the authors prefer to titrate narcotic dosage according to respiratory effort after reversal of the neuromuscular blockade at the conclusion of the operation. Bupivacaine 0.25% (maximum 1 mL/kg) may also be infiltrated into incision sites to assist with postoperative pain management.

Thoracic Epidural Analgesia for pediatrics

More extensive thoracic surgical procedures may be treated with a more aggressive analgesic plan, usually including the use of regional anesthetic techniques. Thoracic epidural analgesia is a logical choice for thoracic procedures and is frequently used in the pediatric population. A primary advantage of epidural analgesia in neonates and infants is the decreased need for intravenous opioids,34 thus decreasing the likelihood of apnea, bradycardia, and occasionally, respiratory arrest.35 Epidural analgesia following thoracotomies may also improve the chances of successful postoperative extubation.36

Thoracic epidural catheters may be placed at the level of the incision in the older child or via a caudal approach in the younger child. The caudal approach was first described in a 3-phase study in which cadaveric and animal trials were performed before the technique was attempted on neonates undergoing biliary surgery.37 Feasibility, safety, and efficacy of thoracic epidural catheters inserted via the caudal route were well demonstrated. The technique starts with the identification of the sacral hiatus and advancement of an 18-gauge intravenous catheter (18-gauge Tuohy or Crawford needles may also be used) through the sacrococcygeal membrane into the epidural space. The epidural space may be expanded with normal saline, after which a 20-gauge catheter is advanced to the desired level (the distance to the desired level is measured before advancing the catheter). The importance of radiographic confirmation of the epidural catheter’s tip following insertion was emphasized in a retrospective study.38

Stimulating epidural catheters have also been successfully placed using the technique described by Tsui and colleagues.39,40 The stimulating epidural catheter (Arrow International Inc., Reading, PA) is flushed with normal saline and then inserted via an 18-gauge intravenous catheter initially placed in the epidural space. An electric current of 1 to 10 mA is applied through the catheter as it is advanced cephalad. The level of muscle twitch indicates the level of the catheter; therefore, neuromuscular blockade cannot be used at the time of catheter placement.

Recently, ultrasound has been used to locate the tip of caudally advanced epidural catheters.41,42 Ultrasound has the advantage of being noninvasive and can be used in small infants in whom there is a clear window for visualization due to incomplete ossification of the posterior elements of the spinal canal.

Direct placement of a thoracic epidural catheter may also be attempted; however, it is less frequently done due to the risk of spinal cord injury. In a prospective multicenter study in France, no complications related to direct thoracic epidural catheter placement were noted in children,43 but data gathered from the same group suggested that thoracic epidural catheters should be placed by experienced anesthesiologists. In a recent study, ultrasound guidance for placement of lumbar and thoracic epidural catheters was compared to traditional loss-of-resistance technique.44 The group concluded that, in experienced hands, ultrasound reduces both the duration of catheter placement and the incidence of bony contacts.

Perhaps the most important decision is when to place the epidural catheter relative to the induction of general anesthesia. In an older, sedated child, direct placement of the catheter may be indicated with the child being his/her own monitor for neural symptoms. Direct placement of a thoracic epidural catheter in an anesthetized person is still controversial. However, caudal placement is generally considered safe in the anesthetized child.

A combination of local anesthetics, epidural opioids, and alpha-2 agonists may be used to provide optimal analgesia.45 Use of epidural local anesthetic solution alone necessitates a higher rate of infusion to obtain adequate analgesia.46 Close attention must be paid to local anesthetic infusion in order to avoid toxicity. The recommended maximal infusion rates for bupivacaine are 0.4 mg/kg/h in older infants and 0.2 to 0.25 mg/kg/h in neonates.47 The addition of opioids to epidural solutions may also reduce the risk of local anesthetic toxicity by allowing less local anesthetic to be used.47 In a prospective randomized double-blind study, the addition of fentanyl 2 mcg/mL to an epidural solution of bupivacaine 1 mg/mL was shown to improve analgesia when compared to bupivacaine 1 mg/mL alone in infants up to 6 months of age undergoing thoracotomy.48

Safety concerns have been raised regarding elevated concentrations of bupivacaine49,50,51 during prolonged (>48 hour) infusions in neonates and infants. In a recent study of infant patients who received continuous epidural ropivacaine infusion in the dose of 0.2 to 0.4 mg/kg/h for up to 72 hours, plasma concentrations of bound and unbound ropivacaine were found to be below toxic levels.52 This, coupled with a better safety profile regarding cardiotoxicity and resuscitation from overdose53,54 makes ropivacaine a wiser choice compared to bupivacaine in young infants.

Patients who are treated with continuous epidural analgesia, particularly after a thoracotomy, are often monitored in an intensive care unit. Monitoring should include the following measures:

• Continuous ECG and pulse oximetry

• Recording of hourly vital signs, including heart and respiratory rate, blood pressure, and oxygen saturation

• Pain assessment at least every 4 hours

• Monitoring epidural catheter insertion site every 12 to 24 hours

• Setting alarms to detect bradycardia, bradypnea, and apnea

In addition to the above, rescue analgesic medication should be ordered for breakthrough pain along with naloxone to treat opioid-induced respiratory depression. A bag and mask, along with an oxygen source, must be available at the bedside to treat signs and symptoms of respiratory depression.

Potential complications include local anesthetic toxicity related to intravascular administration or prolonged infusions at high rates, epidural hematoma and/or abscess formation, meningitis, superficial cellulitis, and abnormal catheter location during insertion. When assessing or monitoring for local anesthetic toxicity, physicians and nurses must remember that an infant or young child will not report any symptoms and may only manifest restlessness or agitation.47

SPECIFIC CONDITIONS

Examples of several types of intrathoracic conditions requiring surgical intervention in infants and children are now presented. Congenital cystic adenomatous malformations are presented as a specific example of an intrathoracic lesion requiring thoracoscopy/thoracotomy in an infant. In addition, several intrathoracic conditions common to older pediatric patients (foreign body in the airway and anterior mediastinal mass) are reviewed.

CONGENITAL CYSTIC ADENOMATOUS MALFORMATIONS

Congenital cystic adenomatous malformations (CCAMs) were initially described by Ch’in and Tang in 1949.55 CCAMs are predominantly a unilateral lesion, derived from an abnormality in the formation of parenchymal lung tissue that results in adenomatous overgrowth of terminal bronchiolar structures and formation of cystic structures of various sizes (Table 21–2). CCAMs communicate with the bronchopulmonary tree, resulting in air trapping, and may have normal arterial blood supply. This contrasts with bronchopulmonary sequestrations (BPS), which are composed of a nonfunctioning mass of tissue lacking connection to the tracheobronchial tree, and in which blood is supplied by an anomalous systemic artery. Although the overall incidence of CCAMs is low (approximately 1 in 25,000 births),56 CCAMs remain the most common pediatric cystic thoracic lesion, accounting for approximately 25% congenital lung malformations. Hybrid lung masses that appear to demonstrate clinicopathological characteristics typical of both CCAMs and sequestration lesions have also been described.57,58

Table 21–2. Characteristics of CCAMs

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CCAMs are categorized by clinical or pathological criteria (Table 21–3). Adzick and colleagues classified CCAMs based on a combination of ultrasound and gross anatomical features,59 with prognosis determined by the size of the mass and the resultant degree of physiological derangement. Polyhydramnios (secondary to esophageal compression), mediastinal shift, and lung hypoplasia can occur with large masses. Interventions in utero to decompress the lesion via thoraco-abdominal or thoraco-amniotic shunting or resection of the mass may be indicated. Alternatively, resection may be performed using an ex utero intrapartum therapeutic approach. Postpartum, even in asymptomatic infants and children, resection of the mass is warranted due to the risk of infection and/or malignant transformation.60-65

Table 21–3. Classification of CCAMs by Clinical or Pathological Criteria

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Diagnosis and Timing of Surgery

Most infants with a CCAM are diagnosed prenatally66 by ultrasound imaging or fetal magnetic resonance imaging. One must differentiate CCAMs from congenital diaphragmatic hernias.67,68 Even if regression is anticipated and the chest radiograph is normal, a postnatal CT should be performed, as small lesions frequently are often still present.69 Doppler imaging or angiography can confirm the origin of blood supply to the lesion.

The indication and timing for surgery is controversial. In addition to recurrent infection, the risk of spontaneous pneumothorax and the chance of malignant transformation are often cited as reasons to pursue early surgical resection of a known lesion.70 A review of childhood pulmonary neoplasms by Hancock et al revealed that 8.6% were associated with previously documented cystic lesions.18 Further, early resection may encourage compensatory lung growth.

Most surgeons recommend that lobectomy and resection of a CCAM be performed between 1 and 6 months of age70 in an attempt to balance the desire for early resection against the risks of anesthesia in a neonate.71,72 Truitt et al recommended observation of asymptomatic patients until ages 12 to 18 months, with VATS resection of the lesion to be performed at that time.73 In Aspirot’s series, 75% patients requiring more than 24 hours of postoperative mechanical ventilation were younger than 3 months old.36

Preoperative Assessment

It is likely that surgery will be performed in the face of a concurrent infection due to the frequent occurrence of infections in patients with a CCAM. Infants diagnosed prenatally should undergo a CT scan within the first months of life to confirm the presence and size of the CCAM as well as to determine the appropriate timing for surgical resection. Preoperative assessment should also include echocardiography (if fetal echocardiography was not previously performed) to rule out cardiac disease or compromise. The usual fasting guidelines indexed to patient age are appropriate. A thorough review of the planned procedure, the invasive monitoring necessary, the anticipated need for ICU care and potential complications must be discussed in detail with the parents. Premedication should similarly be used in an age appropriate manner, titrated (or eliminated) based on the degree of respiratory compromise an infant may have at baseline.

Surgery

CCAM resection is via open thoracotomy or a minimally invasive VATS. Knowledge of the surgical approach and the possibility of conversion to an open thoracotomy are critical, as the VATS approach often mandates a OLV technique. OLV may be poorly tolerated in smaller or sicker patients. As such, invasive monitoring may be warranted in this patient subgroup. Pain management strategies will likewise differ depending on the planned surgical approach.

Monitoring, Induction, and Maintenance

The standard monitors include pulse oximetry probes placed on both upper and lower extremities, oscillometric blood pressure measurement, and a 3- or 5-lead electrocardiogram. In neonates, a pulse oximetry probe that suddenly ceases to function may portend hypotension and/or poor peripheral perfusion. Thus, the presence of a second pulse oximetry probe is extremely useful in differentiating between probe failure and a physiological change. Accurate temperature monitoring is also critical and may be accomplished via the use of rectal, esophageal, or nasopharyngeal temperature probes. Placement of an arterial catheter facilitates monitoring of arterial blood gases for optimization of ventilatory parameters.

A standard anesthetic induction for an infant, utilizing either an intravenous or inhalation technique is appropriate, with the caveat to avoid nitrous oxide. The placement of two intravenous lines is recommended to allow for intraoperative administration of blood and/or inotropes, if necessary. In more critically ill infants with mediastinal shift secondary to CCAM, it may be desirable to preserve spontaneous ventilation until lung isolation has been achieved to avoid worsening mediastinal shift and cardiorespiratory collapse.66 OLV will usually be indicated so one must plan for the occurrence of hypoxia and hypercarbia.

Risks

Aspirot et al noted significantly fewer perioperative complications in asymptomatic versus symptomatic patients. For this reason, discussions with parents should reflect the potentially increased risk and possible need for prolonged mechanical ventilatory support for children who have large masses or ongoing infections.36 Ideally, all but the sickest neonates can be tracheally extubated in the operating room at the conclusion of the procedure or shortly thereafter. In a review by Tsai and colleagues of 105 asymptomatic infants who underwent surgical resection of either CCAM or BPS, 103 were tracheally extubated immediately after the surgical procedure.74 There was no associated mortality in this patient group, but a 6.7% morbidity rate was seen due to residual air leakage and need for transfusion.74Therefore, postoperative chest films should be obtained in all patients to rule out pneumothorax or hemothorax. Recovery in an intensive care setting is appropriate, especially for infants with indwelling epidural catheters.

FOREIGN BODY IN THE AIRWAY

Most anesthesiologists will be faced with the need to anesthetize a child for a foreign body in the airway. This often occurs in children under the age of three years—in part due to the use of the mouth to explore nonfood substances in addition to normal food intake and their tendency to be in motion while eating.75 Further, the immaturity or lack of molar teeth can lead to the ingestion of large pieces of food. Commonly aspirated items include grapes, seeds, and small pieces of meat. More dangerous are dried foods capable of swelling (raisins) or small objects such as buttons or balloons, which can cause complete tracheal obstruction. Foreign body aspirations in children most often occur in the right mainstem bronchus (Table 21–4), due to the angle of the right mainstem bronchus relative to the left mainstem bronchus from the trachea76 (Figure 21–3). One should further recognize that the aspirated object may not be associated with an acute event, resulting in the possibility of concurrent lung or mucosal inflammation, infection and/or chronic bronchial obstruction. As such, either intermittent or chronic airway edema and bronchospasm may be present. A preoperative bronchodilator may be indicated to improve the chances of successful object retrieval. The most important preoperative management step is communication with the surgeon or invasive pulmonologist including a shared understanding of where the object is, the anticipated degree of difficulty in extraction, and what steps would be necessary in the event of complete airway obstruction.

Table 21–4. Location of Aspirated Foreign Bodies in Children

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Figure 12–3. The normal anatomy of the tracheobronchial tree with a foreign body in the right mainstem bronchus. The right mainstem bronchus is at a less acute angle relative to the trachea than the left mainstem bronchus. Therefore, aspirated foreign objects are much more likely to be a located in the right airways than the left.

Anesthetic Induction and Airway Management

The induction of anesthesia must be carefully planned with the need for airway manipulation to retrieve the foreign body.77 A flexible bronchoscopy may initially be considered to diagnose and perhaps extricate the object, usually in a pulmonary suite. However, the anesthesiologist is most often faced with the need to induce anesthesia and control respiration while creating ideal conditions for the placement of a rigid bronchoscope. The first choice is the type of induction, with the decision about whether to keep a child spontaneously breathing or use positive pressure ventilation. In part, this decision is dictated by the location of the foreign body and, with positive pressure ventilation, the risk of advancing that object to a place in the respiratory tree that it either obstructs ventilation or is not easily retrievable. Conversely, one must be cautious about the risk of a child coughing during induction resulting in relocation of the object to a tracheal or laryngeal site that causes airway obstruction. The need for a rapid sequence induction may be determined by the urgency of the situation, whether the child has recently ingested food and what the risk of airway compromise is relative to the usual fasting period, indexed by the age of the patient. There is not a particular advantage of one agent (inhaled versus intravenous) over another for anesthetic induction. However, one may consider the administration of atropine or glycopyrrolate to dry airway secretions, prevent bradycardia and to further reduce the risk of bronchoconstriction during airway manipulation.

After induction of anesthesia, the operating room table is usually tuned at a 90-degree angle from the anesthesiologist and a rigid bronchoscope is introduced with a ventilating sideport. This is a critical period of time as the airway is unsecured until the bronchoscope is in place—a smooth transition should be carefully planned. In general, the use of a total intravenous anesthetic at this point is wise, both to avoid operating room air pollution with anesthetic gases as the airway is intermittently open to the room during this process, and to maintain adequate anesthetic depth prior to instrumentation of the airway. If spontaneous ventilation is chosen, then topical airway anesthesia is critical to reduce the depth of anesthesia necessary to tolerate the bronchoscope placement and the optimize ventilation, oxygenation, and hemodynamic stability. If controlled ventilation is chosen, the periods of apnea necessary to remove the object may be short in younger children whose ability to oxygenate may be significantly impaired. Litman et al reviewed 94 cases of pediatric foreign body removal and did not find a significant advantage of one ventilatory technique over the other.78 The anesthesiologist needs to be aware that retrieval of the object may involve one or more re-intubations if the object is larger than the diameter of the bronchoscope, necessitating the technique of securing the object with grasping forceps and then removal of the object by retracting the grasping forceps with the object and the bronchoscope at the same time.

Complications

One can anticipate the potential complication of partial or complete airway obstruction including the risk of prolonged apnea and potential hypoxia. However, depending on the length of time that the object has existed in the airway or bronchial tree, resultant localized irritation, secretion formation or even a postobstructive pneumonia may manifest with continued respiratory compromise, even after object removal. A more serious immediate complication can be pneumomediastinum and/or pneumothorax, which Burton reported to occur after 13% of foreign body removals.79

PEDIATRIC ANTERIOR MEDIASTINAL MASS

The anesthetic management for a patient presenting with an anterior mediastinal mass (AMM) is both complex and hazardous as respiratory and/or circulatory collapse may ensue during the course of the procedure, particularly during induction of anesthesia.80 A thoughtful, staged approach to the perioperative care of these patients is essential.

Preoperative Assessment

Pediatric patients may present either for diagnosis or resection of an AMM. Common causes for an AMM in children include lymphoblastic lymphoma, Hodgkin disease, vascular malformations, neurogenic tumors, germ cell tumors, and bronchogenic cysts.

Symptoms may range from slight shortness of breath to significant dyspnea with stridor, associated with chest pain and superior vena cava syndrome. Symptoms may vary with position; however, the absence of symptoms does not exclude the possibility of cardiorespiratory collapse with anesthetic administration. Further, there is a poor relationship between clinical signs and size of tumor or tracheal compression on imaging studies.81

Preoperative evaluation should include chest radiography, CT, and possibly MRI or positron emission (PET) scanning. Assessment should include the presence and degree of tracheal compression, the tracheal cross-sectional area and the presence of bronchial compression. It may also be important to obtain an estimation of significant respiratory impingement through flow-volume studies (including peak expiratory flow rate) and significant vascular impingement through echocardiography. The degree of symptoms, size and location of the mass, and thoracic anatomical impingement determines the approach to obtaining a biopsy for tissue diagnosis or attempting resection (Figure 21–4).80

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Figure 21–4. A suggested algorithm for the assessment of anesthetic risk and the subsequent management of an anterior mediastinal mass in a child. IPPV = intermittent positive pressure ventilation, PEFR = peak expiratory flow rate. (From: Hack HA, Wright NB, Wynn RF. The anaesthetic management of children with anterior mediastinal masses. Anaesthesia. 2008 Aug;63(8):837-846, reproduced with permission.)

Preoperative measures may be taken to reduce the risk of a surgical procedure and anesthetic induction. Some have advocated for the preoperative use of steroids in the management of AMMs81 as steroids may reduce the inflammatory reaction to the tumor as well as (perhaps) influence its size and vascularity. If feasible, a biopsy under local anesthesia and/or initiation of chemotherapy or limited radiation therapy may reduce the risk of a perioperative complication. Of note, the anterior Chamberlin procedure can be performed in a sitting, slightly sedated spontaneously breathing child under local anesthesia to obtain a tissue diagnosis (Figure 21–5).

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Figure 21–5. Chamberlin procedure under monitored anesthesia care with local infiltration.

Anesthetic Induction and Airway Management

After appropriate review of the imaging and functional studies, an anesthetic plan should be formulated including provisions for unintended airway and circulatory collapse. The availability of a rigid bronchoscope, the ability to easily move the OR table to effect positional changes and the availability of advanced circulatory support (ECMO) may be indicated for large and/or very symptomatic AMMs. Although a mask induction is often chosen to maintain spontaneous ventilation, one must ensure adequate intravenous access prior to establishment of a deep level of anesthesia (which may reduce respiratory muscle tone) and intubation. Other management strategies to consider include keeping the head of the bed elevated, considering a partial lateral decubitus position and using continuous positive airway pressure to maintain functional residual capacity.80,82 One commonly utilized technique is to intubate the trachea without the use of muscle relaxants or positive pressure ventilation to optimize the transpulmonary pressure gradient and improve flow through the respiratory tree.80 Using similar logic, the use of a laryngeal mask airway has been advocated.80

Perioperative Complications

Adult and pediatric patients are at significant risk for perioperative complications from mediastinal mass surgery. This is especially true in children with an immature and more cartilaginous airway. Lam et al found that several factors were associated with increased risk of respiratory compromise or failure: tracheal compression or displacement, superior vena cava and other vascular compression, anterior tumor location, preoperative diagnosis of lymphoma, pericardial effusion, and pleural effusion.83,84 Postoperatively, patients may experience pulmonary edema, bleeding, respiratory failure and hypotension. The extent of the surgery and the intraoperative course will dictate postoperative decision making, including the need for ventilation and recovery in an intensive care unit.

SUMMARY

Thoracic surgery for pediatric patients is both challenging and rewarding. This chapter has focused on key points to guide management and care of these patients, using three representative conditions to illustrate the complexities of thoracic anesthesia in infants and children.

REFERENCES

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