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.

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.)

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 blockade^8,26,27 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

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 bupivacaine^49,50,51 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 overdose^53,54 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:

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