Anesthetic care for pediatric thoracic surgery covers a wide range of ages, concomitant disease processes, and surgical pathology. The clinical scenario ranges from an elective, outpatient procedure on an otherwise healthy patient to an emergent procedure in a neonate with a severe underlying illness or associated congenital heart disease. The surgical pathology may have limited physiologic impact on the patient; or, as in the case of an anterior mediastinal mass, a cystic adenomatoid malformation, or a tracheoesophageal fistula, it may result in significant patient compromise. Newer surgical techniques such as thoracoscopy have additional anesthetic implications.
Preoperative Considerations
There exists a spectrum of diseases for which thoracic surgery is required. For example, a child undergoing a thoracotomy and resection of a pulmonary nodule may have no other associated conditions or may have associated pulmonary parenchymal disease that affects the anesthetic management. As is true for all anesthetics, the preoperative history and physical exam should identify acute problems, underlying medical conditions, and previously undiagnosed problems that may affect perioperative management. Preoperative laboratory evaluation depends more on the clinical status of the patient than the procedure itself. Blood loss is usually minimal during most thoracic procedures, but because of the proximity to the great vessels and the risk for unintentional damage to these structures, blood should be immediately available in the operating room (OR). If the surgery is elective, a type-and-crossmatch should be performed in the preoperative period so that crossmatched blood is available at the start of surgery. If the case is an emergency, a blood sample for type-and-crossmatch can be obtained after the induction of anesthesia and the placement of intravascular catheters, provided the blood bank can expedite processing of the specimen and provision of blood products. In surgical procedures with an elevated risk for significant hemorrhage, incision should be delayed until blood is readily available. Other preoperative studies, such as pulmonary function tests (PFTs), an electrocardiogram (ECG), or echocardiogram are not routinely indicated; rather, they are obtained on the basis of the patient’s medical history and the indication for the surgical procedure.
In patients with compromised respiratory function, preoperative PFTs may assist in estimating the potential risk for intraoperative or postoperative respiratory complications and aid in ensuring that preoperative therapies, such as antibiotics for pulmonary infections or bronchodilators in patients with reactive airway disease, have been optimized. Preoperative PFTs will also help categorize the type of respiratory disease (obstructive or restrictive) and document the response to bronchodilator therapy. Children with significant respiratory impairment (i.e., PFTs <50% predicted for age) may benefit from noninvasive ventilation after tracheal extubation.
Cognitively normal children older than 6 years are usually able to cooperate with pulmonary function testing. However, there are limited data regarding the utility of PFTs in pediatric patients in guiding anesthetic management and postoperative care decisions. Preoperative PFT results that predict poor outcomes in adults after lung resection (such as VO 2 max <10 mL/kg/min, DLCO <40%, and preoperative FEV 1 <60%) cannot necessarily be applied to pediatric patients because there is generally less comorbidity in children, such as associated cardiac disease, compared with adults. It can be expected that most children will experience small decreases in PFTs after thoracotomy. Preoperative PFTs may not identify all patients at risk for postthoracotomy complications, but they can identify some high-risk patients, which can direct preoperative teaching and optimization of respiratory function. All children undergoing thoracotomy, if old enough, should receive preoperative teaching regarding the use of incentive spirometry and high-flow nebulization therapy.
Systemic disease processes are less frequently encountered in children than adults presenting for thoracic surgery. In oncology patients, however, there may be concerns such as previous chemotherapy or the presence of an anterior mediastinal mass. When evaluating the pediatric oncology patient, careful attention should be directed toward his or her disease process and previous chemotherapeutic regimen and the impact these may have on end organ functioning. One class of chemotherapeutic agents of particular interest to the anesthesiologist are anthracyclines such as doxorubicin, because of their association with congestive heart failure.
In the otherwise healthy patient without signs of airway compromise, several options are available for preoperative anxiolysis. Midazolam, the most commonly administered pediatric premedication, is given orally (0.5 mg/kg up to 10–15 mg) 15 to 20 minutes before anesthetic induction. Additional agents that may be included as part of the premedication process include the following:
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High-flow nebulization of albuterol and an anticholinergic agent such as ipratropium in children with reactive airway disease.
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Corticosteroids for patients with airway reactivity or those having airway procedures that may result in postoperative airway edema.
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Antisialagogue such as glycopyrrolate to decrease secretions and blunt cholinergic-mediated airway reactivity. These drugs may be particularly useful if ketamine is employed due to ketamine’s sialagogue effect.
Anesthetic Techniques
Anesthetic induction for thoracic surgery in children can include inhalation with sevoflurane in N 2 O and oxygen (with discontinuation of N 2 O after loss of consciousness), or an intravenous (IV) anesthetic agent. For patients with obstructive airway lesions (tracheal compression from subglottic stenosis or vascular rings), sevoflurane can be administered with a mixture of oxygen and helium. Because helium is less dense than nitrogen, it decreases resistance in areas of turbulent airflow. After loss of consciousness IV access is secured. Once adequate bag-mask ventilation has been demonstrated, either technique can be followed by the administration of a nondepolarizing neuromuscular blocking agent to facilitate tracheal intubation and provide ongoing neuromuscular blockade during the surgical procedure. Potential contraindications to this method include the presence of an anterior mediastinal mass compressing the distal trachea, or a tracheoesophageal fistula (TEF) where the endotracheal tube tip position should be confirmed below the fistula before the administration of a neuromuscular blocking agent.
Endotracheal intubation then follows, with placement of additional venous access if required and arterial monitoring (when indicated) before the start of the procedure. Because thoracic surgical procedures are frequently performed in the lateral decubitus position, access to the extremities to obtain additional venous sites may be limited once the procedure begins. In patients with normal cardiovascular function, the monitoring of central venous or arterial pressure may offer little additional information to improve or influence anesthetic care. Central venous access is generally reserved for cases in which adequate peripheral IV access is unavailable. If central venous access is necessary, ultrasound-guided internal jugular or subclavian vein cannulation on the side of the procedure is recommended. This avoids the possibility of bilateral pneumothoraces (the surgical pneumothorax induced on the side of the thoracotomy and the unintentional pneumothorax as a complication of the venous access procedure). The need for placement of invasive hemodynamic monitoring of arterial blood pressure is guided by the clinical status of the child and the specific surgical procedure and the need for postoperative blood pressure monitoring or blood gas sampling requirements. As many of these procedures use one-lung ventilation (OLV), arterial access may be useful to allow intermittent sampling of blood gases. End-tidal CO 2 monitoring may be inaccurate during thoracic procedures because of alterations in dead space and shunt fraction, especially during OLV. Transcutaneous carbon dioxide monitoring may be considered if continuous monitoring of carbon dioxide is indicated.
One-Lung Ventilation Techniques
Thoracic procedures often require lung deflation and minimal movement on the operative side while ventilating the nonoperative lung. Even during thoracoscopy, where insufflation of CO 2 gas may help collapse the operative lung, OLV should be considered if the surgeon requires additional exposure. In the pediatric patient, there are several options for attaining unilateral lung isolation ( Table 24.1 ).
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Double-Lumen Endotracheal Tube
A double-lumen endotracheal tube (DLT) is the most common method for attaining lung separation in adult patients. However, the smallest commercially available DLT is size 26-French (Fr), which precludes its placement in children weighing less than about 30 to 35 kg or younger than 8 to 10 years of age. Advantages of DLT over other techniques includes (1) rapid and easy separation of the lungs, (2) access to both lungs to facilitate suctioning, (3) ability to rapidly switch to two-lung ventilation if needed, and (4) ability to administer continuous positive airway pressure (CPAP) or oxygen insufflation to the operative lung, when necessary.
Left-sided DLTs are used almost exclusively as they are relatively easy to insert into the appropriate position and their use eliminates the possibility of obstruction of the right upper lobe bronchus given its short distance from the carina. After placement into the trachea and a 90-degree counterclockwise rotation, the DLT is advanced until resistance is encountered, and the tracheal and bronchial cuffs are inflated. Inflation of the bronchial cuff with 1 to 2 mL of air before advancement may help guide the DLT into the correct position, which is verified by auscultation after alternate clamping of tracheal and bronchial lumens and direct visualization using flexible bronchoscopy. When selecting a bronchoscope size, consideration should be given to the fact that the DLT’s bronchial lumen is at least 0.2-mm smaller than the tracheal lumen. When using the 26 to 28 Fr-sized DLTs, a neonatal bronchoscope (outer diameter 2.5–2.7 mm) is needed given the small internal diameter of its two lumens.
If lung isolation has not been achieved after insertion, a DLT may be in four possible incorrect locations, one of which is in the esophagus. The remaining three incorrect possibilities are (1) if the tube has not been advanced far enough, both tracheal and bronchial lumens will be in the trachea; (2) if the tube has been advanced too far, both tracheal and bronchial lumens will be in the left main bronchus; (3) and if the tube was unintentionally advanced into the right main bronchus, the bronchial (and possibly the tracheal) lumen will be located in the right main bronchus.
The correct position will have the tracheal lumen opening into the trachea above the carina and the bronchial lumen opening in the proximal left main bronchus. Confirmation should be performed after initial tube placement by end-tidal carbon dioxide (ETCO 2 ) detection, auscultation, and bronchoscopy. After turning the child to the lateral decubitus position, correct DLT positioning should be reconfirmed using repeat auscultation and flexible bronchoscopy.
If postoperative mechanical ventilation is required, consideration should be given to exchanging the DLT to a single-lumen endotracheal tube to prevent airway complications because of the large size of the DLT.
Univent Endotracheal Tube
The Univent tube (Fuji Systems Corporation, Tokyo, Japan) is a single-lumen endotracheal tube with a moveable bronchial blocker built into its sidewall. The bronchial blocker has a central channel, which can be used for the insufflation of oxygen if needed to treat intraoperative hypoxemia during OLV. After the Univent tube is placed into the trachea, the bronchial blocker is advanced into the main bronchus of the operative lung under direct vision using flexible bronchoscopy. The bronchial blocker is angled and therefore may be easily directed to either main bronchus by twisting the proximal shaft. Advantages of the Univent tube include ease of placement, the ability to easily change from OLV to two-lung ventilation (by deflating the bronchial cuff), and (unlike the standard DLT) the ability to pull the bronchial blocker back into its channel and to leave the Univent tube in place for postoperative ventilation.
Univent tubes are available with internal diameters of 3.5 (uncuffed), 4.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, and 9.0 mm ( Table 24.2 ). The outer diameter is larger than that of a conventional endotracheal tube of the same internal diameter. As a point of reference, the outer diameter of the smallest 3.5 mm Univent tube is equivalent to that of a standard 5.5 mm cuffed endotracheal tube. The internal diameters of the 3.5 and 4.5 mm Univent tubes limit the passage of a standard pediatric bronchoscope with an outside diameter ≥3.5 mm, thereby requiring an ultrathin pediatric bronchoscope to visualize the bronchial blocker. The external diameters of even the smallest of the Univent tubes is such that they are not feasible for patients less than about 6 to 8 years of age.
| Inner Diameter | Outer Diameter of Standard Tube | Maximum Outer Diameter of Univent |
|---|---|---|
| 3.5 mm | 4.9 mm | 8.0 mm a |
| 4.5 mm | 6.2 mm | 9.0 mm b |
| 6.0 mm | 8.2 mm | 11.5 mm c |
a Corresponds to a 6.0 mm internal diameter standard endotracheal tube.
b Corresponds to a 6.5 mm internal diameter standard endotracheal tube.
c Corresponds to a 8.5 mm internal diameter standard endotracheal tube.
Selective Endobronchial Intubation
In infants and young children whose small size precludes placement of a DLT or Univent, there are two additional options for OLV: selective endobronchial intubation with a standard endotracheal tube, or placement of a separate bronchial blocker. The major disadvantage of selective endobronchial intubation is that it is not possible to quickly change from OLV to two-lung ventilation because it requires repositioning of the endotracheal tube from the bronchus into the trachea. Furthermore, movement of the tracheal tube in a small infant in the lateral position under the surgical drapes during a thoracotomy risks hazardous complications such as accidental tracheal extubation. Unintentional movement of the endotracheal tube, which may be associated with surgical manipulation, may dislodge the tube tip from the bronchus into the trachea or the other bronchus. Our practice is to achieve standard endotracheal tube placement in the midportion of the trachea and note the depth of insertion at the gum. The tube is then advanced into the bronchus and the position at the gum is again noted. This allows for a measure of the depth of insertion when manipulating the tube during the surgical procedure. Remember that changes in head and neck position (flexion, extension, rotation) can alter the position of the tip of the tube even if the position at the gum is unchanged and secure.
Right-sided endobronchial intubation is easily accomplished blindly because of the anatomic orientation of the right main bronchus at a less acute angle to the vertical tracheal axis, although these angles tend to be similar in children younger than 3 years of age. A cuffed endotracheal tube is recommended as it facilitates total isolation of the lung, which will help prevent spread of an infectious process or blood from the operative lung to the ventilated nonoperative lung. The cuffed endotracheal tube size chosen for endobronchial intubation of either side should be one-half to one size smaller than usual, based on the patient’s age. This is suggested because the cuff adds to the outer diameter of the tube, and the diameter of the bronchus is smaller than the trachea. When selecting an appropriate size for the endotracheal tube, consideration should be given to the fact that the left mainstem bronchus is approximately 0.5 mm smaller than the right mainstem bronchus, which may necessitate a smaller tube size depending on the lung to be isolated.
Blind placement into the left main bronchus is not as straightforward as for the right main bronchus. The usual orientation of the distal bevel of the tube should be reversed (using a stylet) so that the concave segment becomes convex, ensuring that the tip of the stylet does not extend beyond the tip of the tube. When this is done, the angle of the bevel will face the patient’s right side with the Murphy eye along the left lateral wall of the trachea. Once the endotracheal tube is positioned in the midportion of the trachea, the stylet is removed and the tube advanced. Other maneuvers suggested to aid the successful left main bronchus placement include elevating the right shoulder, turning the head to the right side, or by applying firm pressure to the right side of the thorax. The authors’ preference, and perhaps the easiest technique, is to use bronchoscopic guidance by placement of the flexible bronchoscope through the endotracheal tube and into the left main bronchus, followed by advancement of the tube over the bronchoscope. Fluoroscopic guidance in the supine position with confirmation in the lateral position is a reliable, effective, and more expeditious technique than bronchoscopy for endobronchial endotracheal tube placement in infants. Some practitioners prefer the use of a Magill (no Murphy eye) or Microcuff tube (more distally located balloon cuff, no Murphy eye) to minimize the chance of gas leaking into the operative lung, especially when the main bronchus is short.
Bronchial Blockers
When a DLT or a Univent tube cannot be used because of the patient’s size or technical difficulty, a bronchial blocker should be considered. Several different devices can be used as bronchial blockers, including a Fogarty embolectomy catheter and the Arndt (Cook Critical Care, Bloomington, IN, USA) endobronchial blocker. The latter are available in three sizes (5, 7, and 9 Fr) allowing their effective use in the majority of patients. Fogarty embolectomy catheters (2–4 Fr) may be necessary in neonates. Atrioseptostomy and pulmonary artery catheters have also been used, but they have no advantage over the others and are more expensive. All these devices have a balloon at the distal end that when inflated will occlude the bronchus of the operative lung. Those devices with a central channel provide the advantage of allowing suctioning and application of low flow oxygen and CPAP to the operative lung. Because of the small size of the channel, suctioning will not clear the lung of secretions but it is used to deflate the operative lung and improve surgical visualization. Without the central channel, air or gas cannot exit from the lung once the balloon is inflated; therefore the lung may not completely deflate and may obscure surgical visualization. In these cases, the lung can be manually compressed by the surgeon during a brief period of apnea and the balloon then inflated before the provision of positive-pressure ventilation.
The bronchial blocker can be placed either alongside (extraluminal) or through (coaxial) a standard endotracheal tube. When placed through the tube, there will be a decrease in the internal cross-sectional area, thereby increasing the resistance to airflow. The degree to which this occurs depends on the outer diameter of the bronchial blocker and the inner diameter of the endotracheal tube. When placed inside the endotracheal tube, the blocker may be secured easily as it exits the proximal end of the tube. This can be accomplished using a T-piece bronchoscopic airway adaptor with a self-sealing diaphragm. Other commercially available options include the Arndt adaptor (Cook Critical Care, Bloomington, IN, USA), which has a port for the bronchoscope, one for the anesthesia circuit, and an occlusive port through which the bronchial blocker can be placed. The latter can be twisted to tighten down and hold the bronchial blocker in place. An additional option is to make a small hole in the wall of the proximal endotracheal tube; the bronchial blocker is then passed from the outside to the inside of the tube. The bronchial blocker can then be positioned and secured in place by taping it to the outside of the endotracheal tube, but subsequent manipulation may be more difficult.
The bronchial blocker can be positioned in the main bronchus of the operative side blindly, using fluoroscopic guidance, or most easily and safely under direct vision using flexible bronchoscopy. If bronchoscopy is used, and if the bronchial blocker is passed into the lumen of the endotracheal tube, then the bronchoscope and bronchial blocker must be small enough so both can pass through the endotracheal tube. The ease with which these instruments can be passed through the tube is greatly enhanced by prior application of a silicone spray. The proper fit of these instruments should be checked before induction of anesthesia. Given the external diameter of the bronchial blocker and the neonatal bronchoscope (OD 2.2 mm), a size 4.5 mm or greater tracheal tube is required.
The Arndt bronchial blocker has an inflatable cuff and a central lumen, through which a wire with a looped end can be passed. The bronchial blocker is passed through a specialized adaptor that is placed at the proximal end of the endotracheal tube. This adaptor contains four ports. The bronchial blocker is passed through the appropriate port and placed at the entrance of the endotracheal tube. The bronchoscope is passed through the port and then through the wire loop at the end of the bronchial blocker. The bronchoscope and bronchial blocker are passed under direct vision as a single unit into the main bronchus of the operative side. The wire loop is loosened, and the bronchoscope is withdrawn into the trachea to directly visualize inflation of the blocker balloon. When correct placement has been confirmed, the wire loop is removed from the central channel of the blocker. Once the wire guide is removed from the channel, it cannot be replaced. The Arndt blocker is currently available in three sizes, with the 9-Fr recommended for endotracheal tubes of internal diameter ≥8.0 mm, the 7-Fr for 6.5 to 7.5 mm tubes, and the 5-Fr for 4.5 to 6.0 mm tubes. When the 5-Fr blocker is placed in an endotracheal tube smaller than 6.0 mm, or a 7-Fr placed in an endotracheal tube smaller than 7.0 mm, airway pressures will be increased by 3 to 5 cmH 2 O.
If a child requires an endotracheal tube smaller than 4.5 mm, it may be necessary to place the bronchial blocker alongside the endotracheal tube if the bronchoscope and bronchial blocker will not fit through its lumen. In such cases, the bronchial blocker can be placed directly into the bronchus on the operative side using direct laryngoscopy, through a rigid bronchoscope or under fluoroscopy. Alternatively, the bronchus on the operative side can be intubated; the bronchial blocker passed through the endotracheal tube, which is then withdrawn completely and the trachea reintubated, so that the bronchial blocker lies on the outside of the endotracheal tube. The authors’ preference is to perform direct laryngoscopy, place the bronchial blocker through the glottic opening and into the tracheal lumen followed by tracheal intubation with the endotracheal tube. A flexible bronchoscope is then placed through the endotracheal tube and the bronchial blocker advanced into the bronchus of the operative lung under direct vision.
Regardless of which catheter or placement technique is chosen, there remains a risk for displacement of the bronchial blocker during the surgical procedure or with repositioning of the patient. If this occurs, the bronchial blocker may occlude the tracheal lumen just beyond the endotracheal tube, resulting in inadequate ventilation. Continuous auscultation of breath sounds using a precordial stethoscope on the nonoperative side and monitoring of inflating pressures, respiratory compliance, and P ET CO 2 should help identify this problem rapidly. Clinical experience suggests that inflating the balloon of the bronchial blocker with saline as opposed to air may limit movement and dislodgment during surgical manipulation. Additionally, with any change in the patient’s position, correct placement of the bronchial blocker should be confirmed using flexible bronchoscopy or fluoroscopy. If the patient’s respiratory status deteriorates rapidly during the surgical procedure with physiologic compromise, the balloon of the blocker should be deflated and consideration given to rapidly removing the bronchial blocker.
Anesthetic Management During One-Lung Ventilation
After separation of the lungs using one of the techniques described above, general anesthesia is maintained with a combination of IV and inhaled anesthetic agents. Hypoxic pulmonary vasoconstriction (HPV) maintains oxygenation during OLV by restricting pulmonary blood flow to the unventilated lung. In this setting, the administration of a nonspecific vasodilator (e.g., terbutaline, albuterol, isoproterenol, dobutamine, nicardipine, nitroglycerin, sodium nitroprusside, and inhaled anesthetic agents) may impair HPV and decrease oxygenation. The effects of isoflurane, sevoflurane, and desflurane on oxygenation during OLV are similar. Regardless of which inhaled agent is chosen, its expired concentration should be limited to 0.5 to 1.0 MAC to limit the effect on HPV.
With normal preoperative respiratory function, 100% oxygen may not be required to maintain adequate arterial oxygen saturation during OLV. Therefore the fraction of inspired oxygen can be decreased as needed by utilization of an air-oxygen mixture; the addition of air may have the added benefit of less postoperative atelectasis. Anesthesia is supplemented as needed with IV agents such as fentanyl or remifentanil, ketamine, benzodiazepines, propofol, and dexmedetomidine, none of which affect HPV. Ketamine preserves HPV, whereas propofol potentiates pulmonary vasoconstriction during hypoxia.
During OLV, ventilation should be maintained with tidal volumes of 4 to 8 mL/kg and a judicious amount of PEEP (4–6). Lung protective ventilation, which uses PEEP and avoids excessive tidal volumes (≥10 cc/kg), has been shown to reduce pulmonary complications in adults and children undergoing thoracic surgery. Respiratory rate may be adjusted as needed to maintain normocarbia. Pressure-limited ventilation can be used to deliver the same tidal volume with a lower peak inflating pressure compared with volume-limited ventilation. Hypocarbia should be avoided as it may interfere with HPV. The use of OLV may precipitate hypoxemia in children with preexisting lung disease or an alteration of pulmonary function. Treatment of this may require the intermittent provision of two-lung ventilation or a modification of OLV such as oxygen insufflation or application of CPAP to the operative lung. If adequate oxygenation cannot be maintained during OLV using 100% oxygen to the nonoperative side, CPAP of 4 to 5 cmH 2 O can be applied to the operative lung provided that a DLT, Univent, or bronchial blocker with a central channel has been used. Although this will improve oxygenation, it may also distend the operative lung to some degree and impair surgical visualization. If the above measures fail, it may be necessary to provide intermittent two-lung ventilation. A final option in management of acute severe hypoxemia is for the surgeon to clamp the nonventilated pulmonary artery to reduce shunt fraction.
Anesthetic Management for Thoracoscopy
The reports of successes in the adult population combined with ongoing refinements in technique and the availability of smaller sized equipment have led to the use of thoracoscopy in infants and children. Initially used to biopsy intrathoracic neoplasms, thoracoscopy has now been used in more involved surgical procedures including the treatment of empyema, pleurodesis, and anterior spinal fusion in older children and resection of congenital lung masses, ligation of a patent ductus arteriosus, and TEF ligation and esophageal repair in infants. Various anesthetic techniques have been described in the adult population for thoracoscopy, including local anesthetic infiltration and regional anesthetic techniques; however, in the pediatric population, general anesthesia is required.
The anesthetic technique for thoracoscopy in children is straightforward. After the induction of general anesthesia, OLV is established using one of the techniques previously described. The patient is then positioned in either the supine or lateral decubitus position. After repositioning, the efficacy of OLV is again demonstrated and the endotracheal tube or bronchial blocker repositioned as needed.
There are a number of possible complications related to the thoracoscopic technique. Even more so than with laparoscopy, the rapid absorption of CO 2 from the pleural surfaces necessitates an increase in minute ventilation to avoid hypercarbia. The hemidiaphragm on the operative side, which has been isolated by the technique of OLV, will move cephalad, so trocar entry below the third or fourth intercostal space may result in hepatic or splenic injury. The artificial pneumothorax may decrease blood pressure and cardiac output by altering preload and/or afterload. In addition, inadvertent gas embolism may occur with the use of CO 2 insufflation. CO 2 embolism can occur from direct injection through vascular puncture during insufflation or from the entry of the gas, which is under pressure in the hemithorax, into an internal vessel that has been damaged during the procedure. The physiologic effects and clinical manifestations of gas embolism are dependent on the type and volume of embolized gas, the rate of injection, and the patient’s baseline cardiovascular function. The dead space of the equipment should be flushed with a large volume of CO 2 before placement in the patient to avoid insufflation of air, which has more hemodynamic consequences than CO 2 if embolized.
Treatment of gas embolism begins with the immediate cessation of insufflation or release of the artificial pneumothorax. Because CO 2 is rapidly absorbed from the bloodstream, the cardiovascular changes usually reverse rapidly. Additional treatment, determined by the severity of the cardiovascular changes, includes the administration of fluids to increase preload and inotropic agents to augment cardiac contractility. With severe cardiovascular compromise, placement of the patient in the head-down, left lateral decubitus position (Durant maneuver) may displace the gas out of the right ventricular outflow tract into the apical portion of the right ventricle and restore cardiovascular function. Aspiration from a central venous catheter should be attempted if one is present.
At the completion of the procedure, the pneumothorax is evacuated and two-lung ventilation is reinstituted. Several large-volume breaths are delivered to ensure reexpansion of the lung on the operative side. In most cases, residual neuromuscular blockade is reversed and the patient’s trachea is extubated.
Postoperative analgesia may be enhanced through the use of local anesthetic techniques. Administration of local anesthesia by the surgeon to the incision site or intercostal nerves under direct visualization is both timely and effective. Neuraxial analgesia in the form of an epidural or paravertebral technique may be employed assuming the absence of any contraindications and may be particularly useful in improving pulmonary outcomes after open thoracotomy. Newer fascial plane nerve block and catheter techniques such as serratus plane blocks and erector spinae blocks may also be of utility in improving postoperative pain control and decreasing opioid consumption.
Neonatal Thoracic Surgery
Thoracic surgery in neonates is primarily performed to correct congenital lung anomalies. These include congenital cystic adenomatoid malformation (CCAM), congenital lobar emphysema (CLE), pulmonary sequestration, and tracheoesophageal fistula (TEF) with or without esophageal atresia. All except pulmonary sequestration have an association with additional congenital anomalies, including congenital heart disease. TEF is often found as part of the VATER (or VACTERL) syndrome. VATER and VACTERL syndrome denote a constellation of abnormalities with the following structures. V = Vertebra; A = Anus (atresia); T = Trachea; E = Esophagus; R = Renal (Kidneys); VACTERL as above plus C = Cardiac, L = Limb. These associations necessitate a thorough preoperative evaluation to identify associated congenital anomalies, including echocardiography to rule out congenital heart disease.
When anesthetizing infants with congenital lung lesions, one of the most important preoperative determinations is whether or not positive-pressure ventilation will cause cardiopulmonary deterioration. This could occur in a lesion that contains a bronchial connection to a segment of lung with abnormal parenchyma, such as CLE. In this condition, positive-pressure ventilation results in progressive distention of the abnormal lobe with compression of normal lung because of a ball-valve effect, leading to hypoxemia. Mediastinal shift may torque the great vessels, causing decreased cardiac output and leading to cardiac arrest. If it is not known whether the lesion connects to a bronchus, spontaneous ventilation is indicated until one-lung ventilation of the contralateral lung is achieved or until the chest is opened. Maintenance of spontaneous ventilation can be achieved by carefully titrating a combination of IV and inhaled induction agents, and endotracheal intubation can be performed without muscle relaxation. A rostrally advanced caudal catheter or thoracic epidural catheter can be used to provide analgesia and aid in the preservation of spontaneous ventilation.
If the application of positive pressure is not of concern, routine IV induction of general anesthesia followed by administration of a neuromuscular blocking agent may be performed. Maintenance of general anesthesia is provided by a combination of an inhaled agent and an opioid or regional anesthetic technique. Nitrous oxide is avoided because of the risk for increasing the size of an air-filled mass.
Postoperative analgesia after neonatal thoracic surgery is best accomplished using an epidural catheter that has been advanced to the thoracic level via the caudal space. Infants who remain on mechanical ventilation can receive a continuous opioid infusion.
Congenital Cystic Adenomatoid Malformation
A CCAM is a cystic, solid, or mixed intrapulmonary mass that may communicate with the normal tracheobronchial tree ( Fig. 24.1 ). A CCAM may grow large in utero, causing cardiac compression, decreased cardiac output with hydrops fetalis, and even fetal demise. Fetal surgery or ex-utero intrapartum treatment (EXIT) procedure is now available in some centers for such lesions. More commonly, a CCAM is detected by prenatal ultrasound or magnetic resonance study, does not compromise the fetus, and is surgically excised in the neonatal period or the first 2 months of life. CCAM may be associated with a mediastinal shift and respiratory distress, which necessitates emergent resection. Most cases, however, are asymptomatic and resection is performed as an elective procedure.
