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Department of Anesthesia, Stanford University Medical Center, Stanford, California
Address correspondence to Gregory B. Hammer, MD, Associate Professor, Department of Anesthesia, Room H3580, Stanford University Medical Center, 300 Pasteur Drive, Stanford, CA 94305-5115. Address e-mail to ham{at}leland.stanford.edu
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Surgical Lesions of the Chest |
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Tracheal stenosis may be acquired or congenital. Tracheal stenosis occurs most often because of prolonged tracheal intubation, often in neonates with infant respiratory distress syndrome associated with prematurity. Ischemic injury of the tracheal mucosa may occur because of a tight-fitting endotracheal tube (ETT) at the level of the cricoid cartilage, which becomes scarred and constricted. Subglottic stenosis may develop, resulting in stridor after tracheal extubation. Reintubation may be required because of oxygen desaturation and hypercarbia.
Fiberoptic bronchoscopy is used to evaluate the severity of the stenosis and exclude other causes of stridor (e.g., vocal cord paralysis or laryngomalacia). When general anesthesia is required, inhaled anesthesia may be administered via a face mask, with the fiberoptic bronchoscope inserted through an adaptor in the mask and into the nasopharynx. This is usually performed with the patient breathing spontaneously (1). Alternatively, a laryngeal mask may be used as a conduit (2). Local anesthesia is applied to the vocal cords and trachea through the bronchoscope. Attention must be directed to the dose of local anesthetic used, as systemic absorption may lead to local anesthetic toxicity (3).
A cricoid split procedure may be performed for infants with acquired subglottic stenosis. After diagnostic bronchoscopy, either the patient is intubated with an ETT or a rigid bronchoscope is left in place during the operation. During rigid bronchoscopy, positive pressure ventilation is performed by connecting the anesthesia breathing circuit to the side arm of the bronchoscope. Anesthesia may be maintained with inhaled anesthetics or an IV anesthetic technique, such as propofol and remifentanil (4). A horizontal incision is made over the cricoid cartilage, after which a vertical incision is made through the inferior portion of the thyroid cartilage, the cricoid cartilage, and the first tracheal ring. Typically, an ETT a half size larger than the original tube is placed after the repair.
Congenital tracheal stenosis may be segmental, occurring in the region of the cricoid cartilage, the midtrachea, or just above the carina. In some cases, the stenotic segment is long, including multiple small tracheal cartilages. Infants present with suprasternal, intercostal, and subcostal retractions, which worsen during agitation and with intercurrent respiratory infections.
For patients with severe tracheal stenosis, a laryngotracheoplasty may be performed. This procedure involves the placement of a costal, auricular, or laryngeal cartilage graft into the anterior trachea, the posterior trachea, or both (5). In some cases, a stent may be positioned within the trachea. A previously indwelling tracheostomy tube may be exchanged for an anode tube during the procedure, and this may be either removed or replaced at the end of the operation, depending on whether or not additional staged operations are planned. Rarely, repair of distal tracheal and bronchial stenosis may require cardiopulmonary bypass. Patients may remain intubated and ventilated for a variable period of time after surgery. In these cases, sedation, analgesia, and neuromuscular blockade are maintained after surgery.
Pulmonary sequestrations result from disordered embryogenesis producing a nonfunctional mass of lung tissue supplied by anomalous systemic arteries. Intralobar sequestrations are usually found in the left posterior segments. Arterial supply arises from the aorta, above or below the diaphragm, whereas venous drainage is usually through the pulmonary veins. They are usually isolated anomalies and may not present until late in childhood or adulthood. Extralobar sequestrations occur just above or below the diaphragm and are also usually left-sided. Their arterial supply is from small, anomalous pulmonary or systemic arterial branches, and venous drainage is systemic (e.g., portal or azygous vein). Communication with the foregut and associated anomalies are common, including bronchial agenesis, duplication of the colon, vertebral anomalies, and diaphragmatic defects. Presenting signs include cough, pneumonia, and failure to thrive and often present during the neonatal period, usually before the age of 2 yr. Diagnostic studies include arteriography and computerized tomography (CT) scans of the chest and abdomen. Magnetic resonance imaging may provide high-resolution images, including definition of vascular supply. This may obviate the need for angiography (6). Surgical resection is performed after diagnosis.
Pulmonary sequestrations do not generally become hyperinflated during positive-pressure ventilation. Nitrous oxide administration may result in expansion of these masses, however, and should be avoided.
Pulmonary hypoplasia may be caused by a variety of intrauterine problems, including those that compress the developing lungs (congenital diaphragmatic hernia, tumor, pleural effusion), oligohydramnios (fetal renal failure with oliguria), and absent or poor fetal breathing movements (Werdnig-Hoffman disease, congenital myotonic dystrophy, anencephaly, agenesis of phrenic nerves). Space occupying intrathoracic lesions may cause unilateral lung hypoplasia, whereas the latter conditions usually result in bilateral hypoplasia that is not often amenable to surgery. The scimitar syndrome presents with hypoplasia of the right lung and anomalous pulmonary venous drainage to the inferior vena cava. Chest radiography may reveal a crescent-shaped shadow along the right heart border that resembles a Turkish sword or scimitar. Unilateral lung hypoplasia may be associated with recurrent pneumonia, hypoxemia, or both caused by ventilation/perfusion (V/Q) mismatching and may therefore require surgical resection. Excessive positive-pressure ventilation may result in barotrauma and pneumothorax, pneumomediastinum, or interstitial emphysema on the affected or contralateral side (see discussion below).
Congenital cystic lesions in the thorax may be classified into three categories (7). Bronchogenic cysts result from abnormal budding or branching of the tracheobronchial tree. They may cause respiratory distress, recurrent pneumonia, or atelectasis caused by lung compression. Bronchogenic cysts may be paratracheal, hilar, carinal, or paraesophageal and usually do not communicate with the airways. These cysts are most often unilocular and are filled with mucoid material. Bronchogenic cysts associated with clinical signs are generally treated with surgical excision (8). Rarely, these lesions do communicate with the airway; rupture with spillage of fluid into the tracheobronchial tree during anesthesia has been reported (9). Dermoid cysts are clinically similar to bronchogenic cysts but differ histologically, because they are lined with keratinized, squamous epithelium rather than respiratory (ciliated columnar) epithelium. They usually present later in childhood or adulthood. Cystic adenomatoid malformations (CAM) are structurally similar to bronchioles but lack associated alveoli, bronchial glands, and cartilage (10). Because these lesions communicate with the airway, they may become overdistended because of gas trapping, leading to respiratory distress in the first few days of life. When they are multiple and air filled, CAM may resemble congenital diaphragmatic hernia (CDH) radiographically. Treatment is surgical resection of the affected lobe. As with CDH, prognosis depends on the amount of remaining lung tissue, which may be hypoplastic because of compression in utero (11).
Congenital lobar emphysema often presents with respiratory distress shortly after birth (12). This lesion may be caused by ball-valve bronchial obstruction in utero, causing progressive distal overdistension with fetal lung fluid. The resultant emphysematous lobe may compress the lung bilaterally, resulting in a variable degree of hypoplasia. Congenital cardiac deformities are present in about 15% of patients (13). Radiographic signs of hyperinflation may be misinterpreted as tension pneumothorax or atelectasis on the contralateral side (Fig. 1). Surgical resection is usually performed when the PaO2 is <50 mm Hg despite supplemental oxygen administration (14). Positive-pressure ventilation may exacerbate lung hyperinflation. Nitrous oxide is contraindicated, and isolation of the lungs during anesthesia is desirable.
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A particularly poor prognosis is predicted if CDH is associated with cardiac deformities, a preoperative alveolar-to-arterial oxygen gradient >500 mm Hg, or severe hypercarbia despite vigorous ventilation (23,24). Prognosis has also been correlated with pulmonary compliance and radiographic findings (25–27).
Surgical correction via a subcostal incision with ipsilateral chest tube placement may be performed before or during ECMO (28,29). In patients undergoing surgical repair off ECMO, pulmonary hypertension is the major cause of morbidity and mortality. Hyperventilation to induce a respiratory alkalosis and 100% oxygen should be administered to decrease pulmonary vascular resistance. The anesthetic should be designed to minimize sympathetic discharge that may exacerbate pulmonary hypertension (e.g., a large-dose opioid technique). Infants should be ventilated with small tidal volumes and low inflating pressures to avoid pneumothorax on the contralateral (usually right) side. Both nitric oxide and high-frequency oscillatory ventilation have been used during surgical repair (30,31). A high index of suspicion of right-sided pneumothorax should be maintained, and a thoracostomy tube should be placed in the event of acute deterioration of respiratory or circulatory function. It is also imperative that normal body temperature, intravascular volume, and acid-base status be maintained. Mechanical ventilation is continued after surgery in nearly all cases.
Failure of the central and lateral portions of the diaphragm to fuse results in a retrosternal defect, the foramen of Morgagni. This usually presents with signs of bowel obstruction rather than respiratory distress. Repair is usually performed via an abdominal incision.
Tracheoesophageal fistula (TEF), esophageal atresia, or both occur in approximately 1 in 4000 live births. In 80%–85% of infants, this lesion includes esophageal atresia with a distal esophageal pouch and a tracheal fistulous connection (32,33). The fistula is usually located 1 or 2 tracheal rings above the carina. Afflicted neonates present with spillover of pooled oral secretions from the pouch and may develop progressive gastric distension and tracheal aspiration of acidic gastric contents via the fistula. A common association is the VACTERL complex, consisting of vertebral, anorectal, cardiac, tracheoesophageal, renal, or limb defects (34). Esophageal atresia is confirmed when an orogastric tube passed through the mouth cannot be advanced more than about 7 cm (Fig. 3). The tube should be secured and placed on continuous suction, after which a chest radiograph is diagnostic.
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Esophageal atresia without connection to the trachea occurs much less often. These lesions are generally diagnosed by radiography after inability to pass an orogastric tube, at which time an absence of gas in the abdomen may be noted (Fig. 5). So-called H-type TEF without esophageal atresia is relatively rare. Patients with H-type lesions may present later in childhood or adulthood with recurrent pneumonias or gastric distension during positive-pressure ventilation (39).
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Surgical repair via a left thoracotomy (or right thoracotomy in infants with a right-sided aortic arch) may be performed in the neonatal intensive care unit in premature infants. In this setting, an IV anesthetic with fentanyl for analgesia, a benzodiazepine for amnesia and hypnosis, and a neuromuscular blocking drug may be most pragmatic. Many of these patients have congestive heart failure and are mechanically ventilated both before and after surgery. Larger infants may be well suited for regional anesthesia plus inhaled or short-acting IV anesthesia and planned tracheal extubation in the operating room.
COTA is a localized narrowing of the aorta occurring close to the insertion of the ductus arteriosus into the aorta. COTA occurs in 1 in 1200–2000 live births (42,43). COTA may present in the newborn as a critical aortic obstruction in which the PDA supplies most of the perfusion to the lower body. These patients are frequently critically ill, with a metabolic acidosis and cyanosis of the lower body. Prostaglandin E1 is infused before surgery to maintain ductal patency until surgical correction can be performed.
COTA more typically presents later in childhood with arterial hypertension in the upper extremities and low blood pressure in the lower extremities, with poor or absent femoral pulses. Turner’s syndrome and bicuspid aortic valve or other congenital cardiac defects may be associated with COTA. Cardiomegaly, systemic hypertension, and congestive heart failure may be present.
The surgical treatment of COTA is usually accomplished via a left thoracotomy and may consist of resection of the coarcted segment of aorta with end-to-end anastomosis, subclavian flap repair, or the use of synthetic graft material. Arterial blood pressure should be monitored above and below the coarctation, e.g., with a radial arterial catheter and a blood pressure cuff on a lower extremity. The distal arterial pressure should generally be maintained >45 mm Hg to maintain renal perfusion (44). The patient’s body temperature is often cooled to 35°C to minimize ischemic spinal cord injury during aortic occlusion. Despite this, the incidence of paraplegia after COTA repair is approximately 1 in 250 (44). Proposed mechanisms for paraplegia include inadequate distal perfusion pressure during aortic occlusion, interruption of the blood supply via the anterior spinal artery, and increased cerebrospinal fluid pressure.
Hypertension after surgery may be treated with ß-blockers (e.g., esmolol) or a variety of other drugs (45). Untreated systemic hypertension may be accompanied by abdominal pain and even bowel perforation secondary to mesenteric insufficiency, thought to be caused by arteritis associated with an acute increase in arterial perfusion. These findings may be accompanied by fever, leukocytosis, melena, and abdominal distension and are referred to as postcoarctectomy syndrome. As an alternative to coarctectomy, balloon angioplasty may be performed for both native and recurrent coarctations (46).
Vascular rings are anomalies of the aortic arch, right subclavian artery, or pulmonary arteries that compress the trachea and esophagus. These abnormalities are generally produced by the failure of portions of the fourth or sixth embryonic aortic arches to regress or develop normally. The most common varieties of vascular rings are composed of a double aortic arch, a right-sided arch with a left ductus (or ligamentum) arteriosus, anomalous right subclavian or innominate artery, or a pulmonary artery sling. Most children with vascular rings are asymptomatic or mildly symptomatic during infancy and outgrow their respiratory signs (e.g., stridor) as the trachea becomes more cartilaginous. In cases of severely compromised airways caused by vascular rings, infants present during the first month of life with stridor, recurrent respiratory infections, or dysphagia (47). CXR and barium esophagrams are diagnostic. Surgical repair is generally performed through a left lateral thoracotomy.
Patients with tracheomalacia caused by extrinsic compression may have airway obstruction because of tracheal collapse during the induction of anesthesia and after tracheal extubation. Vascular rings may cause tracheal compression similar to anterior mediastinal masses. Inhaled induction has been recommended, followed by administration of assisted or controlled ventilation before the administration of muscle relaxants (48). A rigid bronchoscope should be at hand, because it may be lifesaving in the event of tracheal collapse. Airway compression may be exacerbated during lateral decubitus positioning, in which case immediate repositioning should be performed. Because of the risk of hemorrhage during surgery, appropriate vascular access should be secured before skin incision, and blood must be available for transfusion.
Childhood
Many of the lesions described above may not be diagnosed until childhood. These include pulmonary sequestration, arteriovenous abnormalities, cystic lesions, lobar emphysema, PDA, COTA, and vascular rings. Other disorders for which thoracic surgery is performed in children, either for definitive treatment or diagnostic purposes, include tumors, infectious diseases, and musculoskeletal deformities.
Tumors of the lung, mediastinum, and pleura may be primary or metastatic (49). Primary tumors of the chest are uncommon in children. Perhaps the most common are lymphoblastic lymphoma, a form of non-Hodgkin’s lymphoma, and Hodgkin’s disease. These neoplasms usually present as an anterior mediastinal (thymic) mass with pleural effusion, dyspnea caused by airways obstruction, pain, or superior vena cava syndrome (swelling of the upper arms, face, and neck) (Fig. 6) (50,51). The induction of anesthesia in patients with anterior mediastinal masses may be associated with severe airway and circulatory collapse (52,53). Accordingly, institutions should have an algorithm in place for the evaluation of these patients, including preoperative CT scanning, echocardiography, and flow-volume studies, as well as their treatment (Fig. 7). Careful consideration should be given to performing a biopsy under local anesthesia or initiating chemotherapy or limited radiation therapy before subjecting the child to general anesthesia to effect a decrease in tumor mass and life-threatening airway or vascular occlusion.
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Empyema is a complication of bacterial pneumonia most often caused by Staphylococcus aureus and Streptococcus pneumoniae. Haemophilus influenzae type b is much less common because of the use of the Haemophilus influenzae type b vaccine in young children (54). Empyema is diagnosed by CXR or CT scan, or both, and is associated with prolonged fever and leukocytosis. Despite therapy with antibiotics and chest tube drainage, with or without pleural streptokinase or urokinase instillation, surgical treatment is often necessary (55). Rarely, lung abscesses that persist despite antibiotics and percutaneous drainage may also require surgical treatment. Surgical lung biopsy may be performed for diagnostic purposes in cases of interstitial lung disease, which may be infectious (Pneumocystis, respiratory syncytial virus, cytomegalovirus) or noninfectious (e.g., nonspecific or allergic).
Pulmonary arteriovenous fistulas and malformations occur most often along with widespread vascular abnormalities, as in patients with Rendu-Osler-Weber syndrome (hereditary hemorrhagic telangiectasis) (56). These lesions may present during infancy or childhood with hypoxemia because of right-to-left shunting of blood, or with congestive heart failure. Acquired arteriovenous fistulas may develop in children with liver disease, increased pulmonary artery pressure (e.g., pulmonary hypoplasia, mitral stenosis, cystic fibrosis), after cavopulmonary shunting, or after chest trauma (57,58). Surgical intervention is warranted when these lesions are focal and severe. Many of these fistulas can be completely or partially coil occluded in the catheterization laboratory. Persistent lesions may require surgical resection.
Pectus excavatum results from excessive growth of the costochondral cartilages, with resultant inward depression of the sternum. Pectus excavatum may be associated with Marfan’s syndrome or chronic airway obstruction with large negative intrathoracic pressure during inspiration. Children with severe deformities may have circulatory impairment caused by distortion of the heart and great vessels, or respiratory compromise caused by lung compression. If possible, surgical repair is deferred until late childhood or adolescence, when the ribs and sternum are more fully calcified. A variety of surgical repairs have been described, ranging from complete resection of the sternum to minimally invasive surgery with placement of a retrosternal strut through small incisions in the lateral chest. Of note, complications of the latter technique include perforation of the lungs and heart (59). Preoperative pulmonary function abnormalities may not be significantly improved after surgery (60,61).
Kyphoscoliosis is a curvature of the spine measuring 10° or more in the frontal plane. This disorder may present as infantile (<3 yr old), juvenile (3–10 yr old), or adolescent (>10 yr old) forms. Kyphoscoliosis may be associated with congenital malformations of the vertebra, neuromuscular disease (e.g., muscular dystrophy), or neoplastic diseases (e.g., neurofibromatosis), or it may be idiopathic. Surgical correction is delayed until the teenage years unless the deformity is severe, and it consists of posterior spinal fusion with instrumentation with or without anterior spinal fusion. The latter may be performed thoracoscopically (62,63).
Ventilation/Perfusion During Thoracic Surgery
Ventilation is normally distributed preferentially to dependent regions of the lung, so that there is a gradient of increasing ventilation from the most nondependent to the most dependent lung segments. Because of gravitational effects, perfusion normally follows a similar distribution, with increased blood flow to dependent lung segments. Therefore, ventilation and perfusion are normally well matched. During thoracic surgery, several factors act to increase V/Q mismatch. General anesthesia, neuromuscular blockade, and mechanical ventilation cause a decrease in functional residual capacity of both lungs. Compression of the dependent lung in the lateral decubitus position may cause atelectasis. Surgical retraction or SLV results in collapse of the operative lung. Hypoxic pulmonary vasoconstriction (HPV), which acts to divert blood flow away from the underventilated lung, thereby minimizing V/Q mismatch, may be diminished by inhaled anesthetics and other vasodilating drugs. These factors apply equally to infants, children, and adults. The overall effect of the lateral decubitus position on V/Q mismatch, however, is different in infants compared with older children and adults.
In adults with unilateral lung disease, oxygenation is optimal when the patient is placed in the lateral decubitus position with the healthy lung dependent (down) and the diseased lung nondependent (up) (64). Presumably, this is related to an increase in blood flow to the dependent, healthy lung and a decrease in blood flow to the nondependent, diseased lung caused by the hydrostatic pressure (or gravitational) gradient between the two lungs. This phenomenon promotes V/Q matching in the adult patient undergoing thoracic surgery in the lateral decubitus position.
In infants with unilateral lung disease, however, oxygenation is improved with the healthy lung up (65). Several factors account for this discrepancy between adults and infants. Infants have a soft, easily compressible rib cage that cannot fully support the underlying lung. Therefore, functional residual capacity is closer to residual volume, making airway closure likely to occur in the dependent lung even during tidal breathing (66). When the adult is placed in the lateral decubitus position, the dependent diaphragm has a mechanical advantage because it is "loaded" by the abdominal hydrostatic pressure gradient. This pressure gradient is reduced in infants, thereby reducing the functional advantage of the dependent diaphragm. The infant’s small size also results in a reduced hydrostatic pressure gradient between the nondependent and dependent lungs. Consequently, the favorable increase in perfusion to the dependent, ventilated lung is reduced in infants.
Finally, the infant’s increased oxygen requirement, coupled with a small functional residual capacity, predisposes the infant to hypoxemia. Infants normally consume 6–8 mL · kg-1 · min-1 of oxygen compared with a normal oxygen consumption in adults of 2–3 mL · kg-1 · min-1 (67). For these reasons, infants are at an increased risk of significant oxygen desaturation during surgery in the lateral decubitus position.
Indications and Techniques for SLV in Infants and Children
Before 1995, nearly all thoracic surgery in children was performed by thoracotomy. In most cases, anesthesiologists ventilated both lungs with a conventional tracheal tube, and the surgeons retracted the operative lung to gain exposure to the surgical field. During the past decade, the use of video-assisted thoracoscopic surgery (VATS) has dramatically increased in both adults and children. Reported advantages of thoracoscopy include smaller chest incisions, reduced postoperative pain, and more rapid postoperative recovery compared with thoracotomy (68–70). Recent advances in surgical technique, as well as technology, including high-resolution microchip cameras and smaller endoscopic instruments, have facilitated the application of VATS in smaller patients.
VATS is being used extensively for pleural debridement in patients with empyema, lung biopsy and wedge resections for interstitial lung disease, mediastinal masses, and metastatic lesions. More extensive pulmonary resections, including segmentectomy and lobectomy, have been performed for lung abscess, bullous disease, sequestrations, lobar emphysema, CAM, and neoplasms. In selected centers, more advanced procedures have been reported, including closure of PDA, repair of hiatal hernias, and anterior spinal fusion.
VATS can be performed while both lungs are being ventilated by using CO2 insufflation and placement of a retractor to displace lung tissue in the operative field. However, SLV is extremely desirable during VATS because lung deflation improves visualization of thoracic contents and may reduce lung injury caused by the use of retractors (71). There are several different techniques that can be used for SLV in children.
Single-Lumen Endotracheal Tube.
The simplest means of providing SLV is to intentionally intubate the ipsilateral mainstem bronchus with a conventional single-lumen ETT (72). When the left bronchus is to be intubated, the bevel of the ETT is rotated 180° and the head turned to the right (73). The ETT is advanced into the bronchus until breath sounds on the operative side disappear. A fiberoptic bronchoscope may be passed through or alongside the ETT to confirm or guide placement. When a cuffed ETT is used, the distance from the tip of the tube to the distal cuff must be shorter than the length of the bronchus so that the upper lobe bronchus is not occluded (74).
This technique is simple and requires no special equipment other than a fiberoptic bronchoscope. This may be the preferred technique of SLV in emergency situations such as airway hemorrhage or contralateral tension pneumothorax.
Problems can occur when using a single-lumen ETT for SLV. If a smaller, uncuffed ETT is used, it may be difficult to provide an adequate seal of the intended bronchus. This may prevent the operated lung from adequately collapsing or fail to protect the healthy, ventilated lung from contamination by purulent material from the contralateral lung. The operated lung cannot be suctioned with this technique. Hypoxemia may occur because of obstruction of the upper lobe bronchus, especially when the short right mainstem bronchus is intubated.
Variations of this technique have been described, including intubation of both bronchi independently with small ETTs (75–78). One mainstem bronchus is initially intubated with an ETT, after which another ETT is advanced over a fiberoptic bronchoscope into the opposite bronchus.
Balloon-Tipped Bronchial Blockers.
A Fogarty embolectomy catheter or an end-hole, balloon-wedge catheter may be used for bronchial blockade to provide SLV (Fig. 8) (79–82). Placement of a Fogarty catheter is facilitated by bending the tip of its stylette toward the bronchus on the operative side. A fiberoptic bronchoscope may be used to reposition the catheter and confirm appropriate placement. When an end-hole catheter is used, the bronchus on the operative side is initially intubated with an ETT. A guidewire is then advanced into that bronchus through the ETT. The ETT is removed, and the blocker is advanced over the guidewire into the bronchus. An ETT is then reinserted into the trachea alongside the blocker catheter. The catheter balloon is positioned in the proximal mainstem bronchus under fiberoptic visual guidance. With an inflated blocker balloon, the airway is completely sealed, providing more predictable lung collapse and better operating conditions than with an ETT in the bronchus.
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Recently, adapters have been used that facilitate ventilation during placement of a bronchial blocker through an indwelling ETT (85,86). The risk of hypoxemia during blocker placement is diminished, and repositioning of the blocker may be performed with fiberoptic guidance during surgery. The ETT must be at least 5.0 mm internal diameter, however, generally limiting the use of this technique to children over the age of 2 yr.
Univent Tube.
The Univent tube (Fuji Systems Corporation, Tokyo, Japan) is a conventional ETT with a second lumen containing a small tube that can be advanced into a bronchus (87–89). A balloon located at the distal end of this small tube serves as a blocker. Univent tubes require a fiberoptic bronchoscope for successful placement. Univent tubes are now available in sizes as small as a 3.5- and 4.5-mm internal diameter for use in children >6 yr old (90).
Because the blocker tube is firmly attached to the main ETT, displacement of the Univent blocker balloon is less likely than when other blocker techniques are used. The blocker tube has a small lumen that allows egress of gas and can be used to insufflate oxygen or suction the operated lung.
A disadvantage of the Univent tube is the large amount of cross-sectional area occupied by the blocker channel, especially in the smaller-sized tubes. Smaller Univent tubes have a disproportionately high resistance to gas flow (91). The Univent tube’s blocker balloon has low-volume, high-pressure characteristics, so mucosal injury can occur during normal inflation (92,93).
Double-Lumen Tubes.
All DLTs are essentially two tubes of unequal length molded together. The shorter tube ends in the trachea and the longer tube in the bronchus. Marraro (94) described a bilumen tube for infants. This tube consists of two separate uncuffed tracheal tubes of different lengths attached longitudinally. This tube is not available in the United States. DLTs for older children and adults have cuffs located on the tracheal and bronchial lumens. The tracheal cuff, when inflated, allows positive-pressure ventilation. The inflated bronchial cuff allows ventilation to be diverted to either or both lungs and protects each lung from contamination from the contralateral side.
Conventional plastic DLTs, once available only in adult sizes (35F, 37F, 39F, and 41F), are now available in smaller sizes. The smallest cuffed DLT is a 26F (Rusch, Duluth, GA), which may be used in children as young as 8 yr old. DLTs are also available in sizes 28F and 32F (Mallinckrodt Medical, Inc., St. Louis, MO), suitable for children 10 yr and older.
DLTs are inserted in children by using the same technique as in adults (95). The tip of the tube is inserted just past the vocal cords, and the stylette is withdrawn. The DLT is rotated 90° to the appropriate side and then advanced into the bronchus. In the adult population, the depth of insertion is directly related to the height of the patient (96). No equivalent measurements are yet available in children. If fiberoptic bronchoscopy is to be used to confirm tube placement, a bronchoscope with a small diameter and sufficient length must be available (97).
A DLT offers the advantage of ease of insertion as well as the ability to suction and oxygenate the operative lung with continuous positive airway pressure. Left DLTs are preferred to right DLTs because of the shorter length of the right main bronchus (98). Right DLTs are more difficult to accurately position because of the increased risk of right upper lobe obstruction.
DLTs are safe and easy to use. There are very few reports of airway damage from DLTs in adults, and none in children. Their high-volume, low-pressure cuffs should not damage the airway if they are not overinflated with air or distended with nitrous oxide while in place.
Guidelines for selecting appropriate tubes (or catheters) for SLV in children are shown in Table 1. There is significant variability in overall size and airway dimensions in children, particularly in teenagers. The recommendation shown in Table 1 are based on average values for airway dimensions. Larger DLTs may be safely used in large teenagers.
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Inhaled anesthetics are often administered in 100% oxygen during maintenance of anesthesia. Isoflurane may be preferred because of less attenuation of HPV compared with other inhaled anesthetics, although this has not been studied in children (99). Nitrous oxide is avoided. Use of IV opioids may facilitate a decrease in the concentration of inhaled anesthetics used and therefore limit impairment of HPV. Alternatively, total IV anesthesia may be used with a variety of drugs. The combination of general anesthesia with regional anesthesia and postoperative analgesia is particularly desirable for thoracotomy but may also be beneficial for VATS, especially when thoracostomy tube drainage, a source of significant postoperative pain, is used after surgery. A variety of regional anesthetic techniques have been described for intraoperative anesthesia and postoperative analgesia, including intercostal and paravertebral blocks, intrapleural infusions, and epidural anesthesia.
Intercostal nerve blocks may be performed before skin incision or under direst vision by the surgeon before chest closure. Because of overlap of sensory dermatomes, nerves above and below the level of surgery must be blocked. This may require large doses and therefore large plasma concentrations of local anesthetics, especially in infants (100). Intraoperative placement of an intercostal catheter for postthoracotomy pain relief has also been described (101,102). Paravertebral blocks provide analgesia comparable to intercostal blockade. Although not reported for postthoracotomy pain in children, the use of continuous paravertebral blockade has been described in children undergoing renal surgery (103). Complications associated with paravertebral blockade include spinal, epidural, and intravascular injection.
The use of intrapleural anesthesia in children was first described in 1988 (104). Although continuous infusions of bupivacaine of 1.25 mg · kg-1 · h-1 were not associated with clinical signs of toxicity in this report, plasma concentrations were as large as 7 µg/mL. Because a relatively large volume of local anesthetic solution is required to achieve satisfactory analgesia with this technique, the use of a more dilute bupivacaine solution has been described (105). In this study of eight children undergoing thoracotomy, bupivacaine 0.1% was infused up to 1.0 mL · kg-1 · h-1 after surgery. The maximum plasma bupivacaine concentration measured was 2.16 µg/mL, and no signs of toxicity were observed. Satisfactory analgesia was achieved in all children. Several studies in adult patients, however, have shown that intrapleural bupivacaine does not produce reliable postthoracotomy analgesia (106–109). In a randomized, prospective, double-blinded study, epidural hydromorphone provided superior analgesia compared with intrapleural bupivacaine after thoracotomy (110).
Of the regional anesthesia techniques described above, only epidural anesthesia facilitates excellent intraoperative anesthesia, a small risk of local anesthetic toxicity, and titratable postoperative analgesia.
Epidural Anesthesia.
To attenuate the stress response associated with thoracic surgery and to provide optimal postoperative analgesia, a combination of epidural opioids and local anesthetics may be used. Although local anesthetics may spread to thoracic dermatomes when administered via the caudal or lumbar epidural space, potentially toxic doses of local anesthetics are required to achieve thoracic analgesia (111,112). When the epidural catheter tip is placed in proximity to the spinal segment associated with surgical incision (i.e., a thoracic epidural catheter is placed for thoracic surgery), segmental anesthesia may be achieved with smaller doses of local anesthetic than those needed when the catheter tip is distant from the surgical site.
In infants, a catheter can usually be advanced from the caudal to the thoracic epidural space (113,114). With the infant in the lateral decubitus position after the induction of general anesthesia, a 20-gauge epidural catheter may be inserted via an epidural needle or an 18-gauge IV catheter placed through the sacrococcygeal membrane. The epidural catheter is then advanced 16–18 cm to the midthoracic epidural space. Minor resistance to passage of the catheter may be overcome by simple flexion or extension of the spine. If continued resistance is encountered, no attempt should be made to advance the catheter further, because the catheter may become coiled within or exit the epidural space.
In older children, a thoracic epidural catheter may be inserted under general anesthesia directly between T4 and T8 to provide intraoperative neuraxial blockade and postoperative analgesia. Although the safety of placing epidural catheters in anesthetized patients has been questioned (115), this technique is widely used by pediatric anesthesia practitioners (116). The incidence of neurologic sequelae related to epidural catheterization in pediatric patients is unknown. Flandin-Blety and Barrier (117) reported five cases of serious neurologic injury in a retrospective review of 24,005 regional anesthetics performed in France and Belgium over a 10-yr period. All of these patients were infants <3 mo old, and the etiology of neurologic injury and association with epidural anesthesia were unknown. In a separate retrospective survey of 119 pediatric hospitals, including more than 150,000 epidural blocks, there were no reports of permanent neurologic injury, epidural hematoma, infection, or death (118). The authors concluded that the risk of a major complication was less than approximately 1:10,000. This complication rate is consistent with that observed in adult patients (119,120), who are usually awake and able to report pain or paresthesias during needle and catheter placement.
A variety of local anesthetics have been used to provide epidural anesthesia and analgesia in infants and children, including chloroprocaine (121), lidocaine (122,123), bupivacaine (124,125), and ropivacaine (125,126). Advantages of lidocaine are that it has less cardiotoxicity than bupivacaine and blood concentrations can be readily measured in most hospital laboratories. Nevertheless, most reports of the use of thoracic epidural anesthesia and analgesia in children include the use of bupivacaine (123,127–130). A new drug, levobupivacaine (Chirocaine®; Purdue Pharma, Norwalk, CT), causes less cardiovascular toxicity than racemic bupivacaine in adults, but no studies have been published in children (131,132).
Clearance and protein binding for local anesthetics are reduced in neonates and young infants, causing the potential for drug accumulation during continuous infusion and increased central nervous system and cardiovascular toxicity (133–135). Maximum infusion rates for lidocaine of 1 mg · kg-1 · h-1 (e.g., 1 mL · kg-1 · h-1 of a 0.1% solution) have been recommended for young infants (123). Plasma concentrations of lidocaine and its principal active metabolite, monoethylglycinexylidide, should be measured twice daily in infants if possible, because both compounds are epileptogenic (135). Maximal bupivacaine infusion rates of 0.2–0.3 mg · kg-1 · h-1 should be used when prolonged epidural infusion is planned in infants <3 mo old.
Epidural opioids are often combined with local anesthetics to provide maximal pain relief and to minimize tachyphylaxis. The concomitant use of opioids allows the use of smaller concentrations of local anesthetics and decreases the risk of local anesthetic toxicity. Epidural morphine (136,137), hydromorphone (138), fentanyl (139), and sufentanil (140) have been used in infants and children. Of these, morphine has the lowest lipid solubility, followed by hydromorphone, fentanyl, and sufentanil (141). Morphine has been associated with delayed respiratory depression and a relatively frequent incidence of pruritus, nausea, and vomiting (142,143). By comparison, hydromorphone has been associated with rapid onset of analgesia, a small incidence of side effects, and a low risk of delayed respiratory depression (127,144–146). More highly lipophilic drugs, such as fentanyl, achieve minimal spread in the epidural space, and optimal postoperative analgesia is achieved only when the epidural catheter is placed at or near the level of surgery (147). In a study comparing side effects with epidural morphine, hydromorphone, and fentanyl, hydromorphone was associated with the least incidence of pruritus, nausea, and vomiting (138). Regimens used for continuous thoracic epidural analgesia in children in published reports are shown in Table 2. Suggested treatment for side effects related to spinal and epidural opioids is shown in Table 3.
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For patients who are not receiving a regional anesthetic technique to provide postoperative analgesia, systemic opioids are used after thoracotomy. Although intermittent IM and subcutaneous injections have been used widely in the past, these routes of administration are painful and are associated with unpredictable and erratic uptake and distribution. Intermittent IV injections with opioids of short or moderate duration are also associated with periods of excessive sedation and inadequate analgesia. The use of methadone, which has a half-life of approximately 19 h in children over the age of 1 yr,1 may provide more continuous analgesia than shorter-acting drugs (154). For moderate to severe pain, intermittent IV doses of methadone between 0.05 and 0.08 mg/kg as needed may be given (155).
Continuous analgesia may be achieved when opioids are administered by continuous IV infusion, with or without patient-controlled analgesia (PCA) dosing. Morphine is the drug used most often for postoperative analgesia. In neonates <1 mo old, clearance is reduced and elimination half-life is prolonged, about three times that in adults (156). For continuous infusions of morphine, an initial dose of 0.025–0.075 mg/kg followed by infusion rates of 0.005–0.015 mg · kg-1 · h-1 result in therapeutic plasma concentrations in neonates (157). Older infants and children require an initial dose of 0.05–0.10 mg/kg followed by an initial infusion rate of 0.01–0.03 mg · kg-1 · h-1. In children receiving PCA, dosing in the range of 0.01–0.03 mg/kg with a lockout interval of 6–10 min, with or without a continuous infusion, has been recommended (158). In children at risk for morphine-induced histamine release, fentanyl (0.0005–0.001 mg · kg-1 · h-1 ± 0.0005–0.001 mg/kg PCA dose) or hydromorphone (0.003–0.005 mg · kg-1 · h-1 ± 0.003–0.005 mg/kg PCA dose) may be used (158).
The side effects that may occur with IV opioid administration are similar to those described with epidural opioids and may be treated similarly (Table 3). With epidural or IV techniques, improved analgesia and a decrease in opioid dosing (and side effects) may be achieved with the concomitant administration of nonopioid analgesics. The use of these adjuvant drugs, including acetaminophen and a variety of nonsteroidal antiinflammatory drugs, has been reviewed elsewhere (159).
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