The spectrum of surgical emergencies that may occur in the first few weeks of life is extensive; the following discussion focuses on the most common ones, but the basic principles provided can be applied to conditions that are not specifically discussed.
Congenital Diaphragmatic Hernia
One of he most challenging of all neonatal surgical emergencies, this malformation involves herniation of the abdominal viscera into the thorax; it has a high (20%-50%) mortality rate regardless of the method of treatment.109-111 Even early prenatal ultrasound diagnosis and attempts at in utero, fetal surgical correction, has done little, if anything, to affect outcome. The incidence of this devastating problem, which has significant short- and long-term morbidity, is reported to be 1 in 2000 to 5000 live births.111,112
In its most common presentation, the abdominal viscera, including the small bowel and colon, liver, and occasionally the kidneys, herniates into the left hemithorax during the first or second trimester of affected pregnancies and interferes with the development of both the lung parenchyma and its blood supply. Infants born with this anomaly present with the classic triad of dyspnea, cyanosis, and apparent dextrocardia. Physical examination reveals a scaphoid abdomen, bowel sounds in the chest, distant or displaced heart sounds, and absent breath sounds in the affected chest. Chest radiography demonstrates loops of gas-filled bowel or a gastric tube in the affected chest; mediastinal shift; absent lung markings in the affected chest; and most ominously, a contralateral pneumothorax. Pneumothorax is an iatrogenic complication that usually occurs as a result of vigorous attempts at ventilation, oxygenation, or resuscitation. The major differential diagnosis is a cystic adenomatoid malformation of the lung or congenital lobar emphysema. Approximately 20% of patients with congenital diaphragmatic hernia have associated congenital heart disease.
Surgical decompression of the herniated abdominal viscera (which may consist of midgut, stomach, colon, kidney, or liver) from the affected hemithorax and repair of the diaphragmatic defect, although essential in the management of this malformation, does not determine ultimate survival. Rather, outcome depends on the pulmonary vasculature and whether it will respond in an exaggerated, hyperreactive fashion to the stimuli that vasoconstrict and elevate pulmonary artery pressure.113,114 Histologic studies of the lungs of children born with this anomaly reveal decreased number and size of the bronchi, lung saccules, and alveoli and abnormalities of the pulmonary vascular bed. The numbers of pulmonary blood vessels are reduced, and the arterial muscularis and media are hypertrophied. Hyperactive pulmonary arterial vasoconstriction caused by hypoxia, hypercarbia, acidosis, pain, or positive-pressure ventilation can set in motion a catastrophic cycle of events in which desaturated blood returning to the lung is preferentially shunted across the still patent ductus arteriosus and atrial septum into the systemic circulation. This "right-to-left" shunting of blood across the ductus and atrial septum is a return of the circulation to the pattern that existed in utero and is referred to as persistent fetal circulation (PFC) or persistent pulmonary hypertension of the newborn (PPHN). The goal of anesthetic management is to prevent this catastrophic cascade from occurring by maximizing arterial oxygenation and preventing pain and metabolic or respiratory acidosis.
The most severely affected infants require immediate intubation and decompression of the stomach as soon as the diagnosis is suspected. This usually takes place in the delivery room or in the NICU before surgery. Medical management is directed at improving oxygenation and increasing pulmonary blood flow. This may be accomplished by the judicious use of muscle relaxants, analgesics, usually fentanyl (1-10 mcg/kg as an initial bolus followed by a continuous infusion of 3-10 mcg/kg/h), hyperventilation using rapid rates (> 100 breaths/min) and low inflating pressures, preventing hypothermia, and correction of acidosis with IV bicarbonate therapy. Interestingly, this is also the basis of intraoperative anesthetic management. Nevertheless, aggressive proactive management may be harmful; barotrauma and volume trauma from too vigorous ventilation may induce alveolar and capillary damage and induce a catastrophic inflammatory cascade. Inhalational anesthetic agents are mostly avoided because of their hypotensive and cardiac depressant effects, and nitrous oxide is contraindicated because it can diffuse into the bowel and further compromise lung function. The importance of inadequate cardiac output in PFC should not be overlooked. Decreased cardiac output leads to decreased pulmonary perfusion and further hypoxemia. Blood returning to the heart from poorly perfused organs arrives with a lower oxygen content that potentiates the hypoxemia caused by right-to-left shunting.
Bohn et al115 advocated the avoidance of the "mad dash" to the OR and recommend instead a 24- to 48-hour period of stabilization.116 Furthermore, they contend that infants who do not respond to this therapy will fail to survive with surgery or any other therapy, including extracorporeal membrane oxygenation (ECMO). Bohn et al117 also suggested a nomogram to predict the extent of pulmonary hypoplasia present in these infants and their chance of survival. They used the preoperative PaCO2 and correlated it and an index of ventilation that is determined by the mean airway pressure times the respiratory rate. If the PaCO2 could be reduced to less than 40 mm Hg and the ventilatory index was less than 1000, survival was almost universal. On the other hand, if PaCO2 and the ventilatory index were greater than 40 mm Hg and 1000, respectively, death was virtually inevitable. Interestingly, these latter infants were found at autopsy to have less than 10% of the normal number of alveoli bilaterally.
Others have approached newborns with congenital diaphragmatic hernia with a different perioperative management strategy.118 They work to stabilize these newborns preoperatively and bring them through their period of PPHN with a strategy of "gentle ventilation." Using low peak inflating pressures and permissive hypercapnia, they are careful to avoid iatrogenic damage from barotrauma to the already hypoplastic lungs of these newborns. After a period of stabilization, during which pulmonary arterial pressure falls, the patient is electively taken to the OR for surgical repair.
Blood loss is minimal during the surgical repair of this problem, and third-space losses can be assumed to average 8 to 10 mL/kg/h. Aside from routine monitoring, these patients require an intravascular arterial and central venous catheter for continuous blood pressure monitoring and for blood gas, hemoglobin, and blood chemistry sampling. Central venous access is obtained either via an umbilical vein or from the jugular or subclavian veins. If the latter approach is attempted, it is essential to avoid a pneumo- or hemothorax in the normal lung. A precordial stethoscope placed in the unaffected right axilla may help alert the anesthesiologist to one of the most feared intraoperative catastrophes, namely, the development of a contralateral pneumothorax. This is heralded by sudden hypoxia, hypotension, or both. Placement of a chest tube when this occurs may be lifesaving. In fact, some authors have suggested the insertion of a prophylactic chest tube on the contralateral side because this complication is so catastrophic.
Vasodilator therapy has also been advocated for perioperative control of the increased pulmonary artery pressures. IV agents suggested include isoproterenol, nitroglycerin, tolazoline, adenosine, and adenosine triphosphate. These are rarely effective because the pulmonary vasodilation produced is matched by an equal decrease in systemic vascular resistance. These have been largely replaced by inhaled nitric oxide (NO).119-121 NO diffuses across alveolar capillary membranes and stimulates cyclic guanylate cyclase, which increases cyclic GMP (cGMP). cGMP is a potent dilator of vascular smooth muscle. Because NO is rapidly metabolized by RBCs, it has a potent local effect and should preferentially dilate only the pulmonary vascular musculature. NO can be used anytime during the perioperative or intraoperative period as needed. Finally, the anesthesiologist should anticipate the possibility of a cardiac arrest during this operation, and vasopressors, including dopamine (4-10 mcg/kg/min) and epinephrine (0.1-1.0 mcg/kg/min) should always be available for emergency intraoperative administration.
The most recent and important innovation in the treatment of infants with congenital diaphragmatic hernia is the perioperative use of ECMO.122,123 Infants who either would not survive by Bohn's criteria or who develop a PFC pattern after a "honeymoon" period may be placed on ECMO to allow the infant's lungs time to develop and restructure. Unfortunately, decisions pathways about when to initiate ECMO therapy (either before or after surgery), when to operate if an infant is on ECMO, and when to withdraw ECMO support are not well defined; they remain parochial decisions that may differ even among physicians within the same institution.
Omphalocele or Gastroschisis
Abdominal wall defects are rare and although at first glance appear to be similar, they are in fact quite different. An omphalocele is a central, midline defect and is always associated with other congenital anomalies. It occurs because of failure of the gut to return to the abdominal cavity at the 10th week of gestation. The herniated bowel is covered by the amnion, which protects it from fluid loss; infection; and a chemical, amniotic fluid burn. The apex of the herniated sac is the umbilical cord. A gastroschisis, on the other hand, is not a midline defect and is therefore rarely associated with other defects. It results from an intrauterine vascular accident that results in the interruption of the abdominal wall and musculature. The herniated bowel is not covered by any membrane, is "burned" by the amniotic fluid, and is covered by an inflammatory coating or peel. It is subject to tremendous postnatal evaporative fluid losses as well as infection. In gastroschisis, the umbilical cord is found to the side of the herniated bowel.
The optimal method for operative management of infants with congenital abdominal wall defects remains controversial. Two options exist, either primary fascial closure with or without intra- and postoperative muscle paralysis or a staged repair using either a silicone elastomer silo or a primary skin closure. Primary fascial closure of omphalocele or gastroschisis carries the risk of placing the abdominal contents under pressure, which may produce a reduction in cardiac output, hypotension, bowel ischemia, venous stasis, and postoperative respiratory and renal failure.24,25,124 When primary fascial closure cannot be achieved, either because of the large size of the defect or because it critically compromises respiratory or cardiovascular function, the alternative approach is a staged repair using either a silicone elastomer silo or a skin closure with secondary fascial closure. When using the silo, the defect is reduced over several days until a stable infant with a small defect can be taken to the OR for final repair. The staged silicone elastomer repair carries an increased risk of infection.
Traditional criteria for deciding on which course to choose have been based on the size of the defect; the presence of associated congenital anomalies; or clinical observations of the infant's respiratory rate, pulmonary compliance, blood pressure, skin color, and peripheral perfusion during fascial approximation. Unfortunately, these clinical observations may not be reliable, particularly in paralyzed, anesthetized infants.
Infants are transported to the OR by placing the exposed bowel in a bag designed for this purpose. It helps maintain normothermia and reduces evaporative fluid losses. Patients are fluid resuscitated with a balanced salt solution; preoxygenated; anesthetized with fentanyl (10-12.5 mcg/kg), pancuronium, and oxygen; and intubated. In addition to routine monitoring, we routinely place catheters in the right radial artery, an internal jugular vein, and in the stomach. An oral or nasal gastric tube both decompresses the abdomen and allows measurement of intragastric pressure by fluid filling the tube. Yaster et al24,25 suggested that successful management of omphalocele or gastroschisis can be successfully and reliably determined by the intraoperative measurement of intragastric and CVPs (Fig. 63-5). In this treatment algorithm, primary repair is always attempted. However, if the intragastric pressure rises above 20 mm Hg or the CVP increases by 4 mm Hg or more after closure of the abdominal fascia, the primary repair is abandoned and a staged repair with a silicone elastomer chimney is performed. This algorithm avoids the consequences of acutely elevating intra-abdominal pressure. After surgery, the patient is taken to the NICU intubated and placed on controlled mechanical ventilation. Infants treated with a staged repair have their chimneys gradually reduced over 5 to 10 days. Central venous and intragastric pressure can be used to guide this therapy as well.
An algorithm for the intra- and postoperative management of children with congenital abdominal wall defects. Note that one measures intragastric pressures and changes in central venous pressure (CVP). ECG, electrocardiography; IGP, intragastric pressure; NICU, neonatal intensive care unit; OR, operating room.
Newborn infants with abdominal wall defects have significantly increased fluid requirements because of the increase in insensible losses that occur when eviscerated bowel is exposed to the environment. Additionally, they have enormous "third-space" losses because of the traumatized, inflamed bowel and adynamic ileus that develops perioperatively. Fluid requirements are even greater in gastroschisis patients because the herniated viscera lack a protective covering, resulting in a chemical burn preoperatively.
Intestinal Obstruction, Necrotizing Enterocolitis, and Pyloric Stenosis
Intestinal obstruction is among the most common surgical emergencies encountered in newborns and is characterized by feeding intolerance, bilious or projectile vomiting, and abdominal distension. Common sites of obstruction include the pylorus; duodenum; jejunum–ileum, particularly the terminal ileum; and the anus. NEC, on the other hand, is caused by a bacterial invasion of previously injured or ischemic bowel wall.125-127 It is characterized by intestinal obstruction, gangrene, perforation, intramural air ("pneumatosis intestinalis"), and peritonitis. Patients are usually premature and are often septic, hypotensive, thrombocytopenic, and in respiratory failure. Metabolic and respiratory acidosis and electrolyte disturbances are also common. Although the initial management is nonoperative and supportive (eg, decompression, antibiotics, correction of hematologic abnormalities), evidence of intestinal gangrene (eg, positive results of paracentesis), pneumoperitoneum, and clinical deterioration results in the need for emergency exploratory laparotomy.
Duodenal obstruction typically presents within the first hours of life and is extremely common in children with trisomy 21 (Down syndrome). An abdominal radiograph will show the classic "double bubble" sign or a dilated, air-filled stomach and proximal duodenum. Because these children present so early in life, usually within the first 12 hours, they are rarely dehydrated or hypochloremic. Small and large bowel obstructions typically present later, usually 2 to 7 days after birth, and are often associated with hemodynamic compromise and metabolic disturbances. Jejunal or ileal atresias are thought to be caused by intrauterine vascular accidents. Meconium ileus is an obstruction of the small bowel caused by inspissated, abnormal meconium and is pathognomic of cystic fibrosis. At the time of presentation, these infants do not have the lung disease associated with this devastating disease. Malrotations of the bowel also present with obstruction and are very common in patients with congenital diaphragmatic hernia and omphalocele or gastroschisis. Infants with Hirschsprung disease have a functional distal obstruction caused by a lack of ganglia in the rectum and distal colon. Imperforate anus, which should be readily obvious in the delivery room, requires special attention because of the many anomalies associated with it. At one time called the VATER syndrome for vertebral, anal, tracheoesophageal fistula (TEF), esophageal atresia (see below), and renal anomalies, this syndrome also has a 20% incidence of significant congenital heart disease. Patients diagnosed with it should have an echocardiogram obtained before surgery.
Finally, despite being a congenital defect, pyloric stenosis usually does not present until 2 to 6 weeks of age. This is one of the most common surgical emergencies in newborns. Infants with pyloric stenosis have prolonged, repeated projectile nonbilious vomiting that results in a hypochloremic, hypokalemic metabolic alkalosis and profound dehydration. Interestingly, one would expect that the body's response to this alkalosis would be to eliminate bicarbonate in the urine. However, the sodium losses in pyloric stenosis are so great and the dehydration so profound that hydrogen ion is wasted in the urine in place of sodium with a resultant "paradoxical aciduria." Although it is considered to be an urgent surgical procedure, pyloric stenosis never requires immediate emergency surgical correction. Rather, patients require fluid resuscitation, restoration of an effective circulating volume, and correction of metabolic derangements. Only when this is done should surgery and anesthesia be performed. An easy way to assess successful resuscitation is to measure urine pH. When the urine pH is no longer acidotic (pH >6), it is usually safe to proceed with anesthesia and surgery.
Regardless of the underlying pathology, the major anesthetic challenge with this entire group of surgical patients is maintaining an adequate circulating blood volume and preventing the pulmonary aspiration of gastric contents. Virtually all newborns presenting for emergency abdominal surgery are intravascularly depleted secondary to the enormous ongoing third-space losses. Sepsis, bowel manipulation, peritonitis, the use of contrast agents, and the release of vasoactive peptides significantly deplete the circulating blood volume and ECF space of water and electrolytes. In the presence of NEC, third-space fluid replacement therapy in the perioperative period may exceed 100 to 200 mL/kg/h. Fresh-frozen plasma, platelets, and PRBCs are often needed and should be used early in surgery in response to clinical and laboratory evidence of coagulopathy. Additionally, critically ill, septic patients may not be able to tolerate these enormous fluid shifts, and 4 to 10 mcg/kg/min of dopamine should be infused to help maintain blood pressure and blood flow. Both arterial and CVP monitors are required to monitor intravascular volume in these situations.
All newborns presenting for emergency abdominal surgery may aspirate their abdominal contents at the induction of anesthesia. Therefore, methods that minimize these risks, such as an awake intubation or a rapid sequence induction with cricoid pressure, must be used. We prefer to maintain anesthesia with the fentanyl, pancuronium, and oxygen technique for this group of patients. Potent inhalational anesthetics are often poorly tolerated in this group of infants. Nitrous oxide is almost never used in these patients because it will further distend the bowel and complicate intestinal perfusion and fascial closure.
Esophageal Atresia and Tracheoesophageal Fistula
Ninety percent of infants born with a TEF have a blind esophageal pouch and a fistula connecting the distal esophagus and the distal trachea, usually within 1 to 2 cm of the carina (Fig. 63-6).128,129 About 30% to 50% of these infants have the associated anomalies of the VATER syndrome (see above). The most common associated defect is cardiac and necessitates an echocardiogram before surgery.130 Often suspected prenatally by polyhydramnios, infants present with excessive salivation ("mucousy mouth"), choking, coughing, aspiration pneumonia, and cyanosis. Attempts at feeding are met with explosive vomiting, and it is impossible to pass an oral (nasal) gastric tube. Indeed, a chest radiograph of a coiled oral gastric tube in the cervical esophageal pouch is diagnostic of TEF. Because of the potential for aspiration, contrast media should not be instilled to confirm this diagnosis.
Three most common types of esophageal atresia and tracheoesophageal fistula (TEF). A. Proximal atresia and distal TEF account for 80%-90% of cases. B. Pure esophageal atresia with no TEF accounts for 10% of cases. C. H-type TEF accounts for 3% of cases.
The tracheal to distal esophageal fistula aerates the gastrointestinal tract and allows for regurgitation of gastric juice up the fistula into the lung. Thus, pulmonary aspiration occurs by 2 methods. The first involves aspiration of saliva or attempted feedings from the blind esophageal pouch and the second by gastric juice contamination via the fistula tract. If significant aspiration pneumonia occurs, definitive corrective surgery is deferred, and a decompressing gastrostomy is placed under local or caudal anesthesia.131
As soon as the diagnosis is confirmed, the child is placed in a head-up position, and the upper pouch is decompressed with a large-bore sump (Replogle) tube. After the diagnostic workup the child is transported to the OR for corrective repair, which has historically been performed through a right-sided thoracotomy. Increasingly, thoracoscopic surgical repair is being performed with excellent results.132,133 Routine monitors are placed. The authors highly recommend the use of a strategically placed precordial stethoscope during this surgical repair. The precordial stethoscope is placed in the left axilla and carefully secured in place with both a "double-stick" and clear plastic adhesive dressing. This immediately alerts the anesthesiologist to a change in the endotracheal tube position from the juxtacarinal position to the right mainstem bronchus. Adequate IV access and a radial artery catheterization complete the preinduction preparation.
Immediately before intubation, the infant is given 0.15 mg IV of atropine, and the esophageal pouch is suctioned. Then with the infant in a semi-sitting position, the trachea is intubated while the patient is awake. This allows the appropriate positioning of the endotracheal tube without positive-pressure ventilation, which can cause gastric distension through the fistula. Then, in the classic technique, with the infant spontaneously breathing sevoflurane, the endotracheal tube is positioned below the fistula but above the carina by deliberately intubating the right mainstem bronchus and then slowly pulling back the tube until breath sounds are heard in the left axilla and not in the stomach. Isolation of the fistula is possible because in most cases, the fistula is approximately 0.5 to 1.0 cm above the carina on the posterior surface of the trachea. If the endotracheal tube has a side ("Murphy eye") hole, it should be turned to the left, opposite to its normal orientation, to maximize left lung ventilation. Even if the endotracheal tube does not have a side hole, it is helpful to turn the bevel of the tube 180 degrees, so that the curve of the tube faces forward. This will reduce ventilation into the fistula and stomach. After being positioned, the endotracheal tube is secured with the "fishmouth" technique to avoid displacement of the endotracheal tube down the right main stem bronchus or, more ominously, into the fistula tract itself (see Fig. 63-4). Indeed, this is why the precordial stethoscope is so securely placed in the left axilla.
After the endotracheal tube has been positioned, anesthetic management is based on the presence or absence of a decompressive gastrostomy and by the preferential flow of gases down the path of least resistance, namely through the fistula tract into the stomach. Positive-pressure ventilation may allow oxygen and other gasses to bypass the lungs and acutely dilate the stomach. This interferes with ventilation and venous return and can lead to cardiopulmonary arrest and gastric rupture; if this occurs, an emergency decompressive gastrostomy may be lifesaving. Unfortunately, the insertion of a gastrostomy may substitute one problem for another. Airflow resistance through the fistula–stomach–gastrostomy may be so low that ventilation of the lungs becomes impossible. The gastrostomy may need to be intermittently clamped and unclamped or left partially clamped through the procedure. Some have advocated the use of a Fogarty catheter placed either through a bronchoscope or through a gastric endoscope to occlude the fistula tract if this becomes a problem.134 Great caution must be exercised when using a Fogarty catheter alongside an endotracheal tube; if the catheter slips out of the fistula tract into the trachea, it can completely occlude the end of the endotracheal tube. Thus, because of these myriad problems with positive-pressure ventilation, many anesthesiologists recommend an anesthetic technique that uses spontaneous ventilation with sevoflurane. Alternatively, others believe that paralysis may be a safe and effective alternative as long as the fistula can be effectively isolated by careful positioning of the endotracheal tube.
Unfortunately, in the authors' experience, it is rarely possible to have a spontaneously breathing newborn sufficiently anesthetized with sevoflurane without compromising blood pressure and oxygenation. This is particularly true in the repair of an esophageal atresia with TEF because this surgery is performed in the lateral position. An intriguing option, which is our preferred technique, is to supplement spontaneous ventilation with a potent vapor general anesthetic with a caudally placed thoracic epidural anesthetic.135,136
The caudal approach to the epidural space is remarkably easy to perform in newborns and does not require specialized equipment even though small-diameter Crawford needles (17-20 gauge) and catheters (19-24 Fr) are now commercially available. The epidural space of young children and infants is filled with loosely packed fat and blood vessels, making it possible to advance a caudally placed catheter as far as the thorax. Typically, either 0.5 to 1 mL/kg of 0.25% bupivacaine with epinephrine (5 mcg/mL) or 0.5 mL/kg of 3% chloroprocaine (15 mg/kg) with epinephrine is administered, and the inspired sevoflurane concentration is significantly reduced.132 Using this combination technique, patients can be adequately anesthetized and hemodynamically stable even while breathing spontaneously. Analgesia can be maintained with this technique postoperatively as well.
Surgery is performed in the left lateral decubitus position. During the surgical repair, the right lung is compressed and packed away, which may result in hypoxia. Additionally, the infant may become hypoxemic if the trachea or endotracheal tube is compressed and occluded by the surgeon. Alternatively, the endotracheal tube can become obstructed by blood clots or may migrate into the fistula tract. Thus, to provide a greater margin of safety, the authors routinely use 100% oxygen during these anesthetics even in premature infants who are at risk of developing retinopathy of prematurity.
Failure of neural tube closure early in intrauterine development results in a spectrum of abnormalities ranging from spina bifida occulta, a relatively benign process, to myelomeningocele, an abnormality involving vertebral bodies, the spinal cord, and the brainstem. The brainstem lesion (ie, Arnold-Chiari malformation) may be the cause of rather than the effect of the failure of neural tube closure. Ninety percent of infants with myelomeningocele have Arnold-Chiari malformation, which consists of downward displacement of the brainstem and cerebellar tonsils through the cervical spinal canal. This together with an obliteration of the foramina of the fourth ventricle blocks the normal circulation of cerebrospinal fluid (CSF) and leads to progressive hydrocephalus. Associated skeletal anomalies, particularly of the lower extremities, and urodynamic problems are common, and patients born with this defect undergo multiple corrective surgical procedures in their lifetimes.137 Thus, fetal corrective surgery has been proposed and has shown some preliminary positive results.138,139
Infants with a meningomyelocele are transported to the OR in the prone position. The defect is covered with moist, sterile dressings, and great care is taken to avoid contamination and infection. If the meningocele is ruptured, Ringer lactate solution is used to replace CSF losses milliliter for milliliter or at an approximate rate of 4 to 6 mL/kg/h.
The infant must be turned supine for intubation, and positioning is crucial to facilitate this maneuver. A foam head ring or OR towels folded into a ring is covered with a sterile drape or towel. The baby is then turned to the supine position with the defect resting in the pocket of the ring. Towels are then placed under the child's back to build up a level platform for intubation (Fig. 63-7). Anesthesia is induced with either inhalational or IV agents (thiopental or propofol). Virtually any anesthetic technique is possible for this operation as long as it allows for rapid extubation after surgery. Succinylcholine does not cause catastrophic hyperkalemia in patients with this defect.140 After the trachea has been intubated, the endotracheal tube is secured with a "fishmouth" technique (see Fig. 63-4), and the infant is turned to the prone position for surgery.
Positioning of newborn with myelomeningocele for endotracheal intubation.
Spinal anesthesia may be used alone or in combination with general anesthesia for this surgery. When combined with a general anesthetic, the patient is induced as described above. After being turned prone and surgery starts, the surgeon drops 0.5 to 0.7 mg/kg of hyperbaric tetracaine (5 mg/mL) directly into the open meningomyelocele sac.142 Within minutes, the concentration of inhaled general anesthetic is reduced to a level that provides immobility and allows the child to tolerate the endotracheal tube. Less commonly, spinal anesthesia may be used as the sole anesthetic for this repair. Using a small-gauge needle, 0.5 to 0.7 mg/kg of hyperbaric tetracaine (5 mg/mL) with epinephrine is injected into the most inferior region of the meningomyelocele sac. Supplemental doses are administered as described above for the combined approach.
The decision to place a ventricular-peritoneal (VP) shunt at the time of the initial surgery or several days later is a surgical one. Some surgeons defer placement of the VP shunt because they fear that the drain will become infected. Additionally, because 5% to 10% of these patients do not develop hydrocephalus, some surgeons prefer to wait until it develops rather than treating it expectantly.
After birth, the increase in arterial oxygen that occurs by breathing room air results in the closure of the ductus arteriosus. In premature infants, this may not occur and often results in a large left-to-right shunt, heart failure, pulmonary edema, and an inability to be weaned from mechanical ventilation. Medical management consists of fluid restriction, diuretic therapy, digoxin, and 0.2 mg/kg of the cyclooxygenase (COX) inhibitor indomethacin. Other COX inhibitors, such as ibuprofen, may also be effective.142,143 When they are not effective, surgical correction becomes essential if the child is to be weaned from mechanical ventilation. Unfortunately, in the smallest of premature infants (<1000 g), indomethacin is often unsuccessful because it significantly impairs renal function.
Because these infants have been fluid restricted and are intravascularly volume depleted before surgery, volume expansion with Ringer lactate solution is essential to prevent profound hypotension during the induction of anesthesia even when a fentanyl anesthetic is used. Fentanyl (10-50 mcg/kg has become the most common anesthetic technique used.8,46 Obviously, nitrous oxide must be avoided and 100% oxygen is often required to maintain oxyhemoglobin concentrations above 90%, especially after the chest is opened and the lung is retracted. Lung retraction, which is necessary to provide surgical exposure, may result in vagal stimulation, and if the infant has not been pretreated with atropine or pancuronium, bradycardia and hypotension results. During closure of the ductus, hemorrhage and exsanguination may occur if this fragile structure is inadvertently torn by the surgeon. Thus, typed and crossmatched blood should always be available before the start of surgery. Additionally, closure of the ductus is associated with an abrupt increase in diastolic blood pressure, which may contribute to the development of intraventricular hemorrhage in this patient population.
Recently, epidural anesthesia has been used to treat postoperative pain in these infants and to reduce intraoperative anesthetic requirements. Both local anesthetics and epidurally administered opioids are effective. Typically, opioids are administered via a caudal approach, and local anesthetics are administered via a caudally placed catheter that has been advanced to the thorax. Finally, because these infants are so fragile, many centers advocate the closure of a patent ductus in NICU rather than transporting the infant to the OR.144