In this chapter, we review principles of anesthetic management of some common and unique surgical procedures that are within the purview of the general pediatric surgeon. The first section contains a discussion of concerns for intraabdominal procedures, especially in neonates and small infants. The second section reviews the unique aspects of some common surgical conditions of the abdomen that are of interest to pediatric anesthesiologists and describes the key anesthetic implications for each of these conditions. Anesthetic considerations for indwelling vascular access placement (e.g., port placement or Broviac catheters) are also covered.
General Considerations
Intraabdominal procedures in children run the gamut from simple hernia repairs in healthy children to complex bowel resections (e.g., necrotizing enterocolitis) in extremely ill, premature infants. Preoperative assessment allows the anesthesiologist the opportunity to explore underlying comorbidities and the need for preoperative preparation, including volume resuscitation. Many abdominal diseases will present with vomiting and diarrhea and will be accompanied by sequestration of fluid within the abdominal cavity and electrolyte abnormalities. Therefore, estimation of volume status is crucial and preoperative volume resuscitation is often required.
The preoperative physical exam is focused on determination of cardiorespiratory vital signs and evaluation of the child’s upper airway. Indicators of hypovolemia include lethargy, weight loss, tachycardia, dry mucous membranes, cold mottled skin, poor peripheral capillary refill, and a sunken fontanel in the young infant. More advanced findings include metabolic acidosis, oliguria, and hypotension.
Abdominal distention may result from bowel edema, accumulation of fluid or air in the bowel, and pneumoperitoneum if intestinal perforation has occurred. It can cause elevation of the diaphragm which leads to a decrease in the patient’s functional residual capacity (FRC); in a small infant, this decrease in FRC can lead to atelectasis, alveolar collapse, and ultimately hypoxemia and respiratory failure. Small infants with acute abdominal processes require a full set of preoperative laboratory studies, including a complete blood count with platelets, a comprehensive metabolic panel, and coagulation studies. Although a type and screen may be appropriate in most cases, a type-and-crossmatch should be obtained if there is a possibility of blood loss requiring red cell transfusion. When bowel ischemia is likely, such as with necrotizing enterocolitis, arterial or venous blood gas analysis is indicated to determine the severity of the underlying metabolic acidosis. Premedication should be administered to treat existing pain or anxiety. There is no proven benefit to the administration of medications that aim to prevent pulmonary aspiration of gastric contents and reduce gastric acidity. In fact, metoclopramide, a prokinetic agent, should not be administered if there is the possibility of an intestinal obstruction. Children with suspected bowel obstruction should receive gastric decompression with an indwelling nasogastric tube (orogastric in small infants) before induction of general anesthesia.
Intraoperatively, the major anesthetic considerations include management of hypovolemia, acidosis, and hypothermia. Standard monitors are usually sufficient, but the disease process and any underlying patient morbidity should determine the need for more invasive monitoring such as direct arterial measurement or central venous access. Measures to ensure normothermia include core temperature monitoring (esophageal or rectal), warming of the operation room (OR), humidification of the breathing circuit, use of an intravenous fluid warming device, and use of a forced air or water heating blanket underneath and around the child. Overhead radiant heaters can be used for neonates and small infants during induction of anesthesia and placement of monitors. During a laparotomy in a small infant, beware of advancing the esophageal catheter into the stomach where it will reflect the warmer temperature from the OR lights. An indwelling urinary catheter is indicated if the procedure will last more than about 4 hours or if large intraoperative fluid fluctuations are anticipated.
When a large surface area of bowel is exposed, insensible losses are deceptively high (at least 10 mL/kg/h) and will warrant liberal fluid administration. Hypovolemia can result from unanticipated bleeding, or third space loss from bowel exposure or edema. Neonates with large abdominal defects such as gastroschisis or omphalocele often require more than 50 mL/kg of isotonic fluid over the duration of the procedure. To allow for adequate volume resuscitation, many pediatric anesthesiologists will insert two peripheral intravenous catheters. Isotonic crystalloid solutions are appropriate for most volume resuscitations. The occasional child may require inotropic therapy with dopamine or epinephrine if hypotension persists despite seemingly adequate volume resuscitation, especially when there is an intraabdominal process associated with sepsis.
Infants and children presenting for urgent abdominal surgery are considered to have a full stomach and thus are at increased risk for pulmonary aspiration of gastric contents during induction of general anesthesia. Decreased gastric emptying in these patients may be caused by the pathologic abdominal process or from anticholinergic medications, such as opioids. Children undergoing elective abdominal procedures that are minor and not associated with pathologic processes that interfere with normal gastric emptying can be managed with normal fasting guidelines.
The indwelling nasogastric tube should be suctioned immediately before induction of general anesthesia. It can be removed to facilitate airway management and replaced after insertion of the endotracheal tube.
In most children, rapid sequence induction and intubation (RSI) is similar to that for adults: preoxygenation and administration of a rapid-acting hypnotic agent along with a rapid-acting neuromuscular blocker. The benefit of cricoid pressure to prevent regurgitation and aspiration of gastric contents remains controversial and is still debated.
It is important to remember to maximally maintain upper airway patency while waiting for relaxation to occur; despite the avoidance of manual ventilation, oxygenation can still occur via bulk flow of oxygen from the anesthesia circuit as long as the upper airway is kept open by neck extension and chin lift.
Classic application of RSI is sometimes not possible in certain children. Preoxygenation may not be feasible in the struggling child who refuses mask placement, and apneic oxygenation may be unsuccessful (i.e., result in oxyhemoglobin desaturation) in infants because of their vanishingly small FRC and high oxygen consumption. Furthermore, because the use of succinylcholine may be hazardous in children with undiagnosed myopathies, it is often replaced with rocuronium, which has a longer onset of action, except in very high doses. For all these aforementioned reasons, many pediatric anesthesiologists prefer a modified RSI that consists of “gentle” positive pressure ventilation breaths (i.e., relatively low inspired pressures to cause modest chest rise) before endotracheal intubation. Awake intubations are rarely, if ever, performed on neonates, except during episodes of severe cardiorespiratory instability or suspected difficult airway.
The anesthesia maintenance technique during an abdominal procedure depends on the severity of the child’s illness. For procedures that are not expected to require postoperative mechanical ventilation, a balanced technique of an inhaled agent and an opioid is appropriate. When postoperative mechanical ventilation is expected, an opioid-based technique (while still including sufficient inhaled agent to ensure unconsciousness) is preferred because it can be continued into the postoperative period to decrease the child’s overall stress response and provide ongoing analgesia and sedation. In the absence of hypovolemia, small infants and neonates tend to remain hemodynamically stable after relatively large amounts of opioids. Nitrous oxide should probably be avoided even in superficial abdominal wall procedures (e.g., simple hernia repair) because its use is associated with bowel distention.
Regional analgesia via the lumbar or caudal epidural route may be useful for intraoperative and postoperative pain relief when the child is hemodynamically stable and does not demonstrate evidence of bacteremia or sepsis.
Neonates that undergo major abdominal surgery often benefit from postoperative mechanical ventilation. This practice allows liberal titration of opioids and a decreased stress response without the risk for apnea during this phase of large fluid requirements and intravascular fluid shifts secondary to intestinal “third spacing.” Muscle relaxation will also assist with ventilation during this “third spacing” stage. The postoperative plan should be proactively discussed with the neonatologists, surgeon, and pediatricians who will be managing the patient in the postoperative period.
A variety of pediatric abdominal procedures are now being performed laparoscopically. This includes appendectomy, pyloromyotomy, hernia repair, Nissen fundoplication, and bowel resection, just to name a few. The most important consideration in the management of patients undergoing laparoscopy is the close monitoring of intraabdominal pressure (IAP) during abdominal insufflation. In older children, the laparoscopic methods and anesthetic implications are the same as for adults. In younger children and infants, increases in IAP may result in cardiopulmonary compromise. In several studies of small children, an IAP less than 12 mm Hg appears to be safe whereas an IAP above 12 mm Hg has been associated with hypotension, bradycardia, and difficulty with ventilation secondary to a loss of FRC and a decrease in lung compliance. In children with cyanotic congenital heart disease, an IAP greater than 6 mm Hg may cause increased pulmonary vascular resistance (PVR) that results in right-to-left shunting.
Despite the small size of vulnerable vessels, carbon dioxide embolism may cause hemodynamic compromise during laparoscopy in infants. Although rare, neonates may be susceptible to this particular complication because of damage or insufflation of a residual patent umbilical vein.
Congenital Diaphragmatic Hernia
A congenital diaphragmatic hernia (CDH) consists of a defect in the diaphragm that allows the abdominal contents to enter and remain within the thoracic cavity during fetal life. It occurs in approximately 1 in 3000 live births, is usually accompanied by polyhydramnios, and is often detected by prenatal ultrasound. The most critical consequence of this anomaly is the prevention of normal prenatal lung growth. It leads to pulmonary hypoplasia, decreased cross-sectional area of the pulmonary vasculature, and changes in surfactant production and availability. Severe cases may lead to left ventricular hypoplasia.
There are three identified variations of CDH. The most common is the left-sided, posterior defect through the foramen of Bochdalek ( Fig. 23.1 ). This breech of diaphragmatic integrity allows herniation of both small and large bowel and solid organs. Less commonly, CDH occurs through a right-sided or anterior defect through the foramen of Morgagni. These are not usually associated with severe pulmonary hypoplasia, but rather are signs of intestinal obstruction because only a small part of the liver and large bowel become herniated into the thoracic cavity. The least common form of CDH occurs as a hiatal hernia (<2%).
The manifestations of severe CDH are apparent immediately after birth as respiratory distress; they are also often detected before birth via prenatal ultrasound. Newborns with CDH will demonstrate chest wall retractions, tachypnea, cyanosis, absence of breath sounds on the affected side, and the classically appearing scaphoid abdomen that indicates a lack of intestines within the abdominal cavity. Bowel sounds may be heard in the chest. Diagnosis is confirmed by a “baby-gram” radiograph, which demonstrates bowel in the thoracic cavity and a gasless abdominal cavity ( Fig. 23.1 ). Approximately 25% of affected infants have associated cardiac anomalies. Depending on the location of the hernia, the mediastinum may shift and cause cardiac compromise. Although most of these patients are diagnosed at birth, up to 10% of affected patients with mild CDH may remain undiagnosed until later in childhood or even into adulthood.
Pulmonary hypoplasia and hypoxemia are associated with persistent pulmonary hypertension and failure to transition normally from fetal to adult circulatory function. Elevated right-sided heart pressures cause right-to-left shunting through the ductus arteriosus. Persistent hypoxemia, hypercarbia, and acidosis also contribute to keeping the ductus open. Right-to-left shunting can also occur through a patent foramen ovale or ventricular septal defect, if present. This vicious cycle can only be broken by the establishment of normoxemia and normal lung function. Concomitant congenital heart disease contributes to this process and reduces overall survival.
Once diagnosed, management consists of immediate tracheal intubation and institution of mechanical ventilation. Bag-and-mask positive pressure ventilation should be minimized in an effort to reduce gastric distention because the stomach or small intestine may be contained within the thoracic cavity. A naso- or orogastric tube should be immediately inserted to decompress the upper digestive tract. A chest radiograph will confirm the diagnosis and rule out a pneumothorax on the contralateral side.
In the past, infants with CDH were brought immediately to surgery to remove the abdominal contents from the thoracic cavity and allow lung reexpansion and growth. However, this practice was not associated with good results because the affected lung is hypoplastic, not atelectatic. Currently, corrective surgery is performed on a semielective basis within the first few weeks of life when the infant has achieved optimal medical stabilization.
The initial successful management of pulmonary hypertension is the key to survival. In the immediate newborn period, the goal of ventilatory management is to provide oxygenation and ventilation without triggering a pulmonary vasospasm crisis. That goal is a Pa o 2 greater than 50 mm Hg, with the acceptance of a lower oxygen saturation and hypercapnia while trying to maintain a pH greater than 7.2. Permissive hypercapnia (Pa co 2 of 40–60 mm Hg) has been shown to greatly improve survival. Permitting higher Pa co 2 has allowed for less volume and pressure to be used for ventilation, thus, minimizing barotrauma and volutrauma. Inotropic support may be needed to maintain perfusion, and inhaled nitric oxide and milrinone may be utilized to reduce afterload, both of which may improve pulmonary blood flow. The inability to reduce the P co 2 or reduce the alveolar-to-arterial oxygen gradient to less than 500 mm Hg despite maximal ventilatory techniques (e.g., using the oscillator or jet ventilator) is associated with a poor outcome and is an indication for institution of extracorporeal membrane oxygenation (ECMO). Other signs that indicate the need for ECMO include preductal oxygen saturations less than 85%, peak inspiratory pressures greater than 25 cmH 2 O, hypotension resistant to pressors, and inadequate perfusion based on urine output and increasing lactate. Although pulmonary vasodilator therapy with inhaled nitric oxide may help stabilize a patient, it does not reduce mortality or the need for ECMO. CDH surgery consists of an abdominal incision and reduction of the herniated viscera. Repair is planned once the pulmonary system has stabilized. This stabilization is marked by an adequate urine output, normotension, an adequate preductal oxygen saturation, and a pulmonary artery pressure less than systemic arterial pressure. The diaphragmatic defect is closed by primary repair or by using a synthetic patch. In most cases, a chest tube is placed on the affected side, and some surgeons will also insert a contralateral chest tube to protect against pneumothorax from aggressive ventilator therapy. Unexplained intraoperative decreases in lung compliance, hypoxemia, or hypotension are suggestive of a contralateral pneumothorax and should warrant immediate chest tube placement. The surgery can be performed in the operating room after medical stabilization, or in the neonatal intensive care unit (NICU) while the patient remains on ECMO.
Ventilatory management during CDH repair consists of a balance between avoiding barotrauma (particularly in the unaffected normal lung) and decreasing hypoxemia, hypercarbia, and acidosis, all of which increase PVR. Simultaneous pulse oximetry at preductal (right upper extremity) and postductal (lower extremity) sites allow early detection of right-to-left shunting from pulmonary hypertension. Right radial artery cannulation will allow continuous blood pressure measurement and assessment of preductal oxygenation. Additional anesthetic priorities during CDH repair include adequate volume expansion, especially when high ventilatory pressures are required, and use of a high-dose opioid technique to minimize elevations in PVR. It is important to administer adequate intravenous fluids to ensure adequate preload, but care must be taken to avoid pulmonary edema. Mechanical ventilation is continued in the postoperative period in all but the most minor defects.
Biliary Atresia
Biliary atresia occurs in about 1 in 15,000 live births. It is thought to occur as a result of inflammation of the bile ducts leading to obliteration of the extrahepatic biliary tract. The result is that bile cannot be emptied properly from the liver. It manifests as direct hyperbilirubinemia within the first several weeks of life and, if left untreated, can lead to cirrhosis. Infants with biliary atresia require a surgical anastomosis between the duodenum and an intrahepatic biliary duct known as a Kasai procedure. Repair must be done in the first 60 days of life to optimize clinical outcomes. Anesthetic concerns are primarily those of decreased hepatic function and its sequelae, such as clotting factor deficiency, hypoalbuminemia, increased abdominal girth/ascites, and avoidance of medications that are metabolized in the liver. In the absence of a coagulopathy, epidural analgesia is preferred for postoperative pain relief. Long-term postoperative complications after the Kasai procedure include recurrent ascending cholangitis and chronic cirrhosis. Many of these children will ultimately require liver transplantation.
Hirschsprung’s Disease
Hirschsprung’s disease (congenital aganglionic megacolon) describes a condition of the absence of parasympathetic ganglion cells in the lower colon, leading to a functional obstruction of the large bowel. It is the most common cause of large bowel obstruction in the newborn and typically presents in the first few days of life as abdominal distention and a failure to pass meconium. The diagnosis should be considered in any neonate that has not passed meconium by 48 hours of life or in any older infant with a history of chronic constipation. On rare occasions, these children may become very ill with toxic megacolon, peritonitis, and colonic perforation. Because of the association with cardiac anomalies (2%–5%) and trisomy 21 (5%–15%), a cardiac work-up may be necessary before operative intervention.
Treatment consists of removal of the nonfunctional part of the colon and reanastomosis to the rectum; a diversion colostomy may or may not be required. In many centers, the intraabdominal resection is accomplished using a laparoscopic approach before the perineal repair.
During the perineal repair, the infant is positioned at the end of the OR table in the lithotomy position. The anesthesiologist should anticipate this relocation and prepare the lengths of the monitoring wires, breathing circuit, and IV tubing accordingly. Maintaining normothermia in the infant may be challenging, so core temperature monitoring is essential with warming of the OR, warming of intravenous fluids, and/or a forced air heating blanket as necessary.
Imperforate Anus
Imperforate anus (anal atresia) is diagnosed shortly after birth on physical exam or after an evaluation for failure of the infant to pass meconium in the first days of life; prenatal ultrasounds are often normal. This anomaly ranges in severity from a mild stenosis with a thin obstructive band that is punctured at the bedside to a more severe atresia that is associated with other anomalies. Although the defect usually appears superficial, it can be associated with underlying pelvic neuromuscular abnormalities. Anal atresia is a component of the VATER syndrome: V ertebral anomalies, A nal atresia, T racheo- E sophageal fistula, and R enal/genitourinary malformations. The updated acronym, VACTERL, includes C ardiac and L imb anomalies.
Infants may undergo primary repair in the neonatal period or undergo a staged repair involving a colostomy. Repair of some type is urgent if the child is unable to pass stool. Repair is less urgent in female infants with a rectovaginal fistula that allows passage of meconium. Ultimately, the corrective procedure, a posterior sagittal anorectoplasty (Pena procedure or PSARP), is performed during the first year of life. Unique anesthetic concerns include the delineation of coexisting anomalies and assessment of fluid and electrolyte imbalance. Management of life-threatening comorbidities takes priority over repair. The procedure usually begins in the prone position and is completed in the supine or lithotomy position. Even after correction, these children may suffer from urinary and/or fecal incontinence.
Indwelling Intravenous Access
One of the most commonly performed surgical procedures in children is the intraoperative placement of an indwelling venous catheter such as a Broviac, Hickman, or subcutaneous port. The catheter is usually inserted into one of the central veins of the neck and a portion of it is tunneled underneath the skin for improved stability and to decrease the risk for infection at the site of insertion. Children with chronic diseases will require placement of indwelling venous access for long-term parenteral nutrition, administration of antibiotics, or administration of chemotherapy or other types of chronically administered medications.
Preoperative evaluation of the patient should consist of a thorough review of the patient’s underlying comorbidities. Preoperative midazolam can be administered by the oral or intravenous route. There are no unique considerations for induction and maintenance of general anesthesia. The procedure is performed with the child in the Trendelenburg position (to maximize vein size and minimize the risk for venous air embolism), with the head hyperextended and turned to the opposite side of the line insertion. Therefore, after draping of the patient, airway access is limited, and for this reason, we prefer endotracheal intubation for the procedure. Some pediatric anesthesiologists are comfortable with a supraglottic airway.
General anesthesia is also utilized during removal of the tunneled catheter when its use is no longer necessary. The catheter may be used to administer intravenous induction agents at the start of the procedure but should not be removed before establishing adequate peripheral venous access. Significant blood loss can occasionally occur from a tear in the vein that contained the tunneled catheter and a venous air embolism is possible. Endotracheal intubation is not required for this procedure as it often takes less than 10 minutes to perform and surgical draping is minimal.
Inguinal Hernia
Inguinal hernia repair is one of the most commonly performed surgical procedures in children. A unilateral hernia is usually diagnosed on routine physical exam in healthy school aged children. Bilateral hernias occur more commonly in premature infants and because of the potential risk for incarceration, will usually be repaired before the child is discharged from the hospital. Therefore, these children will present with all of the usual medical problems associated with prematurity.
There are many ways to anesthetize children for hernia repairs. Different factors are taken into consideration when deciding on an anesthetic technique, including the health of the child, preference of the surgeon, and the skills of the anesthesia provider. Older children with uncomplicated unilateral hernias can receive maintenance of general anesthesia by facemask or supraglottic airway with inhaled agents. When laparoscopic examination of the contralateral side is performed, endotracheal intubation and neuromuscular blockade may be indicated, depending on the surgeon’s preference for abdominal wall relaxation and desired degree of intraabdominal insufflation.
Pain relief for inguinal hernia repair consists primarily of regional analgesia. Caudal analgesia with dilute local anesthesia is often used for bilateral repair, and a peripheral nerve block is used for unilateral repair. However, in ambulatory children in whom a caudal block may cause lower extremity weakness, bilateral peripheral nerve blocks are often performed. Analgesia should be supplemented with a small dose of intravenous opioid and nonopioid analgesics, including acetaminophen and ketorolac.
The anesthetic technique for bilateral hernia repair for the small infant is different from that of the older child. The hernias can consist of large bulging sacs (in the male) and can present a surgical challenge. For these cases, we prefer general anesthesia with neuromuscular blockade and endotracheal intubation. In some cases of extreme prematurity and small size (e.g., less than 3 kg), when the infant is scheduled to return to the intensive care unit, we may choose to maintain endotracheal intubation into the postoperative period while the infant fully recovers. Caudal analgesia is often performed for postoperative pain relief. The use of spinal anesthesia without sedatives is an option in these cases, especially in former preterm infants that may be at risk for development of postoperative apnea. There is a reduction in the risk for postoperative apnea when preoperative sedatives are not used compared with general anesthesia. Infants without a history of apnea in the preoperative period have also shown a reduced risk for postoperative apnea when spinal anesthesia was used compared with general anesthesia. However, the risk of anesthetic failure is higher with spinals compared with general anesthesia.
Intussusception
Intussusception is the telescoping of a portion of bowel (usually the distal ileum) into an adjacent portion of the bowel with subsequent swelling and intestinal obstruction. Occasionally, this obstruction may be severe enough to cause intestinal ischemia and perforation. The classic description is the patient that presents with the triad of vomiting, abdominal pain, and rectal bleeding (“currant jelly” stool). Although the cause of intussusception is generally unknown, it may be associated with a polyp or enlarged intestinal lymph nodes (Peyer’s patches). It usually occurs in infants and toddlers (ages 2 months to 5 years). In severe or protracted cases, bowel ischemia and sepsis may develop, and these patients may have severe dehydration and electrolyte imbalances. The diagnosis is confirmed radiographically, via ultrasound or plain film. In younger children up to age 3 years, intussusception can usually be treated by a nonsurgical reduction using a barium or air enema. In older children and those who fail nonoperative reduction, exploratory laparoscopy and manual reduction is required, using general anesthesia with RSI. The primary anesthetic concerns for this procedure consist of fluid resuscitation, correction of electrolyte abnormalities, maintenance of normothermia, and provision of postoperative analgesia.
Malrotation and Midgut Volvulus
Malrotation is defined as an abnormal twisting of the intestine as it migrates back into the fetal abdominal cavity from its embryonic extraabdominal location during the latter part of the first trimester at approximately 10 weeks gestation. When this twisting compromises the blood supply of the intestine (superior mesenteric artery), the condition is known as a volvulus ( Fig. 23.2 ). Malrotation with resulting midgut volvulus is one of the only true pediatric surgical emergencies. Infants who develop volvulus from malrotation usually become symptomatic sometime in the first 2 months of life, although mild cases can remain asymptomatic for years. Symptoms include bilious vomiting or signs of intestinal perforation and ischemia if the volvulus has progressed. These infants can be quite ill and may present with a sepsis-like picture; the condition can be fulminant and fatal if left untreated. Severely ill children may require fluid and blood resuscitation and endotracheal intubation in the preoperative period. Preoperatively, a naso- or orogastric tube is placed to decompress the stomach and antibiotics are initiated to prevent infection. Children with malrotation may have additional congenital anomalies that should be investigated before surgery if time permits.
