General Abdominal and Urologic Surgery

“The Full Stomach”: The Risk for Pulmonary Aspiration of Gastric Contents

Many abdominal surgeries are emergent procedures that require a rapid induction of anesthesia and protection of the airway to prevent regurgitation and pulmonary aspiration. Adhering to fasting guidelines for elective surgery does not ensure that the stomachs of children with acute abdomens are empty of liquids and solids. The only metric that has been associated with gastric emptying after an acute emergency in children is the time interval between the last food ingested and the occurrence of the pathologic event or trauma. However, there is no firm fasting interval after a trauma that predicts a zero risk of regurgitation and aspiration. The presence or absence of bowel sounds is also not predictive of gastric emptying or of the risk of regurgitation. Preoperatively, some children with acute abdomens are administered oral contrast agent before abdominal ultrasonography and/or computed tomography (CT) to visualize the stomach contents and to estimate their volumes. However, these radiologic tools may not provide reliable estimates of the volume of the gastric contents. Indeed, the absence of gastric contents in these scans does not eliminate the risk of vomiting and regurgitation. Consequently, there is no evidence that delaying the surgical procedure for the express purpose of emptying the stomach will reduce the risk of regurgitation; postponing may actually increase the risk of complications by delaying the urgently needed surgical attention to the acute abdomen.

Rapid-Sequence Induction

Rapid-sequence induction (RSI) is recommended for children with a full stomach to quickly secure the airway. This approach is intended to minimize the risk of aspiration, although it is not evidence-based. The strategy is to predetermine the drug doses for the child and have all the required airway equipment (age- and size-appropriate) ready to use. The predetermined drug doses are administered in a rapid sequence and when muscle relaxation has been achieved, the trachea is intubated and the cuff (if used) inflated. Many clinicians apply cricoid pressure to occlude the esophageal lumen during RSI, although not a single randomized trial has compared the frequency of regurgitation and aspiration with cricoid pressure during RSI with that with an inhalational or slow IV induction in either children or adults as summarized in a recent Cochrane review. Recently, the presence of microaspirates in the tracheas of 95 adults at risk for regurgitation (obese, those with diabetes, and those with gastroesophageal reflux) was compared with and without cricoid pressure during induction of elective surgery. There was no difference in the frequency of microaspirates in the two groups. This lack of evidence, combined with both theoretical and actual complications associated with RSI and cricoid pressure in children, has led to great skepticism regarding their roles in preventing pulmonary aspiration in children who are at risk, although large population-based studies are lacking. Only 74% of anesthesiologists in Northern Ireland perform RSI for children scheduled for appendectomy, 78% in the United States use it for pyloromyotomy, and 83% in England use it for forearm fractures within 2 hours of eating and after recent opioid administration. In two surveys, 16% and 28% of anesthesiologists in the United States and United Kingdom, respectively, reported that a number of children with full stomachs had experienced gastric regurgitation despite using RSI with cricoid pressure; several of them progressed to serious harm and even death.

Despite the lack of evidence supporting the effectiveness of RSI in children with full stomachs, we continue to recommend this approach for the majority of children at risk. Whether cricoid pressure during RSI contributes substantively to preventing regurgitation performed remains unclear. Based on evidence from non-randomized controlled studies (RCTs), a recent Cochrane review concluded that cricoid pressure may not be necessary to safely achieve RSI. The authors assert that well-designed and properly conducted RCTs should be encouraged to assess the safety and effectiveness of cricoid pressure in infants and children; however, because the frequency of pulmonary aspiration is so small, it would take many thousands of cases to establish a substantive outcome and likely would not be readily approved by an institutional review board.

Complications of RSI, for the most part, relate to improperly performed RSI (e.g., excessive cricoid pressure distorting the anatomy of the airway, causing difficulty in securing the airway) or poor selection of patients (those with a known difficult airway, where a more measured approach must take precedence over concerns for possible aspiration).

RSI in infants and children requires more planning than in older children and adults for several reasons. First, the induction drugs should be flushed into the child's veins using a separate flush syringe to ensure a rapid bolus administration of the drugs. Succinylcholine remains useful for rapid-sequence tracheal intubation for brief procedures. The introduction of intermediate-acting neuromuscular blocking drugs (NMBDs) with rapid onset, coupled with concerns about the risk of hyperkalemia after succinylcholine in children with undiagnosed neuromuscular diseases (especially males <8 years of age), has dramatically reduced the use of succinylcholine in elective surgery. With the shift from succinylcholine to nondepolarizing NMBDs for rapid paralysis in young children, inability to intubate and prolonged paralysis may present serious, possible life-threatening problems. However, with the availability of sugammadex, the use of rocuronium (1.2 mg/kg) represents a safe alternative to succinylcholine. Second, preoxygenation is often difficult in infants and children because they commonly resist the tight application of the face mask needed to fully denitrogenate the lungs. Failure to ventilate the lungs after induction and before tracheal intubation may result in desaturation more rapidly in young infants and children than older children, and in those with upper respiratory tract infections or other causes of a limited oxygen reserve. During laryngoscopy and intubation, mask ventilation with 100% oxygen should begin when the saturation reaches 95%, to attenuate the nadir in oxygen saturation that follows. Third, the force needed to occlude the esophagus when applying cricoid pressure to infants and children is poorly understood and poorly applied, can distort the view of the larynx during laryngoscopy, may not occlude the lumen of the esophagus, and may actually deform the lumen of the trachea if excessive force is applied. For example, as little as 10-N force will distort the shape of the cricoid ring and reduce the lumen by 50% in children younger than 5 years of age. Effective cricoid pressure that occludes the esophagus in children and permits bag-and-mask ventilation with up to 40 cm H ₂ O peak inspiratory pressure without gastric insufflation is known as a modified RSI. Thus, if the first attempt at tracheal intubation fails or the child desaturates during laryngoscopy, properly maintained cricoid pressure allows bag-and-mask ventilation to restore oxygenation, without increasing the risk of regurgitation. A third technique that uses low insufflation pressures, known as the controlled RSI technique, has also been proposed. In the United Kingdom, a recent survey of adult anesthetists that documented a large variability in how the RSI was performed has prompted calls for evidence-based guidelines for RSI in infants and children.

Indications for Preoperative Nasogastric Tube Placement

Although there are no published guidelines for placing nasogastric tubes preoperatively, it is reasonable to insert a tube preoperatively to allow drainage of gastrointestinal fluids in cases of documented bowel obstruction (e.g., ileus, strangulated bowel, pyloric obstruction) or in other situations in which the risk of aspiration is judged to be substantial. The child may experience discomfort when a nasogastric tube is inserted preoperatively, but this must be balanced against the need to decompress the stomach and reduce the risk of regurgitation during induction of anesthesia. For every other indication, the nasogastric tube may be placed after tracheal intubation. It should be noted that the presence of a nasogastric tube may decrease lower esophageal sphincter tone, increase the risk for reflux, and reduce the ability to clear refluxed gastric contents from the distal esophagus. Thus the anesthesiologist is faced with the dilemma of whether or not to remove the nasogastric tube that was placed before induction of anesthesia. It may be reasonable to apply suction to the nasogastric tube, evacuate all of the gastric contents, and then remove the nasogastric tube before inducing anesthesia because it is unclear whether cricoid pressure, even if properly applied, prevents wicking of gastric contents along the path created by the nasogastric tube. It should be further noted that even with a well-placed nasogastric tube, one can never guarantee that the stomach has been completely emptied.

Fluid Balance

Many acute abdominal emergencies are associated with pronounced and significant shifts in fluids, mainly in the form of dehydration, electrolyte losses, third-space fluid shifts, and hypovolemia. In most instances, correction of these derangements is mandatory before proceeding with anesthesia and surgery. However, when a large fraction of the bowel becomes strangulated and ischemic, large volumes of fluid may be sequestered in the bowel. In these cases, hypovolemia should be suspected and resuscitation initiated as anesthesia is rapidly induced. In some elective cases (e.g., bowel resection because of inflammatory bowel disease), fluid and electrolyte resuscitation should routinely be a focus of special interest, because the child may not be fully compensated at the time of surgery.

To date, published studies have suggested that resuscitation with crystalloid fluids and colloids have equipoise. In children, initial resuscitation is usually undertaken with balanced salt solutions. A recent Cochrane review concluded that the use of isotonic intravenous (IV) fluids with sodium concentrations similar to that of plasma reduces the risk of hyponatremia. Although colloids may result in less tissue edema and less volume infused, the expense may not justify their routine use. In fact, some have even questioned the use of colloids in patients with sepsis.

Potential for Strangulated or Ischemic Bowel and Sepsis

The need for anesthesia and surgery becomes more urgent when the bowel is potentially ischemic and/or necrotic. For example, if a volvulus is suspected, immediate action is necessary; otherwise the child is at risk for massive bowel necrosis necessitating resection of dead bowel with subsequent short bowel syndrome, a condition associated with serious lifelong medical problems or even death. Even if the child is far from optimally resuscitated, anesthesia must be induced and maintained, preferably with anesthetics that maintain circulatory homeostasis, while simultaneously correcting the dehydration (or hypovolemia) and electrolyte imbalance. The situation is somewhat less critical in the child with an incarcerated inguinal hernia, although delay of even this surgery should be minimized.

Ischemic bowel may release a host of mediators that can cause severe hemodynamic instability. Children with acute intraabdominal disease should always be regarded as being at risk for bacterial translocation and possible septicemia. Those with overt sepsis are usually easy to identify and may have already been admitted to the pediatric intensive care unit. However, children with incipient or early sepsis may not exhibit overt signs. Accordingly, the signs of sepsis should be actively sought. If septicemia is present or suspected, appropriate IV antibiotics should be administered without delay, preferably before anesthesia and surgery. Children with sepsis or presepsis can be extremely unstable and may require inotropic and/or vasoactive drugs. Immediately after induction of anesthesia vascular sympathetic tone may be attenuated, leading to sudden hemodynamic instability. Thus, when a substantial segment of the bowel becomes ischemic, the anesthesiologist must maintain anesthesia without depressing the circulation excessively, acutely resuscitate the child with appropriate fluids, correct electrolyte imbalances, particularly potential hyperkalemia, and consider the use of inotropic and/or vasoactive medications as needed. It should be noted that hemodynamic instability might acutely worsen when ischemic bowel is suddenly reperfused or immediately after the abdominal cavity is opened. In such cases, close communication with the surgeon is paramount. Furthermore, the presence of sepsis-induced acute lung injury may reduce pulmonary compliance. Thus the anesthesiologist needs to prepare for invasive monitoring (arterial and central venous pressures) and an intraoperative ventilator that is capable of delivering high positive end-expiratory pressure (PEEP).

Presence of Abdominal Compartment Syndrome

Acute intraabdominal disease processes may lead to a critically increased intraabdominal pressure (IAP). If the IAP increases above the capillary perfusion pressure of the intraabdominal organs, an abdominal compartment syndrome can develop. Organ perfusion will become compromised and ischemia and/or necrosis may develop. The most commonly affected organs in this situation are the bowels, kidneys, and liver. Abdominal compartment syndrome occurs less frequently in children than in adults. Causes of abdominal compartment syndrome include burns, extracorporeal membrane oxygenation, closure of gastroschisis or omphalocele (see Chapter 37 ), abdominal trauma, abdominal surgery, and a host of other intraabdominal pathologies, including necrotizing enterocolitis, Hirschsprung enterocolitis, perforated bowel, diaphragmatic hernia, and Wilms tumor. Insufficient perfusion of the bowel may cause an ileus, translocation of bacteria, lactate accumulation, and production of mediators that cause hemodynamic instability. Increased IAP can reduce liver blood flow, which will reduce hepatic function, mainly manifested as an inability to metabolize lactate, impaired drug metabolism, and, in severe cases, impaired synthesis of coagulation factors. Because the pressure is also transmitted to the retroperitoneal space, renal function may become impaired, resulting in oliguria or anuria and reduced excretion of drugs. In addition, cranial displacement of the abdominal contents and splinting of the diaphragm may seriously compromise ventilation.

If acute intraabdominal compartment syndrome is suspected, then the IAP should be monitored to prevent the pressures from exceeding the critical threshold of 20 to 25 mm Hg. IAP can be measured indirectly by transducing a nasogastric tube or bladder catheter. Some define compartment syndrome when the vesicular (bladder) pressure exceeds 10 to 12 mm Hg. The diagnosis of intraabdominal compartment syndrome should be suspected when the triad of (1) massive abdominal distention, (2) increased bladder pressures and increased peak inspiratory airway pressures, and (3) evidence of hepatic, renal, and/or cardiac dysfunction are present.

Children with acute intraabdominal compartment syndrome are often hemodynamically unstable. Although decompression of the abdomen by a laparotomy will immediately normalize the IAP, reperfusion of the ischemic tissues almost always releases a host of biologically active substances that cause profound hypotension. These substances may also precipitate acute renal failure and lead to a disseminated intravascular coagulopathy. As in the case of sepsis, the anesthesiologist must be fully prepared to address these challenges by ensuring that blood products are present in the operating room and vasopressors are drawn up and available before induction of anesthesia. Some children will require a patch abdominoplasty as a temporizing measure to protect abdominal organs that require delayed primary closure of the anterior abdominal wall.

Preoperative Laboratory Testing and Investigations

Most minor elective cases (e.g., umbilical or inguinal hernia repair) do not require any preoperative workup beyond a basic history and physical examination. Many centers require a preoperative urine (or hemoglobin) screen for pregnancy in females who have reached menarche (see Chapter 4 ). More complex elective cases may warrant additional laboratory testing, including basic hematology screening and electrolyte profile.

Preoperative laboratory testing is strongly advised in more critically ill children. Liver and renal function tests, coagulation profile, and serum albumin concentration should be assessed and blood typed and crossmatched. In children with sepsis or who have an acute intraabdominal compartment syndrome, a preoperative chest radiograph may indicate the severity of pulmonary involvement. An echocardiogram may be needed to assess myocardial contractility and volume status if cardiac dysfunction is suspected.

Monitoring Requirements

Routine elective cases rarely require more than standard monitoring equipment. In children undergoing major intraabdominal procedures, invasive arterial and central venous blood pressure monitoring may be indicated. A multiple-lumen central venous line inserted at the beginning of the procedure will facilitate administration of inotropic and/or vasoactive drugs, in addition to measuring central venous pressure; ultrasound-guided insertion is strongly recommended. These lines are of great value in the immediate postoperative period for blood sampling, drug administration, ongoing assessment of intravascular volume status, and parenteral nutrition. Transesophageal echocardiographic, transesophageal Doppler, or continuous noninvasive cardiac output (CO) evaluation may provide valuable intraoperative and postoperative information regarding the child's volume status, as well as cardiac contractility (see also Chapter 52 ).

A urinary catheter with a pediatric urometer (i.e., a graduated collection receptacle), which provides an accurate measure of urine output, is a useful monitor for most intraabdominal procedures. Maintaining a stable hourly urine output may safeguard against the development of hypovolemia and possibly prerenal azotemia (see the section “ Laparoscopic Surgery ” for discussion of changes in urine output with increased IAP).

Monitoring IAP is important during laparoscopic surgery, although it is of minimal value in omphalocele and gastroschisis surgeries, as long as the abdomen remains open. Once the abdomen is closed, however, IAP provides useful prognostic information regarding intraabdominal organ (e.g., renal) blood flow, circulatory stability, and respiratory embarrassment (see Chapter 37 ).

Choice of Anesthetic

The anesthesiologist may use his or her personal preference of anesthetic technique for the management of both elective and emergency intraabdominal surgery in children. However, airway management associated with intraabdominal surgery requires careful consideration. Even when the child is not at increased risk for regurgitation and aspiration, the risk of regurgitation can be increased if the surgeon positions the child in the Trendelenburg position and/or insufflates the peritoneal cavity with carbon dioxide (CO ₂ ) during laparoscopic surgery. A particular concern arises when the surgeon decides to decompress distended bowel by creating an enterotomy and directly draining the fluid, or by “milking” or “stripping” the bowel in a retrograde direction until the contents can be vented with a nasogastric tube. The latter method can cause massive intestinal regurgitation that exceeds the capacity of the nasogastric tube causing pulmonary aspiration. It is for this reason and others that a laryngeal mask airway (LMA) should not be used during intraabdominal surgery; we strongly recommend that the trachea should be intubated with a cuffed tube as standard practice in these cases.

Regional anesthetic techniques may be useful adjuncts in children undergoing both minor and major abdominal surgery. Those who have had open abdominal procedures will require IV opioids or the use of a continuous epidural infusion of local anesthetics with or without opioids for perioperative pain management (see Chapter 44 ). Analgesia is commonly supplemented with parenteral nonsteroidal antiinflammatory drugs and/or acetaminophen. In most children who have had laparoscopic surgery, adequate postoperative analgesia may be achieved by infiltrating local anesthetics at the port insertion sites. However, referred shoulder pain, the result of accumulated air under the diaphragm, may require IV opioids. In critically unstable children or those with sepsis, the use of neuroaxial anesthesia is not recommended because sympathetic blockade may further exacerbate the hemodynamic instability and the catheter could provide a nidus for infection.

Reduced Renal Function

Children with chronic renal disease have impaired renal function, which may affect drug dosing and disposition, as well as cause secondary effects on the cardiovascular system. In the most severe cases, the child may require dialysis to balance fluids and electrolytes. In children with renal disease, it is essential to determine the degree of renal impairment by consulting the child's nephrologist and reviewing the serum creatinine, blood urea nitrogen, sodium, and potassium concentrations (see also Chapter 28 ). Because renal impairment may also affect clotting, a coagulation profile, including platelet count, should be reviewed preoperatively if substantial blood loss is anticipated. These children are prone to fluid overload, particularly those who are anuric and dialysis dependent. Apart from clinical signs associated with fluid overload, measuring the child's weight and comparing it with their normal weight is a simple means to assess the child's current volume status. If cardiac function or volume status remains in doubt, an echocardiogram should be obtained. Children with chronic renal insufficiency often have impaired left ventricular function even before they require dialysis, so a preoperative echocardiogram may be indicated ; pericardial effusion is also a concern.

For children undergoing dialysis, the most recent date of dialysis should be documented. Overhydration and/or hypervolemia and hyperkalemia should be corrected preoperatively with dialysis. Although dialysis corrects these abnormalities, and may transiently improve platelet function (peritoneal dialysis yielding more consistent improvement than hemodialysis), it is best to avoid dialysis within 12 hours of anesthesia to preclude a relative hypovolemia and to allow sufficient time for body fluids to reequilibrate (see Chapter 28 ). Postdialysis laboratory indexes of serum electrolytes (particularly potassium), hemoglobin or hematocrit, renal function (creatinine and blood urea nitrogen), and the child's weight loss should be assessed. For children who undergo hemodialysis, IV access and blood pressure measurements should not be obtained in the extremity ipsilateral to the arteriovenous fistula.

Systemic Arterial Hypertension

Systemic hypertension is common in renal insufficiency in adults but is far less common in children. Nonetheless, some children with urologic disorders develop systemic hypertension associated with disturbances in the renin-angiotensin system. As in adults, it is important to control systemic hypertension before induction to avoid wide swings in blood pressure. In contrast to adults, however, hypervolemia is an important cause of hypertension in children with renal insufficiency that should be considered and treated preoperatively. Children and adults are often treated with similar antihypertensive medications (see Chapter 28 ). All medications should be continued up to and including the morning of surgery to maintain intraoperative and postoperative hemodynamic stability with the exception of angiotensin-converting enzyme (ACE) inhibitors. The latter drugs should be stopped 1 day before surgery to avoid intraoperative hypotension ; however, withholding this medication may also lead to rebound hypertension postoperatively. If these medications are not withheld, vasopressors may be required during anesthesia to stabilize the blood pressure. Because therapy-resistant renal hypertension is an indication for nephrectomy, one should anticipate and be prepared to treat wide fluctuations in blood pressure, including severe hypertension during the first stage of the operation and profound hypotension when the responsible kidney is removed. Therefore, long-acting antihypertensive agents are best avoided during the early stages of a nephrectomy in a child.

Corticosteroid Medications

Children with renal disease may be chronically treated with corticosteroids as part of their medical management (e.g., children with proteinuria or who have undergone previous renal transplant surgery). In such cases, a stress dose of parenteral corticosteroids during surgery is indicated, with continued supplementation until the child resumes his or her normal corticosteroid medication by the enteral route. In more complex situations, consultation with a pediatric nephrologist or endocrinologist is warranted to optimize corticosteroid supplementation, although in more straightforward cases, a dose of 2.5 mg/kg of IV hydrocortisone two to three times each day is usually adequate (see Chapter 27 ).

Infection or Sepsis

Obstructive urinary tract disease or chronic renal insufficiency increases the risk for urinary tract infections. If treated properly, the infection should not interfere with anesthesia. However, in children with overt signs of systemic illness or septicemia, the anesthetic and postoperative courses may be difficult.