The esophagus is a pliable muscular tube that extends from the pharynx to the stomach (Fig. 16-1). It is located behind the trachea and in front of the thoracic aorta and traverses the diaphragm to enter the esophagogastric junction, sometimes called the cardia. Approximately 5 cm above the junction with the stomach is the lower esophageal sphincter (LES), a circular band of smooth muscle tissue, which functions to prevent the reflux of stomach contents into the esophagus. The normal resting pressure of the LES is approximately 30 torr. This pressure is maintained by stimulation provided by innervation from the vagus nerve. Ordinarily the sphincter remains constricted except during the act of swallowing. Anticholinergic drugs, such as atropine or glycopyrrolate, and pregnancy decrease the resting pressure of the lower esophagus. Drugs that increase the lower esophageal pressure include metoclopramide (Reglan) and antacids. The main function of the esophagus is to conduct ingested material to the stomach.¹^,²

FIG. 16-1 Digestive system and its associated structures.

Disorders of the esophagus

Gastroesophageal reflux disease (GERD) occurs when stomach acid is chronically forced past the LES into the distal portion of the esophagus. Symptoms usually consist of chronic heartburn and substernal pain. Stomach acid refluxes into the esophagus when the pressure in the stomach exceeds the barrier pressure exerted by the LES. This reflux typically occurs because of a weakened LES or an increase in gastric pressure caused by such factors as pregnancy, obesity, or supine positioning. Aside from the distress caused by chronic heartburn, GERD can cause the formation of precancerous cells in the distal esophagus (Barrett’s esophagus). In addition, the presence of GERD indicates that the patient has an increased risk of refluxing stomach contents into his or her esophagus and aspirating it in the PACU.

A hiatal hernia occurs when a portion of the upper stomach protrudes or herniates through the diaphragm. Ultimately this causes a stricture or narrowing to form where the diaphragm surrounds the stomach and causes a weakening of the LES. Symptoms of a hiatal hernia include chronic heartburn, pain, and vomiting. Patients with a hiatal hernia need constant observation for active and passive vomiting during the emergent phase of anesthesia. Monitoring patient with a hiatal hernia is especially important if the surgery was performed on an emergency basis when the patient had a full stomach.³

The stomach

The stomach can be anatomically divided into the following three sections: the fundus, the body, and the pyloric portion (Fig. 16-2). The fundus is the dome of the stomach, where peptic juice is secreted. The body is the middle portion of the stomach and is lined with parietal cells that secrete hydrochloric acid. The pH of the solution as secreted is approximately 0.8, which is extremely acidic. The total gastric secretion on a 24-hour basis is approximately 2 L. This volume normally has a pH of 1 to 3.5. Histamine has a major role in hydrochloric acid production by the parietal cells in the stomach, which is an effect mediated by histamine₂ receptors, vagal stimulation, and the hormone gastrin. Activation on any one of these receptors potentiates the response of the other to stimulation. Blockade of the activated receptor produces a reduction in acid response because the potentiating effect of the stimulation is reduced. The third portion of the stomach is the pyloric portion, where a thick viscous mucus and the hormone gastrin are secreted. At the end of the antrum is the pylorus, an opening surrounded by a strong band of sphincter muscle that controls the amount of gastric contents that enter the duodenum.

FIG. 16-2 Anatomy of the stomach.

(From Hall JE: Guyton and Hall textbook of medical physiology, ed 12, Philadelphia, 2010, Saunders.)

The vagus nerve (the main nerve for the outflow of the parasympathetic nervous system) provides the nerve supply to the stomach. Stimulation of the vagus causes increased motility of the stomach and the secretion of stomach acid, pepsin, and gastrin. As a result, a vagotomy is sometimes performed during gastric surgery to decrease gastric motility and acid production. This procedure used to be a common surgical treatment for peptic ulcer disease, but is rarely performed now because of great improvements in the medical management of this disorder.

Nervous and hormonal stimulation have profound effects on gastric volume and pH. More specifically, stimulation of the parasympathetic nervous system causes increased gastric secretion, and stimulation of the sympathetic nervous system causes decreased gastric secretion. Consequently, pain and fear, which activate the sympathetic nervous system, decrease gastric emptying. In addition, the administration of opioids and active labor prolong gastric emptying. Food, depending on the type and amount, passes through the stomach at a variable rate. For example, foods rich in carbohydrates pass through the stomach in a few hours, whereas proteins exit more slowly. The emptying time for fats is the slowest. Fluids, however, pass through the stomach rather rapidly. In fact, 90% of 750 mL of ingested saline solution exits the stomach within 30 minutes. In addition, 150 mL of fluids taken 1 or 2 hours before induction of anesthesia stimulates peristalsis and facilitates gastric emptying. Consequently, the small sips of water taken with the preoperative oral medications may in fact contribute to lower intraoperative and postoperative gastric volumes. It must be emphasized that fasting, regardless of the duration, does not guarantee that the stomach is completely empty of fluids or food.⁴^,⁵

Effect of pregnancy on gastric motility and secretions

During pregnancy, many alterations occur as a result of the enlarged uterus and altered hormonal state. Because of the enlarged uterus, the stomach and intestine are moved cephalad and the axis of the stomach is shifted to a more horizontal position. The gastric emptying time is increased in women who are at least 34 weeks pregnant. In regard to the gastric volume and pH, no difference between pregnant and nonpregnant states seems to exist. Consequently, pregnant patients who have had nothing by mouth (NPO) for elective surgery do not have any additional risk of aspiration pneumonitis than do nonpregnant patients. However, research findings suggest that pregnant patients who have heartburn may be at greater risk for regurgitation and subsequent development of aspiration pneumonitis. In addition, if intramuscular opioids are given during labor, gastric emptying time is substantially delayed. Epidural anesthesia with local anesthetics does not seem to affect gastric volume or pH; however, if opioids are introduced into the epidural space, a delay in gastric emptying occurs.⁶^,⁷

Postoperative nausea and vomiting

Postoperative nausea and vomiting (PONV) continues to be ongoing concern to anesthesia providers and patients, alike. Occurring in as many as one third of all surgical patients and in 80% of high-risk patients PONV is the most commonly occurring postoperative complication. Research shows that surgical patients classify nausea and vomiting as the most undesirable postsurgical complication and identify it as being more undesirable than postoperative pain. In addition to patient dissatisfaction, PONV creates significant health care concerns and increases institutional and individual costs of surgical procedures. Vomiting is associated with wound dehiscence, aspiration, increased intracranial pressure, and increased cardiovascular demand, placing compromised patients at risk for a myocardial infarction. PONV is a common cause of unanticipated hospital admissions, delayed discharge from the PACU, increased demand on provider staffing, and increased material costs. The resulting increased morbidity and mortality, decreased patient satisfaction, and increased health care costs make the prevention and management of PONV a significant priority for health care providers in the surgical setting.

Nausea and vomiting involves a complex interplay between various structures in the body including the vomiting center in the brain stem, the closely associated chemoreceptor trigger zone, the vestibular labyrinth in the ear, vagal afferent neurons in the gastrointestinal tract, the limbic system, and the cerebral cortex. Each of these sites contributes to the triggering of vomiting by releasing single or multiple neurotransmitters, including serotonin, acetylcholine, histamine, dopamine, opioids, and neurokinins. Adding to the complexity, these anatomic structures often possess a variety of receptors for each of the neurotransmitters, each receptor producing its own specific physiologic result when stimulated.

A great deal of research on PONV over the past few years has yielded drugs that have certainly improved the outcomes of the patient in regard to PONV. The 5-HT3 antagonists, such as ondansetron, tropisetron, granisetron, and dolasetron, competitively antagonize the effect of 5-HT at the 5-HT₃ receptor site. Other drug therapies are the antihistamines (promethazine and dimenhydrinate), anticholinergics (scopolamine), neuroleptics (droperidol and triflupromazine), and glucocorticoids, such as dexamethasone. The pathophysiology and pharmacology of PONV is discussed at length in Chapter 29.

With recent research and the advent of new pharmacologic agents, the ability to prevent and efficaciously treat PONV has greatly improved, even for those patients at highest risk for these complications. Under the auspices of the American Society of PeriAnesthesia Nurses, a multidisciplinary panel met to review current literature regarding the prevention and treatment of PONV and formulate a multimodal, multidisciplinary, evidenced-based set of guidelines to guide the practice of those taking care of surgical patients.⁸ Chief among these recommendations are that each patient should be assessed for the four evidenced-based risk factors for PONV (female gender, nonsmoker, a history of PONV or motion sickness, and administration of postoperative opioids); pharmacologic interventions should be based on the assessed risk for PONV; multimodal interventions, often consisting of more than one pharmacologic intervention targeting different drug receptors are superior to a single intervention; and rescue therapy should consist of administration of a different class of drug targeted at a different set of receptors than the ones given prophylactically.⁸

The basics of care for vomiting in the PACU setting indicate that the patient should be placed in a head-down position and given oxygen immediately. The purpose of the head-down position is to allow fluid to flow away from the lungs rather than into the lungs. Consequently, the patient should be placed in this position if aspiration is suspected. Fluid should be suctioned rapidly while administration of oxygen continues. If the patient’s airway is obstructed by large particles, fingers or forceps should be used to clear the debris and then oxygen should be administered. The physician or anesthesia provider should be notified immediately. Further treatment may include intubation and mechanical ventilation. Steroids and antibiotics may also be administered.

A patient in recovery from a general anesthetic should be assessed for possible passive regurgitation, especially if the patient was not intubated during surgery. Clinical signs include dyspnea, cyanosis of varying degrees, and tachycardia. On auscultation of the lungs, abnormal sounds are usually heard. If the assessment indicates the possibility of this syndrome, oxygen should be administered and the physician notified at once.

The incidence rate for this syndrome is higher in patients who had a full stomach at induction of anesthesia, who underwent intestinal or emergency surgery, or who have a suspected hiatal hernia. The best treatment is prevention. These patients should have a complete return of consciousness before the endotracheal tube is removed. If the endotracheal tube is to be removed in the PACU, the patient should be placed in a lateral position with the head down. Oxygen should be administered, and suction should be available for immediate use before the extubation is performed.⁹^–¹²

The intestine

The duodenum, which is a part of the small intestine, arises at the pylorus of the stomach and ends at the duodenojejunal junction. The duodenum is divided into the following four segments: superior, descending, transverse, and ascending. The common bile duct and the main pancreatic duct empty into the descending duodenum. The main functions of the stomach and the first portion of the duodenum are to alter the form of food and to supply enzymes for digestion.

The jejunum begins at the descending duodenum at the duodenojejunal angle. It constitutes the first two fifths of the small intestine, and the ileum occupies the distal three fifths of the small intestine. The mesentery, which contains blood vessels, nerves, lymphatics, lymph nodes, and fat, stabilizes the small bowel and prevents it from twisting and constricting its blood supply.

The digestive glands secrete large quantities of water to aid in the digestive process. Between 5 and 10 L of water are estimated to enter the small intestine, and approximately 500 mL leave the ileum and enter the colon. Among the important materials absorbed from the small intestine are sodium, bicarbonate, chloride, calcium, iron, carbohydrates, fats, and amino acids.

Sodium is absorbed by the small intestine at a rate of 25 to 35 g/day. This absorption accounts for approximately 16% of all the sodium in the body. When a patient has extreme diarrhea, sodium can be depleted to a lethal level within a few hours.¹³^,¹⁴

The colon and rectum

At the end of the small intestine is the ileocecal valve, which functions to prevent backflow of fecal material from the colon into the small intestine.

The colon is divided anatomically into the cecum, ascending colon, transverse colon, and descending and sigmoid colon. The functions of the colon are the absorption of water and electrolytes, which occurs principally in the proximal half of the colon, and the storage of fecal material, which occurs in the distal colon. The contents of the cecum are mainly liquid, as compared with the solid material contained in the sigmoid colon. Therefore, if a patient has undergone a colostomy, knowledge of the portion of the colon from which the stoma originates is important for determining whether the excreted fecal material has the normal amount of water content.

Of surgical importance is the appendix, which arises from the cecum at its inferior tip. The appendix represents a special type of intestinal obstruction when it becomes inflamed by hyperplasia of submucosal lymphoid follicles, fecaliths, foreign bodies, or tumors.

The rectum functions entirely as an excretory canal and has no digestive function. It begins anatomically at the distal end of the sigmoid colon and ends at the anus. It is tubular and has two layers. The innermost layer is the lumen of the intestinal tract, and the outermost layer is skeletal muscle of the pelvic floor. The muscle is innervated by the parasympathetic nervous system.¹³

The anus

The anus is the termination of the alimentary canal. It is encircled by striated muscle and innervated by somatic sympathetic and parasympathetic fibers. Because of the parasympathetic innervation of the rectum and anus, parasympathetic stimulation can occur during a rectal examination or surgical procedure. This parasympathetic reflex can also occur when a patient is recovering from a general anesthetic. If a physician deems a rectal examination necessary, the perianesthesia nurse should be prepared to monitor the patient for bradycardia and laryngospasm, which can result from stimulation of the anus and rectum.

The liver

The importance of the liver is generally underestimated. Its proper functioning is critical to almost every other system within the body, and its derangement can compromise normal homeostasis in multiple ways.

The liver is located in the right upper quadrant of the abdomen. It has a dual blood supply that consists of the hepatic artery and the portal vein. The hepatic artery supplies highly oxygenated blood directly from the descending aorta while the portal vein drains blood from the organs of the GI tract. This portal circulation ensures that nutrients, drugs, and other foreign substances absorbed from the GI tract are processed by the liver before they enter the general circulation. The sinusoids, which surround the hepatocytes (liver cells), empty into a venous system that eventually forms the hepatic vein and empties into the inferior vena cava. Approximately 1600 mL of blood per minute flow through the liver; this amount is approximately 30% of the cardiac output. The hepatocytes absorb nutrients from the portal venous blood; store and release proteins, lipids, and carbohydrates; excrete bile salts; synthesize plasma proteins, glucose, cholesterol, and fatty acids; and metabolize exogenous and endogenous compounds.

The liver is the most important storage organ in the body. It absorbs glucose in the form of glycogen, maintains a normal glucose concentration in the body, and stores amino acids, iron, and vitamins. The liver can store up to 400 mL of blood in the sinusoids. If a person loses an appreciable amount of blood, the liver can release stored blood into the circulation to replace what was lost.

The liver performs many vital physiologic functions that have a significant effect on the pharmacologic actions of many of the drugs used in the perioperative period. More specifically, the liver performs biotransformation of drugs with the cytochrome P-450 microsomal enzyme system. Consequently, knowledge of protein synthesis and drug biotransformation is of critical importance to the perianesthesia nurse.

Protein synthesis

The liver is responsible for the synthesis of most of the proteins found in the plasma. Albumin is the most notable of the plasma proteins synthesized by the liver. Albumin synthesis is regulated by the state of nutrition; therefore a nutritional deficit can result in reduced albumin production. Because many drugs used in anesthesia are protein bound, a reduction in the albumin level can have a significant effect on the pharmacologic action of the drugs. Because the protein-binding sites are reduced, the unbound, pharmacologically active fraction of the drug is increased, which ultimately leads to an increased sensitivity to the drug or a prolonged action. The liver also synthesizes the enzyme pseudocholinesterase (plasma cholinesterase). This protein is the principal enzyme in the metabolism of succinylcholine and the ester-type local anesthetics. Succinylcholine, which is the principal depolarizing skeletal muscle relaxant in use, has an inverse correlation between duration of action and pseudocholinesterase levels. Therefore any patient with suspected liver dysfunction who has received succinylcholine during surgery should be closely monitored for respiratory depression in the immediate postoperative period. Finally, the liver produces a large proportion of the protein substances used in coagulation; therefore patients in liver failure are at risk for coagulopathies.

Drug biotransformation

The enzymes needed for oxidation and conjugation in the liver are called the microsomal enzymes. These enzymes are part of the cytochrome P-450 microsomal system. Exposure to certain drugs, including barbiturates and some anesthetics, can lead to an increase in the amount of microsomal enzymes in the liver. This process is commonly called enzyme induction. Enzyme induction increases the rate of drug biotransformation. Patients with severe liver disease may have reduced microsomal activity in the liver. As a result, drugs such as thiopental, diazepam, and meperidine have a prolonged action caused by a decreased rate of drug biotransformation by the microsomal enzymes. Consequently, patients with severe hepatic disease should be closely monitored for respiratory and cardiovascular depression in the PACU phase of the anesthetic experience.¹^,⁵

The gallbladder

The gallbladder is a thin-walled, pear-shaped organ attached to the inferior surface of the liver (Fig. 16-3) whose function is to store bile from the liver and release it into the small intestines to aid in the digestion of fats. Anatomically, it is divided into the fundus; the distal tip; the corpus (body), the middle body portion; the infundibulum, a pouch-like structure; and the neck, which leads to the cystic duct. The cystic duct joins the common hepatic duct to form the common bile duct. The common bile duct and the main pancreatic duct of Wirsung usually join at the choledochoduodenal junction, which is a passageway through the duodenal wall. The muscle of the choledochoduodenal junction is the sphincter of Oddi, which regulates the flow of bile into the duodenum. Many common opioid analgesics can produce spasm of the sphincter of Oddi and the duodenum and can increase the pressure in the biliary tree.

FIG. 16-3 Gallbladder and its extrahepatic ducts.

(From Buck CJ: 2012 ICD-9-CM professional edition, St. Louis, 2012, Saunders.)

Cholelithiasis is a common occurrence in patients with chronic gallbladder disease. As many as 20 million people have some form of cholelithiasis. Gallstones are composed of cholesterol, which is almost insoluble in pure water. The causes of gallstones include an excess of cholesterol in the bile, chronic inflammation of the epithelium, excessive absorption of bile acids from the bile, and excessive absorption of water from the bile. Laparoscopic cholecystectomy is one of the most common abdominal surgeries and offers a clear advancement over the open removal of the gallbladder (see Chapters 40 and 47).¹⁵^,¹⁶

The pancreas

The pancreas is situated in the upper abdomen behind the stomach. It is a slender organ that consists of a head, a body, and a tail (Fig. 16-4). Its main duct, through which pass the pancreatic enzymes, runs the entire length of the gland and opens into the duodenum along with the common bile duct. Scattered throughout the pancreas are small clusters of cells called the islets of Langerhans. They are responsible for the production and secretion of hormones that they empty directly into the blood stream; therefore the islets of Langerhans are considered an endocrine gland. The following three types of cells are found in the islets of Langerhans: alpha, beta, and delta. The alpha cells are associated with the production of the hormone glucagon, and the beta cells are associated with insulin. The physiologic significance of the delta cells has not been determined.