section epub:type=”chapter” id=”c0080″ role=”doc-chapter”> The hepatobiliary and gastrointestinal system is a common cause of concern in the postoperative setting. A significant number of surgical procedures involve the gastrointestinal tract, and anesthetic drugs sometimes have a profound influence on this organ system. This requires the perianesthesia nurse in the postanesthesia care unit to have a strong understanding of the organs’ general functions in this system. This chapter discusses each organ’s overall function and some of the possible postoperative complications that may involve the gastrointestinal tract. Of specific interest to the perianesthesia nurse is the section on postoperative nausea and vomiting (PONV), one of the most common and distressing anesthesia-related complications. biliary; cholelithiasis; chyme; enteric system; gastritis; ileas; nausea; pancreatitis; peptic ulcer; vomiting The hepatobiliary and gastrointestinal system is a common cause of concern in the postoperative setting. A significant number of surgical procedures involve the gastrointestinal (GI) tract and anesthetic drugs sometimes have a profound influence on this organ system. This requires the perianesthesia nurse in the postanesthesia care unit (PACU) to have a strong understanding of the organs’ general functions in this system. This chapter discusses each organ’s overall function and some of the possible postoperative complications that may involve the GI tract. Of specific interest to the perianesthesia nurse is the section on postoperative nausea and vomiting (PONV), one of the most common and distressing anesthesia-related complications. Definitions Biliary Pertaining to the gallbladder and bile ducts. Cholelithiasis The presence of gallstones obstructing the common bile duct stone. Chyme The semifluid partially digested food passed from the stomach into the duodenum. Enteric System The GI tract. Gastritis Inflammation of the gastric mucosa. Ileas The absence of normal intestinal peristalsis leading to an intestinal obstruction. Nausea A nonspecific symptom characterized by the sensation of unease and discomfort in the stomach with an involuntary urge to vomit. Pancreatitis Inflammation of the pancreas. Peptic Ulcer An excoriated area of the gastric or duodenal mucosa caused by the digestive action of gastric acid. Vomiting The forceful voluntary or involuntary emptying of the stomach contents through the mouth, which is often, but not always, preceded by nausea. 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 that 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, increasing the risk of gastric reflux. Drugs that increase the lower esophageal pressure include metoclopramide (Reglan) and antacids. The LES can be overcome by positive pressure ventilation in the operating room, increasing the risk of aspiration for the patient in the PACU. The main function of the esophagus is to conduct ingested material to the stomach.1,2 Front with of human with head turned to one side shows digestive system along with associated labels (clockwise) as follows: Tongue, sublingual salivary gland, larynx, trachea, liver, stomach, spleen, splenic flexure of colon, descending colon, sigmoid colon, anal canal, rectum, vermiform appendix, cecum, ileum, ascending colon, hepatic flexure of colon, transverse colon, diaphragm, esophagus, pharynx, submandibular salivary gland, and parotid gland. An arrow from the top of liver with stomach below points toward their magnified view and associated structures with labels (clockwise) as follows: Spleen, pancreas, duodenum, gallbladder, cystic duct, and common hepatic duct. 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 factors such 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 the contents into the lungs in the PACU. A hiatal hernia occurs when a portion of the upper stomach protrudes or herniates up 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 a 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 can be anatomically divided into the following three sections: the fundus, the body, and the pyloric antrum (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 with a normal pH of 1 to 3.5. The production of hydrochloric acid by the parietal cells is mediated by histamine, vagal stimulation, and the hormone gastrin. Blocking the histamine receptor (H2) by drugs such as cimetidine or ranitidine to reduce acid production is a common treatment for GERD. The third portion of the stomach is the pyloric portion where 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 smooth muscle creating the pyloric sphincter that controls the amount of gastric contents that enter the duodenum.4 Anatomy of stomach shows labels (clockwise) as follows: Cardial notch, fundus, greater curvature, body, pyloric antrum, pyloric canal, pyloric sphincter, pyloric constriction, duodenum, pyloric orifice, angular incisures, lesser curvature, cardia, and abdominal esophagus. The vagus nerves (the primary nerves for the outflow of the parasympathetic nervous system) provide the predominant 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. Current guidelines for preoperative fasting are discussed fully in Chapter 14.5,6 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 compared with 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.7,8 Care of the pregnant patient is discussed in Chapter 51. PONV continues to be of 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. Nausea and vomiting involves a complex interplay among various structures in the body including the vomiting center in the brainstem, the closely associated chemoreceptor trigger zone, the vestibular labyrinth in the ear, vagal afferent neurons in the GI 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 (5HT), acetylcholine, histamine, dopamine, and neurokinins. Adding to the complexity, these anatomic structures often possess a variety of receptors for each of the neurotransmitters, with each receptor producing its own specific physiologic result when stimulated. Current practice guidelines covering the prevention and management of PONV and the care of patients experiencing PONV are presented in Chapter 29.9 The duodenum, the first section of the small intestine, arises at the pylorus of the stomach and stretches 25 to 30 cm to the duodenojejunal junction. The duodenum is a C-shaped tubular structure located below the stomach. The ampulla of Vater located in the duodenum is the confluence of the common bile duct draining bile from the gallbladder and the pancreatic duct draining digestive enzymes from the pancreas. The main functions of the stomach and the duodenum are to transform solid food into liquid slurry, regulate the entry of this slurry into the rest of the digestive tract, and supply enzymes for digestion. The jejunum begins at the distal end of the 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 majority of digestion and nutrient absorption occurs in the small intestine. With the digestive enzymes from the stomach and the additional enzymes from the pancreas and bile salts from the gallbladder, most of the breakdown and digestion of food takes place in the duodenum. The jejunum and ileum have special microscopic structures called microvilli that increase the surface area of these portions of the small intestine, allowing for absorption of nutrients, vitamins, minerals, and medications. By the time the remnants of a meal have reached the end of the small intestine, almost all of the nutritional value has been removed.10,11 Sodium is absorbed by the small intestine at a rate of 25 to 35 g/d. 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.10,11 At the end of the small intestine is the ileocecal valve, which functions to ensure only forward flow of material from the small intestine to the colon. The colon is divided anatomically into the cecum, ascending colon, transverse colon, and descending and sigmoid colon (Fig. 16.3). 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 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. Large intestine along with arteries and veins shows labels (starting from top right) as follows: Splenic (left colic) flexure, taeniae coli, inferior mesenteric artery and vein, fatty appendage, descending colon, sigmoid artery and vein, haustra, sigmoid colon, superior rectal artery and vein, anus, external anal sphincter muscle, rectum, mesentery, ileum, vermiform appendix, cecum, ileocecal valve, ascending colon, hepatic (right colic) flexure, superior mesenteric artery, inferior vena cava, hepatic portal vein, aorta, splenic vein, and transverse colon.
16: The Hepatobiliary and Gastrointestinal System
Abstract
Keywords
The esophagus
Disorders of the Esophagus
The stomach
Effect of Pregnancy on Gastric Motility and Secretions
Postoperative Nausea and Vomiting
The intestine
The colon and rectum
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