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Diseases of the gastrointestinal system
The principal function of the gastrointestinal (GI) tract is to provide the body with a supply of water, nutrients, and electrolytes. Each division of the GI tract—esophagus, stomach, small and large intestines—is adapted for specific functions such as passage, storage, digestion, and absorption of food. Impairment of any part of the GI tract may have significant effects on a patient coming for surgery.
Procedures to evaluate and treat diseases of the gastrointestinal system
Upper gastrointestinal endoscopy
Upper GI endoscopy, or esophagogastroduodenoscopy (EGD), can be done for diagnostic and/or therapeutic purposes and is usually performed in the left lateral decubitus position. It involves placement of an endoscope into the esophagus and through the stomach and pylorus and into the duodenum. EGD is a relatively safe procedure with a mortality rate ranging from 0.01 to 0.4 per 1000 persons and an overall complication range of 0.6 to 5.4 per 1000 persons. Most complications are cardiopulmonary in nature. EGD may be performed with or without sedation/anesthesia. If deep sedation/general anesthesia is chosen, the anesthesiologist shares the upper airway with the gastroenterologist, which introduces a unique challenge. In addition, these procedures are frequently performed outside of the main operating room suite, challenging anesthesiologists to provide a high level of patient safety with little or no immediate backup while simultaneously meeting the efficiency demands of the endoscopy center. Currently there is no consensus on which anesthetic medication(s) or technique is best for minimizing complications and maximizing efficiency.
Respiratory complications of EGD include desaturation, airway obstruction, laryngospasm, and aspiration. Studies suggest that the incidence of respiratory complications in nonintubated patients is higher than in intubated patients and that there is no decrement in efficiency because of endotracheal intubation.
Because there is no consensus for the best anesthetic technique for upper GI endoscopy, and because the expectations vary between gastroenterologists and anesthesiologists, the anesthesiologist must have a thorough understanding of both diagnostic and therapeutic EGD procedures and patient comorbidities to formulate an appropriate anesthetic plan. Many patients for diagnostic endoscopy can be managed without the assistance of an anesthesiologist. Typically, an anesthesia team is involved if a patient is not a good candidate for mild to moderate sedation or there are other comorbid conditions that pose challenges to nonanesthesiologists, such as the need for endotracheal intubation. Patients with a difficult airway or at risk of airway obstruction (e.g., patients with sleep apnea) require an endotracheal tube, especially if prone positioning will be used. Patients at risk for aspiration, such as those with a full stomach, gastroparesis, achalasia, and morbid obesity, may also require endotracheal intubation.
Endoscopic procedures that may be technically challenging or unusually stimulating (e.g., bile or pancreatic stent changes, dilations, per oral endoscopic myotomy) usually require general anesthesia to ensure control of noxious stimuli. Patients with complex medical conditions should have their procedures done in an operating room suite or in a hospital setting with ready access to appropriate extra equipment and personnel and to have a higher level of postoperative care.
Colonoscopy
Like EGD, colonoscopy can be done for diagnostic or therapeutic purposes and with or without deep sedation/anesthesia. There is no consensus on the anesthetic technique that best maximizes safety and efficiency.
A major concern prior to colonoscopy is bowel preparation, with its high risk of dehydration and the required period of fasting necessary to provide a safe anesthetic. Most bowel preps are completed the evening prior to the procedure, and a traditional 6- to 8-hour nothing-by-mouth (NPO) period is requested by the anesthesiologist to decrease the risk of pulmonary aspiration of gastric contents. Recent prep protocols may call for some of the bowel prep to be done the day before the colonoscopy and some on the morning of the procedure. This method, known as the split-dose bowel prep, may provide a superior prep and has greater patient tolerance. It has been shown that gastric residual volume is the same after a split-prep with 2 hours of fasting in the morning as when there is an overnight fast with the traditional prep. This suggests that the risk of aspiration may be similar for these two preps. However, a consensus has not yet been reached in this regard.
Other diagnostic tools
High-resolution manometry (HRM) should be done if a motility disorder is suspected. HRM uses a catheter that can detect pressures at 1-cm or smaller intervals along the length and circumference of the catheter. Thus it allows pressure readings to be made simultaneously along the entire length of the esophagus, including at the upper and lower esophageal sphincters. The patient is given small aliquots of fluid to swallow after the catheter has been placed through the esophagus and into the proximal stomach. The catheter passes through the gastroesophageal (GE) junction. Measurements are made in a three-dimensional display of time, distance down the esophagus, and pressure at all points along the esophagus. This creates a test result called esophageal pressure topography.
A barium contrast study is a noninvasive study that remains useful, especially for patients who are poor candidates for endoscopy. It can demonstrate esophageal reflux, hiatal hernias, ulcerations, erosions, and strictures.
Reflux testing can be done via ambulatory esophageal pH recordings over a 24- to 48-hour period using a transmitter anchored to the esophageal mucosa or a transnasal wire electrode.
Diseases of the esophagus
Symptoms of esophageal disease
To evaluate esophageal symptoms, a thorough clinical history can provide some clues and help focus the evaluation. The most common symptoms of esophageal disease are dysphagia, heartburn, and regurgitation. Others include chest pain, odynophagia, and globus sensation.
Dysphagia is a symptom referring to difficulty swallowing. Patients typically describe a sensation of food getting stuck in the chest or throat. Dysphagia can be classified based on its anatomic origin (i.e., oropharyngeal or esophageal). Oropharyngeal dysphagia is commonly seen after head and neck surgery and with certain neurologic conditions such as stroke and Parkinson disease. Esophageal dysphagia is classified based on its physiology (i.e., mechanical or due to dysmotility) ( Table 17.1 ). The clinical history of the dysphagia—better or worse with solids or liquids, episodic or constant, or progressive in character—helps guide the diagnostic workup. Dysphagia only for solid food usually indicates a structural disorder, and dysphagia for both liquids and solids suggests a motility disorder.
TABLE 17.1
Etiologies of Dysphagia
| Mechanical Disorders
Benign Strictures
|
Malignant Strictures
|
Motility Disorders
|
Heartburn is a symptom described as burning or discomfort behind the sternum, possibly radiating to the neck. The association between heartburn and gastroesophageal reflux disease (GERD) is so strong that current management of heartburn includes empirical treatment for GERD, realizing that in a few patients the “heartburn” could have a cardiac cause. Regurgitation refers to the effortless return of gastric contents into the pharynx without the nausea or retching that would be experienced with vomiting.
Chest pain caused by esophageal disease is often difficult to distinguish from chest pain due to a cardiac origin. The description of heartburn in addition to the pain may be helpful to clarify that the discomfort is caused by gastroesophageal reflux. Odynophagia is pain with swallowing. This symptom is often described with esophagitis of infectious origin and with esophageal ulcers. Globus sensation is the feeling of “a lump in the throat.” Patients with this sensation are often referred for a dysphagia evaluation.
EGD permits direct visualization of esophageal abnormalities as well as collection of biopsy and cytology specimens. It is the best form of evaluation when mechanical causes of dysphagia are suspected. This modality can also detect mucosal lesions and the presence of Barrett esophagus. It allows for dilation of strictures during the examination.
Esophageal motility disorders
Esophageal motility disorders frequently present with dysphagia, heartburn, or chest pain. The most common disorders are achalasia, diffuse esophageal spasm, and GERD.
The chicago classification
Using HRM, the Chicago Classification of esophageal motility assesses 10 swallows and can classify patients as having (1) normal esophageal motility, (2) abnormal GE junction relaxation, (3) a major motility disorder with normal GE junction relaxation, or (4) borderline peristalsis.
Achalasia
Achalasia is a neuromuscular disorder of the esophagus with an incidence of 1 per 100,000 persons per year. It consists of esophageal outflow obstruction caused by inadequate relaxation of the lower esophageal sphincter (LES) and a dilated hypomotile esophagus. It is theorized that there is loss of ganglion cells in the myenteric plexus in the esophageal wall as a result of either a degenerative neuronal disease or an infection. This is followed by absence of the inhibitory neurotransmitters nitric oxide and vasoactive intestinal polypeptide on the LES. Thus there is unopposed cholinergic stimulation of the LES, and it consequently fails to relax. The end result is hypertension of the LES, reduced peristalsis, and esophageal dilatation with impaired emptying of food into the stomach and thus food stasis in the esophagus.
Symptoms include dysphagia with both liquids and solids (95%), regurgitation (60%), heartburn (40%), and chest pain (40%). In the long term, this disease is associated with an increased risk of esophageal cancer. Pulmonary aspiration is common, with resultant pneumonia, lung abscess, and/or bronchiectasis. The diagnosis of achalasia can be made by esophagram, which reveals the classic “bird’s beak” appearance. EGD can exclude other structural issues, but esophageal manometry is the standard for definitive diagnosis. With HRM and the Chicago Classification, achalasia can be classified into three distinct patterns. Type I (classic) involves minimal esophageal pressurization and has a better outcome, with myotomy as the initial treatment rather than dilation or botulinum toxin injection. Type II shows pressurization of the entire esophagus and has the best outcome regardless of the initial treatment. Type III involves esophageal spasm with premature contractions and has the worst outcome.
Treatment.
All treatments for achalasia are palliative. They can relieve the obstruction caused by the LES but cannot correct the peristaltic deficiency of the esophagus. Medications, including nitrates and calcium channel blockers, can be used to try to relax the LES. Invasive measures include endoscopic botulinum toxin injection, pneumatic dilation, laparoscopic Heller myotomy, and per oral endoscopic myotomy (POEM). The POEM procedure involves endoscopically dividing the circular muscular layer of the LES but leaving the longitudinal muscular layer intact. Therefore it may offer the efficacy of surgery with the morbidity of an endoscopic procedure. However, the procedure is not without risk. Up to 40% of patients will develop a pneumothorax or pneumoperitoneum, and half of these will require a chest tube or peritoneal drain. Dilation is the most effective nonsurgical treatment, and laparoscopic Heller myotomy remains the best surgical treatment of achalasia. Esophagectomy can be considered in very advanced disease and would eliminate the risk of esophageal cancer as well as mitigate symptoms.
Anesthetic concerns.
Patients with achalasia are at high risk of perioperative aspiration and must be treated using full-stomach precautions. The dilated esophagus may retain food for many days after ingestion, so the duration of fasting is misleading in terms of aspiration risk. A large-bore nasogastric tube can be inserted to decompress and empty the esophagus prior to induction, or a large-channel endoscope can be passed to evacuate most of the esophageal contents. Rapid-sequence induction/endotracheal intubation or awake intubation is required in all patients.
Patients presenting for repair via POEM require general anesthesia and mechanical ventilation. Prior to the procedure, patients may fast for up to 48 hours. The procedure is performed in the supine position, and the esophagus is insufflated with carbon dioxide. During insufflation, patients may have an increase in end-tidal carbon dioxide (ETCO 2 ) that can be managed with controlled mechanical ventilation.
Distal esophageal spasm
Distal esophageal spasm (DES) is now the preferred term for describing diffuse esophageal spasm because it is typically the distal portion of the esophagus that is spastic. DES typically occurs in elderly patients and is most likely due to autonomic nervous system dysfunction. An esophagram may show a “corkscrew esophagus” or a “rosary bead esophagus.” Pain produced by esophageal spasm may mimic angina pectoris; it frequently responds favorably to treatment with nitroglycerin, which can confuse the clinical picture. The antidepressants trazodone and imipramine can decrease chest pain due to distal esophageal spasm. The phosphodiesterase inhibitor sildenafil can also reduce this pain.
Esophageal structural disorders
Esophageal diverticula
Esophageal diverticula are outpouchings of the wall of the esophagus. The most common locations for these are pharyngoesophageal (Zenker diverticulum), midesophageal, and epiphrenic (supradiaphragmatic diverticulum).
Zenker diverticulum ( Fig. 17.1 ) appears in a natural zone of weakness in the posterior hypopharyngeal wall (Killian triangle) and can cause significant bad breath from retention of food particles consumed up to several days previously. A midesophageal diverticulum may be caused by traction from old adhesions or inflamed lymph nodes or by propulsion associated with esophageal motility abnormalities. An epiphrenic diverticulum may be associated with achalasia. Large symptomatic esophageal diverticula are removed surgically.
Small or midsize Zenker diverticula are usually asymptomatic. If they become large and filled with food, they can compress the esophagus and cause dysphagia. Regurgitation of food contents and the risk of aspiration of this material from a diverticulum can occur at any time during anesthesia—during induction, during endotracheal intubation, after intubation, or with surgical manipulation—and there can be leakage around the endotracheal tube cuff. Various anesthetic regimens are acceptable during surgical repair of a Zenker diverticulum, with a top priority given to efforts to prevent aspiration. The effectiveness of cricoid pressure in reducing the risk of aspiration during rapid-sequence induction/intubation is doubtful in this situation. A preoperative barium swallow analyzed by an expert in this technique could help determine whether cricoid pressure will be useful or not. If the diverticular sac is immediately behind the cricoid cartilage, cricoid pressure might force the contents of the sac into the pharynx rather than protect the patient from regurgitation. Most often, general anesthesia is induced in the head-up position without cricoid pressure.
Regardless of anesthetic technique, the pouch may be emptied prior to anesthetic induction by the patient exerting external pressure. Insertion of a nasogastric tube should be avoided because it can perforate the diverticulum. For transesophageal echocardiography the probe needs to be inserted very carefully to prevent perforation of the diverticulum.
Hiatal hernia
A hiatal hernia is a herniation of part of the stomach into the thoracic cavity through the esophageal hiatus in the diaphragm. A sliding hiatal hernia is one in which the GE junction and fundus of the stomach slide upward. This type of hernia is seen in about 30% of patients having upper GI tract radiographic examinations. Many of these patients are asymptomatic (i.e., no symptoms of reflux). This hernia may result from weakening of the anchors of the GE junction to the diaphragm, from longitudinal contraction/shortening of the esophagus, or from increased intraabdominal pressure. A paraesophageal hernia is one in which the GE junction stays in its normal location, and a pouch of stomach is herniated next to the GE junction through the esophageal hiatus. Hiatal hernias are very infrequently repaired. The fact that most patients with hiatal hernias do not have symptoms of reflux esophagitis emphasizes the importance of the integrity of the LES.
Esophageal tumors
Esophageal cancer occurs in 4 to 5 per 100,000 people in the United States. It usually presents with progressive dysphagia to solid food and weight loss. Esophageal cancer has a poor survival rate because abundant esophageal lymphatics lead to early lymph node metastases. Esophageal cancer can be a squamous cell cancer or an adenocarcinoma. Formerly, most esophageal cancers were of the squamous cell type and situated about midesophagus. Today most esophageal cancers are adenocarcinomas and are located at the lower end of the esophagus. It is postulated that adenocarcinomas are linked to the dramatic increase in GERD, Barrett esophagus, and obesity.
Esophagectomy.
Esophagectomy can be a curative or palliative option for malignant esophageal lesions. It can also be considered when benign obstructive conditions are not responsive to conservative management. There are several surgical approaches to esophagectomy, including transthoracic, transhiatal, and minimally invasive. Minimally invasive esophagectomy combines a laparoscopic resection of the GE junction and the proximal stomach with a thoracoscopic resection of the esophagus. Survival rates at 5 years with any of these surgical approaches ranges from 12% to 60%.
Morbidity and mortality.
The morbidity and mortality of esophagectomy are quite high. Morbidity rates can be as high as 50% in specialized high-volume centers, and mortality rates approach 5%. Most major postoperative complications are cardiovascular, and these contribute to poor outcomes. Acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS) has been reported as high as 25% to 38% of esophagectomies; more recent evidence of ALI is less than 10%. However, if ARDS develops, mortality approaches 50%.
The cause of ARDS in the setting of esophagectomy is not completely understood, but it may be that inflammatory mediators, pulmonary cytokines, and gut-related endotoxins trigger the pulmonary dysfunction. Another contributing factor may be the use of prolonged one-lung ventilation. The current practice of protective lung ventilation (limiting the tidal volume during mechanical ventilation to 6 mL/kg plus positive end-expiratory pressure [PEEP]) likely decreases ventilator-associated trauma. A history of smoking, low body mass index, long duration of surgery, cardiopulmonary instability, and the occurrence of a postoperative anastomotic leak also increase the risk of ARDS.
Other common postoperative complications include anastomotic leaks, dumping syndrome, and esophageal stricture.
Anesthetic implications.
Patients are often malnourished (protein-calorie malnutrition) before esophagectomy and for many months afterward. Fortunately, over the past decade, regular surveillance of patients with Barrett esophagus has led to the diagnosis of some esophageal cancers in very early stages, so these patients typically arrive for surgery in good nutritional balance. Some patients presenting for esophagectomy have had chemotherapy and/or radiation therapy, so pancytopenia, dehydration, and lung injury can be present.
In the postoperative period, patients may need to return to the operating room for correction of an anastomotic leak. They may have acute lung injury, sepsis, or shock. There is a very significant risk of aspiration in all patients who have had an esophagectomy, a risk that persists for life.
Recurrent laryngeal nerve injury has been described in patients after esophagectomy, likely related to the cervical portion of the surgery. A vocal cord palsy can lead to airway compromise during extubation and clearly increases the risk of aspiration. Spontaneous resolution of recurrent laryngeal nerve palsy has been described in about 40% of patients.
Thoracic epidural analgesia for perioperative pain management has been shown to reduce the incidence of pulmonary complications and promote earlier return of bowel function. The latter facilitates expeditious resumption of enteric feeding. The best analgesic drugs for thoracic epidural analgesia are uncertain. Local anesthetics, local anesthetics combined with opioids, and opioids alone can be used. Hemodynamic variables and fluid management will be affected by the choice of the epidural analgesic medication(s).
Gastroesophageal reflux disease
GERD is defined as gastroesophageal reflux that causes bothersome symptoms, mucosal injury in the esophagus or at extraesophageal sites, or a combination of both. It is a common problem, with approximately 15% of adults in the United States being affected based on self-reporting of chronic heartburn. The most common symptoms are heartburn and regurgitation. Dysphagia and chest pain are less commonly noted.
Pathophysiology of GERD
Natural antireflux mechanisms consist of the LES, the crural diaphragm, and the anatomic location of the GE junction below the diaphragmatic hiatus. The LES opens with swallowing and closes afterward to prevent gastric acid in the stomach from refluxing into the esophagus. At rest, the LES exerts a pressure high enough to prevent gastric contents from entering the esophagus.
With GE junction incompetence, gastric contents can reenter the esophagus, causing symptoms and/or mucosal damage. Three common mechanisms of incompetence are (1) transient LES relaxation (elicited by gastric distention), (2) LES hypotension (average resting tone, 13 mm Hg in patients with GERD vs. 29 mm Hg in patients without GERD), and (3) anatomic distortion of the GE junction such as with a hiatal hernia. The reflux contents may include hydrochloric acid, pepsin, pancreatic enzymes, and bile. Bile is a cofactor in the development of Barrett metaplasia and adenocarcinoma.
Complications of GERD
Chronic peptic esophagitis is caused by reflux of acidic gastric fluid into the esophagus, producing retrosternal discomfort (i.e., heartburn). Local complications include esophagitis, strictures, ulcers, Barrett metaplasia, and its associated risk of adenocarcinoma. With the laryngopharyngeal reflux variant of GERD, gastric contents reflux into the pharynx, larynx, and tracheobronchial tree, resulting in chronic cough, bronchoconstriction, pharyngitis, laryngitis, bronchitis, or pneumonia. Recurrent pulmonary aspiration can lead to progressive pulmonary fibrosis or chronic asthma. It is notable that up to 50% of patients with asthma have either endoscopic evidence of esophagitis or an increased esophageal acid exposure on 24-hour ambulatory pH monitoring.
Treatment
Therapy for GERD includes lifestyle modification, including avoidance of foods that reduce LES tone (e.g., fatty and fried foods, alcohol, peppermint, chocolate) and avoidance of acidic foods (e.g., citrus and tomato products). Pharmacologic measures aim to inhibit gastric acid secretion, with proton pump inhibitors being more effective than histamine (H 2 ) receptor antagonists. These drugs do not prevent reflux but increase the pH of the reflux, which allows esophagitis to heal. Surgical options for severe symptoms include laparoscopic Nissen fundoplication, in which an antireflux barrier is created by wrapping the proximal stomach around the distal esophagus.
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