Nutritional, Gastrointestinal, and Endocrine Disease

Perioperative Considerations

Changes in anatomy and physiology related to obesity affect anesthetic planning and management. Preoperative assessment should focus on determining the presence and status of comorbid conditions. This assessment will allow for measures to be taken to minimize the risk of perioperative complications, including determining if certain additional testing is required, if the patient is scheduled at an appropriate surgical venue, and if adequate postoperative resources are available if needed.

Standard preoperative fasting guidelines should be observed and the decision to use aspiration prophylaxis made on an individual basis for those patients who are high risk or symptomatic. Careful consideration should be made regarding the use of sedative premedication to achieve anxiolysis, as patients with obesity may be more sensitive to the respiratory depressant effects. If used, these should be given in incremental doses and carefully titrated to effect.

Depending on the habitus of the patient, several logistical challenges may be encountered related to monitoring, procedures, and positioning. The amount and distribution of subcutaneous fat in the extremities may make obtaining peripheral intravenous access difficult and necessitate central venous access depending on the procedure. Similarly, the increased width or conical shape of the upper arms may make the use of a noninvasive blood pressure cuff inaccurate or unreliable and necessitate alternative cuff location (forearm or lower leg) or invasive arterial line access for blood pressure monitoring. As operative room tables are often narrow, positioning may be a challenge (also see Chapter 19 ). Additional reinforcement or pressure point padding may be required to ensure adequate security and support, especially in the event that extreme angles of tilt are required for the procedure.

Before induction of anesthesia, an airway assessment should be made to determine risk factors for difficult mask ventilation or laryngeal intubation (also see Chapter 16 ). Securing an airway in patients with obesity may be challenging because of the redundancy of oropharyngeal tissue, increased neck circumference, reduced mobility of the cervical spine, or increased anterior-posterior chest dimension. Induction of anesthesia may also be complicated by rapid desaturation with apnea. A rapid decrease in blood oxygen saturation is multifactorial with causes including increased metabolic requirements (increased oxygen consumption and carbon dioxide production) and reduced functional residual capacity. ^, Ensuring adequate preoxygenation or providing apneic oxygenation allows for increased time to desaturation. Optimizing positioning by placing the patient in reverse Trendelenburg (back up or ramped position) will increase functional residual capacity by reducing atelectasis in dependent areas of the lung, improve ventilation-perfusion matching, and caudally displace chest tissue to allow for easier mask ventilation and view on laryngoscopy.

No anesthetic type has proven superior in patients with obesity. However, in patients with elevated risk for respiratory or airway-related problems regional anesthesia should be considered if feasible. When general anesthesia is used, ventilatory management may be challenging and require additional pressure support or positive end-expiratory pressure to ensure adequate ventilation and avoid alveolar collapse. Choice of medications depends on patient-specific factors and comorbidities with consideration of altered drug metabolism and elimination with increased adipose tissue. As mentioned previously, anesthetic medications should be administered in incremental doses and titrated to effect to avoid oversedation or hypoventilation on emergence or postextubation. Ensuring adequate extubation criteria is important, as sedation or interim airway swelling and edema from the surgery or positioning may further complicate an already challenging intubation. As patients with obesity are at increased risk for postoperative pulmonary complications, including hypoxemia or hypercarbia from atelectasis, hypoventilation, or airway obstruction, additional noninvasive ventilatory support in the recovery room may be required to ensure adequate ventilation and gas exchange.

Bariatric Surgery

Adult bariatric surgery is a therapeutic option in patients with severe obesity who have failed conservative treatments, such as lifestyle modifications and medical management. Bariatric surgery results in significant sustained weight loss and a reduction in obesity-related comorbidities and cardiovascular events. The strategic approaches for surgically assisted weight loss fall into three categories: gastric restriction, intestinal malabsorption, or a combination of both.

Malabsorptive procedures include jejunoileal bypass or biliopancreatic diversion. These operations have the advantage of promoting significant weight loss by extensively bypassing the small intestine. Although these were the most commonly performed approaches when bariatric surgery was first created, they are now infrequently performed because of their related nutritional and metabolic complications.

Restrictive procedures include gastric banding and sleeve gastrectomy. By creating a small gastric pouch and outlet, these procedures promote weight loss through several mechanisms, including appetite suppression and early satiety, reduced secretion of gastric hormones (i.e., ghrelin), and possibly vagal nerve compression. Whereas sleeve gastrectomies involve resection of the greater curvature of the stomach, banding procedures use adjustable or fixed bands to wrap the top portion of the stomach to the desired size. Gastric banding has fewer complications and lower morbidity and mortality, as it requires no cutting into gastrointestinal structures. Restrictive-based procedures take a longer time to achieve weight loss. However, the normal absorptive physiology of the small intestine is left intact, and nutritional deficiencies rarely occur.

The most common combined bariatric procedure is the Roux-en-Y gastric bypass. This procedure involves creating a small gastric pouch, which is then connected to the jejunum. It is the most complex of the approaches and requires the longest operative time and hospital length of stay. Because of its combined gastric restriction and malabsorption approaches, it promotes the greatest weight loss and improvement in obesity-related comorbidities; however, these patients require lifelong nutritional surveillance and supplementation. As such, it is often reserved for patients with clinically severe obesity.

Bariatric surgeries are often performed laparoscopically because of the benefits of decreased pain, decreased complication rates, shorter recovery times, and outcome efficacy comparable to that of their open counterparts. In addition to the weight loss and high-resolution rate of comorbid conditions such as hypertension and diabetes, patients report improvement in their quality of life. Overall, perioperative mortality from bariatric surgeries ranges from 0.1% to 2.0%, with gastric banding having the lowest mortality and Roux-en-Y gastric bypass having the highest. Risk factors for mortality include male sex, older age, BMI ≥50.0 kg/m², diabetes mellitus, obstructive sleep apnea, and performance at a low-volume bariatric surgical center.

Perioperative Considerations

Malnutrition is associated with several complications in the perioperative period, including increased rates of infection, poor wound healing and anastomotic integrity, bacterial overgrowth in the gastrointestinal tract, increased time spent in the intensive care unit and hospital length of stay, and increased need for mechanical ventilation. It is also associated with increased mortality after organ transplant, major intraabdominal, or cardiothoracic surgeries. As such, it is important to identify patients who are malnourished and, when possible, intervene to improve their nutritional state in an effort to reduce complications and improve outcomes.

Assessing nutritional status preoperatively is complex; however, the combined use of a comprehensive history and physical examination and nutritional risk screening tool is a helpful approach. Certain laboratory testing may also help to identify malnourishment, including reduced serum protein markers, such as albumin, prealbumin, or transferrin. Of these, prealbumin may allow for the earliest detection of changes in nutritional status, given that its half-life is only 2 days; however, it should be measured in conjunction with C-reactive protein levels, as inflammation can raise the level of prealbumin and affect result interpretation. Reduced serum levels of cholesterol, zinc, iron, vitamin B ₁₂ , or folic acid may also indicate malnourishment. In the postoperative setting the adequacy of nutritional support may be assessed by the patient's overall clinical course and wound healing. Daily clinical assessment, trend in lean body mass, calorimetry, and laboratory results may also inform the patient's nutritional status.

Refeeding syndrome describes the metabolic disturbance that occurs after rapid nutritional repletion in a severely malnourished patient. Hypophosphatemia is the hallmark disturbance of the syndrome and occurs for several reasons. Initial glucose load from feeding leads to increased insulin levels, which in turn result in a rapid movement of extracellular phosphate, potassium, and magnesium into the intracellular compartment. Insulin also leads to the production of molecules that require phosphate, such as adenosine triphosphate and 2,3-diphosphoglycerate, which leads to further phosphate depletion. Hypophosphatemia in turn leads to tissue hypoxia, myocardial dysfunction, respiratory failure, hemolysis, rhabdomyolysis, and seizures. Refeeding syndrome can be avoided by having a cautious and carefully titrated approach to nutritional repletion.

For severely malnourished patients, TPN or enteral feeding should be administered for 7 to 10 days before an electric surgery to improve outcomes. Nutritional replacement should be continued as long as possible before a surgical procedure. With TPN, consideration should be made regarding the presence of insulin in the infusion, as regular monitoring of the patient's glucose and electrolytes may be required. With enteral replacement, consideration should be made regarding the patient's risk of aspiration of gastric contents with the benefit of continued nutritional replacement to keep the patient at goal level.

Intraoperative goals for anesthetic management rely on considering the various metabolic, physiologic, and pharmacologic changes in malnourished patients. General principles for management include preventing hypoglycemia, preventing hypothermia, treating and preventing dehydration, correcting electrolytes, identifying and treating infections, correcting micronutrient deficiencies, careful positioning and padding, and emotional support.

Perioperative Considerations

As the proportion of older patients with IBD is increasing, there is an increase in the complexity of comorbid conditions that require care in the perioperative setting. Increased perioperative morbidity of patients with IBD is seen in those who are malnourished, aged 60 to 80 years, on long-term immunosuppressive therapy, requiring emergent operation, and treated in low-volume centers. Type of surgical intervention is also related to perioperative morbidity, with increased risk in patients undergoing a total proctocolectomy with J pouch rather than ileostomy, a repair for fistulizing disease rather than strictureplasty or stoma revision, and an open rather than laparoscopic approach.

Before elective surgery, medical optimization should be performed to address possible nutritional deficiencies and associated coagulopathy, hypovolemia, and electrolyte or acid–base disturbance in order to reduce the associated morbidity. Because of the elevated risk for venous thromboembolic events in patients with IBD, perioperative pharmacologic prophylaxis is recommended. Perioperative medical management in patients with IBD varies depending on the type of IBD, the clinical circumstance of the patient, and the urgency of the surgery. The classes of medications used for patients with IBD include antidiarrheals, antiinflammatories, immunosuppressants, antibiotics, and other investigational drugs. Special consideration should be taken requiring the discontinuation and resumption of each type of immunosuppressive medication, as failure to hold or continue them may increase the risk of perioperative complications. Glucocorticoids should continue throughout the perioperative period with consideration for supplemental stress dosing before surgery.

Although no specific type of anesthetic is preferred for patients with IBD, consideration should be taken regarding the interaction of common IBD drugs with anesthetic medications. Cyclosporine increases minimum alveolar concentration of volatile anesthetics. Azathioprine may partially antagonize the effect of nondepolarizing neuromuscular blocking agents, and cyclosporine and infliximab may enhance their potency.

Perioperative Considerations

Patients with GERD are at greater risk for aspiration. As such, anesthetic planning and management aim to minimize the chance for pulmonary aspiration of gastric contents and its associated morbidity. Depending on the volume, acidity, and composition of the gastric contents, aspiration may lead to airway obstruction, chemical injury and inflammation, pneumonia, acute respiratory distress syndrome, and/or respiratory failure. Risk factors for aspiration pneumonitis include gastric fluid pH less than 2.5, volume of aspirate more than 0.4 mL/kg, aspirate containing particulate matter, and pregnancy greater than 18 weeks' gestation. Premedication with antacids or histamine2-receptor antagonists may help to reduce the extent of injury if aspiration occurs, and prokinetic agents may help to reduce the aspirate volume. Proton pump inhibitors (PPIs) should be continued leading up to surgery.

Rapid-sequence induction and intubation (RSII) is often the induction technique of choice in patients at risk of aspiration pneumonitis. The goal of RSII is to complete the sequence of events from awake with intact airway reflexes to endotracheal intubation with the cuff inflated within the shortest time interval allowable. It is during this interval that the complete loss of airway reflexes occur and pulmonary aspiration risk is the highest. If a difficult intubation is anticipated on preoperative airway evaluation, an awake intubation may be indicated over an RSII. With RSII, achieving adequate depth of anesthesia (with or without neuromuscular blockade) is essential to avoid coughing, straining, or active vomiting with airway manipulation. Positive-pressure ventilation is avoided between induction and intubation to decrease the risk of gastric insufflation. Thorough preoxygenation and apneic oxygenation are necessary to increase the time until hypoxemia develops with apnea. Positioning with the head of the bed elevated places the larynx above the LES and aids in reducing the risk of passive regurgitation and aspiration. Although the application of cricoid pressure during RSII is often used to reduce the incidence of aspiration of gastric contents, its use is controversial. Multiple studies of cricoid pressure during RSII provide inconclusive results regarding technique and efficacy, and some studies suggest potential harm with cricoid pressure. Patients at risk for aspiration on induction and intubation are also at risk on emergence and extubation. Precautions to minimize aspiration during emergence include decompressing the stomach with an orogastric tube, elevating the head of the bed, and ensuring intact airway reflexes before extubation.

Surgical management of GERD is reserved for patients unable to tolerate medical therapy, for those with persistent symptoms necessitating long-term therapy, or for those who develop complications despite optimal medical therapy. Of the various endoscopic and surgical interventions available, the most common antireflux operation is the Nissen fundoplication. The operation is most often performed laparoscopically and consists of reducing the herniated stomach, repairing the diaphragmatic defect, and performing a gastric wrap around the stomach and LES to prevent the regurgitation of gastric contents. Although the Nissen fundoplication is the most effective and durable antireflux procedure, it also has the greatest potential for postoperative dysphagia, difficulty with vomiting, and gas bloating.