Chapter 26 Nutritional and Gastrointestinal Disease
Obesity
1. What is a desired body mass index (BMI)? What BMI defines morbid obesity? What BMI defines “super obese”? What BMI defines “super-super obese”?
2. What organ systems can be affected by obesity?
3. What is the metabolic syndrome and what is its significance?
4. How is the diagnosis of metabolic syndrome made?
5. What are the contributory factors to morbid obesity?
6. What are four main considerations when anesthetizing a morbidly obese patient?
7. What were some of the complications with the older weight loss operations such as jejunoileal bypass?
8. What are three significant and beneficial effects of modern gastric bypass?
Malnutrition
9. What is the definition of malnutrition? Why might malnutrition be present in surgical patients?
10. Is enteral or intravenous nutrition preferable for most patients who require supplemental feedings? Why?
11. What is refeeding syndrome? What is the pathophysiology of refeeding syndrome? What are the signs of refeeding syndrome?
12. What are four perioperative considerations for the malnourished patient? What are the considerations for the critically ill enterally fed patient?
Inflammatory bowel disease
13. What is the presumed pathophysiology of inflammatory bowel disease (IBD)? What are some of the factors that are associated with IBD?
14. What are the major differences between ulcerative colitis and Crohn’s disease?
15. What is the preferred anesthetic technique for a patient with IBD?
16. How do drugs used in the treatment of IBD interact with anesthetic drugs?
Gastroesophageal reflux disease
17. What is the definition of gastroesophageal reflux disease (GERD)?
18. What is the pathophysiology of GERD?
19. What are the signs and symptoms of GERD?
20. What is the risk of pulmonary aspiration on induction of anesthesia?
21. Does the rapid sequence induction (RSI) with cricoid pressure (Sellick maneuver) prevent pulmonary aspiration? Why or why not?
22. What is the mechanism of development of subcutaneous emphysema, pneumomediastinum, or pneumoperitoneum after a Nissen fundoplication?
Diabetes mellitus
23. What is the definition of diabetes? What types of complications are associated with long-term poorly controlled diabetes?
24. What is autonomic neuropathy? What perioperative risks are associated with autonomic neuropathy?
25. Why are the historical classifications of insulin-dependent and noninsulin-dependent diabetes inferior to type 1 and type 2 diabetes?
26. What is the major treatment goal in both types of diabetes?
27. What are the four categories of oral hypoglycemic agents?
28. What is hemoglobin A1C (glycosylated hemoglobin)? What is its significance in the management of diabetes?
29. What is the recommended management of preoperative diabetes medicines?
30. What blood glucose levels should be maintained perioperatively? What are some potential complications of severe perioperative hyperglycemia?
31. At what level of preoperative glucose should an operation be postponed?
Hyperthyroidism (thyrotoxicosis) and thyroid storm
32. What is the definition of hyperthyroidism?
33. What are some common causes of hyperthyroidism?
35. What are the signs and symptoms of hyperthyroidism?
36. What is the difference between hyperthyroidism and thyroid storm?
37. What are the signs and symptoms of thyroid storm?
38. What conditions may cause a thyrotoxic patient to develop thyroid storm?
39. What medications are used in the management of thyroid storm?
40. What is the Wolfe-Chaikoff effect?
41. What are the anesthetic considerations for a patient with hyperthyroidism?
Hypothyroidism
43. What is the definition of hypothyroidism?
44. What are the causes of hypothyroidism?
45. What are the signs and symptoms of hypothyroidism?
46. What is the difference between primary and secondary hypothyroidism?
47. What are the airway considerations (both preoperative and postoperative) in a patient undergoing thyroid surgery?
48. Is it necessary to delay surgery in hypothyroid patients and achieve a euthyroid state before operating?
49. What is intraoperative laryngeal nerve monitoring and what is its impact on the anesthetic plan?
Pheochromocytoma and paraganglioma
50. What is the embryologic cell of origin of the pheochromocytoma and what is the difference between it and a paraganglioma?
51. What hormones are produced by these tumors and what are their common signs and symptoms?
52. How common are pheochromocytomas and paragangliomas tumors?
53. How should perioperative hypertension and tachycardia associated with pheochromocytoma and paraganglioma be managed?
Multiple endocrine neoplasia and neuroendocrine tumors
54. What is the MEN-1 (multiple endocrine neoplasia-1) syndrome? What is its inheritance pattern?
55. What is the MEN-2 (multiple endocrine neoplasia-2) syndrome? What is its inheritance pattern?
56. What specific tumors are commonly found in patients with MEN-1?
57. What are the subtypes of MEN-2?
58. What are the anesthetic implications of MEN-1 and MEN-2?
59. What are carcinoid and neuroendocrine tumors and what hormones do they produce?
60. Why are midgut carcinoid tumors often asymptomatic? When do they become symptomatic?
61. What is carcinoid syndrome? What is the usual treatment for a carcinoid crisis?
62. What are the perioperative implications of carcinoid and neuroendocrine tumors?
Adrenal insufficiency and steroid replacement
63. What are the principal hormones of the adrenal cortex?
64. What is the mechanism by which stress stimulates the release of cortisol?
65. What is the function of cortisol in the body?
66. What is Addison’s syndrome? What are the symptoms?
67. What is the difference between primary and secondary (or tertiary) adrenocortical insufficiency?
68. What are the frequent causes of primary adrenocortical insufficiency?
69. What are the frequent causes of secondary or tertiary adrenocortical insufficiency?
70. What is addisonian crisis (acute adrenal failure)? What are its symptoms and causes?
71. What are the common causes of pituitary apoplexy? What are the signs, symptoms, and treatment of pituitary apoplexy?
72. What is the effect of etomidate on adrenal function?
73. What is the general approach to perioperative steroid replacement in the patient who has steroid-induced adrenal insufficiency?
74. What is critical illness-related corticosteroid insufficiency (CIRCI)?
Cushing’s syndrome
75. What is Cushing’s syndrome? What are the signs and symptoms of Cushing’s syndrome and how is it diagnosed?
76. What is the difference between primary and secondary (or tertiary) Cushing’s syndrome?
77. What is the difference between Cushing’s syndrome and Cushing’s disease?
78. What are the common causes of secondary Cushing’s syndrome?
79. What are the anesthetic considerations in a patient with Cushing’s syndrome?
Answers*
Obesity
1. A desirable BMI is generally considered to be 18 to 25. Morbid obesity is a BMI of 40 or more. Super obese is a BMI of 50 or more and super-super obese is a BMI of 60 or more. (463)
2. Morbid obesity can affect virtually any organ system of the body. Commonly affected systems are cardiovascular (hypertension, stroke, right heart failure), endocrine (reproductive hormonal imbalances, impaired fertility, diabetes), and gastrointestinal (hiatal hernias and gastroesophageal reflux from increased intraabdominal pressure). Involvement of the pulmonary system can include low residual volumes, rapid desaturation, restrictive lung disease, and obstructive sleep apnea. Skeletal problems may include back pain and osteoarthritis, particularly of the knees. Some malignancies (colon and breast) are associated with obesity as are some psychological disorders such as depression. (463)
3. Metabolic syndrome is a term that applies to the combined complications of obesity. There are six components of the metabolic syndrome: abdominal obesity, atherogenic dyslipidemia, elevated blood pressure, insulin resistance (glucose intolerance), a proinflammatory state, and a prothrombotic state. Diagnosis and treatment is important because it alone predicts approximately 25% of all new-onset cardiovascular disease. (463-464)
4. Diagnosis of metabolic syndrome is made by the presence of three out of five of the following: abdominal obesity, elevated triglycerides, low HDL, elevated blood pressure, elevated fasting glucose. (463)
5. The causes of obesity are multifactorial. They include genetic, environmental, metabolic, and psychosocial factors. While caloric consumption is important, the urge to eat (or overeat) can be modulated by hormones. Fasting releases several orexigenic (appetite-stimulating) hormones and can cause inflammation. (464)
6. Four major considerations in the anesthetic management of the morbidly obese patient include the risk of aspiration of gastric contents, securing the airway, the logistics of caring for a large patient, and emergence technique.
7. Unlike current operations that restrict the gastrointestinal tract, the jejunoileal bypass developed in 1954, was a malabsorptive operation developed for the treatment of hyperlipidemia, atherosclerosis, and obesity. It was abandoned by the 1980s because it causes unacceptable complications, including uveitis, kidney dysfunction, intestinal bacterial overgrowth, and liver damage. (464)
8. Gastric bypass patients generally have improvements in quality of life and comorbidities. There is improvement in hypertension, diabetes, and/or obstructive sleep apnea. Several orexigenic (appetite stimulating) hormones are diminished by bariatric surgery. Ghrelin secretion by the gastric fundus and proximal small intestine is increased after nonsurgical weight loss but is unchanged or decreased after bariatric surgical procedures. Other intestinal hormones that regulate appetite and glucose metabolism also are affected favorably by surgery. These include glucagon-like peptide-1, glucose-dependent insulinotropic peptide, and peptide YY. (464)
Malnutrition
9. Malnutrition may be present when there is weight loss of 10% to 20% over a short time, when weight is less than 90% of ideal body weight, or when BMI is less than 18.5. Healthy patients may quickly become malnourished after an accident or acute illness and critically ill patients develop malnutrition if they are not fed. Malnutrition can occur quickly when caloric requirements exceed intake due to decreased intake, impaired absorption, or an increased metabolic rate. (464-465)
10. Enteral nutrition is the preferred method of feeding because it is believed to maintain the absorptive gastrointestinal villi and reduce transmucosal bacterial transfer into the blood stream. It results in improved patient outcomes, less infection, less ventilator days, and less intensive care unit days. Long-term feeding usually requires a gastrostomy or jejunostomy. Postpyloric (jejunal) placement is frequently preferred as a means to limit regurgitation and the risk of aspiration, although the risk of aspiration with gastric feeding tubes is low. In patients who have pancreatitis, jejunal placement is favored in order to avoid stimulation of pancreatic enzyme secretion. In contrast, intravenous feeding (total parental nutrition or TPN) is preferred for patients who do not have a functioning gastrointestinal tract. TPN is considered acceptable for short-term feedings. Risks of long-term TPN include central venous catheter sepsis, thrombosis, hyperglycemia, iatrogenic hypoglycemia, and fatty liver. (465)
11. Refeeding syndrome is caused by rapid, acute nutritional replacement of a malnourished patient. It is characterized by increased ATP production, a significant fall in plasma phosphate, respiratory failure, and cardiac failure. Metabolic rate is increased with a significant rise in carbon dioxide (CO2) production and respiratory acidosis. The syndrome may be prevented by slowly increasing the nutritional intake toward caloric goals. (465)
12. Perioperative considerations for the malnourished patient include muscle weakness, immunocompromise, preoperative fasting, and perioperative glucose monitoring. Muscle weakness may lead to respiratory failure and immunocompromise may predispose patients to infection. Preoperative fasting is often an issue in enterally fed critically ill patients, particularly burn and trauma patients. One must weigh the risk of aspiration on induction against the benefit of keeping nutrition at maintenance levels. In the absence of definitive studies, expert opinion generally supports efforts to continue nutrition as much as possible. However, preliminary data supports the safety of a short fast (45 minutes) when the feeding tube is located beyond the ligament of Treitz. Perioperative glucose monitoring is necessary in patients receiving TPN, because insulin is typically included. Blood glucose should be monitored for procedures more than 2 hours in duration. (465)
Inflammatory bowel disease
13. IBD is believed to result from an aberrant response by the bowel mucosal immune system to normal luminal flora. The precise trigger for the activation of the immune system in IBD is unclear and likely multifactorial. Patients typically present with complaints of abdominal pain, fever, and diarrhea. There may be a genetic basis since there is an increased risk in close family members. Caucasians are more susceptible to IBD and Jewish people are at greater risk for Crohn’s disease. Environmental factors may include smoking, appendectomy, antibiotics, oral contraceptives, and NSAIDs. (465)
14. There are two categories of inflammatory bowel disease: ulcerative colitis and Crohn’s disease. Ulcerative colitis is restricted to the large intestine and manifests itself as inflammation and loss of colonic mucosa. Crohn’s disease can affect any part of the digestive tract and may cause transmural inflammation leading to abscesses or granulomatous disease. Although they are distinct entities, distinction between the two may be difficult to make when Crohn’s manifests itself by only affecting the colon. (465)
15. Specific anesthetic agents are neither preferred nor contraindicated for patients with IBD. Patients taking steroids should continue prior to surgery and may require supplementation because of iatrogenic adrenal insufficiency. (465)
16. Certain medications prescribed to treat IBD may have anesthetic implications. Interactions between anesthetic and antineoplastic agents are not fully documented in the literature. Cyclosporine is reported to increase the minimum alveolar concentration of volatile agents and to be additive with barbiturates or fentanyl in an animal model. Phosphodiesterase effects of azathioprine may partially antagonize nondepolarizing neuromuscular blockade, although this is controversial. Cyclosporine, infliximab, and aminoglycosides potentiate the nondepolarizing neuromuscular blocking agents. (465-466)
Gastroesophageal reflux disease
17. GERD is the retrograde movement of gastric contents through the lower esophageal sphincter (LES) into the esophagus. If gastric contents also move past the upper esophageal sphincter into the pharynx, pulmonary aspiration of gastric acid and particulate matter may result. Pulmonary aspiration of gastric contents is a serious, potentially life-threatening complication. (466)
18. Reflux occurs when the lower esophageal sphincter is incompetent or when LES pressure is less than intraabdominal (or intragastric) pressure. This may result from esophageal dysmotility or from a hiatal hernia, where the LES may be displaced cephalad into the thoracic cavity. The LES loses the diaphragmatic contribution to its function and the diaphragm can also obstruct the esophagus. Associated conditions include pregnancy, obesity, obstructive sleep apnea, gastric hypersecretion, gastric outlet obstruction, gastric neuropathy, and increased intraabdominal pressure. (466)
19. GERD is an extremely common syndrome in which 20% of people have heartburn (the most reliable symptom) at least once per week. Four to ten percent have heartburn daily. Other problems include noncardiac chest pain, dysphagia, pharyngitis, cough, asthma, hoarseness, laryngitis, sinusitis, and dental erosions. (466)
20. The risk of pulmonary aspiration on induction of anesthesia is not well-established. Significant GERD occurs in at least 30% to 50% of pregnant women; however, the incidence of aspiration is low. The mechanism is primarily a progesterone-mediated relaxation of LES tone, with possible contributions from elevated intraabdominal pressure, delayed gastric emptying, and decreased bowel transit. (466)
21. The customary approach to induction is RSI with cricoid pressure (CP, also called Sellick’s maneuver) to obstruct the potential flow of gastric contents into the pharynx and trachea. However, the putative benefits of the RSI and CP remain controversial.
Cricoid pressure can be ineffective if not properly applied. Some undesired side effects of CP include increased risk of regurgitation and failed intubation. Based on studies of the radiographic anatomy, improperly performed CP may not align the cricoid and esophagus properly with the solid cervical spine underneath. If the cricoid and esophagus are displaced laterally, they may overlie muscle and the upper esophagus may not be occluded. The significance of this failure of alignment is by no means a settled issue. The exact opposite view, that lateral displacement does not impair barrier function, has also been articulated. Complications are more likely in the elderly, children, pregnant women, patients with cervical injury, patients with difficult airways, and patients where there is difficulty palpating the cricoid cartilage. (466, Table 29-1)
22. Nissen fundoplication surgery may be associated with subcutaneous air in the neck and chest, but is benign and self-limited because carbon dioxide (CO2) gas is rapidly resorbed by the body. Likewise, pneumoperitoneum and pneumomediastinum are common, occurring in up to 86% of patients due to dissection of the phrenoesophageal ligament. Pneumothorax, in contrast, is not a normal consequence of laparoscopic surgery. (466-467)
Diabetes mellitus
23. Diabetes mellitus is elevated blood glucose levels due to a relative lack of endogenous insulin. It is the most common endocrine disease and affects 15 to 20 million Americans (7% to 8% of the American population). It is associated with complications in most organ systems resulting largely from microangiopathy and macroangiopathy. Risk of complications of diabetes increases with increasing hemoglobin A1C levels. Large and small vessel coronary artery disease is common and was originally advanced as an indication for perioperative β-blockade in the original papers on the subject. Diabetic renal failure in young and middle-aged adults is the leading cause of renal failure requiring hemodialysis. Retinopathy occurs in 80% to 90% of those who require insulin for at least 20 years. Autonomic neuropathy occurs in 20% to 40% of patients with long-standing diabetes, particularly those with peripheral sensory neuropathy, renal failure, or systemic hypertension. Cardiac autonomic neuropathy may mask angina pectoris and obscure the presence of coronary artery disease. Gastroparesis, which may cause delayed gastric emptying, is a sign of autonomic neuropathy affecting the vagus nerves. (467)
24. Autonomic neuropathy is a dysfunction of the autonomic nervous system, which occurs as a result of damage to small nerve fibers. This results in loss of vagally controlled heart rate, a decrease in peripheral sympathetic nervous system tone resulting in orthostatic hypotension, decreases in peripheral blood flow, and diminished sweating. These patients are at an increased risk of delayed gastric emptying, perioperative hemodynamic instability, cardiac arrhythmias, silent myocardial infarction, impaired respiration, and cardiopulmonary arrest. In addition, these patients have a blunted response to atropine, making the early treatment of bradycardia essential. (467)
25. The historical classification of diabetes was made in terms of the presence or absence of insulin requirement. This was unsatisfactory because nearly all diabetics develop a need for insulin at some point. The current classification is Type 1 (T1DM) and Type 2 (T2DM) diabetes. T1DM is typically characterized by the absence of any insulin production from the pancreas. T2DM involves a relative lack of insulin plus resistance to endogenous insulin. (467)
26. Blood glucose control is the major treatment goal in both types of diabetes. T1DM always requires insulin to prevent hyperglycemia and ketoacidosis. It is commonly heralded at an early age by a dramatic episode of ketoacidosis. Type 2 diabetics may require insulin, but often only require oral hypoglycemic agents, weight loss, or dietary management. The onset of T2DM usually is more insidious and constitutes the majority of diabetics. They are often overweight, so dietary control and weight loss is important, but the cornerstone of management of both types is pharmacologic. (467)
27. There are four categories of oral hypoglycemic agents based on their function. Some increase pancreatic insulin production (glyburide and repaglinide). Some reduce glucose load by decreasing hepatic production (metformin). Some reduce intestinal absorption of glucose (acarbose) and others increase glucose uptake by fat and muscle (rosiglitazone). (467)
28. Glycosylated hemoglobin (hemoglobin A1C), or glycohemoglobin, is formed during hyperglycemia. Glucose can permanently combine with hemoglobin in erythrocytes and form hemoglobin A1C. Since the erythrocyte life span is 120 days, hemoglobin A1C levels give an indication of how well the diabetes is being controlled over time. Normal hemoglobin A1C levels are less than 6%. (467)
29. A well-controlled diabetic may not require special treatment before and during surgery. It is common in those on insulin treatment to reduce the morning dose by 30% to 50% to prevent hypoglycemia due to fasting. Sulfonylurea drugs may be continued until the evening before surgery, but these drugs may also produce hypoglycemia in the absence of morning caloric intake and are generally recommended to be held the morning of surgery.
30. The optimal level of glucose control in the perioperative and critical care setting remains controversial. Attempts to maintain glucose levels below 108 mg/dL in critically ill patients may result in excess cardiovascular mortality compared with those patients in whom the level was controlled in the 140 to 180 mg/dL range. There are several formulas for sliding scale insulin administration, maintenance infusions of 5% dextrose, and periodic blood glucose monitoring for the perioperative management of insulin-dependent diabetics. Some potential complications of severe perioperative hyperglycemia include ketoacidosis, dehydration, hyperosmolar nonketotic coma, secondary effects on neurologic outcome after cerebral ischemia, and the risk of surgical wound infection. (468)
31. There is no established standard to apply to the question of how high a preoperative glucose level is too high for surgery. (468)
Hyperthyroidism (thyrotoxicosis) and thyroid storm
32. Hyperthyroidism is the condition caused by elevated circulating levels of the unbound thyroid hormones triiodothyronine (T3), and tetraiodothyronine (thyroxine, or T4). (468)
33. Some common causes of hyperthyroidism include Graves’ disease, struma ovarii (thyroid tissue in an ovarian teratoma), a human chorionic gonadotropin hormone (hCG)-secreting hydatidiform mole, pregnancy (hCG has weak thyroid stimulating activity), and administration of iodinated contrast dye to a susceptible patient. Amiodarone can lead to both hypothyroidism and hyperthyroidism. (468)
34. Graves’ disease is the most common cause of hyperthyroidism. It is an autoimmune condition where thyrotropin receptor antibodies continuously mimic the effect of thyroid-stimulating hormone (TSH). (468)
35. Mild to moderate hyperthyroidism is manifested by cardiac, neurologic, constitutional, and gastrointestinal signs and symptoms. Thyroid hormone increases cardiac sensitivity to catecholamines, causing hypertension, tachyarrhythmias, high-output congestive heart failure, and angina, even in the absence of coronary plaques. Patients may exhibit tremor, hyperreflexia, irritability, and periodic paralysis (hypokalemia and proximal muscle weakness). Constitutional signs may include fever and heat intolerance. Gastrointestinal symptoms may include nausea, vomiting, diarrhea, hepatic dysfunction, and jaundice. Hyperthyroidism is confirmed by demonstrating elevated thyroid hormone levels in blood. (468)
36. The difference between hyperthyroidism (thyrotoxicosis) and thyroid storm is a matter of degree. Thyroid storm is the most severe form of the disorder. It is a life-threatening, emergent clinical syndrome with a mortality rate of approximately 30% despite treatment. (468)
37. Worsening signs and symptoms of thyrotoxicosis characterize thyroid storm. There may be severe cardiac dysfunction, hyperglycemia, hypercalcemia, hyperbilirubinemia, hyperthermia, hypovolemia, altered mental status, seizures, or coma. (468)
38. Thyroid storm may be triggered in a thyrotoxic patient by any of several stresses, including infection, stroke, or trauma, especially to the thyroid gland. It may also occur with surgery, diabetic ketoacidosis, or incorrect antithyroid drug discontinuation. The administration of certain drugs including pseudoephedrine, aspirin, excess iodine intake, contrast dye, or amiodarone may also trigger thyroid storm. (468)
39. The initial medical treatment of thyroid storm is to reduce thyroid hormone synthesis. Thionamides, such as propylthiouracil (PTU) and methimazole (MMI), inhibit thyroid peroxidase (TPO), which catalyzes the incorporation of iodide into thyroglobulin to produce T3 and T4. At least an hour after giving the thionamide, large doses of stable iodide are given. β-blocking drugs are used to reduce adrenergic symptoms. Although propranolol is the traditional choice, other β-blockers (atenolol, metoprolol, or esmolol) have been used. Propranolol additionally inhibits peripheral conversion of T4 to the more potent hormone T3. Corticosteroids should also be administered since these patients usually have relative adrenal insufficiency. Finally, plasmapheresis may be a useful adjunct to reduce circulating thyroid hormone levels by removing T3 and T4 from the blood stream. (468)
40. The Wolfe-Chaikoff effect is a paradoxical effect whereby large doses of iodide suppress gene transcription of thyroid peroxidase rather than incorporate additional iodide into thyroglobulin. The large doses of iodine thus reduce the gland’s capacity to produce and release hormone. This benefit is temporary, lasting about a week. (468)
41. There is limited evidence-based literature for operative anesthetic management of patients with hyperthyroidism, and no comparative data. It is usually recommended to favor agents that do not cause increased heart rate or sympathetic activation; however, this advice has never been subjected to testing. It is generally advisable to undertake only that which cannot be delayed until thyroid hormone secretion has been controlled by medical management or by radioiodine ablation. (468)
42. Although thyroid storm associated with surgery can occur intraoperatively, it is most likely to present 6 to 18 hours after the surgical procedure. Perioperative thyroid storm treatment is aimed toward decreasing the amount of circulating thyroid hormone and toward decreasing the increase in sympathetic nervous system stimulation. An esmolol infusion can be started and titrated to the desired hemodynamic and cardiovascular effects. Dexamethasone may be administered to block the release of thyroid hormone as well as from the thyroid gland and the peripheral conversion of T4 to T3. Propylthiouracil may be administered to block the uptake of iodine from the thyroid gland, after which iodine may be administered to inhibit the release of thyroid hormone from the thyroid gland. Treatment should also be supportive, with the monitoring and treatment of abnormalities in the patient’s intravascular fluid status, electrolytes, glucose, and body temperature. Thyroid storm may be difficult to distinguish from other hypermetabolic states, including malignant hyperthermia, pheochromocytoma, neuroleptic malignant syndrome, and sepsis. Dantrolene can be beneficial and should be considered if there is suspicion of malignant hyperthermia. (469)
Hypothyroidism
43. Hypothyroidism is the condition caused by decreased circulating levels of the unbound thyroid hormones triiodothyronine (T3) and tetraiodothyronine (thyroxine, or T4). (469)
44. Hypothyroidism is either congenital (cretinism) or acquired. Acquired hypothyroidism may be due to an absence of dietary iodine (so-called “endemic goiter”) or inflammation. Hashimoto’s thyroiditis is a chronic autoimmune disease characterized by progressive destruction of the thyroid gland. Hypothyroidism may also be iatrogenic (from the medical or surgical treatment of hyperthyroidism). At least half of patients who receive radioactive iodine treatment for hyperthyroidism are hypothyroid 10 years later. Hypothyroidism may also occur after hypothalamic or pituitary disease or surgery. (469)
45. The onset of hypothyroidism is usually insidious and the symptoms often nonspecific. There may be easy fatigability, lethargy, cold intolerance, periorbital edema, weakness, weight gain, dry skin, or brittle hair. There may be myxedema in severe cases with reduced cardiac output, attenuated deep tendon reflexes, and nonpitting pretibial edema. Untreated, there may be electrolyte disturbances, hypoventilation, hypothermia, or coma. (469)
46. Primary hypothyroidism is present if there are low T3 and T4 levels but an elevated TSH. In secondary hypothyroidism, all three thyroid-related hormones are reduced. Subclinical primary hypothyroidism is present in about 5% of the American population. It has a prevalence of more than 13% in otherwise healthy elderly patients, especially women.
47. Patients undergoing thyroid surgery may have physical or functional obstruction of the airway. An enlarged thyroid gland may deviate or compress the trachea, causing difficulty breathing when sleeping supine or during the induction of general anesthesia. Postoperative obstruction may occur if the patient develops a neck hematoma or tracheomalacia. Tracheomalacia can occur from chronic compression of the tracheal rings by a goiter. Deep extubation is sometimes used to minimize coughing, minimize straining, and reduce the theoretical likelihood of elevations of venous and arterial pressures in the neck. Functional obstruction may occur due to surgical trauma to the recurrent laryngeal nerves. Unilateral laryngeal nerve injury produces voice impairment, but is not a threat to airway function. Bilateral recurrent laryngeal nerve injury compromises the function of the posterior cricoarytenoid muscles, the muscles responsible for separating the cords during breathing. This can lead to life-threatening inspiratory airway obstruction, which may only be relieved by intubation or tracheostomy. Paralyzed vocal cords do not abduct during the respiratory cycle and may appear apposed in the midline when seen during direct laryngoscopy. Accidental removal of the parathyroid glands can occur in patients undergoing a total thyroidectomy. Clinically this can manifest as laryngospasm or inspiratory stridor secondary to the sensitivity of the laryngeal muscles to hypocalcemia. Signs of hypocalcemia after this complication do not usually manifest until 24 to 72 hours after the procedure. (469)
48. Asymptomatic mild to moderate hypothyroidism does not place a patient at an increased risk of perioperative morbidity. There is no unusual sensitivity to inhaled anesthetics, sedatives, or narcotics. Symptomatic or severe hypothyroidism should necessitate surgical delay for thyroid hormone replacement until resolution of neurologic and cardiovascular abnormalities. (469)
49. Some surgeons request the use of a laryngeal nerve monitoring (NIMS endotracheal tube) as a safety measure during thyroid surgery. These are specialized endotracheal tubes with electrodes positioned in the immediate vicinity of the vocal cords. They send an EMG signal to a receiver whenever the vocal cords contract, so if the surgeon stimulates a laryngeal nerve an audible signal provides a warning. With the NIMS tube, no muscle relaxant should be used. (469)
Pheochromocytoma and paraganglioma
50. A pheochromocytoma is a catecholamine-secreting adrenal medullary tumor. The cell of embryologic origin is the neural crest cell. Paraganglioma is the name given to these tumors when they occur outside the adrenal gland. (469-470)
51. These tumors typically produce the adrenal medullary hormones dopamine, norepinephrine, and/or epinephrine. The most common symptoms are headache, palpitations, sweating, and tremulousness. The most common sign is hypertension. Severe hypertension during anesthesia and surgical manipulations is a well-recognized manifestation of pheochromocytoma; 8% to 10% of tumors are asymptomatic. The diagnosis is made by analyzing a 24-hour urine collection of catecholamine or catecholamine metabolite levels. (469-470)
52. The prevalence of pheochromocytomas and paragangliomas in the general population has been reported to be as high as 1 in 2000. (470)
53. For the perioperative management of pheochromocytomas and paragangliomas, the nonspecific α-blocking agent phenoxybenzamine might not be the agent of choice. Since α2-agonists generally produce bradycardia, sedation, and lower blood pressure, phenoxybenzamine (with α2-blocking properties) could increase blood pressure and increase pulse. Phenoxybenzamine, however, remains the agent most often recommended by authors of review articles and case series and is the agent with which there is the greatest clinical experience worldwide. It has a long pharmacologic half-life but is very expensive because it has no other clinical application. It is useful for the chronic treatment of patients with unresectable catecholamine secreting tumors.
Multiple endocrine neoplasia and neuroendocrine tumors
54. Multiple endocrine neoplasia-1, described by Wermer in 1954, is characterized by a triad of tumors of the pancreas, parathyroid, and pituitary. Its inheritance is autosomal dominant. (470)
55. MEN-2 is characterized by autosomal dominant inherited medullary thyroid carcinoma and other associated tumors, including pheochromocytomas and parathyroid tumors. (471)
56. In MEN-1, pancreas tumors usually secrete gastrin (50%), insulin, glucagon, vasoactive intestinal polypeptide, or pancreatic polypeptide. Pituitary tumors are usually secreting adenomas (prolactin 60%, growth hormone 25%) although some are nonfunctioning adenomas. Parathyroid adenomas are present in 95%, are the most common tumor in the syndrome, and usually present as hypercalcemia. All four parathyroid glands usually must be removed surgically because all are involved by the disease. Other tumors may include adrenal cortical adenomas, carcinoids, neuroendocrine tumors, lipomas, angiofibromas, and collagenomas. (470)
57. There are two subtypes of MEN-2: MEN-2a, described by Sipple in 1961, and MEN-2b, described by Williams et al in 1966. MEN-2a includes pheochromocytoma, medullary thyroid carcinoma, and parathyroid adenoma. MEN-2b includes mucosal neuromas, pheochromocytoma, and medullary thyroid carcinoma. (471)
58. There are no specific anesthetic implications of MEN-1. Anesthetic implications of MEN-2 relate to its components and associated conditions. MEN-2 may be associated with pheochromocytomas or with Von Hippel-Lindau syndrome, which in turn may include cerebellar tumors. (470-471)
59. Carcinoids and neuroendocrine tumors are dispersed cells of neural crest embryologic origin. These tumors produce serotonin or other peptide hormones. When these tumors arise in the midgut, they are called carcinoid tumors; but when they arise elsewhere in the body, the current terminology is for them to be called neuroendocrine tumors. (471)
60. Midgut carcinoids are usually asymptomatic until they cause bowel obstruction or appendicitis because their venous drainage is via the portal vein to the liver, which detoxifies the excess serotonin they produce. (471)
61. Carcinoid syndrome is a constellation of systemic symptoms of serotonin excess. These include diarrhea, flushing, palpitations, and bronchoconstriction. It results from tumors outside the hepatic portal drainage field or when there is extensive metastatic liver disease. Octreotide may help ameliorate these symptoms. (471)
62. Perioperative considerations of carcinoid and neuroendocrine tumors result from the direct hemodynamic effects of serotonin. These are not problematic in the context of perioperative anesthetic care and an escalation of hemodynamic monitoring is seldom required as a consequence of the endocrine activity of the tumor. There should be a high index of suspicion in the face of right-sided valvular heart disease or right heart failure. Echocardiography should be considered as a diagnostic tool. Right heart failure is due to the sclerosing effect of serotonin on the tricuspid and pulmonic valves. It may be the cause of death in 50% of patients with carcinoid syndrome. (471)
Adrenal insufficiency and steroid replacement
63. The principal hormones of the adrenal cortex are cortisol and aldosterone. (471)
64. Cortisol production in the adrenal cortex is stimulated by adrenocorticotropic hormone (ACTH) released from the pituitary gland. ACTH is secreted in response to hypothalamic corticotropin releasing hormone (CRH). Stress stimulates the hypothalamus to release CRH, which increases blood cortisol levels. Cortisol exerts negative feedback influence on the production of both CRH and ACTH. (471)
65. Cortisol is responsible for the conversion of norepinephrine to epinephrine in the adrenal medulla. It also maintains homeostasis of the cardiovascular system, especially in the presence of stress. It maintains vascular tone and endothelial integrity, preserving intravascular volume by reducing vascular permeability. It also potentiates the vasoconstrictor effects of catecholamines. When cortisol levels are deficient, systemic vascular resistance and myocardial contractility are decreased. Cortisol also plays an important role in gluconeogenesis, sodium retention, potassium excretion, and antiinflammatory effects. (471)
66. Addison’s syndrome is chronic insufficient cortisol production and secretion, with or without aldosterone insufficiency. The symptoms of adrenal insufficiency are nonspecific. They include fatigue, malaise, lethargy, weight loss, anorexia, arthralgia, myalgia, nausea, vomiting, abdominal pain, diarrhea, and fever. (471)
67. Primary adrenocortical insufficiency is the nonfunctioning of the adrenal glands. Patients may also have hyponatremia and hyperkalemia along with aldosterone deficiency. Secondary adrenocortical insufficiency is the failure of the pituitary to stimulate the adrenals. Tertiary insufficiency is the failure of the hypothalamus to stimulate the pituitary, and thus the adrenals. (471)
68. The etiology of primary adrenocortical insufficiency is usually immunologic (an autoantibody), malignant, or infectious. Malignant causes are generally metastatic cancer, commonly from lung or breast. Infectious causes include tuberculosis. (471)
69. Secondary or tertiary adrenocortical insufficiency usually stems from exogenously administered steroids. Aldosterone production, under the stimulus of the renin-angiotensin system, is unimpaired. (471)
70. Acute adrenal failure (addisonian crisis) is circulatory shock caused by cortisol deficiency. It generally occurs in patients with primary adrenal insufficiency along with a superimposed acute stress, such as trauma, surgery, or infection. Symptoms include hyponatremia, hyperkalemia, hypovolemic shock, and myocardial and vascular unresponsiveness to catecholamines. (471)
71. Pituitary apoplexy generally occurs after acute pituitary hemorrhage, swelling, or infarction of a large pituitary adenoma. It may also occur following cardiopulmonary bypass or postpartum hypotension (Sheehan’s syndrome). It is also associated with diabetes, hypertension, sickle cell anemia, and acute shock.
72. Etomidate is associated with significant but transient (<24 hours) suppression of adrenal cortical function, even after a single dose of the drug. This is especially clinically significant in setting of CIRCI. (472)
73. Steroid-induced adrenal suppression is highly variable and its duration is unpredictable, from days to perhaps years. Since the consequences of a short course of steroids are minimal, anticipatory treatment is generally safe. The dosage for replacement therapy should be adequate but not excessive. The scientific foundation is based on surgical research in primates where administering supplements 10 times the normal cortisol production rates was not superior to simply replacing the normal daily production of cortisol. The daily cortisol production rate is between 20 and 30 mg/day. In surgical patients, the recommended approach is to begin at the time of surgery with a dose between 1 and 5 times the daily production, no more than 100 to 150 mg of cortisol equivalent per day with a tapered replacement over 48 to 72 hours. The potential risks of the administration of supplemental doses of corticosteroid to patients in the perioperative period are few. Of concern are impaired wound healing and an increased rate of infections. (472)
74. The term CIRCI recently has been applied to clinical situations where there is prior steroid treatment and the adrenal response to critical illness and other stresses is inadequate. The patient may not otherwise meet traditional criteria for adrenocortical dysfunction. One hundred to three hundred milligrams per day of IV hydrocortisone eliminates a preexisting need for vasopressors. Signs and symptoms include unexplained vasopressor-dependent refractory hypotension, a discrepancy between the anticipated severity of the patient’s disease and the present state of the patient, or high fever without apparent cause or not responding to antibiotics. There may also be hypoglycemia, hyponatremia, hyperkalemia, neutropenia, or eosinophilia. (472)
Cushing’s syndrome
75. Cushing’s syndrome is the presence of elevated cortisol levels in the blood. Patients with Cushing’s syndrome have a typical physical appearance characterized by rounding of the face, truncal obesity, thin extremities, an upper thoracic fat pad (“buffalo hump”), purple abdominal striae, and thinning of the skin. Physiologic effects of chronic elevated corticosteroid levels include weight gain, hypertension, hypercoagulability, muscle weakness, glucose intolerance, gonadal dysfunction, and osteoporosis. Diagnosis is confirmed by an elevated 24-hour urinary free cortisol. (472-473)
76. Primary Cushings is hypercortisolism independent of pituitary adrenocorticotropic hormone (ACTH) secretion, usually due to a hyperfunctioning adrenal gland or an adrenal adenoma. Secondary and tertiary disease occur from elevated circulating levels of ACTH or an ACTH-like substance. (472)
77. Cushings disease usually refers to one specific form of secondary Cushing’s, that of adrenal cortical hyperfunction due to excess production of ACTH by a pituitary adenoma. This accounts for 60% to 70% of patients with Cushing’s syndrome. (472)
78. After Cushing’s disease, the remainder of secondary Cushing’s syndrome patients have ectopic sources of ACTH. These may include primary cancers of the adrenal or metastatic cancers such as lung (usually small-cell), thyroid, prostate, pancreas, or intrathoracic neuroendocrine tumors. Secondary Cushing’s may also occur with exogenous administration of cortisol-like medications or synthetic ACTH. (472-473)
79. Cushing’s syndrome patients may be more susceptible to the effects of muscle relaxants than normal, leading to prolonged muscle relaxation and weakness. Because of this, Cushing’s patients may be subject to unanticipated postoperative respiratory failure, even after laparoscopic surgery. (473)
