PANCREAS

Physiology

Pancreatic islet cells produce insulin, glucagon, human pancreatic polypeptide, and somatostatin. Insulin, derived from proinsulin, consists of an alpha and beta chain connected by a C peptide. The basal secretion level is raised in a biphasic response to stimulation. The rapid phase may release stored preformed insulin in response to glucose, amino acids, glucagon, and some gastrointestinal hormones. With continuous glucose administration, both preformed and new insulin is released in the delayed phase. Release is stimulated by the vagal nerve and b-adrenergic receptors and inhibited by b-adrenergic blockers, sympathomimetic amines (e.g., epinephrine, norepinephrine), and somatostatin, which also inhibits glucagon. Stress triggers the release of glucagon, glucocorticoids, GH, and catecholamines, which are antagonists to insulin, resulting in glycogenolysis, gluconeogenesis, ketogenesis, lipolysis, and nitrogen wasting. Stress also affects wound healing, electrolyte and fluid balance, and susceptibility to infection.

Dysfunction

There are two types of diabetes mellitus with seemingly different causes, but they are both associated with similar complications. Type I (i.e., juvenile onset) usually appears in patients younger than 25 years who are insulin deficient, ketosis prone, and usually not obese. The cause is thought to be an autoimmune response to beta cells triggered by infection. The insulin levels of these patients are generally difficult to control. Type II (i.e., adult onset) has a more gradual onset. Patients are generally obese, over 40 years old, ketosis resistant, and more stable and easier to control. It is thought to be the more inheritable form of diabetes. Obesity reduces the number of insulin receptors on insulin-responsive cells, altering glucose tolerance. With fasting and weight loss, the number of receptors increases to normal levels.

In addition to random fasting blood sugar levels, screening for diabetes is accomplished with the 2-hour postprandial glucose tolerance test, using a fixed amount of glucose after a 3-day period of carbohydrate loading. Serum glucose determinations are 10% to 15% higher than whole blood determinations; therefore, it is important to know which test is performed.

Surgical diabetic patients under stress or anesthesia are thought to undergo hormone imbalances, causing glucose intolerance. They are also at greater perioperative risk due to disease-impaired cardiovascular, renal, and neurologic systems. Before surgery, careful assessment of these systems is important, as is assessing glucose control and modifying the patient’s regimen if necessary.

Symptoms of angina, which must be sought, may be absent. Autonomic dysfunction presents with orthostatic hypotension, nocturnal diarrhea, early satiety, or difficulties with erections and ejaculations in the male patient. Nocturia, dry mouth, blurred vision, weakness, palpitations, hunger, and nightmares are symptoms related to poor glucose control. The effects associated with hypoglycemia may be masked by neuropathies or b-adrenergic blockers (e.g., propranolol).

A thorough examination of the heart and peripheral pulses is necessary with an examination for bruits and orthostasis. An electrocardiogram should be obtained preoperatively and postoperatively to detect a silent myocardial infarction. Laboratory data should include preoperative fasting glucose, electrolytes, blood urea nitrogen, creatinine, chest radiograph, and clean-catch urinalysis. Long-term control can be assessed with the hemoglobin A1C determination, which is elevated with high glucose levels due to incorporation of glucose into the hemoglobin molecule. Levels remain elevated for 4 to 6 weeks, the lifespan of an erythrocyte. Before surgery, the patient in ketoacidosis should be stabilized as much as possible or surgery should be delayed to establish better glucose control or clear up bacteria in the urine. Diabetics are at increased risks for diseases with a predilection for immunocompromised patients, such as invasive fungal and bacterial infections. In addition, they suffer from poor wound healing, as may be evident after surgical procedures.