[Anesthesia and diabetes mellitus]

There are two types of diabetes mellitus. Type I, insulin-dependent diabetes (IDDM), which becomes manifest before the age of 40, is the result of an absolute deficiency of insulin. Type II, the non-insulin-dependent diabetes (NIDDM), develops in the elderly and is caused by a relative insulin deficiency. Patients with type-I diabetes are prone to the development of ketoacidosis, while type II causes hyperglycaemic, hyperosmolar, nonketotic coma. Apart from these acute metabolic alterations, the long-term complications of diabetes are of concern to the anaesthesiologist. Hypertension, coronary artery disease, renal insufficiency and autonomic neuropathy are common and can result in myocardial ischaemia, cardiovascular instability and gastroparesis, with an increased risk of aspiration. Limited movement of the atlanto-occipital joint can cause difficult intubation. To avoid perioperative metabolic catastrophy, blood glucose concentration should be kept between 6.7 and 10 mmol.l-1 (120-180 mg.dl-1). Hypoglycaemia can result in neurological damage, whereas hyperglycaemia causes impaired wound healing and susceptibility to infections and worsens ischaemic damage to the myocardium and brain. Perioperative diabetes management depends on the severity of the surgical procedure and the type of diabetes. All type-I diabetics, whatever operation being performed, need insulin. The intravenous route is recommended as it allows better adjustment. After determination of the fasting blood glucose level, insulin is given at a dosage of 0.5-1 U.h-1 (at gluc < 11.1 mmol.l-1), 1.5-2 U.h-1 (at gluc 11.1-16.7 mmol.l-1) or 3 U.h-1 (at gluc > 16.7 mmol.l-1). In addition, 5-10 g glucose.h-1 is given. In type-II diabetes the oral antidiabetic drug is withheld. During minor surgery the blood glucose concentration is monitored frequently, and if necessary insulin (with gluc > 13.9 mmol.l-1) or glucose is given. In most cases of major surgery insulin therapy will be necessary. Administration should follow the guidelines listed for type-I diabetes. Whether the intravenous or the subcutaneous route is used for insulin, repeated glucose determinations are mandatory. If ketoacidosis develops the volume depletion is treated with normal saline. For hyperglycaemia and acidosis insulin (3-6 U.h-1) with 10-20 mmol.h-1 potassium phosphate is given. Bicarbonate is only indicated when the serum pH is lower than 7.1. It must be borne in mind that perioperative management of diabetes does not end with postanaesthesia care.