Chronic uncontrolled blood glucose levels can lead to effects in virtually every organ system leading to increased morbidity and mortality in diabetic patients (Fig. 34.1). Preoperative evaluation of a diabetic patient should focus on the following factors.

A thorough history and physical examination (including functional status), laboratory testing, chest radiograph (cardiomegaly), and an electrocardiogram (silent myocardial infarction) are essential in evaluation of diabetic patients. Noninvasive and invasive cardiac testing may be necessary in high-risk patients. Blood sugar control in the previous 3–4 weeks can be assessed by measuring hemoglobin A_1C level (normal 4–6 %). Medications taken by patients should be inquired. In addition, patients may be taking either insulin or oral hypoglycemic agents. Patients with DM may have restricted movements at the temporomandibular (TMJ) and atlanto-occipital joints, thereby potentially making laryngoscopy difficult. The presence of obesity may further aid to problems in airway management.

Patients should be instructed to continue their antihyperglycemic regimen until the evening prior to their surgery, and perhaps skip the AM dose or receive half their morning insulin dose on the day of surgery (see chapter on preoperative evaluation), to prevent hypoglycemia (insulin time chart, Table 34.2). Patients on insulin pump (baseline insulin infusion of short-acting insulin) may be continued on their basal regimen. It is important to remember that patients on metformin may be more prone to developing lactic acidosis. Therefore, metformin may be stopped 24 h before surgery and restarted postoperatively. Blood glucose level (finger stick) should be checked prior to taking a diabetic patient to the operating room. Also, surgery in DM patients should be scheduled as early in the morning, as possible.

Autonomic neuropathy occurs in 20–40 % of patients with diabetes mellitus. Patients lack compensatory mechanisms to deal with hemodynamic fluctuations and hypoxia and are prone to sudden cardiac death, arrhythmias, and myocardial infarction. Signs and symptoms of autonomic imbalance include lack of pulse rate variability with respiration, resting tachycardia, orthostatic hypotension, lack of sweating, gastroparesis, impotence, and bladder dysfunction. Orthostatic hypotension may be demonstrated by a positive tilt test (decrease in blood pressure approximately 30 mmHg when moving from a supine to an upright position). Bradycardia may be unresponsive to atropine or ephedrine and may require administration of epinephrine.

High blood glucose levels can lead to a life-threatening condition called diabetic ketoacidosis. This usually occurs in type I diabetics, but can also occur in type II diabetics. Due to the lack of insulin, there is profound hyperglycemia with blood glucose levels up to 500 mg/dl. There is an increase in anaerobic metabolism leading to an accumulation of ketone bodies (acetoacetate, β-hydroxybutyrate). Infection is the commonest precipitating factor in causing diabetic ketoacidosis.

This syndrome usually occurs in elderly patients with type II DM. This clinical condition is characterized by:

Hypoglycemia is the most feared complication in patients with DM. DM patients may not tolerate blood glucose levels lower than 50 mg/dl, as they have chronically elevated blood glucose levels. Hypoglycemia leads to catecholamine secretion causing sweating, tachycardia, and hypertension. Central nervous symptoms may include dizziness, seizures, and coma. Hypoglycemia may be difficult to recognize in anesthetized patients, those taking beta blockers, or in patients with severe autonomic neuropathy. Renal failure prolongs the duration of action of insulin and hypoglycemic agents, making these patients prone to developing hypoglycemia. Treatment includes a high degree of suspicion and prompt administration of 50 ml of 50 % dextrose intravenously.

Although the lowest blood glucose level prior to surgery in DM patients is under debate, the general consensus is to proceed with surgery with a blood glucose level between 100 and 200 mg/dl. Patients with a blood glucose level greater than 180 mg/dl may be given regular (short-acting) insulin, keeping in mind that 1 unit of regular insulin (subcutaneously/intravenously) will decrease the blood glucose level by about 25–30 mg/dl.

Blood glucose levels should be measured intraoperatively every 45 min–1 h. Mild to moderately elevated blood glucose levels may be managed by small doses of regular insulin. Higher blood glucose levels (>400 mg/dl) are managed by running an insulin infusion, adequate hydration and potassium supplementation. This is because insulin increases the uptake of glucose and potassium into the cells, thereby, leading to hypoglycemia and hypokalemia in the plasma.

A blood glucose level should be measured in the recovery room before discharging the patient. Pain, nausea, and vomiting should be treated appropriately. It is important to remember that nausea and vomiting in a patient with DM may be a sign of severe hyperglycemia. Similarly, hypoglycemia should also be watched for and treated aggressively. Patients should be started on an insulin sliding scale or their oral antihyperglycemic regimen once oral intake is begun. Comorbid conditions, such as hypertension, coronary artery disease, and renal failure, should be taken into account in treating DM patients.