Diabetes is a condition of elevated blood glucose caused by a number of factors and affects approximately 8% of the population.¹ There are 2 types: type 1, which refers to an absolute deficiency, and type 2, which refers to a relative deficiency of insulin. Diabetes is the leading cause of kidney failure and blindness in adults, as well as a major cause of heart disease and stroke. Diabetic patients are challenging to anesthesiologists and often present with comorbidities and complications, including obesity, neurologic disease, kidney disease, cardiovascular disease, and metabolic abnormalities. Perioperative assessment should focus on prevention of complications that occur in higher frequency in diabetic patients. These include postoperative infections and cardiovascular events such as stroke, myocardial ischemia, and heart failure.^{2,3 and 4} The cornerstone of prevention is perioperative glucose control.^{5,6 and 7}

In the United States, the Centers for Disease Control and Prevention and the American Diabetes Association estimate that 25% of diabetic patients are unaware that they have the disease. Preoperative glucose testing confirms this finding. Diabetic complications such as retinopathy, nephropathy, neuropathy, or cardiovascular disease may be present before a diagnosis of diabetes is made. A fasting blood glucose obtained in preoperative clinic or on the day of surgery provides an important opportunity to screen patients with suspected or known diabetes.⁸

Perhaps a better measure of glycemic history in diabetic patients is the hemoglobin A1C (presented as the percent of glycosylated hemoglobin). Over the life span of a red blood cell (up to 3 months), glucose will attach to hemoglobin and provide an estimate of average blood glucose levels over several months. In general, ideal hemoglobin A1C levels should be below 8%. More aggressive glucose control to a percentage less than 8% may lead to frequent episodes of hypoglycemia. Criteria used to distinguish normal categories of hyperglycemia are presented in Table 19–1.⁹

Perioperatively, other conditions can increase blood glucose levels including surgical stress, infections, corticosteroid use, total parenteral nutrition, kidney or liver disease, or pregnancy. Perioperative hyperglycemia is associated with increased length of stay, complications, and mortality in surgical and hospitalized patients, even in those without a history of diabetes.^10,11

Cardiovascular Problems

Cardiovascular risk is substantial in diabetic patients and is of significant importance to the perioperative physician. There is mounting evidence that glucose control is important to prevent adverse outcomes in hospitalized patients and in critical care settings, although how tightly blood glucose levels should be maintained is still a matter of debate.¹² In general, there is a direct relationship between fasting blood glucose concentration and the risk of having a cardiovascular event, such as sudden cardiac death, acute myocardial infarction, or stroke. Fasting plasma glucose levels greater than 110 mg/dL are associated with substantial cardiovascular risk.¹³ Among patients who have had a myocardial infarction, diabetes is an independent risk factor for increased morbidity and ­mortality.¹⁴ Other studies demonstrate that those with the highest glucose values at the time of an acute myocardial infarction also have the highest mortality rates.¹⁵

Neuropathy

Peripheral neuropathy can lead to heel ulceration, poor wound healing, and increased rates of perioperative infection. Preoperatively, clinicians should evaluate for pressure ulcers and protect lower extremities from pressure intraoperatively. Perioperative glycemic control will decrease these complications.

Autonomic neuropathy may be detected by the presence of orthostatic hypotension, resting tachycardia, and loss of heart rate variability. This may signal intraoperative difficulties. Gastroparesis may increase the risk of aspiration. Consider a prokinetic agent if appropriate (metoclopramide).

Nephropathy

Nephropathy or renal insufficiency may be present. Pretreat for contrast-induced nephropathy and decrease the use of nephrotoxic drugs such as aminoglycosides and nonsteroidal anti-inflammatory drugs. If contrast is being used, metformin should be discontinued prior to surgery and for 48 hours after the use of contrast.¹⁶ Consider checking a creatinine prior to restarting metformin.

Retinopathy

Retinopathy is often a late complication of diabetes. Optimize blood pressure and glycemic control perioperatively to decrease the risk of further damage. Maintain proper eye protection.

Airway Problems

Airway concerns are always a special consideration in diabetics, as “stiff joint syndrome” may be present affecting temporomandibular and cervical spine mobility, particularly in type 1 diabetics. An inability to approximate the palmar surfaces while pressing the hands together (a positive “prayer sign”) is associated with cervical spine immobility and a potential difficult intubation.

In the preoperative clinic, diabetic patients should be screened for cardiovascular risk factors, including a family history of heart disease or stroke and a history of smoking, as well as hypertension and hyperlipidemia. Standard electrocardiogram screening may not be useful in predicting occult heart disease.¹⁷ There should be a low threshold for screening for cardiac disease with more definitive testing such as an exercise stress test, resting echocardiogram, dipyridamole thallium scintigraphy, or a dobutamine stress echocardiogram. Consulting the American College of Cardiology and American Heart Association guidelines to characterize perioperative cardiac risk is recommended.¹⁸ In addition, consideration should be given to perioperative β blockers,¹⁹ lipid-lowering therapy, and antiplatelet agents as appropriate.