In both diabetic and non-diabetic populations, hyperglycemia in the perioperative period is an independent marker of poor surgical outcomes (delayed wound healing, increased rate of infection, prolonged hospital stay, higher postoperative mortality). Hyperglycemia (greater than 140 mg/dl) is a frequent occurrence with a prevalence of 20 to 40% in the general surgery and 80 to 90% in the cardiac surgery population.

The stress of surgery, anesthesia, and illness increases secretion of counter-regulatory hormones (cortisol, glucagon, growth hormone, catecholamines), which in turn causes decreased insulin secretion, increased insulin resistance, decreased peripheral utilization of glucose, increased lipolysis and proteolysis. As a consequence, gluconeogenesis and glycogenolysis increase, which subsequently results in worsening hyperglycemia termed as stress hyperglycemia. Uncontrolled hyperglycemia instigates osmotic diuresis (causing fluid and electrolyte imbalance), ketogenesis and increased generation of pro-inflammatory cytokines with resultant mitochondrial injury, endothelial dysfunction and immune deregulation. Hence, achieving good glucose control during the perioperative period is associated with beneficial post-surgical outcomes.

The severity of hyperglycemia also depends on the type of anesthesia and surgery, with increased glucose elevations seen in cases of general anesthesia or thoracic/abdominal surgeries as opposed to epidural/local anesthesia or peripheral/laparoscopic surgeries, respectively.

In critically ill patients, multiple randomized controlled trials (RCTs) like NICE-SUGAR  study have compared conventional (less than 180 mg/dl) versus intensive (81 to 108 mg/dl) glucose control with results remarkable for a higher incidence of severe hypoglycemia and increased mortality in patients subjected to intensive glucose control.  However, due to the lack of RCTs in non-critically ill patients, most of the data is extrapolated from studies conducted on the critically ill. 

Multiple societies have put forth guidelines for optimal glucose management in the perioperative period. For patients undergoing ambulatory surgery, the Society for Ambulatory Anesthesia recommends intraoperative blood glucose (BG) levels less than 180 mg/dl. In critically ill patients, the Society of Critical Care Medicine recommends initiating insulin therapy for BG higher than 150 mg/dl, the American College of Physicians advises against the use of intensive insulin therapy with a BG target of 140 to 200 mg/dl. The Society of Thoracic Surgeons advocates intra-operative blood glucose less than 180 mg/dl and lower than 110 mg/dl in the pre-meal or fasting state. In the non-critically ill hospitalized patients, Endocrine Society recommends pre-meal glucose targets less than 140 mg/dl and random glucose levels lower than 180 mg/dl while the Joint British Diabetes Societies propose blood glucose levels of 108 to 180 mg/dl in most patients with an acceptable range between 72 to 216 mg/dl. The Endocrine Society also outlines higher target glucose of under 200 mg/dl is acceptable in non-critically ill hospitalized patients with a terminal illness and with limited life expectancy or at high risk for hypoglycemia. American Diabetes Association (ADA) recommends a target glucose range of 80 to 180 mg/dl in the perioperative period and 140 to 180 mg/dl for the majority of critically ill and non-critically ill patients.

Although the optimal glycemic target remains unclear, a reasonable goal in the majority of perioperative patients is to maintain blood glucose in the range of 140 to 180 mg/dl with the intent of avoiding both hypoglycemia (under 70 mg/dl) and severe hyperglycemia (over 180 mg/dl).