Glycemic control in critically ill surgical patients: risks and benefits

Abstract

Glucose metabolism in humans is exceedingly complex. At baseline, it is controlled by elaborate signaling mechanisms, and these mechanisms are profoundly altered by the surge of catecholamines and cytokines associated with acute postsurgical and post-traumatic stress. These alterations in signaling mechanisms result in hyperglycemia; although this hyperglycemia can start very rapidly after the traumatic or surgical insult, it can persist during the entire period of critical illness and even afterward. Numerous randomized clinical trials have been conducted to determine if hyperglycemia is associated with increased mortality in surgical patients. These studies have had different conclusions that are difficult to interpret in light of differences in study methodology, but there is certainly ample evidence that inadequately controlled hyperglycemia causes harm due to increased infectious morbidity, and possibly increased mortality. As we have become more proficient in controlling hyperglycemia, the concept of insulin resistance, determined as the amount of insulin required to achieve hyperglycemia, has come to the fore. Insulin resistance is not a static concept, and may change before significant events such as infection. Patients with elevated and persistent insulin resistance have been demonstrated to suffer increased infectious morbidity and mortality, albeit in nonrandomized studies. Along with insulin resistance, the concept of glycemic variability, the amount of variation in serum blood glucose over time, has also become relevant; increased variability has been associated with hypoglycemia and mortality. Both of these risks can result from aggressive insulin therapy, and glycemic control protocols must be appropriately planned and implemented to avoid hypoglycemia and excessive externally induced variability. Computer-assisted protocols may be of significant benefit in optimizing glycemic control. The most recent recommendations available are to keep serum blood glucose levels below 150 mg/dL and to avoid hypoglycemia.