The Rationale for Permissive Hyperglycemia in Critically Ill Patients with Diabetes

Abstract

Avoiding extreme deviations from pre-morbid physiology is amajor aimin the management of several conditions in critically ill patients. For example, vasopressors are commonly used to avoid relative hypotension in patients with chronic hypertension. Similarly, lower blood oxygen levels and higher blood carbon dioxide levels are targeted in patients with severe chronic obstructive pulmonary disease (COPD). Finally, slow correction of serum sodium is recommended in patients with chronic hyponatremia. An important exception to this logical consideration of baseline physiology and biochemistry has been blood glucose management in the intensive care unit (ICU). The most recent, and largest, randomized controlled trial on glycemic control in ICU patients, the Normoglycemia in Intensive Care Evaluation and Surviving Using Glucose Algorithm Regulation (NICE SUGAR) trial, demonstrated improved survival by targeting a blood glucose concentration of 6–10 mmol/l compared to 4–6 mmol/l [1]. Thus, since the publication of NICE SUGAR, the more ‘liberal’ target of 6–10 mmol/l has been recommended in international guidelines in critically ill patients and in patients undergoing cardiac surgery [2, 3]. However, several issues remain unresolved: whether uniform glycemic control should be used in all patients in the ICU; whether the recommended target is ‘liberal’ enough for patients with diabetes mellitus; and whether current practice is safe? In response to these issues, in this chapter, we introduce the novel concepts of relative hypoglycemia and permissive hyperglycemia in critically ill patients. In addition, we discuss experimental and clinical evidence that provides the rationale for applying a more liberal glycemic target in critically ill patients with diabetes in order to avoid relative hypoglycemia.