Special issues: glucose and the brain.

PURPOSE: This review focuses on the neurologic issues concerning the treatment of hypo- or hyperglycemia in the critically ill patient. DATA SOURCES: Articles written in English and identified through the Bibliographic Retrieved Service Colleague database. STUDY SELECTION: Articles chosen on the basis of their relevance to the issue of blood glucose management and its neurologic effects in critically ill patients. DATA EXTRACTION: Data from articles were analyzed to obtain a scientific foundation and rationale for treating abnormal blood glucose levels. DATA SYNTHESIS: Moderate hypoglycemia may evoke a significant stress response, behavioral changes, and alterations in cerebral blood flow and metabolism. It is unclear what effect prolonged or repeated episodes of moderate hypoglycemia may have on patient outcome. However, alterations in cerebral vascular physiology must be addressed when caring for patients with cerebral ischemia or intracranial compliance problems. Depending on its severity, hypoglycemia has varying influences on neurologic damage after ischemia. Hyperglycemia may impair neuronal recovery following cerebral ischemia. However, the detrimental effects of hyperglycemia vary depending on the types of brain ischemia sustained (focal or global). Evidence suggests that hyperglycemia during global and incomplete global ischemia events is detrimental to neurologic outcome. However, the relationship between hyperglycemia and outcome after focal ischemia is controversial. CONCLUSION: Because both hypo- and hyperglycemia may produce neurologic changes, aggressive management of abnormal glucose values is warranted.