Date Published: February 13, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Daniel Agustín Godoy, Mario Di Napoli, Alberto Biestro, Rainer Lenhardt.
Many neurosurgery patients may have unrecognized diabetes or may develop stress-related hyperglycemia in the perioperative period. Diabetes patients have a higher perioperative risk of complications and have longer hospital stays than individuals without diabetes. Maintenance of euglycemia using intensive insulin therapy (IIT) continues to be investigated as a therapeutic tool to decrease morbidity and mortality associated with derangements in glucose metabolism due to surgery. Suboptimal perioperative glucose control may contribute to increased morbidity, mortality, and aggravate concomitant illnesses. The challenge is to minimize the effects of metabolic derangements on surgical outcomes, reduce blood glucose excursions, and prevent hypoglycemia. Differences in cerebral versus systemic glucose metabolism, time course of cerebral response to injury, and heterogeneity of pathophysiology in the neurosurgical patient populations are important to consider in evaluating the risks and benefits of IIT. While extremes of glucose levels are to be avoided, there are little data to support an optimal blood glucose level or recommend a specific use of IIT for euglycemia maintenance in the perioperative management of neurosurgical patients. Individualized treatment should be based on the local level of blood glucose control, outpatient treatment regimen, presence of complications, nature of the surgical procedure, and type of anesthesia administered.
Several observational and interventional studies have indicated that hyperglycemia (hyperG) in diabetic and nondiabetic neurosurgical patients is associated with adverse outcomes, such as an increased prevalence of complications, prolonged hospital stay, and higher mortality rates [1–5]. In addition there are deleterious effects of glucose deficit on brain metabolism [6, 7]. Individuals with previously unknown hyperG are at greater risk than those with preexisting diabetes mellitus (DM) . Available evidence shows that hyperG has negative consequences on the whole organism, including the brain [9–12]. Undiagnosed DM and hospital-induced hyperG increase postoperative complications, hospital costs, and length of stay [13–15]. hyperG is closely linked to prognosis in different brain injury scenarios . Nevertheless, no consensus exists as to whether hyperG is directly responsible for poor outcomes or if it is just an epiphenomenon of brain damage [10–12, 16]. It has been hypothesized, therefore, that strict blood glucose control could have a favorable impact on patient outcome . Consequently, increasing interest has evolved for tight blood glucose control using intensive insulin therapy (IIT) in neurocritically ill patients. Tight blood glucose control has been defined as glucose controlled within a range of 80 to 110 mg/dL (4.40 to 6.10 mmol/L). However, more recent data suggest possible deleterious effects of IIT on brain tissue. To date, solid clinical evidence to justify IIT in neurocritically ill patients does not exist [4, 16].
Recently a systematic review was published from a meta-analysis of 21 trials in heterogenic populations of critically ill patients, including stroke and head trauma . On the basis of this systematic review, the American College of Physicians recommended not using IIT under any circumstances in hospitalized patients . Actually, tight blood glucose control does not have any solid evidence for its implementation in the perioperative neurosurgical period or in victims of any cerebral injury from any cause [12, 13, 33].
There are no guidelines or recommendations establishing the method of choice and optimal monitoring frequency. The American Diabetes Association  suggests “frequent” monitoring, while the “Surviving Sepsis Campaign” suggests monitoring every 1-2 hours .
No specific trial has addressed the question of what the best management of hypoG is, while experimental data suggest new strategies to reduce brain damage due to severe hypoG . Nowadays, IIT is the most prevalent cause of the development of hypoG. Available evidence suggests that hypoG must be avoided by all means and must be treated urgently, because it is closely linked to worse short- and long-term outcomes [6–8, 42]. We recommend implementing alerts when blood glucose values are near 90 mg/dL (5.0 mmol/L) in neurocritically ill patients because microdialysis monitoring showed that even normal blood glucose levels can also induce cellular derangement in brain-injured patients [59, 68].
The optimal range of blood glucose levels in neurosurgical and neurocritically ill patients has not been determined and remains controversial. No consensus exists on blood glucose level goals for the perioperative period; however, several organizations have established general targets for neurocritically ill and neurosurgery patients [12, 16]. The question of optimal blood glucose goals cannot be answered with certainty, especially in neurocritically ill patients [12, 13, 16, 30, 33]. The brain is very vulnerable to extreme blood glucose level variations. It was demonstrated that an energy crisis may even occur with blood glucose levels within normal range [59, 68]. Therefore, it would be essential to know what the safe lower limit is. However, neither PET scanners nor microdialysis are available in every ICU. The American Diabetes Association and the American Association of Clinical Endocrinologists , based on the available evidence, set an upper limit at 180 mg/dL (10 mmol/L), at which insulin therapy should be started. This would also propose to maintain blood glucose levels between 140 and 180 mg/dL (7.8–10.0 mmol/L)  in critically ill patients and in the perioperative period. The available clinical data do not support tight glucose control with IIT in this critically ill subpopulation [12, 16]. Two meta-analyses of all patient types treated with IIT drew similar conclusions [81, 82].