Impact of tight glycemic control on cerebral glucose metabolism after severe brain injury: A microdialysis study*:

Continuous glucose control in the ICU: report of a 2013 round table meeting

Achieving adequate glucose control in critically ill patients is a complex but important part of optimal patient management. Until relatively recently, intermittent measurements of blood glucose have been the only means of monitoring blood glucose levels. With growing interest in the possible beneficial effects of continuous over intermittent monitoring and the development of several continuous glucose monitoring (CGM) systems, a round table conference was convened to discuss and, where possible, reach consensus on the various aspects related to glucose monitoring and management using these systems. In this report, we discuss the advantages and limitations of the different types of devices available, the potential advantages of continuous over intermittent testing, the relative importance of trend and point accuracy, the standards necessary for reporting results in clinical trials and for recognition by official bodies, and the changes that may be needed in current glucose management protocols as a result of a move towards increased use of CGM. We close with a list of the research priorities in this field, which will be necessary if CGM is to become a routine part of daily practice in the management of critically ill patients.

Glucose and the injured brain-monitored in the neurointensive care unit

Brain has a continuous demand for energy that is met by oxidative metabolism of oxygen and glucose. This demand is compromised in the injured brain and if the inadequate supply persists it will lead to permanent tissue damage. Zero values of cerebral glucose have been associated with infarction and poor neurological outcome. Furthermore, hyperglycemia is common in patients with neurological insults and associated with poor outcome. Intensive insulin therapy (IIT) to control blood glucose has been suggested and used in neurointensive care with conflicting results. This review covers the studies reporting on monitoring of cerebral glucose with microdialysis in patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH) and ischemic stroke. Studies investigating IIT are also discussed. Available data suggest that low cerebral glucose in patients with TBI and SAH provides valuable information on development of secondary ischemia and has been correlated with worse outcome. There is also indication that the location of the catheter is important for correlation between plasma and brain glucose. In conclusion considering catheter location, monitoring of brain glucose in the neurointensive care not only provides information on imminent secondary ischemia it also reveals the effect of peripheral treatment on the injured brain.

The influence of parenteral glutamine supplementation on glucose homeostasis in critically ill polytrauma patients--A randomized-controlled clinical study

BACKGROUND & AIMS

Rapid onset of resistance to insulin is a prominent component of stress metabolism in multiple trauma patients. Recent studies have clarified the role of amino acids (especially glutamine) in glucose transportation and the benefits of parenteral alanyl-glutamine supplementation (0.3-0.6 g/kg/day) in glucose homeostasis. The aims of this study are to evaluate the incidence of hyperglycemic episodes and the need for exogenous insulin to maintain stable glucose levels in critically ill polytrauma patients supplemented with parenteral glutamine dipeptide (Dipeptiven(®)) versus standard nutritional support.

METHODS

This was an open-label randomized-controlled trial of 82 polytrauma patients aged 20-60 years old, randomly assigned into two equal groups independent of sex, age and Injury Severity Score. We excluded patients with diabetes mellitus, or renal or hepatic failure. One group received parenteral Dipeptiven(®) supplementation of 0.5 g/kg/day and the other received standard isocaloric isoproteinic nutritional support.

RESULTS

We found that 63% of patients in the glutamine-supplemented group had no hyperglycemic episodes; only 37% required exogenous insulin (mean daily requirement of 44 units/day). In the control group, 51% of patients required insulin (mean daily requirement 63 unit/day; p = 0.0407).

CONCLUSIONS

The effect of glutamine supplementation on glucose homeostasis is associated with a lower incidence of hyperglycemia among critically ill polytrauma patients, and leads to a lower mean daily dose of insulin. Controlled-trials.com Identifier: ISRCTN71592366 (http://www.controlled-trials.com/ISRCTN71592366/ISRCTN71592366).

Glycemic control after brain injury: boon and bane for the brain

Hyperglycemia is a common phenomenon in the early phase of brain injury (BI). The management of blood glucose levels after BI, however, is subject of a growing debate. The occurrence of elevated blood glucose concentrations is linked to increased mortality and worse neurologic outcomes indicating the necessity for therapeutic glucose-lowering. Intensive glucose-lowering therapy, on the other hand, inevitably results in an increased rate of hypoglycemic episodes with detrimental effects on the injured brain. In this review, we give an overview on the current knowledge about causes and pathophysiological consequences of dysglycemia in patients with BI and offer some suggestions for clinical glucose management.

Systemic glucose variability predicts cerebral metabolic distress and mortality after subarachnoid hemorrhage: a retrospective observational study

Introduction

Cerebral glucose metabolism and energy production are affected by serum glucose levels. Systemic glucose variability has been shown to be associated with poor outcome in critically ill patients. The objective of this study was to assess whether glucose variability is associated with cerebral metabolic distress and outcome after subarachnoid hemorrhage.

Methods

A total of 28 consecutive comatose patients with subarachnoid hemorrhage, who underwent cerebral microdialysis and intracranial pressure monitoring, were studied. Metabolic distress was defined as lactate/pyruvate ratio (LPR) >40. The relationship between daily glucose variability, the development of cerebral metabolic distress and hospital outcome was analyzed using a multivariable general linear model with a logistic link function for dichotomized outcomes.

Results

Daily serum glucose variability was expressed as the standard deviation (SD) of all serum glucose measurements. General linear models were used to relate this predictor variable to cerebral metabolic distress and mortality at hospital discharge. A total of 3,139 neuromonitoring hours and 181 days were analyzed. After adjustment for Glasgow Coma Scale (GCS) scores and brain glucose, SD was independently associated with higher risk of cerebral metabolic distress (adjusted odds ratio = 1.5 (1.1 to 2.1), P = 0.02). Increased variability was also independently associated with in hospital mortality after adjusting for age, Hunt Hess, daily GCS and symptomatic vasospasm (P = 0.03).

Conclusions

Increased systemic glucose variability is associated with cerebral metabolic distress and increased hospital mortality. Therapeutic approaches that reduce glucose variability may impact on brain metabolism and outcome after subarachnoid hemorrhage.

Incretins and the intensivist: what are they and what does an intensivist need to know about them?

Hyperglycaemia occurs frequently in the critically ill, even in those patients without a history of diabetes. The mechanisms underlying hyperglycaemia in this group are complex and incompletely defined. In health, the gastrointestinal tract is an important modulator of postprandial glycaemic excursions and both the rate of gastric emptying and the so-called incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, are pivotal determinants of postprandial glycaemia. Incretin-based therapies (that is, glucagon-like peptide- 1 agonists and dipeptidyl-peptidase-4 inhibitors) have recently been incorporated into standard algorithms for the management of hyperglycaemia in ambulant patients with type 2 diabetes and, inevitably, an increasing number of patients who were receiving these classes of drugs prior to their acute illness will present to ICUs. This paper summarises current knowledge of the incretin effect as well as the incretin-based therapies that are available for the management of type 2 diabetes, and provides suggestions for the potential relevance of these agents in the management of dysglycaemia in the critically ill, particularly to normalise elevated blood glucose levels.

Cerebral metabolic effects of exogenous lactate supplementation on the injured human brain

PURPOSE

Experimental evidence suggests that lactate is neuroprotective after acute brain injury; however, data in humans are lacking. We examined whether exogenous lactate supplementation improves cerebral energy metabolism in humans with traumatic brain injury (TBI).

METHODS

We prospectively studied 15 consecutive patients with severe TBI monitored with cerebral microdialysis (CMD), brain tissue PO2 (PbtO2), and intracranial pressure (ICP). Intervention consisted of a 3-h intravenous infusion of hypertonic sodium lactate (aiming to increase systemic lactate to ca. 5 mmol/L), administered in the early phase following TBI. We examined the effect of sodium lactate on neurochemistry (CMD lactate, pyruvate, glucose, and glutamate), PbtO2, and ICP.

RESULTS

Treatment was started on average 33 ± 16 h after TBI. A mixed-effects multilevel regression model revealed that sodium lactate therapy was associated with a significant increase in CMD concentrations of lactate [coefficient 0.47 mmol/L, 95% confidence interval (CI) 0.31-0.63 mmol/L], pyruvate [13.1 (8.78-17.4) μmol/L], and glucose [0.1 (0.04-0.16) mmol/L; all p < 0.01]. A concomitant reduction of CMD glutamate [-0.95 (-1.94 to 0.06) mmol/L, p = 0.06] and ICP [-0.86 (-1.47 to -0.24) mmHg, p < 0.01] was also observed.

CONCLUSIONS

Exogenous supplemental lactate can be utilized aerobically as a preferential energy substrate by the injured human brain, with sparing of cerebral glucose. Increased availability of cerebral extracellular pyruvate and glucose, coupled with a reduction of brain glutamate and ICP, suggests that hypertonic lactate therapy has beneficial cerebral metabolic and hemodynamic effects after TBI.

Glucose administration after traumatic brain injury improves cerebral metabolism and reduces secondary neuronal injury

Clinical studies have indicated an association between acute hyperglycemia and poor outcomes in patients with traumatic brain injury (TBI), although optimal blood glucose levels needed to maximize outcomes for these patients' remain under investigation. Previous results from experimental animal models suggest that post-TBI hyperglycemia may be harmful, neutral, or beneficial. The current studies determined the effects of single or multiple episodes of acute hyperglycemia on cerebral glucose metabolism and neuronal injury in a rodent model of unilateral controlled cortical impact (CCI) injury. In Experiment 1, a single episode of hyperglycemia (50% glucose at 2 g/kg, i.p.) initiated immediately after CCI was found to significantly attenuate a TBI-induced depression of glucose metabolism in cerebral cortex (4 of 6 regions) and subcortical regions (2 of 7) as well as to significantly reduce the number of dead/dying neurons in cortex and hippocampus at 24 h post-CCI. Experiment 2 examined effects of more prolonged and intermittent hyperglycemia induced by glucose administrations (2 g/kg, i.p.) at 0, 1, 3 and 6h post-CCI. The latter study also found significantly improved cerebral metabolism (in 3 of 6 cortical and 3 of 7 subcortical regions) and significant neuroprotection in cortex and hippocampus 1 day after CCI and glucose administration. These results indicate that acute episodes of post-TBI hyperglycemia can be beneficial and are consistent with other recent studies showing benefits of providing exogenous energy substrates during periods of increased cerebral metabolic demand.

Beyond intracranial pressure: optimization of cerebral blood flow, oxygen, and substrate delivery after traumatic brain injury

Monitoring and management of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) is a standard of care after traumatic brain injury (TBI). However, the pathophysiology of so-called secondary brain injury, i.e., the cascade of potentially deleterious events that occur in the early phase following initial cerebral insult—after TBI, is complex, involving a subtle interplay between cerebral blood flow (CBF), oxygen delivery and utilization, and supply of main cerebral energy substrates (glucose) to the injured brain. Regulation of this interplay depends on the type of injury and may vary individually and over time. In this setting, patient management can be a challenging task, where standard ICP/CPP monitoring may become insufficient to prevent secondary brain injury. Growing clinical evidence demonstrates that so-called multimodal brain monitoring, including brain tissue oxygen (PbtO₂), cerebral microdialysis and transcranial Doppler among others, might help to optimize CBF and the delivery of oxygen/energy substrate at the bedside, thereby improving the management of secondary brain injury. Looking beyond ICP and CPP, and applying a multimodal therapeutic approach for the optimization of CBF, oxygen delivery, and brain energy supply may eventually improve overall care of patients with head injury. This review summarizes some of the important pathophysiological determinants of secondary cerebral damage after TBI and discusses novel approaches to optimize CBF and provide adequate oxygen and energy supply to the injured brain using multimodal brain monitoring.

Physiological monitoring of the severe traumatic brain injury patient in the intensive care unit

Traumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. Despite encouraging animal research, pharmacological agents and neuroprotectants have disappointed in the clinical environment. Current TBI management therefore is directed towards identification, prevention, and treatment of secondary cerebral insults that are known to exacerbate outcome after injury. This strategy is based on a variety of monitoring techniques that include the neurological examination, imaging, laboratory analysis, and physiological monitoring of the brain and other organ systems used to guide therapeutic interventions. Recent clinical series suggest that TBI management informed by multimodality monitoring is associated with improved patient outcome, in part because care is provided in a patient-specific manner. In this review we discuss physiological monitoring of the brain after TBI and the emerging field of neurocritical care bioinformatics.

Multimodality monitoring in the neurointensive care unit: a special perspective for patients with stroke

Multimodality monitoring (MMM) is a recently developed method that aids in understanding real-time brain physiology. Early detection of physiological disturbances is possible with the help of MMM, which allows identification of underlying causes of deterioration and minimization of secondary brain injury (SBI). MMM is especially helpful in comatose patients with severe brain injury because neurological examinations are not sensitive enough to detect SBI. The variables frequently examined in MMM are hemodynamic parameters such as intracranial pressure, cerebral perfusion pressure, and mean arterial pressure; brainspecific oxygen tension; markers for brain metabolism including glucose, lactate, and pyruvate levels in brain tissue; and cerebral blood flow. Continuous electroencephalography can be performed, if needed. The majority of SBIs stem from brain tissue hypoxia, brain ischemia, and seizures, which lead to a disturbance in brain oxygen levels, cerebral blood flow, and electrical discharges, all of which are easily detected by MMM. In this review, we discuss the clinical importance of physiological variables as well as the practical applicability of MMM in patients with stroke.

Moderate and severe traumatic brain injury: pathophysiology and management

Traumatic brain injury (TBI) is a serious disorder that is all too common. TBI ranges in severity from mild concussion to a severe life-threatening state. Across this spectrum, rational therapeutic approaches exist. Early identification that TBI has occurred in a patient is paramount to optimal outcome. Proper clinical management should be instituted as soon as possible by appropriately trained medical providers. More seriously injured patients must be triaged to advanced care centers. It is only through this rational approach to TBI that patients may expect to achieve optimal clinical and functional outcome.

Stress hyperglycemia: an essential survival response!

Stress hyperglycemia is common in critically ill patients and appears to be a marker of disease severity. Furthermore, both the admission as well as the mean glucose level during the hospital stay is strongly associated with patient outcomes. Clinicians, researchers and policy makers have assumed this association to be causal with the widespread adoption of protocols and programs for tight in-hospital glycemic control. However, a critical appraisal of the literature has demonstrated that attempts at tight glycemic control in both ICU and non-ICU patients do not improve health care outcomes. We suggest that hyperglycemia and insulin resistance in the setting of acute illness is an evolutionarily preserved adaptive responsive that increases the host's chances of survival. Furthermore, attempts to interfere with this exceedingly complex multi-system adaptive response may be harmful. This paper reviews the pathophysiology of stress hyperglycemia and insulin resistance and the protective role of stress hyperglycemia during acute illness.

Early neurological deterioration after subarachnoid haemorrhage: risk factors and impact on outcome

BACKGROUND

Early neurological deterioration occurs frequently after subarachnoid haemorrhage (SAH). The impact on hospital course and outcome remains poorly defined.

METHODS

We identified risk factors for worsening on the Hunt-Hess grading scale within the first 24 h after admission in 609 consecutively admitted aneurysmal SAH patients. Admission risk factors and the impact of early worsening on outcome was evaluated using multivariable analysis adjusting for age, gender, admission clinical grade, admission year and procedure type. Outcome was evaluated at 12 months using the modified Rankin Scale (mRS).

RESULTS

211 patients worsened within the first 24 h of admission (35%). In a multivariate adjusted model, early worsening was associated with older age (OR 1.02, 95% CI 1.001 to 1.03; p=0.04), the presence of intracerebral haematoma on initial CT scan (OR 2.0, 95% CI 1.2 to 3.5; p=0.01) and higher SAH and intraventricular haemorrhage sum scores (OR 1.05, 95% CI 1.03 to 1.08 and 1.1, 95% CI 1.01 to 1.2; p<0.001 and 0.03, respectively). Early worsening was associated with more hospital complications and prolonged length of hospital stay and was an independent predictor of death (OR 12.1, 95% CI 5.7 to 26.1; p<0.001) and death or moderate to severe disability (mRS 4-6, OR 8.4, 95% CI 4.9 to 14.5; p=0.01) at 1 year.

CONCLUSIONS

Early worsening after SAH occurs in 35% of patients, is predicted by clot burden and is associated with mortality and poor functional outcome at 1 year.

Update on the management of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Outcome after SAH is mainly determined by the initial severity of the hemorrhage. Neuroimaging, in particular computed tomography, and aneurysm repair techniques, such as coiling and clipping, as well as neurocritical care management, have improved during the last few years. The management of a patient with SAH should have an interdisciplinary approach with case discussions between the neurointensivist, interventionalist and the neurosurgeon. The patient should be treated in a specialized neurointensive care unit of a center with sufficient SAH case volume. Poor-grade patients can be observed for complications and delayed cerebral ischemia through continuous monitoring techniques in addition to transcranial Doppler ultrasonography such as continuous electroencephalography, brain tissue oxygenation, cerebral metabolism, cerebral blood flow and serial vascular imaging. Neurocritical care should focus on neuromonitoring for delayed cerebral ischemia, management of hydrocephalus, seizures and intracranial hypertension, as well as of medical complications such as hyperglycemia, fever and anemia.

Trauma and aggressive homeostasis management

Homeostasis refers to the capacity of the human body to maintain a stable constant state by means of continuous dynamic equilibrium adjustments controlled by a medley of interconnected regulatory mechanisms. Patients who sustain tissue injury, such as trauma or surgery, undergo a well-understood reproducible metabolic and neuroendocrine stress response. This review discusses 3 issues that concern homeostasis in the acute care of trauma patients directly related to the stress response: hyperglycemia, lactic acidosis, and hypothermia. There is significant reason to question the "conventional wisdom" relating to current approaches to restoring homeostasis in critically ill and trauma patients.

High glucose variability increases cerebral infarction in patients with spontaneous subarachnoid hemorrhage

PURPOSE

High glucose variability is a significant marker for poor outcome in critically ill patients. We evaluated the impact of high glucose variability on cerebral infarction following spontaneous subarachnoid hemorrhage (SAH).

MATERIALS AND METHODS

Consecutive adult patients with spontaneous SAH and Hunt Hess score of at least 3 were retrospectively identified. Patients were excluded if their intensive care unit length of stay was less than 24 hours or if there were less than 5 glucose assessments. Glucose values from the first 7 days of intensive care unit admission were assessed. Variability was calculated as the average change in glucose over time for each patient. Classification and regression tree analysis was used to determine high vs low glucose variability, and the incidence of cerebral infarction was compared. Multivariate analysis was used to control for confounding variables.

RESULTS

There were 42 patients. Classification and regression tree analysis revealed a change in glucose greater than 9.52 mg/dL/h as the determinant for high variability. The incidence of cerebral infarction was 64% when glucose variability was high vs 20% when it was low (P=.006). Multivariate analysis identified high glucose variability (odds ratio [95% confidence interval]=11.4 [1.9-70.2], P=.008) and female sex (odds ratio [95% confidence interval]=5.2 [1-26.8], P=.047) as independent predictors for cerebral infarction.

CONCLUSION

Glucose variability is a significant predictor of cerebral infarction in patients with severe spontaneous SAH.

[Aneurysmal subarachnoid hemorrhage]

Acute subarachnoid hemorrhage (SAH) is a severe and acute life-threatening cerebrovascular disease. Approximately 80% of all acute non-traumatic SAHs are the result of a ruptured cerebrovascular aneurysm. Despite advances in diagnosis and treatment a high morbidity and mortality still exists. Apart from the primary cerebral damage there are also secondary complications, such as vasospasm, rebleeding, hydrocephalus, cerebral edema or hydrocephalus. For an appropriate therapy an understanding of the extensive pathophysiology, the options in diagnostics and therapy and the complications of the disease are essential. Anesthesiologists are decisively involved in the therapy of the primary and secondary damages and subsequently in the outcome as well. This article provides an overview of the perioperative and intensive care management of patients with SAH.

Guidelines for the use of an insulin infusion for the management of hyperglycemia in critically ill patients

OBJECTIVE

To evaluate the literature and identify important aspects of insulin therapy that facilitate safe and effective infusion therapy for a defined glycemic end point.

METHODS

Where available, the literature was evaluated using Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) methodology to assess the impact of insulin infusions on outcome for general intensive care unit patients and those in specific subsets of neurologic injury, traumatic injury, and cardiovascular surgery. Elements that contribute to safe and effective insulin infusion therapy were determined through literature review and expert opinion. The majority of the literature supporting the use of insulin infusion therapy for critically ill patients lacks adequate strength to support more than weak recommendations, termed suggestions, such that the difference between desirable and undesirable effect of a given intervention is not always clear.

RECOMMENDATIONS

The article is focused on a suggested glycemic control end point such that a blood glucose ≥ 150 mg/dL triggers interventions to maintain blood glucose below that level and absolutely <180 mg/dL. There is a slight reduction in mortality with this treatment end point for general intensive care unit patients and reductions in morbidity for perioperative patients, postoperative cardiac surgery patients, post-traumatic injury patients, and neurologic injury patients. We suggest that the insulin regimen and monitoring system be designed to avoid and detect hypoglycemia (blood glucose ≤ 70 mg/dL) and to minimize glycemic variability.Important processes of care for insulin therapy include use of a reliable insulin infusion protocol, frequent blood glucose monitoring, and avoidance of finger-stick glucose testing through the use of arterial or venous glucose samples. The essential components of an insulin infusion system include use of a validated insulin titration program, availability of appropriate staffing resources, accurate monitoring technology, and standardized approaches to infusion preparation, provision of consistent carbohydrate calories and nutritional support, and dextrose replacement for hypoglycemia prevention and treatment. Quality improvement of glycemic management programs should include analysis of hypoglycemia rates, run charts of glucose values <150 and 180 mg/dL. The literature is inadequate to support recommendations regarding glycemic control in pediatric patients.

CONCLUSIONS

While the benefits of tight glycemic control have not been definitive, there are patients who will receive insulin infusion therapy, and the suggestions in this article provide the structure for safe and effective use of this therapy.

Protecting the brain during neurosurgical procedures: strategies that can work

PURPOSE OF REVIEW

The quest for neuroprotection strategies during periods of neuronal vulnerability persists despite decades of basic and clinical research. This review will focus on the latest developments in the area of clinical brain protection with the major emphasis on strategies that can be beneficial during neurosurgical procedures.

RECENT FINDINGS

Brain protection in neurosurgical patients may be achieved by nonpharmacological and pharmacological strategies. Pharmacological neuroprotection including anaesthetic administration have not been recently shown to be successful. Alternatively, nonpharmacological strategies including maintenance of cerebral perfusion by adequate control of mean arterial pressure (≥80 mmHg), liberal normoglycaemia (7.8-10 mmol/l), adequate haemoglobin levels (preoperative ≥120 g/l and intraoperative ≥90 g/l) and induction of hypertension (20-40% of preoperative values) in certain neurosurgical situations can be beneficial as neuroprotectants during neurosurgery. Mild hypothermia (32-35°C) failed to achieve neuroprotective effects in several situations of brain injury.

SUMMARY

The findings of this review suggest that the anaesthesiologist is compelled to use nonpharmacological strategies sometimes based on empiric evidence to protect the brain during neurosurgical procedures. These strategies are simple, have high benefit/risk ratios and are inexpensive. Rigorous controlled clinical studies are needed to investigate the neuroprotective efficacy of these commonly used nonpharmacological methods.

Clinical review: neuromonitoring - an update

Critically ill patients are frequently at risk of neurological dysfunction as a result of primary neurological conditions or secondary insults. Determining which aspects of brain function are affected and how best to manage the neurological dysfunction can often be difficult and is complicated by the limited information that can be gained from clinical examination in such patients and the effects of therapies, notably sedation, on neurological function. Methods to measure and monitor brain function have evolved considerably in recent years and now play an important role in the evaluation and management of patients with brain injury. Importantly, no single technique is ideal for all patients and different variables will need to be monitored in different patients; in many patients, a combination of monitoring techniques will be needed. Although clinical studies support the physiologic feasibility and biologic plausibility of management based on information from various monitors, data supporting this concept from randomized trials are still required.

Intensive Care Management of Subarachnoid Haemorrhage

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating disease associated with high mortality and poor outcome in many survivors. Aggressive treatment by a comprehensive multidisciplinary team is associated with improved outcome, but the intensive care management of SAH presents significant challenges. Multimodal neuromonitoring may detect secondary insults before irreversible neuronal damage has occurred, and is increasingly being used to guide treatment. This article reviews current trends in the intensive care management of SAH from aspects of initial resuscitation to recent developments in the prevention and management of complications, including delayed cerebral ischaemia. Evidence from clinical trials and recent consensus guidance is reviewed.

Update on multimodality monitoring

Brain injury is a dynamic process marked by an initial damaging insult followed by a cascade of physical, electrical, and metabolic changes capable of resulting in further patient disability. These subclinical changes should be detected at a time when therapeutic intervention is most efficacious and preemptive. Multimodality monitoring is the practice by which a variety of brain monitors are utilized to deliver care, specific to the needs of the individual patient, in an attempt to minimize secondary injury and long-term disability. Intracranial pressure, continuous electroencephalography, brain tissue oxygen, cerebral microdialysis, cerebral blood flow, and jugular oximetry monitoring have been utilized to direct treatment of the critical ill neurologic and neurosurgical patient. Optimization of monitoring technique and protocol is an ongoing effort of intensivists in the field of neurocritical care.

Optimal glycemic control in neurocritical care patients: a systematic review and meta-analysis

INTRODUCTION

Hyper- and hypoglycemia are strongly associated with adverse outcomes in critical care. Neurologically injured patients are a unique subgroup, where optimal glycemic targets may differ, such that the findings of clinical trials involving heterogeneous critically ill patients may not apply.

METHODS

We performed a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing intensive insulin therapy with conventional glycemic control among patients with traumatic brain injury, ischemic or hemorrhagic stroke, anoxic encephalopathy, central nervous system infections or spinal cord injury.

RESULTS

Sixteen RCTs, involving 1248 neurocritical care patients, were included. Glycemic targets with intensive insulin ranged from 70-140 mg/dl (3.9-7.8 mmol/L), while conventional protocols aimed to keep glucose levels below 144-300 mg/dl (8.0-16.7 mmol/L). Tight glycemic control had no impact on mortality (RR 0.99; 95% CI 0.83-1.17; p = 0.88), but did result in fewer unfavorable neurological outcomes (RR 0.91; 95% CI 0.84-1.00; p = 0.04). However, improved outcomes were only observed when glucose levels in the conventional glycemic control group were permitted to be relatively high [threshold for insulin administration > 200 mg/dl (> 11.1 mmol/L)], but not with more intermediate glycemic targets [threshold for insulin administration 140-180 mg/dl (7.8-10.0 mmol/L)]. Hypoglycemia was far more common with intensive therapy (RR 3.10; 95% CI 1.54-6.23; p = 0.002), but there was a large degree of heterogeneity in the results of individual trials (Q = 47.9; p<0.0001; I2 = 75%). Mortality was non-significantly higher with intensive insulin in studies where the proportion of patients developing hypoglycemia was large (> 33%) (RR 1.17; 95% CI 0.79-1.75; p = 0.44).

CONCLUSIONS

Intensive insulin therapy significantly increases the risk of hypoglycemia and does not influence mortality among neurocritical care patients. Very loose glucose control is associated with worse neurological recovery and should be avoided. These results suggest that intermediate glycemic goals may be most appropriate.

Severe traumatic brain injury

PURPOSE OF REVIEW

Although adherence to traumatic brain injury (TBI) guidelines has been associated with improved patient outcomes, guideline adherence remains suboptimal in practice. With neurologists becoming increasingly involved in specialized neurointensive care units and in the care of patients with severe TBI, familiarization with these guidelines is essential.

RECENT FINDINGS

Intracranial monitoring of different physiologic variables has increased in the past few years. Intracranial pressure (ICP)-driven therapy has been replaced by ICP-cerebral perfusion pressure (CPP)-driven therapy. More recently, the importance of brain oxygen optimization in addition to ICP-CPP has been recognized, and clinical trials are underway to study the effect of this approach. Surgical management of patients with TBI is also evolving rapidly with further studies on decompressive craniectomy. These are significant advances to improve TBI outcomes.

SUMMARY

This article summarizes the routine monitoring of patients with severe TBI and offers insight into some novel physiologic monitoring devices available. The guidelines for management of patients with severe TBI are summarized along with outcome measures.

Risk factors for hypoglycaemia in neurocritical care patients

PURPOSE

To identify risk factors for hypoglycaemia in neurocritical care patients receiving intensive insulin therapy (IIT).

METHODS

We performed a nested case-control study. All first episodes of hypoglycaemia (glucose <80 mg/dL, <4.4 mmol/L) in neurocritical care patients between 1 March 2006 and 31 December 2007 were identified. Patients were treated according to the local IIT protocol, with target blood glucose levels between 4.5 and 6.0 mmol/L (81.0-108.0 mg/dL). The first hypoglycaemic event of every patient (index moment) was used to match to a control patient. Possible risk factors preceding the index moment were scored using hospital records and analysed with conditional logistic regression.

RESULTS

Of 786 neurocritical care patients, 449 developed hypoglycaemia (57.1 %). Independent risk factors for hypoglycaemia were lowering nutrition 6 h before the index moment without insulin dose reduction (odds ratio (OR) 5.25, 95 % confidence interval (95 % CI) 1.32-20.88), mechanical ventilation (OR 2.59, 95 % CI 1.56-4.29), lowering the dosage of norepinephrine 3 h before the index moment (OR 2.44, 95 % CI 1.07-5.55), a hyperglycaemic event (>10 mmol/L, >180.0 mg/dL) in the 24 h preceding the index moment (OR 2.40, 95 % CI 1.26-4.58), gastric residual in the 6 h preceding the index moment without insulin dose reduction (OR 1.76, 95 % CI 1.05-2.96) and dosage of insulin at the index moment (OR 0.83, 95 % CI 0.76-0.90).

CONCLUSION

Hypoglycaemia occurs in a considerable proportion of neurocritical care patients. We recommend the identification of these risk factors in these patients to avoid the occurrence of hypoglycaemia.

Relationship between systemic glucose and cerebral glucose is preserved in patients with severe traumatic brain injury, but glucose delivery to the brain may become limited when oxidative metabolism is impaired: implications for glycemic control

OBJECTIVE

To clarify the dynamics of glucose delivery to the brain and the effects of changes in blood glucose after severe traumatic brain injury.

DESIGN

Retrospective analysis of a prospective observational cohort study.

SETTING

Neurosurgical intensive care unit of a university hospital.

PATIENTS

Seventeen patients with acute traumatic brain injury monitored with cerebral and subcutaneous microdialysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

For continuous, accurate systemic monitoring, glucose was measured in the interstitial space of subcutaneous adipose tissue using microdialysis, and 39 specific episodes of spontaneous rises in glucose were identified. During these episodes, there was a significant positive linear relationship between systemic glucose levels and brain glucose concentrations measured by microdialysis (p < .0001). The basal lactate/pyruvate ratio, with a threshold of 25, was adopted to distinguish between disturbed and presumably preserved cerebral oxidative metabolism. Using normal vs. elevated lactate/pyruvate ratio as variable factor, the relationship between brain and systemic glucose during the episodes could be described by two significantly distinct parallel lines (p = .0001), which indicates a strong additive effect of subcutaneous glucose and lactate/pyruvate ratio in determining brain glucose. The line describing the relationship under disturbed metabolic conditions was lower than in presumably intact metabolic conditions, with a significant difference of 0.648 ± 0.192 mM (p = .002). This let us to accurately predict that in this situation systemic glucose concentrations in the lower range of normality would result in critical brain glucose levels.

CONCLUSIONS

The linear relationship between systemic and brain glucose in healthy subjects is preserved in traumatic brain-injured patients. As a consequence, in brain tissue where oxidative metabolism is disturbed, brain glucose concentrations might possibly drop below the critical threshold of 0.8 mM to 1.0 mM when there is a reduction in systemic glucose toward the lower limits of the "normal" range.

Implementation of cerebral microdialysis at a community-based hospital: A 5-year retrospective analysis

Background:

Cerebral microdialysis (MD) provides valuable information about brain metabolism under normal and pathologic conditions. The CMA 600 microdialysis analyzer received US Food and Drug Administration (FDA) approval for clinical use in the United States in 2005. Since then, cerebral MD has been increasingly utilized nationally in the multimodal monitoring of traumatic brain injury (TBI), stroke, aneurysmal subarachnoid hemorrhage, and brain tumors. We describe a 5-year, single-institutional experience using cerebral MD at a community-based hospital, Legacy Emanuel Medical Center (LEMC). Implications for the adoption and utility of MD in medical centers with limited resources are discussed.

Methods:

This is a retrospective chart review and data analysis of 174 consecutive patients who had cerebral MD as part of multimodal brain monitoring. All cerebral MD catheters were placed by board-certified, attending neurosurgeons at LEMC. Clinical severity in the TBI patients was reported using initial Glasgow Coma Scale (GCS); radiologic severity was graded with the Marshall CT grading scale. Measures of the risks of MD placement included post-placement hemorrhage, cerebral infection, and dislodgement.

Results:

Between July 2005 and July 2010, 248 cerebral MD catheters were placed in 174 patients undergoing multimodal brain monitoring. One hundred and eighty-five catheters were placed at the time of open craniotomy. None were associated with cranial infection. Patients ranged in age from 5 months to 90 years, with a mean of 49 years. The male to female ratio was 1.4:1. The underlying pathologies were: TBI (126), cerebral vascular accident (24), aneurysmal subarachnoid hemorrhage (17), and tumor (7).

Conclusions:

Cerebral MD was readily implemented in a community-based hospital. No cerebral hemorrhages or infections were attributed to cerebral MD. Examples of how MD may be a useful adjunct in the clinical decision making of patients with brain injuries are presented.

Potential non-hypoxic/ischemic causes of increased cerebral interstitial fluid lactate/pyruvate ratio: a review of available literature

Microdialysis, an in vivo technique that permits collection and analysis of small molecular weight substances from the interstitial space, was developed more than 30 years ago and introduced into the clinical neurosciences in the 1990s. Today cerebral microdialysis is an established, commercially available clinical tool that is focused primarily on markers of cerebral energy metabolism (glucose, lactate, and pyruvate) and cell damage (glycerol), and neurotransmitters (glutamate). Although the brain comprises only 2% of body weight, it consumes 20% of total body energy. Consequently, the ability to monitor cerebral metabolism can provide significant insights during clinical care. Measurements of lactate, pyruvate, and glucose give information about the comparative contributions of aerobic and anaerobic metabolisms to brain energy. The lactate/pyruvate ratio reflects cytoplasmic redox state and thus provides information about tissue oxygenation. An elevated lactate pyruvate ratio (>40) frequently is interpreted as a sign of cerebral hypoxia or ischemia. However, several other factors may contribute to an elevated LPR. This article reviews potential non-hypoxic/ischemic causes of an increased LPR.

"Moderate intensive insulin therapy" is associated with remission of high intracranial pressure in patients with vascular or infectious central nervous system diseases

Intensive insulin therapy (IIT), targeting blood glucose between 80 mg/dL and 110 mg/dL ("strict IIT"), has been associated with rapid remission of high intracranial pressure (ICP), but its use is limited due to a high risk of hypoglycemia. The aim of this retrospective study was to assess whether "moderate IIT" (target range for blood glucose: 80-140 mg/dL) could have the same beneficial effect on ICP with a lower risk of hypoglycemia. We retrospectively analyzed the records of 64 patients with high ICP due to vascular or infectious central nervous system diseases. Patients treated with moderate IIT (n=32) after 2005 were compared with patients treated with a conventional approach (n=32, target <180 mg/dL) before 2005. We assessed daily ICP during the first 14 days. Secondary endpoints were the rate of hypoglycemic events and outcome. ICP was significantly lower during the second week in patients treated with moderate IIT (mean±standard deviation [SD] daily ICP on days 8-14: 16±5 mmHg compared to 12±4 mmHg, p<0.001). The risk of hypoglycemic events (<40 mg/dL) did not differ significantly between the groups (0 vs. 1 patient, p=0.5). Moderate IIT is associated with remission of high ICP. In contrast to strict IIT, its use seems not to be limited by an increased risk of severe hypoglycemia.

Perioperative glucose control in neurosurgical patients

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.

Hyperglycemia in nondiabetic patients during the acute phase of stroke

OBJECTIVE

To determine patterns of hyperglycemic (HG) control in acute stroke.

METHODS

Anonymous survey through Internet questionnaire. Participants included Latin-American physicians specialized in neurocritical care.

RESULTS

The response rate was 74%. HG definition varied widely. Fifty per cent considered it when values were >140 mg/dL (7.8 mmol/L). Intravenous (IV) regular insulin was the drug of choice for HG correction. One fifth of the respondents expressed adherence to a protocol. Intensive insulin therapy (IIT) was used by 23%. Glucose levels were measured in all participants at admission. Routine laboratory test was the preferred method for monitoring. Reactive strips were more frequently used when monitoring was intensive. Most practitioners (56.7%) monitored glucose more than two times daily throughout the Intensive Care Unit stay.

CONCLUSIONS

There is considerable variability and heterogeneity in the management of elevated blood glucose during acute phase of stroke by the surveyed Latin-American physicians.

Contemporary view on neuromonitoring following severe traumatic brain injury

Evolving brain damage following traumatic brain injury (TBI) is strongly influenced by complex pathophysiologic cascades including local as well as systemic influences. To successfully prevent secondary progression of the primary damage we must actively search and identify secondary insults e.g. hypoxia, hypotension, uncontrolled hyperventilation, anemia, and hypoglycemia, which are known to aggravate existing brain damage. For this, we must rely on specific cerebral monitoring. Only then can we unmask changes which otherwise would remain hidden, and prevent adequate intensive care treatment. Apart from intracranial pressure (ICP) and calculated cerebral perfusion pressure (CPP), extended neuromonitoring (SjvO₂, ptiO₂, microdialysis, transcranial Doppler sonography, electrocorticography) also allows us to define individual pathologic ICP and CPP levels. This, in turn, will support our therapeutic decision-making and also allow a more individualized and flexible treatment concept for each patient. For this, however, we need to learn to integrate several dimensions with their own possible treatment options into a complete picture. The present review summarizes the current understanding of extended neuromonitoring to guide therapeutic interventions with the aim of improving intensive care treatment following severe TBI, which is the basis for ameliorated outcome.

Critical care management of severe traumatic brain injury in adults

Traumatic brain injury (TBI) is a major medical and socio-economic problem, and is the leading cause of death in children and young adults. The critical care management of severe TBI is largely derived from the "Guidelines for the Management of Severe Traumatic Brain Injury" that have been published by the Brain Trauma Foundation. The main objectives are prevention and treatment of intracranial hypertension and secondary brain insults, preservation of cerebral perfusion pressure (CPP), and optimization of cerebral oxygenation. In this review, the critical care management of severe TBI will be discussed with focus on monitoring, avoidance and minimization of secondary brain insults, and optimization of cerebral oxygenation and CPP.

Nutritional support and brain tissue glucose metabolism in poor-grade SAH: a retrospective observational study

Introduction

We sought to determine the effect of nutritional support and insulin infusion therapy on serum and brain glucose levels and cerebral metabolic crisis after aneurysmal subarachnoid hemorrhage (SAH).

Methods

We used a retrospective observational cohort study of 50 mechanically ventilated poor-grade (Hunt-Hess 4 or 5) aneurysmal SAH patients who underwent brain microdialysis monitoring for an average of 109 hours. Enteral nutrition was started within 72 hours of admission whenever feasible. Intensive insulin therapy was used to maintain serum glucose levels between 5.5 and 7.8 mmol/l. Serum glucose, insulin and caloric intake from enteral tube feeds, dextrose and propofol were recorded hourly. Cerebral metabolic distress was defined as a lactate to pyruvate ratio (LPR) > 40. Time-series data were analyzed using a general linear model extended by generalized estimation equations (GEE).

Results

Daily mean caloric intake received was 13.8 ± 6.9 cal/kg and mean serum glucose was 7.9 ± 1 mmol/l. A total of 32% of hourly recordings indicated a state of metabolic distress and < 1% indicated a state of critical brain hypoglycemia (< 0.2 mmol/l). Calories received from enteral tube feeds were associated with higher serum glucose concentrations (Wald = 6.07, P = 0.048), more insulin administered (Wald = 108, P < 0.001), higher body mass index (Wald = 213.47, P < 0.001), and lower body temperature (Wald = 4.1, P = 0.043). Enteral feeding (Wald = 1.743, P = 0.418) was not related to brain glucose concentrations after accounting for serum glucose concentrations (Wald = 67.41, P < 0.001). In the presence of metabolic distress, increased insulin administration was associated with a relative reduction of interstitial brain glucose concentrations (Wald = 8.26, P = 0.017), independent of serum glucose levels.

Conclusions

In the presence of metabolic distress, insulin administration is associated with reductions in brain glucose concentration that are independent of serum glucose levels. Further study is needed to understand how nutritional support and insulin administration can be optimized to minimize secondary injury after subarachnoid hemorrhage.