Lactate and excitatory amino acids measured by microdialysis are decreased by pentobarbital coma in head-injured patients

Pentobarbital coma for management of intracranial hypertension following traumatic brain injury: Lack of early response to treatment portends poor outcomes

INTRODUCTION

Traumatic brain injury (TBI) results in the death of over 50,000 and the permanent disability of 80,000 individuals annually in the United States. Much of the permanent disability is the result of secondary brain injury from intracranial hypertension (ICH). Pentobarbital coma is often instituted following the failure of osmotic interventions and sedation to control intracranial pressure (ICP). The goal of this study was to evaluate the efficacy of pentobarbital coma with respect to ICP management and long-term functional outcome.

METHODS

Traumatic brain injury patients who underwent pentobarbital coma at a level 1 trauma center between 2014 and 2021 were identified. Patient demographics, injury characteristics, Glasgow Coma Scale (GCS) scores, intracranial pressures (ICPs), and outcomes were obtained from the trauma registry as well as inpatient and outpatient medical records. The proportion of ICPs below 20 for each hospitalized patient-day was calculated. The primary outcome measured was GCS score at the last follow-up visit.

RESULTS

25 patients were identified, and the majority were male (n ​= ​23, 92%) with an average age of 30.0 years ​± ​12.9 and median injury severity score of 30 (21.5-33.5). ICPs were monitored for all patients with a median of 464 (326-1034) measurements. The average hospital stay was 16.9 days ​± ​11.5 and intensive care stay was 16.9 ​± ​10.8 days. 9 (36.0%) patients survived to hospital discharge. Mean follow-up time in months was 36.9 ​± ​28.0 (min-max 3-80). 7 of the 9 surviving patients presented as GCS 15 on follow-up and the remaining were both GCS 9. Patients presenting at last follow-up with GCS 15 had a significantly higher proportion of controlled ICPs throughout their hospitalization compared to patients who expired or with follow-up GCS <15 (GCS 15: 88% ​± ​10% vs. GCS <15 or dead: 68% ​± ​22%, P ​= ​0.006). A comparison of the daily proportion of controlled ICPs by group revealed negligible differences prior to pentobarbital initiation. Groups diverged nearly immediately upon pentobarbital coma initiation with a higher proportion of controlled ICPs for patients with follow-up GCS of 15.

CONCLUSION

Patients that do not have an immediate response to pentobarbital coma therapy for ICH universally had poor outcomes. Alternative therapy or earlier palliation should be considered for such patients. In contrast, patients whose ICPs responded quickly to pentobarbital had excellent long-term outcomes.

Current status and outlook for the management of intracranial hypertension after traumatic brain injury: decompressive craniectomy, therapeutic hypothermia, and barbiturates

INTRODUCTION

Increased intracranial pressure (ICP) has been associated with poor neurological outcomes and increased mortality in patients with severe traumatic brain injury (TBI). Traditionally, ICP-lowering therapies are administered using an escalating approach, with more aggressive options reserved for patients showing no response to first-tier interventions, or with refractory intracranial hypertension.

DEVELOPMENT

The therapeutic value and the appropriate timing for the use of rescue treatments for intracranial hypertension have been a subject of constant debate in literature. In this review, we discuss the main management options for refractory intracranial hypertension after severe TBI in adults. We intend to conduct an in-depth revision of the most representative randomised controlled trials on the different rescue treatments, including decompressive craniectomy, therapeutic hypothermia, and barbiturates. We also discuss future perspectives for these management options.

CONCLUSIONS

The available evidence appears to show that mortality can be reduced when rescue interventions are used as last-tier therapy; however, this benefit comes at the cost of severe disability. The decision of whether to perform these interventions should always be patient-centred and made on an individual basis. The development and integration of different physiological variables through multimodality monitoring is of the utmost importance to provide more robust prognostic information to patients facing these challenging decisions.

A scoping review of pediatric microdialysis: A missed opportunity for microdialysis in the pediatric neuro-oncology setting

Background

Brain microdialysis is a minimally invasive technique for monitoring analytes, metabolites, drugs, neurotransmitters, and/or cytokines. Studies to date have centered on adults with traumatic brain injury, with a limited number of pediatric studies performed. This scoping review details past use of brain microdialysis in children and identifies potential use for future neuro-oncology trials.

Methods

In December 2020, Cochrane Library: CENTRAL, Embase, PubMed, Scopus, and Web of Science: Core Collection were searched. Two reviewers screened all articles by title and abstract review and then full study texts, using microdialysis in patients less than 18 yo.

Results

Of the 1171 articles screened, 49 were included. The 49 studies included 472 pediatric patients (age range 0–17 years old), in the brain (21), abdominal (16), and musculoskeletal (12) regions. Intracerebral microdialysis was performed in 64 collective patients, with a median age of 11 years old, and predominance in metabolic evaluations.

Conclusion

Historically, pediatric microdialysis was safely performed within the brain in varied neurologic conditions, except neuro-oncology. Adult brain tumor studies using intratumoral/peritumoral microdialysis sampling can inform future pediatric studies to advance diagnosis and treatment options for such aggressive tumors.

A novel step-down infusion method of barbiturate therapy: Its safety and effectiveness for intracranial pressure control

Intracranial pressure (ICP) has to be maintained quite constant, because increased ICP caused by cerebrovascular disease and head trauma is fatal. Although controlling ICP is clinically critical, only few therapeutic methods are currently available. Barbiturates, a group of sedative-hypnotic drugs, are recognized as secondary treatment for controlling ICP. We proposed a novel "step-down infusion" method, administrating barbiturate (thiamylal) after different time point from the start of treatment under normothermia, at doses of 3.0 (0-24 h), 2.0 (24-48 h), 1.5 (48-72 h), and 1.0 mg/kg/h (72-96 h), and evaluated its safety and effectiveness in clinical. In 22 patients with severe traumatic brain injury or severe cerebrovascular disease (Glasgow coma scale ≤8), thiamylal concentrations and ICP were monitored. The step-down infusion method under normothermia maintained stable thiamylal concentrations (<26.1 µg/ml) without any abnormal accumulation/elevation, and could successfully keep ICP <20 mmHg (targeted management value: ICP <20 mmHg) in all patients. Moreover the mean value of cerebral perfusion pressure (CPP) was also maintained over 65 mmHg during all time course (targeted management value: CPP >65 mmHg), and no threatening changes in serum potassium or any hemodynamic instability were observed. Our novel "step-down infusion" method under normothermia enabled to maintain stable, safe thiamylal concentrations to ensure both ICP reduction and CPP maintenance without any serious side effects, may provide a novel and clinically effective treatment option for patients with increased ICP.

Temporal effects of barbiturate coma on intracranial pressure and compensatory reserve in children with traumatic brain injury

Background

The aim was to study the effects of barbiturate coma treatment (BCT) on intracranial pressure (ICP) and intracranial compensatory reserve (RAP index) in children (< 17 years of age) with traumatic brain injury (TBI) and refractory intracranial hypertension (RICH).

Methods

High-resolution monitoring data were used to study the effects of BCT on ICP, mean arterial pressure (MAP), cerebral perfusion pressure (CPP), and RAP index. Four half hour long periods were studied: before bolus injection and at 5, 10, and 24 hours thereafter, respectively, and a fifth tapering period with S-thiopental between < 100 and < 30 μmol/L. S-thiopental concentrations and administered doses were registered.

Results

Seventeen children treated with BCT 2007–2017 with high-resolution data were included; median age 15 (range 6–17) and median Glasgow coma score 7 (range 3–8). Median time from trauma to start of BCT was 44.5 h (range 2.5–197.5) and from start to stop 99.0 h (range 21.0–329.0). Median ICP was 22 (IQR 20–25) in the half hour period before onset of BCT and 16 (IQR 11–20) in the half hour period 5 h later (p = 0.011). The corresponding figures for CPP were 65 (IQR 62–71) and 63 (57–71) (p > 0.05). The RAP index was in the half hour period before onset of BCT 0.6 (IQR 0.1–0.7), in the half hour period 5 h later 0.3 (IQR 0.1–0.7) (p = 0.331), and in the whole BCT period 0.3 (IQR 0.2–0.4) (p = 0.004). Eighty-two percent (14/17) had favorable outcome (good recovery = 8 patients and moderate disability = 6 patients).

Conclusion

BCT significantly reduced ICP and RAP index with preserved CPP. BCT should be considered in case of RICH.

Current status and outlook for the management of intracranial hypertension after traumatic brain injury: decompressive craniectomy, therapeutic hypothermia, and barbiturates

INTRODUCTION

Increased intracranial pressure has been associated with poor neurological outcomes and increased mortality in patients with severe traumatic brain injury. Traditionally, intracranial pressure-lowering therapies are administered using an escalating approach, with more aggressive options reserved for patients showing no response to first-tier interventions, or with refractory intracranial hypertension.

DEVELOPMENT

The therapeutic value and the appropriate timing for the use of rescue treatments for intracranial hypertension have been a subject of constant debate in literature. In this review, we discuss the main management options for refractory intracranial hypertension after severe traumatic brain injury in adults. We intend to conduct an in-depth revision of the most representative randomised controlled trials on the different rescue treatments, including decompressive craniectomy, therapeutic hypothermia, and barbiturates. We also discuss future perspectives for these management options.

CONCLUSIONS

The available evidence appears to show that mortality can be reduced when rescue interventions are used as last-tier therapy; however, this benefit comes at the cost of severe disability. The decision of whether to perform these interventions should always be patient-centred and made on an individual basis. The development and integration of different physiological variables through multimodality monitoring is of the utmost importance to provide more robust prognostic information to patients facing these challenging decisions.

A systematic review of cerebral microdialysis and outcomes in TBI: relationships to patient functional outcome, neurophysiologic measures, and tissue outcome

OBJECTIVE

To perform a systematic review on commonly measured cerebral microdialysis (CMD) analytes and their association to: (A) patient functional outcome, (B) neurophysiologic measures, and (C) tissue outcome; after moderate/severe TBI. The aim was to provide a foundation for next-generation CMD studies and build on existing pragmatic expert guidelines for CMD.

METHODS

We searched MEDLINE, BIOSIS, EMBASE, Global Health, Scopus, Cochrane Library (inception to October 2016). Strength of evidence was adjudicated using GRADE.

RESULTS

(A) Functional Outcome: 55 articles were included, assessing outcome as mortality or Glasgow Outcome Scale (GOS) at 3-6 months post-injury. Overall, there is GRADE C evidence to support an association between CMD glucose, glutamate, glycerol, lactate, and LPR to patient outcome at 3-6 months. (B) Neurophysiologic Measures: 59 articles were included. Overall, there currently exists GRADE C level of evidence supporting an association between elevated CMD measured mean LPR, glutamate and glycerol with elevated ICP and/or decreased CPP. In addition, there currently exists GRADE C evidence to support an association between elevated mean lactate:pyruvate ratio (LPR) and low PbtO2. Remaining CMD measures and physiologic outcomes displayed GRADE D or no evidence to support a relationship. (C) Tissue Outcome: four studies were included. Given the conflicting literature, the only conclusion that can be drawn is acute/subacute phase elevation of CMD measured LPR is associated with frontal lobe atrophy at 6 months.

CONCLUSIONS

This systematic review replicates previously documented relationships between CMD and various outcome, which have driven clinical application of the technique. Evidence assessments do not address the application of CMD for exploring pathophysiology or titrating therapy in individual patients, and do not account for the modulatory effect of therapy on outcome, triggered at different CMD thresholds in individual centers. Our findings support clinical application of CMD and refinement of existing guidelines.

Management of raised intracranial pressure in children with traumatic brain injury

Increased intracranial pressure (ICP) is associated with worse outcome after traumatic brain injury (TBI). The current guidelines and management strategies are aimed at maintaining adequate cerebral perfusion pressure and treating elevated ICP. Despite controversies, ICP monitoring is important particularly after severe TBI to guide treatment and in developed countries is accepted as a standard of care. We provide a narrative review of the recent evidence for the use of ICP monitoring and management of ICP in pediatric TBI.

Neurotrauma

Neurotrauma continues to be a significant cause of morbidity and mortality. Prevention of primary neurologic injury is a critical public health concern. Early and thorough assessment of the patient with neurotrauma with high index of suspicion of traumatic spinal cord injuries and traumatic vascular injuries requires a multidisciplinary approach involving prehospital providers, emergency physicians, neurosurgeons, and neurointensivists. Critical care management of the patient with neurotrauma is focused on the prevention of secondary injuries. Much research is still needed for potential neuroprotection therapies.

S100B and NSE as useful postmortem biochemical markers of traumatic brain injury in autopsy cases

Postmortem analysis of relevant biomarkers might aid in characterizing causes of death and survival times in legal medicine. However, there are still no sufficiently established results of practical postmortem biochemical investigations in cases of traumatic brain injury (TBI). The two biomarkers--S100 protein subunit B (S100B) and neuronal specific enolase (NSE)--could be of special interest. Therefore, the aim of the present study was to investigate changes in their postmortem levels for further determination of brain damage in TBI. In 17 cases of TBI (average age, 58 years) and in 23 controls with different causes of death (average age, 59 years), serum and cerebrospinal fluid (CSF) samples were analyzed with a chemiluminescence immunoassay for marker expression. An increase in serum S100B, as well as a subsequent decrease after survival times>4 days, were detected in TBI cases (p<0.01). CSF NSE values >6,000 ng/mL and CSF S100B levels >10,000 ng/mL seem to indicate a TBI survival time of at least 15 min (p<0.01). It is of particular interest that CSF S100B levels (p<0.01) and serum S100B levels (p<0.05) as well as CSF NSE values (p<0.01) were significantly higher in TBI cases in comparison to the controls, especially when compared with fatal non-head injuries. In conclusion, the present findings emphasize that S100B and NSE are useful markers in postmortem biochemistry in cases of suspected TBI. Further, S100B may be helpful to estimate the survival time of fatal injuries in legal medicine.

Microdialysis in the neurocritical care unit

Effective monitoring is critical for neurologically compromised patients, and several techniques are available. One of these tools, cerebral microdialysis (MD), was designed to detect derangements in cerebral metabolism. Although this monitoring device began as a research instrument, favorable results and utility have broadened its clinical applications. Combined with other brain monitoring techniques, MD can be used to estimate cerebral vulnerability, to assess tissue outcome, and possibly to prevent secondary ischemic injury by guiding therapy. This article reviews the literature regarding the past, present, and future uses of MD along with its advantages and disadvantages in the intensive care unit setting.

Use of biomarkers for diagnosis and management of traumatic brain injury patients

BACKGROUND

Advances in the understanding of human biochemistry and physiology have provided insight into new pathways by which we can understand traumatic brain injury (TBI). Increased sophistication of laboratory techniques and developments in the field of proteomics has led to the discovery and rapid detection of new biomarkers not previously available.

OBJECTIVE

To review recent advances in biomarker research for traumatic brain injury, describe the features of the ideal biomarker and to explore the potential role of these biomarkers in improving clinical management of brain injured patients.

METHODS

Through a literature review of recent research on TBI biomarkers and through experience with TBI research, important elements of biomarker development are described together with potential applications to patient care.

CONCLUSIONS

TBI biomarkers could have a significant impact on patient care by assisting in the diagnosis, risk stratification and management of TBI. Biomarkers could provide major opportunities for the conduct of clinical research, including confirmation of injury mechanism(s) and drug target identification. Continuing studies by the authors' group are now being conducted to elucidate more fully the relationships between new biomarkers and severity of injury and clinical outcomes in all severities of TBI patients.

Neuroprotective effects of lactate in brain ischemia: dependence on anesthetic drugs

Lactate is a major energy source for the brain, especially when glucose is not available in sufficient amounts. In the present study, we administered sodium l-lactate (250 mg/kg) to mice before or after middle cerebral artery occlusion (MCAO) to test whether lactate can be neuroprotective in brain ischemia. Permanent ischemia for 24h caused a large hemispheric lesion and a severe loss of body weight. Administration of lactate shortly (15-30 min) before MCAO strongly reduced cell death and weight loss, but only when isoflurane was used for anesthesia. Under pentobarbital anesthesia, lactate was inactive. After transient ischemia, when isoflurane or ketamine-xylazine were used as anesthetic drugs, lactate was effective when given immediately after reperfusion. In separate experiments, we found that plasma lactate levels are also strongly influenced by anesthetic drugs. Thus, isoflurane anesthesia as well as lactate administration caused strongly increased plasma levels of lactate whereas pentobarbital anesthesia significantly reduced plasma lactate. We conclude that exogenous lactate is neuroprotective in an in vivo-model of brain ischemia, but that its action is strongly influenced by the type of anesthetic agent used.

Pentobarbital coma for refractory intra-cranial hypertension after severe traumatic brain injury: mortality predictions and one-year outcomes in 55 patients

OBJECTIVE

To identify predictors of mortality and long-term outcomes in survivors after pentobarbital coma (PBC) in patients failing current treatment standards for severe traumatic brain injuries (TBI). This is a retrospective cohort study of severe TBI patients receiving PBC at Level I Trauma Center and tertiary university hospital.

METHODS

Four thousand nine hundred thirty-four patients were admitted to the trauma intensive care unit with severe TBI (head Abbreviated Injury Scale >or= 3) between April 1998 and December 2004. Six hundred eleven received intracranial pressure (ICP) monitoring and 58 received PBC. Three patients underwent craniotomy for intracranial mass lesion and were excluded. The study group received standardized medical management for severe TBI including opiates, benzodiazepines, elevation of the head of bed, avoidance of hypotension and hypercapnia and hyperosmolar therapy (HOsmRx). In addition, 31 of 55 patients (56%) underwent placement of intraventricular catheters for cerebrospinal fluid drainage. If routine medical management and cerebrospinal fluid diversion failed to control ICP, then the patient was determined to have refractory intracranial hypertension (RICH) and PBC treatment was initiated. PBC was performed with pentobarbital infusion with continuous electroencephalogram monitoring to ensure adequate burst suppression. The measurements include serum sodium (Na) and osmolality (Osm) were assessed as indicators for initiation of PBC and to estimate the 50% mortality cut-points when controlling for ICP. Follow-up functional outcomes were assessed using the Glasgow Outcome Scale and stratified according to admission Glasgow Coma Scale score and Marshall computed tomography classification. Of the 55 PBC patients, 22 (40%) survived at discharge. 19 of 22 had long-term follow-up (1 year or more) available. Of these, 13 (68%) were normal or functionally independent (Glasgow Outcome Scale score 4 or 5). Serum Na and Osm were associated with death (p < 0.05) when controlling for ICP. The 50% mortality cut-points were Na of 160 mEq/L and Osm of 330 mOsm/kg H2O. Median minimum cerebral perfusion pressure after PBC was 42 mm Hg in survivors and 34 mm Hg in nonsurvivors (p = 0.013).

CONCLUSIONS

In patients with severe TBI and RICH, survival at discharge of 40% with good functional outcomes in 68% of survivors at 1 year or more can be achieved with PBC after failure of HOsmRx. Based on 50% mortality cut-points, analysis suggests the limits of HOsmRx to be Na of 160 mEq/L and Osm of 330 mOsm/Kg H2O. Maintenance of higher cerebral perfusion pressure after PBC is associated with survival. PBC treatment of RIH may be even more important when other treatments of RIH, such as decompressive craniectomy, are not available.

Current and evolving management of traumatic brain injury

This article discuss the pathophysiology of traumatic brain injury and increased intracranial pressure, the consequences and treatment of secondary insults, and strategies for the medical and nursing management of the patient who has traumatic brain injury.

Relevance of intracranial hypertension for cerebral metabolism in aneurysmal subarachnoid hemorrhage. Clinical article

OBJECT

Intracranial hypertension, defined as intracranial pressure (ICP) >/= 20 mm Hg, is a complication typically associated with head injury. Its impact on cerebral metabolism, ICP therapy, and outcome has rarely been studied in patients with aneurysmal subarachnoid hemorrhage (aSAH); such an assessment is the authors' goal in the present study.

METHODS

Cerebral metabolism was prospectively studied in 182 patients with aSAH. The database was retrospectively analyzed with respect to ICP. Patients were classified into 2 groups based on ICP. There were 164 with low ICP (<20 mm Hg) and 18 with high ICP (>or=20 mm Hg, measured>6 hours/day). Cerebral microdialysis parameters of energy metabolism, glycerol, and glutamate levels were analyzed hourly from the brain parenchyma of interest for 7 days. The 12-month outcome in these patients was evaluated.

RESULTS

In the high ICP group, extended ICP therapy including decompressive craniectomy was necessary in 7 patients (39%). Cerebral glycerol levels and the lactate/pyruvate ratio were pathologically increased on Days 1-7 after aSAH (p<0.001). The excitotoxic neurotransmitter glutamate and glycerol, a marker of membrane degradation, further increased on Days 5-7, probably reflecting the development of secondary brain damage. An ICP>or=20 mm Hg was shown to have a significant influence on the 12-month Glasgow Outcome Scale (GOS) score (p=0.001) and was a strong predictor of mortality (OR=24.6; p<0.001). Glutamate (p=0.012), the lactate/pyruvate ratio as a marker of anaerobic metabolism (p=0.028), age (p<0.001), and Fisher grade (p=0.001) also influenced the GOS score at 12 months.

CONCLUSIONS

The authors confirmed the relevance of intracranial hypertension as a severe complication in patients with aSAH. Because high ICP is associated with a severely deranged cerebral metabolism and poor outcome, future studies focusing on metabolism-guided, optimized ICP therapy could help minimize secondary brain damage and improve prognosis in patients with aSAH.

Emergency treatment options for pediatric traumatic brain injury

Traumatic brain injury is a leading killer of children and is a major public health problem around the world. Using general principles of neurocritical care, various treatment strategies have been developed to attempt to restore homeostasis to the brain and allow brain healing, including mechanical factors, cerebrospinal fluid diversion, hyperventilation, hyperosmolar therapies, barbiturates and hypothermia. Careful application of these therapies, normally in a step-wise fashion as intracranial injuries evolve, is necessary in order to attain maximal neurological outcome for these children. It is hopeful that new therapies, such as early hypothermia or others currently in preclinical trials, will ultimately improve outcome and quality of life for children after traumatic brain injury.

Barbiturate infusion for intractable intracranial hypertension and its effect on brain oxygenation

OBJECTIVE

Barbiturate-induced coma can be used in patients to treat intractable intracranial hypertension when other therapies, such as osmotic therapy and sedation, have failed. Despite control of intracranial pressure, cerebral infarction may still occur in some patients, and the effect of barbiturates on outcome remains uncertain. In this study, we examined the relationship between barbiturate infusion and brain tissue oxygen (PbtO2).

METHODS

Ten volume-resuscitated brain-injured patients who were treated with pentobarbital infusion for intracranial hypertension and underwent PbtO2 monitoring were studied in a neurosurgical intensive care unit at a university-based Level I trauma center. PbtO2, intracranial pressure (ICP), mean arterial pressure, cerebral perfusion pressure (CPP), and brain temperature were continuously monitored and compared in settings in which barbiturates were or were not administered.

RESULTS

Data were available from 1595 hours of PbtO2 monitoring. When pentobarbital administration began, the mean ICP, CPP, and PbtO2 were 18 +/- 10, 72 +/- 18, and 28 +/- 12 mm Hg, respectively. During the 3 hours before barbiturate infusion, the maximum ICP was 24 +/- 13 mm Hg and the minimum CPP was 65 +/- 20 mm Hg. In the majority of patients (70%), we observed an increase in PbtO2 associated with pentobarbital infusion. Within this group, logistic regression analysis demonstrated that a higher likelihood of compromised brain oxygen (PbtO2 < 20 mm Hg) was associated with a decrease in pentobarbital dose after controlling for ICP and other physiological parameters (P < 0.001). In the remaining 3 patients, pentobarbital was associated with lower PbtO2 levels. These patients had higher ICP, lower CPP, and later initiation of barbiturates compared with patients whose PbtO2 increased.

CONCLUSION

Our preliminary findings suggest that pentobarbital administered for intractable intracranial hypertension is associated with a significant and independent increase in PbtO2 in the majority of patients. However, in some patients with more compromised brain physiology, pentobarbital may have a negative effect on PbtO2, particularly if administered late. Larger studies are needed to examine the relationship between barbiturates and cerebral oxygenation in brain-injured patients with refractory intracranial hypertension and to determine whether PbtO2 responses can help guide therapy.

Brain metabolite levels assessed by lactate-edited MR spectroscopy in premature neonates with and without pentobarbital sedation

BACKGROUND AND PURPOSE

Pentobarbital is known to affect cerebral metabolism; pentobarbital sedation is, however, frequently used for MR imaging and MR spectroscopy, especially in children. Accurate assessment of the brain metabolite levels is important, particularly in neonates with suspected brain injury. We investigated whether pentobarbital sedation has any effect on the ratios of spectral metabolites lactate, N-acetylaspartate, or choline in a group of premature neonates.

MATERIALS AND METHODS

MR spectroscopy was performed in 43 premature neonates, all with normal concurrent MR imaging and normal neurodevelopmental outcome at 12 months of age. Of those neonates, 14 (33%) required pentobarbital (Nembutal 1 mg/kg) sedation during MR spectroscopy; the remaining 29 neonates did not receive any sedation. Ratios of lactate, choline, and N-acetylaspartate were calculated in the basal ganglia, thalami, and corticospinal tracts and compared between those neonates with and without sedation.

RESULTS

Small amounts of brain lactate were detected in all of the premature neonates. The basal ganglia lactate/choline and lactate/N-acetylaspartate ratios were significantly lower, by 17% and 25% respectively, in the neonates with pentobarbital sedation compared with the age-matched neonates without sedation (P < .05). Sedation did not affect the lactate level in the thalami or the corticospinal tracts. The N-acetylaspartate/choline ratios were unaffected by pentobarbital sedation.

CONCLUSION

Pentobarbital sedation is associated with lower lactate/choline and lactate/N-acetylaspartate ratios in the basal ganglia of premature neonates, as determined by proton MR spectroscopy. Investigators should be aware of this phenomenon for accurate interpretation of their MR spectroscopy results.

Quantification of burst suppression and bispectral index with 2 different bolus doses of thiopentone sodium

Metabolic suppression caused by barbiturates is a major mechanism responsible for their cerebral protective potential. Maximal cerebral metabolic suppression is believed to coincide with electroencephalographic burst suppression. However, many neurosurgical procedures associated with cerebral ischemic threat are still performed in the absence of electroencephalogram monitoring, especially in developing nations. The present study was designed to assess the degree of burst suppression with 2 different doses of thiopentone sodium administered on the background of isoflurane anesthesia intraoperatively. Forty-one patients without any intracranial pathology undergoing elective spinal surgery under a general anesthetic consisting of N2O (60%) in O2 (40%) and isoflurane to maintain a bispectral index (BIS) value of 45 were randomized to receive a thiopentone bolus of either 3 or 5 mg/kg. BIS, burst suppression ratio (BSR), systolic blood pressure, and heart rate were recorded before the bolus and every 15 seconds for first 2 minutes and every 30 seconds for another 8 minutes. During the 10-minute study period after the administration of thiopentone bolus, BIS values were significantly lower in the group that received thiopentone 5 mg/kg compared with the group that received thiopentone 3 mg/kg (P<0.02). BSR>25% was seen in 7 out of 21 patients in the 3 mg/kg group and 10 out of 20 patients in the 5 mg/kg group. There was a statistically insignificant prolongation of the duration of burst suppression with thiopentone 5 mg/kg [243 s (range 75 to 435 s)] compared with thiopentone 3 mg/kg [171 s (30 to 465 s)]. The number of patients who had a BSR >50% was higher among patients who received thiopentone 5 mg/kg as compared with those who received a dose of 3 mg/kg [9/20 vs. 3/21(P<0.02)]. We conclude that thiopentone in a bolus dose of 3 to 5 mg/kg produces only a short duration of incomplete burst suppression. Also, in this dose range, burst suppression does not occur consistently in all patients. The present data suggest that bolus doses of thiopentone in the range of 3 to 5 mg/kg may have very limited value in providing significant metabolic suppression required for intraoperative cerebral protection during temporary ischemic episodes.

Oxygen tension controls the expansion of human CNS precursors and the generation of astrocytes and oligodendrocytes

Human neural precursor proliferation and potency is limited by senescence and loss of oligodendrocyte potential. We found that in vitro expansion of human postnatal brain CD133(+) nestin(+) precursors is enhanced at 5% oxygen, while raising oxygen tension to 20% depletes precursors and promotes astrocyte differentiation even in the presence of mitogens. Higher cell densities yielded more astrocytes regardless of oxygen tension. This was reversed by noggin at 5%, but not 20%, oxygen due to a novel repressive effect of low oxygen on bone morphogenetic protein (BMP) signaling. When induced to differentiate by mitogen withdrawal, 5% oxygen-expanded precursors generated 17-fold more oligodendrocytes than cells expanded in 20% oxygen. When precursors were expanded at 5% oxygen and then differentiated at 20% oxygen, oligodendrocyte maturation was further enhanced 2.5-fold. These results indicate that dynamic control of oxygen tension regulates different steps in fate and maturation and may be crucial for treating neurodegenerative diseases.

Neuroanesthesiology review--2006

In this article, we will provide a review of the 2006 literature of interest to those readers who provide perioperative care to patients with neurologic disease. This evaluation of the literature is not intended to be comprehensive, nor were systematic criteria used to include or exclude articles. Instead, the authors attempted to highlight those articles of greatest clinical relevance or those that provided unique insights into the physiology, pharmacology, and pathomechanisms of neurologic function for practicing clinicians and clinician-investigators. This article focuses on intracranial hemorrhage, anesthetic considerations in neurosurgical patients, cerebral hemodynamics, electrophysiologic monitoring, neuroprotection, and traumatic brain injury.

Effects of Mannitol Bolus Administration on Intracranial Pressure, Cerebral Extracellular Metabolites, and Tissue Oxygenation in Severely Head-Injured Patients

BACKGROUND

Osmotic agents are widely used to lower elevated intracranial pressure (ICP). However, little data are available regarding cerebral oxygenation and metabolism in the traumatized brains studied under clinical conditions. The present prospective, open-labeled clinical study was designed to investigate whether administration of mannitol, with the aim of reducing moderate intracranial hypertension, improves cerebral metabolism and oxygenation in patients after severe traumatic brain injury (TBI).

METHODS

Multimodal cerebral monitoring (MCM), consisting of intraparenchymal ICP, tissue oxygenation (ptiO2), and micro dialysis measurements was initiated in six male TBI patients (mean age 45 years; Glasgow Coma Scale score <9). A total of 14 mannitol boli (20%, 0.5g/kg, 20 minutes infusion time) were administered to treat ICP exceeding 20 mm Hg (2.7 kPa). Temporal alterations determined by MCM after mannitol infusions were recorded for 120 minutes. Microdialysates were assayed immediately for extracellular glucose, lactate, pyruvate, and glutamate concentrations.

RESULTS

Elevated ICP was successfully treated in all cases. This effect was maximal 40 minutes after start of infusion (25 +/- 6 mm Hg [3.3 +/- 0.8 kPa] to 17 +/- 3 mm Hg [2.3 +/- 0.4 kPa], p < 0.05) and lasted up to 100 minutes. Cerebral ptiO2 remained unaffected (21 +/- 5 mm Hg [2.8 +/- 0.7 kPa] to 23 +/- 6 mm Hg [3.1 +/- 0.8 kPa], n.s.). Microdialysate concentrations of all analytes rose unspecifically by 10% to 40% from baseline, reaching maximum concentrations 40 to 60 minutes after start of the infusion.

CONCLUSIONS

Mannitol efficiently reduces increased ICP. At an ICP of up to 30 mm Hg [4 kPa] it does not affect cerebral oxygenation. Unspecific increases of extracellular fluid metabolites can be explained by transient osmotic dehydration. Additional mechanisms, such as increased cerebral perfusion and blood volume, might explain an accelerated return to baseline.

Changes in cerebral energy metabolites induced by impact-acceleration brain trauma and hypoxic-hypotensive injury in rats

The aim of this study was to describe, in rats, brain energy metabolites changes after different levels of head trauma (T) complicated by hypoxia-hypotension (HH). Male Sprague Dawley rats (n = 7 per groups) were subjected to T by impact-acceleration with 450-g weight drop from 1.50 or 1.80 m (T 1.50 or T 1.80), or to a 15-min period of HH (controlled hemorrhage to mean arterial pressure [MAP] of 40 mm Hg, and mechanical ventilation with N(2) 90%/O(2) 10%), or to their association (T followed by HH). Invasive MAP, intraparenchymental intracranial pressure (ICP), and cerebral blood flow (CBF using Laser Doppler flowmetry) were recorded during the 5 post-traumatic hours. Cerebral microdialysis was used to measure each hour interstitial brain glucose, lactate, pyruvate, and glutamate. For the entire period, the levels of cerebral glucose, pyruvate, and glutamate were not statistically different between groups. In addition, there were no differences associated with the lactate-glucose ratio. Lactate was significantly higher overtime only in T 1.80 + HH group (p < 0.001 vs. every other groups). The lactate-pyruvate ratio increased with trauma level, and was significantly different vs. sham for the entire study period in T 1.50 + HH, in T 1.80, and in T 1.80 + HH. There was no correlation between CBF variations and the lactate-pyruvate ratio (r(2) = 0.00001). The cerebral perfusion pressure was greater than 70 mm Hg in all groups. The prolonged post-traumatic impairment in brain energy metabolism may be related to traumatic brain injury (TBI) severity. It became worse when T was complicated by HH, but was not related to changes in CBF.

[Cerebral ischemic threshold in clinical practice]

The ischemic threshold is reached when the availability of oxygen in the cerebral tissue does not cover oxygen requirement. For a patient sedated, with constant PaO(2) and haemoglobin, the cerebral blood flow (CBF) global and local is the essential factor to maintain such a balance. At a cellular level, ischemia occurs when the CBF is below 20-25 ml/min. However, this threshold probably varies with the patient and also within the normal or perilesional tissue. A cerebral perfusion pressure (CPP) of 60 mmHg, recommended for a cerebral perfusion allowing a sufficient CBF for normal brain, does not prevent ischemia. Monitoring aimed to control parameters of the aerobic metabolism (PtiO(2), SjO(2) and microdialysis) and to detect the ischemic threshold allows to adapt the CPP to each patient and continuously.

Increased Lactate Levels Impair the Coagulation System—A Potential Contributing Factor to Progressive Hemorrhage After Traumatic Brain Injury

Progressive intracerebral contusions are a major problem in the management of patients with severe traumatic brain injury that is also linked to worse outcome. Microdialysis studies have revealed that lactate levels are very high inside contusions, corresponding to significant acidosis. The current study was performed in an effort to investigate whether the lactate accumulation inside cerebral contusions may be a contributing factor to the prolonged bleeding inside contusions. We have investigated the effects of lactic acidosis on the coagulation system with rotational thromboelastometry. It was a laboratory study involving 6 healthy volunteers. Blood was drawn and the pH was adjusted by addition of lactic acid in vitro. The pH levels studied were 7.4, 7.2, 7.0, and 6.8. The pH was also readjusted to 7.4 by addition the buffer THAM to blood initially adjusted to a pH of 6.8 to study the reversibility of potential adverse effects induced by the lactic acidosis. We found the coagulation to be significantly impaired by lactic acidosis (P = 0.000l). The impairment found was reversible after correction of the acidosis by a buffer. In conclusion, we found that lactic acidosis impaired the coagulation system. The impairment caused by lactic acidosis may be one factor causing the progressive hemorrhage in posttraumatic cerebral contusions, known to have high levels of lactate and correspondingly low pH. It may also be important to consider in bleeding trauma patients.

[Cerebral microdialysis as a clinical tool]

Microdialysis is the only technique available for cerebral metabolic monitoring in the clinical setting. By the mean of a probe inserted in the brain, it provides an extracellular space sampling. Values of various substrates including cerebral glucose, lactate, pyruvate, glycerol or glutamate can be obtained at the bedside at intervals between minutes and hours. Values are critically dependent on the flow of the perfusion liquid and reflect a highly localized cerebral metabolism. Cerebral microdialysis improves our understanding of acute neurological events such as intracranial hypertension or decrease in brain tissue oxygen pressure. Cerebral microdialysis can be used for detection of ischaemia, especially after malignant stroke or vasospasm complicating subarachnoid haemorrhage. In these cases, it may influence the therapeutic management. Moreover, it permits the assessment of metabolic changes after therapeutic interventions. Finally, some markers (like lactate/pyruvate ratio) are related to outcome, especially after traumatic brain injury.

Intracerebral microdialysis and intracranial compliance monitoring of patients with traumatic brain injury

OBJECTIVE

The aims of this study were to get an impression of the relationships between intracranial compliance (IC) and Lactate/Pyruvate (L/P) ratio and temperature and L/P ratio, and to determine if patients with low IC had an increased vulnerability for the secondary insult hyperthermia (as reflected in the L/P ratio). The effects of coma treatment on the results were also studied.

METHODS

Ten TBI patients were monitored for IC, in vivo microdialysis (MD) and bladder temperature. Mean Glasgow Coma Scale (GCS) score was 7 (range 4-10). Three patients underwent induced coma treatment. Three statistical models were used to look at the relationships between IC, temperature and L/P ratio in patients with and without coma.

RESULTS

We found that with high temperature L/P ratios increased as IC decreased (P < 0.0001). The patients with coma treatment had significantly higher average L/P ratios (P < 0.02). The effect of IC on the L/P ratio differed by coma treatment (P < 0.02). The temperature effect was not dependent on coma treatment (P < 0.49).

CONCLUSIONS

These findings suggest the importance of avoiding hyperthermia in TBI patients, especially in patients with low or decreased IC (monitored or anticipated). The present technical solution seems promising for analysis of complex clinical data.

Microdialysis in traumatic brain injury--methodology and pathophysiology

The application of clinical microdialysis to monitor changes in cerebral extracellular chemistry is now well established in several neurosurgical units worldwide. In neuro-intensive care the technique has been predominantly applied to patients with traumatic brain injury and subarachnoid haemorrhage. There is no doubt that microdialysis has increased and continues to increase our understanding of the pathophysiology of these conditions. Current studies are addressing the potential role of microdialysis as a clinical monitoring technique assisting in the management of patients on an intention to treat basis. This involves establishing the relationship between microdialysis and outcome, and the effect of therapeutic manoeuvres on the chemistry. This manuscript describes the place of microdialysis in traumatic brain injury in terms of the fundamental principles, methodology, pathophysiology and clinical application.

Continuous EEG monitoring for the detection of seizures in traumatic brain injury, infarction, and intracerebral hemorrhage: "to detect and protect"

Brain injury results in a primary pathophysiologic response that enables the brain to have seizures. Seizures occur frequently after traumatic and nontraumatic intracerebral bleeding. These seizures can be nonconvulsive, and if one does not monitor for seizures, one will not know they are occurring. The use of continuous EEG monitoring (cEEG) to detect brain arrhythmias after a primary insult, much in way that cardiac arrhythmias are detected after myocardial infarction, can influence treatment decisions and mitigate some of the pathophysiologic natural history of brain injuries. Seizures after brain injury worsen clinical outcome and need to be treated. In summary, cEEG is a valuable clinical instrument "to detect and protect," i.e., to detect seizures and protect the brain from seizure-related injury in critically ill patients, whose brains are often in a particularly vulnerable state.

Translational neurochemical research in acute human brain injury: the current status and potential future for cerebral microdialysis

Microdialysis (MD) was introduced as an intracerebral sampling method for clinical neurosurgery by Hillered et al. and Meyerson et al. in 1990. Since then MD has been embraced as a research tool to measure the neurochemistry of acute human brain injury and epilepsy. In general investigators have focused their attention to relative chemical changes during neurointensive care, operative procedures, and epileptic seizure activity. This initial excitement surrounding this technology has subsided over the years due to concerns about the amount of tissue sampled and the complicated issues related to quantification. The interpretation of mild to moderate MD fluctuations in general remains an issue relating to dynamic changes of the architecture and size of the interstitial space, blood-brain barrier (BBB) function, and analytical imprecision, calling for additional validation studies and new methods to control for in vivo recovery variations. Consequently, the use of this methodology to influence clinical decisions regarding the care of patients has been restricted to a few institutions. Clinical studies have provided ample evidence that intracerebral MD monitoring is useful for the detection of overt adverse neurochemical conditions involving hypoxia/ischemia and seizure activity in subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), thromboembolic stroke, and epilepsy. There is some data strongly suggesting that MD changes precede the onset of secondary neurological deterioration following SAH, hemispheric stroke, and surges of increased ICP in fulminant hepatic failure. These promising investigations have relied on MD-markers for disturbed glucose metabolism (glucose, lactate, and pyruvate) and amino acids. Others have focused on trying to capture other important neurochemical events, such as excitotoxicity, cell membrane degradation, reactive oxygen species (ROS) and nitric oxide (NO) formation, cellular edema, and BBB dysfunction. However, these other applications need additional validation. Although these cerebral events and their corresponding changes in neurochemistry are important, other promising MD applications, as yet less explored, comprise local neurochemical provocations, drug penetration to the human brain, MD as a tool in clinical drug trials, and for studying the proteomics of acute human brain injury. Nevertheless, MD has provided new important insights into the neurochemistry of acute human brain injury. It remains one of very few methods for neurochemical measurements in the interstitial compartment of the human brain and will continue to be a valuable translational research tool for the future. Therefore, this technology has the potential of becoming an established part of multimodality neuro-ICU monitoring, contributing unique information about the acute brain injury process. However, in order to reach this stage, several issues related to quantification and bedside presentation of MD data, implantation strategies, and quality assurance need to be resolved. The future success of MD as a diagnostic tool in clinical neurosurgery depends heavily on the choice of biomarkers, their sensitivity, specificity, and predictive value for secondary neurochemical events, and the availability of practical bedside methods for chemical analysis of the individual markers. The purpose of this review was to summarize the results of clinical studies using cerebral MD in neurosurgical patients and to discuss the current status of MD as a potential method for use in clinical decision-making. The approach was to focus on adverse neurochemical conditions in the injured human brain and the MD biomarkers used to study those events. Methodological issues that appeared critical for the future success of MD as a routine intracerebral sampling method were addressed.

Réunion de neuroanesthésie-réanimation. Prise en charge anesthésique du patient en hypertension intracrânienne aiguë

Transcranial Doppler and, if possible, measurement of intracranial pressure (ICP) allow preoperative diagnosis of acute intracranial hypertension (ICH) after brain trauma. The main goal of the anaesthesiologist is to prevent the occurrence of secondary brain injuries and to avoid cerebral ischaemia. Treatment of high ICP is mainly achieved with osmotherapy. High-dose mannitol administration (1.4 to 2 g/kg given in bolus doses) may be considered a better option than conventional doses, especially before emergency evacuation of a cerebral mass lesion. Hypertonic saline seems as effective as mannitol without rebound effect and without diuresis increase. Haemostasis should be normalized before neurosurgery and invasive blood pressure monitoring is mandatory. For anaesthesia induction, thiopental or etomidate may be used. In case of ICH, halogenated and nitrous oxide should be avoided. Until the dura is open, mean arterial pressure should be maintained around 90 mmHg (or cerebral perfusion pressure around 70 mmHg). If a long-lasting (several hours) extracranial surgery is necessary, ICP should be monitored and treatment of ICH should have been instituted before.

Management of Increased Intracranial Pressure in the Critically Ill Child With an Acute Neurological Injury

Increased intracranial pressure reflects the presence of mass effect in the brain and is associated with a poor outcome in children with acute neurological injury. If sustained, it has a negative effect on cerebral blood flow and cerebral perfusion pressure, can cause direct compression of vital cerebral structures, and can lead to herniation. The management of the patient with increased intracranial pressure involves the maintenance of an adequate cerebral perfusion pressure, prevention of intracranial hypertension, and optimization of oxygen delivery. This article reviews the neurological assessment, pathophysiology, and management of increased intracranial pressure in the critically ill child who has sustained an acute neurological injury.

Effect of mild hypothermia on brain dialysate lactate after fluid percussion brain injury in rodents

OBJECTIVE

To investigate the effects of mild hypothermia on brain microdialysate lactate after fluid percussion traumatic brain injury (TBI) in rats.

METHODS

Brain dialysate lactate before and after fluid percussion brain injury (2.1 +/- 0.2 atm) was measured in rats with preinjury mild hypothermia (32 degrees C), postinjury mild hypothermia (32 degrees C), injury normothermia (37 degrees C), and the sham control group. Mild hypothermia (32 degrees C) was induced by partial immersion in a water bath (0 degrees C) under general anesthesia and maintained for 2 hours.

RESULTS

In the normothermia TBI group, brain extracellular fluid lactate increased from 0.311 +/- 0.03 to 1.275 +/- 0.08 mmol/L within 30 minutes after TBI (P < 0.01) and remained at a high level (0.546 +/- 0.05 mmol/L) (P < 0.01) at 2 hours after injury. In the postinjury mild hypothermic group, brain extracellular fluid lactate increased from 0.303 +/- 0.03 to 0.875 +/- 0.05 mmol/L at 15 minutes after TBI (P < 0.01) and then gradually decreased to 0.316 +/- 0.04 mmol/L at 2 hours after TBI (P > 0.05). In the preinjury mild hypothermic group, brain extracellular fluid lactate remained at normal levels after injury (P > 0.05).

CONCLUSION

The cerebral extracellular fluid lactate level increases significantly after fluid percussion brain injury. Preinjury mild hypothermia completely inhibits the cerebral lactate accumulation, and early postinjury mild hypothermia significantly blunts the increase of cerebral lactate level after fluid percussion injury.

Choice of anesthetics

The choice of anesthetics for vascular surgical patients is not only determined by the kind and extent of the surgical procedure but also by patient comorbidities. Frequently, patients have a history of hypertension, peripheral vascular and coronary artery disease,cerebrovascular disease, and renal impairment. The goal of the chosen anesthetic technique is to protect organ function, mainly of the brain and the heart. In some instances regional anesthesia might be preferred, but no difference in outcome between the two techniques has been shown conclusively. Vascular emergencies are particularly challenging for the anesthesiologist, but in recent years the development of stent graft insertion has improved the short-term outcome in many of these procedures.

Acute intraoperative cerebral oedema: are current therapies evidence based?

Acute intraoperative ischaemic cerebral oedema following torrential haemorrhage from the left intracranial internal carotid artery occurred during resection of a recurrent middle cranial fossa meningioma. A series of immediate anaesthetic interventions was effective in reducing brain oedema, allowed for surgical haemostasis, and resulted in no permanent sequelae to patient outcome. A review of the literature indicates that direct evidence for the efficacy of extremely early interventions as described in this case report is lacking and must be extrapolated from other brain injury models.

Increased S-nitrosothiols and S-nitrosoalbumin in cerebrospinal fluid after severe traumatic brain injury in infants and children: indirect association with intracranial pressure

Nitric oxide (NO) is implicated in both secondary damage and recovery after traumatic brain injury (TBI). Transfer of NO groups to cysteine sulfhydryls on proteins produces S-nitrosothiols (RSNO). S-nitrosothiols may be neuroprotective after TBI by nitrosylation of N-methyl-D-aspartate receptor and caspases. S-nitrosothiols release NO on decomposition for which endogenous reductants (i.e., ascorbate) are essential, and ascorbate is depleted in cerebrospinal fluid (CSF) after pediatric TBI. This study examined the presence and decomposition of RSNO in CSF and the association between CSF RSNO level and physiologic parameters after severe TBI. Cerebrospinal fluid samples (n = 72) were obtained from 18 infants and children on days 1 to 3 after severe TBI (Glasgow Coma Scale score < 8) and 18 controls. Cerebrospinal fluid RSNO levels assessed by fluorometric assay peaked on day 3 versus control (1.42 +/- 0.11 micromol/L vs. 0.86 +/- 0.04, P< 0.05). S-nitrosoalbumin levels were also higher after TBI (n = 8, 0.99 +/- 0.09 micromol/L on day 3 vs. n = 6, 0.42 +/- 0.02 in controls, P< 0.05). S-nitrosoalbumin decomposition was decreased after TBI. Multivariate analysis showed an inverse relation between CSF RSNO and intracranial pressure and a direct relation with barbiturate treatment. Using a novel assay, the presence of RSNO and S-nitrosoalbumin in human CSF, an approximately 1.7-fold increase after TBI, and an association with low intracranial pressure are reported, supporting a possible neuroprotective role for RSNO. The increase in RSNO may result from increased NO production and/or decreased RSNO decomposition.

Effect of hyperventilation on extracellular concentrations of glutamate, lactate, pyruvate, and local cerebral blood flow in patients with severe traumatic brain injury

OBJECTIVE

To determine the potential adverse effects of brief periods of hyperventilation commonly used for acute neurologic deterioration.

DESIGN

Prospective clinical trial.

SETTING

University medical school.

PATIENTS

Twenty patients with severe traumatic brain injury.

INTERVENTIONS

The effect of 30 mins of hyperventilation (mean PaCO2, 24.6 mm Hg) on the extracellular metabolites associated with ischemia, and on local cerebral blood flow was studied by using microdialysis and local cerebral blood flow techniques. Normal appearing brain adjacent to evacuated hemorrhagic contusions or underlying evacuated subdural hematomas was studied. Hyperventilation trials were done 24-36 hrs after injury and again at 3-4 days after injury. Dialysate concentrations of glutamate, lactate, and pyruvate were measured before and for 4 hrs after the hyperventilation trials.

MEASUREMENTS AND MAIN RESULTS

At 24-36 hrs, hyperventilation led to a >or=10% increase in the extracellular concentrations of glutamate in 14 of 20 patients, with concentrations in those 14 patients 13.7-395% above baseline; a >or=10% increase in lactate in 7 of 20 patients (11.6-211% above baseline); and a >or=10% increase in the lactate/pyruvate ratio in eight of 20 patients (10.8-227% above baseline). At 3-4 days after injury, ten of 13 patients had an increase in glutamate of >or=10%, while only three of 13 patients had an increase in extracellular lactate and two of 13 patients had an increase in the lactate/pyruvate ratio of this magnitude. The hyperventilation associated increases in extracellular glutamate and lactate concentrations were significant ( P<.05; one-sample Student's -test) at both time points after injury, as was the lactate/pyruvate ratio at 24-36 hrs. A >or=10% decline in local cerebral blood flow was observed with hyperventilation in five of 20 patients at 24-36 hrs (range, 10.2-18.7% below baseline), and in ten of 13 patients studied at 3-4 days (11.3-54% below baseline). There was no correlation with the presence or absence of local CO2 vasoresponsivity and increases in the extracellular metabolites at either the early or late time points.

CONCLUSIONS

In brain tissue adjacent to cerebral contusions or underlying subdural hematomas, even brief periods of hyperventilation can significantly increase extracellular concentrations of mediators of secondary brain injury. These hyperventilation-induced changes are much more common during the first 24-36 hrs after injury than at 3-4 days.

Multi-modal monitoring of acute brain injury

OBJECTIVE

To review the scientific basis for and utility of the traditional cerebral monitors used currently in neurointensive care, together with research techniques that are soon likely to become used in managing severe head injury and subarachnoid haemorrhage.

DESIGN AND CONTENT

Firstly, the pathophysiology of acute brain injury including cerebral haemodynamics, oxygen and metabolism and the role of secondary insults are discussed. Secondly, the importance of assessment of cerebrovascular autoregulation and reactivity is reviewed together with methods for its continuous non-invasive measurement using transcranial Doppler and intracranial pressure/arterial pressure recordings. Thirdly, the respective roles of jugular venous oxygen and brain tissue oxygen monitoring are analysed. Fourthly, the use of cerebral microdialysis is described, together with an overview of its utility.

CONCLUSION

Cerebral multimodal monitoring can be helpful for the optimal management of acute brain injury and essential for future exploratory trials of neuroprotective drugs.

How can we measure substrate, metabolite and neurotransmitter concentrations in the human brain?

Cerebral injury and disease is associated with fundamental derangements in metabolism, with changes in the concentration of important substrates (e.g. glucose), metabolites (e.g. lactate) and neurotransmitters (e.g. glutamate and y-aminobutyric acid) in addition to changes in oxygen utilization. The ability to measure these substances in the human brain is increasing our understanding of the pathophysiology of trauma, stroke, epilepsy and tumours. There are several techniques in clinical practice already in use and new methods are under evaluation. Such techniques include the use of cerebral probes (e.g. microdialysis. voltammetry and spectrophotometry) and functional imaging (e.g. positron emission tomography and magnetic resonance spectroscopy). This review describes these techniques in terms of their principles and clinical applications.

Advanced monitoring in the neurology intensive care unit: microdialysis

Cerebral microdialysis is a relatively new technique for measuring the levels of brain extracellular chemicals, which to date has predominantly been used as a research tool. This review considers the technical aspects of microdialysis, the importance of the commonly measured chemicals, and the use of microdialysis to monitor patients with ischemic stroke, head injury, and subarachnoid hemorrhage. The advantages and disadvantages of microdialysis are discussed, as is its future potential.

Neurointensive care of the nonaccidentally injured child

Childhood victims of NAT with severe brain injury require a multidisciplinary approach to their management if a good outcome is to occur. Despite the grave prognosis of these patients, an initial aggressive treatment strategy is warranted, because enough children go on to a meaningful life. A vigilant evaluation for multisystem injuries and vigorous resuscitation should be followed by prompt surgical intervention as indicated. Most NAT victims do not require surgical treatment of their brain injury, but do require ICP monitoring. A stepwise approach to the treatment of elevated ICP optimizes CPP, minimizes secondary brain injury, and increases the chances of a meaningful recovery. The future holds promise for these patients because a concerted effort is underway to understand pediatric TBI on a molecular level, and targeted therapies based on current basic research will certainly improve the neurointensive care, and eventual neurologic outcomes, of these children.

Amino acid concentrations in the blood of the jugular vein and peripheral artery after traumatic brain injury: decreased release of glutamate into the jugular vein in the early phase

The gross behavior of excitatory amino acids in patients with traumatic brain injury (TBI), including uptake, transport, metabolism, and clearance, was investigated by analysis of the levels of 41 amino acids in the blood of the jugular vein (JV), which is the primary venous drainage conduit of the brain, and a peripheral artery. Blood samples from the JV and a peripheral artery of eight patients with TBI were collected at 6 h, 6 to 24 h, and over 24 h after TBI, and analyzed using high performance liquid chromatography. Blood samples from 101 normal subjects were also measured. The levels of glutamate (Glu), gamma-aminobutyric acid (GABA), aspartate, glutamine, and cystine deviated from the normal range, and were considered pathological. The level of Glu in the JV was significantly lower than that in the artery (p < 0.05), and the level of GABA in the JV was significantly higher than that in the artery (p < 0.01), but the other three amino acids showed no significant differences. Significantly chronological changes in the difference between the blood levels in the JV and artery were observed for Glu. Measurement of the Glu level in the JV and artery may indicate gross metabolic change in the brain following TBI.

Evidence for lactate uptake after rat fluid percussion brain injury

Traumatic brain injury (TBI) places enormous early energy demand on brain tissue to reinstate normal ionic balance. Glucose declines and lactate increases after TBI as demonstrated in clinical and lab studies, suggesting increased glycolysis. This led us to hypothesize that high extracellular fluid (ECF) lactate may be beneficial after TBI. We measured cerebral dialysate lactate and glucose, and arterial lactate and glucose, before & after rat Fluid Percussion Injury (FPI) (2.06 +/- 0.13 atm) with and without i.v. lactate infusion (100 mM x 4.5 hours) to test the hypotheses that arterial lactate determines ECF lactate. 14C-lactate autoradiography was also performed, to demonstrate whether lactate is taken up by traumatized brain.

RESULTS

Dialysate lactate was always significantly higher than arterial. After lactate infusion, both the dialysate and the arterial lactate were significantly increased (P < 0.0001). Dialysate lactate increased within 10 min. following FPI, with significantly higher values in the lactate infusion group (82% higher with lactate infusion after FPI). Dialysate glucose fell following FPI, with a more severe decline in the saline group (129% lower), suggesting lactate infusion preserves or "spares" glucose in ECF. In our autoradiographic study, i.v. 14C-lactate accumulated at the injury site, with levels 2-4 times higher than in contralateral cortex. In conclusion, arterial lactate augmentation thus increases brain dialysate lactate and results in less reduction in ECF glucose, after FPI. Infused lactate accumulates at the injury site, where metabolism is probably the greatest.