Early ischaemia after severe head injury. Preliminary results in patients with diffuse brain injuries

Anemia management after acute brain injury

Anemia is frequent among brain-injured patients, where it has been associated with an increased risk of poor outcome. The pathophysiology of anemia in this patient population remains multifactorial; moreover, whether anemia merely reflects a higher severity of the underlying disease or is a significant determinant of the neurological recovery of such patients remains unclear. Interestingly, the effects of red blood cell transfusions (RBCT) in moderately anemic patients remain controversial; although hemoglobin levels are increased, different studies observed only a modest and inconsistent improvement in cerebral oxygenation after RBCT and raised serious concerns about the risk of increased complications. Thus, considering this "blood transfusion anemia paradox", the optimal hemoglobin level to trigger RBCT in brain-injured patients has not been defined yet; also, there is insufficient evidence to provide strong recommendations regarding which hemoglobin level to target and which associated transfusion strategy (restrictive versus liberal) to select in this patient population. We summarize in this review article the more relevant studies evaluating the effects of anemia and RBCT in patients with an acute neurological condition; also, we propose some potential strategies to optimize transfusion management in such patients.

Physiopathology of anemia and transfusion thresholds in isolated head injury

BACKGROUND

Blood transfusion strategies among patients with critical illness use a restrictive hemoglobin threshold. However, among patients with head injury, no outcome differences have been shown between either liberal or restrictive strategies. Several studies and literature reviews suggest that anemia is associated with markers of tissue ischemia. The paucity of prospective data confuses the association between surrogates of tissue ischemia and neurological outcome.

METHODS

A narrative review of transfusion practices among patients in the acute phase of head injury was performed using PubMed, MEDLINE, EMBASE, Cochrane, and WEB of Science databases. A total of 104 articles were reviewed.

RESULTS

There are few data to guide clinical practice. Clinicians use blood hemoglobin concentrations to trigger transfusion. Markers of potential cerebral injury are not in regular use despite experimental and observational data rising from histologic examination, microdialysis, oximetry, and flow-based multimonitoring systems recommending their use to titrate blood transfusion in neurotrauma.

CONCLUSION

The generalization of transfusion triggers is common practice. Evidence-based approaches to transfusions strategies in head injury are lacking and not based on an understanding of cerebral physiopathology.

Controversies in the management of adults with severe traumatic brain injury

Despite progress in the management of adults with severe traumatic brain injury, several controversies persist. Among the unresolved issues of greatest concern to neurocritical care clinicians and scientists are the following: (1) the best use of technological advances and the data obtained from multimodality monitoring; (2) the use of mannitol and hypertonic saline in the management of increased intracranial pressure; (3) the use of decompressive craniectomy and barbiturate coma in refractory increased intracranial pressure; (4) therapeutic hypothermia as a neuroprotectant; (5) anemia and the role of blood transfusion; and (6) venous thromboembolism prophylaxis in severe traumatic brain injury. Each of these strategies for managing severe traumatic brain injury, including the postulated mechanism(s) of action and beneficial effects of each intervention, adverse effects, the state of the science, and critical care nursing implications, is discussed.

Anemia and red blood cell transfusion in neurocritical care

INTRODUCTION

Anemia is one of the most common medical complications to be encountered in critically ill patients. Based on the results of clinical trials, transfusion practices across the world have generally become more restrictive. However, because reduced oxygen delivery contributes to 'secondary' cerebral injury, anemia may not be as well tolerated among neurocritical care patients.

METHODS

The first portion of this paper is a narrative review of the physiologic implications of anemia, hemodilution, and transfusion in the setting of brain-injury and stroke. The second portion is a systematic review to identify studies assessing the association between anemia or the use of red blood cell transfusions and relevant clinical outcomes in various neurocritical care populations.

RESULTS

There have been no randomized controlled trials that have adequately assessed optimal transfusion thresholds specifically among brain-injured patients. The importance of ischemia and the implications of anemia are not necessarily the same for all neurocritical care conditions. Nevertheless, there exists an extensive body of experimental work, as well as human observational and physiologic studies, which have advanced knowledge in this area and provide some guidance to clinicians. Lower hemoglobin concentrations are consistently associated with worse physiologic parameters and clinical outcomes; however, this relationship may not be altered by more aggressive use of red blood cell transfusions.

CONCLUSIONS

Although hemoglobin concentrations as low as 7 g/dl are well tolerated in most critical care patients, such a severe degree of anemia could be harmful in brain-injured patients. Randomized controlled trials of different transfusion thresholds, specifically in neurocritical care settings, are required. The impact of the duration of blood storage on the neurologic implications of transfusion also requires further investigation.

Hyperoxia: good or bad for the injured brain?

PURPOSE OF REVIEW

For decades it was assumed that cerebral ischemia was a major cause of secondary brain injury in traumatic brain injury, and management focused on improving cerebral perfusion and blood flow. Following the observation of mitochondrial dysfunction in traumatic brain injury and the widespread use of brain tissue oxygen tension (P(br)O(2) monitoring, however, recent work has focused on the use of hyperoxia to reduce the impact of traumatic brain injury.

RECENT FINDINGS

Previous work on normobaric hyperoxia utilized very indirect measures of cerebral oxygen metabolism (intracranial pressure, brain oxygen tension and microdialysis) as outcome variables. Interpretation of these measures is controversial, making it difficult to determine the impact of hyperoxia. A recent study, however, utilized positron emission tomography to study the impact of hyperoxia on patients with acute severe traumatic brain injury and found no improvement on cerebral metabolic rate for oxygen with this intervention.

SUMMARY

Despite suggestive data from microdialysis studies, direct measurement of the ability of the brain to utilize oxygen indicates that hyperoxia does not increase oxygen utilization. This, combined with the real risk of oxygen toxicity, suggests that routine clinical use is not appropriate at this time and should await appropriate prospective outcome studies.

Cerebral arterio-venous pCO2 difference, estimated respiratory quotient, and early posttraumatic outcome: comparison with arterio-venous lactate and oxygen differences

Arterio-venous pCO2 difference (AVDpCO2) and estimated respiratory quotient, the ratio between AVDpCO2 and arterio-venous O2 difference, may be potentially useful estimators of irreversible posttraumatic global cerebral ischemia. Our aim was to evaluate their relevance, along with arterio-venous lactate difference (AVDL) and lactate oxygen index (LOI), in early outcome prediction. The retrospective study involved 55 patients with severe head injury, admitted consecutively in a multidisciplinary intensive care unit of a general hospital. A retrograde jugular catheter was placed as soon as possible, allowing for 324 simultaneous arterio-jugular samples to be taken throughout the first 48-hour postinjury. Early brain death (within 48 h) was assumed to be due to early global ischemia. A multivariate model including clinical and radiologic descriptors and jugular bulb variables showed that a widening of AVDL and LOI was associated with early brain death. Whereas in the patients who died, a progressive worsening of AVDpCO2 and estimated respiratory quotient, associated with corresponding changes in AVDL and LOI were observed, in patients who survived the widening of AVDpCO2 normalized along with that of arterio-venous O2 difference. These findings suggest that the isolated measurement of widening AVDpCO2 is not specific for global cerebral ischemia, but its observation over time could be potentially more useful.

Assessment of intra-cranial pressure after severe traumatic brain injury by transcranial Doppler ultrasonography

PRIMARY OBJECTIVE

To investigate the potential of transcranial Doppler ultrasonography in estimating post-traumatic intra-cranial pressure early after severe traumatic brain injury.

RESEARCH DESIGN

The group of 24 patients was analysed for the observation of an early post-traumatic cerebral haemodynamic by middle cerebral artery blood velocity measuring.

METHODS AND PROCEDURES

The standard method of measuring the mean blood middle cerebral artery velocity by transcranial Doppler ultrasonic device was performed.

MAIN OUTCOMES AND RESULTS

The increased duration of intra-cranial hypertension correlated to the middle cerebral artery low blood velocity (p = 0.042; r = -0.498) (n = 17) and to elevated pulsatility indices (p = 0.007; r = 0.753) (n = 11) significantly. The increased duration of lowered cerebral perfusion pressure correlated to the middle cerebral artery low blood velocity significantly (p = 0.001; r = -0.619) (n = 24).

CONCLUSIONS

The significance of transcranial Doppler ultrasonography as a method to estimate an early post-traumatic intra-cranial pressure after severe brain injury was confirmed. This simple and non-invasive technique could be easily used in daily clinical practice and precede intra-cranial pressure monitoring in selected patients.

Clinical outcome of severe head injury in different protocol-driven therapies

In the past 5 years cerebral perfusion pressure (CPP) management has become mainstream in the treatment of severe head injuries. The American Association of Neurological Surgeons guidelines (2000) suggest that CPP should be maintained at least 70 mmHg; however, there is still debate about optimal CPP level. The purpose of this study is to evaluate the effectiveness of three widely used therapies: intracranial pressure (ICP)-targeted therapy, CPP-targeted therapy with CPP > 70 mmHg, and modified CPP-targeted therapy with CPP > 60 mmHg. The clinical procedures, complications, and patient outcomes are compared. Data including patient age, sex, initial Glasgow Coma Score (GCS), ICP, CPP, fluid status, amount of mannitol and vasopressor used, daily intake and output, complications, and clinical results were collected from 213 patients with severe head injuries over a 12-year period. Patients were categorized into three groups (ICP, CPP, modified CPP [mCPP]) according to treatment protocol used. Retrospective data collection was by chart review. The mortality rate was 28.6%, 14.3%, and 13.5% in groups ICP, CPP, and mCPP, respectively. Highest intake/output ratio, amount of vasopressor used, and pulmonary complication rates were seen in group CPP patients. Group mCPP patients showed the best clinical outcome and lowest complication rate. Though CPP-targeted therapy is the most recommended therapeutic protocol, our data showed that the outcome is as good in the mCPP-targeted group with CPP > 60 mmHg as in the CPP-targeted group, but complications are fewer in the mCPP group.

Lack of utility of arteriojugular venous differences of lactate as a reliable indicator of increased brain anaerobic metabolism in traumatic brain injury

Object

Ischemic lesions are highly prevalent in patients with traumatic brain injuries (TBIs) and are the single most important cause of secondary brain damage. The prevention and early treatment of these lesions is the primary aim in the modern treatment of these patients. One of the most widely used monitoring techniques at the bedside is quantification of brain extracellular level of lactate by using arteriojugular venous differences of lactate (AVDL). The purpose of this study was to determine the sensitivity, specificity, and predictive value of AVDL as an indicator of increases in brain lactate production in patients with TBIs.

Methods

Arteriojugular venous differences of lactate were calculated every 6 hours using samples obtained though a catheter placed in the jugular bulb in 45 patients with diffuse head injuries (57.8%) or evacuated brain lesions (42.2%). Cerebral lactate concentration obtained with a 20-kD microdialysis catheter implanted in undamaged tissue was used as the de facto gold standard.

Six hundred seventy-three AVDL determinations and cerebral microdialysis samples were obtained simultaneously; 543 microdialysis samples (81%) showed lactate values greater than 2 mmol/L, but only 21 AVDL determinations (3.1%) showed an increase in brain lactate. No correlation was found between AVDL and cerebral lactate concentration (ρ = 0.014, p = 0.719). Arteriojugular venous differences of lactate had a sensitivity and specificity of 3.3 and 97.7%, respectively, with a false-negative rate of 96.7% and a false-positive rate of 2.3%.

Conclusions

Arteriojugular venous differences of lactate do not reliably reflect increased cerebral lactate production and consequently are not reliable in ruling out brain ischemia in patients with TBIs. The clinical use of this monitoring method in neurocritical care should be reconsidered.

Clinical outcome of severe head injury using three different ICP and CPP protocol-driven therapies

In the past 5 years, cerebral perfusion pressure (CPP) management has become the standard in the treatment of severe head injuries. Guidelines published in 2000 suggest that CPP should be at least 70 mmHg; however, there is still debate about the optimal CPP. The purpose of the present study was to evaluate the effectiveness of these three widely used therapies: (i) intracranial pressure (ICP) targeted; (ii) CPP-targeted with CPP >70 mmHg; and (iii) modified CPP-targeted (mCPP) therapy with CPP >60 mmHg. The clinical procedures, complications and outcomes of patients in the different groups were compared. Data, including patient age, sex, initial Glasgow Coma Scale, ICP, CPP, fluid status, amount of mannitol and vasopressor used, daily fluid intake and output, complications and clinical results, were collected from 213 patients with severe head injuries over a 12-year period. Patients were categorized into three groups (ICP, CPP, mCPP) according to the treatment protocol used. Retrospective data collection was performed by chart review. The mortality rate was 28.6%, 14.3% and 13.5% in the ICP, CPP, and mCPP groups, respectively. Highest intake/output ratio, amount of vasopressor used and pulmonary complications were seen in the CPP patients. The mCPP patients showed the best clinical outcome and lowest complication rate. Although CPP-targeted therapy is the most recommended therapeutic protocol, our data show that patients treated with modified CPP-target therapy with CPP >60 mmHg have better clinical outcomes and fewer complications.

Quantitation of ischemic events after severe traumatic brain injury in humans: a simple scoring system

BACKGROUND

Cerebral ischemia is recognized as one of the most important mechanisms responsible for secondary brain damage following severe traumatic brain injury (TBI), contributing to an increased mortality and a worse neurologic outcome.

METHOD

A simple 5-item scoring system, taking into account the occurrence of specific potentially brain-damaging events (hypoxemia, hypotension, low cerebral blood flow, herniation, and low cerebral perfusion pressure) has been tested in a large population of severe TBI patients. Aims of this retrospective study were to validate the ability of the proposed ischemic score to predict neurologic outcome and to correlate the ischemic score with the results of microdialysis-based neurochemical monitoring and brain tissue oxygen monitoring.

FINDINGS

In a population of 172 severe TBI patients, a significant correlation was found between ischemic score and neurologic outcome, both at 3 months (r = -0.32; P < 0.01) and at 6 months (r = -0.31; P < 0.01). Significant correlations were also found with the most important neurochemical analytes.

CONCLUSIONS

The ischemic score proposed here, may be determined during the acute intensive care unit period, and correlates closely with outcome, which can only be determined 3 to 6 months, after injury. It also shows a correlation with neurochemical analytes.

Hyperventilation in head injury: a review

The aim of this review was to consider the effects of induced hypocapnia both on systemic physiology and on the physiology of the intracranial system. Hyperventilation lowers intracranial pressure (ICP) by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume. The downside of hyperventilation, however, is that cerebral vasoconstriction may decrease cerebral blood flow to ischemic levels. Considering the risk-benefit relation, it would appear to be clear that hyperventilation should only be considered in patients with raised ICP, in a tailored way and under specific monitoring. Controversy exists, for instance, on specific indications, timing, depth of hypocapnia, and duration. This review has specific reference to traumatic brain injury, and is based on an extensive evaluation of the literature and on expert opinion.

Delayed bilateral craniectomy for treatment of traumatic brain swelling in children: case report and review of the literature

INTRODUCTION

Head injury is the leading cause of accidental death in children. Recent reports have shown the benefit of decompressive craniectomy in children and the role of early timing has been emphasized. However, there is still a lack of data to determine the optimal time for performing craniectomy.

CASE REPORT

In contrast to most reports in the literature, this case report demonstrates successful bilateral decompressive craniectomy in a 10-year-old girl with multiple posttraumatic intracranial lesions and massive traumatic brain swelling on the 8th posttraumatic day.

CONCLUSIONS

Various pathophysiological mechanisms in the genesis of posttraumatic brain swelling make different treatment strategies necessary. Continuous monitoring of intracranial pressure (ICP), as well as serial cranial computed tomography (CCT), can help to differentiate between these mechanisms. Furthermore, repeated clinical and neurophysiological investigations are important for the timing of craniectomy.

Delayed Precursor Cell Markers Expression in Hippocampus following Cold-Induced Cortical Injury in Mice

The purpose of this study was to examine the possibility of neuronal remodeling and repair after cold-induced brain injury using immunoassay of nestin and 3CB2 (potential precursor cell markers). Male ddN strain mice were subjected to cold-induced cortical injury. Animals were divided into the following six groups: (1) 1 day after injury, (2) 1 week after injury, (3) 2 weeks after injury, (4) 1 month after injury, (5) sham controls, and (6) normal controls. Western blot analysis (n = 3 in each group) and histological examination (n = 5 in each group) were performed. At 1 day and 1 week after injury, TUNEL-positive cells were observed, while immunoreactivity of nestin and 3CB2 was absent. At 1 month after injury, expression of both nestin and 3CB2 was observed in the ipsilateral hippocampus. Nestin was expressed in GFAP- or 3CB2-positive astrocytes at 1 month after injury, and nestin expression with TUC-4 (immature neuron marker) was present in the hippocampal cell layer. The findings demonstrate delayed nestin expression in both glia and neuronlike cells after brain injury. The present study suggests that the delayed nestin expression in glia and neuron-like cells might be part of the adaptation to injury.

Assessment of jugular blood oxygen and lactate indices for detection of cerebral ischemia and prognosis

Levels of jugular blood oxygen saturation (SjvO2) and lactate have been proposed as indicators of cerebral ischemia and prognosis. However, sensitivity and specificity of these markers remain unknown. We retrospectively analyzed records of a series of 43 comatose patients at risk for cerebral ischemia, mainly after head injuries or subarachnoidal hemorrhage. Their SjvO2, jugulo-arterial lactate difference (VADLactate), and lactate-oxygen index (LOI) were determined every 8 hours. An increase in VADLactate and LOI was found, indicative of ischemia on CT scan, with threshold values of 0.30 mmol/L and 0.15, respectively. Sensitivity and specificity were 100% and 64%, respectively, for the VADLactate threshold, and 90% and 55%, respectively, for the LOI threshold. Regarding prediction of a poor outcome, only an increase in VADLactate had a predictive value with a sensitivity of 100% and specificity of 67%. No threshold value with sufficient sensitivity and specificity was found for SjvO2, as indicator of either ischemia or outcome. During progression to brain death, VADLactate and LOI reached abnormal levels earlier than cerebral perfusion pressure or SjvO2. They reacted markedly to focal ischemia due to vasospasm. Hyperlactacidemia rendered VADLactate and LOI uninterpretable by causing a brain lactate influx. Present data, if confirmed by a prospective study, would justify inclusion of intermittent VADLactate and LOI determinations in the multimodal cerebral monitoring.

ICP threshold in CPP management of severe head injury patients

BACKGROUND

Elevated intracranial pressure (ICP) is significantly associated with high mortality rate in severe head injury (SHI) patients. However, there is no absolute agreement regarding the level at which ICP must be treated. The objective of this study was to compare the outcomes of severe head injury patients treated by setting the ICP threshold at >or=20 mm Hg or >or=25 mm Hg.

METHODS

Treatment protocol in this study consisted of therapeutic maneuvers designed to maximize cerebral profusion pressure (CPP) and control ICP. Twenty-seven patients with severe head injury and intracranial hypertension (ICP >or=20 mm Hg) were enrolled and fourteen cases were allocated to the group of ICP threshold >or=25 mm Hg. Six-month clinical outcomes were evaluated using the Glasgow Outcome Score (GOS).

RESULTS

There were no statistically significant differences in clinical parameters between the groups. Logistic regression identified the presence of basal cisterns on the initial computed tomography (CT) scan as a significant predictor of good outcome. ICP threshold did not influence outcome.

CONCLUSIONS

This study supported a recommended ICP threshold of 20 to 25 mm Hg in SHI management. However, in cases with an absence of basal cisterns on initial CT scan, the probability of good outcome may be higher using an ICP threshold of >or=20 mm Hg.

Detection of early ischemia in severe head injury by means of arteriovenous lactate differences and jugular bulb oxygen saturation. Relationship with CPP, severity indexes and outcome. Preliminary analysis

Early ischemia may be highly relevant in patients with severe head injuries. The aims of the study were: 1) to define if abnormal arteriovenous lactate difference (AVDL) and jugular bulb oxygen saturation (SjO2) are found in the early 24 hrs post injury; 2) to compare if abnormalities of SjO2 and of AVDL were associated with a specific typology of severity indexes and outcome; 3) to detect any association between abnormal AVDL and SjO2 with levels of cerebral perfusion pressure (CPP). The study involved 29 patients, with CPP, AVDL and SjO2 measured within 24 hours post-injury.

RESULTS

1) Abnormal AVDL was found in 21% while abnormal SjO2 was detected in 38% of the patients; 2) abnormal AVDL was associated with cases of most severe injury; 3) CPP level below 60 mmHg was associated with abnormal AVDL and SjO2. Low CPP appeared to be the most likely measurable cause of early ischemia. Abnormalities of AVDL appeared to be more sensitive, than SjO2, with regard to detection of the most severe cases.

The traveling intensive care unit patient. Road trips

Transport of critically ill or injured patients in the hospital is a necessary part of ICU care. Although the overall severity of misadventures occurring during patient transfer is minimal, potential complications risk patient deterioration in settings that may not be equipped to handle cardiovascular, respiratory, or neurologic emergencies safely. The critical care team should provide the same level of monitoring and care to the transported patient outside the ICU as he or she receives the unit. Each hospital should have a system that meets acceptable standards for safe transfer of the ICU patient, which minimizes risk and maximizes diagnostic and treatment yield.

Failure of cerebral autoregulation in an experimental diffuse brain injury model

The normal cerebral circulation has the ability to maintain a stable cerebral blood flow over a wide range of cerebral perfusion pressures and this is known as cerebral autoregulation. Autoregulation may be impaired in the injured brain. Closed head injury was induced in 28 Sprague-Dawley rats weighing 400-450 g. Four groups were studied: control and groups, head injured by weight drop from one meter height using 350 g, 400 g and 450 g respectively. CBF was monitored using laser-Doppler flowmetry along with monitoring of ICP and arterial blood pressure. If the correlation coefficient between CBF and CPP was > 0.85 and CPP was within normal range, loss of autoregulation was hypothesized. Loss of autoregulation was seen in all groups of injured rats during first four hours. A statistically significant difference (p = 0.041) was seen in the trequency of loss of autoregulation between injured and control animals. No loss of autoregulation was observed in the control group. In conclusion CBF and CPP provide information about loss of autoregulation in diffuse brain injury. Decrease in CBF and increase of ICP is observed as a result of loss of cerebral autoregulation. Knowledge of loss of autoregulation could help in the management of head injured patients.

Cerebral perfusion changes in traumatic diffuse brain injury; IMP SPECT studies

Diffuse brain injury (DBI) is characterized by axonal degeneration and neuronal damage which cause diffuse brain atrophy. We have investigated the time course of abnormalities in cerebral perfusion distribution in cases of DBI by using Iodine-123-IMP SPECT, and the relationship to the appearance of diffuse brain atrophy. SPECT scans were performed on eight patients with diffuse brain injury due to closed cranial trauma in acute and chronic stages. All patients showed abnormalities in cerebral perfusion with decreases in perfusion, even in non-depicted regions on MRI, and the affected areas varied throughout the period of observation. Diffuse brain atrophy appeared in all patients. In some patients, diffuse brain atrophy was observed at or just after the time when the maximum number of lesions on SPECT were seen. The abnormalities in cerebral perfusion in cases of DBI might therefore be related to axonal degeneration and neuronal damage which causes diffuse brain atrophy.

Identification of posttraumatic ischemia and hyperperfusion by determination of the effect of induced arterial hypertension on carbon dioxide reactivity

BACKGROUND AND PURPOSE

Both ischemia and hyperperfusion are known phenomena that follow traumatic brain injury. Cerebral carbon dioxide reactivity is diminished in both conditions. Differentiation is important because ischemia is thought to be a major factor of secondary neuronal loss and is potentially amenable to therapy by manipulation of cerebral perfusion pressure.

METHODS

The response of transcranial Doppler-based carbon dioxide reactivity to pharmacologically induced hypertension was studied sequentially in 29 patients with severe to moderate head injury to identify ischemia and luxury perfusion. After simultaneous baseline registration of the carbon dioxide reactivity of both middle cerebral arteries by two-channel transcranial Doppler, systolic arterial pressure was raised approximately 20 mm Hg by means of phenylephrine (Neosynephrine) infusion, and the carbon dioxide reactivity test was repeated.

RESULTS

A significant improvement of impaired (< 2%/mm Hg) carbon dioxide reactivity after arterial pressure was raised by 20 mm Hg (signaling ischemia) was found in 32 of 124 evaluated middle cerebral arteries. Further deterioration of impaired reactivity occurred in only four tested hemispheres. While ischemic conditions were identified during the entire study period, hyperperfusion was encountered only after day 3.

CONCLUSIONS

Ischemia after traumatic brain injury is a frequent phenomenon, whereas hyperperfusion is rare. Whether therapeutic optimization of carbon dioxide reactivity can improve the outcome of head-injury patients needs to be evaluated in further studies.

Neurochemical mechanisms in brain injury and treatment: a review

This article reviews cellular energy transformation processes and neurochemical events that take place at the time of brain injury and shortly thereafter emphasizing hypoxia-ischemia, cerebrovascular accident, and traumatic brain injury. New interpretations of established concepts, such as diffuse axonal injury, are discussed; specific events, such as free radical production, excess production of excitatory amino acids, and disruption of calcium homeostasis, are reviewed. Neurochemically-based interventions are also presented: calcium channel blockers, excitatory amino acid antagonists, free radical scavengers, and hypothermia treatment. Concluding remarks focus on the role of clinical neuropsychologists in validation of treatment interventions.

Cerebral lactate production in relation to intracranial pressure, cranial computed tomography findings, and outcome in patients with severe head injury

Severe head injury is frequently associated with focal or global disturbances of cerebral blood flow and metabolism. Routine monitoring of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in these patients does not provide information about critically reduced local or global cerebral blood flow. Measurements of cerebral lactate difference, Lactate-Oxygen-Index (LOI) and cerebral oxygen extraction were evaluated for advanced monitoring by comparing these parameters with ICP, cranial computed tomography (CCT) findings, and outcome in a group of severely head-injured patients. In 21 patients with severe brain trauma (GCS < or = 8), arterial as well as jugular venous lactate levels and oxygen saturation were measured in vitro every 6 h after admission of patients to the intensive care unit (ICU) throughout the acute course of treatment. Arterial blood pressure, blood gases, and ICP were assessed by standard monitoring measurements. CCT was performed initially after admission of the patients to the hospital, during the acute period in the ICU, if indicated, and 10 to 14 days after trauma. Outcome was classified according to the Glasgow outcome scale (GOS) at six months after injury. Data were averaged in each patient for every day after trauma and over the entire monitoring period. Resulting values were tested for correlation by regression analysis. Additionally, the data of the group of patients with normal to minimally elevated mean ICP (ICP < 20 mmHg, n = 12) were compared to those of the patients with increased mean ICP (ICP > 20 mmHg, n = 9). The cerebral lactate difference in all patients on the day of trauma was significantly increased as compared to the later period (0.20 vs. 0.11-0.07 mmol/l, p < 0.05), but was not different with high or normal to minimally elevated ICP. In patients with intracranial hypertension, the cerebral lactate difference remained significantly increased from the first to the fifth day after injury, whereas it normalized in this period in the group with normal to minimally elevated ICP. Averaged over the acute course, patients with increased ICP had significantly higher mean lactate differences (0.18 +/- 0.16 vs. 0.067 +/- 0.025 mmol/l, p = 0.001) and higher mean LOIs (0.072 +/- 0.071 vs. 0.028 +/- 0.013, p = 0.011). There was a significant correlation of increased mean cerebral lactate difference to poor outcome (r = 0.46, p = 0.035). Cerebral oxygen extraction in all patients tended to increase on the day of trauma (36.7% vs. 29.2% to 31.5% during the subsequent course), but this difference was not significant. The initial degree of brain swelling, classified by CCT according to Marshall et al. (1991), showed no correlation with cerebral lactate differences, ICP, O2-extraction, or outcome. Neither was there a correlation of cerebral oxygen extraction to ICP nor to outcome. In conclusion, the severity of brain trauma and outcome of patients was reflected by increased cerebral lactate production. Unchanged values of global cerebral oxygen extraction suggest that the regulatory mechanisms of brain oxygen supply were not impaired by trauma. Measurements of cerebral lactate differences and brain oxygen extraction may contribute to advanced monitoring in severe head injury.