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

Imaging Guidance for Therapeutic Delivery: The Dawn of Neuroenergetics

Modern neurocritical care relies on ancillary diagnostic testing in the form of multimodal monitoring to address acute changes in the neurological homeostasis. Much of our armamentarium rests upon physiological and biochemical surrogates of organ or regional level metabolic activity, of which a great deal is invested at the metabolic-hemodynamic-hydrodynamic interface to rectify the traditional intermediaries of glucose consumption. Despite best efforts to detect cellular neuroenergetics, current modalities cannot appreciate the intricate coupling between astrocytes and neurons. Invasive monitoring is not without surgical complication, and noninvasive strategies do not provide an adequate spatial or temporal resolution. Without knowledge of the brain's versatile behavior in specific metabolic states (glycolytic vs oxidative), clinical practice would lag behind laboratory empiricism. Noninvasive metabolic imaging represents a new hope in delineating cellular, nigh molecular level energy exchange to guide targeted management in a diverse array of neuropathology.

Primary or Secondary Decompressive Craniectomy: Different Indication and Outcome

Background:

Intracranial hypertension can cause secondary damage after a traumatic brain injury. Aggressive medical management might not be sufficient to alleviate the increasing intracranial pressure (ICP), and decompressive craniectomy (DC) can be considered. Decompressive craniectomy can be divided into categories, according to the timing and rationale for performing the procedure: primary (done at the time of mass lesion evacuation) and secondary craniectomy (done to treat refractory ICP). Most studies analyze primary and secondary DC together. Our hypothesis is that these two groups are distinct and the aim of this retrospective study is to evaluate the differences in order to better predict outcome after DC.

Methods:

Seventy patients had DC over a period of four years at our center. They were divided into two groups based on the timing of the DC. Primary DC (44 patients) was done within 24 hours of the injury for mass lesion evacuation. Secondary DC (26 patients) was done after 24 hours and purely for the treatment of refractory ICP. Pre-op characteristics and post-op outcomes were compared between the two groups.

Results:

There was a significant difference in the mechanism of injury, the pupil abnormalities and Marshall grade between primary and secondary DC. There was also a significant difference in outcome with primary DC showing 45.5% good outcome and 40.9% mortality and secondary DC showing 73.1% good outcome and 15.4% mortality.

Conclusions:

Primary and secondary DC have different indications and patients characteristics. Outcome prediction following DC should be adjusted according to the surgical indication.

Use of hyperbaric oxygen in traumatic brain injury: retrospective analysis of data of 20 patients treated at a tertiary care centre

Traumatic brain injury (TBI) related impact results in a permanent need for help in performing daily activities. Standard treatment consists of removing the cause, restore perfusion, support metabolic requirement and limit inflammatory and oxidative damage. Hyperbaric oxygen therapy (HBOT) is one such newer promising treatment that enhances neurological recovery to some extent. HBOT is intermittent inhalation of 100% oxygen at greater than normal atmospheric pressure and is internationally accepted for its role in well-defined indications. It is hypothesised that HBO has a role in reviving 'idling neurons', also called the ischemic penumbra defined as area of reduced cerebral blood flow, abolished synaptic activity but preserved structural integrity. We carried out a retrospective analysis of medical records of 20 patients of TBI who had been treated with HBOT in addition to standard management. These were placed in Group A (test group) and received at least 30 sessions of HBO along with standard treatment. The patients were assessed along the Disability Rating Scale (DRS), Glasgow coma scale (GCS) and Rancho Los Amigos Scale (RLAS). Another 20 patients of TBI, matched in age and severity of brain injury, who received standard treatment but not HBOT, were selected as the control group (Group B). Assessment on the DRS showed maximum improvement in patients with scores of 22-24 (vegetative state).The percentage of patients in the test group fell from 45% to 5% whereas only 20% patients in Group B had similar progress. After the treatment, a significantly higher proportion of HBOT treated subjects showed a good response in cognitive functions, as measured by RLA. In group A, 90% patients had a score of ≤ 3 and in Group B 95% had a similar score, which improved to ≥ 3 in 60% patients versus 30% patients respectively. In both groups maximum patients are in 1-6 months post-injury category and within the groups this category showed the greatest recovery, with a greater improvement in the test group as compared to control group.

A prospective, randomized clinical trial to compare the effect of hyperbaric to normobaric hyperoxia on cerebral metabolism, intracranial pressure, and oxygen toxicity in severe traumatic brain injury

Object

Oxygen delivered in supraphysiological amounts is currently under investigation as a therapy for severe traumatic brain injury (TBI). Hyperoxia can be delivered to the brain under normobaric as well as hyperbaric conditions. In this study the authors directly compare hyperbaric oxygen (HBO2) and normobaric hyperoxia (NBH) treatment effects.

Methods

Sixty-nine patients who had sustained severe TBIs (mean Glasgow Coma Scale Score 5.8) were prospectively randomized to 1 of 3 groups within 24 hours of injury: 1) HBO2, 60 minutes of HBO2 at 1.5 ATA; 2) NBH, 3 hours of 100% fraction of inspired oxygen at 1 ATA; and 3) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Brain tissue PO2, microdialysis, and intracranial pressure were continuously monitored. Cerebral blood flow (CBF), arteriovenous differences in oxygen, cerebral metabolic rate of oxygen (CMRO2), CSF lactate and F2-isoprostane concentrations, and bronchial alveolar lavage (BAL) fluid interleukin (IL)–8 and IL-6 assays were obtained pretreatment and 1 and 6 hours posttreatment. Mixed-effects linear modeling was used to statistically test differences among the treatment arms as well as changes from pretreatment to posttreatment.

Results

In comparison with values in the control group, the brain tissue PO2 levels were significantly increased during treatment in both the HBO2 (mean ± SEM, 223 ± 29 mm Hg) and NBH (86 ± 12 mm Hg) groups (p < 0.0001) and following HBO2 until the next treatment session (p = 0.003). Hyperbaric O2 significantly increased CBF and CMRO2 for 6 hours (p ≤ 0.01). Cerebrospinal fluid lactate concentrations decreased posttreatment in both the HBO2 and NBH groups (p < 0.05). The dialysate lactate levels in patients who had received HBO2 decreased for 5 hours posttreatment (p = 0.017). Microdialysis lactate/pyruvate (L/P) ratios were significantly decreased posttreatment in both HBO2 and NBH groups (p < 0.05). Cerebral blood flow, CMRO2, microdialysate lactate, and the L/P ratio had significantly greater improvement when a brain tissue PO2 ≥ 200 mm Hg was achieved during treatment (p < 0.01). Intracranial pressure was significantly lower after HBO2 until the next treatment session (p < 0.001) in comparison with levels in the control group. The treatment effect persisted over all 3 days. No increase was seen in the CSF F2-isoprostane levels, microdialysate glycerol, and BAL inflammatory markers, which were used to monitor potential O2 toxicity.

Conclusions

Hyperbaric O2 has a more robust posttreatment effect than NBH on oxidative cerebral metabolism related to its ability to produce a brain tissue PO2 ≥ 200 mm Hg. However, it appears that O2 treatment for severe TBI is not an all or nothing phenomenon but represents a graduated effect. No signs of pulmonary or cerebral O2 toxicity were present.

Neuroprotective effects of erythropoietin on acute metabolic and pathological changes in experimentally induced neurotrauma

OBJECT

Head trauma is a dynamic process characterized by a cascade of metabolic and molecular events. Erythropoietin (EPO) has been shown to have neuroprotective effects in animal models of traumatic brain injury (TBI). Acute in vivo mechanisms and pathological changes associated with EPO following TBI are unknown. In this study the authors compare acute metabolic and pathological changes following TBI with and without systemically administered EPO.

METHODS

Right frontal lobe microdialysis cannulae and right parietal lobe percussion hubs were inserted into 16 Sprague-Dawley rats. After a 4- to 5-day recovery, TBI was induced via a DragonFly fluid-percussion device at 2.5-2.8 atm. Rats were randomized into 2 groups, which received 5000 U/kg EPO or normal saline intraperitoneally 30 minutes after TBI. Microdialysis samples for glucose, lactate, pyruvate, and glutamate were obtained every 25 minutes for 10 hours. Rats were killed, their brains processed for light microscopy, and sections stained with H & E.

RESULTS

Erythropoietin administered 30 minutes after TBI directly affects acute brain metabolism. Brains treated with EPO maintain higher levels of glucose 4-10 hours after TBI (p<0.01), lower levels of lactate 6-10 hours after TBI (p<0.01), and lower levels of pyruvate 7.5-10 hours after TBI (p<0.01) compared with saline-treated controls. Erythropoietin maintains aerobic metabolism after TBI. Systemic EPO administration reduces acute TBI-induced lesion volume (p<0.05).

CONCLUSIONS

Following TBI, neuron use initially increases, with subsequent depletion of extracellular glucose, resulting in increased levels of extracellular lactate and pyruvate. This energy requirement can result in cell death due to increased metabolic demands. These data suggest that the neuroprotective effect of EPO may be partially due to improved energy metabolism in the acute phase in this rat model of TBI.

Lactate in veterinary critical care: pathophysiology and management

The measurement of blood lactate in people has proven to be a useful tool in the diagnosis, monitoring, and prognosis of a wide range of clinical syndromes. Its use in small animals is increasing, and several studies have been completed that demonstrate its potential role in critical care. This article summarizes the current state of knowledge regarding the physiology and pathophysiology of lactate production and lactic acidosis; current indications and the utility of measurement in a critical care setting are described; novel applications in the evaluation of cavitary effusions are highlighted; and a guide to the therapy of lactic acidosis is presented.

Hyperbaric oxygen in traumatic brain injury

OBJECTIVES

This critical literature review examines historical and current investigations on the efficacy and mechanisms of hyperbaric oxygen (HBO) treatment in traumatic brain injury (TBI). Potential safety risks and oxygen toxicity, as well as HBO's future potential, are also discussed.

METHODS

Directed literature review.

RESULTS

Historically, cerebral vasoconstriction and increased oxygen availability were seen as the primary mechanisms of HBO in TBI. HBO now appears to be improving cerebral aerobic metabolism at a cellular level, namely, by enhancing damaged mitochondrial recovery. HBO given at the ideal treatment paradigm, 1.5 ATA for 60 minutes, does not appear to produce oxygen toxicity and is relatively safe.

DISCUSSION

The use of HBO in TBI remains controversial. Growing evidence, however, shows that HBO may be a potential treatment for patients with severe brain injury. Further investigations, including a multicenter prospective randomized clinical trial, will be required to definitively define the role of HBO in severe TBI.

Identifying traumatic brain injury in patients with isolated head trauma: are arterial lactate and base deficit as helpful as in polytrauma?

BACKGROUND

Increase in lactate (LAC) within the central nervous system after head trauma is an established marker of traumatic brain injury (TBI).

OBJECTIVE

To investigate the utility of arterial base deficit (BD) and LAC in identifying TBI in patients with isolated head injury (IHI).

MATERIALS AND METHODS

TBI was defined as Glasgow Coma Scale < or =8, head Abbreviated Injury Severity Score >2 or brain haematoma on CT scan. Patients were divided into two groups: IHI with and without TBI. Data were reported as means (SDs). 131 patients with IHI were studied (mean (SD) age 39 (19) years, 78% male).

RESULTS

17% of the patients sustained TBI. The mean differences for arterial BD (0.65 mmol/l, 95% CI -0.8 to 2.1) and LAC (0.34 mmol/l, 95% CI -0.7 to 1.4) in patients with and without TBI were not significant. Analysis of receiver operating characteristic curves confirmed that arterial BD and LAC were unable to detect TBI in patients with IHI.

CONCLUSION

Arterial BD and LAC are poor predictors of TBI in isolated head trauma.

Effects of sequential changes from conventional ventilation to high-frequency oscillatory ventilation at increasing mean airway pressures in an ovine model of combined lung and head injury

BACKGROUND

The objective of this study was to determine the intracranial, cardiovascular and respiratory changes induced by conversion to high-frequency oscillator ventilation from conventional mechanical ventilation at increasing airway pressures.

METHODS

In this study, 11 anaesthetized sheep had invasive cardiovascular and intracranial monitors placed. Lung injury was induced by saline lavage and head injury was induced by inflation of an intracranial balloon catheter. All animals were sequentially converted from conventional mechanical ventilation to high-frequency oscillator ventilation at target mean airway pressures of 16, 22, 28, 34 and 40 cm H(2)O. The mean airway pressure was achieved by adjusting positive end expiratory pressure while on conventional mechanical ventilation, and continuous distending pressures while on high-frequency oscillator ventilation. Cerebral lactate production, oxygen consumption and venous oximetry were measured and analysed in relation to changes in transcranial Doppler flow velocity. Transcranial Doppler profiles together with other physiological parameters were measured at each airway pressure.

RESULTS

Cerebral perfusion pressure was significantly lower during high-frequency oscillator ventilation than during conventional mechanical ventilation (CMV: 45, 34, 22, 6, 9 mmHg vs. HFOV: 33, 20, 19, 5, 5 mmHg at airway pressures mentioned above, P = 0.02). Intracranial pressure and cerebrovascular resistance increased with increasing intrathoracic pressures (P = 0.001). Cerebral metabolic indices demonstrated an initial increase in anaerobic metabolism followed by a decrease in cerebral oxygen consumption progressing to cerebral infarction as intrathoracic pressures were further increased in a stepwise fashion. Arterial PaCO(2) increased significantly after converting from conventional mechanical ventilation to high-frequency oscillator ventilation (P = 0.001). However, no difference was observed between conventional mechanical ventilation and high-frequency oscillator ventilation when intracranial pressure, metabolic and transcranial Doppler indices were compared at equivalent mean airway pressures.

CONCLUSIONS

The use of high positive end expiratory pressure with conventional mechanical ventilation or high continuous distending pressure with high-frequency oscillator ventilation increased intracranial pressure and adversely affected cerebral metabolic indices in this ovine model. Transcranial Doppler is a useful adjunct to intracranial pressure and intracranial venous saturation monitoring when major changes in ventilation strategy are adopted.

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.

Critical appraisal of Perez et al: Jugular venous oxygen saturation or arteriovenous difference of lactate content and outcome in children with severe traumatic brain injury

OBJECTIVE

To review the findings and discuss the implications of jugular venous bulb oxygenation monitoring in children with severe traumatic brain injury.

DESIGN

A critical appraisal of Perez et al, Jugular venous oxygen saturation or arteriovenous difference of lactate content and outcome in children with severe traumatic brain injury.

FINDINGS

Two episodes of jugular venous bulb desaturation and abnormal values of arteriovenous difference in lactate content are associated with poor neurologic outcome in children with severe traumatic brain injury-risk ratio 6.6 (95% confidence interval, 1.5-29.7) and risk ratio 17.6 (95% confidence interval, 2.5-122.5), respectively. This confirms the findings of previously reported adult studies.

CONCLUSIONS

This study is the first to demonstrate that jugular venous monitoring may aid in predicting the neurologic outcome of children with severe traumatic brain injury. More studies need to be performed (particularly on safety) before adopting jugular venous bulb oxygenation monitoring as a prediction tool or, ultimately, as a therapeutic intervention to help manage and improve outcome for children with severe traumatic brain injury.

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.

[Prognostic factors in severe head injury]

The knowledge of the so called prognostic factors or indicators involved in severe head injury (SHI) is an issue of great interest to make predictions about the future of patients with this pathology. Those indicators constitute the basic elements of the different prognostic formulas or models carried out in order to make predictions in SHI. The mentioned models, therefore, will be constructed by a group of variables (prognostic indicators or factors) and several scales (prognostic scales) that are useful for measuring the final outcome of these patients. In this paper we resume, after an exhaustive review of the literature, the knowledge about the prognostic factors related to SHI. These indicators have been classified as follows: clinical, radiological, physiological, and biochemical. Moreover, we have briefly described the prognostic scales more commonly used in SHI.

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.

Jugular venous oxygen saturation or arteriovenous difference of lactate content and outcome in children with severe traumatic brain injury

OBJECTIVE

To assess the association between neurologic out-come and the alterations of jugular venous oxygen saturation (SjvO2) or the increase in arteriovenous difference of lactate content (AVDL) in children with severe traumatic brain injury.

DESIGN

Observational prospective cohort study.

SETTING

Multidisciplinary pediatric intensive care unit of a university hospital.

PATIENTS

A total of 27 pediatric patients with severe traumatic brain injury, with a Glasgow Coma Scale after resuscitation of <9, who were admitted to the pediatric intensive care unit within 36 hrs after injury.

INTERVENTIONS

Intermittent measurement of SjvO2 and AVDL.

MEASUREMENTS AND MAIN RESULTS

SjvO2 and AVDL were assessed simultaneously every 6 hrs. The primary dependent variable measured was assessed independently 3 months after trauma according to the Pediatric Cerebral Performance Category. Patients were classified into two groups: group 1 (favorable outcome, Pediatric Cerebral Performance Category 1-3) and group 2 (unfavorable outcome, Pediatric Cerebral Performance Category 4-6); 81% were included in group 1 and 19% in group 2. A total of 354 measurements of SjvO2 and AVDL were made, with a mean of 13.1 +/- 7.9 per patient. The number of abnormal measurements of SjvO2 and increased AVDL used to predict the neurologic outcome was selected according to the area under the receiver operating characteristic curve. Mortality was 15% (four patients). The strongest association was found between a poor neurologic outcome and two or more pathologic AVDL measurements (higher than -0.37 mmol/L; relative risk, 17.6; 95% confidence interval, 2.5-112.5; p = .001). The presence of two or more measurements of SjvO2 of < or = 55% was significantly associated with a poor neurologic outcome (relative risk, 6.6; 95% confidence interval, 1.5-29.7; p = .003). The frequency of measurements of SjvO2 of > or = 75% was not different between groups 1 and 2.

CONCLUSION

In children with severe traumatic brain injury, two or more measurements of SjvO2 of < or = 55% or two or more pathologic AVDL measurements were associated with a poor neurologic outcome. Further studies are needed to recommend the use of these variables as a guideline to optimize treatment.

Cerebral metabolism after fluid-percussion injury and hypoxia in a feline model

Object. Currently, there are no good clinical tools to identify the onset of secondary brain injury and/or hypoxia after traumatic brain injury (TBI). The aim of this study was to evaluate simultaneously early changes of cerebral metabolism, acid—base homeostasis, and oxygenation, as well as their interrelationship after TBI and arterial hypoxia.

Methods. Cerebral biochemistry and O2 supply were measured simultaneously in a feline model of fluid-percussion injury (FPI) and secondary hypoxic injury. After FPI, brain tissue PO2 decreased from 33 ± 5 mm Hg to 10 ± 4 mm Hg and brain tissue PCO2 increased from 55 ± 2 mm Hg to 81 ± 9 mm Hg, whereas cerebral pH fell from 7.1 ± 0.06 to 6.84 ± 0.14 (p < 0.05 for all three measures). After 40 minutes of hypoxia, brain tissue PO2 and pH decreased further to 0 mm Hg and 6.48 ± 0.28, respectively (p < 0.05), whereas brain tissue PCO2 remained high at 83 ± 13 mm Hg. Secondary hypoxic injury caused a drastic increase in cerebral lactate from 513 ± 69 µM/L to 3219 ± 490 µM/L (p < 0.05). The lactate/glucose ratio increased from 0.7 ± 0.1 to 9.1 ± 2 after hypoxia was introduced. The O2 consumption decreased significantly from 18.5 ± 1.1 µl/mg/hr to 13.2 ± 2.1 µl/mg/hr after hypoxia was induced.

Conclusions. Cerebral metabolism, O2 supply, and acid—base balance were severely compromised ultra-early after TBI, and they declined further if arterial hypoxia was present. The complexity of pathophysiological changes and their interactions after TBI might explain why specific therapeutic attempts that are aimed at the normalization of only one component have failed to improve outcome in severely head injured patients.

Monitoring arterio-venous differences of glucose and lactate in the anesthetized rat with or without brain damage with ultrafiltration and biosensor technology

Continuous monitoring of arterio-venous glucose and lactate differences may serve as a diagnostic tool to assess normal brain function and brain pathology. We describe a method and some results obtained with arterio-venous measurements of glucose and lactate in the blood of the halothane-anesthetized rat and after brain injury. The method is based on low flow rate ultrafiltration for continuous collection of blood filtrate combined with flow injection analysis and biosensors for the detection of glucose and lactate. We measured the glucose and lactate concentration every minute in the jugular vein and the aorta at control conditions and during and after inflation of an embolectomy-balloon for 2 min. Net cerebral lactate efflux and glucose uptake was seen under control conditions and at low blood lactate levels. During brain injury both lactate release and glucose uptake were reduced and there was a net lactate influx at high arterial lactate levels. These results indicate that the flux of lactate in and out of the brain is not only dependent on the lactate concentration in the brain, but on blood levels as well, possibly because of bi-directional flux through the monocarboxylate transporter type 1.

Effects of hyperbaric oxygenation therapy on cerebral metabolism and intracranial pressure in severely brain injured patients

OBJECT

Hyperbaric oxygenation (HBO) therapy has been shown to reduce mortality by 50% in a prospective randomized trial of severely brain injured patients conducted at the authors' institution. The purpose of the present study was to determine the effects of HBO on cerebral blood flow (CBF), cerebral metabolism, and intracranial pressure (ICP), and to determine the optimal HBO treatment paradigm.

METHODS

Oxygen (100% O2, 1.5 atm absolute) was delivered to 37 patients in a hyperbaric chamber for 60 minutes every 24 hours (maximum of seven treatments/patient). Cerebral blood flow, arteriovenous oxygen difference (AVDO2), cerebral metabolic rate of oxygen (CMRO2), ventricular cerebrospinal fluid (CSF) lactate, and ICP values were obtained 1 hour before and 1 hour and 6 hours after a session in an HBO chamber. Patients were assigned to one of three categories according to whether they had reduced, normal, or raised CBF before HBO. In patients in whom CBF levels were reduced before HBO sessions, both CBF and CMRO2 levels were raised 1 hour and 6 hours after HBO (p < 0.05). In patients in whom CBF levels were normal before HBO sessions, both CBF and CMRO2 levels were increased at 1 hour (p < 0.05), but were decreased by 6 hours after HBO. Cerebral blood flow was reduced 1 hour and 6 hours after HBO (p < 0.05), but CMRO2 was unchanged in patients who had exhibited a raised CBF before an HBO session. In all patients AVDO2 remained constant both before and after HBO. Levels of CSF lactate were consistently decreased 1 hour and 6 hours after HBO, regardless of the patient's CBF category before undergoing HBO (p < 0.05). Intracranial pressure values higher than 15 mm Hg before HBO were decreased 1 hour and 6 hours after HBO (p < 0.05). The effects of each HBO treatment did not last until the next session in the hyperbaric chamber.

CONCLUSIONS

The increased CMRO2 and decreased CSF lactate levels after treatment indicate that HBO may improve aerobic metabolism in severely brain injured patients. This is the first study to demonstrate a prolonged effect of HBO treatment on CBF and cerebral metabolism. On the basis of their data the authors assert that shorter, more frequent exposure to HBO may optimize treatment.

Predictive value of proton magnetic resonance spectroscopy in pediatric closed head injury

We studied 26 infants (1-18 months old) and 27 children (18 months or older) with acute nonaccidental (n = 21) or other forms (n = 32) of traumatic brain injury using clinical rating scales, a 15-point MRI scoring system, and occipital gray matter short-echo proton MRS. We compared the differences between the acutely determined variables (metabolite ratios and the presence of lactate) and 6- to 12-month outcomes. The metabolite ratios were abnormal (lower NAA/Cre or NAA/Cho; higher Cho/Cre) in patients with a poor outcome. Lactate was evident in 91% of infants and 80% of children with poor outcomes; none of the patients with a good outcome had lactate. At best, the clinical variables alone predicted the outcome in 77% of infants and 86% of children, and lactate alone predicted the outcome in 96% of infants and 96% of children. No further improvement in outcome prediction was observed when the lactate variable was combined with MRI ratios or clinical variables. The findings of spectral sampling in areas of brain not directly injured reflected the effects of global metabolic changes. Proton MRS provides objective data early after traumatic brain injury that can improve the ability to predict long-term neurologic outcome.

Increased inspired oxygen concentration as a factor in improved brain tissue oxygenation and tissue lactate levels after severe human head injury

OBJECT

Early impairment of cerebral blood flow in patients with severe head injury correlates with poor brain tissue O2 delivery and may be an important cause of ischemic brain damage. The purpose of this study was to measure cerebral tissue PO2, lactate, and glucose in patients after severe head injury to determine the effect of increased tissue O2 achieved by increasing the fraction of inspired oxygen (FiO2).

METHODS

In addition to standard monitoring of intracranial pressure and cerebral perfusion pressure, the authors continuously measured brain tissue PO2, PCO2, pH, and temperature in 22 patients with severe head injury. Microdialysis was performed to analyze lactate and glucose levels. In one cohort of 12 patients, the PaO2 was increased to 441+/-88 mm Hg over a period of 6 hours by raising the FiO2 from 35+/-5% to 100% in two stages. The results were analyzed and compared with the findings in a control cohort of 12 patients who received standard respiratory therapy (mean PaO2 136.4+/-22.1 mm Hg). The mean brain PO2 levels increased in the O2-treated patients up to 359+/-39% of the baseline level during the 6-hour FiO2 enhancement period, whereas the mean dialysate lactate levels decreased by 40% (p < 0.05). During this O2 enhancement period, glucose levels in brain tissue demonstrated a heterogeneous course. None of the monitored parameters in the control cohort showed significant variations during the entire observation period.

CONCLUSIONS

Markedly elevated lactate levels in brain tissue are common after severe head injury. Increasing PaO2 to higher levels than necessary to saturate hemoglobin, as performed in the O2-treated cohort, appears to improve the O2 supply in brain tissue. During the early period after severe head injury, increased lactate levels in brain tissue were reduced by increasing FiO2. This may imply a shift to aerobic metabolism.

[Evaluation of ischemic repercussions of intracranial hypertension]

The main risk involved in severe intracranial hypertension is, the occurrence of cerebral ischaemia, either locally during herniation or globally as a consequence of reduced cerebral perfusion pressure (CPP). Neurological features of ischaemia occur at a late stage. A continuous monitoring of brain function with EEG or evoked potential techniques, while largely used in the operating room have not been so far fully evaluated in the intensive care setting. Therefore, ischaemic criteria based on the registration of haemodynamic or metabolic data are gaining importance in management of increased intracranial pressure (ICP). Transcranial Doppler of middle cerebral arteries allows at any time the detection of a decrease in brain perfusion. An increased pulsatility index has been repeatedly demonstrated to correlate with decreased CPP. From these reports, the lower limit of autoregulation in brain injured patients appears to be much higher (70 mmHg) than previously estimated (40 mmHg). However, therapies with a cerebral vasoconstrictor impact and associated vasospasm are to be considered for a correct interpretation of Doppler data. Moreover, as a reduced cerebral blood flow is not necessarily insufficient to meet metabolic requirements, a routine insight in cerebral oxygenation and lactate production must be available. Continuous monitoring of jugular blood oxyhaemoglobin saturation (SjO2) measures the reserve of oxygen extraction and a decrease in SjO2 below 50% is considered as to indicate an impending cerebral ischaemia. Indeed, critically reduced CPP under a 70 mmHg limit is reflected by venous desaturation episodes. Increased cerebral lactate production, routinely appraisable by serial measurements of [(a-v) lactate], may afford confirmation of an existing ischaemia. ICP and CPP monitoring remains the basis for intensive care surveillance during the phase of intracranial hypertension, with alarming settled at admitted critical values (ICP = 30 mmHg; CPP = 70 mmHg). As ischaemic threshold for cerebral blood flow may be different in patients and in normal experimental animals, the reliability of these critical values of ICP and CPP is uncertain. Therefore, transcranial Doppler, jugular metabolic monitoring and, as recently available, cortical tissue PO2 monitoring are mandatory for early detection and assessment of ischaemia.