The use of hyperventilation and its impact on cerebral ischemia in the treatment of traumatic brain injury

Optimal inhaled oxygen and carbon dioxide concentrations for post-cardiac arrest cerebral reoxygenation and neurological recovery

Prolonged cerebral hypoperfusion after the return of spontaneous circulation (ROSC) from cardiac arrest (CA) may lead to poor neurological recovery. In a 7-min asphyxia-induced CA rat model, four combinations of inhaled oxygen (iO2) and carbon dioxide (iCO2) were administered for 150 min post-ROSC and compared in a randomized animal trial. At the end of administration, the partial pressure of brain tissue oxygenation (PbtO2) monitored in the hippocampal CA1 region returned to the baseline for the 88% iO2 [ΔPbtO2, median: -0.39 (interquartile range: 5.6) mmHg] and 50% iO2 [ΔpbtO2, -2.25 (10.9) mmHg] groups; in contrast, PbtO2 increased substantially in the 88% iO2+12% iCO2 [ΔpbtO2, 35.05 (16.0) mmHg] and 50% iO2+12% iCO2 [ΔpbtO2, 42.03 (31.7) mmHg] groups. Pairwise comparisons (post hoc Dunn's test) indicated the significant role of 12% iCO2 in augmenting PbtO2 during the intervention and improving neurological recovery at 24 h post-ROSC. Facilitating brain reoxygenation may improve post-CA neurological outcomes.

Association between the first 24 hours PaCO2 and all-cause mortality of patients suffering from sepsis-associated encephalopathy after ICU admission: A retrospective study

OBJECTIVE

The relationship between the levels of the first 24-h PaCO2 and the prognosis of sepsis-associated encephalopathy (SAE) remains unclear, and the first 24-h optimal target for PaCO2 is currently inconclusive. This study was performed to investigate the correlation between PaCO2 and all-cause mortality for SAE patients, establish a reference range of the initial 24-hour PaCO2 for clinicians in critical care, and explain the possible pathophysiological mechanisms of abnormal PaCO2 levels as a higher mortality risk factor for SAE.

METHODS

The baseline information and clinical data of patients were extracted from the fourth edition Medical Information Mart for Intensive Care database (MIMIC-IV 2.0). Multivariate logistic regressions were performed to assess the relationship between PaCO2 and all-cause mortality of SAE. Additionally, restricted cubic splines, Kaplan-Meier Survival analyses, propensity score matching (PSM) analyses, and subgroup analyses were conducted.

RESULTS

A total of 5471 patients were included in our cohort. In the original and matched cohort, multivariate logistic regression analysis showed that normocapnia and mild hypercapnia may be associated with a more favorable prognosis of SAE patients, and survival analysis supported the findings. In addition, a U-shaped association emerged when examining the initial 24-hour PaCO2 levels in relation to 30-day, 60-day, and 90-day mortality using restricted cubic splines, with an average cut-off value of 36.3mmHg (P for nonlinearity<0.05). Below the cut-off value, higher PaCO2 was associated with lower all-cause mortality, while above the cut-off value, higher PaCO2 was associated with higher all-cause mortality. Subsequent subgroup analyses revealed similar results for the subcohort of GCS≤8 compared to the original cohort. Additionally, when examining the subcohort of GCS>8, a L-shaped relationship between PaCO2 and the three clinical endpoints emerged, in contrast to the previously observed U-shaped pattern. The findings from the subcohort of GCS>8 suggested that patients experiencing hypocapnia had a more unfavorable prognosis, which aligns with the results obtained from corresponding multivariate logistic regression analyses.

CONCLUSION

The retrospective study revealed the association between the first 24-h PaCO2 and all-cause mortality risk (30-day, 60-day, and 90-day) for patients with SAE in ICU. The range (35mmHg-50mmHg) of PaCO2 may be the optimal target for patients with SAE in clinical practice.

Dual titration of minute ventilation and sweep gas flow to control carbon dioxide variations in patients on venovenous extracorporeal membrane oxygenation

BACKGROUND

The implantation of venovenous extracorporeal membrane oxygenation (VV-ECMO) support to manage severe acute respiratory distress syndrome generates large variations in carbon dioxide partial pressure (PaCO₂) that are associated with intracranial bleeding. We assessed the feasibility and efficacy of a pragmatic protocol for progressive dual titration of sweep gas flow and minute ventilation after VV-ECMO implantation in order to limit significant PaCO₂ variations.

PATIENTS AND METHODS

A protocol for dual titration of sweep gas flow and minute ventilation following VV-ECMO implantation was implemented in our unit in September 2020. In this single-centre retrospective before-after study, we included patients who required VV-ECMO from March, 2020 to May, 2021, which corresponds to two time periods: from March to August, 2020 (control group) and from September, 2020 to May, 2021 (protocol group). The primary endpoint was the mean absolute change in PaCO₂ in consecutive arterial blood gases samples drawn over the first 12 h following VV-ECMO implantation. Secondary endpoints included large (> 25 mmHg) initial variations in PaCO₂, intracranial bleedings and mortality in both groups.

RESULTS

Fifty-one patients required VV-ECMO in our unit during the study period, including 24 in the control group and 27 in the protocol group. The protocol was proved feasible. The 12-h mean absolute change in PaCO₂ was significantly lower in patients of the protocol group as compared with their counterparts (7 mmHg [6-12] vs. 12 mmHg [6-24], p = 0.007). Patients of the protocol group experienced less large initial variations in PaCO₂ immediately after ECMO implantation (7% vs. 29%, p = 0.04) and less intracranial bleeding (4% vs. 25%, p = 0.04). Mortality was similar in both groups (35% vs. 46%, p = 0.42).

CONCLUSION

Implementation of our protocol for dual titration of minute ventilation and sweep gas flow was feasible and associated with less initial PaCO₂ variation than usual care. It was also associated with less intracranial bleeding.

European Stroke Organisation (ESO) guidelines on the management of space-occupying brain infarction

Space-occupying brain oedema is a potentially life-threatening complication in the first days after large hemispheric or cerebellar infarction. Several treatment strategies for this complication are available, but the size and quality of the scientific evidence on which these strategies are based vary considerably. The aim of this Guideline document is to assist physicians in their management decisions when treating patients with space-occupying hemispheric or cerebellar infarction. These Guidelines were developed based on the European Stroke Organisation (ESO) standard operating procedure and followed the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. A working group identified 13 relevant questions, performed systematic reviews and meta-analyses of the literature, assessed the quality of the available evidence, and wrote evidence-based recommendations. An expert consensus statement was provided if not enough evidence was available to provide recommendations based on the GRADE approach. We found high-quality evidence to recommend surgical decompression to reduce the risk of death and to increase the chance of a favourable outcome in adult patients aged up to and including 60 years with space-occupying hemispheric infarction who can be treated within 48 hours of stroke onset, and low-quality evidence to support this treatment in older patients. There is continued uncertainty about the benefit and risks of surgical decompression in patients with space-occupying hemispheric infarction if this is done after the first 48 hours. There is also continued uncertainty about the selection of patients with space-occupying cerebellar infarction for surgical decompression or drainage of cerebrospinal fluid. These Guidelines further provide details on the management of specific subgroups of patients with space-occupying hemispheric infarction, on the value of monitoring of intracranial pressure, and on the benefits and risks of medical treatment options. We encourage new high-quality studies assessing the risks and benefits of different treatment strategies for patients with space-occupying brain infarction.

Partial pressure of arterial carbon dioxide after resuscitation from cardiac arrest and neurological outcome: A prospective multi-center protocol-directed cohort study

AIMS

Partial pressure of arterial carbon dioxide (PaCO₂) is a regulator of cerebral blood flow after brain injury. We sought to test the association between PaCO₂ after resuscitation from cardiac arrest and neurological outcome.

METHODS

A prospective protocol-directed cohort study across six hospitals.

INCLUSION CRITERIA

age ≥18, non-traumatic cardiac arrest, mechanically ventilated after return of spontaneous circulation (ROSC), and receipt of targeted temperature management. Per protocol, PaCO₂ was measured by arterial blood gas analyses at one and six hours after ROSC. We determined the mean PaCO₂ over this initial six hours after ROSC. The primary outcome was good neurological function at hospital discharge, defined a priori as a modified Rankin Scale ≤3. Multivariable Poisson regression analysis was used to test the association between PaCO₂ and neurological outcome.

RESULTS

Of the 280 patients included, the median (interquartile range) PaCO₂ was 44 (37-52) mmHg and 30% had good neurological function. We found mean PaCO₂ had a quadratic (inverted "U" shaped) association with good neurological outcome, with a mean PaCO₂ of 68 mmHg having the highest predictive probability of good neurological outcome, and worse neurological outcome at higher and lower PaCO₂. Presence of metabolic acidosis attenuated the association between PaCO₂ and good neurological outcome, with a PaCO₂ of 51 mmHg having the highest predictive probability of good neurological outcome among patients with metabolic acidosis.

CONCLUSION

PaCO₂ has a "U" shaped association with neurological outcome, with mild to moderate hypercapnia having the highest probability of good neurological outcome.

Perioperative Management of Severe Traumatic Brain Injury: What Is New?

PURPOSE OF THE REVIEW

Severe traumatic brain injury (TBI) continues to represent a global public health issue, and mortality and morbidity in TBI patients remain substantial. There are ongoing international collaborations to provide guidelines for perioperative care and management of severe TBI patients. In addition, new pharmacologic agents are being tested along with cognitive rehabilitation to improve functional independence and outcome in TBI patients. This review will discuss the current updates in the guidelines for the perioperative management of TBI patients and describe potential new therapies to improve functional outcomes.

RECENT FINDINGS

In the most recent guidelines published by The Brain Trauma Foundation, therapeutic options were reviewed based on new and revised evidence or lack of evidence. For example, changes and/or updates were made to the recommendations for the use of sedation and hypothermia in TBI patients, and new evidence was provided for the use of cerebrospinal fluid drainage as a first-line treatment for increased intracranial pressure (ICP). In addition to the guidelines, new 'multi-potential' agents that can target several mechanisms are being tested along with cognitive rehabilitation.

SUMMARY

The major goal of perioperative management of TBI patients is to prevent secondary damage. Therapeutic measures based on established guidelines and recommendations must be instituted promptly throughout the perioperative course to reduce morbidity and mortality.

Head Trauma

Head trauma is a common cause of significant morbidity and mortality in dogs and cats. Traumatic brain injury may occur after head trauma. Understanding the pathophysiology of primary and secondary injury after head trauma is essential for management. This article reviews the pathophysiology of head trauma, patient assessment and diagnostics, and treatment recommendations.

Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a "two-hit" model

Hypoxic ischemic brain injury (HIBI) after cardiac arrest (CA) is a leading cause of mortality and long-term neurologic disability in survivors. The pathophysiology of HIBI encompasses a heterogeneous cascade that culminates in secondary brain injury and neuronal cell death. This begins with primary injury to the brain caused by the immediate cessation of cerebral blood flow following CA. Thereafter, the secondary injury of HIBI takes place in the hours and days following the initial CA and reperfusion. Among factors that may be implicated in this secondary injury include reperfusion injury, microcirculatory dysfunction, impaired cerebral autoregulation, hypoxemia, hyperoxia, hyperthermia, fluctuations in arterial carbon dioxide, and concomitant anemia.Clarifying the underlying pathophysiology of HIBI is imperative and has been the focus of considerable research to identify therapeutic targets. Most notably, targeted temperature management has been studied rigorously in preventing secondary injury after HIBI and is associated with improved outcome compared with hyperthermia. Recent advances point to important roles of anemia, carbon dioxide perturbations, hypoxemia, hyperoxia, and cerebral edema as contributing to secondary injury after HIBI and adverse outcomes. Furthermore, breakthroughs in the individualization of perfusion targets for patients with HIBI using cerebral autoregulation monitoring represent an attractive area of future work with therapeutic implications.We provide an in-depth review of the pathophysiology of HIBI to critically evaluate current approaches for the early treatment of HIBI secondary to CA. Potential therapeutic targets and future research directions are summarized.

Reconsidering the role of decompressive craniectomy for neurological emergencies

OBJECTIVE

There is little doubt that decompressive craniectomy can reduce mortality. However, there is concern that any reduction in mortality comes at an increase in the number of survivors with severe neurological disability.

METHOD

Over the past decade there have been several randomised controlled trials comparing surgical decompression with standard medical therapy in the context of ischaemic stroke and severe traumatic brain injury. The results of each trial are evaluated.

RESULTS

There is now unequivocal evidence that a decompressive craniectomy reduces mortality in the context of "malignant" middle infarction and following severe traumatic brain injury. However, it has only been possible to demonstrate an improvement in outcome by categorizing a mRS of 4 and upper severe disability as favourable outcome. This is contentious and an alternative interpretation is that surgical decompression reduces mortality but exposes a patient to a greater risk of survival with severe disability.

CONCLUSION

It would appear unlikely that further randomised controlled trials will be possible given the significant reduction in mortality achieved by surgical decompression. It may be that observational cohort studies and outcome prediction models may provide data to determine those patients most likely to benefit from surgical decompression.

Evidence-based guidelines for the management of large hemispheric infarction : a statement for health care professionals from the Neurocritical Care Society and the German Society for Neuro-intensive Care and Emergency Medicine

Large hemispheric infarction (LHI), also known as malignant middle cerebral infarction, is a devastating disease associated with significant disability and mortality. Clinicians and family members are often faced with a paucity of high quality clinical data as they attempt to determine the most appropriate course of treatment for patients with LHI, and current stroke guidelines do not provide a detailed approach regarding the day-to-day management of these complicated patients. To address this need, the Neurocritical Care Society organized an international multidisciplinary consensus conference on the critical care management of LHI. Experts from neurocritical care, neurosurgery, neurology, interventional neuroradiology, and neuroanesthesiology from Europe and North America were recruited based on their publications and expertise. The panel devised a series of clinical questions related to LHI, and assessed the quality of data related to these questions using the Grading of Recommendation Assessment, Development and Evaluation guideline system. They then developed recommendations (denoted as strong or weak) based on the quality of the evidence, as well as the balance of benefits and harms of the studied interventions, the values and preferences of patients, and resource considerations.

Recommendations for management of large hemispheric infarction

PURPOSE OF REVIEW

Large hemispheric infarction is a devastating disease that continues to be associated with significant mortality and morbidity. Most often these patients are admitted to the ICU requiring significant physician and nursing resources. This review will address some of the ICU management issues and review the evidence supporting medical and surgical management of malignant cerebral edema.

RECENT FINDINGS

The most recent changes in management of large hemispheric infarct include the American Heart Association and Neurocritical Care Guidelines. These guidelines address airway management and mechanical ventilation, blood pressure control, fluid management, and glucose and temperature control. In addition, they addressed the indication for surgical management of cerebral edema. We review the recent guidelines updates and trials of surgical management of large hemispheric infarcts.

SUMMARY

Large hemispheric infarcts continue to have significant morbidity and mortality. Recent guidelines have provided an excellent framework to help intensivists manage these complicated patients. Recent surgical data continue to support early hemicraniectomy even in elderly patients.

Effects of PaCO2 derangements on clinical outcomes after cerebral injury: A systematic review

OBJECTIVE

Partial pressure of arterial carbon dioxide (PaCO2) is a major regulator of cerebral blood flow (CBF). Derangements in PaCO2 have been thought to worsen clinical outcomes after many forms of cerebral injury by altering CBF. Our aim was to systematically analyze the biomedical literature to determine the effects of PaCO2 derangements on clinical outcomes after cerebral injury.

METHODS

We performed a search of Cochrane Library, PUBMED, CINHAL, conference proceedings, and other sources using a comprehensive strategy. Study inclusion criteria were (1) human subjects; (2) cerebral injury; (3) mechanical ventilation post-injury; (4) measurement of PaCO2; and (5) comparison of a clinical outcome measure (e.g. mortality) between different PaCO2 exposures. We performed a qualitative analysis to collate and summarize effects of PaCO2 derangements according to the recommended methodology from the Cochrane Handbook.

RESULTS

Seventeen studies involving different etiologies of cerebral injury (six traumatic brain injury, six post-cardiac arrest syndrome, two cerebral vascular accident, three neonatal ischemic encephalopathy) met all inclusion and no exclusion criteria. Three randomized control trials were identified and only one was considered a high quality study as per the Cochrane criteria for assessing risk of bias. In 13/17 (76%) studies examining hypocapnia, and 7/10 (70%) studies examining hypercapnia, the exposed group (hypercapnia or hypocapnia) was associated with poor clinical outcome.

CONCLUSION

The majority of studies in this report found exposure to hypocapnia and hypercapnia after cerebral injury to be associated with poor clinical outcome. However, the optimal PaCO2 range associated with good clinical outcome remains unclear.

Association between initial prescribed minute ventilation and post-resuscitation partial pressure of arterial carbon dioxide in patients with post-cardiac arrest syndrome

BACKGROUND

Post-cardiac arrest hypocapnia/hypercapnia have been associated with poor neurological outcome. However, the impact of arterial carbon dioxide (CO2) derangements during the immediate post-resuscitation period following cardiac arrest remains uncertain. We sought to test the correlation between prescribed minute ventilation and post-resuscitation partial pressure of CO2 (PaCO2), and to test the association between early PaCO2 and neurological outcome.

METHODS

We retrospectively analyzed a prospectively compiled single-center cardiac arrest registry. We included adult (age ≥ 18 years) patients who experienced a non-traumatic cardiac arrest and required mechanical ventilation. We analyzed initial post-resuscitation ventilator settings and initial arterial blood gas analysis (ABG) after initiation of post-resuscitation ventilator settings. We calculated prescribed minute ventilation:MVmL/kg/min=tidalvolumeTV/idealbodyweightIBWxrespiratoryrateRRfor each patient. We then used Pearson's correlation to test the correlations between prescribed MV and PaCO2. We also determined whether patients had normocapnia (PaCO2 between 30 and 50 mmHg) on initial ABG and tested the association between normocapnia and good neurological function (Cerebral Performance Category 1 or 2) at hospital discharge using logistic regression analyses.

RESULTS

Seventy-five patients were included. The majority of patients were in-hospital arrests (85%). Pulseless electrical activity/asystole was the initial rhythm in 75% of patients. The median (IQR) TV, RR, and MV were 7 (7 to 8) mL/kg, 14 (14 to 16) breaths/minute, and 106 (91 to 125) mL/kg/min, respectively. Hypocapnia, normocapnia, and hypercapnia were found in 15%, 62%, and 23% of patients, respectively. Good neurological function occurred in 32% of all patients, and 18%, 43%, and 12% of patients with hypocapnia, normocapnia, and hypercapnia respectively. We found prescribed MV had only a weak correlation with initial PaCO2, R = -0.40 (P < 0.001). Normocapnia was associated with good neurological function, odds ratio 4.44 (95% CI 1.33 to 14.85).

CONCLUSIONS

We found initial prescribed MV had only a weak correlation with subsequent PaCO2 and that early Normocapnia was associated with good neurological outcome. These data provide rationale for future research to determine the impact of PaCO2 management during mechanical ventilation in post-cardiac arrest patients.

Post-resuscitation care for survivors of cardiac arrest

Cardiac arrest can occur following a myriad of clinical conditions. With advancement of medical science and improvements in Emergency Medical Services systems, the rate of return of spontaneous circulation for patients who suffer an out-of-hospital cardiac arrest (OHCA) continues to increase. Managing these patients is challenging and requires a structured approach including stabilization of cardiopulmonary status, early consideration of neuroprotective strategies, identifying and managing the etiology of arrest and initiating treatment to prevent recurrence. This requires a closely coordinated multidisciplinary team effort. In this article, we will review the initial management of survivors of OHCA, highlighting advances and ongoing controversies.

Association Between Postresuscitation Partial Pressure of Arterial Carbon Dioxide and Neurological Outcome in Patients With Post–Cardiac Arrest Syndrome

Background—

Partial pressure of arterial CO 2 (Pa co 2 ) is a regulator of cerebral blood flow after brain injury. Recent guidelines for the management of cardiac arrest recommend maintaining Pa co 2 at 40 to 45 mm Hg after successful resuscitation; however, there is a paucity of data on the prevalence of Pa co 2 derangements during the post–cardiac arrest period and its association with outcome.

Methods and Results—

We analyzed a prospectively compiled and maintained cardiac arrest registry at a single academic medical center. Inclusion criteria are as follows: age ≥18, nontrauma arrest, and comatose after return of spontaneous circulation. We analyzed arterial blood gas data during 0 to 24 hours after the return of spontaneous circulation and determined whether patients had exposure to hypocapnia and hypercapnia (defined as Pa co 2 ≤30 mm Hg and Pa co 2 ≥50 mm Hg, respectively, based on previous literature). The primary outcome was poor neurological function at hospital discharge, defined as Cerebral Performance Category ≥3. We used multivariable logistic regression, with multiple sensitivity analyses, adjusted for factors known to predict poor outcome, to determine whether post–return of spontaneous circulation hypocapnia and hypercapnia were independent predictors of poor neurological function. Of 193 patients, 52 (27%) had hypocapnia only, 63 (33%) had hypercapnia only, 18 (9%) had both hypocapnia and hypercapnia exposure, and 60 (31%) had no exposure; 74% of patients had poor neurological outcome. Hypocapnia and hypercapnia were independently associated with poor neurological function, odds ratio 2.43 (95% confidence interval, 1.04–5.65) and 2.20 (95% confidence interval, 1.03–4.71), respectively.

Conclusions—

Hypocapnia and hypercapnia were common after cardiac arrest and were independently associated with poor neurological outcome. These data suggest that Pa co 2 derangements could be potentially harmful for patients after resuscitation from cardiac arrest.

The frequency of cerebral ischemia/hypoxia in pediatric severe traumatic brain injury

INTRODUCTION

The frequency of adverse events, such as cerebral ischemia, following traumatic brain injury (TBI) is often debated. Point-in-time monitoring modalities provide important information, but have limited temporal resolution.

PURPOSE

This study examines the frequency of an adverse event as a point prevalence at 24 and 72 h post-injury, compared with the cumulative burden measured as a frequency of the event over the full duration of monitoring.

METHODS

Reduced brain tissue oxygenation (PbtO(2) < 10 mmHg) was the adverse event chosen for examination. Data from 100 consecutive children with severe TBI who received PbtO(2) monitoring were retrospectively examined, with data from 87 children found suitable for analysis. Hourly recordings were used to identify episodes of PbtO(2) less than 10 mmHg, at 24 and 72 h post-injury, and for the full duration of monitoring.

RESULTS

Reduced PbtO(2) was more common early than late after injury. The point prevalence of reduced PbtO(2) at the selected time points was relatively low (10 % of patients at 24 h and no patients at the 72-h mark post-injury). The cumulative burden of these events over the full duration of monitoring was relatively high: 50 % of patients had episodes of PbtO(2) less than 10 mmHg and 88 % had PbtO(2) less than 20 mmHg.

CONCLUSION

Point-in-time monitoring in a dynamic condition like TBI may underestimate the overall frequency of adverse events, like reduced PbtO(2), particularly when compared with continuous monitoring, which also has limitations, but provides a dynamic assessment over a longer time period.

Early derangements in oxygen and glucose metabolism following head injury: the ischemic penumbra and pathophysiological heterogeneity

INTRODUCTION

Conclusive evidence of cerebral ischemia following head injury has been elusive. We aimed to use (15)O and (18)Fluorodeoxyglucose positron emission tomography (PET) to investigate pathophysiological derangements following head injury.

RESULTS

Eight patients underwent PET within 24 h of injury to map cerebral blood flow (CBF), cerebral oxygen metabolism (CMRO2), oxygen extraction fraction (OEF), and cerebral glucose metabolism (CMRglc). Physiological regions of interest (ROI) were generated for each subject using a range of OEF values from very low (<10), low (10-30), normal range (30-50), high (50-70), and critically high (> or =70%). We applied these ROIs to each subject to generate data that would examine the balance between blood flow and metabolism across the injured brain independent of structural injury.

DISCUSSION

Compared to the normal range, brain regions with higher OEF demonstrate a progressive CBF reduction (P < 0.01), CMRO2 increase (P < 0.05), and no change in CMRglc, while regions with lower OEF are associated with reductions in CBF, CMRO2, and CMRglc (P < 0.01). Although all subjects demonstrate a decrease in CBF with increases in OEF > 70%, CMRO2 and CMRglc were generally unchanged. One subject demonstrated a reduction in CBF and small fall in CMRO2 within the high OEF region (>70%), combined with a progressive increase in CMRglc.

CONCLUSIONS

The low CBF and maintained CMRO2 in the high OEF ROIs is consistent with classical cerebral ischemia and the presence of an 'ischemic penumbra' following early head injury, while the metabolic heterogeneity that we observed suggests significant pathophysiological complexity. Other mechanisms of energy failure are clearly important and further study is required to delineate the processes involved.

Management of intracranial hypertension

Effective management of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. Medical management of increased intracranial pressure should include sedation, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Management of intracranial hypertension

Effective treatment of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. medical management of increased intracranial pressure should include sedation and paralysis, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Hyperventilation following head injury: effect on ischemic burden and cerebral oxidative metabolism

OBJECTIVE

To determine whether hyperventilation exacerbates cerebral ischemia and compromises oxygen metabolism (CMRO2) following closed head injury.

DESIGN

A prospective interventional study.

SETTING

A specialist neurocritical care unit.

PATIENTS

Ten healthy volunteers and 30 patients within 10 days of closed head injury.

INTERVENTIONS

Subjects underwent oxygen-15 positron emission tomography imaging of cerebral blood flow, cerebral blood volume, CMRO2, and oxygen extraction fraction. In patients, positron emission tomography studies, somatosensory evoked potentials, and jugular venous saturation (SjO2) measurements were obtained at Paco2 levels of 36+/-3 and 29+/-2 torr.

MEASUREMENTS AND MAIN RESULTS

We estimated the volume of ischemic brain and examined the efficiency of coupling between oxygen delivery and utilization using the sd of the oxygen extraction fraction distribution. We correlated CMRO2 to cerebral electrophysiology and examined the effects of hyperventilation on the amplitude of the cortical somatosensory evoked potential response. Patients showed higher ischemic brain volume than controls (17+/-22 vs. 2+/-3 mL; p<or=.05), with worse matching of oxygen delivery to demand (p<.001). Hyperventilation consistently reduced cerebral blood flow (p<.001) and resulted in increases in oxygen extraction fraction and ischemic brain volume (17+/-22 vs. 88+/-66 mL; p<.0001), which were undetected by SjO2 monitoring. Mean CMRO2 was slightly increased following hyperventilation, but responses were extremely variable, with 28% of patients demonstrating a decrease in CMRO2 that exceeded 95% prediction intervals for zero change in one or more regions. CMRO2 correlated with cerebral electrophysiology, and cortical somatosensory evoked potential amplitudes were significantly increased by hyperventilation.

CONCLUSIONS

The acute cerebral blood flow reduction and increase in CMRO2 secondary to hyperventilation represent physiologic challenges to the traumatized brain. These challenges exhaust physiologic reserves in a proportion of brain regions in many subjects and compromise oxidative metabolism. Such ischemia is underestimated by common bedside monitoring tools and may represent a significant mechanism of avoidable neuronal injury following head trauma.

Clinical review: Therapy for refractory intracranial hypertension in ischaemic stroke

The treatment of patients with large hemispheric ischaemic stroke accompanied by massive space-occupying oedema represents one of the major unsolved problems in neurocritical care medicine. Despite maximum intensive care, the prognosis of these patients is poor, with case fatality rates as high as 80%. Therefore, the term 'malignant brain infarction' was coined. Because conservative treatment strategies to limit brain tissue shift almost consistently fail, these massive infarctions often are regarded as an untreatable disease. The introduction of decompressive surgery (hemicraniectomy) has completely changed this point of view, suggesting that mortality rates may be reduced to approximately 20%. However, critics have always argued that the reduction in mortality may be outweighed by an accompanying increase in severe disability. Due to the lack of conclusive evidence of efficacy from randomised trials, controversy over the benefit of these treatment strategies remained, leading to large regional differences in the application of this procedure. Meanwhile, data from randomised trials confirm the results of former observational studies, demonstrating that hemicraniectomy not only significantly reduces mortality but also significantly improves clinical outcome without increasing the number of completely dependent patients. Hypothermia is another promising treatment option but still needs evidence of efficacy from randomised controlled trials before it may be recommended for clinical routine use. This review gives the reader an integrated view of the current status of treatment options in massive hemispheric brain infarction, based on the available data of clinical trials, including the most recent data from randomised trials published in 2007.

In vivo measurement of tissue damage, oxygen saturation changes and blood flow changes after experimental traumatic brain injury in rats using susceptibility weighted imaging

Traumatic brain injury (TBI) is a prevalent disease, and many TBI patients experience disturbed cerebral blood flow (CBF) after injury. Moreover, TBI is difficult to quantify with conventional imaging modalities. In this paper, we utilized susceptibility weighted imaging (SWI) as a means to monitor functional blood oxygenation changes and to quantify CBF changes in animals after trauma. In this study using six rats, brain trauma was induced by a weight drop model and the brain was scanned over four time points: pre trauma, and 4 h, 24 h and 48 h post trauma. Five rats survived and one died after trauma. A blood phase analysis using filtered SWI phase images suggested that three rats recovered after 48 h and two rats deteriorated. SWI also suggested that CBF decreased by up to 26%. The CBF change is in agreement with the results of arterial spin labeling methods conducted in this study and with previously published results. Furthermore, SWI revealed an enlargement of the major venous vasculature in deep brain structures, in accordance with the location of diffuse axonal injury. Compared with the traditional, invasive, clinical monitoring of cerebral vascular damage and reduction in blood flow, this method offers a novel, safe and noninvasive approach to quantify changes in oxygen saturation and CBF and to visualize structural changes in blood vasculature after TBI.

Recognizing and treating ischemic insults to the brain: the role of brain tissue oxygen monitoring

This article describes the potential application of brain tissue oxygen monitoring technology in the care of patients who have sustained traumatic brain injury (TBI) or subarachnoid hemorrhage (SAH). To accomplish this objective, a review of the intracranial dynamics that are created by primary and secondary brain injury, and the challenges of optimizing oxygen delivery to the injured brain are presented. Furthermore, interventions that facilitate cerebral oxygen supply and reduce oxygen consumption are identified. Finally, application of this technology is highlighted by using case vignettes of patients who have TBI or SAH.

Continuous regional cerebral blood flow monitoring in the neurosurgical intensive care unit

The aim of this study was to examine the intracranial pressure (ICP) and regional cerebral blood flow (rCoBF) changes during the acute stage of severe head injury and to improve outcome by modifying treatment modalities using real-time ICP and rCoBF data. Twenty patients with moderate or severe head injury that were monitored in our neurosurgical intensive care unit were included in this study. The changes in ICP, rCoBF and the relationship of ICP/rCoBF were observed. In patients with high ICP and low rCoBF, mannitol improves the rCoBF and decreases the ICP of these patients. When low rCoBF exists, hyperventilation may lead to a rapid further decline of rCoBF, however, some hyperemic brains respond well to hyperventilation treatment. Triple-H therapy is suitable for those with low rCoBF without significantly high ICP, which is an abnormal condition considered to be caused by vasospasm.

Intracerebral Hemorrhage

INTRODUCTION

Intracerebral hemorrhage (ICH) occurs from the rupture of small vessels into the brain parenchyma and accounts for approximately 10% of all strokes in the United States, and carries with it a significantly high morbidity and mortality.

SUMMARY

This article reviews the course and management of ICH. The most common chronic vascular diseases that lead to ICH are chronic hypertension and cerebral amyloid angiopathy. Additional factors that predispose to ICH include vascular malformations, chronic alcohol use, hypocholesterolemia, and use of anticoagulant medications. The understanding of mechanisms leading to ICH has advanced significantly, but questions regarding site predilection and timing of spontaneous hemorrhage still remain. Management in the acute setting is first focused on reducing hematoma expansion. Although no specific therapy has yet been proven effective, promising agents, particularly recombinant Factor VIIa, are on the horizon. Subsequent care is focused on controlling hemostasis, hemodynamics, and intracranial pressure in efforts to minimize secondary brain injury.

CONCLUSION

The morbidity and mortality associated with ICH remain high despite recent advances in our understanding of the clinical course of ICH. Novel preventive and acute treatment therapies are needed and may be on the horizon.

Metabolic crisis without brain ischemia is common after traumatic brain injury: a combined microdialysis and positron emission tomography study

Brain trauma is accompanied by regional alterations of brain metabolism, reduction in metabolic rates and possible energy crisis. We hypothesize that microdialysis markers of energy crisis are present during the critical period of intensive care despite the absence of brain ischemia. In all, 19 brain injury patients (mean GCS 6) underwent combined positron emission tomography (PET) for metabolism of glucose (CMRglu) and oxygen (CMRO(2)) and cerebral microdialysis (MD) at a mean time of 36 h after injury. Microdialysis values were compared with the regional mean PET values adjacent to the probe. Longitudinal MD data revealed a 25% incidence rate of metabolic crisis (elevated lactate/pyruvate ratio (LPR) > 40) but only a 2.4% incidence rate of ischemia. Positron emission tomography imaging revealed a 1% incidence of ischemia across all voxels as measured by oxygen extraction fraction (OEF) and cerebral venous oxygen content (CvO(2)). In the region of the MD probe, PET imaging revealed ischemia in a single patient despite increased LPR in other patients. Lactate/pyruvate ratio correlated negatively with CMRO(2) (P < 0.001), but not with OEF or CvO(2). Traumatic brain injury leads to a state of persistent metabolic crisis as reflected by abnormal cerebral microdialysis LPR that is not related to ischemia.

The Impact of Prehospital Endotracheal Intubation on Outcome in Moderate to Severe Traumatic Brain Injury

BACKGROUND

Although early intubation to prevent the mortality that accompanies hypoxia is considered the standard of care for severe traumatic brain injury (TBI), the efficacy of this approach remains unproven.

METHODS

Patients with moderate to severe TBI (Head/Neck Abbreviated Injury Scale [AIS] score 3+) were identified from our county trauma registry. Logistic regression was used to explore the impact of prehospital intubation on outcome, controlling for age, gender, mechanism, Glasgow Coma Scale score, Head/Neck AIS score, Injury Severity Score, and hypotension. Neural network analysis was performed to identify patients predicted to benefit from prehospital intubation.

RESULTS

A total of 13,625 patients from five trauma centers were included; overall mortality was 22.9%, and 19.3% underwent prehospital intubation. Logistic regression revealed an increase in mortality with prehospital intubation (odds ratio, 0.36; 95% confidence interval, 0.32-0.42; p < 0.001). This was true for all patients, for those with severe TBI (Head/Neck AIS score 4+ and/or Glasgow Coma Scale score of 3-8), and with exclusion of patients transported by aeromedical crews. Patients intubated in the field versus the emergency department had worse outcomes. Neural network analysis identified a subgroup of patients with more significant injuries as potentially benefiting from prehospital intubation.

CONCLUSION

Prehospital intubation is associated with a decrease in survival among patients with moderate-to-severe TBI. More critically injured patients may benefit from prehospital intubation but may be difficult to identify prospectively.

Subcortical White Matter Metabolic Changes Remote from Focal Hemorrhagic Lesions Suggest Diffuse Injury after Human Traumatic Brain Injury

OBJECTIVE:

We used positron emission tomographic studies to prospectively examine the relationship between glucose and oxidative metabolism in the subcortical white matter (WM) acutely after traumatic brain injury (TBI). The objective was to determine the nature, extent, and degree of metabolic abnormalities in subcortical brain regions remote from hemorrhagic lesions.

METHODS:

Sixteen normal volunteers and 10 TBI patients (Glasgow Coma Scale score, 4–10; age, 17–64 yr; 6 with focal and 4 with diffuse injury) were studied. Each subject underwent dynamic positron emission tomographic studies using [15O]CO, 15O2, [15O]H2O, and fluorodeoxyglucose plus a magnetic resonance imaging scan acutely after TBI. Parametric images of the metabolic rate of oxygen and metabolic rate of glucose were generated, and a molar oxygen-to-glucose utilization ratio was calculated. Data from gray matter and WM remote from hemorrhagic lesions, plus whole brain, were analyzed.

RESULTS:

There was a significant reduction in the subcortical WM oxygen-to-glucose utilization ratio after TBI compared with normal values (3.99 ± 0.77 versus 5.37 ± 1.00; P &lt; 0.01), whereas the mean cortical gray matter and whole-brain values remained unchanged. WM metabolic changes, which were diffuse throughout the hemispheres, were characterized by a reduction in the metabolic rate of oxygen without a concomitant drop in the metabolic rate of glucose.

CONCLUSION:

The extent and degree of subcortical WM metabolic abnormalities after moderate and severe TBI suggest that diffuse WM injury is a general phenomenon after such injuries. This pervasive finding may indicate that the concept of focal traumatic injury, although valid from a computed tomographic imaging standpoint, may be misleading when considering metabolic derangements associated with TBI.

Sustained moderate reductions in arterial CO2 after brain trauma Time-course of cerebral blood flow velocity and intracranial pressure

OBJECTIVE

In healthy volunteers cerebral blood flow starts to recover towards baseline within a few minutes of continued hyperventilation due to normalisation of perivascular pH. We investigated the time-course of changes in middle cerebral artery mean flow velocity (FVm) and intracranial pressure (ICP) in head-injured patients during sustained moderate reductions in arterial partial pressure of CO(2) (PaCO(2)).

DESIGN

Observational study.

PATIENTS

Twenty-seven sedated, mechanically ventilated patients with severe head injury.

INTERVENTIONS

Measurements were made during and after routine determination of CO(2)-reactivity: an acute 20% increase in respiratory minute volume was followed by a 10-min stabilisation period and 50 min of continued moderate hyperventilation at a constant PaCO(2) (>3.5 kPa).

MEASUREMENTS AND RESULTS

FVm was monitored with transcranial Doppler, ICP was monitored with intraparenchymal probes. During the 50-min period with stable PaCO(2) FVm increased in 36% of patients. All other patients showed a decline in FVm over the same time period. Overall FVm recovery was -0.03+/-0.14%.min(-1). The time-course of ICP changes was significantly different from that of FVm, with ICP reaching its lowest value earlier than FVm (23+/-12 vs 37+/-20 min; P = 0.001) and returning more rapidly towards baseline than FVm (0.23+/-0.23 vs -0.03+/-0.14%.min(-1); P< 0.0001).

CONCLUSIONS

Head-injured patients may adapt differently to hyperventilation than healthy volunteers. Potentially harmful reductions in cerebral blood flow may persist beyond the duration of useful ICP reduction.

The impact of hypoxia and hyperventilation on outcome after paramedic rapid sequence intubation of severely head-injured patients

BACKGROUND

An increase in mortality has been documented in association with paramedic rapid sequence intubation (RSI) of severely head-injured patients. This analysis explores the impact of hypoxia and hyperventilation on outcome.

METHODS

Adult severely head-injured patients (Glasgow Coma Scale score of 3-8) unable to be intubated without neuromuscular blockade underwent paramedic RSI using midazolam and succinylcholine; rocuronium was administered after confirmation of tube position. Standard ventilation parameters were used for most patients; however, one agency instituted use of digital end-tidal carbon dioxide (ETCO2) and oxygen saturation (Spo2) monitoring during the trial. Each patient undergoing digital ETCO2/Spo2 monitoring was matched to three historical nonintubated controls on the basis of age, gender, mechanism, and Abbreviated Injury Scale scores for each of six body regions. Logistic regression was used to explore the impact of oxygen desaturation during laryngoscopy and postintubation hypocapnia and hypoxia on outcome. The relationship between hypocapnia and ventilatory rate was explored using linear regression and univariate analysis. In addition, trial patients and controls were compared with regard to mortality and the incidence of "good outcomes" using an odds ratio analysis.

RESULTS

Of the 426 trial patients, a total of 59 had complete ETCO2/Spo2 monitoring data; these were matched to 177 controls. Logistic regression revealed an association between the lowest ETCO2 value and final ETCO2 value and mortality. Matched-controls analysis confirmed an association between hypocapnia and mortality. A statistically significant association between ventilatory rate and ETCO2 value was observed (r = -0.13, p < 0.0001); the median ventilatory rate associated with the lowest recorded ETCO2 value was significantly higher than for all other ETCO2 values (27 mm Hg vs. 19 mm Hg, p < 0.0001). In addition, profound desaturations during RSI and hypoxia after intubation were associated with higher mortality than matched controls. Overall mortality was 41% for trial patients versus 22% for matched controls (odds ratio, 2.51; 95% confidence interval, 1.33-4.72; p = 0.004).

CONCLUSIONS

Hyperventilation and severe hypoxia during paramedic RSI are associated with an increase in mortality.

Air medical transport of severely head-injured patients undergoing paramedic rapid sequence intubation

INTRODUCTION

The San Diego Paramedic Rapid Sequence Intubation (RSI) Trial documented an increase in mortality with paramedic RSI of patients with severe traumatic brain injury. This analysis explores the impact of air medical transport of trial patients on outcome.

METHODS

Adult trauma victims with severe traumatic brain injury (Glasgow Coma Scale score of 3 to 8) were prospectively enrolled. Paramedics performed RSI using midazolam and succinylcholine; air medical crews could be called at the discretion of ground paramedics, generally for anticipated prolonged transports. Patients were matched to historical controls using the following parameters: age, gender, mechanism, injury of severity score, and abbreviated injury scale scores for each body system. Patients transported by air and ground were compared with regard to demographics, clinical parameters, vital signs, arterial blood gas data, and outcome.

RESULTS

A total of 336 patients were included (79 air medical and 257 ground transports). No significant differences arose between the groups with regard to demographic, clinical, vital sign, and arterial blood gas data. Air medical patients had decreased mortality (28% vs 31%, OR 0.9), and ground patients had increased mortality versus matched controls (33% vs 22%, OR 1.8). Discordant groups analysis revealed a statistically significant effect of transport personnel on outcome (P=.009). Neither advanced procedures nor the use of mannitol accounted for the improved outcomes; air medical crews used capnometry to guide ventilation on all study patients.

CONCLUSION

Air medical transport of severely head-injured patients undergoing paramedic RSI was associated with improved outcomes. Improved ventilation by capnometry may account for part of these improvements.

Cerebral pathophysiology and critical care neurology: basic hemodynamic principles, cerebral perfusion, and intracranial pressure

Pediatric neurologic intensive care differs from standard pediatric intensive care in two important respects. First, the diagnosis, monitoring, and management of problems related to disorders of cerebral perfusion and intracranial pressure (ICP) are central to nearly all of pediatric neurologic and neurosurgical intensive care. Second, various clinical problems normally encountered in the intensive care unit (ICU) have additional implications when associated with neurologic disease. Regardless of the cause, treatment should be undertaken as expeditiously as possible and should be based on the principles of resuscitation, reducing the volume of the intracranial contents, and reassessment. This chapter aims to outline some basic principles underlying the diagnosis and management of elevated ICP in children.

Defining ischemic burden after traumatic brain injury using 15O PET imaging of cerebral physiology

Whereas postmortem ischemic damage is common in head injury, antemortem demonstration of ischemia has proven to be elusive. Although 15O positron emission tomography may be useful in this area, the technique has traditionally analyzed data within regions of interest (ROIs) to improve statistical accuracy. In head injury, such techniques are limited because of the lack of a priori knowledge regarding the location of ischemia, coexistence of hyperaemia, and difficulty in defining ischemic cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO2) levels. We report a novel method for defining disease pathophysiology following head injury. Voxel-based approaches are used to define the distribution of oxygen extraction fraction (OEF) across the entire brain; the standard deviation of this distribution provides a measure of the variability of OEF. These data are also used to integrate voxels above a threshold OEF value to produce an ROI based upon coherent physiology rather than spatial contiguity (the ischemic brain volume; IBV). However, such approaches may suffer from poor statistical accuracy, particularly in regions with low blood flow. The magnitude of these errors has been assessed in modeling experiments using the Hoffman brain phantom and modified control datasets. We conclude that this technique is a valid and useful tool for quantifying ischemic burden after traumatic brain injury.

Incidence and mechanisms of cerebral ischemia in early clinical head injury

Antemortem demonstration of ischemia has proved elusive in head injury because regional CBF reductions may represent hypoperfusion appropriately coupled to hypometabolism. Fifteen patients underwent positron emission tomography within 24 hours of head injury to map cerebral blood flow (CBF), cerebral oxygen metabolism (CMRO2), and oxygen extraction fraction (OEF). We estimated the volume of ischemic brain (IBV) and used the standard deviation of the OEF distribution to estimate the efficiency of coupling between CBF and CMRO2. The IBV in patients was significantly higher than controls (67 +/- 69 vs. 2 +/- 3 mL; P < 0.01). The coexistence of relative ischemia and hyperemia in some patients implies mismatching of perfusion to oxygen use. Whereas the saturation of jugular bulb blood (SjO2) correlated with the IBV (r = 0.8, P < 0.01), SjO2 values of 50% were only achieved at an IBV of 170 +/- 63 mL (mean +/- 95% CI), which equates to 13 +/- 5% of the brain. Increases in IBV correlated with a poor Glasgow Outcome Score 6 months after injury (rho = -0.6, P < 0.05). These results suggest significant ischemia within the first day after head injury. The ischemic burden represented by this "traumatic penumbra" is poorly detected by bedside clinical monitors and has significant associations with outcome.

Treatment of space-occupying cerebral infarction

OBJECTIVE

Patients with a hemispheric infarct accompanied by massive edema have a poor prognosis; the case fatality rate may be as high as 80%, and most survivors are left severely disabled. Various treatment strategies have been proposed to limit brain tissue shifts and to reduce intracranial pressure, but their use is controversial. We performed a systematic search of the literature to review the evidence of efficacy of these therapeutic modalities.

DATA SOURCES

Literature searches were carried out on MEDLINE and PubMed.

STUDY SELECTION

Studies were included if they were published in English between 1966 and February 2002 and addressed the effect of osmotherapy, hyperventilation, barbiturates, steroids, hypothermia, or decompressive surgery in supratentorial infarction with edema in animals or humans.

DATA SYNTHESIS

Animal studies of medical treatment strategies in focal cerebral ischemia produced conflicting results. If any, experimental support for these strategies is derived from studies with animal models of moderately severe focal ischemia instead of severe space-occupying infarction. None of the treatment options have improved outcome in randomized clinical trials. Two large nonrandomized studies of decompressive surgery yielded promising results in terms of reduction of mortality and improvement of functional outcome.

CONCLUSIONS

There is no treatment modality of proven efficacy for patients with space-occupying hemispheric infarction. Decompressive surgery might be the most promising therapeutic option. For decisive answers, randomized, controlled clinical trials are needed.

Effect of hyperventilation on cerebral blood flow in traumatic head injury: clinical relevance and monitoring correlates

OBJECTIVE

To investigate the effect of hyperventilation on cerebral blood flow in traumatic brain injury.

DESIGN

A prospective interventional study.

SETTING

A specialist neurocritical care unit.

PATIENTS

Fourteen healthy volunteers and 33 patients within 7 days of closed head injury.

INTERVENTIONS

All subjects underwent positron emission tomography imaging of cerebral blood flow. In patients, PaCO2 was reduced from 36 +/- 1 to 29 +/- 1 torr (4.8 +/- 0.1 to 3.9 +/- 0.1 kPa) and measurements repeated. Jugular venous saturation (SjvO2 ) and arteriovenous oxygen content differences (AVDO2 ) were monitored in 25 patients and values related to positron emission tomography variables.

MEASUREMENTS AND MAIN RESULTS

The volumes of critically hypoperfused and hyperperfused brain (HypoBV and HyperBV, in milliliters) were calculated based on thresholds of 10 and 55 mL.100g(-1).min(-1), respectively. Whereas baseline HypoBV was significantly higher in patients ( p<.05), baseline HyperBV was similar to values in healthy volunteers. Hyperventilation resulted in increases in cerebral perfusion pressure (p <.0001) and reductions in intracranial pressure (p <.001), whereas SjvO2 (>50%) and AVDO2 (<9 mL/mL) did not exceed global ischemic thresholds. However, despite these beneficial effects, hyperventilation shifted the cerebral blood flow distribution curve toward the hypoperfused range, with a decrease in global cerebral blood flow (31 +/- 1 to 23 +/- 1 mL.100g(-1).min(-1); p<.0001) and an increase in HypoBV (22 [1-141] to 51 [2-428] mL; p<.0001). Hyperventilation-induced increases in HypoBV were apparently nonlinear, with a threshold value between 34 and 38 torr (4.5-5 kPa).

CONCLUSIONS

Hyperventilation increases the volume of severely hypoperfused tissue within the injured brain, despite improvements in cerebral perfusion pressure and intracranial pressure. Significant hyperperfusion is uncommon, even at a time when conventional clinical management includes a role for modest hyperventilation. These reductions in regional cerebral perfusion are not associated with ischemia, as defined by global monitors of oxygenation, but may represent regions of potentially ischemic brain tissue.

Helicopter transport of pediatric trauma patients in an urban emergency medical services system: a critical analysis

BACKGROUND

Helicopter transport of pediatric trauma patients in an urban Emergency Medical Services system remains controversial.

METHODS

A retrospective review of pediatric patients transported by helicopter to a pediatric trauma center in Los Angeles, California, was conducted over a 3-year period. Pediatric patients (age < 15 years) are transported by helicopter if ground transport to a pediatric trauma center would exceed 20 minutes. Emergency Medical Services reports and hospital records were reviewed for key prehospital and outcome indicators.

RESULTS

One hundred eighty-nine patients met the study inclusion criteria. The median age was 5 years (range, 0-14 years). The most common mechanisms of injury were falls and automobile versus pedestrian crashes. Eighty-two percent of patients had a Revised Trauma Score > 7. Of the 175 (93%) patients whose hospital records were available, 24 (14%) were intubated in the emergency department, 32 (18%) were admitted to the intensive care unit, and 7 (4%) were taken directly to the operating room. Injury Severity Scores (ISSs) were as follows: ISS 0 to 15, 146 (83%); ISS 16 to 30, 26 (15%); and ISS > 30, 3 (2%). Fifty-seven (33%) patients were discharged home from the emergency department.

CONCLUSION

The majority of pediatric trauma patients transported by helicopter in our study sustained minor injuries. A revised policy to better identify pediatric patients who might benefit from helicopter transport appears to be warranted.

Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study

Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Conversely, positron emission tomography (PET) establishes metabolism of the whole brain, but only for the duration of the scan. The objective of this study was to apply both techniques to head-injured patients simultaneously to assess the relation between microdialysis (glucose, lactate, lactate/pyruvate [L/P] ratio, and glutamate) and PET (cerebral blood flow [CBF], cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen) parameters. Microdialysis catheters were inserted into the frontal cerebral cortex and adipose tissue of the anterior abdominal wall of 17 severely head-injured patients. Microdialysis was performed during PET scans, with regions of interest defined by the location of the microdialysis catheter membrane. An intervention (hyperventilation) was performed in 13 patients. The results showed that combining PET and microdialysis to monitor metabolism in ventilated patients is feasible and safe, although logistically complex. There was a significant relation between the L/P ratio and the OEF (Spearman r = 0.69, P = 0.002). There was no significant relation between CBF and the microdialysis parameters. Moderate short-term hyperventilation appeared to be tolerated in terms of brain chemistry, although no areas were sampled by microdialysis where the OEF exceeded 70%. Hyperventilation causing a reduction of the arterial carbon dioxide tension by 0.9 kPa resulted in a significant elevation of the OEF, in association with a reduction in glucose, but no significant elevation in the L/P ratio or glutamate.