Monitoring of brain tissue PO2 in traumatic brain injury: effect of cerebral hypoxia on outcome

Brain tissue oxygen combined with intracranial pressure monitoring versus isolated intracranial pressure monitoring in patients with traumatic brain injury: an updated systematic review and meta-analysis

Monitoring intracranial pressure (ICP) is pivotal in the management of severe traumatic brain injury (TBI), but secondary brain injuries can arise despite normal ICP levels. Cerebral tissue oxygenation monitoring (PbtO2) may detect neuronal tissue infarction thresholds, enhancing neuroprotection. We performed a systematic review and meta-analysis to evaluate the effects of combined cerebral tissue oxygenation (PbtO2) and ICP compared to isolated ICP monitoring in patients with TBI. PubMed, Embase, Cochrane, and Web of Sciences databases were searched for trials published up to June 2023. A total of 16 studies comprising 37,820 patients were included. ICP monitoring was universal, with additional placement of PbtO2 in 2222 individuals (5.8%). The meta-analysis revealed a reduction in mortality (OR 0.57, 95% CI 0.37-0.89, p = 0.01), a greater likelihood of favorable outcomes (OR 2.28, 95% CI 1.66-3.14, p < 0.01), and a lower chance of poor outcomes (OR 0.51, 95% CI 0.34-0.79, p < 0.01) at 6 months for the PbtO2 plus ICP group. However, these patients experienced a longer length of hospital stay (MD 2.35, 95% CI 0.50-4.20, p = 0.01). No significant difference was found in hospital mortality rates (OR 0.81, 95% CI 0.61-1.08, p = 0.16) or intensive care unit length of stay (MD 2.46, 95% CI - 0.11-5.04, p = 0.06). The integration of PbtO2 to ICP monitoring improved mortality outcomes and functional recovery at 6 months in patients with TBI. PROSPERO (International Prospective Register of Systematic Reviews) CRD42022383937; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=383937.

Future of neurocritical care: Integrating neurophysics, multimodal monitoring, and machine learning

Multimodal monitoring (MMM) in the intensive care unit (ICU) has become increasingly sophisticated with the integration of neurophysical principles. However, the challenge remains to select and interpret the most appropriate combination of neuromonitoring modalities to optimize patient outcomes. This manuscript reviewed current neuromonitoring tools, focusing on intracranial pressure, cerebral electrical activity, metabolism, and invasive and noninvasive autoregulation monitoring. In addition, the integration of advanced machine learning and data science tools within the ICU were discussed. Invasive monitoring includes analysis of intracranial pressure waveforms, jugular venous oximetry, monitoring of brain tissue oxygenation, thermal diffusion flowmetry, electrocorticography, depth electroencephalography, and cerebral microdialysis. Noninvasive measures include transcranial Doppler, tympanic membrane displacement, near-infrared spectroscopy, optic nerve sheath diameter, positron emission tomography, and systemic hemodynamic monitoring including heart rate variability analysis. The neurophysical basis and clinical relevance of each method within the ICU setting were examined. Machine learning algorithms have shown promise by helping to analyze and interpret data in real time from continuous MMM tools, helping clinicians make more accurate and timely decisions. These algorithms can integrate diverse data streams to generate predictive models for patient outcomes and optimize treatment strategies. MMM, grounded in neurophysics, offers a more nuanced understanding of cerebral physiology and disease in the ICU. Although each modality has its strengths and limitations, its integrated use, especially in combination with machine learning algorithms, can offer invaluable information for individualized patient care.

The Impact of Invasive Brain Oxygen Pressure Guided Therapy on the Outcome of Patients with Traumatic Brain Injury: A Systematic Review and Meta-Analysis

Traumatic brain injury (TBI) is a major public health burden, causing death and disability worldwide. Intracranial hypertension and brain hypoxia are the main mechanisms of secondary brain injury. As such, management strategies guided by intracranial pressure (ICP) and brain oxygen (PbtO₂) monitoring could improve the prognosis of these patients. Our objective was to summarize the current evidence regarding the impact of PbtO₂-guided therapy on the outcome of patients with TBI. We performed a systematic search of PubMed, Scopus, and the Cochrane library databases, following the protocol registered in PROSPERO. Only studies comparing PbtO₂/ICP-guided therapy with ICP-guided therapy were selected. Primary outcome was neurological outcome at 3 and 6 months assessed by using the Glasgow Outcome Scale; secondary outcomes included hospital and long-term mortality, burden of intracranial hypertension, and brain tissue hypoxia. Out of 6254 retrieved studies, 15 studies (n = 37,245 patients, of who 2184 received PbtO₂-guided therapy) were included in the final analysis. When compared with ICP-guided therapy, the use of combined PbO₂/ICP-guided therapy was associated with a higher probability of favorable neurological outcome (odds ratio 2.21 [95% confidence interval 1.72-2.84]) and of hospital survival (odds ratio 1.15 [95% confidence interval 1.04-1.28]). The heterogeneity (I²) of the studies in each analysis was below 40%. However, the quality of evidence was overall low to moderate. In this meta-analysis, PbtO₂-guided therapy was associated with reduced mortality and more favorable neurological outcome in patients with TBI. The low-quality evidence underlines the need for the results from ongoing phase III randomized trials.

Effect of inotropic agents on oxygenation and cerebral perfusion in acute brain injury

Introduction

Tissue hypoxia and insufficient energy delivery is one of the mechanisms behind the occurrence of several complications in acute brain injured patients. Several interventions can improve cerebral oxygenation; however, the effects of inotropic agents remain poorly characterized.

Methods

Retrospective analysis including patients suffering from acute brain injury and monitored with brain oxygen pressure (PbtO2) catheter, in whom inotropic agents were administered according to the decision of the treating physician's decision; PbtO2 values were collected before, 1 and 2 h after the initiation of therapy from the patient data monitoring system. PbtO2 “responders” were patients with a relative increase in PbtO2 from baseline values of at least 20%.

Results

A total of 35 patients were included in this study. Most of them (31/35, 89%) suffered from non-traumatic subarachnoid hemorrhage (SAH). Compared with baseline values [20 (14–24) mmHg], PbtO2 did not significantly increase over time [19 (15–25) mmHg at 1 h and 19 (17–25) mmHg at 2 h, respectively; p = 0.052]. A total of 12/35 (34%) patients were PbtO2 “responders,” in particular if low PbtO2 was observed at baseline. A PbtO2 of 17 mmHg at baseline had a sensibility of 84% and a specificity of 91% to predict a PbtO2 responder. A significant direct correlation between changes in PbtO2 and cardiac output [r = 0.496 (95% CI 0.122 to 0.746), p = 0.01; n = 25] and a significant negative correlation between changes in PbtO2 and cerebral perfusion pressure [r = −0.389 (95% CI −0.681 to −0.010), p = 0.05] were observed.

Conclusions

In this study, inotropic administration significantly increased brain oxygenation in one third of brain injured patients, especially when tissue hypoxia was present at baseline. Future studies should highlight the role of inotropic agents in the management of tissue hypoxia in this setting.

Management of Severe Traumatic Brain Injury in Pediatric Patients

The optimal management of severe traumatic brain injury (TBI) in the pediatric population has not been well studied. There are a limited number of research articles studying the management of TBI in children. Given the prevalence of severe TBI in the pediatric population, it is crucial to develop a reference TBI management plan for this vulnerable population. In this review, we seek to delineate the differences between severe TBI management in adults and children. Additionally, we also discuss the known molecular pathogenesis of TBI. A better understanding of the pathophysiology of TBI will inform clinical management and development of therapeutics. Finally, we propose a clinical algorithm for the management and treatment of severe TBI in children using published data.

The Impact of Short-Term Hyperoxia on Cerebral Metabolism: A Systematic Review and Meta-Analysis

BACKGROUND

Cerebral ischemia due to hypoxia is a major cause of secondary brain injury and is associated with higher morbidity and mortality in patients with acute brain injury. Hyperoxia could improve energetic dysfunction in the brain in this setting. Our objectives were to perform a systematic review and meta-analysis of the current literature and to assess the impact of normobaric hyperoxia on brain metabolism by using cerebral microdialysis.

METHODS

We searched Medline and Scopus, following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement; we searched for retrospective and prospective observational studies, interventional studies, and randomized clinical trials that performed a hyperoxia challenge in patients with acute brain injury who were concomitantly monitored with cerebral microdialysis. This study was registered in PROSPERO (CRD420211295223).

RESULTS

We included a total of 17 studies, with a total of 311 patients. A statistically significant reduction in cerebral lactate values (pooled standardized mean difference [SMD] - 0.38 [- 0.53 to - 0.23]) and lactate to pyruvate ratio values (pooled SMD - 0.20 [- 0.35 to - 0.05]) was observed after hyperoxia. However, glucose levels (pooled SMD - 0.08 [- 0.23 to 0.08]) remained unchanged after hyperoxia.

CONCLUSIONS

Normobaric hyperoxia may improve cerebral metabolic disturbances in patients with acute brain injury. The clinical impact of such effects needs to be further elucidated.

Utilization of Brain Tissue Oxygenation Monitoring and Association with Mortality Following Severe Traumatic Brain Injury

BACKGROUND

The aim of this study was to describe the utilization patterns of brain tissue oxygen (PbtO₂) monitoring following severe traumatic brain injury (TBI) and determine associations with mortality, health care use, and pulmonary toxicity.

METHODS

We conducted a retrospective cohort study of patients from United States trauma centers participating in the American College of Surgeons National Trauma Databank between 2008 and 2016. We examined patients with severe TBI (defined by admission Glasgow Coma Scale score ≤ 8) over the age of 18 years who survived more than 24 h from admission and required intracranial pressure (ICP) monitoring. The primary exposure was PbtO₂ monitor placement. The primary outcome was hospital mortality, defined as death during the hospitalization or discharge to hospice. Secondary outcomes were examined to determine the association of PbtO₂ monitoring with health care use and pulmonary toxicity and included the following: (1) intensive care unit length of stay, (2) hospital length of stay, and (3) development of acute respiratory distress syndrome (ARDS). Regression analysis was used to assess differences in outcomes between patients exposed to PbtO₂ monitor placement and those without exposure by using propensity weighting to address selection bias due to the nonrandom allocation of treatment groups and patient dropout.

RESULTS

A total of 35,501 patients underwent placement of an ICP monitor. There were 1,346 (3.8%) patients who also underwent PbtO₂ monitor placement, with significant variation regarding calendar year and hospital. Patients who underwent placement of a PbtO₂ monitor had a crude in-hospital mortality of 31.1%, compared with 33.5% in patients who only underwent placement of an ICP monitor (adjusted risk ratio 0.84, 95% confidence interval 0.76-0.93). The development of the ARDS was comparable between patients who underwent placement of a PbtO₂ monitor and patients who only underwent placement of an ICP monitor (9.2% vs. 9.8%, adjusted risk ratio 0.89, 95% confidence interval 0.73-1.09).

CONCLUSIONS

PbtO₂ monitor utilization varied widely throughout the study period by calendar year and hospital. PbtO₂ monitoring in addition to ICP monitoring, compared with ICP monitoring alone, was associated with a decreased in-hospital mortality, a longer length of stay, and a similar risk of ARDS. These findings provide further guidance for clinicians caring for patients with severe TBI while awaiting completion of further randomized controlled trials.

The Predictive Power of Near-Infrared Spectroscopy in Improving Cognitive Problems in Patients Undergoing Brain Surgeries: A Systematic Review

One of the main objectives in neurosurgical procedures is the prevention of cerebral ischemia and hypoxia leading to secondary brain injury. Different methods for early detection of intraoperative cerebral ischemia and hypoxia have been used. Near-infrared spectroscopy (NIRS) is a simple, non-invasive method for monitoring cerebral oxygenation increasingly used today. The aim of this study was to systematically review the brain monitoring with NIRS in neurosurgery. The search process resulted in the detection of 324 articles using valid keywords on the electronic databases, including Embase, PubMed, Scopus, Web of Science, and Cochrane Library. Subsequently, the full texts of 34 studies were reviewed, and finally 11 articles (seven prospective studies, three retrospective studies, and one randomized controlled trial) published from 2005 to 2020 were identified as eligible for systematic review. Meta-analysis was not possible due to high heterogeneity in neurological and neurosurgical conditions of patients, expression of different clinical outcomes, and different standard reference tests in the studies reviewed. The results showed that NIRS is a non-invasive cerebral oximetry that provides continuous and measurable cerebral oxygenation information and can be used in a variety of clinical settings.

GdDO3NI Enhanced Magnetic Resonance Imaging Allows Imaging of Hypoxia After Brain Injury

BACKGROUND

Brain tissue hypoxia is a common consequence of traumatic brain injury (TBI) due to the rupture of blood vessels during impact and it correlates with poor outcome. The current magnetic resonance imaging (MRI) techniques are unable to provide a direct map of tissue hypoxia.

PURPOSE

To investigate whether GdDO3NI, a nitroimidazole-based T₁ MRI contrast agent allows imaging hypoxia in the injured brain after experimental TBI.

STUDY TYPE

Prospective.

ANIMAL MODEL

TBI-induced mice (controlled cortical impact model) were intravenously injected with either conventional T₁ agent (gadoteridol) or GdDO3NI at 0.3 mmol/kg dose (n = 5 for each cohort) along with pimonidazole (60 mg/kg) at 1 hour postinjury and imaged for 3 hours following which they were euthanized.

FIELD STRENGTH/SEQUENCE

7 T/T₂ -weighted spin echo and T₁ -weighted gradient echo.

ASSESSMENT

Injured animals were imaged with T₂ -weighted spin-echo sequence to estimate the extent of the injury. The mice were then imaged precontrast and postcontrast using a T₁ -weighted gradient-echo sequence for 3 hours postcontrast. Regions of interests were drawn on the brain injury region, the contralateral brain as well as on the cheek muscle region for comparison of contrast kinetics. Brains were harvested immediately post-imaging for immunohistochemical analysis.

STATISTICAL TESTS

One-way analysis of variance and two-sample t-tests were performed with a P < 0.05 was considered statistically significant.

RESULTS

GdDO3NI retention in the injury region at 2.5-3 hours post-injection was significantly higher compared to gadoteridol (mean retention fraction 63.95% ± 27.43% vs. 20.68% ± 7.43% for gadoteridol at 3 hours) while it rapidly cleared out of the muscle region. Pimonidazole staining confirmed the presence of hypoxia in both gadoteridol and GdDO3NI cohorts, and the later cohort showed good agreement with MRI contrast enhancement.

DATA CONCLUSION

GdDO3NI was successfully shown to visualize hypoxia in the brain post-TBI using T₁ -weighted MRI at 2.5-3 hours postcontrast.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 1.

Brain tissue oxygenation guided therapy and outcome in non-traumatic subarachnoid hemorrhage

Brain hypoxia can occur after non-traumatic subarachnoid hemorrhage (SAH), even when levels of intracranial pressure (ICP) remain normal. Brain tissue oxygenation (PbtO₂) can be measured as a part of a neurological multimodal neuromonitoring. Low PbtO₂ has been associated with poor neurologic recovery. There is scarce data on the impact of PbtO₂ guided-therapy on patients’ outcome. This single-center cohort study (June 2014–March 2020) included all patients admitted to the ICU after SAH who required multimodal monitoring. Patients with imminent brain death were excluded. Our primary goal was to assess the impact of PbtO₂-guided therapy on neurological outcome. Secondary outcome included the association of brain hypoxia with outcome. Of the 163 patients that underwent ICP monitoring, 62 were monitored with PbtO₂ and 54 (87%) had at least one episode of brain hypoxia. In patients that required treatment based on neuromonitoring strategies, PbtO₂-guided therapy (OR 0.33 [CI 95% 0.12–0.89]) compared to ICP-guided therapy had a protective effect on neurological outcome at 6 months. In this cohort of SAH patients, PbtO₂-guided therapy might be associated with improved long-term neurological outcome, only when compared to ICP-guided therapy.

Forecasting intracranial hypertension using multi-scale waveform metrics

OBJECTIVE

Acute intracranial hypertension is an important risk factor of secondary brain damage after traumatic brain injury. Hypertensive episodes are often diagnosed reactively, leading to late detection and lost time for intervention planning. A pro-active approach that predicts critical events several hours ahead of time could assist in directing attention to patients at risk.

APPROACH

We developed a prediction framework that forecasts onsets of acute intracranial hypertension in the next 8 h. It jointly uses cerebral auto-regulation indices, spectral energies and morphological pulse metrics to describe the neurological state of the patient. One-minute base windows were compressed by computing signal metrics, and then stored in a multi-scale history, from which physiological features were derived.

MAIN RESULTS

Our model predicted events up to 8 h in advance with an alarm recall rate of 90% at a precision of 30% in the MIMIC-III waveform database, improving upon two baselines from the literature. We found that features derived from high-frequency waveforms substantially improved the prediction performance over simple statistical summaries of low-frequency time series, and each of the three feature classes contributed to the performance gain. The inclusion of long-term history up to 8 h was especially important.

SIGNIFICANCE

Our results highlight the importance of information contained in high-frequency waveforms in the neurological intensive care unit. They could motivate future studies on pre-hypertensive patterns and the design of new alarm algorithms for critical events in the injured brain.

A Swine Model of Severe Propranolol Toxicity Permitting Direct Measurement of Brain Tissue Oxygenation

INTRODUCTION

High-dose insulin (HDI) therapy has been used successfully for beta-blocker toxicity, but needs further study when hypotension persists despite HDI. The objective was to develop a model of propranolol toxicity with persistent hypotension despite HDI and to develop means to measure cerebral oxygen tension (PbrO₂).

METHODS

Eight anesthetized Yorkshire pigs were instrumented with a tracheostomy, Swan-Ganz catheter, arterial catheter, and intra-cerebral pressure and oxygen monitor. Intravenous propranolol was given until the initial point of toxicity (POT); 25% reduction from baseline mean arterial pressure (MAP) × heart rate (HR). At the initial POT, normal saline (NS) bolus and infusion along with HDI infusion were started. The propranolol infusion was titrated up slowly to induce hypotension. Group 2 pigs received a norepinephrine (NE) infusion after a secondary POT defined as a MAP < 50 mmHg. NE was titrated to maintain subsequent MAPs > 50 mmHg. Cardiac output, HR, MAP, PbrO₂, and intracranial pressure were then recorded every 5 min until death or 4 h. Systemic vascular resistance, potassium, and glucose were also measured. Surviving pigs were euthanized.

RESULTS

Two pigs received unique doses for protocol development. One pig developed a tachyarrhythmia prior to protocol, one failed to reach secondary POT, leaving 2 pigs in each group reaching secondary POT. The range of PbrO₂ recordings for group 1 was 12.7-48.5 mmHg and 9.2-26.2 mmHg for group 2.

CONCLUSION

We report a pilot study swine model of propranolol toxicity with hypotension despite HDI, in which physiologic measures including PbrO₂ are achieved. Our toxicity model can be used in the future, and the hemodynamic and brain monitoring model may prove important for subsequent research in various contexts.

The effects of normovolemic anemia and blood transfusion on cerebral microcirculation after severe head injury

BACKGROUND

Cerebral regional microcirculation is altered following severe head injury. In addition to tissue disruption, partial pressure of tissue oxygenation is impaired due to an increase in the oxygen tissue gradient. The heterogenic distribution of cerebral microcirculation is multifactorial, and acute anemia challenges further the delivery of oxygen to tissues. Currently, a restrictive transfusion threshold is globally applied; however, it is unclear how anemia modifies regional cerebral microcirculation; hence, it is unclear if by aiming to a global endpoint, specific anatomical regions undergo ischemia. This study aims to quantify the temporal changes in cerebral microcirculation after severe head injury, under the effect of anemia and transfusion. It also aims to assess its effects specifically at the ischemic penumbra compared to contralateral regions and its interactions with axonal integrity in real time. Twelve ovine models were subjected to a severe contusion and acceleration-deceleration injury. Normovolemic anemia to a restrictive threshold was maintained after injury, followed by autologous transfusion. Direct quantification of cerebral microcirculation used cytometric count of color-coded microspheres. Axonal injury was assessed using amyloid precursor protein staining.

RESULTS

A mixed-effect regression model from pre-transfusion to post-transfusion times with a random intercept for each sheep was used. Cerebral microcirculation amongst subjects with normal intracranial pressure was maintained from baseline and increased further after transfusion. Subjects with high intracranial pressure had a consistent reduction of their microcirculation to ischemic thresholds (20-30 ml/100 g/min) without an improvement after transfusion. Cerebral PtiO₂ was reduced when exposed to anemia but increased in a 9.6-fold with transfusion 95% CI 5.6 to 13.6 (p value < 0.001).

CONCLUSIONS

After severe head injury, the exposure to normovolemic anemia to a restrictive transfusion threshold, leads to a consistent reduction on cerebral microcirculation below ischemic thresholds, independent of cerebral perfusion pressure. Amongst subjects with raised intracranial pressure, microcirculation does not improve after transfusion. Cerebral oxymetry is impaired during anemia with a statistically significant increase after transfusion. Current transfusion practices in neurocritical care are based on a rigid hemoglobin threshold, a view that excludes cerebral metabolic demands and specific needs. An RCT exploring these concepts is warranted.

The future of non-invasive cerebral oximetry in neurosurgical procedures: A systematic review

Background:Cerebral hypoxia is one of the most important causes of secondary brain injury during neurosurgical procedures and in neurointensive care. In patients with brain injury, cerebrovascular reactivity may be impaired and a decrease in mean arterial pressure or cerebral perfusion pressure may lead to inadequate cerebral blood flow and secondary ischemia. There are several techniques available to measure brain oxygenation. In particular, near infrared spectroscopy (NIRS) is a non-invasive neuromonitoring technique and there has been a rapid expansion of clinical evidence that NIRS reduces perioperative neurologic complications.  Methods:This systematic review synthesizes prospective and retrospective cohort studies that investigate the benefit of using NIRS in prevention of perioperative neurologic complications. The methodological quality of these studies is appraised.Results:Seven studies were included in this systematic review. The methodological quality of each study was assessed. They had representative patient populations, clear selection criteria and clear descriptions of study designs. Reproducible study protocols with ethics board approval were present. Clinical results were described in sufficient detail and were applicable to patient undergoing neurosurgical procedures and in neurointensive care. Limitations included small sample sizes and lack of reference standard.Conclusions:This systematic review synthesizes the most current evidence of non-invasive, inexpensive, and continuous measurement of cerebral oxygenation by NIRS. Results gained from these studies are clinically useful and shed light on how this neuromonitoring technique is beneficial in preventing perioperative neurological complications.

Brain Oxygen Optimization in Severe Traumatic Brain Injury Phase-II: A Phase II Randomized Trial

OBJECTIVES

A relationship between reduced brain tissue oxygenation and poor outcome following severe traumatic brain injury has been reported in observational studies. We designed a Phase II trial to assess whether a neurocritical care management protocol could improve brain tissue oxygenation levels in patients with severe traumatic brain injury and the feasibility of a Phase III efficacy study.

DESIGN

Randomized prospective clinical trial.

SETTING

Ten ICUs in the United States.

PATIENTS

One hundred nineteen severe traumatic brain injury patients.

INTERVENTIONS

Patients were randomized to treatment protocol based on intracranial pressure plus brain tissue oxygenation monitoring versus intracranial pressure monitoring alone. Brain tissue oxygenation data were recorded in the intracranial pressure -only group in blinded fashion. Tiered interventions in each arm were specified and impact on intracranial pressure and brain tissue oxygenation measured. Monitors were removed if values were normal for 48 hours consecutively, or after 5 days. Outcome was measured at 6 months using the Glasgow Outcome Scale-Extended.

MEASUREMENTS AND MAIN RESULTS

A management protocol based on brain tissue oxygenation and intracranial pressure monitoring reduced the proportion of time with brain tissue hypoxia after severe traumatic brain injury (0.45 in intracranial pressure-only group and 0.16 in intracranial pressure plus brain tissue oxygenation group; p < 0.0001). Intracranial pressure control was similar in both groups. Safety and feasibility of the tiered treatment protocol were confirmed. There were no procedure-related complications. Treatment of secondary injury after severe traumatic brain injury based on brain tissue oxygenation and intracranial pressure values was consistent with reduced mortality and increased proportions of patients with good recovery compared with intracranial pressure-only management; however, the study was not powered for clinical efficacy.

CONCLUSIONS

Management of severe traumatic brain injury informed by multimodal intracranial pressure and brain tissue oxygenation monitoring reduced brain tissue hypoxia with a trend toward lower mortality and more favorable outcomes than intracranial pressure-only treatment. A Phase III randomized trial to assess impact on neurologic outcome of intracranial pressure plus brain tissue oxygenation-directed treatment of severe traumatic brain injury is warranted.

Cerebral Microcirculation during Experimental Normovolaemic Anemia

Anemia is accepted among critically ill patients as an alternative to elective blood transfusion. This practice has been extrapolated to head injury patients with only one study comparing the effects of mild anemia on neurological outcome. There are no studies quantifying microcirculation during anemia. Experimental studies suggest that anemia leads to cerebral hypoxia and increased rates of infarction, but the lack of clinical equipoise, when testing the cerebral effects of transfusion among critically injured patients, supports the need of experimental studies. The aim of this study was to quantify cerebral microcirculation and the potential presence of axonal damage in an experimental model exposed to normovolaemic anemia, with the intention of describing possible limitations within management practices in critically ill patients. Under non-recovered anesthesia, six Merino sheep were instrumented using an intracardiac transeptal catheter to inject coded microspheres into the left atrium to ensure systemic and non-chaotic distribution. Cytometric analyses quantified cerebral microcirculation at specific regions of the brain. Amyloid precursor protein staining was used as an indicator of axonal damage. Animals were exposed to normovolaemic anemia by blood extractions from the indwelling arterial catheter with simultaneous fluid replacement through a venous central catheter. Simultaneous data recording from cerebral tissue oxygenation, intracranial pressure, and cardiac output was monitored. A regression model was used to examine the effects of anemia on microcirculation with a mixed model to control for repeated measures. Homogeneous and normal cerebral microcirculation with no evidence of axonal damage was present in all cerebral regions, with no temporal variability, concluding that acute normovolaemic anemia does not result in short-term effects on cerebral microcirculation in the ovine brain.

Monitoring of brain and systemic oxygenation in neurocritical care patients

Maintenance of adequate oxygenation is a mainstay of intensive care, however, recommendations on the safety, accuracy, and the potential clinical utility of invasive and non-invasive tools to monitor brain and systemic oxygenation in neurocritical care are lacking. A literature search was conducted for English language articles describing bedside brain and systemic oxygen monitoring in neurocritical care patients from 1980 to August 2013. Imaging techniques e.g., PET are not considered. A total of 281 studies were included, the majority described patients with traumatic brain injury (TBI). All tools for oxygen monitoring are safe. Parenchymal brain oxygen (PbtO2) monitoring is accurate to detect brain hypoxia, and it is recommended to titrate individual targets of cerebral perfusion pressure (CPP), ventilator parameters (PaCO2, PaO2), and transfusion, and to manage intracranial hypertension, in combination with ICP monitoring. SjvO2 is less accurate than PbtO2. Given limited data, NIRS is not recommended at present for adult patients who require neurocritical care. Systemic monitoring of oxygen (PaO2, SaO2, SpO2) and CO2 (PaCO2, end-tidal CO2) is recommended in patients who require neurocritical care.

A Prospective Randomized Study of Brain Tissue Oxygen Pressure-Guided Management in Moderate and Severe Traumatic Brain Injury Patients

The purpose of this study was to compare the effect of PbtO₂-guided therapy with traditional intracranial pressure- (ICP-) guided treatment on the management of cerebral variables, therapeutic interventions, survival rates, and neurological outcomes of moderate and severe traumatic brain injury (TBI) patients. From 2009 to 2010, TBI patients with a Glasgow coma scale <12 were recruited from 6 collaborative hospitals in northern Taiwan, excluding patients with severe systemic injuries, fixed and dilated pupils, and other major diseases. In total, 23 patients were treated with PbtO₂-guided management (PbtO₂ > 20 mmHg), and 27 patients were treated with ICP-guided therapy (ICP < 20 mmHg and CPP > 60 mmHg) in the neurosurgical intensive care unit (NICU); demographic characteristics were similar across groups. The survival rate in the PbtO₂-guided group was also significantly increased at 3 and 6 months after injury. Moreover, there was a significant correlation between the PbtO₂ signal and Glasgow outcome scale-extended in patients from 1 to 6 months after injury. This finding demonstrates that therapy directed by PbtO₂ monitoring is valuable for the treatment of patients with moderate and severe TBI and that increasing PaO₂ to 150 mmHg may be efficacious for preventing cerebral hypoxic events after brain trauma.

Normobaric oxygen worsens outcome after a moderate traumatic brain injury

Traumatic brain injury (TBI) is a multifaceted injury and a leading cause of death in children, young adults, and increasingly in Veterans. However, there are no neuroprotective agents clinically available to counteract damage or promote repair after brain trauma. This study investigated the neuroprotective effects of normobaric oxygen (NBO) after a controlled cortical impact in rats. The central hypothesis was that NBO treatment would reduce lesion volume and functional deficits compared with air-treated animals after TBI by increasing brain oxygenation thereby minimizing ischemic injury. In a randomized double-blinded design, animals received either NBO (n = 8) or normal air (n = 8) after TBI. Magnetic resonance imaging (MRI) was performed 0 to 3 hours, and 1, 2, 7, and 14 days after an impact to the primary forelimb somatosensory cortex. Behavioral assessments were performed before injury induction and before MRI scans on days 2, 7, and 14. Nissl staining was performed on day 14 to corroborate the lesion volume detected from MRI. Contrary to our hypothesis, we found that NBO treatment increased lesion volume in a rat model of moderate TBI and had no positive effect on behavioral measures. Our results do not promote the acute use of NBO in patients with moderate TBI.

Brain tissue oxygenation and cerebral metabolic patterns in focal and diffuse traumatic brain injury

INTRODUCTION

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. There are reasons to believe that knowledge of brain tissue oxygenation (BtipO2) would add information with the potential of improving patient outcome. The aim of this study was to examine BtipO2 and cerebral metabolism using the Neurovent-PTO probe and cerebral microdialysis (MD) in TBI patients.

METHODS

Twenty-three severe TBI patients with monitoring of physiological parameters, ICP, CPP, BtipO2, and MD for biomarkers of energy metabolism (glucose, lactate, and pyruvate) and cellular distress (glutamate, glycerol) were included. Patients were grouped according to injury type (focal/diffuse) and placement of the Neurovent-PTO probe and MD catheter (injured/non-injured hemisphere).

RESULTS

We observed different patterns in BtipO2 and MD biomarkers in diffuse and focal injury where placement of the probe also influenced the results (ipsilateral/contralateral). In all groups, despite fairly normal levels of ICP and CPP, increased MD levels of glutamate, glycerol, or the L/P ratio were observed at BtipO2 <5 mmHg, indicating increased vulnerability of the brain at this level.

CONCLUSION

Monitoring of BtipO2 adds important information in addition to traditional ICP and CPP surveillance. Because of the different metabolic responses to very low BtipO2 in the individual patient groups we submit that brain tissue oximetry is a complementary tool rather than an alternative to MD monitoring.

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

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

Brain tissue oxygenation and cerebral perfusion pressure thresholds of ischemia in a standardized pig brain death model

BACKGROUND

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. Monitoring brain tissue oxygenation (BtipO2) is of considerable clinical interest, but the exact threshold level of ischemia has been difficult to establish due to the complexity of the clinical situation. The objective of this study was to use the Neurovent-PTO (NV) probe, and to define critical cerebral oxygenation- and CPP threshold levels of cerebral ischemia in a standardized brain death model caused by increasing the ICP in pig. Ischemia was defined by a severe increase of cerebral microdialysis (MD) lactate/pyruvate ratio (L/P ratio > 30).

METHODS

BtipO2, L/P ratio, Glucose, Glutamate, Glycerol and CPP were recorded using NV and MD probes during gradual increase of ICP by inflation of an epidural balloon catheter with saline until brain death was achieved.

RESULTS

Baseline level of BtipO2 was 22.9 ± 6.2 mmHg, the L/P ratio 17.7 ± 6.1 and CPP 73 ± 17 mmHg. BtipO2 and CPP decreased when intracranial volume was added. The L/P ratio increased above its ischemic levels, (>30)when CPP decreased below 30 mmHg and BtipO2 to <10 mmHg.

CONCLUSIONS

A severe increase of ICP leading to CPP below 30 mmHg and BtipO2 below 10 mmHg is associated with an increase of the L/P ratio, thus seems to be critical thresholds for cerebral ischemia under these conditions.

Position of probe determines prognostic information of brain tissue PO2 in severe traumatic brain injury

BACKGROUND

Monitoring brain tissue PO2 (PbtO2) is part of multimodality monitoring of patients with traumatic brain injury (TBI). However, PbtO2 measurement is a sampling of only a small area of tissue surrounding the sensor tip.

OBJECTIVE

To examine the effect of catheter location on the relationship between PbtO2 and neurological outcome.

METHODS

A total of 405 patients who had PbtO2 monitoring as part of standard management of severe traumatic brain injury were studied. The relationships between probe location and resulting PbtO2 and outcome were examined.

RESULTS

When the probe was located in normal brain, PbtO2 averaged 30.8 ± 18.2 compared with 25.6 ± 14.8 mm Hg when placed in abnormal brain (P < .001). Factors related to neurological outcome in the best-fit logistic regression model were age, PbtO2 probe position, postresuscitation motor Glasgow Coma Scale score, and PbtO2 trend pattern. Although average PbtO2 was significantly related to outcome in univariate analyses, it was not significant in the final logistic model. However, the interaction between PbtO2 and probe position was statistically significant. When the PbtO2 probe was placed in abnormal brain, the average PbtO2 was higher in those with a favorable outcome, 28.8 ± 12.0 mm Hg, compared with those with an unfavorable outcome, 19.5 ± 13.7 mm Hg (P = .01). PbtO2 and outcome were not related when the probe was placed in normal-appearing brain.

CONCLUSION

These results suggest that the location of the PbtO2 probe determines the PbtO2 values and the relationship of PbtO2 to neurological outcome.

Monitoring of brain oxygenation in surgery of ruptured middle cerebral artery aneurysms

Background:

The occurrence of brain ischemic lesions, due to temporary arterial occlusion or incorrect placement of the definitive clip, is a major complication of aneurysm surgery. Temporary clipping is a current technique during surgery and there is no reliable method of predicting the possibility of ischemia due to extended regional circulatory interruption. Even with careful inspection, misplacement of the definitive clip can be difficult to detect. Brain tissue oxygen concentration (PtiO₂) was monitored during surgery of middle cerebral artery (MCA) aneurysm presenting with subarachnoid hemorrhage (SAH), for detection of changes in brain oxygenation due to reduced blood flow, as a predictor of ischemic events, during temporary clipping and after definitive clipping.

Methods:

PtiO₂ was monitored during surgery of 13 patients harboring MCA aneurysms presenting with SAH, using a polarographic microcatheter (Licox, GMS, Kiel, Germany) placed in the territory of MCA.

Results

A decrease in PtiO₂ values was verified in every period of temporary clipping. Brain infarction occurred in 2 patients; in both cases, there was a decrease in PtiO₂ greater than 80% from basal value, a minimum value of less than 2 mmHg persisting for 2 or more minutes during temporary clipping, and an incomplete recovery of PtiO₂ after definitive clipping. In 2 patients, incomplete recovery of values after definitive clipping led to verification of inappropriate placement and repositioning of the clip.

Conclusion:

The results suggest that intraoperative monitoring of PtiO₂ may be a useful method of detection of changes in brain tissue oxygenation during MCA aneurysm surgery. Postoperative infarction in the territory of MCA developed in cases with an abrupt decrease of PtiO₂ and a very low and persistent minimum value, during temporary clipping, and an incomplete recovery after definitive clipping. Verification of clip position should be considered when there is an incomplete recovery or a persistent fall in PtiO₂ after definitive clipping.

Monitoring of brain tissue oxygenation in surgery of middle cerebral artery incidental aneurysms

Introduction:

The management of incidental unruptured aneurysms remains a matter of controversy; middle-sized or large anterior circulation incidental aneurysms, in young or middle age patients, should be considered for treatment. Surgical clipping is an accepted treatment for middle cerebral artery unruptured aneurysms. Ischemic events can occur even in cases of incidental aneurysm surgery. Since regional cerebral blood flow can be compromised due to temporary arterial clipping or to incorrect placement of defi nitive clip, we performed intra-operative monitoring of brain tissue oxygen concentration (PtiO₂), to detect changes in brain oxygenation due to reduced blood fl ow, eventually leading to ischemia, during surgery of middle cerebral artery incidental aneurysms.

Methods:

PtiO₂ monitoring was performed during surgery of eight patients harboring incidental MCA aneurysms, using a polarographic microcatheter (Licox, GMS – Kiel, Germany), placed in the temporal lobe on the side of the lesion, from dural opening to dural closure.

Results:

Basal values varied between 2.3 and 27.3 mmHg; these values are lower than those previously described in the literature as “normal” for uninjured brain or in cases of subarachnoid hemorrhage. In all patients, a significant decrease in PtiO2 was found in every period of temporary clipping of MCA. Post-operative infarction in the territory of middle cerebral artery occurred in one patient and, in that case, there was a persistent minimum value of 0.6 mmHg, without recovery after the placement of the definitive clip. In another patient, an incorrect placement of the definitive clip could be predicted by a decrease in PtiO₂ value.

Conclusions:

PtiO₂ monitoring during aneurysm surgery shows brain tissue perfusion in real time and there is a correlation between any episode of reduced blood flow to the affected vascular territory during surgery and a decrease of PtiO2 values. Unexpected low basal values were obtained in “uninjured” brain, with no influence from subarachnoid hemorrhage. The values of risk for brain infarction during temporary arterial occlusion still need further studies, but an incomplete recovery or a persistent fall in PtiO₂ values after definitive clipping should be considered as an indication for verification of the position of the clip.

A method for measuring brain partial pressure of oxygen in unanesthetized unrestrained subjects: the effect of acute and chronic hypoxia on brain tissue PO(2)

The level of tissue oxygenation provides information related to the balance between oxygen delivery, oxygen utilization, tissue reactivity and morphology during physiological conditions. Tissue partial pressure of oxygen (PtO(2)) is influenced by the use of anesthesia or restraint. These factors may impact the absolute level of PtO(2). In this study we present a novel fiber optic method to measure brain PtO(2). This method can be used in unanesthetized, unrestrained animals, provides absolute values for PO(2), has a stable calibration, does not consume oxygen and is MRI compatible. Brain PtO(2) was studied during acute hypoxia, as well as before and after 28 days of high altitude acclimatization. A sensor was chronically implanted in the frontal cortex of eight Wistar rats. It is comprised of a fiber optic probe with a tip containing material that fluoresces with an oxygen dependent lifetime. Brain PtO(2) declines by 80% and 76% pre- and post-acclimatization, respectively, when the fraction of inspired oxygen declines from 0.21 to 0.08. In addition, a linear relationship between brain PtO(2) and inspired O(2) levels was demonstrated r(2)=0.98 and r(2)=0.99 (pre- and post-acclimatization). Hypoxia acclimatization resulted in an increase in the overall brain PtO(2) by approximately 35%. This paper demonstrates the use of a novel chronically implanted fiber optic based sensor for measuring absolute PtO(2). It shows a very strong linear relationship in awake animals between inspired O(2) and tissue O(2), and shows that there is a proportional increase in PtO(2) over a range of inspired values after exposure to chronic hypoxia.

Judgments of critical care nurses about risk for secondary brain injury

BACKGROUND

Interdisciplinary care for patients with traumatic brain injury focuses on treating the primary brain injury and limiting further brain damage from secondary injury. Intensive care unit nurses have an integral role in preventing secondary brain injury; however, little is known about factors that influence nurses' judgments about risk for secondary brain injury.

OBJECTIVE

To investigate which physiological and situational variables influence judgments of intensive care unit nurses about patients' risk for secondary brain injury, management solely with nursing interventions, and management by consulting another member of the health care team.

METHODS

A multiple segment factorial survey design was used. Vignettes reflecting the complexity of real-life scenarios were randomly generated by using different values of each independent variable. Surveys containing the vignettes were sent to nurses at 2 level I trauma centers. Multiple regression was used to determine which variables influenced judgments about secondary brain injury.

RESULTS

Judgments about risk for secondary brain injury were influenced by a patient's oxygen saturation, intracranial pressure, cerebral perfusion pressure, mechanism of injury, and primary diagnosis, as well as by nursing shift. Judgments about interventions were influenced by a patient's oxygen saturation, intracranial pressure, and cerebral perfusion pressure and by nursing shift. The initial judgments made by nurses were the most significant variable predictive of follow-up judgments.

CONCLUSIONS

Nurses need standardized, evidence-based content for management of secondary brain injury in critically ill patients with traumatic brain injury.

Traumatic brain injury in children: recent advances in management

To define and discuss new developments in the field of pediatric traumatic brain injury (TBI). Review of several recent key studies on therapy since publication of the first U.S. traumatic brain injury guidelines in 2003. In addition, we discuss new developments in the use of biomarkers of brain injury in TBI diagnosis and also discuss recent advances in bedside neuromonitoring that may be helpful in the setting of pediatric brain injury. Important new information on optimal cerebral perfusion pressure management, cerebrospinal fluid drainage, decompressive craniectomy, hypothermia, biomarkers of brain injury along with advances in neuromonitoring are presented. The 2003 guidelines have stimulated important new research. This is reshaping bedside care.

NICEM consensus on neurological monitoring in acute neurological disease

This manuscript summarises the consensus on neuromonitoring in neuro-intensive care promoted and organised by the Neuro-Intensive Care and Emergency Medicine (NICEM) Section of the European Society of Intensive Care Medicine (ESICM). It is expected that continuous monitoring using multi-modal techniques will help to overcome the limitations of each individual method and will provide a better diagnosis. More specific treatment can then be applied; however, it remains to be determined which combination of parameters is optimal. The questions discussed and addressed in this manuscript are: (1) Who should have ICP monitoring and for how long? (2) What ICP technologies are available and what are their relative advantages/disadvantages? (3) Should CPP monitoring and autoregulation testing be used? (4) When should brain tissue oxygen tension (PbrO(2)) be monitored? (5) Should structurally normal or abnormal tissue be monitored with PbrO(2)? (6) Should microdialysis be considered in complex cases? It is hoped that this document will prove useful to clinicians working in NICU and also to those developing specialist NICU services within their hospital practice.

Intra-arterial papaverine used to treat cerebral vasospasm reduces brain oxygen

INTRODUCTION

Intra-arterial papaverine (IAP) is used to treat symptomatic cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH). IAP, however, can increase intracranial pressure (ICP). In this study we examined whether IAP alters brain oxygen (BtO2).

METHODS

Poor clinical grade (Hunt & Hess IV or V) SAH patients who underwent continuous ICP and BtO2 monitoring during IAP infusion for symptomatic cerebral vasospasm were evaluated as part of a prospective observational study.

RESULTS

Data are available for five patients (median age 58) who received IAP for cerebral vasospasm 4 to 7 days after SAH. In each patient, angiographic vasospasm was improved on postinfusion angiogram. Mean ICP before IAP was 23.04 +/- 1.18 mmHg; it increased immediately after IAP infusion and remained elevated (29.89 +/- 1.18 mmHg; p < 0.05) during IAP and for approximately 10 minutes after IAP ended. Baseline mean arterial pressure (MAP) was 110.55 +/- 1.36 mmHg. During IAP treatment MAP remained stable (110.90 +/- 2.00 mmHg; p = 0.31). Mean BtO2 before IAP was 32.99 +/- 1.45 mmHg. There was a significant BtO2 decrease in all patients during IAP to a mean of 22.96 +/- 2.9 mmHg (p < 0.05). BtO2 returned to baseline within 10 minutes after IAP ended. There was a modest relationship between the ICP increase and BtO2 decrease (R2 = 0.526).

CONCLUSION

IAP infusion to treat cerebral vasospasm following SAH can increase ICP and reduce BtO2. The IAP-induced reduction in BtO2 may help explain why IAP, although it reverses arterial narrowing, does not improve patient outcome.

Critical care of neurotrauma

Traumatic brain injury often affects people in their most productive years, inflicting a significant burden on families and society. The advances in modern critical care have improved survival of patients; thus more patients live after traumatic brain injury, which raises an important issue about their neurologic outcome. At the present time, there are limited data regarding methods to optimize neurologic recovery. In this review, we try to bring information from different sources to show new approaches to achieve that goal. Some of the techniques employed are investigational and some are waiting to find broader application in intensive care units across the country.

Neuromonitoring: brain oxygenation and microdialysis

Patients with cerebral lesions run a high risk of developing cerebral hypoxic and ischemic damage due to secondary insults. To minimize the risk of secondary cerebral hypoxia and ischemia, new monitoring techniques of cerebral oxygenation and metabolism have been developed and may help to understand the pathophysiology of secondary brain damage for a better treatment and outcome in critical patients. Cerebral microdialysis is a relatively new technique for measuring brain molecules of the extracellular space. The technical aspects, the interpretation of the commonly measured parameters, the use of the two commonly used oxygenation parameters (jugular venous oxygen saturation and monitoring of brain tissue PO(2) and the microdialysis technique to monitor cerebral metabolism in patients with head injury), subarachnoid hemorrhage, and ischemic stroke are considered. Pitfalls of the techniques and their future potential are discussed.

Brain tissue oxygen guided treatment supplementing ICP/CPP therapy after traumatic brain injury

OBJECTIVE

To evaluate the effects of a brain tissue oxygen (P(ti)O(2)) guided treatment in patients with traumatic brain injury.

METHODS

P(ti)O(2) was monitored in 93 patients with severe traumatic brain injury. Forty patients admitted from 1993 to 1996 were treated with intracranial pressure/cerebral perfusion pressure (ICP/CPP) management alone (ICP < 20 mm Hg, CPP > 70 mm Hg). Fifty three patients admitted from 1997 to 2000 were treated using ICP/CPP management, but in this second group CPP was also increased as individually required to raise the P(ti)O(2) above 1.33 kPa (10 mm Hg) (P(ti)O(2) guided group).

RESULTS

Cerebral hypoxic phases with P(ti)O(2) values below 1.33 kPa occurred significantly less often in the P(ti)O(2) guided group. P(ti)O(2) values were higher over the whole monitoring period. No statistical differences could be observed in outcome at six months, despite a positive trend in the P(ti)O(2) guided group.

CONCLUSIONS

Cerebral hypoxic events can be reduced significantly by increasing cerebral perfusion pressure as required. To show a clear beneficial effect of P(ti)O(2) guided cerebral perfusion pressure management on outcome, a multicentre randomised trial needs to be undertaken.