Direct cerebral oxygenation monitoring--a systematic review of recent publications

Monitoring of Brain Tissue Oxygen Tension in Cardiac Arrest: a Translational Systematic Review from Experimental to Clinical Evidence

BACKGROUND

Cardiac arrest (CA) is a sudden event that is often characterized by hypoxic-ischemic brain injury (HIBI), leading to significant mortality and long-term disability. Brain tissue oxygenation (PbtO2) is an invasive tool for monitoring brain oxygen tension, but it is not routinely used in patients with CA because of the invasiveness and the absence of high-quality data on its effect on outcome. We conducted a systematic review of experimental and clinical evidence to understand the role of PbtO2 in monitoring brain oxygenation in HIBI after CA and the effect of targeted PbtO2 therapy on outcomes.

METHODS

The search was conducted using four search engines (PubMed, Scopus, Embase, and Cochrane), using the Boolean operator to combine mesh terms such as PbtO2, CA, and HIBI.

RESULTS

Among 1,077 records, 22 studies were included (16 experimental studies and six clinical studies). In experimental studies, PbtO2 was mainly adopted to assess the impact of gas exchanges, drugs, or systemic maneuvers on brain oxygenation. In human studies, PbtO2 was rarely used to monitor the brain oxygen tension in patients with CA and HIBI. PbtO2 values had no clear association with patients' outcomes, but in the experimental studies, brain tissue hypoxia was associated with increased inflammation and neuronal damage.

CONCLUSIONS

Further studies are needed to validate the effect and the threshold of PbtO2 associated with outcome in patients with CA, as well as to understand the physiological mechanisms influencing PbtO2 induced by gas exchanges, drug administration, and changes in body positioning after CA.

Avoiding brain hypoxia in severe traumatic brain injury in settings with limited resources - A pathophysiological guide

Cerebral oxygenation represents the balance between oxygen delivery, consumption and utilization by the brain, and therefore reflects the adequacy of cerebral perfusion. Different factors can influence the amount of oxygen to the brain including arterial blood pressure, hemoglobin levels, systemic oxygenation, and transfer of oxygen from blood to the cerebral microcirculation. A mismatch between cerebral oxygen supply and demand results in cerebral hypoxia/ischemia, and is associated with secondary brain damage and worsened outcome after acute brain injury. Therefore, monitoring and prompt treatment of cerebral oxygenation compromise is warranted in both neuro and general intensive care unit populations. Several tools have been proposed for the assessment of cerebral oxygenation, including non-invasive/invasive or indirect/direct methods, including Jugular Venous Oxygen Saturation (SjO2), Partial Brain Tissue Oxygen Tension (PtiO2), Near infrared spectroscopy (NIRS), Transcranial Doppler, electroencephalography and Computed Tomography. In this manuscript, we aim to review the pathophysiology of cerebral oxygenation, describe monitoring technics, and generate recommendations for avoiding brain hypoxia in settings with low availability of resources for direct brain oxygen monitoring.

Temporal Patterns in Brain Tissue and Systemic Oxygenation Associated with Mortality After Severe Traumatic Brain Injury in Children

BACKGROUND

Brain tissue hypoxia is an independent risk factor for unfavorable outcomes in traumatic brain injury (TBI); however, systemic hyperoxemia encountered in the prevention and/or response to brain tissue hypoxia may also impact risk of mortality. We aimed to identify temporal patterns of partial pressure of oxygen in brain tissue (PbtO2), partial pressure of arterial oxygen (PaO2), and PbtO2/PaO2 ratio associated with mortality in children with severe TBI.

METHODS

Data were extracted from the electronic medical record of a quaternary care children's hospital with a level I trauma center for patients ≤ 18 years old with severe TBI and the presence of PbtO2 and/or intracranial pressure monitors. Temporal analyses were performed for the first 5 days of hospitalization by using locally estimated scatterplot smoothing for less than 1,000 observations and generalized additive models with integrated smoothness estimation for more than 1,000 observations.

RESULTS

A total of 138 intracranial pressure-monitored patients with TBI (median 5.0 [1.9-12.8] years; 65% boys; admission Glasgow Coma Scale score 4 [3-7]; mortality 18%), 71 with PbtO2 monitors and 67 without PbtO2 monitors were included. Distinct patterns in PbtO2, PaO2, and PbtO2/PaO2 were evident between survivors and nonsurvivors over the first 5 days of hospitalization. Time-series analyses showed lower PbtO2 values on day 1 and days 3-5 and lower PbtO2/PaO2 ratios on days 1, 2, and 5 among patients who died. Analysis of receiver operating characteristics curves using Youden's index identified a PbtO2 of 30 mm Hg and a PbtO2/PaO2 ratio of 0.12 as the cut points for discriminating between survivors and nonsurvivors. Univariate logistic regression identified PbtO2 < 30 mm Hg, hyperoxemia (PaO2 ≥ 300 mm Hg), and PbtO2/PaO2 ratio < 0.12 to be independently associated with mortality.

CONCLUSIONS

Lower PbtO2, higher PaO2, and lower PbtO2/PaO2 ratio, consistent with impaired oxygen diffusion into brain tissue, were associated with mortality in this cohort of children with severe TBI. These results corroborate our prior work that suggests targeting a higher PbtO2 threshold than recommended in current guidelines and highlight the potential use of the PbtO2/PaO2 ratio in the management of severe pediatric TBI.

A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation

In recent years, cerebral blood oxygen saturation has become a key indicator during the perioperative period. Cerebral blood oxygen saturation monitoring is conducive to the early diagnosis and treatment of cerebral ischemia and hypoxia. The present study discusses the three most extensively used clinical methods for cerebral blood oxygen saturation monitoring from different aspects: working principles, relevant parameters, current situations of research, commonly used equipment, and relative advantages of different methods. Furthermore, through comprehensive comparisons of the methods, we find that near-infrared spectroscopy (NIRS) technology has significant potentials and broad applications prospects in terms of cerebral oxygen saturation monitoring. Despite the current NIRS technology, the only bedside non-invasive cerebral oxygen saturation monitoring technology, still has many defects, it is more in line with the future development trend in the field of medical and health, and will become the main method gradually.

Individualized Brain Tissue Oxygen-Monitoring Probe Placement Helps to Guide Therapy and Optimizes Outcome in Neurocritical Care

Background/Objective

In order to monitor tissue oxygenation in patients with acute neurological disorders, probes for measurement of brain tissue oxygen tension (ptO₂) are often placed non-specifically in a right frontal lobe location. To improve the value of ptO₂ monitoring, placement of the probe into a specific area of interest is desirable. We present a technique using CT-guidance to place the ptO₂ probe in a particular area of interest based on the individual patient’s pathology.

Methods

In this retrospective cohort study, we analyzed imaging and clinical data from all patients who underwent CT-guided ptO₂ probe placement at our institution between October 2017 and April 2019. Primary endpoint was successful placement of the probe in a particular area of interest rated by two independent reviewers. Secondary outcomes were complications from probe insertion, clinical consequences from ptO₂ measurements, clinical outcome according to the modified Rankin Scale (mRS) as well as development of ischemia on follow-up imaging. A historical control group was selected from patients who underwent conventional ptO₂ probe placement between January 2010 and October 2017.

Results

Eleven patients had 16 CT-guided probes inserted. In 15 (93.75%) probes, both raters agreed on the correct placement in the area of interest. Each probe triggered on average 0.48 diagnostic or therapeutic adjustments per day. Only one infarction within the vascular territory of a probe was found on follow-up imaging. Eight out of eleven patients (72.73%) reached a good outcome (mRS ≤ 3). In comparison, conventionally placed probes triggered less diagnostic and therapeutic adjustment per day (p = 0.007). Outcome was worse in the control group (p = 0.024).

Conclusion

CT-guided probe insertion is a reliable and easy technique to place a ptO₂ probe in a particular area of interest in patients with potentially reduced cerebral oxygen supply. By adjusting treatment aggressively according to this individualized monitoring data, clinical outcome may improve.

Checklists to guide the supportive and critical care of tuberculous meningitis

The assessment and management of tuberculous meningitis (TBM) is often complex, yet no standardised approach exists, and evidence for the clinical care of patients, including those with critical illness, is limited. The roles of proformas and checklists are increasing in medicine; proformas provide a framework for a thorough approach to patient care, whereas checklists offer a priority-based approach that may be applied to deteriorating patients in time-critical situations. We aimed to develop a comprehensive assessment proforma and an accompanying 'priorities' checklist for patients with TBM, with the overriding goal being to improve patient outcomes. The proforma outlines what should be asked, checked, or tested at initial evaluation and daily inpatient review to assist supportive clinical care for patients, with an adapted list for patients in critical care. It is accompanied by a supporting document describing why these points are relevant to TBM. Our priorities checklist offers a useful and easy reminder of important issues to review during a time-critical period of acute patient deterioration. The benefit of these documents to patient outcomes would require investigation; however, we hope they will promote standardisation of patient assessment and care, particularly of critically unwell individuals, in whom morbidity and mortality remains unacceptably high.

Checklists to guide the supportive and critical care of tuberculous meningitis

The assessment and management of tuberculous meningitis (TBM) is often complex, yet no standardised approach exists, and evidence for the clinical care of patients, including those with critical illness, is limited. The roles of proformas and checklists are increasing in medicine; proformas provide a framework for a thorough approach to patient care, whereas checklists offer a priority-based approach that may be applied to deteriorating patients in time-critical situations. We aimed to develop a comprehensive assessment proforma and an accompanying 'priorities' checklist for patients with TBM, with the overriding goal being to improve patient outcomes. The proforma outlines what should be asked, checked, or tested at initial evaluation and daily inpatient review to assist supportive clinical care for patients, with an adapted list for patients in critical care. It is accompanied by a supporting document describing why these points are relevant to TBM. Our priorities checklist offers a useful and easy reminder of important issues to review during a time-critical period of acute patient deterioration. The benefit of these documents to patient outcomes would require investigation; however, we hope they will promote standardisation of patient assessment and care, particularly of critically unwell individuals, in whom morbidity and mortality remains unacceptably high.

Pathophysiology and Management of Intracranial Hypertension and Tissular Brain Hypoxia After Severe Traumatic Brain Injury: An Integrative Approach

Monitoring intracranial pressure in comatose patients with severe traumatic brain injury (TBI) is considered necessary by most experts. Acute intracranial hypertension (IHT), when severe and sustained, is a life-threatening complication that demands emergency treatment. Yet, secondary anoxic-ischemic injury after brain trauma can occur in the absence of IHT. In such cases, adding other monitoring modalities can alert clinicians when the patient is in a state of energy failure. This article reviews the mechanisms, diagnosis, and treatment of IHT and brain hypoxia after TBI, emphasizing the need to develop a physiologically integrative approach to the management of these complex situations.

Adjustable and Rigid Fixation of Brain Tissue Oxygenation Probe (Licox) in Neurosurgery: From Bench to Bedside

Multimodal neuromonitoring has become a fundamental part of management for many neurosurgical disorders such as subarachnoid hemorrhage and severe traumatic brain injury. Brain tissue oxygen tension monitoring requires insertion of a probe into the brain parenchyma through a single multiple lumen bolt, or in a subcutaneously tunneled fashion. As those patients often require early magnetic resonance imaging, typically using bolts is disadvantageous due to massive metal artifact. Similarly, subcutaneous tunneling is often problematic as suture fixation can loosen over time. We hereby report a new method of fixation of the Licox brain tissue oxygenation probe with 1 or 2 3-way taps that are attached to a standard plastic cannula, resulting in a stable connection with no need for further direct sutures around the probe and above all with no metal artifacts, which negates magnetic resonance imaging. The extended fixation system was first tested with cardiopulmonary resuscitation in a brain injured porcine model. It was thereafter adopted in our daily clinical practice.

Local and global challenges in pediatric traumatic brain injury outcome and rehabilitation assessment

Traumatic brain injury (TBI) is a major public health problem associated with high morbidity and mortality rates in children in both high- and low- and middle-income countries. Predicting outcome after pediatric TBI is challenging given the wide range of injury and non-injury-related factors which may have an impact. Some of these factors are relevant globally (like heterogeneity in patient and injury-related factors and research methodology) and others are more specific to local contexts (like sociodemographic and cultural factors). The assessment of rehabilitation outcomes post-TBI are similarly challenging given the various methodological limitations, disparities in access to rehabilitation, and limited awareness of deficits, which are encountered globally, as well as the lack of services in the local settings. In this article, we discuss these global and local challenges to outcome and rehabilitation assessment following pediatric TBI.

Pathophysiological central nervous system changes in a porcine model of acetaminophen-induced acute liver failure

BACKGROUND

Critical care management of patients suffering from acute liver failure (ALF) continues to be challenging. Animal models studying the pathophysiological central nervous system alterations during the course of ALF provide an opportunity to improve diagnostic and therapeutic strategies. The aim of this study was to analyse the course of cerebral oxygenation in addition to conventional neuromonitoring during the course of acetaminophen-induced ALF.

METHODS

ALF was induced by intrajejunal acetaminophen administration in 20 German landrace pigs. All animals underwent invasive hemodynamic and neuromonitoring and were maintained under standardized intensive care support. Neuromonitoring consisted of continuous intraparenchymatous recording of intracranial pressure and brain partial oxygen pressure. Hemodynamic and ventilation parameters were continuously recorded; laboratory parameters were analysed every eight hours. Mean values were compared using the Wilcoxon test.

RESULTS

Acute liver failure occurred in all intoxicated animals after 23±2h, resulting in death due to ALF after further 15±2h. Continuous neuromonitoring was performed in all animals during the whole experiment without observing signs of intracranial haemorrhage. Two hours after manifestation of ALF an increase in brain tissue oxygen (PtiO2) was observed. Brain oxygenation stayed stable until nine hours before death. Intracranial pressure (ICP) remained basically at a plateau level until manifestation of ALF. In the following ten hours a linear and slow increase was observed until five hours before death, followed by a fast and continuous rise in ICP to a final level of 35±1mmHg. Cerebral perfusion pressure (CPP) began to decrease 25h prior to exitus, further decreasing to 18±2mmHg at the end of the experiment. A strong negative linear correlation was found between PtiO2 and ICP (R=0.97). Arterial partial pressure of oxygen (PaO2) below 100mmHg was associated with lower PtiO2 levels. Changes in arterial partial pressure of carbon dioxide (PaC02) did not influence PtiO2 values. Hemoglobin values below 7g/dl were associated with lower PtiO2 values.

CONCLUSIONS

The results of our experiments demonstrate that ICP and PtiO2 measurements indicate impending damage well before serious complications occur and their use should be considered in order to protect endangered brain function in the presence of acetaminophen-induced ALF.

Effects of positive end-expiratory pressure on brain tissue oxygen pressure of severe traumatic brain injury patients with acute respiratory distress syndrome: A pilot study

PURPOSE

To verify whether high positive end-expiratory pressure levels can increase brain tissue oxygen pressure, and also their effects on pulse oxygen saturation, intracranial pressure, and cerebral perfusion pressure.

MATERIAL AND METHODS

Twenty traumatic brain injury patients with acute respiratory distress syndrome were submitted to positive end-expiratory pressure levels of 5, 10, and 15 cm H2O progressively. The 3 positive end-expiratory pressure levels were used during 20 minutes for each one, whereas brain tissue oxygen pressure, oxygen saturation, intracranial pressure, and cerebral perfusion pressure were recorded.

RESULTS

Brain tissue oxygen pressure and oxygen saturation increased significantly with increasing positive end-expiratory pressure from 5 to 10 and from 10 to 15 cm H2O (P=.0001 and P=.0001 respectively). Intracranial pressure and cerebral perfusion pressure did not differ significantly with increasing positive end-expiratory pressure from 5 to 10 and from 10 to 15 cm H2O (P=.16 and P=.79 respectively).

CONCLUSIONS

High positive end-expiratory pressure levels increased brain tissue oxygen pressure and oxygen saturation, without increase in intracranial pressure or decrease in cerebral perfusion pressure. High positive end-expiratory pressure levels can be used in severe traumatic brain injury patients with acute respiratory distress syndrome as a safe alternative to improve brain oxygenation.

Brain tissue oxygen monitoring identifies cortical hypoxia and thalamic hyperoxia after experimental cardiac arrest in rats

BACKGROUND

Optimization of cerebral oxygenation after pediatric cardiac arrest (CA) may reduce neurological damage associated with the post-CA syndrome. We hypothesized that important alterations in regional partial pressure of brain tissue oxygen (PbO2) occur after resuscitation from CA and that clinically relevant interventions such as hyperoxia and blood pressure augmentation would influence PbO2.

METHODS

Cortical and thalamic PbO2 were monitored in immature rats subjected to asphyxial CA (9 or 12 min asphyxia) and sham-operated rats using oxygen sensors.

RESULTS

Thalamus and cortex showed similar baseline PbO2. Postresuscitation, there was early and sustained cortical hypoxia in an insult-duration dependent fashion. In contrast, thalamic PbO2 initially increased fourfold and afterwards returned to baseline values. PbO2 level was dependent on the fraction of inspired O2, and the response to oxygen was more pronounced after a 9 vs. 12 min CA. After a 12 min CA, PbO2 was modestly affected by blood pressure augmentation using epinephrine in the thalamus but not in the cortex.

CONCLUSION

After asphyxial pediatric CA, there is marked regional variability of cerebral oxygenation. Cortical hypoxia is pronounced and appears early, whereas thalamic hyperoxia is followed by normoxia. Compromised PbO2 in the cortex may represent a relevant and clinically measurable therapeutic target aimed at improving neurological outcome after pediatric CA.

The relationship between intracranial pressure and brain oxygenation in children with severe traumatic brain injury

BACKGROUND

Intracranial pressure (ICP) monitoring is a cornerstone of care for severe traumatic brain injury (TBI). Management of ICP can help ensure adequate cerebral blood flow and oxygenation. However, studies indicate that brain hypoxia may occur despite normal ICP and the relationship between ICP and brain oxygenation is poorly defined. This is particularly important for children in whom less is known about intracranial dynamics.

OBJECTIVE

To examine the relationship between ICP and partial pressure of brain tissue oxygen (PbtO2) in children with severe TBI (Glasgow Coma Scale score ≤ 8) admitted to Red Cross War Memorial Children's Hospital, Cape Town.

METHODS

The relationship between time-linked hourly and high-frequency ICP and PbtO2 data was examined using correlation, regression, and generalized estimating equations. Thresholds for ICP were examined against reduced PbtO2 using age bands and receiver-operating characteristic curves.

RESULTS

Analysis using more than 8300 hourly (n = 75) and 1 million high-frequency data points (n = 30) demonstrated a weak relationship between ICP and PbtO2 (r = 0.05 and r = 0.04, respectively). No critical ICP threshold for low PbtO2 was identified. Individual patients revealed a strong relationship between ICP and PbtO2 at specific times, but different relationships were evident over longer periods.

CONCLUSION

The relationship between ICP and PbtO2 appears complex, and several factors likely influence both variables separately and in combination. Although very high ICP is associated with reduced PbtO2, in general, absolute ICP has a poor relationship with PbtO2. Because reduced PbtO2 is independently associated with poor outcome, a better understanding of ICP and PbtO2 management in pediatric TBI seems to be needed.

Continuous brain tissue oxygenation monitoring in the management of pediatric stroke

BACKGROUND

Direct invasive monitoring of brain tissue oxygenation (PbtO(2)) has been routinely utilized to predict cerebral ischemia and to prevent secondary injury in patients with traumatic brain injury (TBI) and vasospasm secondary to subarachnoid hemorrhage (SAH). The safety and utility of these devices in the pediatric population have been examined in a few small studies. No studies, however, have examined the use of PbtO(2) monitoring in stroke patients.

METHODS

Retrospective chart review of the first two consecutive, critically ill pediatric patients in the pediatric intensive care unit requiring brain tissue oxygen monitoring for newly diagnosed cerebral ischemia. ICP, CPP, PbtO(2), SaO(2), BP, and RR were all continually monitored during their care and were retrospectively collected and reviewed.

RESULTS

We present two pediatric stroke patients managed in a critical care setting with PbtO(2) monitoring in addition to ICP, MAP, CPP, and SaO(2). Both patients had multiple events of low brain tissue oxygen (PbtO(2) <20 torr), independent of abnormal values in other monitoring parameters, which required physician intervention. No new ischemic damage occurred after PbtO(2) monitoring began in either patient.

CONCLUSIONS

There is currently inadequate data to support the application of PbtO(2) monitoring in children with stroke to prevent progressive ischemia and to improve outcome. However, the positive results for these two patients support the need for further study in this area.

Radial oxygen gradients over rat cortex arterioles

PURPOSE

We present the results of the visualisation of radial oxygen gradients in rats' cortices and their potential use in neurocritical management.

METHODS

PO₂ maps of the cortex of ten sedated, intubated and controlled ventilated Wistar rats were obtained with a camera (SensiMOD, PCO, Kelheim, Germany). Those pictures were analysed and edited by a custom-made software. A virtual matrix, designed to evaluate the cortical O₂ partial pressure, was placed vertically to the artery under investigation, and afterwards multiple regions of interest were measured (width 10 pixels, length 15-50 pixels). The results showed a map of the cerebral oxygenation, which allowed us to calculate radial oxygen gradients over arterioles. Three groups were defined according to the level of the arterial pO₂: PaO₂ < 80, PaO₂ 80-120 and PaO₂ > 120. Gradients were analysed from the middle of the vessel to its border (1), from the border into the parenchyma next to the vessel (2) and a combination of both (3).

RESULTS

Gradient 1 showed significantly different cortical pO₂ values between the three different groups. The mean pO₂ values were 2.62, 5.29 and 5.82 mmHg/mm. Gradient 2 measured 0.56, 0.90 and 1.02 mmHg/mm respectively. Gradient 3 showed significant results between the groups with values of 3.18, 6.19 and 6.84 mmHg/mm.

CONCLUSION

Using these gradients, it is possible to describe and compare the distribution of oxygen to the brain parenchyma. With the presented technique, it is possible to detect pO₂ changes in the oxygen supply of the brain cortex.

The physiology behind direct brain oxygen monitors and practical aspects of their use

INTRODUCTION

Secondary neuronal injury is implicated in poor outcome after acute neurological insults. Outcome can be improved with protocol-driven therapy. These therapies have largely been based on monitoring and control of intracranial pressure and the maintenance of an adequate cerebral perfusion pressure.

DISCUSSION

In recent years, brain tissue oxygen partial pressure (PbtO2) monitoring has emerged as a clinically useful modality and a complement to intracranial pressure monitors. This review examines the physiology of PbtO2 monitors and practical aspects of their use.

Methods of monitoring brain oxygenation

INTRODUCTION

Posttraumatic brain ischemia or hypoxia is a major potential cause of secondary injury that may lead to poor outcome. Avoidance, or amelioration, of this secondary injury depends on early diagnosis and intervention before permanent injury occurs. However, tools to monitor brain oxygenation continuously in the neuro-intensive care unit have been lacking.

DISCUSSION

In recent times, methods of monitoring aspects of brain oxygenation continuously by the bedside have been evaluated in several experimental and clinical series and are potentially changing the way we manage head-injured patients. These monitors have the potential to alert the clinician to possible secondary injury and enable intervention, help interpret pathophysiological changes (e.g., hyperemia causing raised intracranial pressure), monitor interventions (e.g., hyperventilation for increased intracranial pressure), and prognosticate. This review focuses on jugular venous saturation, brain tissue oxygen tension, and near-infrared spectroscopy as practical methods that may have an important role in managing patients with brain injury, with a particular focus on the available evidence in children. However, to use these monitors effectively and to understand the studies in which these monitors are employed, it is important for the clinician to appreciate the technical characteristics of each monitor, as well as respective strengths and limitations of each. It is equally important that the clinician understands relevant aspects of brain oxygen physiology and head trauma pathophysiology to enable correct interpretation of the monitored data and therefore to direct an appropriate therapeutic response that is likely to benefit, not harm, the patient.

Brain tissue oxygen monitoring: a study of in vitro accuracy and stability of Neurovent-PTO and Licox sensors

OBJECT

Periods of brain tissue ischemia are common after severe head injury, and their occurrence and duration are negatively correlated with outcome. Accurate and reliable measurement of brain tissue oxygenation (B(ti) pO(2)) may be a key to improve patient outcome after severe head injury. Knowledge of stability and accuracy of the B(ti) pO(2) systems is crucial. We have therefore conducted a bench test study of new Neurovent-PTO (NV) and Licox (LX) oxygen tension catheters to evaluate the sensor accuracy, response time to different oxygen tensions, response to temperature changes and long-term stability.

METHODS

For all experiments five new fluorescent NV sensors and five new electrochemical LX sensors were used. The catheter probes were placed into a container filled with a buffer solution. The solution was equilibrated with five high precision calibration gases. The accuracy of the probes was recorded after an equilibration period of 20 min in O(2) concentrations of 5, 10, 20, 30 and 40 mmHg at 37.0 +/- 0.2 degrees C. The probe response to an increase in temperature from 37.0 degrees C to 38.5 degrees C to 40.0 degrees C in two different gases with O(2) concentrations of 10 and 20 mmHg were analysed. We also recorded the time for reaching 90% of a new oxygen concentration level when switching from one concentration to another. Finally, to test if there was a time-dependant drift in pO(2) recordings, all sensors were left in 10 mmHg O(2) solution for 10 days, and recordings were taken every 24 h.

RESULTS

In all gas concentrations, NV and LX sensors measured pO(2) with high accuracy and stability in vitro (mean differences from calculated values were for NV 0.76-1.6 mmHg and for LX -0.46-0.26 mmHg). Both sensors showed a shorter response time to pO(2) increase (for NV 56 +/- 22 s and for LX 78 +/- 21 s) compared to pO(2) decrease (for NV 131 +/- 42 s and for LX 215 +/- 63 s). NV pO(2) values were more stable for changes in temperature, while LX sensors showed larger standard deviations with increasing temperature (the difference from the calculated values in 19.7 mmHg O(2) at 40 degrees C were for NV probes between 0.5 and 1.7 mmHg and LX between -2.3 and 1.9 mmHg). Both sensors gave stable results with low standard deviations during long-term (10 days) use, but with a slight elevation of measured pO(2) levels by time.

CONCLUSIONS

Both NV and LX were accurate in detecting different oxygen tensions, and they did not deviate over longer recording times. However, LX needed a significantly longer time to detect changes in pO(2) levels compared to NV. Furthermore, LX probes showed an increased standard deviation with higher temperatures.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 1: Relationship with outcome

INTRODUCTION

Intracranial pressure (ICP) monitoring and cerebral perfusion pressure (CPP) management are the current standards to guide care of severe traumatic brain injury (TBI). However, brain hypoxia and secondary brain injury can occur despite optimal ICP and CPP. In this study, we used brain tissue oxygen tension (PbtO(2)) monitoring to examine the association between multiple patient factors, including PbtO(2), and outcome in pediatric severe TBI.

MATERIALS AND METHODS

In this prospective observational study, 52 children (less than 15 years) with severe TBI were managed with continuous PbtO(2) and ICP monitoring. The relationships between outcome [Glasgow Outcome Score (GOS) and Pediatric Cerebral Performance Category Scale] and clinical, radiologic, treatment, and physiological variables, including PbtO(2), were examined using multiple logistic regression analysis.

RESULTS

Outcome was favorable in 40 patients (77%) and unfavorable (mortality, 9.6%; n = 5) in 12 (23%). In univariate analysis, the following variables had a significant association with unfavorable outcome: initial GCS, computed tomography classification, ICP(peak), mICP(24), mICP, CPP(low), CPP(<40), pupil reactivity, PbtO(2)(low), PbtO(2) < 5 mmHg, PbtO(2) < 10 mmHg, mPbtO(2)(24), and time-severity product. PbtO(2) parameters had the strongest independent association with poor outcome in multiple regression analysis. In particular, when PbtO(2) was <5 mmHg for >1 h, the adjusted OR for poor outcome was 27.4 (95% confidence interval, 1.9-391). No variables apart from PbtO(2) were independently associated with mortality when controlled for PbtO(2).

CONCLUSION

Reduced PbtO(2) is shown to be an independent factor associated with poor outcome in pediatric severe TBI in the largest study to date. It appears to have a stronger association with outcome than conventionally evaluated measures.

Does adherence to treatment targets in children with severe traumatic brain injury avoid brain hypoxia? A brain tissue oxygenation study

OBJECTIVE

Most physicians rely on conventional treatment targets for intracranial pressure, cerebral perfusion pressure, systemic oxygenation, and hemoglobin to direct management of traumatic brain injury (TBI) in children. In this study, we used brain tissue oxygen tension (PbtO2) monitoring to examine the association between PbtO2 values and outcome in pediatric severe TBI and to determine the incidence of compromised PbtO2 in patients for whom acceptable treatment targets had been achieved.

METHODS

In this prospective observational study, 26 children with severe TBI and a median postresuscitation Glasgow Coma Scale score of 5 were managed with continuous PbtO2 monitoring. The relationships between outcome and the 6-hour period of lowest PbtO2 values and the length of time that PbtO2 was less than 20, 15, 10, and 5 mmHg were examined. The incidence of reduced PbtO2 for each threshold was evaluated where the following targets were met: intracranial pressure less than 20 mmHg, cerebral perfusion pressure greater than 50 mmHg, arterial oxygen tension greater than 60 mmHg (and peripheral oxygen saturation > 90%), and hemoglobin greater than 8 g/dl.

RESULTS

There was a significant association between poor outcome and the 6-hour period of lowest PbtO2 and length of time that PbtO2 was less than 15 and 10 mmHg. Multiple logistic regression analysis showed that low PbtO2 had an independent association with poor outcome. Despite achieving the management targets described above, 80% of patients experienced one or more episodes of compromised PbtO2 (< 20 mmHg), and almost one-third experienced episodes of brain hypoxia (PbtO2 < 10 mmHg).

CONCLUSION

Reduced PbtO2 is associated with poor outcome in pediatric severe TBI. In addition, many patients experience episodes of compromised PbtO2 despite achieving acceptable treatment targets.

Continuous monitoring and intervention for cerebral ischemia in tuberculous meningitis

OBJECTIVE

Tuberculous meningitis (TBM) is a massive global problem. The mortality and morbidity associated with the severe form of the disease are exceptionally high. Even when increased intracranial pressure is treated and full conventional therapy is commenced, cerebral ischemia can develop and is associated with a particularly poor prognosis. We sought to evaluate our experience with two patients with severe TBM and cerebral oxygenation monitoring.

DESIGN

Case report.

SETTING

Red Cross Children's Hospital, Cape Town.

PATIENTS

Two comatose patients with TBM.

INTERVENTIONS

Targeted interventions against low cerebral oxygenation in one patient.

MEASUREMENTS AND MAIN RESULTS

Cerebral tissue oxygenation (Ptio2) was measured. In both patients, Ptio2 monitoring demonstrated delayed cerebral ischemia despite the institution of full conventional therapy and the control of intracranial pressure. These data confirm that the vascular involvement in TBM is potentially progressive and that failure to diagnose infarction initially is not merely due to a delay in the radiologic appearance. The first patient developed extensive infarction, consistent with Ptio2 readings, and subsequently died after treatment withdrawal. Intervention in the second patient successfully reversed a precipitous decline of the Ptio2 readings and may have prevented infarction in this patient.

CONCLUSIONS

The development of delayed cerebral ischemia in TBM despite treatment is confirmed in these two patients. The reversal of a decline in Ptio2 readings suggests a possible benefit for cerebral oxygenation monitoring in selected patients with severe TBM.