Brain tissue oxygen (PtiO2): a clinical comparison of two monitoring devices

The Role of Brain Tissue Oxygenation Monitoring in the Management of Subarachnoid Hemorrhage: A Scoping Review

Monitoring of brain tissue oxygenation (PbtO2) is an important component of multimodal monitoring in traumatic brain injury. Over recent years, use of PbtO2 monitoring has also increased in patients with poor-grade subarachnoid hemorrhage (SAH), particularly in those with delayed cerebral ischemia. The aim of this scoping review was to summarize the current state of the art regarding the use of this invasive neuromonitoring tool in patients with SAH. Our results showed that PbtO2 monitoring is a safe and reliable method to assess regional cerebral tissue oxygenation and that PbtO2 represents the oxygen available in the brain interstitial space for aerobic energy production (i.e., the product of cerebral blood flow and the arterio-venous oxygen tension difference). The PbtO2 probe should be placed in the area at risk of ischemia (i.e., in the vascular territory in which cerebral vasospasm is expected to occur). The most widely used PbtO2 threshold to define brain tissue hypoxia and initiate specific treatment is between 15 and 20 mm Hg. PbtO2 values can help identify the need for or the effects of various therapies, such as hyperventilation, hyperoxia, induced hypothermia, induced hypertension, red blood cell transfusion, osmotic therapy, and decompressive craniectomy. Finally, a low PbtO2 value is associated with a worse prognosis, and an increase of the PbtO2 value in response to treatment is a marker of good outcome.

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.

Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

Evaluation of a New Multiparameter Brain Probe for Simultaneous Measurement of Brain Tissue Oxygenation, Cerebral Blood Flow, Intracranial Pressure, and Brain Temperature in a Porcine Model

BACKGROUND

A novel multiparameter brain sensor (MPBS) allows the simultaneous measurement of brain tissue oxygenation (ptiO₂), cerebral blood flow (CBF), intracranial pressure (ICP), and brain temperature with a single catheter. This laboratory investigation evaluates the MPBS in an animal model in relation to established reference probes.

METHODS

The study group consisted of 17 juvenile male pigs. Four MPBS and four reference probes were implanted per pig and compared simultaneously. The measured parameters were challenged by standardized provocations such as hyperoxia, dobutamine, and norepinephrine application, hypercapnia and hypoxia in combination with and without a controlled cortical impact (CCI) injury. Mean values over 2 min were collected for predefined time points and were analyzed using Bland-Altman plots.

RESULTS

The protocol was successfully conducted in 15 pigs of which seven received CCI. ICP and ptiO₂ were significantly influenced by the provocations. Subtraction of MPBS from reference values revealed a mean difference (limits of agreement) of 3.7 (- 20.5 to 27.9) mm Hg, - 2.9 (- 7.9 to 2.1) mm Hg, and 5.1 (- 134.7 to 145.0) % for ptiO₂, ICP, and relative CBF, respectively.

CONCLUSIONS

The MPBS is a promising measurement tool for multiparameter neuromonitoring. The conducted study demonstrates the in vivo functionality of the probe. Comparison with standard probes revealed a deviation which is mostly analogous to other multiparameter devices. However, further evaluation of the device is necessary before it can reliably be used for clinical decision making.

Erythrocytes Are Oxygen-Sensing Regulators of the Cerebral Microcirculation

Energy production in the brain depends almost exclusively on oxidative metabolism. Neurons have small energy reserves and require a continuous supply of oxygen (O2). It is therefore not surprising that one of the hallmarks of normal brain function is the tight coupling between cerebral blood flow and neuronal activity. Since capillaries are embedded in the O2-consuming neuropil, we have here examined whether activity-dependent dips in O2 tension drive capillary hyperemia. In vivo analyses showed that transient dips in tissue O2 tension elicit capillary hyperemia. Ex vivo experiments revealed that red blood cells (RBCs) themselves act as O2 sensors that autonomously regulate their own deformability and thereby flow velocity through capillaries in response to physiological decreases in O2 tension. This observation has broad implications for understanding how local changes in blood flow are coupled to synaptic transmission.

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.

Parenchymal brain oxygen monitoring in the neurocritical care unit

Patients admitted to the neurocritical care unit (NCCU) often have serious conditions that can be associated with high morbidity and mortality. Pharmacologic agents or neuroprotectants have disappointed in the clinical environment. Current NCCU management therefore is directed toward identification, prevention, and treatment of secondary cerebral insults that evolve over time and are known to aggravate outcome. This strategy is based on a variety of monitoring techniques including use of intraparenchymal monitors. This article reviews parenchymal brain oxygen monitors, including the available technologies, practical aspects of use, the physiologic rationale behind their use, and patient management based on brain oxygen.

Multi frequency phase fluorimetry (MFPF) for oxygen partial pressure measurement: ex vivo validation by polarographic clark-type electrode

Background

Measurement of partial pressure of oxygen (P_O2) at high temporal resolution remains a technological challenge. This study introduces a novel P_O2 sensing technology based on Multi-Frequency Phase Fluorimetry (MFPF). The aim was to validate MFPF against polarographic Clark-type electrode (CTE) P_O2 measurements.

Methodology/Principal Findings

MFPF technology was first investigated in N = 8 anaesthetised pigs at F_IO2 of 0.21, 0.4, 0.6, 0.8 and 1.0. At each F_IO2 level, blood samples were withdrawn and P_O2 was measured in vitro with MFPF using two FOXY-AL300 probes immediately followed by CTE measurement. Secondly, MFPF-P_O2 readings were compared to CTE in an artificial circulatory setup (human packed red blood cells, haematocrit of 30%). The impacts of temperature (20, 30, 40°C) and blood flow (0.8, 1.6, 2.4, 3.2, 4.0 L min⁻¹) on MFPF-P_O2 measurements were assessed. MFPF response time in the gas- and blood-phase was determined. Porcine MFPF-P_O2 ranged from 63 to 749 mmHg; the corresponding CTE samples from 43 to 712 mmHg. Linear regression: CTE = 15.59+1.18*MFPF (R² = 0.93; P<0.0001). Bland Altman analysis: mean_diff 69.2 mmHg, range_diff -50.1/215.6 mmHg, 1.96-SD limits -56.3/194.8 mmHg. In artificial circulatory setup, MFPF-P_O2 ranged from 20 to 567 mmHg and CTE samples from 11 to 575 mmHg. Linear regression: CTE = −8.73+1.05*MFPF (R² = 0.99; P<0.0001). Bland-Altman analysis: mean_diff 6.6 mmHg, range_diff -9.7/20.5 mmHg, 1.96-SD limits -12.7/25.8 mmHg. Differences between MFPF and CTE-P_O2 due to variations of temperature were less than 6 mmHg (range 0–140 mmHg) and less than 35 mmHg (range 140–750 mmHg); differences due to variations in blood flow were less than 15 mmHg (all P-values>0.05). MFPF response-time (monoexponential) was 1.48±0.26 s for the gas-phase and 1.51±0.20 s for the blood-phase.

Conclusions/Significance

MFPF-derived P_O2 readings were reproducible and showed excellent correlation and good agreement with Clark-type electrode-based P_O2 measurements. There was no relevant impact of temperature and blood flow upon MFPF-P_O2 measurements. The response time of the MFPF FOXY-AL300 probe was adequate for real-time sensing in the blood phase.

Extracellular brain pH with or without hypoxia is a marker of profound metabolic derangement and increased mortality after traumatic brain injury

Cerebral hypoxia and acidosis can follow traumatic brain injury (TBI) and are associated with increased mortality. This study aimed to evaluate a relationship between reduced pH(bt) and disturbances of cerebral metabolism. Prospective data from 56 patients with TBI, receiving microdialysis and Neurotrend monitoring, were analyzed. Four tissue states were defined based on pH(bt) and P(bt)O(2): 1--low P(bt)O(2)/pH(bt), 2--low pH(bt)/normal P(bt)O(2), 3--normal pH(bt)/low P(bt)O(2), and 4--normal pH(bt)/P(bt)O(2)). Microdialysis values were compared between the groups. The relationship between P(bt)O(2) and lactate/pyruvate (LP) ratio was evaluated at different pH(bt) levels. Proportional contribution of each state was evaluated against mortality. As compared with the state 4, the state 3 was not different, the state 2 exhibited higher levels of lactate, LP, and glucose and the state 1--higher LP and reduced glucose (P<0.001). A significant negative correlation between LP and P(bt)O(2) (rho=-0.159, P<0.001) was stronger at low pH(bt) (rho=-0.201, P<0.001) and nonsignificant at normal pH(bt) (P=0.993). The state 2 was a significant discriminator of mortality categories (P=0.031). Decreased pH(bt) is associated with impaired metabolism. Measuring pH(bt) with P(bt)O(2) is a more robust way of detecting metabolic derangements.

Assessment of physiological parameters within glioblastomas in awake patients: a prospective clinical study

OBJECT

Multiparametric brain monitoring probes now make it possible to measure cerebral physiology. This prospective clinical study was designed to evaluate the pathophysiological environment of tumoural and peritumoural tissue O(2), CO(2), pH, HCO(3)- and temperature of awake patients with glioblastoma.

METHODS

A Neurotrend multiparametric sensor was placed using intraoperative image guidance into glioblastoma after biopsy under general anesthetic. Postoperative monitoring was then performed in awake patients.

RESULTS

Twelve patients were recruited and monitoring was performed, and well tolerated in 9 for up to 22 hrs. Mean glioblastoma tumour values were: tissue oxygen pressure (PtiO(2)) 21.0 mmHg, standard deviation +/- 7.9; PtiCO(2) 60.2 +/- 17.2 mmHg; temperature 36.9 +/- 0.4 degrees C, pH 7.08 + 0.2; and HCO(3) 17.1 +/- 3.7. Mean peritumoural brain values in 5 patients were PtiO(2) 29.1 +/- 27.6 mmHg; PtiCO(2) 48.6 +/- 7.0 mmg; temperature 36.4 +/- 0.6 degrees C; pH 7.20 +/- 0.09 and HCO(3) 19.1 +/- 3.5. There were trends for the PtiO(2) to decrease with increasing brain depth. As glioblastoma PtiCO(2) levels decreased, pH increased. There were no relationships between either tumoural PtiO(2) and pH, or PtiO(2) and PtiCO(2), however there were large intra- and inter-tumoural variation in monitoring values. There were technical problems in some patients with the Neurotrend sensor that limited its application, and that compromised aspects of data collection and interpretation, particularly of PtiO(2).

CONCLUSION

This study has shown that this novel approach to monitoring glioma pathophysiology is feasible and well tolerated by patients. The data, much of which is novel, contributes to the knowledge of glioblastoma pathophysiology. However, further study and clinical exploitation awaits the development of a more reliable multiparametric sensor.

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.

Transient changes in brain tissue oxygen in response to modifications of cerebral perfusion pressure: an observational study

BACKGROUND

The relative merits of the mechanisms for the maintenance of brain tissue oxygenation (PbtO(2)) have been much debated. There is a wealth of studies regarding various factors that may determine the absolute value and changes in PbtO(2). However, only a few of them analyzed fast (few minutes) and transient behavior of PbtO(2) in response to variations (waves) of intracranial pressure (ICP) and cerebral perfusion pressure (CPP).

METHODS

This was a retrospective analysis and observational study. PbtO(2), arterial blood pressure (ABP), and ICP waveforms were digitally monitored in 23 head-injured patients, admitted to the Neuroscience Critical Care Unit, who were sedated, paralyzed, and ventilated. Computer recordings were retrospectively reviewed. The dynamic changes in PbtO(2) in response to transient changes in ABP and ICP were investigated.

RESULTS

Several patterns of response to short-lasting arterial hypotension and hypertension, intracranial hypertension, cerebral vasocycling, and cerebral hyperemia were observed and characterized. During the majority of the transient events, PbtO(2) generally followed the direction of changes in CPP. Only during episodes of hyperemia, CPP and PbtO(2) changed in the opposite direction. Changes in PbtO(2) were delayed after dynamic changes in ABP, CPP, and ICP. The CPP-PbtO(2) delay during changes provoked by variations in ABP was 35.0 s (range: maximum 827.0 s; minimum 0.0 s) compared with changes induced by variations in ICP of 0.0 s (range: maximum 265.0 s; minimum 0.0 s); the difference was significant at P < 0.0001.

CONCLUSIONS

PbtO(2) is more than a number; it is rather a waveform following rapid changes in ICP and ABP. We show that PbtO(2) generally tracks the direction of CPP irrespective of the state of cerebral autoregulation.

[Aneurysmal subarachnoid hemorrhage. Significance and complications]

Despite substantial improvement in the management of patients with aneurysmal subarachnoid hemorrhage (SAH), including early aneurysm occlusion by endovascular techniques and surgical procedures, a significant percentage of patients with SAH still experience serious sequelae of neurological or cognitive deficits as a result of primary hemorrhage and/or secondary brain damage. Available neuromonitoring methods for early recognition of ischemia include, among others, measurement of brain tissue O(2) partial pressure, brain metabolism with microdialysis and monitoring of regional blood flow. The triple-H therapy (arterial hypertension, hypervolemia and hemodilution) is the treatment of choice of a symptomatic vasospasm and leads to an enduring recession of ischemic symptoms, if initiated early after the onset of a vasospasm-linked ischemic neurological deficit. Further promising therapy approaches are the administration of highly selective ET(A) receptor antagonists and intracisternal administration of vasodilators in depot form. This review summarizes the major neurological and non-neurological complications following aneurysm occlusion. Possible neuromonitoring techniques to improve diagnosis and therapy for treatment of symptomatic vasospasm as well as extracranial complications are discussed.

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

This review has been compiled to assess publications related to the clinical application of direct cerebral tissue oxygenation (PtiO2) monitoring published in international, peer-reviewed scientific journals. Its goal was to extract relevant, i.e. positive and negative information on indications, clinical application, safety issues and impact on clinical situations as well as treatment strategies in neurosurgery, neurosurgical anaesthesiology, neurosurgical intensive care, neurology and related specialties. For completeness' sake it also presents some related basic science research. PtiO2 monitoring technology is a safe and valuable cerebral monitoring device in neurocritical care. Although a randomized outcome study is not available its clinical utility has repeatedly been clearly confirmed because it adds a monitoring parameter, independent from established cerebral monitoring devices. It offers new insights into cerebral physiology and pathophysiology. Pathologic values have been established in peer-reviewed research, which are not only relevant to outcome but are treatable. The benefits clearly outweigh the risks, which remains unchallenged in all publications retrieved. It is particularly attractive because it offers continuous, real-time data and is available at the bedside.

The role of tissue oxygen monitoring in patients with acute brain injury

Cerebral ischaemia is implicated in poor outcome after brain injury, and is a very common post-mortem finding. The inability of the brain to store metabolic substrates, in the face of high oxygen and glucose requirements, makes it very susceptible to ischaemic damage. The clinical challenge, however, remains the reliable antemortem detection and treatment of ischaemic episodes in the intensive care unit. Outcomes have improved in the traumatic brain injury setting after the introduction of progressive protocol-driven therapy, based, primarily, on the monitoring and control of intracranial pressure, and the maintenance of an adequate cerebral perfusion pressure through manipulation of the mean arterial pressure. With the increasing use of multi-modal monitoring, the complex pathophysiology of the injured brain is slowly being unravelled, emphasizing the heterogeneity of the condition, and the requirement for individualization of therapy to prevent secondary adverse hypoxic cerebral events. Brain tissue oxygen partial pressure (Pb(O2) monitoring is emerging as a clinically useful modality, and this review examines its role in the management of brain injury.