Continuous monitoring of the microcirculation in neurocritical care: an update on brain tissue oxygenation

Brain health: A concern for anaesthesiologists and intensivists

Damage to the brain can have disastrous and long-lasting consequences. The European Society of Anaesthesiology and Intensive Care (ESAIC) is aware of the importance of taking good care of the brain, both of patients and of anaesthesia and intensive care unit (ICU) caregivers, and has organised a complete learning track on brain health to bring this concern to the attention of practitioners. This learning track included an online Focus Meeting on Brain Health (November 25, 2023). We here provide readers with a digest of the information that was delivered during that meeting in an opinion paper driven by the authors' own reading of the literature. It is divided according to the meeting's sessions, including how to improve the health of an injured brain, how to keep a young or old brain healthy, how to keep a healthy adult brain unimpaired, how monitoring can impact brain health in the operating room and in the intensive care unit, and how to keep the anaesthesia and ICU caregivers' brain healthy. Each part is a brief and focused summary. The main delivered messages are that the management of injured brain patients involves an adequate choice of sedation, adequate brain monitoring, and focused attention to specific points depending on the underlying pathology; that several measures can be undertaken to protect the brain of the very young needing anaesthesia; that it is possible to detect older patients at risk of postoperative neurocognitive disorders, and that dedicated perioperative management by a multidisciplinary expert team may improve their outcomes; that apparently healthy adult brains may suffer during anaesthesia; that the electroencephalogram may track peri-operative brain dysfunction, and that female patients should be given special care in this respect; that multimodal brain monitoring helps to detect pathological processes and to maintain brain homeostasis; and that burnout in anaesthesiologists can be effectively fought using personal, organisational, managerial and legal approaches.

The Association of Cerebral Oxygen Desaturation with Postoperative Cognitive Dysfunction in Older Patients: A Review

Postoperative cognitive dysfunction (POCD) is a neurological complication associated with surgery and anesthesia that is commonly observed in older patients, and it can significantly affect patient prognosis and survival. Therefore, predicting and preventing POCD is important. Regional cerebral oxygen saturation (rSO2) reflects cerebral perfusion and oxygenation, and decreased intraoperative cerebral oxygen saturation has been reported to increase the risk of POCD. In this review, we elucidated the important relationship between the decline in rSO2 and risk of POCD in older patients. We also emphasized the importance of monitoring rSO2 during surgery to predict and prevent adverse perioperative cognitive outcomes. The findings reveal that incorporating intraoperative rSO2 monitoring into clinical practice has potential benefits, such as protecting cognitive function, reducing perioperative adverse outcomes, and ultimately improving the overall quality of life of older adults.

Transfusion increased skin blood flow when initially low in volume-resuscitated patients without acute bleeding

Background

Alterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation.

Methods

A prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT.

Results

Overall, SBFBT did not significantly change after RBCT [from 79.8 (4.3-479.4) to 83.4 (4.9-561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3-279.3) vs. 136.3 (6.5-479.4) perfusion units; p < 0.01], mixed or central venous oxygen saturation (62.5 ± 9.2 vs. 67.3% ± 12.0%; p < 0.01) and CVP (8.3 ± 5.1 vs. 10.3 ± 5.6 mmHg; p = 0.03) at baseline than non-responders. SBFBT increased in responders [from 41.3 (4.3-279.3) to 93.1 (9.8-561.6) perfusion units; p < 0.01], and decreased in the non-responders [from 136.3 (6.5-479.4) to 80.0 (4.9-540.8) perfusion units; p < 0.01] after RBCT. Pre-transfusion SBFBT was independently associated with a 20% increase in SBFBT after RBCT. Baseline SBFBT had an area under receiver operator characteristic of 0.73 (95% CI, 0.68-0.83) to predict SBFBT increase; A SBFBT of 73.0 perfusion units (PU) had a sensitivity of 71.4% and a specificity of 70.4% to predict SBFBT increase after RBCT. No significant differences in SBFBT were observed after RBCT in different subgroup analyses.

Conclusion

The skin blood flow is globally unaltered by red blood cell transfusions in non-bleeding critically ill patients after initial resuscitation. However, a lower SBFBT at baseline was associated with a relative increase in skin tissue perfusion after RBCT.

The effect of increased positive end expiratory pressure on brain tissue oxygenation and intracranial pressure in acute brain injury patients

Cerebral hypoxia is an important cause of secondary brain injury. Improving systemic oxygenation may increase brain tissue oxygenation (PbtO2). The effects of increased positive end-expiratory pressure (PEEP) on PbtO2 and intracranial pressure (ICP) needs to be further elucidated. This is a single center retrospective cohort study (2016-2021) conducted in a 34-bed Department of Intensive Care unit. All patients with acute brain injury under mechanical ventilation who were monitored with intracranial pressure and brain tissue oxygenation (PbtO2) catheters and underwent at least one PEEP increment were included in the study. Primary outcome was the rate of PbtO2 responders (increase in PbtO2 > 20% of baseline) after PEEP increase. ΔPEEP was defined as the difference between PEEP at 1 h and PEEP at baseline; similarly ΔPbtO2 was defined as the difference between PbtO2 at 1 h after PEEP incrementation and PbtO2 at baseline. We included 112 patients who underwent 295 episodes of PEEP increase. Overall, the median PEEP increased form 6 (IQR 5-8) to 10 (IQR 8-12) cmH2O (p = 0.001), the median PbtO2 increased from 21 (IQR 16-29) mmHg to 23 (IQR 18-30) mmHg (p = 0.001), while ICP remained unchanged [from 12 (7-18) mmHg to 12 (7-17) mmHg; p = 0.42]. Of 163 episode of PEEP increments with concomitant PbtO2 monitoring, 34 (21%) were PbtO2 responders. A lower baseline PbtO2 (OR 0.83 [0.73-0.96)]) was associated with the probability of being responder. ICP increased in 142/295 episodes of PEEP increments (58%); no baseline variable was able to identify this response. In PbtO2 responders there was a moderate positive correlation between ΔPbtO2 and ΔPEEP (r = 0.459 [95% CI 0.133-0.696]. The response in PbtO2 and ICP to PEEP elevations in brain injury patients is highly variable. Lower PbtO2 values at baseline could predict a significant increase in brain oxygenation after PEEP increase.

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.

Physiological Monitoring in Patients with Acute Brain Injury: A Multimodal Approach

Neurocritical care management of acute brain injury (ABI) is focused on identification, prevention, and management of secondary brain injury (SBI). Physiologic monitoring of the brain and other organ systems has a role to predict patient recovery or deterioration, guide individualized therapeutic interventions, and measure response to treatment, with the goal of improving patient outcomes. In this review, we detail how specific physiologic markers of brain injury and neuromonitoring tools are integrated and used in ABI patients to develop therapeutic approaches to prevent SBI.

Impact of hyperoxia and phenylephrine on cerebral oxygenation: An experimental clinical study

BACKGROUND

Oxygen supply to the brain is of special importance during intracranial surgery because it may be compromised by intracranial pathology. A high arterial blood pressure (mean arterial pressure above 80 mmHg) and a high arterial oxygen tension (PaO₂ above 12 kPa) is therefore often targeted in these patients, when for example intracranial pressure is increased or when a mass effect on brain tissue from a tumour is present, and it is pursued by administering vasopressors such as phenylephrine and by increasing inspiratory oxygen fraction (FiO₂ ). However, whether these interventions increase cerebral oxygenation remains uncertain. We aimed to investigate the effect of hyperoxia and phenylephrine on brain tissue oxygen tension (PbtO₂ ) in patients undergoing craniotomy.

METHODS

In this experimental study, we included 17 adult patients scheduled for elective craniotomy. After securing a stable baseline of the oxygen probe, PbtO₂ was measured in white matter peripherally in the surgical field during general anaesthesia. Primary comparisons were PbtO₂ before versus after an increase in FiO₂ from 0.30 to 0.80 as well as before versus after a bolus dose of phenylephrine (0.1-0.2 mg depending on patient haemodynamics). Data were analysed with the Wilcoxon signed rank test.

RESULTS

We obtained complete data sets in 11 patients undergoing the FiO₂ increase and six patients receiving the phenylephrine bolus. PbtO₂ was 22 (median; 5%-95% range, 4.6-54) mmHg during 30% oxygen, 68 (8.4-99) mmHg during 80% oxygen (p = .004 compared to 30% oxygen), 21 (4.5-81) mmHg before phenylephrine, and 19 (4.2-56) mmHg after phenylephrine (p = .56 compared to before phenylephrine).

CONCLUSION

In patients undergoing craniotomy under general anaesthesia, brain tissue oxygen tension increased with a high inspiratory oxygen fraction but remained unchanged after a bolus dose of phenylephrine.

A Systematic Review on Traumatic Brain Injury Pathophysiology and Role of Herbal Medicines in its Management

BACKGROUND

Traumatic brain injury (TBI) is a worldwide problem. Almost about sixtynine million people sustain TBI each year all over the world. Repetitive TBI linked with increased risk of neurodegenerative disorder such as Parkinson, Alzheimer, traumatic encephalopathy. TBI is characterized by primary and secondary injury and exerts a severe impact on cognitive, behavioral, psychological and other health problem. There were various proposed mechanism to understand complex pathophysiology of TBI but still there is a need to explore more about TBI pathophysiology. There are drugs present for the treatment of TBI in the market but there is still need of more drugs to develop for better and effective treatment of TBI, because no single drug is available which reduces the further progression of this injury.

OBJECTIVE

The main aim and objective of structuring this manuscript is to design, develop and gather detailed data regarding about the pathophysiology of TBI and role of medicinal plants in its treatment.

METHOD

This study is a systematic review conducted between January 1995 to June 2021 in which a consultation of scientific articles from indexed periodicals was carried out in Science Direct, United States National Library of Medicine (Pubmed), Google Scholar, Elsvier, Springer and Bentham.

RESULTS

A total of 54 studies were analyzed, on the basis of literature survey in the research area of TBI.

CONCLUSION

Recent studies have shown the potential of medicinal plants and their chemical constituents against TBI therefore, this review targets the detailed information about the pathophysiology of TBI and role of medicinal plants in its treatment.

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.

Factors Associated With Brain Tissue Oxygenation Changes After RBC Transfusion in Acute Brain Injury Patients

OBJECTIVES

Anemia is common after acute brain injury and can be associated with brain tissue hypoxia. RBC transfusion (RBCT) can improve brain oxygenation; however, predictors of such improvement remain unknown. We aimed to identify the factors associated with PbtO2 increase (greater than 20% from baseline value) after RBCT, using a generalized mixed model.

DESIGN

This is a multicentric retrospective cohort study (2012-2020).

SETTING

This study was conducted in three European ICUs of University Hospitals located in Belgium, Switzerland, and Austria.

PATIENTS

All patients with acute brain injury who were monitored with brain tissue oxygenation (PbtO2) catheters and received at least one RBCT.

INTERVENTION

Patients received at least one RBCT. PbtO2 was recorded before, 1 hour, and 2 hours after RBCT.

MEASUREMENTS AND MAIN RESULTS

We included 69 patients receiving a total of 109 RBCTs after a median of 9 days (5-13 d) after injury. Baseline hemoglobin (Hb) and PbtO2 were 7.9 g/dL [7.3-8.7 g/dL] and 21 mm Hg (16-26 mm Hg), respectively; 2 hours after RBCT, the median absolute Hb and PbtO2 increases from baseline were 1.2 g/dL [0.8-1.8 g/dL] (p = 0.001) and 3 mm Hg (0-6 mm Hg) (p = 0.001). A 20% increase in PbtO2 after RBCT was observed in 45 transfusions (41%). High heart rate (HR) and low PbtO2 at baseline were independently associated with a 20% increase in PbtO2 after RBCT. Baseline PbtO2 had an area under receiver operator characteristic of 0.73 (95% CI, 0.64-0.83) to predict PbtO2 increase; a PbtO2 of 20 mm Hg had a sensitivity of 58% and a specificity of 73% to predict PbtO2 increase after RBCT.

CONCLUSIONS

Lower PbtO2 values and high HR at baseline could predict a significant increase in brain oxygenation after RBCT.

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.

Neurovascular physiology and neurocritical care

The neurological intensive care unit plays an integral role in the management of cerebrovascular disease in the acute and perioperative period. Understanding the use of intracranial pressure (ICP) monitoring and how to apply the appropriate intervention for ICP elevation to ensure adequate cerebral perfusion is the foundation of neurocritical care. Careful management of the interplay between cerebral and systemic physiology, particularly in disorders of cerebral autoregulation, is critical in preventing secondary brain injury. Finally, understanding the cerebral pathophysiology of the underlying injured brain in acute stroke, subarachnoid hemorrhage, and arterial stenosis can help to guide the optimal use of interventional endovascular procedures in these disease states.

The Importance of PbtO2 Probe Location for Data Interpretation in Patients with Intracerebral Hemorrhage

Background/objective

Monitoring of brain tissue oxygen tension (P_btO₂) provides insight into brain pathophysiology after intracerebral hemorrhage (ICH). Integration of probe location is recommended to optimize data interpretation. So far, little is known about the importance of P_btO₂ catheter location in ICH patients.

Methods

We prospectively included 40 ICH patients after hematoma evacuation (HE) who required P_btO₂-monitoring. P_btO₂-probe location was evaluated in all head computed tomography (CT) scans within the first 6 days after HE and defined as location in the healthy brain tissue or perilesional when the catheter tip was located within 1 cm of a focal lesion (hypodense or hyperdense). Generalized estimating equations were used to investigate levels of P_btO₂ in relation to different probe locations.

Results

Patients were 60 [51–66] years old and had a median ICH-volume of 47 [29–60] mL. Neuromonitoring probes remained for a median of 6 [2–11] days. P_btO₂-probes were located in healthy brain tissue in 18/40 (45%) patients and in perilesional brain tissue in 22/40 (55%) patients. In the acute phase after HE (0–72 h), P_btO₂ levels were significantly lower (21 ± 12 mmHg vs. 29 ± 10 mmHg, p = 0.010) and brain tissue hypoxia (BTH) was more common in the perilesional area as compared to healthy brain tissue (46% vs. 19%, adjOR 4.0, 95% CI 1.54–10.58, p = 0.005). Episodes of BTH significantly decreased over time in patients with probes in perilesional location (p = 0.001) but remained stable in normal appearing area (p = 0.485). A significant association between BTH and poor functional outcome was only found when probes were located in the perilesional brain tissue (adjOR 6.6, 95% CI 1.3–33.8, p = 0.023).

Conclusions

In the acute phase, BTH was more common in the perilesional area compared to healthy brain tissue. The improvement of BTH in the perilesional area over time may be the result of targeted treatment interventions and tissue regeneration. Due to the localized measurement of invasive neuromonitoring devices, integration of probe location in the clinical management of ICH patients and in research protocols seems mandatory.

Pioglitazone Therapy and Fractures: Systematic Review and Meta- Analysis

INTRODUCTION

Thiazolidinediones are a group of synthetic medications used in type 2 diabetes treatment. Among available thiazolidinediones, pioglitazone is gaining increased attention due to its lower cardiovascular risk in type 2 diabetes mellitus sufferers and seems a promising future therapy. Accumulating evidence suggests that diabetic patients may exert bone fractures due to such treatments. Simultaneously, the female population is thought to be at greater risk. Still, the safety outcomes of pioglitazone treatment especially in terms of fractures are questionable and need to be clarified.

METHODS

We searched MEDLINE, Scopus, PsyInfo, eLIBRARY.ru electronic databases and clinical trial registries for studies reporting an association between pioglitazone and bone fractures in type 2 diabetes mellitus patients published before Feb 15, 2016. Among 1536 sources that were initially identified, six studies including 3172 patients proved relevant for further analysis.

RESULT

Pooled analysis of the included studies demonstrated that after treatment with pioglitazone patients with type 2 diabetes mellitus had no significant increase in fracture risk [odds ratio (OR): 1.18, 95% confidence interval (CI): 0.82 to 1.71, p=0.38] compared to other antidiabetic drugs or placebo. Additionally, no association was found between the risk of fractures and pioglitazone therapy duration. The gender of the patients involved was not relevant to the risk of fractures, too.

CONCLUSION

Pioglitazone treatment in diabetic patients does not increase the incidence of bone fractures. Moreover, there is no significant association between patients' fractures, their gender and the period of exposure to pioglitazone. Additional longitudinal studies need to be undertaken to obtain more detailed information on bone fragility and pioglitazone therapy.

Overview of Neurovascular Physiology

PURPOSE OF REVIEW

Neurophysiology is a complex network of cellular, electrical, and vascular systems which function to maximize neuronal functioning and brain performance. The brain exists in a closed system made up of parenchyma, cerebrospinal fluid, and blood with any increase in volume leading to a corresponding decrease in one of the components. Once these compensatory mechanisms are exhausted, there is a precipitous increase in the intracranial pressure leading to decreases in cerebral perfusion and resulting ischemia. The cerebral vasculature has significant control over the total volume of blood and regional flow throughout the brain via autoregulation. Through this process, blood flow is tightly regulated to prevent fluctuations and is coupled precisely with metabolic demand. Moreover, oxygen delivery and aerobic respiration are essential for proper brain functioning and can become deranged in various disease states leading to cellular injury and death.

RECENT FINDINGS

Ongoing trials have provided evidence that in addition to targeted therapy for intracranial pressure monitoring, optimizing brain tissue oxygenation and cerebral autoregulation may lead to improved clinical outcomes. An understanding of neurophysiology is not only essential for treating patients suffering from intracranial injury but also for the development of novel monitoring and therapeutic techniques.

Multimodality Monitoring in Neurocritical Care: Decision-Making Utilizing Direct And Indirect Surrogate Markers

Substantial progress has been made to create innovative technology that can monitor the different physiological characteristics that precede the onset of secondary brain injury, with the ultimate goal of intervening prior to the onset of irreversible neurological damage. One of the goals of neurocritical care is to recognize and preemptively manage secondary neurological injury by analyzing physiologic markers of ischemia and brain injury prior to the development of irreversible damage. This is helpful in a multitude of neurological conditions, whereby secondary neurological injury could present including but not limited to traumatic intracranial hemorrhage and, specifically, subarachnoid hemorrhage, which has the potential of progressing to delayed cerebral ischemia and monitoring postneurosurgical interventions. In this study, we examine the utilization of direct and indirect surrogate physiologic markers of ongoing neurologic injury, including intracranial pressure, cerebral blood flow, and brain metabolism.

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.

Intracranial Multimodality Monitoring for Delayed Cerebral Ischemia

Management of patients with aneurysmal subarachnoid hemorrhage focuses on prevention of rebleeding by early treatment of the aneurysm, as well as detection and management of neurologic and medical complications. Early detection of delayed cerebral ischemia and management of modifiable contributing causes such as vasospasm take a central role, with the goal of preventing irreversible cerebral injury. In efforts to prevent delayed cerebral ischemia, multimodality monitoring has emerged as a promising tool in detecting subclinical physiologic changes before infarction occurs. However, there has been much variability in the utilization of this technology. Recent consensus guidelines discuss the role of multimodality monitoring in acute brain injury. In this review, we evaluate these guidelines and the utility of each modality of multimodality monitoring in aneurysmal subarachnoid hemorrhage.

Brain Oxygenation Monitoring

A mismatch between cerebral oxygen supply and demand can lead to cerebral hypoxia/ischemia and deleterious outcomes. Cerebral oxygenation monitoring is an important aspect of multimodality neuromonitoring. It is increasingly deployed whenever intracranial pressure monitoring is indicated. Although there is a large body of evidence demonstrating an association between cerebral hypoxia/ischemia and poor outcomes, it remains to be determined whether restoring cerebral oxygenation leads to improved outcomes. Randomized prospective studies are required to address uncertainties about cerebral oxygenation monitoring and management. This article describes the different methods of monitoring cerebral oxygenation, their indications, evidence base, limitations, and future perspectives.

Perihemorrhagic ischemia occurs in a volume-dependent manner as assessed by multimodal cerebral monitoring in a porcine model of intracerebral hemorrhage

BACKGROUND

Changes in the perihemorrhagic zone (PHZ) of intracerebral hemorrhage (ICH) are variable. Different mechanisms contribute to secondary neuronal injury after ICH. This multimodal monitoring study investigated early changes in the PHZ of ICH.

METHODS

Twenty-four swine were anesthetized, ventilated, and underwent monitoring of vital parameters. Next to an intracranial pressure-probe (ICP), microdialysis (MD), thermodiffusion cerebral blood flow (td-CBF), and oxygen probes (PbrO2) were placed into the gray white matter junction for 12 h of monitoring. ICH was induced using the autologous blood injection model. Pre-defined volumes were 0 ml (sham), 1.5 ml ipsilateral (1.5 ml), 3.0 ml ipsilateral (3.0 ml), and 3.0 ml contralateral (3.0 ml contra).

RESULTS

ICP equally increased in all groups after ICH. In the 3.0 ml group tissue oxygenation decreased to ischemic values of 9 ± 7 mmHg early after 6 h of monitoring. This decrease was associated with a significant perfusion reduction from 36 ± 8 ml/100 g/min to 20 ± 10 ml/100 g/min. MD correlated with a threefold lactate/pyruvate ratio increase. Measurements in all other groups were unchanged.

CONCLUSION

Multimodal monitoring demonstrates volume-dependent changes of tissue oxygenation, blood flow, and ischemic MD markers in the PHZ independent of increased ICP suggesting early moderate ischemia. No evidence was found for the existence of a perihemorrhagic ischemia in the small hematoma groups.

Fluid responsiveness and brain tissue oxygen augmentation after subarachnoid hemorrhage

BACKGROUND

The objective of this study was to investigate the relationship between cardiac index (CI) response to a fluid challenge and changes in brain tissue oxygen pressure (PbtO(2)) in patients with subarachnoid hemorrhage (SAH).

METHODS

Prospective observational study was conducted in a neurological intensive care unit of a university hospital. Fifty-seven fluid challenges were administered to ten consecutive comatose SAH patients that underwent multimodality monitoring of CI, intracranial pressure (ICP), and PbtO(2), according to a standardized fluid management protocol.

RESULTS

The relationship between CI and PbtO(2) was analyzed with logistic regression utilizing generalized estimating equations. Of the 57 fluid boluses analyzed, 27 (47 %) resulted in a ≥ 10 % increase in CI. Median absolute (+5.8 vs. +1.3 mmHg) and percent (20.7 vs. 3.5 %) changes in PbtO(2) were greater in CI responders than in non-responders within 30 min after the end of the fluid bolus infusion. In a multivariable model, a CI response was independently associated with PbtO(2) response (adjusted odds ratio 21.5, 95 % CI 1.4-324, P = 0.03) after adjusting for mean arterial pressure change and end-tidal CO(2). Stroke volume variation showed a good ability to predict CI and PbtO(2) response with areas under the ROC curve of 0.86 and 0.81 with the best cut-off values of 9 % for both responses.

CONCLUSION

Bolus fluid resuscitation resulting in augmentation of CI can improve cerebral oxygenation after SAH.

Feasibility of near-infrared spectroscopic tomography for intraoperative functional cerebral monitoring: a primate study

OBJECTIVE

The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource suitable for monitoring such changes, we detected the hemodynamic events induced in the brain of a primate model, using high-density near-infrared spectroscopy combined with tomographic reconstruction methods and validated the findings using established radiologic and histologic techniques.

METHODS

Continuous monitoring of the relative changes in the components of the cerebral hemoglobin signal was performed using high-density near-infrared spectroscopy (270 source-detector channel array) in anesthetized bonnet macaques with the brain exposed to induced ischemia and other acute events. A comparative analysis (exact binomial test) applied to reconstructed 3-dimensional images before and after the events and between cerebral hemispheres, combined with postprocedure magnetic resonance imaging, and postmortem histopathologic examination of the macaques' brains was performed to document and validate the spatial features revealed by the optical findings.

RESULTS

Relative changes in the measured and calculated components of the hemoglobin signal, in response to the performed manipulations, revealed substantial concurrence among the reconstructed 3-dimensional images, magnetic resonance imaging of the macaques' brains, and postmortem histopathologic examination findings. Concurrence was seen when the manipulated hemoglobin concentration and associated oxygenation levels were either increased or decreased, and whether they were bilateral or restricted to a specified hemisphere.

CONCLUSIONS

Continuous near-infrared spectroscopy tomography has been shown to accurately capture and localize cerebral ischemia, vasodilatation, and hemorrhage in primates in real time. These findings are directly applicable to clinical intraoperative functional cerebral monitoring.

Brain perfusion and oxygenation

Maintenance of brain perfusion and oxygenation is of paramount importance to patient outcome with various types of brain injuries (traumatic, ischemic, and hemorrhagic). Historically, monitoring of intracranial pressure and cerebral perfusion pressure has been the mainstay of neuromonitoring techniques used at the critical care bedside to monitor brain perfusion and oxygenation. This article describes the bedside neuromonitoring techniques that have emerged for use with these patients in the critical care area. To give the reader an understanding of the functionality of these neuromonitoring techniques, the article first summarizes the physiology of brain perfusion and oxygenation.

[Multimodal neuromonitoring in traumatic brain injury: contribution of PTiO2]

The main goal of exhaustively monitoring neurocritical patients is to avoid secondary injury. In the last few years we have witnessed an increase in brain monitoring tools, beyond the checking of intracranial and brain perfusion pressures. These widely used systems offer valuable but possibly insufficient information. Awareness and correction of brain hypoxia is a useful and interesting measure, not only for diagnostic purposes but also when deciding treatment, and to predict an outcome. In this context, it would be of great interest to use all the information gathered from brain oxygenation monitoring systems in conjunction with other available multimodal monitoring devices, in order to offer individualized treatment for each patient.

Neurotraumatology

Neurotraumatology has its roots in ancient history, but its modern foundations are the physical examination, imaging to localize the pathology, and thoughtful medical and surgical decision making. The neurobiology of cranial and spinal injury is similar, with the main goal of therapies being to limit secondary injury. Brain injury treatment focuses on minimizing parenchymal swelling within the confined cranial vault. Spine injury treatment has the additional consideration of spinal coumn stability. Current guidelines for non-operative and operative management are reviewed in this chapter.

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.

Multimodality monitoring in the neurointensive care unit: a special perspective for patients with stroke

Multimodality monitoring (MMM) is a recently developed method that aids in understanding real-time brain physiology. Early detection of physiological disturbances is possible with the help of MMM, which allows identification of underlying causes of deterioration and minimization of secondary brain injury (SBI). MMM is especially helpful in comatose patients with severe brain injury because neurological examinations are not sensitive enough to detect SBI. The variables frequently examined in MMM are hemodynamic parameters such as intracranial pressure, cerebral perfusion pressure, and mean arterial pressure; brainspecific oxygen tension; markers for brain metabolism including glucose, lactate, and pyruvate levels in brain tissue; and cerebral blood flow. Continuous electroencephalography can be performed, if needed. The majority of SBIs stem from brain tissue hypoxia, brain ischemia, and seizures, which lead to a disturbance in brain oxygen levels, cerebral blood flow, and electrical discharges, all of which are easily detected by MMM. In this review, we discuss the clinical importance of physiological variables as well as the practical applicability of MMM in patients with stroke.

[Aneurysmal subarachnoid hemorrhage]

Acute subarachnoid hemorrhage (SAH) is a severe and acute life-threatening cerebrovascular disease. Approximately 80% of all acute non-traumatic SAHs are the result of a ruptured cerebrovascular aneurysm. Despite advances in diagnosis and treatment a high morbidity and mortality still exists. Apart from the primary cerebral damage there are also secondary complications, such as vasospasm, rebleeding, hydrocephalus, cerebral edema or hydrocephalus. For an appropriate therapy an understanding of the extensive pathophysiology, the options in diagnostics and therapy and the complications of the disease are essential. Anesthesiologists are decisively involved in the therapy of the primary and secondary damages and subsequently in the outcome as well. This article provides an overview of the perioperative and intensive care management of patients with SAH.

Multimodal intracranial monitoring: implications for clinical practice

This article presents an overview of intracranial monitoring techniques during the perioperative and intensive care management of neurologic patients. Various regional and global brain monitors are available; some modalities are well established whereas others are new to the clinical arena and their indications are still being evaluated. Indications for monitoring are reviewed, modalities critically evaluated, and future directions identified.

Cerebral blood flow and the injured brain: how should we monitor and manipulate it?

PURPOSE OF REVIEW

Cerebral ischemia plays a major role in the pathophysiology of the injured brain, including traumatic brain injury and subarachnoid hemorrhage, thus improvement in outcome may necessitate monitoring and optimization of cerebral blood flow (CBF). To interpret CBF results in a meaningful way, it may be necessary to quantify cerebral autoregulation as well as cerebral metabolism. This review addresses the recent evidence related to the changes in CBF and its monitoring/management in traumatic brain injury.

RECENT FINDINGS

Recent evidence on the management of patients with traumatic brain injury have focused on the importance of cerebral autoregulation in maintaining perfusion, which necessitates the measurement of CBF. However, adequate CBF measurements alone would not indicate the amount of oxygen delivered to neuronal tissues. Technologic advancements in measurement devices have enabled the assessment of the metabolic state of the cerebral tissue for the purpose of guiding therapy, progress as well as prognostification.

SUMMARY

Current neurocritical care management strategies are focused on the prevention and limitation of secondary brain injury where neuronal insult continues to evolve during the hours and days after the primary injury. Appropriately chosen multimodal monitoring including CBF and management measures can result in reduction in mortality and morbidity.

Detection of Cerebral Compromise With Multimodality Monitoring in Patients With Subarachnoid Hemorrhage

BACKGROUND:

Studies in traumatic brain injury suggest that monitoring techniques such as brain tissue oxygen (Pbto2) and cerebral microdialysis may complement conventional intracranial pressure (ICP) and cerebral perfusion pressure (CPP) measurements.

OBJECTIVE:

In this study of poor-grade (Hunt and Hess grade IV and V) subarachnoid hemorrhage (SAH) patients, we examined the prevalence of brain hypoxia and brain energy dysfunction in the presence of normal and abnormal ICP and CPP.

METHODS:

SAH patients who underwent multimodal neuromonitoring and cerebral microdialysis were studied. We examined the frequency of brain hypoxia and energy dysfunction in different ICP and CPP ranges and the relationship between Pbto2 and the lactate/pyruvate ratio (LPR).

RESULTS:

A total of 2394 samples from 19 patients were analyzed. There were 149 samples with severe brain hypoxia (Pbto2 ≤10 mm Hg) and 347 samples with brain energy dysfunction (LPR &gt;40). The sensitivities of abnormal ICP or CPP for elevated LPR and reduced Pbto2 were poor (21.2% at best), and the LPR or Pbto2 was abnormal in many instances when ICP or CPP was normal. Severe brain hypoxia was often associated with an LPR greater than 40 (86% of samples). In contrast, mild brain hypoxia (≤20 mm Hg) and severe brain hypoxia were observed in only 53% and 36% of samples with brain energy dysfunction, respectively.

CONCLUSION:

Our data demonstrate that ICP and CPP monitoring may not always detect episodes of cerebral compromise in SAH patients. Our data suggest that several complementary monitors may be needed to optimize the care of poor-grade SAH patients.

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.

Invasive and noninvasive assessment of cerebral oxygenation in patients with severe traumatic brain injury

PURPOSE

The aim of this study is to investigate the relationship between invasive brain tissue oxygen pressure (PbrO(2)) and noninvasive regional transcranial oxygen saturation (rSO(2)) in 22 stable patients with severe traumatic brain injury (TBI) during a 16 h period.

METHODS

This was a prospective, observational study carried out in the Neurocritical Care Unit of a level 1 trauma center in a teaching hospital. A total of 41,809 paired records for neuromonitoring variables were analyzed and compared.

RESULTS

A direct and independent correlation between rSO(2) and PbrO(2) was confirmed through adjusted [beta coefficient and (95% confidence interval, CI) = 0.36 (0.35-0.37)] and logistic [PbrO(2) >or=15 mmHg, as a dependent variable; adjusted odds ratio (AOR) and (95% CI) = 1.11 (1.10-1.12)] regression analyses. A receiver-operating characteristic (ROC) curve demonstrated that rSO(2) had low accuracy for detecting moderate (PbrO(2)

CONCLUSIONS

In patients with severe TBI, PbrO(2) and rSO(2) were directly and significantly related. Severe intracerebral hypoxia was better detected by rSO(2) than was moderate intracerebral hypoxia. However, the diagnostic accuracy of rSO(2) was limited, and this measure should not be considered a substitute for routine PbrO(2) monitoring.

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MESH Headings

• Adolescent
• Adult
• Brain/blood supply
• Brain Infarction/physiopathology
• Brain Injuries/blood
• Brain Injuries/physiopathology
• Cerebrovascular Circulation/physiology
• Humans
• Middle Aged
• Monitoring, Physiologic/methods
• Oxygen/blood
• Oxygen Consumption
• Prospective Studies
• Trauma Centers
• Trauma Severity Indices
• Young Adult

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Affiliation(s)

Santiago R Leal-Noval Neuro Critical Care Division, Hospital Universitario Virgen del Rocío, Seville, Spain.
Aurelio Cayuela
Victoria Arellano-Orden
Antonio Marín-Caballos
Vicente Padilla
Carmen Ferrándiz-Millón
Yael Corcia
Claudio García-Alfaro
Rosario Amaya-Villar
Francisco Murillo-Cabezas

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Collaborators Collapse

Patient Transport and Brain Oxygen in Comatose Patients

OBJECTIVE

Transport of critically ill intensive care unit patients may be hazardous. We examined whether brain oxygen (brain tissue oxygen partial pressure [PbtO2]) is influenced by transport to and from a follow-up head computed tomography (transport head computed tomography [tHCT]) scan.

METHODS

Forty-five patients (24 men, 21 women; Glasgow Coma Scale score ≤8; mean age, 47.3 ± 19.0 years) who had a traumatic brain injury (n = 26) or subarachnoid hemorrhage (n = 19) were retrospectively identified from a prospective observational cohort of PbtO2 monitoring in a neurosurgical intensive care unit at a university-based level I trauma center. PbtO2, intracranial pressure, and cerebral perfusion pressure were monitored continuously and compared during the 3 hours before and after 100 tHCT scans.

RESULTS

The mean PbtO2 before and after the tHCT scans for all 100 scans was 37.9 ± 19.8 mm Hg and 33.9 ± 17.2 mm Hg, respectively (P = .0001). A decrease in PbtO2 (&gt;5%) occurred after 54 tHCTs (54%) and in 36 patients (80%). In instances in which a decrease occurred, the average decrease in mean, minimum, and maximum PbtO2 was 23.6%, 29%, and 18.1%, respectively. This decrease was greater when PbtO2 was compromised (&lt;25 mm Hg) before tHCT. An episode of brain hypoxia (&lt;15 mm Hg) was identified in the 3 hours before tHCT in 9 and after tHCT in 19 instances. On average, an episode of brain hypoxia was 46.6 ± 16.0 (standard error) minutes longer after tHCT than before tHCT (P = .008). Multivariate analysis suggests that changes in lung function (PaO2/fraction of inspired oxygen [FiO2] ratio) may account for the reduced PbtO2 after tHCT (parameter estimate 0.45, 95% confidence interval: 0.024–0.871; P = .04).

CONCLUSION

These data suggest that transport to and from the intensive care unit may adversely affect PbtO2. This deleterious effect is greater when PbtO2 is already compromised and may be associated with lung function.

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.

Impaired expression of neuroprotective molecules in the HIF-1alpha pathway following traumatic brain injury in aged mice

Elderly traumatic brain injury (TBI) patients have higher rates of mortality and worse functional outcome than non-elderly TBI patients. The mechanisms involved in poor outcomes in the elderly are not well understood. Hypoxia-inducible factor-1 alpha (HIF-1alpha) is a basic helix-loop-helix transcription factor that modulates expression of key genes involved in neuroprotection. In this study, we studied the expression of HIF-1alpha and its target survival genes, heme oxygenase-1 (HO-1), vascular endothelial growth factor (VEGF), and erythropoietin (EPO) in the brains of adult versus aged mice following controlled cortical impact (CCI) injury. Adult (5-6 months) and aged (23-24 months) C57Bl/6 mice were injured using a CCI device. At 72 h post-injury, mice were sacrificed and the injured cortex was used for mRNA and protein analysis using real-time reverse transcription--polymerase chain reaction (RT-PCR) and Western blotting protocols. Following injury, HIF-1alpha, HO-1, and VEGF showed upregulation in both the young and aged mice, but in the aged animals the increase in HIF-1alpha and VEGF in response to injury was much lower than in the adult injured animals. EPO was upregulated in the adult injured brain, but not in the aged injured brain. These results support the hypothesis that reduced expression of genes in the HIF-1alpha neuroprotective pathway in aging may contribute to poor prognosis in the elderly following TBI.

Intensive care management of acute stroke: general management

For a long time, patients with severe stroke were facing therapeutic nihilism of the attending physicians. Implementation of do-not-resuscitate-orders may have lead to self-fulfilling prophecies and to a pessimistic overestimation of prognosis of severe stroke syndromes. However, there have been great advances in intensive care management of acute stroke patients and it has been shown that treatment on a specialised neurological intensive care unit improves outcome. In this review, we will present a summary of the current state-of-the-art intensive care management of acute stroke patients. After presenting an overview on general management of stroke intensive care patients, special aspects of neurological intensive care of acute large middle cerebral artery stroke, intracerebral haemorrhage and subarachnoid haemorrhage will be discussed. In part II of the review, surgical management options for acute stroke will be discussed in detail.

Neurologic outcomes with cerebral oxygen monitoring in traumatic brain injury

BACKGROUND

Optimizing cerebral oxygenation is advocated to improve outcome in head-injured patients. The purpose of this study was to compare outcomes in brain-injured patients treated with 2 types of monitors.

METHODS

Patients with traumatic brain injury and a Glasgow Coma Scale score<8 were identified on admission. A polarographic cerebral oxygen/pressure monitor (Licox) or fiberoptic intracranial pressure monitor (Camino) was inserted. An evidence-based algorithm for treatment was implemented. Elements from the prehospital and emergency department records and the first 10 days of intensive care unit (ICU) care were collected. Glasgow Outcome Scores (GOS) were determined every 3 months after discharge.

RESULTS

Over a 3-year period, 145 patients were entered into the study; 81 patients in the Licox group and 64 patients in the Camino group. Mortality, hospital length of stay, and ICU length of stay were equivalent in the 2 groups. More patients in the Licox group achieved a moderate/recovered GOS at 3 months than in the Camino Group (79% vs 61%; P = .09).

CONCLUSION

Three-month GOS revealed a clinically meaningful 18% benefit in patients undergoing cerebral oxygen monitoring and optimization. Six-month outcomes were also better. Unfortunately, these important differences did not reach significance. Continued study of the benefits of cerebral oxygen monitoring is warranted.

Brain tissue oxygen and outcome after severe traumatic brain injury: a systematic review

OBJECTIVE

In this study, available medical literature were reviewed to determine whether brain hypoxia as measured by brain tissue oxygen (Bto2) levels is associated with increased risk of poor outcome after traumatic brain injury (TBI). A secondary objective was to examine the safety profile of a direct BtO2 probe. DATA SOURCE AND EXTRACTION: Clinical studies published between 1993 and 2008 were identified from electronic databases, Index Medicus, bibliographies of pertinent articles, and expert consultation. The following inclusion criteria were applied for outcome analysis: 1) more than 10 patients described, 2) use of a direct Bto2 monitor, 3) brain hypoxia defined as Bto2 <10 mm Hg for >15 or 30 minutes, 4) 6-month outcome data, and 5) clear reporting of patient outcome associated with Bto2. For the analysis, each selected article had to have adequate data to determine odds ratios (ORs) and confidence intervals (CIs). Thirteen studies met the initial inclusion criteria and three were included in the final outcome analysis. Safety data were abstracted from any report where it was mentioned.

DATA SYNTHESIS

The three studies included 150 evaluable patients with severe TBI (Glasgow Coma Scale <or=8). Brain hypoxia was identified in 71 (47%) of these patients. Among the patients with brain hypoxia, 52 (73%) had unfavorable outcome including 39 (55%) who died. In the absence of brain hypoxia, 34 (43%) patients had an unfavorable outcome, including 17 (22%) who died. Overall brain hypoxia (Bto2 <10 mm Hg >15 minutes) was associated with worse outcome (OR 4.0; 95% CI 1.9-8.2) and increased mortality (OR 4.6; 95% CI 2.2-9.6). We reviewed published safety data; in 292 patients monitored with a Bto2 probe, only two adverse events were reported.

CONCLUSION

Summary results indicate that brain hypoxia (<10 mm Hg) is associated with worse outcome after severe TBI and that Bto2 probes are safe. These results imply that treating patients to increase Bto2 may improve outcome after severe TBI. This question will require further study.

[Monitoring of tissue oxygen pressure (PtiO2) in cerebral hypoxia: diagnostic and therapeutic approach]

One of the main causes of secondary cerebral injury is cerebral hypoxia, basically of ischemic origin. However, cerebral tissue oxygenation depends on multiple physiological variables and cerebral hypoxia may be caused by an alteration of any one of them. Although several methods of continuous cerebral oxygenation monitoring of neurocritical patients have been developed, direct and continuous measurement of the oxygen pressure in the cerebral tissue (PtiO2) has been a reality in the handling of the neurocritical patients over recent years. This technique is highlighted by its reliability and value of the information that it provides. This present article presents a review of the most outstanding aspects of the PtiO2 monitoring and proposes a protocol for the interpretation of this monitoring technique. This algorithm attempts to facilitate the identification of the different types of different cerebral hypoxia and of the correct therapeutic choice in the complex decision making process in neurocritical patients at risk of cerebral hypoxia.

Perioperative uses of transcranial perfusion monitoring

Transcranial perfusion monitoring provides early warning of impending brain ischemia and may be used to guide management of cerebral perfusion and oxygenation. The monitoring options include measurement of intracranial and cerebral perfusion pressures, assessment of cerebral blood flow, and assessment of the adequacy of perfusion by measurement of cerebral oxygenation and brain tissue biochemistry. Some monitoring techniques are well established, whereas others are relatively new to the clinical arena and their indications are still being evaluated. Currently available monitoring techniques are reviewed and their appropriateness and application to the perioperative period is discussed.