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.

Neurological Pupil Index and Delayed Cerebral Ischemia after Subarachnoid Hemorrhage: A Retrospective Multicentric Study.

BACKGROUND: Delayed cerebral ischemia (DCI) occurs in around 30% of patients suffering from nontraumatic subarachnoid hemorrhage (SAH) and is associated with poor neurological outcome. Whether the Neurological Pupil index (NPi) derived from the automated pupillometry could help to diagnose the occurrence of DCI remains unknown. The aim of this study was to investigate the association of NPi with the occurrence of DCI in patients with SAH. METHODS: This was a multicenter, retrospective cohort study of consecutive patients with SAH admitted to the intensive care units of five hospitals between January 2018 and December 2020 who underwent daily NPi recordings (every 8 h) during the first 10 days of admission. DCI was diagnosed according to standard definitions (in awake patients) or based on neuroimaging and neuromonitoring (in sedated or unconscious patients). An NPi < 3 was defined as abnormal. The primary outcome of the study was to assess the time course of daily NPi between patients with DCI and patients without DCI. Secondary outcome included the number of patients who had an NPi < 3 before DCI. RESULTS: A total of 210 patients were eligible for the final analysis; DCI occurred in 85 (41%) patients. Patients who developed DCI had similar values of mean and worst daily NPi over time when compared with patients without DCI. Patients with DCI had a higher proportion of at least one NPi < 3 at any moment before DCI when compared with others (39/85, 46% vs. 35/125, 38%, p = 0.009). Similarly, the worst NPi before DCI diagnosis was lower in the DCI group when compared with others (3.1 [2.5-3.8] vs. 3.7 [2.7-4.1], p = 0.05). In the multivariable logistic regression analysis, the presence of NPi < 3 was not independently associated with the development of DCI (odds ratio 1.52 [95% confidence interval 0.80-2.88]). CONCLUSIONS: In this study, NPi measured three times a day and derived from the automated pupillometry had a limited value for the diagnosis of DCI in patients with SAH.

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

BACKGROUND: Cerebral ischemia due to hypoxia is a major cause of secondary brain injury and is associated with higher morbidity and mortality in patients with acute brain injury. Hyperoxia could improve energetic dysfunction in the brain in this setting. Our objectives were to perform a systematic review and meta-analysis of the current literature and to assess the impact of normobaric hyperoxia on brain metabolism by using cerebral microdialysis. METHODS: We searched Medline and Scopus, following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement; we searched for retrospective and prospective observational studies, interventional studies, and randomized clinical trials that performed a hyperoxia challenge in patients with acute brain injury who were concomitantly monitored with cerebral microdialysis. This study was registered in PROSPERO (CRD420211295223). RESULTS: We included a total of 17 studies, with a total of 311 patients. A statistically significant reduction in cerebral lactate values (pooled standardized mean difference [SMD] - 0.38 [- 0.53 to - 0.23]) and lactate to pyruvate ratio values (pooled SMD - 0.20 [- 0.35 to - 0.05]) was observed after hyperoxia. However, glucose levels (pooled SMD - 0.08 [- 0.23 to 0.08]) remained unchanged after hyperoxia. CONCLUSIONS: Normobaric hyperoxia may improve cerebral metabolic disturbances in patients with acute brain injury. The clinical impact of such effects needs to be further elucidated.