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.

Evaluation of nociception in unconscious critically ill patients using a multimodal approach.

This prospective observational study included 80 adults (>18 years) patients admitted to the intensive care unit who were unconscious (Glasgow Coma Scale [GCS] score <9 with a motor response <5) and receiving mechanical ventilation. A tetanic stimulation was used to assess nociception; automated pupillometry (Algiscan, ID-MED, France) was used to compute the pupillary pain index score (PPI), with a PPI > 4 considered as nociception. Concomitantly, the number of skin conductance fluctuations (NSCF) per second, measured using a Skin Conductance Algesimeter (SCA, MEDSTORM Innovation AS, Norway; > 0.27 fluctuations/sec indicating nociception), and the instantaneous Analgesia Nociception Index (iANI, MDoloris Medical Systems, France; <50 indicating nociception) were collected. Tetanic stimulation resulted in a median pupillary dilation of 16 [6-25]% and a PPI of 5 [2-7]. According to the PPI assessment, 44 patients (55%) had nociception, whereas 23 (29%) and 18 (23%) showed nociception according to the algesimeter and iANI assessment, respectively. No significant changes in measured physiologic variables were observed after the tetanic stimulation. There were no correlations between PPI, post-stimulation iANI, and SCA-derived variables. There were no differences in PPI, iANI, and SCA variables in patients with low and normal baseline EEG power at baseline. PERSPECTIVES: Detection of nociception varies across different devices in unconscious critically ill patients. Further studies are required to understand which method to implement for analgesic administration in this patient population.

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.

Evaluation of Nociception Using Quantitative Pupillometry and Skin Conductance in Critically Ill Unconscious Patients: A Pilot Study.

BACKGROUND: Pain assessment is a challenge in critically ill patients, in particular those who are unable to express movements in reaction to noxious stimuli. The purpose of the study was to compare the pupillary response and skin conductance to pain stimulation in critically ill unconscious patients. METHODS: This observational study included adult patients admitted to the intensive care unit (ICU) with acute brain injury (Glasgow Coma Scale < 9 with a motor response < 5) and/or requirements for deep level of sedation. Automated pupillometry (Algiscan, ID-MED, Marseille, France) was used to determine pupillary reflex dilation during tetanic stimulation. The maximum intensity of the stimulation value allowed the determination of a pupillary pain index score ranging from 1 (no nociception) to 9 (high nociception): a pupillary pain index (PPI) score of ≤4 was used to reflect adequate pain control. For skin conductance (SC), the number of SC peaks per second (NSCF) was collected concomitantly to tetanic stimulation. An NSCF of ≤0.07 peak/second was used to reflect adequate pain control. RESULTS: Of the 51 included patients, there were 32 with brain injury and 19 receiving deep sedation. Mean PPI score was 5 (Interquartile Range= 2-7); a total of 28 (55%) patients showed inadequate control of the nociceptive stimulation according to the PPI assessment. Only 15 (29%) patients showed a detectable skin conductance, with NSCF values from 0.07 to 0.47/s. No correlation was found between skin conductance algesimeter (SCA)-derived variables and PPI score or pupillary dilation to pain. CONCLUSIONS: Detection of inadequate pain control might vary according to the method used to assess nociception in ICU patients. A poor agreement between quantitative pupillometry and skin conductance was observed.