Improving Outcomes After Post-Cardiac Arrest Brain Injury: A Scientific Statement From the International Liaison Committee on Resuscitation.

This scientific statement presents a conceptual framework for the pathophysiology of post-cardiac arrest brain injury, explores reasons for previous failure to translate preclinical data to clinical practice, and outlines potential paths forward. Post-cardiac arrest brain injury is characterized by 4 distinct but overlapping phases: ischemic depolarization, reperfusion repolarization, dysregulation, and recovery and repair. Previous research has been challenging because of the limitations of laboratory models; heterogeneity in the patient populations enrolled; overoptimistic estimation of treatment effects leading to suboptimal sample sizes; timing and route of intervention delivery; limited or absent evidence that the intervention has engaged the mechanistic target; and heterogeneity in postresuscitation care, prognostication, and withdrawal of life-sustaining treatments. Future trials must tailor their interventions to the subset of patients most likely to benefit and deliver this intervention at the appropriate time, through the appropriate route, and at the appropriate dose. The complexity of post-cardiac arrest brain injury suggests that monotherapies are unlikely to be as successful as multimodal neuroprotective therapies. Biomarkers should be developed to identify patients with the targeted mechanism of injury, to quantify its severity, and to measure the response to therapy. Studies need to be adequately powered to detect effect sizes that are realistic and meaningful to patients, their families, and clinicians. Study designs should be optimized to accelerate the evaluation of the most promising interventions. Multidisciplinary and international collaboration will be essential to realize the goal of developing effective therapies for post-cardiac arrest brain injury.

Association of admission serum sodium and outcomes following out-of-hospital cardiac arrest.

BACKGROUND: The prognostic association between dysnatremia and outcomes in out-of-hospital cardiac arrest (OHCA) is not well understood. Given hypernatremia is associated with poor outcomes in critical illness and hyponatremia may exacerbate cerebral edema, we hypothesized that dysnatremia on OHCA hospital admission would be associated with worse neurological outcomes. METHODS: We studied adults (≥19 years) with non-traumatic OHCA between 2009 and 2016 who were enrolled in the British Columbia Cardiac Arrest Registry and survived to hospital admission at 2 quaternary urban hospitals. We stratified cases by admission serum sodium into hyponatremic (<135 mmol/L), normonatremic (135-145 mmol/L), and hypernatremic (>145 mmol/L) groups. We used logistic regression models, adjusted for age, sex, shockable rhythm, admission serum lactate, and witnessed arrest, to estimate the association between admission sodium and favorable neurological outcome (cerebral performance category 1-2 or modified Rankin scale 0-3). RESULTS: Of 414 included patients, 63 were hyponatremic, 330 normonatremic, and 21 hypernatremic. In each respective group, 21 (33.3%), 159 (48.2%), and 3 (14.3%) experienced good neurological outcomes. In univariable models, hyponatremia (OR 0.53, 95% CI 0.30-0.93) and hypernatremia (OR 0.19, 95% CI 0.05-0.65) were associated with lower odds of good neurological outcomes compared to the normonatremia group. After adjustment, only hypernatremia was associated with lower odds of good neurological outcomes (OR 0.22, 95% CI 0.05-0.98). CONCLUSIONS: Hypernatremia at admission was independently associated with decreased probability of good neurological outcomes at discharge post-OHCA. Future studies should focus on elucidating the pathophysiology of dysnatremia following OHCA.

Neuroinflammation and the immune system in hypoxic ischaemic brain injury pathophysiology after cardiac arrest.

Hypoxic ischaemic brain injury after resuscitation from cardiac arrest is associated with dismal clinical outcomes. To date, most clinical interventions have been geared towards the restoration of cerebral oxygen delivery after resuscitation; however, outcomes in clinical trials are disappointing. Therefore, alternative disease mechanism(s) are likely to be at play, of which the response of the innate immune system to sterile injured tissue in vivo after reperfusion has garnered significant interest. The innate immune system is composed of three pillars: (i) cytokines and signalling molecules; (ii) leucocyte migration and activation; and (iii) the complement cascade. In animal models of hypoxic ischaemic brain injury, pro-inflammatory cytokines are central to propagation of the response of the innate immune system to cerebral ischaemia-reperfusion. In particular, interleukin-1 beta and downstream signalling can result in direct neural injury that culminates in cell death, termed pyroptosis. Leucocyte chemotaxis and activation are central to the in vivo response to cerebral ischaemia-reperfusion. Both parenchymal microglial activation and possible infiltration of peripherally circulating monocytes might account for exacerbation of an immunopathological response in humans. Finally, activation of the complement cascade intersects with multiple aspects of the innate immune response by facilitating leucocyte activation, further cytokine release and endothelial activation. To date, large studies of immunomodulatory therapies have not been conducted; however, lessons learned from historical studies using therapeutic hypothermia in humans suggest that quelling an immunopathological response might be efficacious. Future work should delineate the precise pathways involved in vivo in humans to target specific signalling molecules.

Cerebral uptake of microvesicles occurs in normocapnic but not hypocapnic passive hyperthermia in young healthy male adults.

Passive hyperthermia causes cerebral hypoperfusion primarily from heat-induced respiratory alkalosis. However, despite the cerebral hypoperfusion, it is possible that the mild alkalosis might help to attenuate cerebral inflammation. In this study, the cerebral exchange of extracellular vesicles (microvesicles), which are known to elicit pro-inflammatory responses when released in conditions of stress, were examined in hyperthermia with and without respiratory alkalosis. Ten healthy male adults were heated passively, using a warm water-perfused suit, up to core temperature + 2°C. Blood samples were taken from the radial artery and internal jugular bulb. Microvesicle concentrations were determined in platelet-poor plasma via cells expressing CD62E (activated endothelial cells), CD31+ /CD42b- (apoptotic endothelial cells), CD14 (monocytes) and CD45 (pan-leucocytes). Cerebral blood flow was measured via duplex ultrasound of the internal carotid and vertebral arteries to determine cerebral exchange kinetics. From baseline to poikilocapnic (alkalotic) hyperthermia, there was no change in microvesicle concentration from any cell origin measured (P-values all >0.05). However, when blood CO2 tension was normalized to baseline levels in hyperthermia, there was a marked increase in cerebral uptake of microvesicles expressing CD62E (P = 0.028), CD31+ /CD42b- (P = 0.003) and CD14 (P = 0.031) compared with baseline, corresponding to large increases in arterial but not jugular venous concentrations. In a subset of seven participants who underwent hypercapnia and hypocapnia in the absence of heating, there was no change in microvesicle concentrations or cerebral exchange, suggesting that hyperthermia potentiated the CO2 /pH-mediated cerebral uptake of microvesicles. These data provide insight into a potential beneficial role of respiratory alkalosis in heat stress. KEY POINTS: The hyperthermia-induced hyperventilatory response is observed in most humans, despite causing potentially harmful reductions in cerebral blood flow. We tested the hypothesis that the respiratory-induced alkalosis is associated with lower circulating microvesicle concentrations, specifically in the brain, despite the reductions in blood flow. At core temperature + 2°C with respiratory alkalosis, microvesicles derived from endothelial cells, monocytes and leucocytes were at concentrations similar to baseline in the arterial and cerebral venous circulation, with no changes in cross-brain microvesicle kinetics. However, when core temperature was increased by 2°C with CO2 /pH normalized to resting levels, there was a marked cerebral uptake of microvesicles derived from endothelial cells and monocytes. The CO2 /pH-mediated alteration in cerebral microvesicle uptake occurred only in hyperthermia. These new findings suggest that the heat-induced hyperventilatory response might serve a beneficial role by preventing potentially inflammatory microvesicle uptake in the brain.

Brain Hypoxia Is Associated With Neuroglial Injury in Humans Post-Cardiac Arrest.

[Figure: see text].

High-normal versus low-normal mean arterial pressure thresholds in critically ill patients: a systematic review and meta-analysis of randomized trials.

PURPOSE: Targeted blood pressure thresholds remain unclear in critically ill patients. Two prior systematic reviews have not shown differences in mortality with a high mean arterial pressure (MAP) threshold, but there have been new studies published since. Thus, we conducted an updated systematic review and meta-analysis of randomized controlled trials (RCTs) that compared the effect of a high-normal vs low-normal MAP on mortality, favourable neurologic outcome, need for renal replacement therapy, and adverse vasopressor-induced events in critically ill patients. SOURCE: We searched six databases from inception until 1 October 2022 for RCTs of critically ill patients targeted to either a high-normal vs a low-normal MAP threshold for at least 24 hr. We assessed study quality using the revised Cochrane risk-of-bias 2 tool and the risk ratio (RR) was used as the summary measure of association. We used the Grading of Recommendations Assessment, Development, and Evaluation framework to assess the certainty of evidence. PRINCIPAL FINDINGS: We included eight RCTs with 4,561 patients. Four trials were conducted in patients following out-of-hospital cardiac arrest, two in patients with distributive shock requiring vasopressors, one in patients with septic shock, and one in patients with hepatorenal syndrome. The pooled RRs for mortality (eight RCTs; 4,439 patients) and favourable neurologic outcome (four RCTs; 1,065 patients) were 1.06 (95% confidence interval [CI], 0.99 to 1.14; moderate certainty) and 0.99 (95% CI, 0.90 to 1.08; moderate certainty), respectively. The RR for the need for renal replacement therapy (four RCTs; 4,071 patients) was 0.97 (95% CI, 0.87 to 1.08; moderate certainty). There was no statistical between-study heterogeneity across all outcomes. CONCLUSION: This updated systematic review and meta-analysis of RCTs found no differences in mortality, favourable neurologic outcome, or the need for renal replacement therapy between critically ill patients assigned to a high-normal vs low-normal MAP target. STUDY REGISTRATION: PROSPERO (CRD42022307601); registered 28 February 2022.

RéSUMé: OBJECTIF: Les seuils de pression artérielle ciblés demeurent incertains chez les patient·es gravement malades. Deux revues systématiques antérieures n'ont pas montré de différences dans la mortalité avec un seuil élevé de pression artérielle moyenne (PAM), mais de nouvelles études ont été publiées depuis. Pour cette raison, nous avons réalisé une revue systématique mise à jour et une méta-analyse d'études randomisées contrôlées (ERC) comparant l'effet d'une PAM normale élevée vs normale faible sur la mortalité, les devenirs neurologiques favorables, la nécessité d'un traitement substitutif de l'insuffisance rénale et les événements indésirables induits par les vasopresseurs chez les patient·es gravement malades. SOURCES: Nous avons effectué des recherches dans six bases de données depuis leur création jusqu'au 1er octobre 2022 pour trouver des ERC portant sur des patient·es gravement malades chez lesquel·les un seuil de PAM normale élevée ou normale faible a été ciblé pendant au moins 24 heures. Nous avons évalué la qualité des études à l'aide de l'outil de risque de biais 2 révisé de Cochrane, et le risque relatif (RR) a été utilisé comme mesure sommaire de l'association. Nous avons utilisé le système de notation GRADE (Grading of Recommendations Assessment, Development, and Evaluation) pour évaluer la certitude des données probantes. CONSTATATIONS PRINCIPALES: Nous avons inclus huit ERC portant sur 4561 personnes traitées. Quatre études ont été menées chez des patient·es à la suite d'un arrêt cardiaque hors de l'hôpital, deux chez des patient·es présentant un choc distributif nécessitant des vasopresseurs, une chez des patient·es présentant un choc septique et une chez des patient·es atteint·es d'un syndrome hépato-rénal. Les RR combinés pour la mortalité (huit ERC; 4439 personnes) et les devenirs neurologiques favorables (quatre ERC; 1065 personnes) étaient respectivement de 1,06 (intervalle de confiance [IC] à 95 %, 0,99 à 1,14; certitude modérée) et de 0,99 (IC 95 %, 0,90 à 1,08; certitude modérée). Le RR pour le besoin de traitement substitutif de l'insuffisance rénale (quatre ERC; 4071 patient·es) était de 0,97 (IC 95 %, 0,87 à 1,08; certitude modérée). Il n'y avait pas d'hétérogénéité statistique entre les études pour tous les critères d'évaluation. CONCLUSION: Ces revue systématique et méta-analyse mises à jour des ERC n'ont révélé aucune différence dans la mortalité, les devenirs neurologiques favorables ou la nécessité d'un traitement substitutif de l'insuffisance rénale entre les patient·es gravement malades assigné·es à une cible de PAM normale élevée vs normale faible. ENREGISTREMENT DE L'éTUDE: PROSPERO (CRD42022307601); enregistrée le 28 février 2022.

A brain-based definition of death and criteria for its determination after arrest of circulation or neurologic function in Canada: a 2023 clinical practice guideline.

This 2023 Clinical Practice Guideline provides the biomedical definition of death based on permanent cessation of brain function that applies to all persons, as well as recommendations for death determination by circulatory criteria for potential organ donors and death determination by neurologic criteria for all mechanically ventilated patients regardless of organ donation potential. This Guideline is endorsed by the Canadian Critical Care Society, the Canadian Medical Association, the Canadian Association of Critical Care Nurses, Canadian Anesthesiologists' Society, the Canadian Neurological Sciences Federation (representing the Canadian Neurological Society, Canadian Neurosurgical Society, Canadian Society of Clinical Neurophysiologists, Canadian Association of Child Neurology, Canadian Society of Neuroradiology, and Canadian Stroke Consortium), Canadian Blood Services, the Canadian Donation and Transplantation Research Program, the Canadian Association of Emergency Physicians, the Nurse Practitioners Association of Canada, and the Canadian Cardiovascular Critical Care Society.

RéSUMé: Ces Lignes directrices de pratique clinique 2023 Lignes directrices de pratique clinique dicale du décès basée sur l'arrêt permanent de la fonction cérébrale qui s'applique à toute personne, ainsi que des recommandations pour la détermination du décès par des critères circulatoires pour des donneurs d'organes potentiels et des recommandations pour la détermination du décès par des critères neurologiques pour tous les patients sous ventilation mécanique, indépendamment de leur potentiel de donneur d'organes. Les présentes Lignes directrices sont approuvées par la Société canadienne de soins intensifs, l'Association médicale canadienne, l'Association canadienne des infirmiers/infirmières en soins intensifs, la Société canadienne des anesthésiologistes, la Fédération des sciences neurologiques du Canada (représentant la Société canadienne de neurologie, la Société canadienne de neurochirurgie, la Société canadienne de neurophysiologie clinique, l'Association canadienne de neurologie pédiatrique, la Société canadienne de neuroradiologie et le Consortium neurovasculaire canadien), la Société canadienne du sang, le Programme de recherche en don et transplantation du Canada, l'Association canadienne des médecins d'urgence, l'Association des infirmières et infirmiers praticiens du Canada, et la Société canadienne de soins intensifs cardiovasculaires (CANCARE) et la Société canadienne de pédiatrie.

Nitric oxide contributes to cerebrovascular shear-mediated dilatation but not steady-state cerebrovascular reactivity to carbon dioxide.

Cerebrovascular CO2 reactivity (CVR) is often considered a bioassay of cerebrovascular endothelial function. We recently introduced a test of cerebral shear-mediated dilatation (cSMD) that may better reflect endothelial function. We aimed to determine the nitric oxide (NO)-dependency of CVR and cSMD. Eleven volunteers underwent a steady-state CVR test and transient CO2 test of cSMD during intravenous infusion of the NO synthase inhibitor NG -monomethyl-l-arginine (l-NMMA) or volume-matched saline (placebo; single-blinded and counter-balanced). We measured cerebral blood flow (CBF; duplex ultrasound), intra-arterial blood pressure and PaCO2${P_{{\rm{aC}}{{\rm{O}}_{\rm{2}}}}}$ . Paired arterial and jugular venous blood sampling allowed for the determination of trans-cerebral NO2- exchange (ozone-based chemiluminescence). l-NMMA reduced arterial NO2- by ∼25% versus saline (74.3 ± 39.9 vs. 98.1 ± 34.2 nM; P = 0.03). The steady-state CVR (20.1 ± 11.6 nM/min at baseline vs. 3.2 ± 16.7 nM/min at +9 mmHg PaCO2${P_{{\rm{aC}}{{\rm{O}}_{\rm{2}}}}}$ ; P = 0.017) and transient cSMD tests (3.4 ± 5.9 nM/min at baseline vs. -1.8 ± 8.2 nM/min at 120 s post-CO2 ; P = 0.044) shifted trans-cerebral NO2- exchange towards a greater net release (a negative value indicates release). Although this trans-cerebral NO2- release was abolished by l-NMMA, CVR did not differ between the saline and l-NMMA trials (57.2 ± 14.6 vs. 54.1 ± 12.1 ml/min/mmHg; P = 0.49), nor did l-NMMA impact peak internal carotid artery dilatation during the steady-state CVR test (6.2 ± 4.5 vs. 6.2 ± 5.0% dilatation; P = 0.960). However, l-NMMA reduced cSMD by ∼37% compared to saline (2.91 ± 1.38 vs. 4.65 ± 2.50%; P = 0.009). Our findings indicate that NO is not an obligatory regulator of steady-state CVR. Further, our novel transient CO2 test of cSMD is largely NO-dependent and provides an in vivo bioassay of NO-mediated cerebrovascular function in humans. KEY POINTS: Emerging evidence indicates that a transient CO2 stimulus elicits shear-mediated dilatation of the internal carotid artery, termed cerebral shear-mediated dilatation. Whether or not cerebrovascular reactivity to a steady-state CO2 stimulus is NO-dependent remains unclear in humans. During both a steady-state cerebrovascular reactivity test and a transient CO2 test of cerebral shear-mediated dilatation, trans-cerebral nitrite exchange shifted towards a net release indicating cerebrovascular NO production; this response was not evident following intravenous infusion of the non-selective NO synthase inhibitor NG -monomethyl-l-arginine. NO synthase blockade did not alter cerebrovascular reactivity in the steady-state CO2 test; however, cerebral shear-mediated dilatation following a transient CO2 stimulus was reduced by ∼37% following intravenous infusion of NG -monomethyl-l-arginine. NO is not obligatory for cerebrovascular reactivity to CO2 , but is a key contributor to cerebral shear-mediated dilatation.

Persistently elevated complement alternative pathway biomarkers in COVID-19 correlate with hypoxemia and predict in-hospital mortality.

Mechanisms underlying the SARS-CoV-2-triggered hyperacute thrombo-inflammatory response that causes multi-organ damage in coronavirus disease 2019 (COVID-19) are poorly understood. Several lines of evidence implicate overactivation of complement. To delineate the involvement of complement in COVID-19, we prospectively studied 25 ICU-hospitalized patients for up to 21 days. Complement biomarkers in patient sera and healthy controls were quantified by enzyme-linked immunosorbent assays. Correlations with respiratory function and mortality were analyzed. Activation of complement via the classical/lectin pathways was variably increased. Strikingly, all patients had increased activation of the alternative pathway (AP) with elevated levels of activation fragments, Ba and Bb. This was associated with a reduction of the AP negative regulator, factor (F) H. Correspondingly, terminal pathway biomarkers of complement activation, C5a and sC5b-9, were significantly elevated in all COVID-19 patient sera. C5a and AP constituents Ba and Bb, were significantly associated with hypoxemia. Ba and FD at the time of ICU admission were strong independent predictors of mortality in the following 30 days. Levels of all complement activation markers were sustained throughout the patients' ICU stays, contrasting with the varying serum levels of IL-6, C-reactive protein, and ferritin. Severely ill COVID-19 patients have increased and persistent activation of complement, mediated strongly via the AP. Complement activation biomarkers may be valuable measures of severity of lung disease and the risk of mortality. Large-scale studies will reveal the relevance of these findings to thrombo-inflammation in acute and post-acute COVID-19.

Goal-Directed Care Using Invasive Neuromonitoring Versus Standard of Care After Cardiac Arrest: A Matched Cohort Study.

PURPOSE: Following return of spontaneous circulation after cardiac arrest, hypoxic ischemic brain injury is the primary cause of mortality and disability. Goal-directed care using invasive multimodal neuromonitoring has emerged as a possible resuscitation strategy. We evaluated whether goal-directed care was associated with improved neurologic outcome in hypoxic ischemic brain injury patients after cardiac arrest. DESIGN: Retrospective, single-center, matched observational cohort study. SETTING: Quaternary academic medical center. PATIENTS: Adult patients admitted to the ICU following return of spontaneous circulation postcardiac arrest with clinical evidence of hypoxic ischemic brain injury defined as greater than or equal to 10 minutes of cardiac arrest with an unconfounded postresuscitation Glasgow Coma Scale of less than or equal to 8. INTERVENTIONS: We compared patients who underwent goal-directed care using invasive neuromonitoring with those treated with standard of care (using both total and matched groups). MEASUREMENTS AND MAIN RESULTS: Goal-directed care patients were matched 1:1 to standard of care patients using propensity scores and exact matching. The primary outcome was a 6-month favorable neurologic outcome (Cerebral Performance Category of 1 or 2). We included 65 patients, of whom 21 received goal-directed care and 44 patients received standard of care. The median age was 50 (interquartile range, 35-61), 48 (74%) were male, and seven (11%) had shockable rhythms. Favorable neurologic outcome at 6 months was significantly greater in the goal-directed care group (n = 9/21 [43%]) compared with the matched (n = 2/21 [10%], p = 0.016) and total (n = 8/44 [18%], p = 0.034) standard of care groups. Goal-directed care group patients had higher mean arterial pressure (p < 0.001 vs total; p = 0.0060 vs matched) and lower temperature (p = 0.007 vs total; p = 0.041 vs matched). CONCLUSIONS: In this preliminary study of patients with hypoxic ischemic brain injury postcardiac arrest, goal-directed care guided by invasive neuromonitoring was associated with a 6-month favorable neurologic outcome (Cerebral Performance Category 1 or 2) versus standard of care. Significant work is required to confirm this finding in a prospectively designed study.

Determining Optimal Mean Arterial Pressure After Cardiac Arrest: A Systematic Review.

The use of cerebral autoregulation monitoring to identify patient-specific optimal mean arterial pressure (MAPOPT) has emerged as a technique to augment cerebral oxygen delivery in post-cardiac arrest patients. Our systematic review aims to determine (a) the average MAPOPT in these patients, (b) the feasibility of identifying MAPOPT, (c) the brain tissue oxygenation levels when MAP is within proximity to the MAPOPT and (d) the relationship between neurological outcome and MAPOPT-targeted resuscitation strategies. We carried out this review in accordance with the PRISMA guidelines. We included all studies that used cerebral autoregulation to determine MAPOPT in adult patients (> 16 years old) who achieved return of spontaneous circulation (ROSC) following cardiac arrest. All studies had to include our primary outcome of MAPOPT. We excluded studies where the patients had any history of traumatic brain injury, ischemic stroke or intracranial hemorrhage. We identified six studies with 181 patients. There was wide variability in cerebral autoregulation monitoring methods, length of monitoring, calculation and reporting of MAPOPT. Amongst all studies, the median or mean MAPOPT was consistently above 65 mmHg (range 70-114 mmHg). Definitions of feasibility varied among studies and were difficult to summarize. Only one study noted that brain tissue oxygenation increased as patients' MAP approached MAPOPT. There was no consistent association between targeting MAPOPT and improved neurological outcome. There is considerable heterogeneity in MAPOPT due to differences in monitoring methods of autoregulation. Further research is needed to assess the clinical utility of MAPOPT-guided strategies on decreasing secondary injury and improving neurological outcomes after ROSC.

Nitric oxide is fundamental to neurovascular coupling in humans.

KEY POINTS: Preclinical models have demonstrated that nitric oxide is a key component of neurovascular coupling; this has yet to be translated to humans. We conducted two separate protocols utilizing intravenous infusion of a nitric oxide synthase inhibitor and isovolumic haemodilution to assess the influence of nitric oxide on neurovascular coupling in humans. Isovolumic haemodilution did not alter neurovascular coupling. Intravenous infusion of a nitric oxide synthase inhibitor reduced the neurovascular coupling response by ∼30%, indicating that nitric oxide is integral to neurovascular coupling in humans. ABSTRACT: Nitric oxide is a vital neurovascular signalling molecule in preclinical models, yet the mechanisms underlying neurovascular coupling (NVC) in humans have yet to be elucidated. To investigate the contribution of nitric oxide to NVC in humans, we utilized a visual stimulus paradigm to elicit an NVC response in the posterior cerebral circulation. Two distinct mechanistic interventions were conducted on young healthy males: (1) NVC was assessed during intravenous infusion of saline (placebo) and the non-selective competitive nitric oxide synthase inhibitor NG -monomethyl-l-arginine (l-NMMA, 5 mg kg-1 bolus & subsequent 50 µg kg-1 min-1 maintenance dose; n = 10). The order of infusion was randomized, counterbalanced and single blinded. A subset of participants in this study (n = 4) underwent a separate intervention with phenylephrine infusion to independently consider the influence of blood pressure changes on NVC (0.1-0.6 µg kg-1 min-1 constant infusion). (2) NVC was assessed prior to and following isovolumic haemodilution, whereby 20% of whole blood was removed and replaced with 5% human serum albumin to reduce haemoglobin concentration (n = 8). For both protocols, arterial and internal jugular venous blood samples were collected at rest and coupled with volumetric measures of cerebral blood flow (duplex ultrasound) to quantify resting cerebral metabolic parameters. l-NMMA elicited a 30% reduction in the peak (P = 0.01), but not average (P = 0.11), NVC response. Neither phenylephrine nor haemodilution influenced NVC. Nitric oxide signalling is integral to NVC in humans, providing a new direction for research into pharmacological treatment of humans with dementia.

Brain Hypoxia Secondary to Diffusion Limitation in Hypoxic Ischemic Brain Injury Postcardiac Arrest.

OBJECTIVES: We sought to characterize 1) the difference in the diffusion gradient of cellular oxygen delivery and 2) the presence of diffusion limitation physiology in hypoxic-ischemic brain injury patients with brain hypoxia, as defined by parenchymal brain tissue oxygen tension less than 20 mm Hg versus normoxia (brain tissue oxygen tension > 20 mm Hg). DESIGN: Post hoc subanalysis of a prospective study in hypoxic-ischemic brain injury patients dichotomized into those with brain hypoxia versus normoxia. SETTING: Quaternary ICU. PATIENTS: Fourteen adult hypoxic-ischemic brain injury patients after cardiac arrest. INTERVENTIONS: Patients underwent monitoring with brain oxygen tension, intracranial pressure, cerebral perfusion pressure, mean arterial pressure, and jugular venous bulb oxygen saturation. Data were recorded in real time at 300Hz into the ICM+ monitoring software (Cambridge University Enterprises, Cambridge, United Kingdom). Simultaneous arterial and jugular venous bulb blood gas samples were recorded prospectively. MEASUREMENTS AND MAIN RESULTS: Both the normoxia and hypoxia groups consisted of seven patients. In the normoxia group, the mean brain tissue oxygen tension, jugular venous bulb oxygen tension, and cerebral perfusion pressure were 29 mm Hg (SD, 9), 45 mm Hg (SD, 9), and 80 mm Hg (SD, 7), respectively. In the hypoxia group, the mean brain tissue oxygen tension, jugular venous bulb oxygen to brain tissue oxygen tension gradient, and cerebral perfusion pressure were 14 mm Hg (SD, 4), 53 mm Hg (SD, 8), and 72 mm Hg (SD, 6), respectively. There were significant differences in the jugular venous bulb oxygen tension-brain oxygen tension gradient (16 mm Hg [sd, 6] vs 39 mm Hg SD, 11]; p < 0.001) and in the relationship of jugular venous bulb oxygen tension-brain oxygen tension gradient to cerebral perfusion pressure (p = 0.004) when comparing normoxia to hypoxia. Each 1 mm Hg increase in cerebral perfusion pressure led to a decrease in the jugular venous bulb oxygen tension-brain oxygen tension gradient by 0.36 mm Hg (95% CI, -0.54 to 0.18; p < 0.001) in the normoxia group, but no such relation was demonstrable in the hypoxia group. CONCLUSIONS: In hypoxic-ischemic brain injury patients with brain hypoxia, there is an elevation in the jugular venous bulb oxygen tension-brain oxygen tension gradient, which is not modulated by changes in cerebral perfusion pressure.

Baseline characteristics and outcomes of patients with COVID-19 admitted to intensive care units in Vancouver, Canada: a case series.

BACKGROUND: Pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with high intensive care unit (ICU) mortality. We aimed to describe the clinical characteristics and outcomes of critically ill patients with coronavirus disease 2019 (COVID-19) in a Canadian setting. METHODS: We conducted a retrospective case series of critically ill patients with laboratory-confirmed SARS-CoV-2 infection consecutively admitted to 1 of 6 ICUs in Metro Vancouver, British Columbia, Canada, between Feb. 21 and Apr. 14, 2020. Demographic, management and outcome data were collected by review of patient charts and electronic medical records. RESULTS: Between Feb. 21 and Apr. 14, 2020, 117 patients were admitted to the ICU with a confirmed diagnosis of COVID-19. The median age was 69 (interquartile range [IQR] 60-75) years, and 38 (32.5%) were female. At least 1 comorbidity was present in 86 (73.5%) patients. Invasive mechanical ventilation was required in 74 (63.2%) patients. The duration of mechanical ventilation was 13.5 (IQR 8-22) days overall and 11 (IQR 6-16) days for patients successfully discharged from the ICU. Tocilizumab was administered to 4 patients and hydroxychloroquine to 1 patient. As of May 5, 2020, a total of 18 (15.4%) patients had died, 12 (10.3%) remained in the ICU, 16 (13.7%) were discharged from the ICU but remained in hospital, and 71 (60.7%) were discharged home. INTERPRETATION: In our setting, mortality in critically ill patients with COVID-19 admitted to the ICU was lower than in previously published studies. These data suggest that the prognosis associated with critical illness due to COVID-19 may not be as poor as previously reported.

Association between intensive care unit occupancy at discharge, afterhours discharges, and clinical outcomes: a historical cohort study.

PURPOSE: There is a paucity of evidence evaluating whether intensive care unit (ICU) discharge occupancy is associated with clinical outcomes. It is unknown whether increased discharge occupancy leads to greater afterhours discharges and downstream consequences. We explore the association between ICU discharge occupancy and afterhours discharges, 72-hr readmission, and 30-day mortality. METHODS: This single-centre, historical cohort study included all patients discharged from the Vancouver General Hospital ICU between 5 April 2010 and 13 September 2017. Data were obtained from the British Columbia Critical Care Database. Occupancy was defined as the number of ICU bed hours utilized divided by the available bed hours for that day. Any discharge between 22:00 and 6:59 was considered afterhours. Logistic regression models adjusting for important covariates were constructed. RESULTS: We included 8,862 ICU discharges representing 7,288 individual patients. There were 1,180 (13.3%) afterhours discharges, 408 (4.6%) 72-hr readmissions, and 574 (6.5%) 30-day post-discharge deaths. Greater discharge occupancy was associated with afterhours discharges (per 10% increase: adjusted odds ratio [aOR], 1.12; 95% confidence interval [CI], 1.03 to 1.20; P = 0.005). Discharge occupancy was not associated with 72-hr readmission (per 10% increase: aOR, 0.97; 95% CI, 0.87 to 1.09; P = 0.62) or 30-day mortality (per 10% increase: aOR, 1.05; 95% CI, 0.95 to 1.16; P = 0.32). Afterhours discharge was not associated with 72-hr readmission (aOR, 1.15; 95% CI, 0.86 to 1.54; P = 0.34) or 30-day mortality (aOR, 1.05; 95% CI, 0.82 to 1.36; P = 0.69). CONCLUSIONS: Greater ICU discharge occupancy was associated with a significant increase in afterhours discharges. Nevertheless, neither discharge occupancy nor afterhours discharge were associated with 72-hr readmission or 30-day mortality.

RéSUMé: OBJECTIF: Il n'existe que peu de données probantes évaluant si le taux d'occupation de l'unité de soins intensifs (USI) au moment du congé est associé aux devenirs cliniques. Nous ne savons pas si un taux d'occupation plus élevé au moment du congé entraîne davantage de congés pendant la nuit et si cette situation a des conséquences. Nous avons exploré l'association entre le taux d'occupation de l'USI au moment du congé et les congés donnés pendant la nuit, la réadmission dans les premières 72 h, et la mortalité à 30 jours. MéTHODE: Cette étude de cohorte historique et monocentrique a englobé tous les patients ayant reçu leur congé de l'USI de l'Hôpital général de Vancouver entre le 5 avril 2010 et le 13 septembre 2017. Les données ont été tirées de la Base de données des soins intensifs de Colombie-Britannique (British Columbia Critical Care Database). Le taux d'occupation était défini comme le nombre d'heures d'occupation de lit de l'USI utilisées divisé par le nombre d'heures d'occupation de lit disponibles pour ladite journée. Tout congé reçu entre 22 h et 6 h 59 était considéré comme survenant pendant la nuit. Des modèles de régression logistique ont été élaborés afin de tenir compte des covariables importantes. RéSULTATS: Nous avons inclus 8862 congés de l'USI, représentant 7288 patients individuels. Au total, il y a eu 1180 (13,3 %) congés donnés pendant la nuit, 408 (4,6 %) réadmissions dans les 72 h suivantes, et 574 (6,5 %) décès à 30 jours après le congé. Un taux d'occupation plus élevé au moment du congé était associé à des congés pendant la nuit (par augmentation de 10 % : rapport de cotes ajusté [RCA], 1,12; intervalle de confiance [IC] 95 %, 1,03 à 1,20; P = 0,005). Le taux d'occupation lors du congé n'a pas été associé à une réadmission dans les premières 72 h (par augmentation de 10 % : RCA, 0,97; IC 95 %, 0,87 à 1,09; P = 0,62) ou à une mortalité à 30 jours (par augmentation de 10 % : RCA, 1,05; IC 95 %, 0,95 à 1,16; P = 0,32). Les congés pendant la nuit n'ont pas été associés à une réadmission dans les 72 h suivantes (RCA, 1,15; IC 95 %, 0,86 à 1,54; P = 0,34) ou à une mortalité à 30 jours (RCA, 1,05; IC 95 %, 0,82 à 1,36; P = 0,69). CONCLUSION: Un taux d'occupation de l'USI plus élevé au moment du congé était associé à une augmentation significative des congés donnés pendant la nuit. Cependant, ni le taux d'occupation lors du congé, ni le congé donné pendant la nuit, n'étaient associés à une réadmission à 72 h ou une mortalité à 30 jours.

The Burden of Brain Hypoxia and Optimal Mean Arterial Pressure in Patients With Hypoxic Ischemic Brain Injury After Cardiac Arrest.

OBJECTIVES: In patients at risk of hypoxic ischemic brain injury following cardiac arrest, we sought to: 1) characterize brain oxygenation and determine the prevalence of brain hypoxia, 2) characterize autoregulation using the pressure reactivity index and identify the optimal mean arterial pressure, and 3) assess the relationship between optimal mean arterial pressure and brain tissue oxygenation. DESIGN: Prospective interventional study. SETTING: Quaternary ICU. PATIENTS: Adult patients with return of spontaneous circulation greater than 10 minutes and a postresuscitation Glasgow Coma Scale score under 9 within 72 hours of cardiac arrest. INTERVENTIONS: All patients underwent multimodal neuromonitoring which included: 1) brain tissue oxygenation, 2) intracranial pressure, 3) jugular venous continuous oximetry, 4) regional saturation of oxygen using near-infrared spectroscopy, and 5) pressure reactivity index-based determination of optimal mean arterial pressure, lower and upper limit of autoregulation. We additionally collected mean arterial pressure, end-tidal CO2, and temperature. All data were captured at 300 Hz using ICM+ (Cambridge Enterprise, Cambridge, United Kingdom) brain monitoring software. MEASUREMENTS AND MAIN RESULTS: Ten patients (7 males) were included with a median age 47 (range 20-71) and return to spontaneous circulation 22 minutes (12-36 min). The median duration of monitoring was 47 hours (15-88 hr), and median duration from cardiac arrest to inclusion was 15 hours (6-44 hr). The mean brain tissue oxygenation was 23 mm Hg (SD 8 mm Hg), and the mean percentage of time with a brain tissue oxygenation below 20 mm Hg was 38% (6-100%). The mean pressure reactivity index was 0.23 (0.27), and the percentage of time with a pressure reactivity index greater than 0.3 was 50% (12-91%). The mean optimal mean arterial pressure, lower and upper of autoregulation were 89 mm Hg (11), 82 mm Hg (8), and 96 mm Hg (9), respectively. There was marked between-patient variability in the relationship between mean arterial pressure and indices of brain oxygenation. As the patients' actual mean arterial pressure approached optimal mean arterial pressure, brain tissue oxygenation increased (p < 0.001). This positive relationship did not persist when the actual mean arterial pressure was above optimal mean arterial pressure. CONCLUSIONS: Episodes of brain hypoxia in hypoxic ischemic brain injury are frequent, and perfusion within proximity of optimal mean arterial pressure is associated with increased brain tissue oxygenation. Pressure reactivity index can yield optimal mean arterial pressure, lower and upper limit of autoregulation in patients following cardiac arrest.

Highs and lows of hyperoxia: physiological, performance, and clinical aspects.

Molecular oxygen (O2) is a vital element in human survival and plays a major role in a diverse range of biological and physiological processes. Although normobaric hyperoxia can increase arterial oxygen content ([Formula: see text]), it also causes vasoconstriction and hence reduces O2 delivery in various vascular beds, including the heart, skeletal muscle, and brain. Thus, a seemingly paradoxical situation exists in which the administration of oxygen may place tissues at increased risk of hypoxic stress. Nevertheless, with various degrees of effectiveness, and not without consequences, supplemental oxygen is used clinically in an attempt to correct tissue hypoxia (e.g., brain ischemia, traumatic brain injury, carbon monoxide poisoning, etc.) and chronic hypoxemia (e.g., severe COPD, etc.) and to help with wound healing, necrosis, or reperfusion injuries (e.g., compromised grafts). Hyperoxia has also been used liberally by athletes in a belief that it offers performance-enhancing benefits; such benefits also extend to hypoxemic patients both at rest and during rehabilitation. This review aims to provide a comprehensive overview of the effects of hyperoxia in humans from the "bench to bedside." The first section will focus on the basic physiological principles of partial pressure of arterial O2, [Formula: see text], and barometric pressure and how these changes lead to variation in regional O2 delivery. This review provides an overview of the evidence for and against the use of hyperoxia as an aid to enhance physical performance. The final section addresses pathophysiological concepts, clinical studies, and implications for therapy. The potential of O2 toxicity and future research directions are also considered.

Effect of Cerebral Perfusion Pressure on Acute Respiratory Distress Syndrome.

BACKGROUND: Increased cerebral perfusion pressure (CPP)>70 mmHg has been associated with acute respiratory distress syndrome (ARDS) after traumatic brain injury (TBI). Since this reported association, significant changes in ventilation strategies and fluid management have been accepted as routine critical care. Recently, individualized perfusion targets using autoregulation monitoring suggest CPP titration>70 mmHg. Given these clinical advances, the association between ARDS and increased CPP requires further delineation. OBJECTIVE: To determine the association between ARDS and increased CPP after TBI. METHODS: We conducted a single-center historical cohort study investigating the association of increased CPP and ARDS after TBI. We collected demographic data and physiologic data for CPP, intracranial pressure, mechanical ventilation, cumulative fluid balance and delta/driving pressure (ΔP). We collected outcomes measures pertaining to duration of ventilation, intensive care unit admission length, hospitalization length and 6-month neurological outcome. RESULTS: In total, 113 patients with severe TBI and multimodal neuromonitoring were included. In total, 16 patients (14%) developed ARDS according to the Berlin definition. There was no difference in the mean CPP during the first 7 days of admission between patients who developed ARDS (74 mmHg SD 18 vs. 73 mmHg SD 18, p=0.86) versus those who did not. Patients who developed ARDS had a higher ΔP (15 mmHg [5] vs. 12 mmHg [4], p=0.016) and lower lung compliance (35 ml/cmH2O [10] vs. 49 ml/cmH2O [18], p=0.024) versus those who did not. CONCLUSION: We did not observe an association between increased CPP and ARDS. Patients with ARDS had higher ΔP and lower lung compliance.

A Systematic Review of the Risks and Benefits of Venous Thromboembolism Prophylaxis in Traumatic Brain Injury.

BACKGROUND: Patients suffering from traumatic brain injury (TBI) are at increased risk of venous thromboembolism (VTE). However, initiation of pharmacological venous thromboprophylaxis (VTEp) may cause further intracranial hemorrhage. We reviewed the literature to determine the postinjury time interval at which VTEp can be administered without risk of TBI evolution and hematoma expansion. METHODS: MEDLINE and EMBASE databases were searched. Inclusion criteria were studies investigating timing and safety of VTEp in TBI patients not previously on oral anticoagulation. Two investigators extracted data and graded the papers' levels of evidence. Randomized controlled trials were assessed for bias according to the Cochrane Collaboration Tool and Cohort studies were evaluated for bias using the Newcastle-Ottawa Scale. We performed univariate meta-regression analysis in an attempt to identify a relationship between VTEp timing and hemorrhagic progression and assess study heterogeneity using an I 2 statistic. RESULTS: Twenty-one studies were included in the systematic review. Eighteen total studies demonstrated that VTEp postinjury in patients with stable head computed tomography scan does not lead to TBI progression. Fourteen studies demonstrated that VTEp administration 24 to 72 hours postinjury is safe in patients with stable injury. Four studies suggested that administering VTEp within 24 hours of injury in patients with stable TBI does not lead to progressive intracranial hemorrhage. Overall, meta-regression analysis demonstrated that there was no relationship between rate of hemorrhagic progression and VTEp timing. CONCLUSIONS: Literature suggests that administering VTEp 24 to 48 hours postinjury may be safe for patients with low-hemorrhagic-risk TBIs and stable injury on repeat imaging.

Individualized perfusion targets in hypoxic ischemic brain injury after cardiac arrest.

Secondary injury is a major determinant of outcome in hypoxic ischemic brain injury (HIBI) after cardiac arrest and may be mitigated by optimizing cerebral oxygen delivery (CDO2). CDO2 is determined by cerebral blood flow (CBF), which is dependent upon mean arterial pressure (MAP). In health, CBF remains constant over the MAP range through cerebral autoregulation. In HIBI, the zone of intact cerebral autoregulation is narrowed and varies for each patient. Maintaining MAP within the intact autoregulation zone may mitigate ischemia, hyperemia and secondary injury. The optimal MAP in individual patients can be determined using real time autoregulation monitoring techniques.