Hyperoxia Early After Hospital Admission in Comatose Patients with Non-Traumatic Out-of-Hospital Cardiac Arrest

Early restricted oxygen therapy after resuscitation from cardiac arrest (ER-OXYTRAC): protocol for a stepped-wedge cluster randomised controlled trial

INTRODUCTION

Cardiac arrest is a critical condition, and patients often experience postcardiac arrest syndrome (PCAS) even after the return of spontaneous circulation (ROSC). Administering a restricted amount of oxygen in the early phase after ROSC has been suggested as a potential therapy for PCAS; however, the optimal target for arterial partial pressure of oxygen or peripheral oxygen saturation (SpO2) to safely and effectively reduce oxygen remains unclear. Therefore, we aimed to validate the efficacy of restricted oxygen treatment with 94%-95% of the target SpO2 during the initial 12 hours after ROSC for patients with PCAS.

METHODS AND ANALYSIS

ER-OXYTRAC (early restricted oxygen therapy after resuscitation from cardiac arrest) is a nationwide, multicentre, pragmatic, single-blind, stepped-wedge cluster randomised controlled trial targeting cases of non-traumatic cardiac arrest. This study includes adult patients with out-of-hospital or in-hospital cardiac arrest who achieved ROSC in 39 tertiary centres across Japan, with a target sample size of 1000. Patients whose circulation has returned before hospital arrival and those with cardiac arrest due to intracranial disease or intoxication are excluded. Study participants are assigned to either the restricted oxygen (titration of a fraction of inspired oxygen with 94%-95% of the target SpO2) or the control (98%-100% of the target SpO2) group based on cluster randomisation per institution. The trial intervention continues until 12 hours after ROSC. Other treatments for PCAS, including oxygen administration later than 12 hours, can be determined by the treating physicians. The primary outcome is favourable neurological function, defined as cerebral performance category 1-2 at 90 days after ROSC, to be compared using an intention-to-treat analysis.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board at Keio University School of Medicine (approval number: 20211106). Written informed consent will be obtained from all participants or their legal representatives. Results will be disseminated via publications and presentations.

TRIAL REGISTRATION NUMBER

UMIN Clinical Trials Registry (UMIN000046914).

Oxygen administration in patients recovering from cardiac arrest: a narrative review

High oxygen tension in blood and/or tissue affects clinical outcomes in several diseases. Thus, the optimal target PaO₂ for patients recovering from cardiac arrest (CA) has been extensively examined. Many patients develop hypoxic brain injury after the return of spontaneous circulation (ROSC); this supports the need for oxygen administration in patients after CA. Insufficient oxygen delivery due to decreased blood flow to cerebral tissue during CA results in hypoxic brain injury. By contrast, hyperoxia may increase dissolved oxygen in the blood and, subsequently, generate reactive oxygen species that are harmful to neuronal cells. This secondary brain injury is particularly concerning. Although several clinical studies demonstrated that hyperoxia during post-CA care was associated with poor neurological outcomes, considerable debate is ongoing because of inconsistent results. Potential reasons for the conflicting results include differences in the definition of hyperoxia, the timing of exposure to hyperoxia, and PaO₂ values used in analyses. Despite the conflicts, exposure to PaO₂ > 300 mmHg through administration of unnecessary oxygen should be avoided because no obvious benefit has been demonstrated. The feasibility of titrating oxygen administration by targeting SpO₂ at approximately 94% in patients recovering from CA has been demonstrated in pilot randomized controlled trials (RCTs). Such protocols should be further examined.

Systematic review of oxygenation and clinical outcomes to inform oxygen targets in critically ill trauma patients

BACKGROUND

Oxygen therapy is frequently administered to critically ill trauma patients to avoid hypoxia, but optimal oxygenation strategies are not clear.

METHODS

We conducted a systematic review of oxygen targets and clinical outcomes in trauma and critically ill patients. We searched Ovid MEDLINE, Cochrane Library, Embase, and Web of Science Core Collection from 1946 through 2017. Our initial search yielded 14,774 articles with 209 remaining after abstract review. We reviewed full text articles of human subjects with conditions of interest, an oxygen exposure or measurement, and clinical outcomes, narrowing the review to 43 articles. We assessed article quality using Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) criteria.

RESULTS

Of the 43 final studies meeting inclusions criteria, 17 focused on trauma and 26 studies focused on medical and/or surgical critical illness without trauma specifically. Four trauma studies supported lower oxygenation/normoxia, two supported higher oxygenation, and 11 supported neither normoxia nor higher oxygenation (five neutral and six supported avoidance of hypoxia). Fifteen critical illness studies supported lower oxygenation/normoxia, one supported higher oxygenation, and 10 supported neither normoxia nor higher oxygenation (nine neutral and one supported avoidance of hypoxia). We identified seven randomized controlled trials (four high quality, three moderate quality). Of the high-quality randomized controlled trials (none trauma-related), one supported lower oxygenation/normoxia and three were neutral. Of the moderate-quality randomized controlled trials (one trauma-related), one supported higher oxygenation, one was neutral, and one supported avoidance of hypoxia.

CONCLUSION

We identified few trauma-specific studies beyond traumatic brain injury; none were high quality. Extrapolating primarily from nontrauma critical illness, reduced oxygen administration targeting normoxia in critically ill trauma patients may result in better or equivalent clinical outcomes. Additional trauma-specific trials are needed to determine the optimal oxygen strategy in critically injured patients.

LEVEL OF EVIDENCE

Systematic review, level IV.

Oxygenation and ventilation targets after cardiac arrest: A systematic review and meta-analysis

AIM

To perform a systematic review and meta-analysis of the literature on oxygenation and ventilation targets after successful resuscitation from cardiac arrest in order to inform an update of international guidelines.

METHODS

The review was performed according to PRISMA and registered on PROSPERO (ID: X). Medline, EMBASE, and the Cochrane Library were searched on August 22, 2019. The population included both adult and pediatric patients with cardiac arrest. Two investigators reviewed abstracts, extracted data, and assessed the risk of bias. Meta-analyses were performed for studies without excessive bias. Certainty of evidence was evaluated using GRADE.

RESULTS

We included 7 trials and 36 observational studies comparing oxygenation or ventilation targets. Most of the trials and observational studies included adults with out-of-hospital cardiac arrest. There were 6 observational studies in children. Bias for trials ranged from low to high risk, with group imbalances and blinding being primary concerns. Bias for observational studies was rated as serious or critical risk with confounding and exposure classification being primary sources of bias. Meta-analyses including two trials comparing low vs high oxygen therapy and two trials comparing hypercapnia vs no hypercapnia were inconclusive. Point estimates of individual studies generally favored normoxemia and normocapnia over hyper- or hypoxemia and hyper- or hypocapnia.

CONCLUSIONS

We identified a large number of studies related to oxygenation and ventilation targets in cardiac arrest. The majority of studies did not reach statistical significance and were limited by excessive risk of bias. Point estimates of individual studies generally favored normoxemia and normocapnia.

A Systematic Review of the Effects of Hyperoxia in Acutely Ill Patients: Should We Aim for Less?

INTRODUCTION

Despite widespread and liberal use of oxygen supplementation, guidelines about rational use of oxygen are scarce. Recent data demonstrates that current protocols lead to hyperoxemia in the majority of the patients and most health care professionals are not aware of the negative effects of hyperoxemia.

METHOD

To investigate the effects of hyperoxemia in acutely ill patients on clinically relevant outcomes, such as neurological and functional status as well as mortality, we performed a literature review using Medline (PubMed) and Embase. We used the following terms: hyperoxemia OR hyperoxemia OR ["oxygen inhalation therapy" AND (mortality OR death OR outcome OR survival)] OR [oxygen AND (mortality OR death OR outcome OR survival)]. Original studies about the clinical effects of hyperoxemia in adult patients suffering from acute or emergency illnesses were included.

RESULTS

37 articles were included, of which 31 could be divided into four large groups: cardiac arrest, traumatic brain injury (TBI), stroke, and sepsis. Although a single study demonstrated a transient protective effect of hyperoxemia after TBI, other studies revealed higher mortality rates after cardiac arrest, stroke, and TBI treated with oxygen supplementation leading to hyperoxemia. Approximately half of the studies showed no association between hyperoxemia and clinically relevant outcomes.

CONCLUSION

Liberal oxygen therapy leads to hyperoxemia in a majority of patients and hyperoxemia may negatively affect survival after acute illness. As a clinical consequence, aiming for normoxemia may limit negative effects of hyperoxemia in patients with acute illness.