Protocol for an individual patient data meta-analysis on blood pressure targets after cardiac arrest

Lower vs. higher blood pressure targets during intensive care of comatose patients resuscitated from out-of-hospital cardiac arrest-a Bayesian analysis of the BOX trial

AIMS

The Blood Pressure and Oxygenation (BOX) targets after out-of-hospital cardiac arrest trial found no statistically significant differences in mortality or neurological outcomes with mean arterial blood pressure targets of 63 vs. 77 mmHg in patients receiving intensive care post-cardiac arrest. In this study, we aimed to evaluate the effect on 1-year mortality and assess heterogeneity in treatment effects (HTEs) using Bayesian statistics.

METHODS AND RESULTS

We analyzed 1-year all-cause mortality, 1-year neurological outcomes, and plasma neuron-specific enolase (NSE) at 48 h using Bayesian logistic and linear regressions primarily with weakly informative priors. HTE was assessed according to age, plasma lactate, time to return of spontaneous circulation, primary shockable rhythm, history of hypertension, and ST-segment elevation myocardial infarction. Absolute and relative differences are presented with probabilities of any clinical benefit and harm. All 789 patients in the intention-to-treat cohort were included. The risk difference (RD) for 1-year mortality was 1.5%-points [95% credible interval (CrI): -5.1 to 8.1], with <33% probability of benefit with the higher target. There was 33% probability for a better neurological outcome (RD: 1.5%-points; 95% CrI: -5.3 to 8.3) and 35.1% for lower NSE levels (mean difference: 1.5 µg/L, 95% CrI: -6.0 to 9.1). HTE analyses suggested potential harms of the higher blood pressure target in younger patients.

CONCLUSION

The effects of a higher blood pressure target on overall mortality among comatose patients resuscitated from out-of-hospital cardiac arrest were uncertain. A potential effect modification according to age warrants additional investigation.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov ID NCT03141099.

Lower versus higher blood pressure targets in comatose patients resuscitated from out-of-hospital cardiac arrest-Protocol for a secondary Bayesian analysis of the box trial

BACKGROUND

The management of blood pressure targets during intensive care after out-of-hospital cardiac arrest (OHCA) remains a topic of debate. The blood Pressure and Oxygenation Targets After OHCA (BOX) trial explored the efficacy of two different blood pressure targets in 789 patients during intensive care after OHCA. In the primary frequentist analysis, no statistically significant differences were found for neurological outcome after 90 days.

METHODS

This protocol outlines secondary Bayesian analyses of 365-day all-cause mortality and two secondary outcomes: neurological outcome after 365 days, and plasma neuron-specific enolase, a biomarker of brain injury, after 48 h. We will employ adjusted Bayesian logistic and linear regressions, presenting results as relative and absolute differences with 95% confidence intervals. We will use weakly informative priors for the primary analyses, and skeptical and evidence-based priors (where available) in sensitivity analyses. Exact probabilities for any benefit/harm will be presented for all outcomes, along with probabilities of clinically important benefit/harm (risk differences larger than 2%-points absolute) and no clinically important differences for the binary outcomes. We will assess whether heterogeneity of treatment effects on mortality is present according to lactate at admission, time to return of spontaneous circulation, primary shockable rhythm, age, hypertension, and presence of ST-elevation myocardial infarction.

DISCUSSION

This secondary analysis of the BOX trial aim to complement the primary frequentist analysis by quantifying the probabilities of beneficial or harmful effects of different blood pressure targets. This approach seeks to provide clearer insights for researchers and clinicians into the effectiveness of these blood pressure management strategies in acute medical conditions, particularly focusing on mortality, neurological outcomes, and neuron-specific enolase.

Blood pressure targets and management during post-cardiac arrest care

Blood pressure is one modifiable physiological target in patients treated in the intensive care unit after cardiac arrest. Current Guidelines recommend targeting a mean arterial pressure (MAP) of higher than 65-70 mmHg using fluid resuscitation and the use of vasopressors. Management strategies will vary based in the setting, i.e. the pre-hospital compared to the in-hospital phase. Epidemiological data suggest that some degree of hypotension requiring vasopressors occur in almost 50% of patients. A higher MAP could theoretically increase coronary blood flow but on the other hand the use of vasopressor may result in an increase in cardiac oxygen demand and arrhythmia. An adequate MAP is paramount for maintaining cerebral blood flow. In some cardiac arrest patients the cerebral autoregulation may be disturbed resulting in the need for higher MAP in order to avoid decreasing cerebral blood flow. Thus far, four studies including little more than 1000 patients have compared a lower and higher MAP target in cardiac arrest patients. The achieved mean difference of MAP between groups has varied from 10-15 mmHg. Based on these studies a Bayesian meta-analysis suggests that the posterior probability that a future study would find treatment effects higher than a 5% difference between groups to be less than 50%. On the other hand, this analysis also suggests, that the likelihood of harm with a higher MAP target is also low. Noteworthy is that all studies to date have focused mainly on patients with a cardiac cause of the arrest with the majority of patients being resuscitated from a shockable initial rhythm. Future studies should aim to include also non-cardiac causes and aim to target a wider separation in MAP between groups.

Higher versus lower blood pressure targets after cardiac arrest: systematic review with individual patient data meta-analysis

PURPOSE

Guidelines recommend targeting mean arterial pressure (MAP) > 65 mmHg in patients after cardiac arrest (CA). Recent trials have studied the effects of targeting a higher MAP as compared to a lower MAP after CA. We performed a systematic review and individual patient data meta-analysis to investigate the effects of higher versus lower MAP targets on patient outcome.

METHOD

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, LILACS, BIOSIS, CINAHL, Scopus, the Web of Science Core Collection, ClinicalTrials.gov, the World Health Organization International Clinical Trials Registry, Google Scholar and the Turning Research into Practice database to identify trials randomizing patients to higher (≥ 71 mmHg) or lower (≤70 mmHg) MAP targets after CA and resuscitation. We used the Cochrane Risk of Bias tool, version 2 (RoB 2) to assess for risk of bias. The primary outcomes were 180-day all-cause mortality and poor neurologic recovery defined by a modified Rankin score of 4-6 or a cerebral performance category score of 3-5.

RESULTS

Four eligible clinical trials were identified, randomizing a total of 1,087 patients. All the included trials were assessed as having a low risk for bias. The risk ratio (RR) with 95% confidence interval for 180-day all-cause mortality for a higher versus a lower MAP target was 1.08 (0.92-1.26) and for poor neurologic recovery 1.01 (0.86-1.19). Trial sequential analysis showed that a 25% or higher treatment effect, i.e., RR<0.75, can be excluded. No difference in serious adverse events was found between the higher and lower MAP groups.

CONCLUSIONS

Targeting a higher MAP compared to a lower MAP is unlikely to reduce mortality or improve neurologic recovery after CA. Only a large treatment effect above 25% (RR<0.75) could be excluded, and future studies are needed to investigate if relevant but lower treatment effect exists. Targeting a higher MAP was not associated with any increase in adverse effects.