ARTICLE REVIEW

The paper “Delayed awakening after cardiac arrest: prevalence and risk factors in the Parisian registry” (1) asks how commonly and how predictably patients who are comatose 48 hours after cardiac arrest and cooling display a return to consciousness, attempting to answer this with patient demographics and clinical information. This conundrum is highly relevant to the specific cohort of Critical Care patients who have not yet declared themselves ‘clearly recovering’ or ‘clearly end-of-life’.
 
This builds on previous literature identifying the ideal timing of neuroprognostication tests for cardiac arrest survivors (2, 3). This is a retrospective case-control study using a prospectively collected data set focusing on out-of-hospital cardiac arrest patients in Paris, France. The aim of the study was to measure the incidence of delayed awakening and to identify the factors associated with it, in a large cohort of comatose cardiac arrest survivors treated with TTM with a standardized protocol of care and prognostication. Hence, predictors of delayed recovery would allow prognostication to assist in resource allocation in increasingly busy Critical Care Units. Neuroprognostication using a multinmodal score was performed at 48hrs after discontinuation of sedatives in those patients that remained comatose. Withdrawal of life-sustaining treatment was considered for indicators of poor prognosis.
 
Overall, 29% showed delayed awakening after cardiac arrest with a median time of wakening 10 hours in early awakeners and 93 hours in late awakeners. Variables significantly associated with delayed awakening included increasing age, poor renal function, need for renal replacement therapy, and the presence of shock post cardiac arrest. The authors hypothesise the delay in metabolism of sedative agents to explain the delayed awakening in older patients or those with impaired renal function. The dosage of sedation administered was not significantly different between the early and delayed recovery groups.
 
The sample size is small (56 delayed awakening patients identified), mainly due to the specific nature of the research question, but also because a large group of patients were excluded from the analysis due to re-sedation, neurological comorbidities, non-cooling post-cardiac arrest, or eventual non-recovery.
 
Given the small size of the cohort of delayed awakeners, the cause for the arrest becomes more significant. The longest delay to consciousness was 12 days; was this a case of carbon monoxide poisoning? Are there specific and significant similarities between the different time-to-recovery cohorts that were not investigated in this study? Although the authors describe the study limitations, the data is at risk of overemphasising the conclusions drawn, as the sample size is so small, the cohort was narrowed by strict exclusions, and variables were selected for likelihood of significance rather than discovered by analysis.
 
In conclusion, this was an interesting topic that is hard to investigate without bias. The paper confirms what is inferred regarding sedative agents and delayed consciousness, but may not provide clinically significant information for the prognosticating clinician; namely how can we prognosticate patients to predict those likely to show delayed recovery? This work provides data regarding the frequency of delayed wakening, but determination of the predictability of recovery will require further larger as well as more specific analyses.
 
Article review was submitted by Henry Murphy and Brijesh Patel on behalf of the ESICM Journal Review Club.

References

 1. Paul et al. Delayed awakening after cardiac arrest: prevalence and risk factors in the Parisian registry. Intensive Care Med Original; Volume 42, Issue 7 / July, 2016, Pages 1128 – 1136.

2.Perman SM, Kirkpatrick JN, Reitsma AM et al (2012) Timing of neuroprognostication in postcardiac arrest therapeutic hypothermia. Crit Care Med 40:719–724
 
3. Sandroni C, Cariou A, Cavallaro F et al (2014) Prognostication in comatose survivors of cardiac arrest: an advisory statement from the European Resuscitation Council and the European Society of Intensive Care Medicine. Intensive Care Med 40:1816–1831