Association between low pH and unfavorable neurological outcome among out-of-hospital cardiac arrest patients treated by extracorporeal CPR: do not dismiss confounders!

Recently, Okada et al. reported an association between low pH value before the implementation of extracorporeal cardiopulmonary resuscitation (ECPR) and 1-month unfavorable neurological outcome among out-of-hospital cardiac arrest (OHCA) patients treated with ECPR. Nevertheless, we believe that some methodological flaws deserve their conclusions. The time duration between OHCA occurrence and blood gas analysis (BGA), a major confounder for misinterpretation, was not taken into account. It is not reported whether the result of BGA analysis was considered and/or treated, and if ECPR implementation decision had been influenced by the results analysis. Furthermore, the no-flow duration and the in-hospital phase confounders for neurological outcome are not included as covariates in the logistic regression. Therefore, we believe that causes and consequences should not be confused: the longer is the no-flow duration, the greater are the metabolic consequences.