Can we really predict outcome after Cardiac Arrest??

This is a single centre retrospective study, admittedly in a small patient cohort, but it offers food for thought in the controversial area of prognostication post out of hospital cardiac arrest. Link to paper

Often, we are presented, due to whatever reason, with patients who may have suffered prolonged downtimes during out of hospital cardiac arrest. We all approach such patients with ‘pint glasses half empty’, as we are aware of the high likelihood of hypoxic brain injury.

Their patients were all cooled to 32-34 degrees. They present a selection of clinical characteristics that may foretell poor neurological outcome:

1. Myoclonus less than 24 hours after the arrest
2. More than 1 brain stem reflex absent by day 3
3. Worse motor response than flexion on day 3

16.5% awakened by day 3 with reflexes and MR better than extension. 80% of these went home and the remaining 20% picked up severe infections, remaining on ICU for a mean of 17 days.

Limitations:

• Mortality in the study was most often preceded by withdrawal of life support raising the possible impact of the clinician’s opinion(s) at the time and their previous beliefs / experiences.This might have magnified the strengths of associations between predictors and unfavorable outcome.
• As they state, to exclude this, you would have to forbid all withdrawal of life support for a defined period time period (3-6 months), which is implausible from both ethical and practical standpoints.
• It may be that outcomes reported here might not reflect those in the UK, as it may be that in these areas of India,  there are significant resource-constraints both with auxiliary equipment and trained personnel.
• Interestingly, their choice of temperature has been shown to potentially increase mortality from pneumonia as demonstrated by previous studies. The current recommendation is no cooler than 36 degrees.
• The biggest grey area here is the ‘down-time’. To me, this is not only time without a circulation, but importantly, without a definitive airway. It is always hard to ascertain this in day-to-day practice, with bystanders involved and often confusing notes from paramedics. They calculate theirs as time to achieve ROSC as the sum of arrest-CPR interval, (time interval between the onset of collapse and onset of CPR, also referred to as the “no-flow state”) and the duration of CPR (“low-flow state”). It was dichotomized to ≤25 min and >25 min based on a previous study.
• There are so many other variables involved here, and outcome data are difficult to palate, even with the tightest statistics (other co-pathologies, different standards of bystander, if any, CPR etc etc.).

For me…..a long down-time greater than 25 minutes is going to potentially hold a bad outcome, and this paper demonstrates that. Further studies….too hard to do!