Predicting outcome of drowning at the scene: A systematic review and meta-analyses

Article: Predicting outcome of drowning at the scene:A systematic review and meta-analyses
Authors: Quan L, Bierens J, Lis R, Rowhani-Rahbar A, Morley P, Perkins G
Journal: Resuscitation, ePub ahead of print (May 2016)

One of the toughest questions to answer in the first few hours to days following the resuscitation of a drowning patient who remains comatose is what factors associated with the patient or the event can be used to determine prognosis.  While numerous studies have been done in the past to help answer this question, most are plagued by low quality data or designs and a focus on overall mortality instead of neurologic outcome. In this systematic review and meta-analysis, the authors focused on scene factors which could possibly help determine prognosis.

Summary

Study Type: Systematic review and meta-analysis

Period: 1979-2015

Inclusion: Cohort and case-control studies reporting:

• Submersion duration 
• Age
• Water temperature
• Salinity
• EMS response time
• Survival and/or neurological outcome

Results

• 24 cohort studies
• Submersion duration strongest predictor
• ≤ 10 min predicted high rate of good outcome
•  ≥ 25 min associated with dismal outcome
• Factors not showing prognostic value
• Age
• Water temperature
• Factors showing some prognostic value
• Salinity: salt water favorable
• EMS response time: the shorter, the better
• Both factors had very weak prognostic value

The most important conclusion of this paper, and one made many times before, is that the longer a person is submerged underwater, the worse chance they have for good neurologic outcome.  While there is no obvious cut-off time, and large variability, this analysis was able to produce a dose-response curve showing a correlation between submersion time and outcome. This time is a marker of anoxic brain injury.  The cut-offs of 10 min and 25 min were used to differentiate between strong chances of good outcome and bad outcome, respectively, but times in between are in a gray zone of uncertainty. An important note is that all of the papers analyzed were judge to have a low or very low level of evidence.