Determining witnessed status for out-of-hospital cardiac arrest.

Objective: Witnessed status is considered a core variable in reporting cardiac arrest data and can be ascertained from either the emergency dispatch recording or the pre-hospital record. The purpose of this study is to compare and assess the quality and consistency of these information sources.

Methods: This retrospective analysis included 1896 cases of out-of-hospital cardiac arrest occurring between September 1, 2012 and December 31, 2014.

Results: We found that there was minimal (kappa=0.30, 95% CI 0.27-0.33) to moderate (kappa=0.64, 95% CI 0.59-0.69) agreement between the pre-hospital record and the emergency dispatch recording when these sources of information are used to determine witnessed status. Witnessed status could not be determined from the emergency dispatch recording in 36.2% (n=684) of eligible cases. Survival was similar regardless of the method used to determine witnessed status. Using a combination of the pre-hospital record and the emergency dispatch recording yielded the highest number of witnessed cases.

Conclusion: The determination of witnessed status in out-of-hospital cardiac arrest may be challenging, as evidenced by the discrepancies in witnessed status when comparing different sources of information. The large number of cases where the witnessed status could not be determined from the emergency dispatch recording precludes its use as the sole source of information. It is reasonable to use the patient care record alone, however it should be recognized that there is misclassification of witnessed status regardless of the method used and this may affect the strength of association between witnessed status and survival.