An update on the impact of bystander cardiopulmonary resuscitation on favorable neurological outcomes of patients with out-of-hospital cardiac arrest accounting for effect modification by witnessed arrest: a post hoc analysis of the SOS-KANTO 2017 study.

AIM

To investigate the role of witnessed arrest as an effect modifier on neurological outcomes following bystander cardiopulmonary resuscitation (CPR) in patients with out-of-hospital cardiac arrest (OHCA).

METHODS

This cohort study was conducted using an OHCA patient registry collected between September 2019 and March 2021 in Japan. The effect modification by witnessed arrest was analyzed using additive and multiplicative interactions with risk adjustment. The main outcome was a cerebral performance category of 1 or 2 at 30 days after OHCA.

RESULTS

A total of 7496 patients from 42 hospitals were analyzed. Witnessed arrest and bystander CPR occurred in 3053 (40.7 %) and 3152 (42.0 %) patients, respectively. The adjusted odds ratio (OR) of witnessed arrest and bystander CPR for favorable neurological outcomes was 11.36 (95 % confidence interval [CI]: 7.10-18.17). The ORs for bystander CPR within each stratum of witnessed arrest were 2.38 (95 % CI: 1.34-4.24) for non-witnessed arrest and 3.80 (95 % CI: 2.61-5.55) for witnessed arrest. The additive interaction was 7.01 (95 % CI: 3.34-10.68) and the multiplicative interaction was 1.60 (95 % CI: 0.80-3.17). In the non-home arrest setting, bystander CPR had an adjusted OR of 1.23 (95 % CI: 0.58-2.62) for non-witnessed arrest and 2.77 (95 % CI: 1.69-4.53) for witnessed arrest. The additive interaction was 4.98 (95 % CI: 1.67-8.29) and the multiplicative interaction was 2.25 (95 % CI: 0.91-5.53).

CONCLUSIONS

The interaction effect of bystander CPR and witnessed arrest exhibited the second strongest form of interaction. The non-significant effect of bystander CPR in non-witnessed arrest in the non-home cardiac arrest setting warrants further investigation.