This study sought to assess the association of the endorsement of DA-COCPR with the increased rates of BCPR and survival, considering the changes to the DA-CPR indices. In alignment with previous reports,18 the continuous shift to compression-only BCPR was accompanied by an increase in BCPR rate during the study period. However, the guidelines endorsing the shift to compression-only BCPR also emphasized the role of dispatchers to detect OHCA and to instruct to callers and bystanders to perform CPR, and hence the continuous quality program for DA-CPR was activated and dispersed throughout Japan19 and other countries.20–23 Indeed, a prominent increase was observed in DA-CPR sensitivity for OHCA but a small increase in bystander’s compliance with DA-CPR was also noted. Therefore, it is likely that the increase in BCPR rate during the study period is mainly attributed to the improved ability of dispatcher to detect OHCA, although the small increase in bystander’s compliance with DA-CPR may reflect the preference of some bystanders for compression-only CPR.
This study showed that association of DA-COCPR with 2-year outcome data differed between unwitnessed and bystander-witnessed cases. In unwitnessed cases, DA-COCPR was not significantly associated with a higher rate of neurologically favorable survival than No-BCPR during any 2-year period. Furthermore, the annual increase in the survival rate in this group, assessed by adjusted unit OR, was much smaller than that for the DA-SCPR. In bystander-witnessed cases, DA-COCPR was consistently associated with a higher survival rate than No-BCPR. The annual increase in survival rate in this BCPR group was larger than that for the No-BCPR group but was smaller than the DA-SCPR. Therefore, the association of DA-COCPR with outcome improvement was evident in bystander-witnessed cases but not in unwitnessed cases.
Two reasons for this difference may be assumed. Theoretically, during the first few minutes of OHCA, rescue breaths are less important than chest compressions because blood oxygen levels remain higher than the critical level. It is possible that instruction of standard CPR to untrained bystanders may prolong the time interval to compressions. Thus, instruction compression-only CPR may be more effective than or as effective as standard CPR for a witnessed OHCA, especially in a community with a short interval for EMS response time.24 The second reason is the increased proportion of untrained bystanders to perform compression-only BCPR in response to dispatcher’s instruction, which in turn causes the decrease in overall quality of chest compressions in this group. It is highly possible that high-quality CPR is essential for survival from unwitnessed OHCA.
Because outcome improvement was observed in EMS-witnessed OHCA cases, the improvement was also attributable to the prehospital confounders after EMS contact with patients and in-hospital confounders. In this context, most paramedics were re-trained for high-quality CPR when they were qualified for intravenous access for patients with shock and hypoglycemia. Application of therapeutic hypothermia and extracorporeal circulation as an in-hospital advanced management of OHCA became common in core emergency hospitals.25,26 Similarly, these advanced managements of patients with OHCA account for the outcome improvement of bystander-witnessed OHCA cases receiving No-BCPR. Also, it should be noted that the annual increase in survival rate in unwitnessed cases receiving DA-COCPR is similar to that in EMS-witnessed OHCA cases, indicating a small contribution of DA-COCPR to the outcome improvement.
The results of this study suggest that DA-COCPR is not an ideal management for unwitnessed OHCA cases. Presumably, the BCPR performed by well-trained bystanders is ideal. Because this observational study in Japan and other observational studies in other countries did not include the quality of the BCPR as a prehospital confounder, the clinical advantage of standard BCPR over compression-only BCPR should be tested in a large randomized controlled trial, including unwitnessed cases in communities with a first responder system that has recruited well-trained volunteers to arrive at the scene.
What is the best or better strategy for the improvement of unwitnessed OHCA? The shift to compression-only BCPR for the untrained layperson should not be accompanied by an educational shift to compression-only CPR. Education for the standard CPR should be preserved in BLS training. Although the time delay until the start of chest compressions is harmful in bystander-witnessed OHCA, this delay may have little influence on the outcome of unwitnessed OHCA. As another strategy, dispatcher should attempt to instruct callers or bystanders to perform standard CPR as a first trial in unwitnessed cases.
Limitations
Factors such as the bystander age, the bystander–patient relationship, bystander training or experience, and the location of the OHCA were not included in the analysis because of lack of these data in unwitnessed cases. Particularly, lack of any data for qualities of BCPR is a potent limitation. A risk of misclassifications for DA-CPR and combination of rescue breaths may have occurred. Also, as in other observational studies, validity of data was another potential limitation.