Letter by Arrich et al Regarding Article, “Bystander-Initiated Rescue Breathing for Out-of-Hospital Cardiac Arrests of Noncardiac Origin”
To The Editor:
With interest we have read the article by Kitamura and colleagues about bystander initiated rescue breathing for out-of-hospital cardiac arrest of noncardiac origin.1 The authors included a large number of patients from a population based registry and concluded that rescue breathing has an incremental benefit for out-of-hospital cardiac arrests of noncardiac origin.
We would like to discuss some aspects of the study design: The main question was a comparison between compression-only CPR to conventional CPR including rescue breathing. The authors, however, included a reference group consisting of patients with unknown type of bystander initiated CPR, denoted as ‘no CPR group,' and rely on indirect comparisons between the main groups. They did so for the analysis of characteristics of the study participants and also for calculating the main effects.
In our opinion this approach might be misleading. As the different interventions cannot necessarily be seen as increasing levels of CPR, the described incremental benefit is not justified by the analysis. When we did a recalculation of the crude numbers presented in Table 3, there was no difference between compression-only CPR and conventional CPR (relative risk 0.81; 95% CI, 0.64 to 1.04, P=0.09).
Further the authors introduced the time interval from collapse to initiation of EMS-CPR >15 minutes to form 2 subgroups. This thoughtful decision in patients with cardiac arrest of noncardiac origin could have been better handled by a test for interaction. In the subgroup of patients with a longer CPR duration, conventional CPR appears superior to compression-only CPR in the crude analysis (relative risk 0.42; 95% CI, 0.21 to 0.86, P=0.02). The authors present a number needed to treat. It would be helpful to have some information about the method used. Numbers needed to treat are sensible only if a causal effect can be assumed. However, in an observational study, confounding will almost always distort a crude effect and accordingly, a number needed to treat is not appropriate if calculated from unadjusted values.
In summary, looking at the available preliminary data, we would conclude that in patients with out-of-hospital cardiac arrest of noncardiac origin there is no difference in good neurological outcome between compression-only CPR and conventional CPR including rescue breathing. Patients with longer duration of CPR might benefit from conventional CPR.
Jasmin Arrich, MD
Harald Herkner, MD, MSc
Anton N. Laggner, MD
Department of Emergency Medicine
Medical University of Vienna
- © 2011 American Heart Association, Inc.
- Kitamura T,
- Iwami T,
- Kawamura T,
- Nagao K,
- Tanaka H,
- Hiraide A,
- for the Implementation Working Group for All-Japan Utstein Registry of the Fire and Disaster Management