In Reply: Dr Manfredini and colleagues raise the possibility that biological factors may in part contribute to the lower survival from in-hospital cardiac arrest that occurs during nights and weekends. The NRCPR database cannot determine true circadian variability in the occurrence of cardiac arrest. Because the number of patients in the hospital is constantly in flux, we do not have a stable denominator with which to calculate circadian rhythmicity. However, we did not identify a lower frequency of events that paralleled the decreased survival we demonstrated during nights and weekends.
Peberdy MA, Praestgaard AH. Survival Patterns With In-Hospital Cardiac Arrest—Reply. JAMA. 2008;299(22):2625-2627. doi:10.1001/jama.299.22.2626