Cluster trials very seldom use a cross-over design for the reason that it is typically tricky to withdraw a cluster level intervention once it has been introduced. However, as in clinical trials, the cross-over design is very powerful statistically (yields precise estimates) in those situations where it is feasible. Such was the case in a cluster trial of methods for cardio-pulmonary resuscitation. One hundred and fourteen clusters (emergency medical services) participated. Adults with non-trauma related cardiac arrest were managed (according to cluster and phase) with either:
- Continuous chest compressions with asynchronous ventilations ten times per minute (experimental method); or
- Compressions interrupted to provide ventilation at a ratio of 30 compressions to two ventilations (standard method).
Nearly 24,000 people with cardiac arrest were included in the study and the survival rate with continuous compressions was slightly lower (at 9.0%) than with the standard interrupted method (at 9.7%). The result was not quite significant on standard statistical analysis. The CLAHRC WM Director thought the interrupted method would seem to be the one to go for, but the accompanying editorial was equivocal  – it would appear that even a trial of 24,000 participants, albeit in clusters, was not enough to resolve the issue. However, the trial methodology is certainly interesting.
— Richard Lilford, CLAHRC WM Director
- Nichol G, Leroux B, Wang H, et al. Trial of Continuous or Interrupted Chest Compressions during CPR. New Engl J Med. 2015; 373(25): 2203-14.
- Koster RW. Continuous or Interrupted Chest Compressions for Cardiac Arrest. New Engl J Med. 2015; 373(25): 2278-9.