With tips from the flight checklist experts, Gawande attempts to revise the WHO checklist. Going through a test run of the checklist helped to weed out problems such as who was supposed to run through the checklist. The biggest issue was that there was too many items. They tried to reconcile items important in one area but not another, ones that were important but rarely relevant, and other issues. There were also communication checks. These attempted to ensure unexpected complications could be handled smoothly with teamwork.

The final list had 19 checks, and went out to 8 sites for a test run. The sites were diverse medical centers with different equipment and clientele. Data was collected before and after institution of the checklists. The verdict was that the checklists had improved care at every site. There were some issues with cultural differences and implementation details, but each hospital was able to customize the list to work for their unique circumstances.

At the end of the testing, although at least 20% of staff said that the list was difficult to use, 93% wanted a checklist used in their own care.