Edward H. Livingston
is undertaken when performance of the intervention risks contamination of the control group. Imagine a multifaceted intervention that involves sedation protocols and measures of arousal levels and readiness for weaning from a mechanical ventilator in a trial of extubation.25 In this scenario, intensive care unit (ICU) personnel performing these functions may be influenced by the effectiveness of the interventions and consciously or unconsciously use them on patients assigned to the control group. In cases such as this, it is best to perform the intervention in one ICU and apply the control intervention in a separate ICU. Instead of randomizing individual patients to intervention or control groups, ICUs are randomized. Each ICU is considered a cluster of patients....