Rapid response systems (RRS) are widely seen as a method to rescue the clinically deteriorating patient. Among the challenges in demonstrating their benefit is accurate identification of physiologic triggers that should warrant activation. This case-control study compared physiologic data in RRS activation patients with a matched set of non-RRS patients to determine potential predictors of life-threatening events. Investigators found that positive criteria were found in 21% of the control admissions and in 61% of patients transferred to the ICU. However, the most notable finding was that 77% of patients who had an arrest did not meet such criteria prior to their event. Criteria most associated with life-threatening events were tachypnea and 100% supplemental oxygen requirements. The authors conclude that early warning signs used to activate RRS are only fair predictors, whereas greater vigilance in respiratory monitoring may lead to improved outcomes from RRS interventions.