What is a key criterion for evaluating the effectiveness of CPR?

Improvement in perfusion or return of spontaneous circulation (ROSC) is a key criterion for evaluating the effectiveness of CPR because these indicators directly reflect the success of resuscitation efforts. When CPR is performed effectively, the goal is to restore adequate blood flow to vital organs, which can be measured by improvements in perfusion. ROSC indicates that the heart has restarted and is functioning again, allowing for proper circulation of oxygenated blood throughout the body. This is crucial in determining whether the CPR was effective in reviving the patient.

In practice, other factors, while important in the overall response and outcome of a cardiac event, do not serve as direct measures of the efficacy of CPR itself. The presence of bystanders can influence the likelihood of receiving CPR but does not assess the quality of the resuscitation performed. The duration of CPR performed may provide context but does not indicate if the CPR was effective. Response from emergency medical services is critical for advanced care but is an external factor that doesn't measure the CPR performance directly.