Which of the following is a critical step to take immediately when a patient is confirmed to have no pulse?

When a patient is confirmed to have no pulse, initiating CPR is the most critical immediate action. This step is vital because performing CPR helps maintain blood flow to vital organs, particularly the brain and heart, until more advanced medical interventions can be provided. Without prompt resuscitation efforts, the patient's chances of survival decrease significantly with each passing minute due to the lack of oxygen-rich blood.

While other actions such as positioning the patient or calling emergency services are important, they may take additional time that can compromise the patient's outcome. In a case of cardiac arrest, the priority is to start chest compressions as soon as possible to restore circulation. Therefore, initiating CPR directly addresses the life-threatening condition of no pulse and is essential in the chain of survival.