In responding to an unconscious casualty, which of the following is a critical first step?

Checking for breathing is indeed a critical first step when responding to an unconscious casualty. This assessment allows the responder to quickly identify the casualty’s respiratory status and determine whether immediate intervention is necessary. If the individual is not breathing or is breathing abnormally, it signals a potential life-threatening situation that may require immediate resuscitation efforts, such as starting CPR.

This initial check is crucial because it informs the responder of the appropriate actions to take next, such as calling for help or beginning chest compressions if there is no breathing. Assessing breathing helps prioritize care—ensuring that the most critical issues are addressed first.

Other options, while important in various emergency situations, do not take precedence before ensuring that the casualty is breathing. For instance, shouting for help may be beneficial, but it must be done after determining the individual's need for assistance based on their breathing status. Similarly, starting chest compressions or administering oxygen are actions that follow the assessment of breathing. Thus, recognizing whether the casualty is breathing is foundational in guiding the next steps in any emergency response.