Also consider establishing some kind of "tell" for the "unconscious" actor to signal that something isn't going right. Perhaps the padding isn't where it's supposed to be, or something didn't line up and some of the force from the compressions is hurting them, etc. Something that signals to the person performing CPR they need to be shifted, or change up the angle, tale a break for a second, or even full on abort. An unobtrusive hand signal, crossing of fingers, foot movement, eyebrow twitch--something that might be hidden from the audience in the chaos but the actors are looking for. Plan out the signal, and establish a plan b or c. Make sure everyone knows how it should be if it's going right, so they can tell when something is going wrong.