You can't do CPR unless you have the patient's chest lying on an incompressible and rigid support of some kind. It's impossible in the water.
The patient who is not breathing most likely has no circulation, either; but in a few cases, you may have someone who is narcotized from high CO2 because they got laryngospasm, or because they tried to avoid drowning. One or two "rescue" breaths may be enough to stimulate spontaneous respirations, which would significantly increase the chance of survival.
I firmly believe that, if you have an unresponsive diver who is not breathing, you should give the best two rescue breaths you can, and then two like crazy to the nearest firm ground. Remember that a patient wearing a backplate doesn't necessary need SMOOTH ground, but just someplace you can support the plate, because they make excellent platforms on which to do CPR.
The patient who is not breathing most likely has no circulation, either; but in a few cases, you may have someone who is narcotized from high CO2 because they got laryngospasm, or because they tried to avoid drowning. One or two "rescue" breaths may be enough to stimulate spontaneous respirations, which would significantly increase the chance of survival.
I firmly believe that, if you have an unresponsive diver who is not breathing, you should give the best two rescue breaths you can, and then two like crazy to the nearest firm ground. Remember that a patient wearing a backplate doesn't necessary need SMOOTH ground, but just someplace you can support the plate, because they make excellent platforms on which to do CPR.