Actually (although it's too late tonight for me to look up the numbers) field CPR often has better results than in-hospital CPR, simply because someone in the field hasn't already had a whole bunch of advanced interventions to keep them from coding. The guy in the hospital who codes may already be on a vent and a bunch of drips . . .
I'm also not aware of any statistics that say CPR has better results when O2 is available. Many, if not most events in the field that lead to CPR are primarily cardiac, in which case O2 may make little difference. One of the few times when it might make a big difference is where the primary cause of arrest is hypoxia, which may well be the case with a diving accident. O2 should be available on commercial dive boats -- it should be full, the crew should know how to use it, and the masks or other methods of provision should be in good order.
I'm also not aware of any statistics that say CPR has better results when O2 is available. Many, if not most events in the field that lead to CPR are primarily cardiac, in which case O2 may make little difference. One of the few times when it might make a big difference is where the primary cause of arrest is hypoxia, which may well be the case with a diving accident. O2 should be available on commercial dive boats -- it should be full, the crew should know how to use it, and the masks or other methods of provision should be in good order.