How does your hospital charge for oxygen for observation patients? Ours has charged it as a service for quite a while. I am re-evaluating our Chargemaster and want to be sure of the appropriate way. We use rev code 460 and CPT 94799. Most of the hospitals I have had contact with use rev code 270 and charge as a supply. I read in a respiratory coding book to charge as a supply with rev code 271. I have also found reference to not charging at all.