Chart 3: Working example of oxygen section for hospital prescription charts (two panels are required on the prescription chart because oxygen may change from continuous to “as required” (PRN) as a patient improves). Chart 3: Working example of oxygen section for hospital prescription charts (two panels are required on the prescription chart because oxygen may change from continuous to “as required” (PRN) as a patient improves). B R O’Driscoll et al. Thorax 2008;63:vi1-vi68 Copyright © BMJ Publishing Group Ltd & British Thoracic Society. All rights reserved.