In total , 73 adult subjects requiring general anesthesia were randomly assigned to one of four groups : nCPAP P0 , nCPAP P5 , FmCPAP P0 , and FmCPAP P5 , where P0 and P5 represent positive end-expiratory pressure ( PEEP ) 0 and 5 cm H2O applied prior to induction .