BACKGROUND:This prospective, randomized trial was undertaken to evaluate the utility of adding end-tidal capnometry (ETC) to pulse oximetry (PO) in patients undergoing procedural sedation and analgesia (PSA) in the emergency department (ED). METHODS:The patients were randomized to monitoring with or without ETC in addition to the current standard of care. Primary endpoints included respiratory adverse events, with secondary endpoints of level of sedation, hypotension, other PSA-related adverse events and patient satisfaction. RESULTS:Of 986 patients, 501 were randomized to usual care and 485 to additional ETC monitoring. In this series, 48％ of the patients were female, with a mean age of 46 years. Orthopedic manipulations (71％), cardioversion (12％) and abscess incision and drainage (12％) were the most common procedures, and propofol and fentanyl were the sedative/analgesic combination used for most patients. There was no difference in patients experiencing de-saturation (SaO2<90％) between the two groups; however, patients in the ETC group were more likely to require airway repositioning (12.9％ vs. 9.3％,P=0.003). Hypotension (SBP<100 mmHg or <85 mmHg if baseline <100 mmHg) was observed in 16 (3.3％) patients in the ETC group and 7 (1.4％) in the control group (P=0.048). CONCLUSIONS:The addition of ETC does not appear to change any clinically significant outcomes. We found an increased incidence of the use of airway repositioning maneuvers and hypotension in cases where ETC was used. We do not believe that ETC should be recommended as a standard of care for the monitoring of patients undergoing PSA.