Following the placement of indwelling radial artery catheter, Sentri nasal cannula will be placed into the nostril of the patients Subjects will be asked to breath normally for a period of five minutes . Nasal breathing will be confirmed by presence of an acceptable CO2 tracing.Blood is drawn from indwelling arterial catheter for blood gas determination 5 minutes after the modified nasal cannulae is in place. At the same time as the arterial blood gas sample is taken, an ETCO2 sample is also obtained. A baseline (without oxygen flow) ETCO2, PaO2, SPO2, respiratory rate and PaCO2 will be recorded. The respiratory rate will be determined by counting the respiration for 15 seconds and multiplying by four. Subjects will not be asked to keep their mouth close when using the nasal cannula as it might alter the variability inherent in patients who mouth breathe during conscious sedation. After a baseline ETCO2 is established, oxygen will be administered at 2,4, and 6 liters per minute for a period of five minutes. At each level of oxygen administration, an average ETC02 reading will be recorded after achieving stable recordings. Simultaneously, PaO2 and PaCO2 will be obtained by drawing arterial blood from arterial indwelling catheter. Heart rate, respiratory rate, blood pressure will also be routinely recorded.