Objective: To compare the efficacy of two oxygen devices (nasal cannula and mask) and two flows for preventing hypoxemia in post anesthesia care unit (PACU).
Material and Method: Five hundred (18-70 year old) patients were enrolled into a randomized, controlled non-inferiority trial at Siriraj Hospital, Mahidol University from May 2013 to December 2014. They received oxygen therapy after general
anesthesia according to their groups by computer-generated randomization. Group I received oxygen nasal cannula 4 liters
per minute and group II received oxygen mask 5 liters per minute. Both methods gave comparable FiO2 (FiO2 = 0.35).
Inclusion criteria were elective surgery, American Society of Anesthesiologist (ASA) physical status 1-3. Exclusion criteria
were unstable pulmonary disease, BMI >35 kg/m2, baseline SpO2 <94%, myopathy, alteration of consciousness, and nasal
problems. The high-risk operations for post operative hypoxemia were excluded. The efficacy of two oxygen devices and flows
were compared in term of preventing hypoxemia in PACU.
Results: Five hundred patients were analyzed (249 patients in the cannula group and 251 patients in the mask group). They
were comparable in demographics and operations. At PACU, none of 500 patients had SpO2 <94% (non-inferiority trial, 95%
CI -0.0152, 0.0152). They were mildly sedated or fully awake and had no respiratory complications.
Conclusion: In low risk patients undergoing low risk operations, both nasal cannula or simple mask with FiO2 = 0.35 are
equally effective for preventing hypoxemia in PACU.

Keywords: Oxygen, PACU, General anesthesia, Nasal cannula, Simple mask, Hypoxemia, Desaturation