Hypoxaemia in adults in the post-anaesthesia care unit

Continuous pulse oximetry was performed on 173 adults after general anaesthesia for elective inpatient surgery, throughout their post-anaesthesia care unit (PACU) stay. Supplemental oxygen was administered for ≥30 min after arrival and subsequently discontinued before discharge to the ward. The mean and minimum oxyhaemoglobin saturation (SpO₂) after discontinuing oxygen were lower than those values achieved during oxygen administration and preoperatively (P < 0.001). At least one hypoxaemic episode (SpO₂ ≤90% for ≥15 sec) occurred in 70 subjects (41%) and 45 of these had a moderatesevere episode (SpO₂ ≥90% for ≤2 min or SpO₂ ≤85%). The hypoxaemic episodes began 20 ±20 min (range 1-100; median 15) after discontinuing supplemental oxygen. Cyanosis was detected in only four of the 70 patients who desaturated. Factors associated with hypoxaemia were: ASA physical status class; surgical duration ≥90 min; and preoperative mean SpO₂ <95%. Factors not associated with hypoxaemia were: age, sex, % ideal body weight, smoking history, preoperative minimum SpO₂, premedication and type of surgery. In conclusion, after discontinuing supplemental oxygen in the PACU, hypoxaemia was common, difficult to detect clinically, and associated with ASA class, surgical duration and preoperative mean SpO₂.