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Objective: To evaluate the immediate effects of positive expiratory pressure therapy on oxygen saturation and ventilation after abdominal surgery.

Background: Positive expiratory pressure therapy to treat postoperative hypoxia is widespread, despite a lack of evidence of effect.

Methods: This randomized, sham-controlled, crossover trial investigated adults 1–2 days after abdominal surgery at Umeå University Hospital, Sweden. The intervention was positive expiratory pressure of 10–15 cm H2O. The control was a sham device. The investigations were ended with deep-breathing maneuvers. Outcomes were the gradient of changes in peripheral oxygen saturation and transcutaneous carbon-dioxide partial pressure (PtcCO2).

Results: Eighty patients were included and randomized and 76 patients were analyzed. Oxygen saturation increased from a baseline mean of 92% to 95%, P < 0.001, during positive expiratory pressure breathing, while PtcCO2 decreased from a mean of 36 to 33 mm Hg, P < 0.001. This was followed by apnea, oxygen desaturations to a mean of 89%, P < 0.001, and increased PtcCO2 before returning to baseline values. The changes in oxygen saturation and PtcCO2 did not differ from sham breathing or deep-breathing maneuvers.

Conclusions: Positive expiratory pressure breathing after abdominal surgery improves oxygen saturation during the maneuver because of hyperventilation, but it is followed by apnea, hypoventilation, and oxygen desaturation. The effect is not different from the expiration to a sham device or hyperventilation. It is time to stop positive expiratory pressure therapy after abdominal surgery, as there is no evidence of effect in previous trials, apart from the adverse effects reported here.