Feasibility and safety of oxygen-free nasal high flow therapy in the acute postoperative period: a single-center randomized feasibility study

Background Routine postoperative oxygen administration in the general ward is widely practiced despite limited evidence of benefit in low-risk surgical patients and increasing concerns regarding delayed detection of hypoventilation and unnecessary hyperoxia. Nasal high flow (NHF) therapy can reduce respiratory effort even without supplemental oxygen, but its feasibility and safety in the general ward during the acute postoperative period remain uncertain. Objective This randomized feasibility study aimed to evaluate the feasibility, safety, and protocol adherence of oxygen-free NHF therapy in the general ward following oral surgery under general anesthesia, and to obtain preliminary physiological data to inform the design of a future confirmatory randomized controlled trial. Methods Adult patients undergoing elective oral surgery under general anesthesia were randomized (1:1:1) to receive NHF with humidified room air at 40 L/min, conventional face mask oxygen at 5 L/min, or no respiratory support during the first 150 minutes in the general ward. Primary outcomes were feasibility-related parameters, including recruitment and protocol completion rates, tolerance of NHF therapy, need for rescue oxygen, and completeness of continuous physiological monitoring. Safety outcomes included the incidence of hypoxemia and clinically significant hypercapnia. Physiological outcomes included respiratory rate, transcutaneous oxygen (tcpO₂) and carbon dioxide (tcpCO₂) partial pressures, and oxygen saturation (SpO₂). Results All 48 enrolled patients completed the study protocol, demonstrating high feasibility with excellent recruitment, protocol adherence, and data completeness. NHF therapy was well tolerated, and no serious adverse respiratory events were observed. The incidence of hypoxemia and hypercapnia was comparable across the groups. Exploratory analyses showed a lower respiratory rate in the NHF group （NHF：11.1±2.8 min ^-1 ; control：14.7±2.7 min ^-1 ; face mask O ₂ : 13.9±3.0 min ^-1 ) without evidence of carbon dioxide retention. In contrast, face mask oxygen therapy frequently resulted in supraphysiological oxygenation, while maintaining comparable tcpCO₂ levels (NHF: 55.0±15.9 mmHg; control: 52.2±10.8 mmHg; face mask: 55.4±10.0 mmHg). Conclusions NHF without supplemental oxygen therapy was safe, and well tolerated as postoperative respiratory management in the general ward. The study addressed key feasibility concerns and provides essential data to support the design of a future adequately powered randomized controlled trial evaluating the clinical effectiveness of oxygen-free NHF. Trial Registration: Trial registration: The study was registered as jRCTs072200018 on June.23, 2020 on the site of Japan Registry of Clinical Trials (jRCT). URL: https://jrct.mhlw.go.jp/latest-detail/jRCTs072200018 The trial started on July 1, 2020 and is currently recruiting.