Transoral Nasal Cannula Oxygen Therapy for Mouth-Breathing Patients in the Postanesthesia Care Unit

Overview

Postoperative hypoxemia is a common complication in the postanesthesia care unit (PACU). Patients who breathe through the mouth after tracheal extubation may receive limited benefit from standard nasal cannula oxygen therapy, because the nasal cavity functions as an ineffective dead space during mouth breathing. Clinical observations suggest that placing the prongs of a nasal cannula inside the mouth (transoral oxygen delivery) rapidly improves oxygenation in these patients. However, no randomized controlled trial has formally verified this effect. This single-center, randomized, controlled, crossover trial will enroll 64 adult patients identified as persistent mouth breathers after extubation in the PACU following elective thoracic or abdominal surgery under general anesthesia. Each participant will receive, in a randomized sequence, both standard nasal cannula oxygen delivery (4 L/min for 10 minutes) and transoral nasal cannula oxygen delivery (4 L/min for 10 minutes), separated by a 5-minute washout period, so that each participant serves as his or her own control. The primary outcome is the incidence of hypoxemia (peripheral oxygen saturation \[SpO2\] \<90% sustained for at least 10 seconds, or oxygenation index \[PaO2/FiO2 ratio\] \<300 mmHg) during each oxygen delivery period. Secondary outcomes include the incidence of SpO2 \<92%, time to achieve SpO2 \>=95%, oxygenation index measured by arterial blood gas analysis, need for escalation of oxygen therapy, vital signs, patient comfort and adverse effects, PACU length of stay, and respiratory complications within 24 hours after surgery. The results are expected to provide high-level evidence for optimizing oxygen therapy strategies for mouth-breathing patients in the PACU.

This is a single-center, randomized, controlled, crossover trial conducted in the Department of Anesthesiology, Pain and Perioperative Medicine, Nanjing First Hospital, Nanjing Medical University, China. Screening and assessment of mouth breathing: Adult patients recovering from general anesthesia for elective thoracic or abdominal surgery are assessed 5 minutes after tracheal extubation using a standardized three-step procedure: (1) visual screening (lip separation \>0.5 cm, visible anterior teeth, and lowered mandibular position, observed for 0-10 s); (2) airflow verification using cotton fiber wisps placed approximately 1 cm in front of both nostrils and the lips to identify the dominant ventilation pathway (10-25 s); and (3) mirror confirmation of exhaled vapor condensation together with observation of tongue position (25-40 s). Persistent mouth breathing is confirmed when all three steps are positive and no spontaneous mouth closure lasting more than 3 seconds occurs during the 40-second observation period. Interventions: (a) Standard nasal cannula oxygen delivery: a standard dual-prong nasal cannula is placed in both nostrils with an oxygen flow of 4 L/min for 10 minutes. (b) Transoral nasal cannula oxygen delivery: the two prongs of the same nasal cannula are joined and placed in the oral vestibule at the inner aspect of the mouth corner (approximately at the buccal mucosa corresponding to the first molar), to a depth of no more than 3 cm, with an oxygen flow of 4 L/min for 10 minutes. A 5-minute washout period, during which nasal oxygen delivery is resumed, separates the two intervention periods. Randomization and sequence: Eligible participants are randomly assigned in a 1:1 ratio to one of two sequences. Sequence A (nasal first): nasal oxygen delivery for 10 minutes, 5-minute washout, then transoral oxygen delivery for 10 minutes. Sequence B (transoral first): transoral oxygen delivery for 10 minutes, 5-minute washout, then nasal oxygen delivery for 10 minutes. Measurements: SpO2 is monitored continuously throughout all periods. Arterial blood gas is sampled at minute 10 of each intervention period through the indwelling radial arterial catheter placed for routine intraoperative monitoring (approximately 1 mL per sample) to calculate the oxygenation index (PaO2/FiO2 ratio). Vital signs, comfort scores, and adverse effects are recorded at predefined time points. Safety management: Continuous pulse oximetry is maintained throughout the study. Predefined safety exit criteria are applied (e.g., SpO2 \<85% sustained for more than 2 minutes, or SpO2 \<88% during any intervention); oxygen therapy is escalated immediately (face mask, reservoir mask, high-flow nasal cannula, or noninvasive ventilation) whenever clinically indicated, and an anesthesiologist is present in the PACU at all times. The same cannula is disinfected with cotton swabs when switched between the nasal and oral routes to prevent cross-infection.