An interventional study of Transoral nasal cannula oxygen delivery in Postoperative Hypoxemia, sponsored by Nanjing First Hospital, Nanjing Medical University. Not yet recruiting at 1 site in China. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-25.
Sponsored by Nanjing First Hospital, Nanjing Medical University · Not applicable, Interventional, and Treatment
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.
Exclusion Criteria:
Participants receive transoral nasal cannula oxygen delivery (4 L/min for 10 minutes), followed by a 5-minute washout period (nasal oxygen delivery resumed), and then standard nasal cannula oxygen delivery (4 L/min for 10 minutes).
Other: Transoral nasal cannula oxygen delivery
Participants receive standard nasal cannula oxygen delivery (4 L/min for 10 minutes), followed by a 5-minute washout period (nasal oxygen delivery resumed), and then transoral nasal cannula oxygen delivery (4 L/min for 10 minutes).
Other: Transoral nasal cannula oxygen delivery
The two prongs of a standard dual-prong 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 to avoid stimulating the gag reflex. Oxygen flow is set at 4 L/min with standard humidification for 10 minutes.
Incidence of hypoxemia during the oxygen delivery periods
Hypoxemia is defined as peripheral oxygen saturation (SpO2) \<90% sustained for at least 10 seconds, or an oxygenation index (PaO2/FiO2 ratio) \<300 mmHg measured by arterial blood gas analysis at minute 10 of the intervention period. The outcome is reported as the proportion of participants experiencing hypoxemia during the nasal oxygen delivery period compared with the transoral oxygen delivery period.
Time frame: During each 10-minute oxygen delivery period in the PACU (each participant undergoes two consecutive intervention periods)
Incidence of SpO2 <92%
Proportion of participants with peripheral oxygen saturation (SpO2) \<92% at any time during each oxygen delivery period.
Time frame: During each 10-minute oxygen delivery period in the PACU
Oxygenation index (PaO2/FiO2 ratio)
Calculated from arterial blood gas sampled through the indwelling radial arterial catheter at minute 10 of each intervention period; compared between the nasal and transoral oxygen delivery periods.
Time frame: At minute 10 of each 10-minute oxygen delivery period
Time to achieve SpO2 >=95%
Time elapsed from the beginning of each intervention until peripheral oxygen saturation reaches \>=95%.
Time frame: From the start of each oxygen delivery period, up to 10 minutes
Proportion of participants requiring escalation of oxygen therapy
Proportion of participants requiring escalation to a simple face mask (\>=6 L/min), reservoir mask, high-flow nasal cannula (HFNC), or noninvasive ventilation (NIV) because of SpO2 \<90% or respiratory distress.
Time frame: Throughout the PACU stay (up to 24 hours after surgery)
Respiratory rate
Respiratory rate (breaths/min) recorded at each predefined time point.
Time frame: Preoperatively; at the start of surgery; at the end of surgery; after extubation; 1 minute before and 1 minute after each change of oxygen delivery route; at PACU discharge
Heart rate
Heart rate (beats/min) recorded at each predefined time point.
Time frame: Preoperatively; at the start of surgery; at the end of surgery; after extubation; 1 minute before and 1 minute after each change of oxygen delivery route; at PACU discharge
Mean arterial pressure (MAP)
Mean arterial pressure (mmHg) recorded at each predefined time point.
Time frame: Preoperatively; at the start of surgery; at the end of surgery; after extubation; 1 minute before and 1 minute after each change of oxygen delivery route; at PACU discharge
Airway plateau pressure
Airway plateau pressure (cmH2O) recorded from the anesthesia ventilator.
Time frame: At the start and at the end of surgery
Positive end-expiratory pressure (PEEP)
Positive end-expiratory pressure (cmH2O) recorded from the anesthesia ventilator.
Time frame: At the start and at the end of surgery
Oral dryness score
Oral dryness assessed with a visual analog scale (VAS) ranging from 0 to 10, where 0 indicates no dryness and 10 indicates the worst imaginable dryness. Higher scores indicate worse (more severe) dryness.
Time frame: Immediately after completion of each 10-minute oxygen delivery period
Overall comfort score
Overall comfort assessed with a visual analog scale (VAS) ranging from 0 to 10, where 0 indicates maximal discomfort and 10 indicates maximal comfort. Higher scores indicate better comfort.
Time frame: Immediately after completion of each 10-minute oxygen delivery period
Pharyngeal irritation / nausea score
Patient-reported pharyngeal irritation and nausea, each graded on a 4-point scale: 0 = none, 1 = mild (symptoms present but tolerable), 2 = moderate (causing discomfort but not requiring intervention), 3 = severe (requiring intervention). Higher scores indicate worse symptoms.
Time frame: Immediately after completion of each 10-minute oxygen delivery period
Length of PACU stay
Total duration of stay in the postanesthesia care unit, in minutes.
Time frame: From PACU admission to PACU discharge (up to 24 hours after surgery)
Respiratory complications within 24 hours after surgery
Composite of reintubation, pneumonia, atelectasis, and requirement for prolonged oxygen therapy, reported as the number and proportion of participants with each event.
Time frame: Within 24 hours after surgery
Plan to share: Yes — All data relevant to the study are included in the article. Data supporting the findings are available from the corresponding author upon reasonable request.
Supporting information: Study protocol, Sap, Icf, Csr
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Nanjing First Hospital, Nanjing Medical University