Heated Humidified Oxygen in PACU Patients

BACKGROUND Hypoxemia is one of the most common and potentially life-threatening complications in the Post-Anesthesia Care Unit (PACU) during recovery from general anesthesia. Patients are particularly vulnerable due to residual anesthetic effects, diminished upper airway muscle tone, atelectasis, and suppression of hypoxic pulmonary vasoconstriction (HPV). Hypoxemia can precipitate arrhythmias, hemodynamic instability, prolonged PACU stay, increased unplanned ICU admissions, and in severe cases, cardiac arrest or hypoxic brain injury. Accordingly, optimizing respiratory management strategies in the PACU to prevent hypoxemia is of considerable clinical importance.

Heated and humidified oxygen therapy delivers inhaled gas at near-core body temperature (37°C) with adequate humidification. The theoretical rationale includes: (1) maintaining optimal HPV function, as hypothermia inhibits HPV and exacerbates intrapulmonary shunting; (2) preserving airway mucociliary clearance and preventing secretion retention; (3) reducing respiratory resistance by minimizing airway irritation; and (4) supporting core temperature maintenance to stabilize cardiopulmonary function.

This study is the first to systematically apply heated and humidified oxygen therapy in a prospective, standardized manner during the immediate short-term recovery period in the PACU, specifically to evaluate its preventive effect on early hypoxemia. The large sample size (2,000 patients) will provide sufficient statistical power for prespecified subgroup analyses.

STUDY DESIGN This is a prospective, multicenter, randomized, superiority trial with a parallel-group design (1:1 allocation ratio). Patient blinding is achieved through a sham-device design: all patients are connected to identical heating devices and circuits, with the device switched off in the control group. Outcome assessors and statistical analysts remain blinded to group allocation.

SAMPLE SIZE Based on an estimated control group hypoxemia rate of 8.0% and an expected 50% relative reduction in the experimental group (4.0%), with α = 0.05 (two-sided), power = 90%, and accounting for approximately 10% dropout, the calculated sample size was 1,752. This was expanded to 2,000 patients (1,000 per group) to enhance subgroup analysis power and overall evidence quality, achieving >95% power for the primary analysis.

INTERVENTIONS All patients receive oxygen at 5 L/min via face mask with the head of the bed elevated to 30°. Experimental group: oxygen heated to 36-37°C using a dry-heat blood/fluid warmer with a flexible heating sleeve, with temperature measured every 5 minutes. Control group: same device but switched off (sham), with simulated temperature measurements recorded as room temperature.

OUTCOME MEASURES Primary outcome: incidence of hypoxemia (SpO₂ ≤ 90% for ≥ 5 seconds) within 10 minutes of intervention initiation.

Secondary outcomes: severe hypoxemia (SpO₂ ≤ 85%), need for airway interventions, lowest SpO₂ value, SpO₂ drop >4%, PACU length of stay, postoperative shivering, and agitation.

Safety outcomes: nasal discomfort, epistaxis, device-related adverse events, and hemodynamic instability.

STATISTICAL ANALYSIS Primary analysis will be performed on the intention-to-treat (ITT) population using Poisson regression with robust error variance, adjusting for study center, to calculate relative risk (RR) and 95% confidence intervals. Subgroup analyses are prespecified for age, sex, BMI, smoking status, ASA class, surgery type, Mallampati class, and intraoperative opioid use. Interim analyses are planned at 25%, 50%, and 75% enrollment, reviewed by an independent Data Safety Monitoring Board (DSMB) using O'Brien-Fleming boundaries to control type I error.

DATA MONITORING An independent Data Safety Monitoring Board (DSMB) will review unblinded data at each interim analysis. All serious adverse events will be reported to the Principal Investigator within 24 hours. The study has received ethical approval from the Medical Ethics Committee of the Second Affiliated Hospital of Xi'an Jiaotong University .

Inclusion criteria

• Age ≥ 18 years
• Undergoing elective or emergency surgery under general anesthesia with endotracheal intubation
• Ramsay Sedation Score of 2-4 at 1 minute after extubation
• ASA physical status class I-III
• Expected PACU stay ≥ 30 minutes
• Patient or legally authorized representative provides written informed consent

Exclusion criteria

• Pre-existing hypoxemia (SpO₂ < 90% on room air)
• Pre-existing diagnosis of severe chronic obstructive pulmonary disease (GOLD grade 3-4), interstitial lung disease, or uncontrolled asthma
• Severe cardiovascular disease (NYHA class III-IV heart failure, unstable angina)
• Neuromuscular disease affecting respiratory function
• Maxillofacial surgery, severe spinal deformity, or other contraindications to face mask oxygen therapy or positioning
• Use of cardiopulmonary bypass during surgery or planned postoperative ICU admission with endotracheal tube in place
• Known intolerance to heated gas