Transnasal Microstream EtCO2 Reduces Hypoxemia During Emergence in Aged Post-Abdomen Surgery

This prospective, randomized controlled study aims to investigate whether transnasal microstream end-tidal carbon dioxide (EtCO₂) monitoring in the post-anesthesia care unit (PACU) reduces the incidence of postoperative hypoxemia in elderly patients (65-80 years, ASA I-III, BMI 18-30 kg/m²) undergoing elective laparoscopic surgery under general anesthesia with endotracheal intubation. A total of 324 patients will be randomized 1:1 to either the control group (standard SpO₂ monitoring and clinical observation with oxygen delivery at 2 L/min via sampling line) or the experimental group (same oxygen delivery plus continuous real-time transnasal microstream EtCO₂ monitoring). The primary outcome is the incidence of hypoxemia (SpO₂ \< 90% for \>15 seconds) after extubation in the PACU. Secondary outcomes include severe hypoxemia (SpO₂ \< 85%), lowest SpO₂ during PACU stay, vital signs at specified time points, PACU length of stay, and other adverse events. Statistical analysis will use chi-square or Fisher's exact test for the primary outcome, with a sample size calculated to detect a reduction in hypoxemia from 33% (control) to 18% (experimental group) (α=0.05, power=80%, plus 20% dropout).

Inclusion Criteria: * Age 65-80 years; * ASA physical status I-III; * BMI 18-30 kg/m²; * Participants scheduled for elective laparoscopic surgery under general anesthesia with endotracheal intubation; * Willing to participate in the study and provide written informed consent Exclusion Criteria: * Patients with nasal bleeding, nasal mucosal injury, nasal cavity occupancy, or other conditions that preclude transnasal carbon dioxide monitoring; * Patients undergoing emergency surgery; * Participants requiring postoperative assisted ventilation via endotracheal intubation or tracheostomy; * Presence of any disease or condition that may cause abnormal end-tidal carbon dioxide waveforms or abnormal baseline pulse oximetry (e.g., congenital heart disease or chronic lung disease); * Severe cardiac insufficiency (≤4 Metabolic Equivalents \[MetS\]); * Severe renal insufficiency (acute kidney injury \[AKI\] or chronic kidney disease \[CKD\] stage 4 or higher); * Severe hepatic insufficiency (Child-Pugh class C or worse); * Allergy to study medications; * Daily alcohol intake ≥60 grams; * History of psychiatric disorders such as depression, severe central nervous system depression, Parkinson's disease, basal ganglion lesions, schizophrenia, epilepsy, Alzheimer's disease; * Participation in another related clinical study within the past 3 months.