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).

Study Title:

Effect of Transnasal Microstream End-Tidal Carbon Dioxide Monitoring on the Incidence of Postoperative Hypoxemia in Elderly Patients Undergoing Laparoscopic Surgery under General Anesthesia with Endotracheal Intubation: A Prospective, Randomized Controlled Study

Principal Investigator: Wu Jianbo Department: Anesthesiology and Perioperative Medicine

Background & Objective:

Postoperative hypoxemia is a common respiratory complication in the post-anesthesia care unit (PACU). Conventional pulse oximetry (SpO₂) has a delayed response to hypoventilation, especially during supplemental oxygen therapy. This study aims to investigate whether adding transnasal microstream end-tidal carbon dioxide (EtCO₂) monitoring in the PACU reduces the incidence of hypoxemia in elderly patients after laparoscopic surgery under general anesthesia.

Study Design:

Prospective, randomized, controlled, interventional study.

Participants:

324 elderly patients (age 65-80 years, ASA I-III, BMI 18-30 kg/m²) scheduled for elective laparoscopic surgery under general anesthesia with endotracheal intubation.

Interventions:

Control group (n=162): Routine monitoring with SpO₂ and clinical observation; oxygen delivery at 2 L/min via sampling line without EtCO₂ monitoring.

Experimental group (n=162): Same oxygen delivery plus continuous real-time transnasal microstream EtCO₂ monitoring.

Primary Outcome:

Incidence of postoperative hypoxemia (SpO₂ < 90% for >15 seconds) after extubation in the PACU.

Secondary Outcomes:

Incidence of severe hypoxemia (SpO₂ < 85% for >15 seconds) Lowest SpO₂ during PACU stay Vital signs at predefined time points

PACU length of stay (Steward Recovery Score ≥ 4)

Other adverse events (e.g., nausea, vomiting, agitation, shivering)

Safety Monitoring:

Device-related adverse events (nasal irritation, bleeding), respiratory events (bradypnea, apnea, airway obstruction), and serious adverse events (e.g., need for advanced airway, cardiovascular events) will be recorded and managed according to a stepwise intervention protocol.

Randomization and Blinding:

1:1 randomization using block randomization (SAS 9.4) with allocation concealment (sealed, opaque envelopes). Partial blinding: participants, outcome assessors, and statisticians blinded; anesthesiologists/operators unblinded.

Sample Size Calculation:

Based on pilot data (expected hypoxemia rate: 33% in control vs. 18% in experimental group), α=0.05, power=80%, plus 20% dropout → 162 patients per group (total N=324).

Statistical Analysis:

SPSS 22.0 will be used. Continuous variables (normal distribution) will be compared using t-test; non-normally distributed variables using Mann-Whitney U test. Categorical variables (e.g., hypoxemia incidence) will be compared using chi-square or Fisher's exact test.

Expected Significance:

This study will provide high-level evidence on whether transnasal microstream EtCO₂ monitoring in the PACU can enhance respiratory safety in elderly patients recovering from laparoscopic surgery, potentially reducing hypoxemia and related complications.

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.

This is a partially masked (single-blind) study. Participants (under sedation and unaware of group assignment), outcome assessors, and the statistician are masked to group allocation. The anesthesia provider who performs the intervention cannot be masked because the EtCO₂ monitoring interface is visible only in the experimental group. Randomization is concealed using sequentially numbered, sealed, opaque envelopes, and the allocation is revealed after extubation just before the intervention. The statistician receives only coded data (Group A/B) and remains blinded until the final analysis is completed.