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

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.