Trending Ability of End-Tidal Capnography to Reflect Arterial Carbon Dioxide Changes in One-Lung Ventilation

Thoracoscopic lung surgery often requires one-lung ventilation, a technique in which only one lung is ventilated while the other is deflated to provide better access for the surgeon. This can lead to changes in blood carbon dioxide (PaCO₂) levels, which must be monitored closely to ensure patient safety. Arterial blood gas sampling remains the gold standard for measuring PaCO₂, but it is invasive, costly, and provides only intermittent data. End-tidal carbon dioxide (ETCO₂) monitoring, available through standard anesthesia devices, offers continuous, noninvasive measurement of exhaled CO₂ and can serve as a surrogate for PaCO₂.

The primary purpose of this study is to evaluate the agreement and trend correlation between ETCO₂ and PaCO₂ in patients undergoing thoracoscopic procedures with one-lung ventilation. If ETCO₂ reliably tracks changes in PaCO₂, clinicians may reduce the number of arterial blood gas samples required during these operations.

Primary objective: To evaluate the trend correlation between ETCO₂ and PaCO₂ over time.

Secondary objective: To determine the degree of agreement between ETCO₂ and PaCO₂

Study Type: Prospective, observational study. Study Setting: Operating rooms where adult patients (≥18 years old) are scheduled for thoracoscopic procedures with one-lung ventilation and require invasive arterial pressure monitoring as part of their routine care.

Duration: Each patient's participation will be limited to the intraoperative period (i.e., from anesthesia induction to the end of surgery).

Intraoperative management will follow a standardized anesthetic protocol, and arterial blood gas samples will be drawn at the anesthesiologist's discretion whenever clinically indicated.

Each time an arterial blood gas sample is taken, the corresponding ETCO₂, PaCO₂, arterial blood pressure, heart rate, and temperature values will be recorded.

Any use of inotropic or antihypertensive infusions will be documented, as such medications can influence hemodynamic stability and possibly ventilatory parameters.

The patient's demographic details (age, sex, height, weight) and the type of surgical procedure will be recorded.

Four-quadrant plots will be generated to assess the concordance of changes in ETCO₂ with changes in PaCO₂ over time.

Bland-Altman plots will be constructed to calculate the mean difference (bias) and 95% limits of agreement for each paired measurement.

Inclusion criteria

• Patients undergoing thoracoscopic lung surgery with one-lung ventilation
• Patients requiring invasive arterial blood pressure monitoring

Exclusion criteria

• Chronic obstructive pulmonary disease (COPD)
• Pulmonary hypertension
• Systemic infection