Objective: To demonstrate the reliability of ETCO₂ in patients with decreased respiratory compliance during pneumoperitoneum and Trendelenburg position for laparoscopic surgery. The decrease in respiratory compliance can increase dead space ventilation; therefore, the gradient between PaCO₂ and ETCO₂ (PaCO₂-PETCO₂) might be higher during pneumoperitoneum than at baseline.

Materials and Methods: Twenty women who underwent laparoscopic gynecological surgery were enrolled. Arterial blood gas samples were collected 10 minutes after induction of anesthesia (T0), 45 minutes after pneumoperitoneum and placement in the Trendelenburg position (T1), and after CO₂ desufflation and placement in the supine position (T2).

Results: The static respiratory compliance significantly decreased from T0 to T1 and increased from T1 to T2. The PaCO₂-PETCO₂ significantly increased from 2.3 (0.3 to 3.9) at T0 to 3.9 (3.0 to 5.1) at T1 (p=0.025). The correlation between ETCO₂ and PaCO₂ was still acceptable at T0 (r=0.513, p=0.021), T1 (r=0.486, p=0.030), and T2 (r=0.539, p=0.014). Adjustment of the ventilator settings according to the ETCO₂ level was not associated with respiratory acidosis at T0, T1, and T2. The plateau pressure during pneumoperitoneum was correlated with the increase in PaCO₂-ETCO₂ (r=0.456, p=0.043). The ratio of the partial pressure of oxygen to the fraction of inspired oxygen (PaO₂/FiO₂ ratio) significantly decreased from 516.0 (433.7 to 583.5) at T0 to 415.0 (311.8 to 468.5) at T1 and 398.0 (350.0 to 475.7) at T2.

Conclusion: The decrease in respiratory compliance during pneumoperitoneum and the Trendelenburg position associated with the increase in PaCO₂-PETCO₂, which was predicted by the plateau pressure.

Keywords: Carbon dioxide, Compliance, Laparoscopy, Pneumoperitoneum, Trendelenberg position