The effect of decreased respiratory compliance during pneumoperitoneum and the trendelenburg position on the reliability of end tidal carbon dioxide monitoring

Objective: To demonstrate the reliability of ETCO ₂ 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 PaCO ₂ and ETCO ₂ (PaCO ₂ -PETCO ₂ ) 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 CO ₂ 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 PaCO ₂ -PETCO ₂ 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 ETCO ₂ and PaCO ₂ 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 ETCO ₂ level was not associated with respiratory acidosis at T0, T1, and T2. The plateau pressure during pneumoperitoneum was correlated with the increase in PaCO ₂ -ETCO ₂ (r=0.456, p=0.043). The ratio of the partial pressure of oxygen to the fraction of inspired oxygen (PaO ₂ /FiO ₂ 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 PaCO ₂ -PETCO ₂ , which was predicted by the plateau pressure.