Strategy to Reduce Hypercapnia in Robot-Assisted Radical Prostatectomy Using Transcutaneous Carbon Dioxide Monitoring: A Prospective Observational Study

Abstract

Purpose: Monitoring end-tidal carbon dioxide partial pressure (P_ETCO₂) is a noninvasive, continuous method, but its accuracy is reduced by prolonged capnoperitoneum and the steep Trendelenburg position in robot-assisted radical prostatectomy (RARP). Transcutaneous carbon dioxide partial pressure (P_TCCO₂) monitoring, which is not affected by ventilator-perfusion mismatch, has been suggested as a suitable alternative. We compared the agreement of noninvasive measurements with the arterial carbon dioxide partial pressure (PaCO₂) over a long period of capnoperitoneum, and investigated its sensitivity and predictive power for detecting hypercapnia.

Patients and methods: The patients who underwent RARP were enrolled in this study prospectively. Intraoperative measurements of P_ETCO₂, P_TCCO₂, and PaCO₂ were analyzed. The primary outcome was the agreement of noninvasive monitoring with PaCO₂ during prolonged capnoperitoneum. Bias and precision between noninvasive measurements and PaCO₂ were assessed using Bland-Altman analysis. The bias and mean absolute difference were compared using a two-tailed Wilcoxon signed-rank test for pairs. The secondary outcome was the sensitivity and predictive power for detecting hypercapnia. To assess this, the Yates corrected chi-square test and the area under the receiver operating characteristic curve were used.

Results: The study analyzed 219 datasets from 46 patients. Compared with P_ETCO₂, P_TCCO₂ had lower bias, greater precision, and better agreement with PaCO₂ throughout the RARP. The mean absolute difference in P_ETCO₂ and PaCO₂ was larger than that of P_TCCO₂ and PaCO_2, and continued to exceed the clinically acceptable range of 5 mmHg after 1 hour of capnoperitoneum. The sensitivity during capnoperitoneum and overall predictive power of P_TCCO₂ for detecting hypercapnia were significantly higher than those of P_ETCO₂, suggesting a greater contribution to ventilator adjustment, to treat hypercapnia.

Conclusion: P_TCCO₂ monitoring measured PaCO₂ more accurately than P_ETCO₂ monitoring during RARP requiring prolonged capnoperitoneum and a steep Trendelenburg position. P_TCCO₂ monitoring also provides more sensitive measurements for ventilator adjustment and detects hypercapnia more effectively than P_ETCO₂ monitoring.

Keywords: capnoperitoneum; end-tidal carbon dioxide monitoring; general anesthesia; intraoperative carbon dioxide monitoring; robotic surgery.

Figure 1

Flow chart of participant recruitment.

Figure 2

Agreement of two noninvasive monitoring systems (P_TCCO₂ and P_ETCO₂) and PaCO₂ by Bland–Altman analysis. Black circles indicate the difference in PaCO₂ and P_TCCO₂ and white circles indicate the difference in PaCO₂ and P_ETCO_2. (A) During the pre-capnoperitoneum period in the supine position, the difference between PaCO₂ and P_TCCO₂ converged on zero, while the difference between PaCO₂ and P_ETCO₂ was greater than zero and the range of agreement was wider. (B) During the period of capnoperitoneum in a steep Trendelenburg position, the difference between PaCO₂ and P_TCCO₂ was closer to zero than the difference between PaCO₂ and P_ETCO₂. The triangles indicate the data for the patient with subcutaneous emphysema: black triangles are the difference between PaCO₂ and P_TCCO₂ and white triangles the difference between PaCO₂ and P_ETCO₂. (C) During the post-capnoperitoneum period in the supine position, the bias in the P_ETCO₂ remained higher, even after CO₂ deflation. The black triangle indicates the difference in PaCO₂ and P_TCCO₂ for the patient with subcutaneous emphysema.