Transcutaneous carbon dioxide measurements in patients undergoing retroperitoneoscopic urologic surgery: A prospective observational study

Purpose: The aim of the current study was to investigate the accuracy of transcutaneous CO2 pressure (PTCCO2) monitoring and the correlation between it and arterial CO2 pressure (PaCO2), so as to determine PaCO2 in patients undergoing retroperitoneoscopic urologic surgery. Methods: 50 patients undergoing retroperitoneoscopic urologic surgery were enrolled in this study. PaCO2, end-tidal carbon dioxide partial pressure (PETCO2), and PTCCO2 values were measured at 4 time points: before pneumoperitoneum, 30 mins, 60 mins and 90 mins after pneumoperitoneum, respectively. The differences of PaCO2 – PETCO2 and PaCO2 - PTCCO2 were calculated. Paired t test, Bland–Altman method, correlation and regression analysis, as well as Fisher’s exact test were employed for the data analysis. Results: Totally 157 samples were obtained. The mean (SD) of PaCO2, PETCO2 and PTCCO2 were 55.5 (7.2) mmHg, 42.3 (5.2) mmHg and 51.9 (84) mmHg, respectively. The absolute difference of PaCO2－PETCO2 was 13.20 ± 4.43 mmHg and 4.35 ± 2.56 mmHg for PaCO2－PTCCO2 (P < 0.0001). And the correlation coefficient (r) between PaCO2 and PETCO2 was 0.79 (r2 = 0.62, P < 0.0001) , whereas that value between PaCO2 and PTCCO2 was 0.91 (r2 = 0.83, P < 0.0001). Meanwhile, the linear regression between PaCO2 and PETCO2 was PETCO2 = 0.60×PaCO2＋9.10 (P < 0.0001), whilst the counterpart between PaCO2 and PTCCO2 was PTCCO2 = 1.07×PaCO2－7.30 (P < 0.0001). The 95% limits of agreement (LOA) of PaCO2 versus PETCO2 was 4.53 to 21.88 mmHg and -3.18 to 10.48 mmHg for PaCO2 versus PTCCO2. Conclusion: PTCCO2 monitoring provided greater accuracy to estimate PaCO2 in patients undergoing retroperitoneoscopic urologic surgery as compared to PETCO2 .