Evaluation of Arterial to End-tidal Carbon Dioxide Pressure Differences during Laparoscopic Renal Surgery in the Lateral Decubitus Position

BACKGROUND: End-tidal carbon dioxide (PEtCO(2)) is a noninvasive reliable technique to measure arterial partial pressure of carbon dioxide (PaCO2) in the body under general anesthesia. However, gradient between PaCO(2) and PEtCO(2) (P[a-Et] CO(2)) is influenced by many factors. AIMS: In the present study, we evaluated the changes in P (a-Et) CO(2) for laparoscopic donor nephrectomy in lateral decubitus position (LDP). SETTINGS AND DESIGN: This was an observational, double-blinded, tertiary care center-based study. METHODS: Thirty-one American Society of Anesthesiologists Class I and Class II patients of either sex undergoing laparoscopic donor nephrectomy in LDP under general anesthesia were included. An arterial cannula was inserted, PaCO(2) was measured at eight predesignated time intervals, and PEtCO(2) was also noted at the corresponding time period. STATISTICAL ANALYSIS: Data were analyzed using a two-way analysis of variance for repeated measurements using one dependent variable and one within-subject factor (time). Quantitative data were presented as mean ± standard deviation or median and interquartile range, as appropriate. RESULTS: The mean P (a-Et) CO(2) gradient was 5.67 ± 1.36 mmHg 10 min after induction of anesthesia in the supine position (T1a). Ten minutes after LDP, P (a-Et) CO(2) gradient was 7.38 ± 1.45 mmHg (T1b) and was higher than T1a. The P (a-Et) CO(2) values 10 min after release of pneumoperitoneum and 10 min after making the patient supine were significantly higher than the T1a value. The highest value of P (a-Et) CO(2) gradient was at 30 min after creation of pneumoperitoneum (T30), i.e., 9.99 ± 1.70 mmHg. Pearson's correlation coefficient showed that the degree of correlation varied considerably during surgery due to interindividual variability (R(2) T1a vs. T60 was 0.61 vs. 0.17). CONCLUSIONS: PEtCO(2) does not reliably predict PaCO(2) in healthy patients scheduled for laparoscopic renal surgery in LDP.