Amixture of 86% of CO2, 10% of N2O, and 4% of oxygen permits laparoscopy under local anesthesia: a pilot study

The aim of this study is to verify that 10 % of N2O in CO2 sufficiently reduces pain to permit laparoscopy under local anesthesia. In nine patients undergoing laparoscopy under local anesthesia for tubal sterilization, a mixture of 86 % of CO2, 10 % of N2O, and 4 % of oxygen (the Gas Mixture) was used for the pneumoperitoneum. For CO2, N2O, and for the Gas Mixture, the pain when blowing over the tongue tip and the pH changes of saline and Hartmann's solution were estimated. In all nine patients, discomfort was minimal and the intervention was well tolerated, similar to 100% N2O. Tongue tip pain (n=15), on VAS scale, was lower with 86 % CO2+ 10% N2O+ 4% O-2 (2.4 +/- 1.4, P=0.005) and much lower with 100 % N2O (0.3 +/- 0.6, P<0.0007) than with pure CO2 (3.6 +/- 1.7). The pH of saline (n=5) decreased from 7.00 +/- 0.07 to 4.18 +/- 0.04 (P=0.001), 6.98 +/- 0.08 (NS), and 4.28 +/- 0.04 (P=0.01) with 100 % CO2, 100 % N2O and the Gas Mixture, respectively. The pH of Hartmann's solution (n=5) decreased similarly from 7.00 +/- 0.07 to 5.18 +/- 0.04 (P=0.01), 7.02 +/- 0.19 (NS), and 5.3 +/- 0.4 (P=0.01), respectively. These data demonstrate that a mixture with 10 % of N2O and 4 % of O-2 in CO2 permits laparoscopy under local anesthesia. This result cannot be explained by direct irritation estimated by tongue tip pain or by pH changes.