An evaluation of gas humidifying devices as a means of intraperitoneal local anesthetic administration for laparoscopic surgery

BACKGROUND: Intraperitoneal local anesthetic administration has been reported to provide perioperative analgesia during laparoscopic procedures. The aim of this in vitro study was to assess the efficiency of commercially available humidification devices to deliver ropivacaine and to determine the effects of modifying the device's position between the insufflator and the Veress needle on the amount of ropivacaine delivered. METHODS: In the first experiment, four humidification devices filled with ropivacaine (0.20%, and 0.75%) were placed at the outlet of a laparoscopic insufflation system delivering a constant carbon dioxide flow. A catheter was connected to the humidifier's outlet and the other end submerged in a calibrated vial containing 25 mL. of 50 % methanol in water. The concentration of ropivacaine collected ill the methanol-water solution was measured using high performance liquid chromatography. In the second experiment, the clinical situation was imitated by placing 3 m of silicone tubing between the humidifier and the collection vial to evaluate its influence on the amount of ropivacaine delivered. Only one humidifier was tested in the second experiment because the other three tested humidification devices did not efficiently deliver ropivacaine. RESULTS: The evaporation-based humidifiers delivered very small or nonmeasurable quantities of ropivacaine. In contrast, the rnicrovibration-based aerosol humidification device delivered significant amounts (89.1%-943%) of the drug. The insertion of silicone tubing between the humidifier and the collecting vial reduced the amount of delivered ropivacaine to 62.3% CONCLUSIONS: The rnicrovibration-based aerosol humidification device may be used to deliver local anesthetics during laparoscopic procedures. Further research is necessary to confirm these results in clinical practice and to provide effective humidification that does not blur the Surgeon's view.