Sorptive loss of volatile and gaseous anesthetics from in vitro drug application systems
In in vitro pharmacological experiments, determination of effective concentration values for various anesthetics depends on understanding the exact concentration of the drugs dissolved in physiological solutions. Actual anesthetic concentration may differ from expectations because of drug adsorption, absorption or other loss, especially in tubing. We tested the hypothesis that delivered concentrations of anesthetics decrease when solutions pass through laboratory tubing and investigated such loss by measuring the entering and exiting dissolved concentrations of two volatile (sevoflurane and isoflurane) and two gaseous (nitrous oxide and xenon) anesthetics. We tested solutions passed through tubes (1 m × 2 mm ID × 4 mm OD) made of five different materials (glass, Teflon, polyethylene (PE), polyvinyl chloride (PVC), and silicon rubber). Exiting concentrations of anesthetics were significantly reduced when they were passed through PVC (>33%) and silicon (>43%) tubes. There were no decreases in anesthetic concentrations with glass, Teflon, or PE tubes. When sevoflurane solution flowed through PVC and silicon tubes, it took 20 and 30 min, respectively, after start of flow until the anesthetic loss became negligible. These results indicate that frequently used PVC and silicon tubes, whereas flexible and easy to handle, have serious drawbacks when used in inhaled anesthetic pharmacology experiments.