Piezoelectric Sorption Anesthetic Sensor

The piezoelectric sorption detection method is evaluated for use in construction of an inexpensive, rugged, compact, and fast sensor for measuring the concentration of inhalation anesthetics. 10 MHz quartz crystals were coated with various substances and their frequency shifts measured upon exposure to varying concentrations of halothane, enflurane, and nitrous oxide. For a silicone rubber coating, the response was found to be linear with concentration, with sufficient signal to allow resolution to approximately 0.05 volume percent for either halothane or enflurane, or to 4 percent for nitrous oxide. The devices were sensitive to halothane and enflurane in proportion to their anesthetic potencies, but were slightly less sensitive to equally potent concentrations of nitrous oxide. They were insensitive to CO2 in the physiologic range, but had a significant response to water vapor. The response time of the detector was primarily a function of washout of the sensing chamber. At a 200 ml/min sample flow rate, the time constant was approximately 100 ins. It is concluded that this detection method is suitable for a variety of applications in anesthesia, although, with the coatings presented here, control of or correction for sample humidity is required.