A MECHANICAL STIMULATOR FOR THE DETERMINATION OF THE MINIMUM ALVEOLAR CONCENTRATION (MAC) OF HALOTHANE IN THE RABBIT

The minimum alveolar concentration (MAC) of halothane was determined in New Zealand White rabbits. Tracheal anaesthetic concentrations were measured using a Siemens Servo Gas Monitor. A stimulator was used to deliver precisely controlled mechanical stimuli for the determination of MAC. Movement of the rabbit's head was recorded using a force transducer attached to the teeth. Evidence is presented that for the determination of MAC a precise nociceptive threshold is preferable to the so-called supramaximal stimulus used in clinical anaesthesia and in determinations of anaesthetic potency. We conclude that techniques for the determination of MAC which disregard either sensitization of sensory mechanisms by producing tissue inflammation or the possibility of nerve compression by severe mechanical stimuli are of questionable value. The use of the mechanical stimulator described, or a similar device, would help in the standardization of the determination of MAC in all species by facilitating the application of a force of controlled amplitude duration and velocity, thereby removing some of the variables which confound comparative studies of MAC.