A mechanical stimulator for the determination of the minimum alveolar concentration (MAC) of halothane in the rabbit

Abstract

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 determination 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.

Effect of acepromazine and butorphanol on isoflurane minimum alveolar concentration in goats

“…The isoflurane MAC was 1.29% using tail clamping as the stimulus (Hikasa et al ., 1998) and 1.2% when the noxious stimulus involved clamping a dewclaw (Antognini & Schwartz, 1993). As MAC may be affected by repeated stimulation of a site (Sobair et al ., 1993) no toe was clamped on more than two occasions in this study.…”

Isoflurane MAC determination in dogs using three intensities of constant-current electrical stimulation

“…Hyperthermia may increase MAC, but did not occur during the study reported here. The presence of peripheral or central sensitization leading to a higher MAC, which has been demonstrated in rabbits (Sobair et al 1993), was unlikely to have occurred in this study because the correlation between MAC TAILCLAMP and the number of clamp stimulations was very weak in each dog. Finally, overestimation of arterial partial pressure of isoflurane because of significant venous admixture was excluded because the ratio between PaO 2 and its inspired fraction (PaO 2 /FIO 2 ) was always higher than 450 mmHg (60 kPa) during the experiments.…”

“…Although some authors (Sobair et al 1993;Antognini & Carstens 1998) have suggested methods to provide a uniform intensity of mechanical noxious stimulation in MAC studies, the majority of studies using the tail clamp provide a poor description of its standardization. Consequently, the relatively high variability found between isoflurane MAC studies using the tail clamp (1.27-1.44%) (Steffey & Howland 1977;Valverde et al 2003;Pypendop et al 2007) can be partially explained by this lack of standardization.…”

Effect of morphine and flunixin meglumine on isoflurane minimum alveolar concentration in goats

“…2002). As MAC may be affected by repeated stimulation of a site (Sobair et al. 1993), no claw was clamped on more than two occasions.…”