The influence of diazepam on the dosage of muscel-relaxants during anaesthesia

The literature on anaesthesiological studies performed to investigate a possible sparing effect of diazepam on the dosage of muscle-relaxants during anaesthesia is reviewed. Despite some conflicting results it can be concluded that diazepam exerts such an effect, thus allowing between 8 and 30% of the amounts of muscle-relaxants, depending on the type of anesthesia used, to be spared. This conclusion is also supported by the results of pharmacological studies in animals, using the head drop method. The mechanism of this effect is discussed on the basis of the relevant published pharmacological evidence from "in vitro" studies and from both animal and human "in vivo" studies. From these reports it is concluded that diazepam, at therapeutic doses, does not act on neuromuscular transmission and that this sparing effect does not result from direct pharmacological interaction with neuromuscular blocking agents. Some studies indicate a minimal action of the product on the skeletal muscle fibre, but this also is not related to the sparing effect. It is furthermore concluded that his sparing effect of diazepam on the dosage of muscle-relaxants during anesthesia is due to a summation of muscle-relaxant actions exerted at different levels of the nervous system, those of diazepam being mainly exerted at the spinal and brainstem level and consisting in inhibition of polysynaptic reflex activity, enhancement of presynaptic inhibition, and depression of gamma-motoneuron activity.