The Effect of Inhalation Anaesthetics on Skeletal and Smooth Muscle

Abstract

The classic indication of anaesthesia depth in different stages and planes is best understood in terms of a progressive depression of certain groups of striated and smooth muscles. This scheme was primarily based on the symptoms of progressive depth of ether anaesthesia, and was later found to be the same for other inhalation anaesthetics. First the muscles of eyes, head, and neck, later of the extremities, were paralysed, followed by the muscles of the trunk and abdomen, and finally the intercostal muscles and those of the diaphragm. At around the same level also smooth muscles of vessels, intestine, pupil, and bronchi started to relax, and finally the heart muscle also failed. The depth of inhalation anaesthesia was regulated by the degree and sites of muscle relaxation required for certain operations. Later, the need for muscle relaxation was fulfilled by peripherally acting muscle relaxants, and the need for deep inhalation anaesthesia no longer existed. This progressive muscle relaxation differed considerably in degree from one inhalation anaesthetics to the other, but the sequence of relaxation was always the same. This points primarily to a central origin of the muscle paralysis caused by inhalation anaesthetics, which is confirmed by the experiments.