ASCENDING RESPIRATORY PARALYSIS UNDER GENERAL ANESTHESIA

Abstract

As a result of the inhalation of a general anesthetic, there develops a progressive ascending paralysis of the muscles of respiration, the extent of which provides a valuable indication of the depth of anesthesia. The muscles that are used in quiet respiration are the diaphragm, which carries on abdominal respiration; the levatores costarum and intercostales externi, which bring about costal inspiration, and the intercostales interni and triangularis sterni, which aid in expiration. All of these costal muscles are innervated by the intercostal nerves, originating in the twelve dorsal segments of the spinal cord. The diaphragm obtains its nerve supply through the phrenic nerve from the fourth cervical segment. An ascending paralysis will affect the costal muscles, innervated from the dorsal portion of the spinal cord, much sooner than the diaphragm, the nerve supply of which originates in the midcervical portion. From the standpoint of the anesthetist, the abdominal respiration can