MECHANISMS OF RESPIRATORY FAILURE UNDER BARBITURATE ANESTHESIA (EVIPAL, PENTOTHAL) 1

Abstract

With the growing use of the barbiturates in anesthesia and in medicine in general, it becomes increasingly important to understand the hazards this entails, not only so that accidents of the past may be explained but, chiefly, so that they can be prevented in the future.In this study our atten- tion has been directed to the respiration.While other systems may also be affected adversely by the barbiturates, the respiration frequently gives the first warning of impending difficulties.Re- spiratory failure often plays an important part in death under these agents.This study was de- signed primarily to investigate the mechanisms leading to respiratory failure under evipal and pentothal anesthesia.Since the barbiturates are qualitatively very similar in their actions, it is probable that the mechanisms described here ap- ply to many members of the group.EQUIPMENT AND PROCEDURES Animals.Mongrel dogs weighing about 10 kilograms were employed.Blood pressure was recorded by means of a Ludwig manometer from the femoral artery.The representative material presented here was chosen from that obtained in experiments on 43 dogs under the two anesthetic agents considered.Aniesthesia.Evipal sodium [1 methyl 5A' cyclohexenyl 5 methyl barbiturate] in 10 per cent aqueous solution was administered intravenously in an initial dose of 50 mgm.per kgm.body weight.This was supplemented intra- venously as needed during the preparation of the animal and the course of the experiment.Pentothal sodium [ethyl (1-methyl-butyl) thiobarbiturate] in 5 per cent aqueous solution was administered intravenously in an initial dose of 25 mgm.per kgm.body weight.Additional anesthetic was added intravenously as needed.The points illustrated hold true for both agents.Sometimes one agent, sometimes the other, is used to demon- strate a given point.Depth of anesthesia was controlled as carefully as pos- sible by observation of the state of a spinal reflex.The flexion reflex of the left semitendinous muscle was