SEDATION AND RESPIRATORY MECHANICS IN MAN

The effects of sedation with halo thane, enflurane or midazolam on respiratory mechanics and lung volumes were studied in young healthy volunteers, in the supine position. Functional residual capacity increased with halothane sedation, but was unchanged with sedation produced by enflurane or midazolam. Sedation with halothane and enflurane, but not midazolam, tended to increase lung static recoil pressure. Total lung capacity was decreased during sedation with midazolam. No evidence was found that sedation with these three agents increased airway resistance. These findings imply that changes in respiratory mechanics induced by the residual effects of anaesthetic agents are unlikely to contribute significantly to the impairment in pulmonary gas exchange which may occur in the period immediately after operation. In a study which examined four subjects lying supine while breathing subanaesthetic concentra-tions of halothane (0.2 minimal alveolar concentra-tion (MAC)), three individuals decreased both their functional residual capacity (FRC) and the tonic muscle activity of the diaphragm and intercostal muscles (Muller et al., 1979). Sedation of recum