Rib cage contribution to resting and carbon dioxide stimulated ventilation during 1 mac isoflurane anaesthesia

Abstract

Using respiratory inductive plethysmography, we have measured rib cage and abdominal motion during isoflurane anaesthesia in 16 healthy day-surgery patients. Anaesthesia was induced with propofol and maintained with 1 MAC isoflurane in air-oxygen via a laryngeal mask. Measurements were taken during both resting ventilation and hyperpnoea induced by rebreathing carbon dioxide. For resting ventilation, the rib cage contributed a mean (sd) of 33 (15) % of the total ventilation whilst awake, and 39 (12) % during anaesthesia (ns). With increasing end-tidal carbon dioxide whilst awake, the subjects showed a mean increase in the percentage rib cage contribution of 7.1 (12.5)%lkPa of carbon dioxide. With isoflurane anaesthesia, there was significant depression of this rib cage recruitment with the mean contribution decreasing by 3.6 (7.4) % kPa-1(P < 0.05). These results indicate that 1 MAC of isoflurane does not selectively depress rib cage motion, except during carbon dioxide stimulated hyperpnoea. © 1991 British Journal of Anaesthesia.