[The effect of epidural analgesia on respiratory muscles]

The effect of epidural analgesia on respiratory functions and muscular power was studied in patients. The subjects had no abnormality of cardiopulmonary system, and were classified into two groups; the adult group whose ages were 21 to 59, and the aged group, 60 to 72. Either 1% or 2% mepivacaine for epidural anesthesia was used to obtain the analgesic level up to Th4 and Th7 in adult group, and Th4 in aged group. The analgesic level was assessed by the pin-prick method. Vital capacity, forced vital capacity, forced expiratory volume 1 second, peak expiratory flow rate, maximal mid-expiratory flow rato, maximal inspiratory pressure and maximal expiratory pressure decreased significantly after epidural anesthesia in all patients whose analgesic levels were up to Th4. In all patients, the change of maximal expiratory pressure was larger than that of maximal inspiratory pressure after epidural analgesia. The patients whose analgesic levels were up to Th7 by 1% mepivacaine in adult group, showed a significant increase of maximal inspiratory pressure. It is concluded that epidural anesthesia diminishes respiratory functions and respiratory muscular power associated with a higher level of analgesia.