[Intraoperative continuous epidural block influences postoperative changes in breathing pattern and thoracoabdominal...

We have examined the changes in breathing pattern and thoracoabdominal movement associated with upper abdominal surgery in order to evaluate the possible influences of nociceptive input on respiration. Sixteen patients scheduled for gastrectomy were studied. Continuous epidural block was instituted prior to the induction of anesthesia and maintained throughout the surgery in 8 of 16 patients (Group 1) while it was instituted upon the peritoneal closure and maintained thereafter in the remaining 8 patients (Group 2). Breathing pattern and thoracoabdominal motion were determined before and after surgery while the patients awake by respiratory inductance plethysmography (Respisomnography, Chest MI). Breathing frequency and minute ventilation increased significantly while tidal volume was unchanged after the operation regardless of the intraoperative epidural block. Furthermore, there were identical shortening of inspiratory time and prolongation of duty ratio (inspiratory time/duration of a breath) in the two groups. Contribution of rib cage movement on tidal volume increased significantly postoperatively in all the patients. However, the changes were significantly smaller in patients receiving intraoperative epidural block. These results indicate that the causes of tachypnea and increased minute ventilation are different from the mechanism responsible for the alteration of thoracoabdominal partitioning of ventilation after upper abdominal surgery. The former may be related to the metabolic changes and, conceivably, unaffected by continuous epidural block. While the latter may be the consequence of the reflex inhibition of the diaphragmatic function that can be, at least partially, modified by continuous epidural block.