Improvement of Diaphragmatic Function by a Thoracic Extradural Block After Upper Abdominal Surgery

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Abstract
The effects on diaphragmatic function of a thoracic epidural block were assessed in 13 patients after upper abdominal surgery (UAS). Lung volumes and tidal changes in chest wall circumferences and gastric (.DELTA.Pgas) and esophageal (.DELTA.Pes) pressures were measured pre- and postoperatively. Volume displacement of the abdomen divided by tidal volume (.DELTA.VAB/VT) and .DELTA.Pgas/.DELTA.Pes were taken as indices of the diaphragmatic contribution to tidal breathing. These respiratory variables were obtained in the postoperative period, before and after epidural injection of 0.5% plain bupivacaine to achieve a block up to the T4 segments. UAS was constantly associated with a decrease in VT, .DELTA.VAB/VT, .DELTA.Pgas/.DELTA.Pes, and forced vital capacity (FVC). Epidural block was associated with an increase in VT, .DELTA.VAB/VT, and FVC. .DELTA.Pgas and .DELTA.Pgas/.DELTA.Pes returned to their preoperative values. It is concluded that: diaphragmatic dysfunction observed after USA is partially reversed by thoracic epidural block; and that inhibitory reflexes of phrenic activity arising from the abdominal compartment (abdominal wall and/or viscera) could be involved in this diaphragmatic dysfunction.