Effects of thoracic extradural block on diaphragmatic electrical activity and contractility after upper abdominal surgery

Abstract

Background: Upper abdominal surgery (UAS) induces diaphragmatic dysfunction. Thoracic extradural block (TEB) using 0.5% bupivacaine improves some pressure and motion indices of diaphragmatic function. However, no direct information on diaphragmatic activity is available after UAS. The aim of this study was to assess diaphragmatic electrical activity (Edi) after UAS before and after TEB. Methods: A postoperative electromyogram was obtained, using intramuscular electrodes inserted by the surgeon in the costal and crural parts of the diaphragm, in 14 patients undergoing abdominal aortic surgery. Tidal changes in abdominal (V(AB)) and rib-cage (V(RC)) volumes, and gastric (ΔPgas), esophageal (ΔPes), and transdiaphragmatic (ΔPdi) pressures were used to measure tidal volume (V(T)) and respiratory rate and to provide indirect indices of diaphragmatic activity from the two ratios V(AB)/V(T) and ΔPgas/ΔPdi. These respiratory variables were obtained preoperatively. Postoperatively, measurements including Edi were obtained before and after a segmental epidural block, reaching a T4 level was achieved with 0.5% plain bupivacaine. Results: Upper abdominal surgery induced an increase in respiratory rate (+28 ± 15%; P < .05), and V(T) (-30 ± 14%; P < .01). After surgery, all patients exhibited electrical diaphragmatic activity that increased with TEB by 48 ± 28% (P < .01) and 60 ± 22% (P