Diaphragmatic shortening after thoracic surgery in humans. Effects of mechanical ventilation and thoracic epidural anesthesia

Abstract

Background: Diaphragmatic function is believed to be inhibited after thoracic surgery and may be improved by thoracic epidural anesthesia.

Methods: Diaphragmatic function after a thoracotomy was monitored by implanting one pair of sonomicrometry crystals and two electromyogram (EMG) electrodes on the costal diaphragm of six patients undergoing an elective pulmonary resection. Crystals and EMG electrodes remained in place for 12-24 h.

Results: During mechanical ventilation, costal diaphragmatic length (as a percent of rest length; %LFRC) decreased passively as tidal volume (VT) increased (%LFRC = 2.81 + 1.12 x 10(-2) VT (ml), r = 0.99). During spontaneous ventilation, the costal shortening (2.1 +/- 2.3 %LFRC) was less than during mechanical ventilation (7.9 +/- 3.0 %LFRC, P < 0.05) at the same VT. Comparing spontaneous ventilation before and 30 min after thoracic epidural anesthesia, there were increases of VT (390 +/- 78 to 555 +/- 75 ml), vital capacity (1.37 +/- 0.16 to 1.68 +/- 0.21 l), and esophageal (-8.5 +/- 1.5 to -10.6 +/- 1.7 cmH2O), gastric (-0.7 +/- 0.8 to +0.8 +/- 0.8 cmH2O), and transdiaphragmatic (7.7 +/- 1.5 to 11.5 +/- 1.9 cmH2O) pressures, but diaphragmatic EMG and shortening fraction remained constant. In three of six patients, epidural anesthesia produced paradoxical segment lengthening upon inspiration.

Conclusions: Thoracotomy and pulmonary resection produce a marked reduction of active diaphragmatic shortening, which is not reversed by thoracic epidural anesthesia despite improvement of other indices of respiratory function.