Effects of interpleural bupivacaine on respiratory muscle strength and pulmonary function

Several reports suggest that interpleural local anesthetics may have deleterious effects on respiratory function. The current study investigated the effects of interpleural bupivacaine on human respiratory muscles and lung function.

Thirteen patients (55 +/- 4 yr old) with normal respiratory function and scheduled for cholecystectomy entered the study before surgery. Respiratory parameters were compared before and after the interpleural administration of 20 ml 0.5% bupivacaine plus 1:200,000 epinephrine while patients were supine; we evaluated breathing pattern, dynamic and static lung volumes, airway conductance, maximal inspiratory pressures (at the mouth; at the esophagus [Pessniff]; at the abdomen [Pgasniff]; and transdiaphragmatic [Pdisniff]), functional reserve (tension-time index) of the diaphragm, and maximal expiratory pressures (at the mouth; at the esophagus [Pescough]; and at the abdomen [Pgacough]). Hemoglobin oxygen saturation by pulse oximetry, heart rate, and mean arterial pressure were continuously monitored.

Respiratory rate (15 +/- 1 to 19 +/- 1 breaths/min; P < 0.01) and heart rate (78 +/- 3 to 83 +/- 3 beats/min; P < 0.01) were slightly increased. Dynamic and static lung volumes, airway conductance, hemoglobin saturation, and the remaining breathing pattern parameters were unchanged. Regarding respiratory muscles, maximal inspiratory pressure at the mouth, Pessniff, and tension-time index of the diaphragm did not change. Pdisniff decreased slightly (102 +/- 10 to 92 +/- 10 cmH2O; P < 0.05) because of a change in Pgasniff (24.2 +/- 7.4 to 18.4 +/- 6.8 cmH2O; P < 0.05). Maximal expiratory pressure at the mouth remained unaltered, but Pgacough decreased (108 +/- 10 to 92 +/- 8 cmH2O; P < 0.01), and Pescough showed a trend to decrease (92 +/- 13 to 78 +/- 10 cmH2O; P = 0.074).

In our experimental conditions, interpleural bupivacaine did not significantly change lung function or inspiratory muscle strength but induced a slight decrease in abdominal muscle strength. Although this effect was minimal, its clinical relevance needs to be evaluated further in patients with impaired respiratory function.