Effects of intercostal nerve blocks on pulmonary mechanics in healthy men

Bilateral block of the 5th through the 11th intercostal nerves was induced in 16 healthy men. In eight of the men, bupivacaine 0.25% was used and in the other eight, etidocaine 0.5%. Before and after induction of the block flow/volume curves, maximal airway pressures, and pulmonary compliance, were recorded, and helium spirometry and multiple and single breath nitrogen wash-outs were performed. There were no differences between the results in the two groups, and the material was therefore pooled. Total lung capacity was decreased by 4%. There was no increase in residual volume, though the maximal expiratory airway pressure decreased by 7%. There was an 8% decrease in functional residual capacity. Pulmonary recoil appeared to be unchanged, as also did the effort-independent peak expiratory flow rates. According to the pulmonary nitrogen clearance index, the overall pulmonary time constant did not alter, while the slope of the alveolar plateau in the single breath nitrogen wash-out test increased by 9%. The significance of the latter finding is unclear, but it is concluded that the nerve block had no obvious effects on pulmonary mechanics, the changes observed rather being attributable to effects on the chest wall.