Effects of intercostal nerve blocks (bupivacaine 0.25% and etidocaine 0.5%) on chest wall mechanics in healthy men.

Bilateral blockade of the 5th to 11th intercostal nerves, inclusive, was produced in 14 healthy subjects. In seven, bupivacaine 0.25% was used, and in the other seven, etidocaine 0.5%. The latter has been found to have a stronger motor-blocking action than the former. Before and after the blockade, the vital capacity (VC), peak expiratory flow rate (PEF), tidal volumes, respiratory variations in rib cage and abdominal circumferences and in oesophageal and intragastric pressures were recorded. By transthoracic electrical impedance pneumography, measures indicating changes in the functional residual capacity (FRC) were obtained. Although it was considered that changes in the parameters investigated mainly demonstrated changes in motor function, no differences were found between the drugs. With this form of blockade they seem to have equivalent effects in this respect. Thus, VC decreased by an average of 7% and PEF by 6%. Signs of a reduction of FRC after the blockade were also observed. The blockade had no effect on the partitioning of costal and abdominal breathing at rest. Analysis of the relations between the fractions of costal and abdominal breathing and the corresponding variations in intragastric pressure gave support to the view that in normal individuals both intercostal and abdominal muscles remain passive during respiration at rest. This is thus achieved by the diaphragm alone.