EFFECT OF HEMIDIAPHRAGMATIC PARESIS CAUSED BY INTERSCALENE BRACHIAL-PLEXUS BLOCK ON BREATHING PATTERN, CHEST-WALL MECHANICS, AND ARTERIAL BLOOD-GASES

We investigated the effects of hemidiaphragmatic paresis caused by interscalene brachial plexus block on breathing patterns, chest wall mechanics, and arterial blood gas tensions using respiratory inductive plethysmography. Ten healthy patients received interscalene block with 20-40 mt 1.5% lidocaine with epinephrine. Rib cage contribution to tidal volume (%RC) increased from 28.9% +/- 9.7% to 50.0% +/- 8.3% (P < 0.01), respiratory frequency (f) increased from 14.6 +/- 3.2/min to 16.3 +/- 2.4/min (P < 0.05), and Pao(2) decreased from 84.7 +/- 7.3 mm Hg to 78.0 +/- 9.5 mm Hg (P < 0.05). No significant changes were observed in tidal volume (VT), minute volume (Vs), or Pace,. These results indicated that VT, VE, and Pace(2) were maintained after interscalene block, apparently by increases in f and %RC to compensate fur hemidiaphragmatic paresis caused by interscalene block. Nevertheless, Pao(2) was reduced, presumably due to increased ventilation-perfusion mismatching. Recognizing that we studied healthy patients, the decrease in Pao(2) may be more in patients with cardiopulmonary disease.