Abstract
Ventilatory pattern (VP) and the hypercapnic ventilatory response (HVR) were investigated in thirteen healthy male volunteers before and after high thoracic epidural anesthesia (HTE) with 1% lidocaine in 6 subjects and 2% lidocaine in the others. Ventilatory variables were determined by pneumotachograph and respiratory inductive plethysmograph (RIP). RIP allowed us to partition the volume change of the lung into the rib cage component and the abdominal one. In resting condition, all parameters were unchanged after HTE with 1% lidocaine. By contrast, after HTE with 2% lidocaine significantly decreased duration of inspiration and volume displacement of the rib cage, and produced significant increase of mean inspiratory flow rate and minute ventilation. Partial pressure of end-tidal CO2 and volume displacement of the abdomen were essentially unchanged. HVR was not altered with HTE with 1% lidocaine, whereas it decreased significantly with 2% lidocaine due entirely to the decrease of the slope of the rib cage component. In both cases, the slope of the abdominal component was un-changed. In summary HTE with 1% lidocaine affected neither VP nor HVR. However, HTE with 2% lidocaine caused significant ventilatory changes. HTE with 2% lidocaine may have a notable effect on the efferent and/or afferent pathway of the intercostal nerve roots.
