Ventilation and ventilatory response to carbon dioxide during caudal anaesthesia with lidocaine or bupivacaine in sedated children.

Resting ventilation, arterial blood-gas tensions and the ventilatory response to carbon dioxide were measured in sedated children before and after caudal anaesthesia using 10 mg.kg-1 of 1.5% lidocaine or 3.3 mg.kg-1 of 0.5% bupivacaine. Expired minute volume decreased slightly after both caudal blocks but end-tidal Pco2 increased slightly after caudal block with lidocaine. No clinical changes in Paco2 and Pao2 were observed in either group. The slope of the CO2 response curves increased significantly after both caudal blocks. The mean plasma levels of lidocaine and bupivacaine were 3.95 +/- 0.64 (s.d.) and 1.33 +/- 0.29 micrograms.ml-1, respectively. These results indicate that the ventilatory response to hypercapnia is markedly improved by the two caudal blocks, but resting ventilation is slightly impaired by caudal block with lidocaine, and from the aspect of pulmonary ventilation bupivacaine is better than lidocaine for caudal anaesthesia.