Ventilation and ventilatory CO2 response in children during halothane anaesthesia after nonopioid (midazolam) and opioid (papaveretum) premedication

The influence of non-opioid (NO) and opioid (O) premedication on ventilation and ventilatory CO2 response was studied in 18 spontaneously breathing children during halothane anaesthesia. Eight patients in Group NO and 10 in Group O were comparable in age, body weight and type of surgery performed. The sedative effect was evaluated and measurements by pneumotachography and in-line capnography were made immediately after induction of sleep, just before the start of surgery, during surgery and after surgery both before and after 3 min of about 2% CO2 inhalation. Immediately after induction the mean value (+/- s.e. mean) of end-tidal CO2 concentration (ETCO2) was 4.86 +/- 0.21% in Group NO and 5.28 +/- 0.22% in Group O. Before and during surgery, minute ventilation (VE) was higher in Group NO (P less than 0.05) mainly due to higher respiratory rates. ETCO2 was similar in the two groups before, during and after surgery. The ratio of VE to CO2 elimination (VCO2) and of dead space (VD) to tidal volume (VT) was higher in Group NO, but ventilatory response to CO2 inhalation immediately before the postoperative period was similar in both groups. It was concluded that opioid premedication resulted in more efficient ventilation during anaesthesia and surgery, and that CO2 response at the end of surgery was maintained in both groups.