Abstract
A pilot study was conducted using a simulated epidural test dose to ascertain the effects adrenaline, adrenaline/clonidine mixture, and clonidine alone on the accepted criteria for determining the occurrence of an epidural intravascular injection. Seventy-five ASA 1 or 2 children aged from six months to twelve years were sequentially allocated to one of three groups: group A: adrenaline 0.5 μg/kg, group AC: adrenaline 0.5 μg/kg and clonidine 0.3 μg/kg, and group C: clonidine 0.3 μg/kg. Effects on heart rate, T-wave amplitude and systolic blood pressure were determined after induction of anaesthesia and stabilization using sevoflurane in nitrous oxide and oxygen. Heart rate varied from baseline in a biphasic manner. The maximal increase in mean heart rate for all groups was <10 beats per minute (bpm). A heart rate rise of >10 bpm was not seen at any time in 54% of groups A and AC and 92% of group C (Chi-square 11.4, P=0.003). T-wave changes were also biphasic. 50% of groups A and AC had no increase in T-wave size of >25% at any sample point, compared with 96% in group C (Chi square=49.4, P<0.0001). 34% of groups A and AC did not have a change in systolic blood pressure of >15 mmHg during the study compared with 100% of group C (Chi-square=30.2, P<0.0001). There were no significant differences between groups A and AC for any parameter. Negative predictive value estimates for the current criteria for intravascular injection were low. Clonidine 0.3 μg/kg produced no effects on the study variables.