Comparison of isoprenaline with adrenaline as components of epidural test dose solutions for halothane anaesthetized children

In this randomized controlled trial we studied the haemodynamic effects of intravenous injection of lignocaine 1 mg/kg with either no additive, isoprenaline 0. 05 microg or 0.075 microg/kg, or adrenaline 0.5 microg/kg in children anaesthetized with halothane. An increase of > or = 10 bpm in heart rate or > or = 20% rise in blood pressure was taken as a positive test response. Adrenaline was confirmed to be an unreliable marker with a positive test in only 67% of cases. For both doses of isoprenaline, the heart rate changes produced a positive test in 100% of cases. There was no statistically significant difference between the two doses of isoprenaline in regard to mean maximum increase in heart rate, mean time of beginning, ending or duration of positive test response and mean time to reach peak heart rate. The positive test response began between 10 and 50 seconds and lastedfor an average of 69 +/- 54 seconds with the lower dose of isoprenaline 0.05 microg/kg No advantage could be seen with the higher dose of isoprenaline. Change in blood pressure was not a useful criterion to detect intravascular injection. Recommendations for the use of isoprenaline as a marker of intravascular injection during regional blockade must be deferred until the safety of this agent's effect on neurological tissue is confirmed.