Reduced efficacy of simulated epidural test doses in sevoflurane-anesthetized adults

To determine the hemodynamic responses to, and the efficacy of epinephrine-containing epidural test doses, during sevoflurane anesthesia, based on the conventional heart rate (HR) increase > or = 20 beats x min(-1), the modified HR increase if > or = 10 beats x min(-1), and the systolic blood pressure (SBP) increase 15 mmHg criteria.

One hundred and twenty patients were randomised to receive sevoflurane 0.5, 1 or 2% end-tidal (n = 40 each) and nitrous oxide 67% in oxygen after tracheal intubation. Each group of patients was further divided into groups receiving 3 ml lidocaine 1.5% plus 15 microg epinephrine (1:200,000) i.v., or 3 ml normal saline (n = 20 each). The HR and SBP were monitored for four minutes after injection of the study drug.

Intravenous injection of the test dose produced HR increases > or = 20 beats x min(-1) in 18 (90%), 16 (80%) and 14 (70%) patients at sevoflurane concentrations at 0.5, 1 and 2%, respectively, while those receiving saline developed no HR changes. Based on the modified HR criterion, sensitivity, specificity, and positive and negative predictive values were all 100% under sevoflurane concentrations of 0.5 and 1%, but not 2%. On the other hand, all patients in the test dose groups and none in the saline groups developed SBP > or = 15 mmHg, ensuring 100% efficacy based on the conventional SBP criterion under all sevoflurane concentrations studied. In all patients receiving the intravenous test dose, peak HR occurred 30-45 sec earlier than that of SBP.

During stable sevoflurane anesthesia, peak HR increase > or = 10 beats x min(-1) should be regarded as a positive response with end-tidal sevoflurane concentration < or = 1%, and peak SBP increase > or = 15 mmHg is applicable at sevoflurane concentrations between 0.5 and 2%.