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

Purpose

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 ≥20 beats·min^?1, the modified HR increase if ≥ 10 beats·min^?1, and the systolic blood pressure (SBP) increase 15 mmHg criteria.

Methods

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 aftertracheal intubation. Each group of patients was further divided into groups receiving 3 ml lidocaine 1.5% plus 15 μg epinephrine (1:200,000) iv, or 3 ml normal saline (n = 20 each). The HR and SBP were monitored for four minutes after injection of the study drug.

Results

Intravenous injection of the test dose produced HR increases ≥20 beats·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 ≥ 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.

Conclusion

During stable sevoflurane anesthesia, peak HR increase ≥ 10 beats·min^?1 should be regarded as a positive response with end-tidal sevoflurane concentration ≤ 1%, and peak SBP increase ≥ 15 mmHg is applicable at sevoflurane concentrations between 0.5 and 2%.