EPINEPHRINE-INDUCED TACHYCARDIA IS DIFFERENT FROM CONTRACTION-ASSOCIATED TACHYCARDIA IN LABORING PATIENTS

Maternal tachycardic responses to the intravenous injection of epineph rine 15 mu g were compared with tachycardic responses induced by the p ain of labor in a double-blind, prospective study of 15 women in activ e labor. After placement of an epidural catheter, maternal heart rate was continuously recorded. Each patient received, in uterine diastole, two injections of a test dose (epinephrine 15 mu g + lidocaine 45 mg) at 2-4 min intervals, once via the epidural catheter and once intrave nously in a random fashion. From the maternal heart rate strips, the a cceleratory phase (bpm) of epinephrine-induced tachycardic responses ( EITRs) and contraction-associated tachycardic responses (CATRs) were c alculated. The upper bound of the 99% confidence interval (CI) to disc riminate between the two groups was estimated. The acceleratory phase of EITRs was 1.85 +/- 0.61 bpm. The acceleratory phase of CATRs was 0. 69 +/- 0.49 (P < 0.0003). The upper bound of the 99% CI was 1.17 bpm. Using this value to discriminate between EITRs and CATRs, all EITRs wo uld be correctly identified. We conclude that on-line analysis of mate rnal tachycardic responses might be used in laboring women to discrimi nate between EITRs and CATRs and further improve the accuracy of an ep inephrine test dose during the performance of epidural analgesia.