Epinephrine-Induced Tachycardia Is Different from Contraction-Associated Tachycardia in Laboring Patients

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Abstract
Maternal tachycardic responses to the intravenous injection of epinephrine 15 micrograms were compared with tachycardic responses induced by the pain of labor in a double-blind, prospective study of 15 women in active 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 micrograms + lidocaine 45 mg) at 2-4 min intervals, once via the epidural catheter and once intravenously in a random fashion. From the maternal heart rate strips, the acceleratory phase (bpm) of epinephrine-induced tachycardic responses (EITRs) and contraction-associated tachycardic responses (CATRs) were calculated. The upper bound of the 99% confidence interval (CI) to discriminate 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 would be correctly identified. We conclude that on-line analysis of maternal tachycardic responses might be used in laboring women to discriminate between EITRs and CATRs and further improve the accuracy of an epinephrine test dose during the performance of epidural analgesia.