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Impact of Labor Analgesia Technique on Maternal Plasma Epinephrine Concentrations and Fetal Bradycardia
Abstract Number: O1-03
Abstract Type: Original Research
CSE labor analgesia may result in a higher rate of uterine tachysystole and fetal bradycardia possibly due to a precipitous decrease in maternal epinephrine concentrations.1,2 As part of a larger study, we performed a subgroup analysis to determine any relationship between maternal plasma epinephrine concentrations and fetal bradycardia after neuraxial analgesia.
Methods: Term, nulliparous patients in spontaneous labor whose cervical dilation was < 4 cm were recruited for the larger study. At first request for neuraxial analgesia, patients were randomized to one of three groups: 1. epidural de novo technique with fentanyl 100μg and 0.125% bupivacaine 15-20mL; 2. CSE technique with intrathecal fentanyl 25μg; or 3. CSE technique with intrathecal 0.5% bupivacaine 2.5mg and fentanyl 15μg. A second randomization was performed to select a subgroup of recruited subjects to undergo maternal plasma epinephrine concentration sampling. Patients randomized to this subgroup underwent venous blood sampling three times: immediately prior to neuraxial analgesia, and 15 and 30 minutes after intrathecal dose or start of epidural catheter dosing. Fetal heart rate (FHR) tracings from 30 minutes prior to through 60 minutes after first local anesthetic dose were collected and analyzed by a perinatologist blinded to group assignment. FHR tracings were graded based on criteria from the NIH Three-Tier FHR Interpretation System3 and analyzed for presence or absence of variable and late decelerations. Tocodynamometer tracings and maternal vital signs were also analyzed.
Results: 38 patients were randomized and analyzed. Figure 1 shows a decrease in plasma epinephrine concentrations from baseline at 15 and 30 min after first local anesthetic dose, but no difference between groups within any time period. Group 3 had a higher incidence of variable FHR decelerations after neuraxial analgesia (P=0.01), but there was no difference between the groups in incidence of late FHR decelerations, FHR classification, maternal hypotension, or uterine tachysystole.
Discussion: Changes in maternal plasma epinephrine concentrations are the same between CSE and epidural techniques. This decrease was not shown to increase rates of uterine tachysystole or late FHR decelerations. The increased rate of variable FHR decelerations in group 3 is likely multifactorial in nature.
1. Anesth Analg. 2004;98:1153-9
2. Obstet. Gynecol. 2008;112:661-6
3. Obstet. Gynecol. 2009;113:41-7