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Relationship between maternal heart rate variability and fetal heart rate deceleration at induction of labor analgesia with intrathecal analgesics - a pilot study-
Abstract Number: SA-12
Abstract Type: Original Research
Objective: Induction of labor analgesia with a small dose of intrathecal local anesthetic with/without an opioid may be associated with an increased frequency of fetal heart rate (FHR) abnormalities. The mechanism underlying such events remains unclear: Some studies suggest an association between FHR changes and increased uterine contractility due to sympathetic blockade from analgesia. Here we measured sympathetic nervous tone to assess the association between sympathetic nervous tone and FHR abnormality. The sympathetic nervous tone was evaluated as low frequency to high frequency (LF/HF) ratio of maternal heart rate variabilities (HRV).
Methods: Eighteen full-term pregnant non-laboring women scheduled for induction of labor under combined spinal-epidural (CSE) analgesia provided informed consent. No women had cardiac arrhythmia or hypertension. Labor was induced using prostaglandin E2 p.o. and intravenous infusion of oxytocin. When a patient required pain relief, electrodes were attached to the distal flexor surface of the left and right forearms and connected to a HRV analysis device (Check My Heart®, Trytech, Tokyo, Japan). After the baseline recordings of HRV, FHR, blood pressure (BP), heart rate (HR), and oxygen saturation (SpO2) in parturients, bupivacaine 2 mg and fentanyl 20 μg were administered into the intrathecal space using a CSE needle via the L3/4 interspace in the sitting position. HRV was analyzed at 5, 10, 15, and 30 min after injections of analgesics in the lateral position. Changes in LF/HF ratio were analyzed using one-way analysis of variance. A p-value < 0.05 was considered statistically significant. In cases with FHR abnormality (late, variable or prolonged deceleration within 30 min after intrathecal analgesia), we analyzed underlying factors using binomial logistic regression analysis.
Results: The LF/HF ratio was significantly reduced at each time point after intrathecal analgesia than before. No significant differences in BP, HR, SpO2 were observed between before and each time point after intrathecal analgesia. Of 18 patients, fetal deceleration was observed in two patients. Binomial logistic regression analysis of factors associated with fetal deceleration demonstrated a greater reduction in LF/HF ratio at 5 min after initiating intrathecal analgesia than before.
Conclusions: Intrathecal analgesia with fentanyl combined with bupivacaine for labor pain significantly decreased the LF/HF ratio. Thus, which suggests that intrathecal analgesia blocked sympathetic activity resulting in parasympathetic nerve predominance. Greater reduction in the LF/HF ratio might be associated with higher incidence of FHR decelerations at induction of labor analgesia.