(1052) Effect of spinal anesthesia on the fetal autonomic nervous system: an experimental study

Spinal anesthesia is the reference technique for scheduled cesarean deliveries. Its main risk is maternal hypotension, which may impact fetal blood gas parameters. Thus our objective was to assess the effects of spinal anesthesia on the fetal autonomic nervous system (ANS).

Study Design:

An experimental study was conducted in pregnant ewes. Prior surgical instrumentation allowed placement of fetal arterial catheters, thoracic electrodes and cerebral electrodes to record the electroencephalogram (EEG). Spinal anesthesia was performed on day 4. Two groups were compared: intrathecal bupivacaine vs isotonic saline solution (SSI, control). Maternal and fetal hemodynamic and blood gas parameters, along with ANS and EEG data, were collected before and after spinal injection. ANS activity was assessed via fetal heart rate variability, including the Fetal Stress Index (FSI), a quantitative marker of parasympathetic tone. Brain activity was analysed both qualitatively and using quantitative markers, including Spectral Edge Frequency (SEF), defined as the frequency below which 95% of the total spectral power is concentrated.

Results:

Fourteen spinal anesthesia were performed (8 bupivacaine, 6 SSI). Maternal hypotension occurred in 62.5% of the bupivacaine group vs none in the SSI group. Maternal systolic blood pressure was lower at 3 min (96 vs 132 mmHg, p = 0.004) and 5 min (89 vs 117 mmHg, p = 0.045). Fetal mean arterial pressure decreased at 3 min (47 vs 59 mmHg, p = 0.014) and 5 min (49 vs 58 mmHg, p = 0.016). No fetal acidosis was observed. In the bupivacaine group, a global increase in fetal ANS activity was found, including a significant rise in FSI at 3 min vs baseline (77.8 vs 55.4, p = 0.046), with no change in the SSI group. SEF was significantly reduced in the bupivacaine group at 10 min (6.4 vs 13.9 Hz, p< 0.01).

Conclusion:

This model of spinal anesthesia in pregnant ewes induced maternal hypotension and fetal changes in hemodynamics, blood gases, ANS, and EEG activity, suggesting an adaptive response to anesthetic stress.