Literature suggests association between subarachnoid opioids and transient fetal bradycardia probably due to uterine hypertonicity. We evaluated the effects of spinal bupivacaine alone or fentanyl -bupivacaine during CSE labor analgesia on uterine basal tone and its association with FHR abnormalities.

This randomized double blind trial was conducted in 30 low risk parturients who requested labor analgesia. After written consent, Group B received spinal analgesia with 2.5mg (0.5%) hyperbaric bupivacaine; Group BF received 2 mg (0.5%) hyperbaric bupivacaine with 15µg fentanyl. A disposable intrauterine pressure catheter (IUP)system, attached to the cardiotocograph machine (SonicaidTM FM800 Encore) , was inserted by a blinded obstetrician after rupture of membranes beyond 3 cm cervical dilatation of active labour. IUP recordings and FHR patterns were noted for 15 minutes prior and 30 minutes following spinal analgesia. The primary outcome was an increase in of uterine basal tone (>10mmHg). As secondary outcomes, incidence of FHR change, maternal hemodynamics, VAS scores, spinal block characteristics, nausea, vomiting, pruritis and neonatal outcome was observed.

In group B, significant decrease in basal tone was observed (p=0.022). Whereas in group BF tone was higher than baseline but did not reach a value of statistical significance . Three parturients in Group BF showed a hypertonus pattern (p=0.102; t-test). Uterine hypertonus with NRFHR pattern occurred in group BF only (28.5%) . Statistical analysis revealed significant difference (p=0.046; χ2test) of non reassuring fetal heart rate (NRFHR) abnormalities in group BF (n=7) when compared to group B (n=2). There was no adverse maternal or neonatal outcome.

There was no evidence of significant hypertonus uterus in either group. A higher incidence of FHR abnormalities was seen with the addition of spinal fentanyl as compared to bupivacaine alone. Labour outcomes as well as neonatal outcomes were comparable between the groups