Oxytocin and Fetal Heart Rate Changes

Oxytocin is used in labor and delivery to increase the frequency of contractions and augment uterine contractile strength, thereby establishing a regular pattern of labor. However, the administration of exogenous oxytocin in the presence of an uncoordinated labor pattern confers a risk for an increase in uterine contraction frequency, resulting in inadequate relaxation periods. This leads to an increase in the basal tone of the uterus, which may lead to a tetanic contraction with the risk of decreased uteroplacental blood flow and fetal hypoxemia. Previous studies investigating low- versus high-dose oxytocin for induction or augmentation of labor have had conflicting results on the effect on fetal heart rate abnormalities. One of the limitations of these studies is that the labor analgesia was not standardized. The combination of low-dose combined spinal epidural analgesia and the high/low dose oxytocin have not been evaluated. One of the proposed mechanisms for nonreassuring fetal heart a tracing after initiation of analgesia is that the pain relief from neuraxial analgesia causes a decrease in catecholamine release by the sympathetic nervous system. The subsequent decrease in the circulating epinephrine concentration contributes to an increase in uterine tone, as epinephrine is a potent tocolytic agent. The increased tone, in turn, leads to a decrease in placental blood flow, and eventually fetal bradycardia. The primary outcome of this study is the incidence of non-reassuring fetal heart rate tracings within the first 60 minutes after the placement of combined spinal epidural analgesia

Inclusion criteria

• Healthy nulliparous or multiparous women at term (37 > weeks' gestation)
• Singleton pregnancy
• Request for neuraxial analgesia
• Oxytocin used for induction of labor or augmentation of labor per institutional protocols

Exclusion criteria

• Use of chronic analgesic medications
• Prior administration of systemic opioid labor analgesia
• Non-vertex presentation
• Contraindication to neuraxial analgesia
• Category 3 fetal heart rate tracing prior to the initiation of combined spinal epidural analgesia