There have been studies reporting that combined spinal-epidural (CSE) with fentanyl and bupivacaine produce fetal bradycardia, (M.Kuczkowski, 2004) (Abrão K, 2009 ). It is unknown whether any differences in risk exist between fentanyl and bupivacaine when used as a part of the CSE procedure. Some authors have reported cases of parturients who developed uterine hyperactivity and fetal bradycardia after subarachnoid administration of fentanyl during labor. (D'Angelo & Eisenach, 1997) (Friedlander JD, 1997). It has been suggested that uterine hypertonus, leading to non-reassuring fetal heart rate tracings, might be an etiologic factor in these situations. (Landau, 2002).

We propose this study to test the hypothesis that administration of epidural fentanyl is associated with a lower incidence of fetal bradycardia compared to intrathecal fentanyl.

After approval by the Institutional Review Board and written informed consent, we plan to prospectively study pregnant patients who undergo neuraxial labor analgesia. All patients will receive combined-spinal-epidural analgesia. Patients will be randomly assigned to one of four groups by means of sealed envelope technique. Group A will receive a spinal dose of preservative-free fentanyl 25 mcg. Group B will receive one dose of spinal preservative-free 0.25% bupivacaine. Group C will receive a spinal combination of preservative-free 0.25% bupivacaine and fentanyl 25 mcg. Group D will receive spinal preservative-free 0.25% bupivacaine and epidural fentanyl 100 mcg. After the procedure, we will monitor the fetal heart rate and tocometry tracings for 20 min. Thereafter, an epidural infusion with a solution containing 0.125% bupivacaine and 2mcg/mL of fentanyl will be started. We will record demographic variables (age, and BMI), obstetric variables (parity, gestational age, cervical dilation, oxytocin infusion) and anesthetic variables (level of insertion of epidural catheter).

Primary outcomes:

Fetal heart rate (baseline, minimal and abnormal patterns)

Secondary outcomes:

• Blood pressure (systolic, diastolic and mean) measured at baseline and every 5 minutes after administration of medication.
• Dermatomal level measured after 20 minutes of medication administration.
• Pain level (visual analogue scale) after 20 minutes of medication administration.
• Patient satisfaction level (1-10 scale) after 20 minutes of medication administration.
• Uterine tone measured with tocometer at baseline and during 20 minutes after medication administration.

Inclusion Criteria:

• Older than 18 years
• Term pregnancy (> 37 weeks)
• Absence of obstetric morbidities
• Active labor
• Request of neuraxial analgesia per patient and/or obstetrician
• Combined spinal-epidural technique

Exclusion Criteria:

• Abnormal fetal heart rate tracing.
• Uterine tachysystole before neuraxial analgesia.
• Baseline blood pressure <90/60 mmHg.
• Allergies to local anesthetics or fentanyl.
• Maternal fever.
• Pruritus before performance of neuraxial analgesia.
• Contraindications for neuraxial technique.
• Unwillingness to participate.

Pregnant patients in labor

The study team will decide about sharing information upon request

Participant will be blinded. The investigators will not be blinded because they are the same care providers. In addition, the volume of intrathecal anesthetic is different when bupivacaine plus fentanyl is used in comparison with only one medication used.