This study investigates the effect of epidural fentanyl on gastric emptying in non-fasted laboring women. Half the women will be randomized to receive low-dose epidural fentanyl (<100 mcg), and half will be randomized to receive high-dose epidural fentanyl (≥100 mcg). Gastric content will be measured by ultrasonography two hours after epidural placement and compared between the groups.

Laboring women are known to be at increased risk of pulmonary aspiration in the event of general anesthesia, due to reduced lower esophageal sphincter pressure and delayed gastric emptying. Reduction in the rate of general anesthesia for cesarean delivery, improvements in airway management and premedication to improve gastric motility and increase gastric pH have greatly reduced the risk of aspiration in laboring women. This has raised questions regarding the need for restrictive fasting policies during labor, and more liberal food policies have become widespread in certain countries and birthing centers. In light of this, it is crucial to elucidate and limit any factors that may increase a woman's risk for aspiration.

Epidural opioids are usually added to the initial epidural bolus and the maintenance infusion, due to associated reduced local anesthetic dose requirements, while improving sensory block and decreasing motor block. However, systemic opioids are known to reduce gastric emptying. The effect of epidural fentanyl on gastric emptying has been investigated previously in various doses using the paracetamol absorption test. In several of these prior studies, epidural fentanyl administered in high doses (above the cut-off value of 100mcg) - either by bolus or infusion was associated with delayed gastric emptying, with no such effect with doses below this 100 mcg threshold. These studies were performed on fasting laboring women only. In addition, the paracetamol absorption test has been widely replaced by gastric ultrasonography to directly assess gastric contents by measuring the Cross-Sectional Area (CSA) of the antrum, and its feasibility has been demonstrated in laboring women.

The aim of our study is to assess the effect of high versus low dose epidural fentanyl on gastric emptying in non-fasted laboring women, using gastric ultrasonography.

Laboring women who consent to participate will be randomized to receive either high dose or low dose fentanyl in the epidural solution. A gastric ultrasound will be performed at the time of epidural placement (baseline) and two hours after the first measurement and will be compared between the two groups. Oral intake will be recorded as well in the 8 hours preceding epidural placement and between ultrasound measurements.

Inclusion Criteria:

• Laboring women ≥18 years of age
• ≥37 weeks gestation
• Singleton pregnancy with cephalad fetus
• Cervical dilatation less than 5cm
• Request for epidural analgesia

Exclusion Criteria:

• Contraindications to neuraxial analgesia
• Chronic opioid consumption
• Increased risk of emergency cesarean delivery - Trial of labor after cesarean delivery (TOLAC), twin pregnancy, non-reassuring fetal heart rate (NRFHR), dysfunctional labor, estimated fetal weight>4000g, body mass index (BMI) ≥ 40kg/m2.
• Increased risk of aspiration - Disorders of the upper gastrointestinal tract (severe gastro-esophageal reflux, history of bariatric surgery), neurological and endocrine disorders associated with gastroparesis (such as multiple sclerosis, diabetes with autonomic neuropathy)
• BMI > 40kg/m2

The participants will be blinded to their group allocation. Upon request for labor epidural analgesia, the epidural will be performed by one of the anesthesiologists working in the delivery room who will receive an envelope with the woman's randomization. The investigator performing the gastric ultrasound will be blinded to the subject's randomization as well.