Labor Analgesics

Key Points

• All opioids cross the placenta — neonatal respiratory depression risk increases when birth occurs while opioid is still circulating in fetal system
• Epidural anesthesia: Most effective labor pain control; bupivacaine + fentanyl in epidural space; blocks T10–S5; most common side effect = maternal hypotension → preload with 500–1000 mL IV fluid before placement
• Opioid agonist-antagonists (butorphanol, nalbuphine): Less respiratory depression than pure opioids — but precipitate withdrawal in opioid-dependent patients; assess history before administering
• Naloxone (Narcan): Opioid antidote; available on all labor units; reverses respiratory depression in birthing person or neonate — do NOT give to neonate of opioid-dependent mother (precipitates withdrawal seizures)
• Nitrous oxide (50% N2O/50% O2): No fetal sedation; patient-controlled; rapid onset and clearance

Analgesic Categories in Labor

Category	Medications	Route	Primary Use
Anxiolytic/adjunct	Hydroxyzine (Vistaril)	PO, IM	Early labor anxiety; augments opioid effect
Antiemetic/adjunct	Promethazine (Phenergan)	PO, IM, IV	Nausea; opioid adjunct
Opioid agonist-antagonist	Butorphanol (Stadol), Nalbuphine (Nubain)	IM, IV, SQ	Moderate–severe labor pain; less respiratory depression than pure opioids
Potent opioid	Fentanyl (Sublimaze)	IV, epidural	Moderate–severe pain; ultra-short acting
Inhaled analgesic	Nitrous oxide (N2O)	Inhaled (self-administered)	Mild–moderate pain; patient-controlled
Regional anesthesia	Bupivacaine + Fentanyl	Epidural catheter	Comprehensive labor analgesia

Systemic Opioid Analgesia

Hydroxyzine (Vistaril)

Class: Anxiolytic/antihistamine. Route: Oral or IM.

Use: Early or latent labor to reduce anxiety and allow rest. Not effective as primary analgesic — no direct pain-relieving properties. Also provides antiemetic and antihistamine effects.

Adverse Effects: Dry mouth, constipation, dizziness, headache, drowsiness.

Promethazine (Phenergan)

Class: Antiemetic/phenothiazine. Route: Oral, rectal, IM (deep), IV.

Use: Nausea and vomiting in labor; adjunct to opioids to reduce required opioid dose and treat opioid-induced nausea.

IV Administration Safety: Must be diluted with 5–10 mL normal saline and administered slowly (over 5–10 minutes) — undiluted IV promethazine is caustic and can cause tissue necrosis.

Opioid Agonist-Antagonists

Butorphanol (Stadol) and Nalbuphine (Nubain)

Mechanism: Partial opioid agonist at kappa receptors + antagonist at mu receptors → provides analgesia with less respiratory depression than pure opioids; ceiling effect on respiratory depression.

Routes: Butorphanol — IM or IV. Nalbuphine — IM, IV, or SQ.

Critical Safety Concern: Both drugs are opioid antagonists at mu receptors — can precipitate acute opioid withdrawal in opioid-dependent patients (sweating, agitation, rapid HR, severe pain, seizures). Assess for opioid use disorder before administration.

Adverse Effects: Dizziness, nausea, sedation, respiratory depression (less than pure opioids), urinary retention (nalbuphine).

Fentanyl

Class: Potent synthetic opioid. Routes: IV (systemic) or epidural.

Properties: Ultra-short-acting; rapidly metabolized; does NOT accumulate in the fetus as significantly as longer-acting opioids. Monitoring: pulse oximetry recommended during IV use; naloxone immediately available.

Adverse Effects: Bradycardia, hypotension, sedation, nausea, respiratory depression (potentially fatal).

Nitrous Oxide (N2O)

• Concentration: Fixed at 50% nitrous oxide / 50% oxygen — cannot be altered by nurse or patient
• Mechanism: Releases neurotransmitters that act like opioids; alters pain perception in the spinal cord dorsal horn
• Control: Patient must hold the mask themselves — gas is NOT free-flowing; requires patient effort to inhale
• Timing: Begin 30 seconds before contraction peak to allow gas to take effect
• Fetal Safety: Does NOT cause fetal sedation — unlike opioids; rapid clearance
• Adverse Effects: Nausea, vomiting, dizziness
• Caution: Do NOT combine with IV opioids — increased respiratory depression risk

Epidural Anesthesia

Medications: Bupivacaine (Marcaine) + Fentanyl infused continuously into the epidural space (outside spinal cord, between vertebrae).

Sensory Block: T10 to S5 — eliminates pain from uterine contractions and perineum while maintaining some perineal pressure sensation.

Most Common Adverse Effect: Maternal hypotension (peripheral vasodilation from sympathetic block).

Pre-Epidural Nursing Actions

1. Obtain provider orders; verify informed consent obtained by anesthesia provider
2. Review platelet count — platelets <150,000/µL increases epidural hematoma risk; notify anesthesia provider
3. Administer IV fluid bolus 500–1,000 mL (lactated Ringer’s or NS) 10–60 minutes prior to insertion (volume expansion to prevent hypotension)
4. Apply continuous EFM; BP monitoring; pulse oximetry
5. Assist patient to sitting or side-lying C-shape position (maximizes vertebral space for needle insertion)

Post-Epidural Nursing Monitoring

• Vital signs q5 min × 30 min after placement (watch for hypotension)
• FHR continuous monitoring — epidural hypotension can reduce uteroplacental perfusion → fetal bradycardia
• Assess motor block level — patient should maintain some leg sensation and ability to flex knees
• Urinary retention risk — bladder assessment or catheterization may be needed
• Fall risk — loss of sensation in lower extremities; bed rest typically required

Epidural Contraindications

Coagulopathy, thrombocytopenia, hypovolemia, allergy to local anesthetic, active infection at insertion site, severe cardiac disease (aortic or mitral valve stenosis, severe left ventricular outflow obstruction).

Naloxone (Narcan) — Opioid Antidote

Mechanism: Competitive opioid receptor antagonist — rapidly displaces opioids from receptors and reverses respiratory depression.

Available on all labor units — due to systemic opioids used for labor analgesia.

Administration:

• Birthing person: IV push for respiratory depression (respiratory rate <12/min, oxygen saturation decreased)
• Neonate: Given if opioid-related respiratory depression after delivery (slow respirations, weak cry, poor color)

Naloxone Caution in Neonates

Do NOT administer naloxone to a neonate of an opioid-dependent mother. In a neonate with maternal opioid dependence, naloxone precipitates acute opioid withdrawal, which can cause seizures. Supportive respiratory care is used instead.

Nursing Priorities

Before Any Analgesic:

• Assess FHR, maternal vital signs, cervical dilation, and stage of labor
• Review opioid history (risk for dependency/withdrawal)
• Confirm opioid antidote (naloxone) availability

After Systemic Opioids:

• Monitor maternal respirations and oxygen saturation
• Assess FHR for decelerations
• Time dose relative to expected delivery — opioids given close to delivery increase neonatal respiratory depression risk
• Keep side rails up; assist with ambulation (sedation risk)

Related Concepts

• uterotonics — Used concurrently during labor induction; analgesics required for augmented labor
• nursing-care-during-the-first-stage-of-labor — Labor monitoring and pain management integration
• pain-management — Pain management principles applied across settings
• fhr-and-uc-intervention-framework — FHR monitoring during analgesic administration
• analgesics — General analgesic drug class principles

Self-Check

1. A patient in labor requests pain medication. She reports occasional heroin use. The provider orders nalbuphine (Nubain). What is the priority nursing action before administering?
2. After an epidural is placed, the patient’s BP drops from 118/74 to 80/50 and FHR shows bradycardia. In what order should the nurse respond?
3. A neonate is born with respiratory depression 45 minutes after the mother received IV fentanyl. The mother is known to use illicit opioids. Should the nurse administer naloxone to the neonate?