Can nitrous oxide be used safely for analgesia in labor, and what are its contraindications, side effects, fetal effects, and alternative pain‑management options?

Nitrous Oxide in Labor and Delivery

Direct Answer

Nitrous oxide (50% N₂O/50% O₂) can be safely used for labor analgesia in most healthy parturients, offering modest pain relief with minimal maternal or fetal side effects, though neuraxial analgesia remains superior for pain control. 1, 2

Safety Profile

Maternal Safety

• Nitrous oxide demonstrates an excellent safety profile when properly administered during labor 2
• The most common side effect is dizziness, occurring in approximately 39% of patients 3, 4
• Other frequent effects include drowsiness, nausea, and headache, all of which are self-limiting 4
• The self-administration mechanism provides inherent safety: if excessive drowsiness occurs, the patient releases the mask and returns to breathing ambient air 3

Fetal and Neonatal Safety

• Nitrous oxide is safe for newborns with no adverse neonatal outcomes documented in systematic reviews 2
• No waiting period is required for breastfeeding after nitrous oxide use due to rapid clearance by exhalation 3

Absolute Contraindications

Avoid nitrous oxide in the following clinical scenarios:

• Patients at risk of hypercapnic respiratory failure (BTS Grade D recommendation) 3, 4
• Known emphysema or significant COPD - nitrous oxide may expand air-filled cavities 3
• Opioid-dependent women on medication-assisted treatment (MAT) - nitrous oxide may be less effective and increases sedation risk 3
• Pneumothorax, bowel obstruction, or intracranial injury 5
• Severe maternal respiratory compromise or hypoxemia 3

COVID-19 Context

• Avoid nitrous oxide during COVID-19 pandemic due to potential aerosolization risk, despite limited analgesic efficacy 3

Efficacy Considerations

Pain Relief Reality

• Nitrous oxide is not a potent labor analgesic but provides adequately effective analgesia for many women 2
• 40-60% of women using nitrous oxide convert to epidural analgesia 1
• Analgesic efficacy is inferior to neuraxial techniques but superior to no intervention 1, 2

Patient Satisfaction

• Despite modest pain relief, satisfaction surveys indicate women value the sense of control and mobility nitrous oxide provides 1
• Most effective for mild-to-moderate labor pain or as a bridge to epidural placement 6, 7

Clinical Algorithm for Use

Step 1: Screen for Contraindications

• Assess respiratory history: any COPD, emphysema, or chronic respiratory disease? If yes → do not use 3
• Check substance use history: is patient on methadone or buprenorphine? If yes → avoid nitrous oxide, offer neuraxial analgesia early 3
• Evaluate hemodynamic stability: any signs of respiratory compromise or hypoxemia? If yes → do not use 3

Step 2: Appropriate Candidates

• Healthy parturients desiring mobility and control 1
• Early labor or mild-to-moderate pain 6, 7
• Women declining or waiting for epidural placement 1
• Postpartum procedures (e.g., perineal repair) 1

Step 3: Administration Protocol

• Use 50:50 mixture (Entonox) via self-administered demand valve 3
• Instruct patient to begin inhalation at contraction onset for rapid effect (within few breaths) 3
• Monitor with pulse oximetry as best practice 3, 4
• Have neuraxial backup plan ready, as conversion rate is high 1

Alternative Pain Management Options

When nitrous oxide is contraindicated or inadequate:

First-Line Alternative

• Neuraxial analgesia (epidural or combined spinal-epidural) provides superior pain control and is the gold standard 3
• Particularly recommended for opioid-dependent women, who should receive early neuraxial analgesia 3

Other Options

• Systemic opioids (fentanyl, morphine) - though less effective than neuraxial and with neonatal effects 6
• Patient-controlled epidural analgesia (PCEA) offers flexibility with reduced drug consumption 3
• Multimodal postpartum analgesia: NSAIDs (ibuprofen, ketorolac) plus acetaminophen 3

Critical Pitfalls to Avoid

• Do not assume nitrous oxide is "safer" than opioids - it has significant side effects (39% dizziness rate) and specific contraindications 4
• Do not use in opioid-dependent patients - this population requires neuraxial techniques for effective analgesia 3
• Do not use without pulse oximetry monitoring when available 3, 4
• Never administer to patients with respiratory compromise - risk of dangerous hypercapnia/hypoxemia swings 3
• Avoid opioid agonist-antagonists (nalbuphine, butorphanol) in any patient who has used nitrous oxide or opioids, as these can precipitate withdrawal 3

Special Populations

Opioid Use Disorder (OUD)

Inhaled nitrous oxide should be avoided because it may be less effective in opioid-dependent women and increases sedation risk with concurrent MAT use 3

Cesarean Section

• Neuraxial anesthesia (spinal or epidural) is strongly preferred over general anesthesia 3
• Nitrous oxide as part of general anesthesia does not preclude breastfeeding due to rapid clearance 3