Is Entonox (50% nitrous oxide/oxygen mixture) contraindicated for pulmonary embolism in children?

Entonox is NOT specifically contraindicated for pulmonary embolism in children, but should be avoided in this clinical scenario due to the risk of hypoxemia.

The BTS guideline explicitly recommends that Entonox should be avoided in patients at risk of hypercapnia or hypoxaemia 1, and children with PE are inherently at risk for hypoxaemia due to impaired gas exchange from pulmonary vascular obstruction.

Key Clinical Reasoning

Why Entonox is Problematic in PE

The 2017 BTS oxygen guideline provides the most relevant guidance here. While Entonox (50:50 nitrous oxide/oxygen mixture) is not explicitly listed as contraindicated for PE, the guideline clearly states that Entonox is best avoided in patients who are at risk of hypercapnia or hypoxaemia 1.

Children with PE fall squarely into this category because:

• PE causes ventilation-perfusion mismatch leading to hypoxemia 2
• PE patients commonly present with dyspnea, hypoxemia, and respiratory compromise 2
• The self-administration mechanism of Entonox creates a dangerous cycle: if the child becomes drowsy from hypoxemia, they release the mask and swing from hyperoxemia (50% oxygen in Entonox) back to hypoxemia on room air 1

Established Contraindications for Entonox

The BTS guideline notes Entonox is contraindicated in:

• Patients with known emphysema (due to gas expansion in air-filled cavities) 1
• Patients at risk of hypercapnic respiratory failure 1
• Patients at risk of hypoxaemia 1

Pediatric Considerations

The 2019 AAP/AAPD pediatric sedation guideline discusses nitrous oxide use in children but focuses on procedural sedation in otherwise healthy ASA class I or II patients 3. This guidance does not apply to acutely ill children with PE, who would not meet these criteria.

Clinical Algorithm for Pain Management in Pediatric PE

Instead of Entonox, consider:

1. First-line: Opioid analgesia (morphine, fentanyl) with appropriate monitoring
2. Adjuncts: Acetaminophen, NSAIDs (if no contraindication to anticoagulation)
3. Oxygen therapy: Titrated to maintain SpO2 94-98% via nasal cannula, simple face mask, or non-rebreather as needed 1

Important Caveats

• The FDA drug label information provided 4 appears to be for pyridoxine (vitamin B6), not Entonox, and is not relevant to this question
• Recent case reports link recreational nitrous oxide abuse to PE through hyperhomocysteinemia 5, 6, 7, 8, 9, 10, but this addresses causation rather than treatment considerations
• No pediatric-specific PE guidelines address Entonox use directly 2, 11, 12

Bottom line: While not an absolute contraindication, Entonox should be avoided in children with PE due to their inherent risk of hypoxemia and the potential for dangerous oxygen saturation fluctuations. Use alternative analgesic strategies with appropriate oxygen supplementation and continuous monitoring.