Is inhaled nitrous oxide (N2O) a suitable treatment option for acute chest pain relief in patients with a history of substance abuse or respiratory conditions?

Nitrous Oxide for Chest Pain Relief: Not Recommended

Inhaled nitrous oxide should not be routinely administered for chest pain relief, particularly in patients with respiratory conditions or those at risk of hypercapnic respiratory failure. The strongest guideline evidence advises against its use in this context due to safety concerns and lack of proven efficacy for acute medical chest pain.

Primary Guideline Recommendations

The British Thoracic Society (BTS) explicitly advises that Entonox (50:50 nitrous oxide/oxygen mixture) is best avoided in patients who are at risk of hypercapnia or hypoxaemia, which includes many patients presenting with chest pain who may have underlying cardiac or respiratory compromise 1.

Critical Safety Concerns in Chest Pain Patients

For patients with respiratory conditions:

• The high oxygen concentration (50%) in Entonox may precipitate hypercapnic respiratory failure in patients at risk, creating dangerous swings between hyperoxaemia and hypoxaemia 1
• Nitrous oxide is contraindicated in patients with known emphysema because it is less dense than air and may expand in air-filled cavities 1
• If patients become drowsy from hypercapnia or sedation, they may release the mask and swing from hyperoxaemia to hypoxaemia, particularly dangerous in those with underlying hypoxaemia 1

For patients with substance abuse history:

• While not explicitly addressed in guidelines, the sedating properties and potential for abuse with nitrous oxide warrant extreme caution 1
• The commonest side effect is dizziness (affecting 39% of users), which could be problematic in patients with substance use disorders 1

Evidence Quality and Efficacy

The evidence base for nitrous oxide in acute chest pain is remarkably weak:

• A Danish review found "no controlled studies concerning the effect of pain treatment in the pre-hospital phase" and noted that "the few available controlled studies conducted inside the hospital have not shown significant pain-relieving effects of nitrous oxide for patients suffering from pain of acute medical or surgical origin" 1
• One older randomized study from 1987 showed pain reduction in 11 of 12 patients with ischemic chest discomfort, but this represents limited and dated evidence 2

ICU Setting Guidance

The Society of Critical Care Medicine provides clear direction: "We suggest not using either local analgesia or nitrous oxide for pain management during chest tube removal in critically ill adults" (Conditional recommendation, Low evidence) 1. While this specifically addresses procedural pain, it reflects the broader concern about nitrous oxide use in critically ill patients who may have chest pain.

Alternative Approach for Chest Pain

Instead of nitrous oxide, the evidence supports:

• Opioids at the lowest effective dose for acute pain management, which have stronger evidence and better safety profiles in monitored settings 1
• For procedural pain in critically ill adults, NSAIDs administered IV, orally, or rectally as an alternative to opioids for discrete procedures (Conditional recommendation, Low evidence) 1
• Neuropathic pain medications (gabapentin, carbamazepine, pregabalin) with opioids if neuropathic component suspected (Strong recommendation, Moderate evidence) 1

Clinical Algorithm for Decision-Making

When evaluating a patient with chest pain:

1. Assess respiratory status first - Check for any signs of respiratory compromise, COPD, emphysema, or risk of hypercapnia 1

2. If respiratory conditions present - Absolutely avoid nitrous oxide; use opioid-based analgesia with appropriate monitoring 1

3. If substance abuse history - Avoid nitrous oxide due to abuse potential and sedating effects; opt for closely monitored opioid therapy 1

4. If no contraindications exist - Even in "ideal" candidates, the lack of proven efficacy for acute medical chest pain makes other analgesics preferable 1

Common Pitfalls to Avoid

• Do not assume nitrous oxide is "safer" than opioids - The evidence shows significant adverse effects including dizziness (39%), drowsiness, and potential for dangerous gas exchange abnormalities 1
• Do not use in emergency departments without appropriate scavenging equipment - Occupational health concerns exist for healthcare workers 3
• Do not confuse evidence from labor analgesia or dental procedures with acute medical chest pain - these are entirely different clinical contexts 1

The pediatric emergency medicine literature notes nitrous oxide has applications for procedural anxiety and minor trauma, but specifically cautions it "should be avoided in patients with pneumothorax, bowel obstruction, intracranial injury, and cardiovascular compromise" 1 - many of which may be present or suspected in chest pain patients.