Is inhaled nitrous oxide appropriate as primary therapy for acute chest pain in an adult?

Nitrous Oxide Should NOT Be Used as Primary Therapy for Acute Chest Pain in Adults

Inhaled nitrous oxide is not recommended for acute chest pain management and should be avoided in this population due to significant safety concerns and lack of efficacy evidence. 1

Primary Guideline Recommendations Against Use

The Society of Critical Care Medicine explicitly suggests not using nitrous oxide for pain management during chest tube removal in critically ill adults (conditional recommendation, low evidence), which extends to broader chest pain contexts. 2

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

Critical Safety Concerns Specific to Chest Pain Patients

Respiratory Compromise Risk

• The high oxygen concentration (50%) in Entonox may precipitate hypercapnic respiratory failure in at-risk patients, creating dangerous swings between hyperoxemia and hypoxemia. 1
• If patients become drowsy from hypercapnia or sedation, they may release the mask and swing from hyperoxemia to hypoxemia, particularly dangerous in those with underlying hypoxemia—a common scenario in chest pain patients. 1

Contraindications Common in Chest Pain Population

• Nitrous oxide is contraindicated in patients with known emphysema because it is less dense than air and may expand in air-filled cavities. 1
• Patients with cardiovascular compromise should avoid nitrous oxide. 3

Lack of Efficacy Evidence

• 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

Recommended Alternative Approach for Acute Chest Pain

First-Line Therapy: Opioids

• Opioids at the lowest effective dose are recommended for acute pain management in critically ill adults, with stronger evidence and better safety profiles in monitored settings. 2, 1
• For general practitioners attending chest pain patients, diamorphine (usually up to 5 mg) or morphine sulfate (usually up to 10 mg) should be given. 2
• British ambulance services traditionally use nitrous oxide, but some ambulance paramedics have used intravenous opioid nalbuphine with good effect and few side effects. 2

Adjunctive Therapies

• Nitrates should be given by sublingual spray or tablet to patients experiencing cardiac pain (unless the patient has already self-administered large doses, or if there is hypotension). 2
• Aspirin in acute myocardial infarction reduces the risk of dying; timing does not seem critical but there is evidence of synergistic effect between aspirin and streptokinase when both are given early. 2
• Oxygen should be considered for reversing any hypoxia, particularly in patients with evidence of heart failure. 2

Alternative Non-Opioid Options (Limited Evidence)

• NSAIDs administered IV, orally, or rectally may be used as an alternative to opioids for discrete and infrequent procedures (conditional recommendation, low evidence). 2

Clinical Decision Algorithm for Chest Pain Analgesia

Step 1: Assess Respiratory Status

• Check for any signs of respiratory compromise, COPD, emphysema, or risk of hypercapnia. 1
• If respiratory conditions present, absolutely avoid nitrous oxide; use opioid-based analgesia with appropriate monitoring. 1

Step 2: Assess Cardiovascular Status

• Evaluate for cardiovascular compromise, which is a contraindication to nitrous oxide. 3
• Most chest pain patients will have some degree of cardiovascular concern by definition.

Step 3: Choose Appropriate Analgesia

• Primary choice: Opioid analgesia (diamorphine 5 mg or morphine 10 mg) with appropriate monitoring. 2
• Add sublingual nitrates for cardiac pain unless contraindicated. 2
• Administer aspirin if acute coronary syndrome suspected. 2
• Provide supplemental oxygen if hypoxia or heart failure present. 2

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
• While one older study from 1987 showed pain relief in 11 of 12 myocardial infarction patients, 4 this contradicts more recent systematic reviews and guideline recommendations that prioritize safety in the modern era. 1

Do Not Confuse Evidence from Other Clinical Contexts

• Evidence from labor analgesia 3 or dental procedures are entirely different clinical contexts and should not be extrapolated to acute medical chest pain. 1
• Pediatric emergency medicine literature notes nitrous oxide "should be avoided in patients with pneumothorax, bowel obstruction, intracranial injury, and cardiovascular compromise." 1

Do Not Delay Definitive Care

• General practitioners should request an emergency (999) response rather than an "urgent" response and stay with the patient until the ambulance arrives. 2
• The focus should be on rapid diagnosis and appropriate treatment (including thrombolysis when indicated) rather than experimenting with analgesic modalities of questionable benefit. 2