Pain Management in Myocardial Infarction

Primary Analgesic: Morphine Sulfate

• The American College of Cardiology recommends morphine sulfate administered intravenously in doses of 2 to 4 mg with increments of 2 to 8 mg repeated at 5 to 15-minute intervals as the analgesic of choice for myocardial infarction, due to its ability to block sympathetic efferent discharge centrally, reduce anxiety and circulating catecholamines, and alleviate work of breathing in patients with acute pulmonary edema 1, 2, 3, 4
• Morphine works through multiple beneficial mechanisms beyond simple analgesia, including reducing myocardial oxygen demand by decreasing preload and afterload, and is particularly beneficial in patients with acute pulmonary edema 3, 4

Dosing Protocol

• The initial dose of morphine sulfate should be 2 to 4 mg IV, then titrate with increments of 2 to 8 mg repeated at 5 to 15-minute intervals based on pain relief and hemodynamic response, with relatively large cumulative doses of 2 to 3 mg/kg occasionally required 1, 3, 4

Managing Morphine Side Effects

• For respiratory depression, administer naloxone 0.1 to 0.2 mg IV every 15 minutes, though this will reverse pain relief as well 2
• For excessive bradycardia, give atropine 0.5 to 1.5 mg IV 2
• For hypotension with inappropriate bradycardia, use leg elevation, fluids, and atropine 3, 4

Alternative Opioid Analgesics

• If morphine is contraindicated, hydromorphone is an acceptable alternative 3, 4

Adjunctive Anti-Ischemic Therapy for Pain

• Intravenous nitroglycerin can be used for ongoing chest pain, starting with 5 to 10 µg/min and increasing by 5 to 10 µg/min every 5 to 10 minutes while monitoring blood pressure 3, 4
• Oxygen should be administered to hypoxemic patients, while routine oxygen in normoxemic patients may increase coronary vascular resistance 2
• Beta-adrenergic blocking agents can reduce myocardial oxygen demand 3, 4

Absolutely Contraindicated Analgesics

• NSAIDs are contraindicated and must be discontinued immediately, as they are associated with increased risk of death, reinfarction, cardiac rupture, hypertension, heart failure, and renal insufficiency 1, 2

Critical Timing Consideration

• Effective analgesia should be promptly administered at the time of diagnosis and not unreasonably delayed to evaluate the results of anti-ischemic therapy or reperfusion 3, 4