The acronym MONA (Morphine, Oxygen, Nitroglycerin, and Aspirin) historically served as a rapid reminder for the initial emergency treatment of a suspected heart attack (MI). While once a routine sequence, the application of MONA has significantly changed as medical science refines the standard of care. The core goal of this initial treatment remains to reduce damage to the heart muscle while managing symptoms. This article explores what each component of MONA entails and how modern guidelines have adjusted this long-standing protocol.
Defining Myocardial Infarction and the Need for MONA
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow to a section of the heart muscle is severely reduced or completely blocked. This blockage is usually caused by a blood clot forming on a ruptured plaque within a coronary artery. The interrupted blood supply leads to ischemia, starving the heart tissue of oxygen and nutrients. If blood flow is not quickly restored, the heart muscle cells suffer irreversible damage and die (necrosis). The necessity of immediate intervention is emphasized by the phrase “time is muscle.” Initial emergency treatments, like those represented by MONA, are designed to stabilize the patient and limit damage until definitive treatment, such as opening the blocked artery, can occur.
Aspirin and Nitroglycerin: Addressing Clotting and Blood Flow
Aspirin (A) and Nitroglycerin (N) are the two components of MONA that directly address the mechanical and circulatory issues of an MI. Aspirin is the most immediate intervention, provided the patient has no known allergy. Its primary function is anti-platelet aggregation, preventing the blood clot causing the MI from growing larger. Aspirin works by irreversibly inactivating the cyclooxygenase (COX-1) enzyme in platelets, blocking the formation of the clot-promoting substance thromboxane A2. The standard loading dose (162 to 325 milligrams) is typically chewed for rapid absorption, stabilizing the coronary blockage and reducing the risk of the clot extending.
Nitroglycerin (N), also known as glyceryl trinitrate, promotes vasodilation (widening of blood vessels). It is converted into nitric oxide, which relaxes the smooth muscle in the walls of the arteries and veins. This dilation lowers the heart’s workload by reducing resistance and improves blood flow to the heart muscle, helping to relieve chest pain (angina). Nitroglycerin is often given sublingually or intravenously, and its use is reserved for patients who continue to experience ischemic chest pain or have uncontrolled hypertension.
Oxygen and Morphine: Symptom Management and Supportive Care
Oxygen (O) and Morphine (M) were traditionally included in MONA as supportive measures to ease symptoms and reduce strain on the heart. Morphine is a powerful opioid analgesic used to relieve severe chest pain persisting despite nitroglycerin use. By alleviating pain, morphine reduces anxiety and lowers the body’s sympathetic nervous system response, which otherwise increases the heart’s oxygen demand and workload. However, the use of morphine is now cautious due to evidence suggesting potential drawbacks. Some studies indicate that morphine may delay or reduce the effectiveness of certain oral antiplatelet medications given to prevent further clotting. For this reason, it is reserved for patients with severe pain unresponsive to other treatments.
Historically, supplemental Oxygen (O) was given routinely to all MI patients to increase oxygen delivery to the ischemic heart muscle. Current evidence challenges this practice, finding that routine oxygen administration is not beneficial for patients who are not hypoxic (blood oxygen saturation is normal, typically above 90% or 94%). Giving too much oxygen (hyperoxia) can cause harm by constricting coronary blood vessels, potentially reducing blood flow to the struggling heart and increasing infarct size.
The Evolution of the MONA Protocol
While MONA remains a helpful teaching tool, its application in modern emergency medicine is guided by rigorous clinical evidence rather than routine. The current standard of care prioritizes immediate anti-clotting and reperfusion strategies over blanket symptom management. The components are selectively applied based on necessity, not administered to every patient. Aspirin (A) remains universally recommended and should be given immediately to nearly all patients without a contraindication. Nitroglycerin (N) is used to manage ongoing chest pain or high blood pressure. Oxygen (O) is administered only when the patient shows signs of low blood oxygen saturation, and Morphine (M) is reserved for severe pain that cannot be controlled by nitroglycerin. This shift reflects a move toward evidence-based medicine, tailoring interventions to the individual patient’s physiological needs.