Why is nitroglycerin (nitro) used to treat pulmonary edema?

From the Guidelines

Nitroglycerin is used for pulmonary edema because it effectively reduces preload and afterload, which decreases the workload on the heart and improves cardiac function. When administered, nitroglycerin causes venodilation, reducing blood return to the heart (preload), and arterial vasodilation, decreasing resistance against which the heart pumps (afterload) 1. This dual action helps reduce pulmonary congestion by decreasing pulmonary capillary pressure and improving left ventricular function.

Key Points to Consider

• For acute pulmonary edema, nitroglycerin is typically started as an IV infusion at 5-10 mcg/min and titrated upward every 3-5 minutes based on response, usually not exceeding 200 mcg/min.
• Sublingual nitroglycerin 0.4 mg can be given while IV access is established.
• Blood pressure must be monitored closely during administration, maintaining systolic BP above 90-100 mmHg to prevent hypotension.
• Nitroglycerin works rapidly, with effects seen within minutes, making it valuable in the emergency management of pulmonary edema, particularly when caused by acute heart failure or acute coronary syndromes.

Important Considerations

• Patients with HF and hypertension, coronary ischemia, or significant mitral regurgitation are often cited as ideal candidates for the use of intravenous nitroglycerin 1.
• However, tachyphylaxis to nitroglycerin may develop within 24 hours, and up to 20% of those with HF may develop resistance to even high doses 1.

Administration and Monitoring

• The use of intravenous nitroglycerin, nitroprusside, or nesiritide may be considered an adjuvant to diuretic therapy for relief of dyspnea in patients admitted with acutely decompensated HF 1.
• It is essential to closely monitor patients for potential side effects and adjust the treatment plan accordingly.

From the FDA Drug Label

Dilatation of the veins promotes peripheral pooling of blood and decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure and pulmonary capillary wedge pressure (preload). Arteriolar relaxation reduces systemic vascular resistance, systolic arterial pressure, and mean arterial pressure (afterload). Dilation of the coronary arteries also occurs Elevated central venous and pulmonary capillary wedge pressures, and pulmonary and systemic vascular resistance are also reduced by nitroglycerin therapy

Nitroglycerin is used to treat pulmonary edema because it reduces preload and afterload, which in turn decreases pulmonary capillary wedge pressure. This reduction in pressure helps to alleviate the fluid buildup in the lungs that characterizes pulmonary edema. The dilation of veins and arterioles caused by nitroglycerin also contributes to this effect by reducing the amount of blood returning to the heart and decreasing the resistance in the pulmonary vasculature. 2 3

From the Research

Treatment of Pulmonary Edema with Nitro

• Nitroglycerin is used to treat pulmonary edema due to its ability to reduce preload and afterload, thereby decreasing the amount of fluid in the lungs 4, 5, 6.
• The use of high-dose intravenous nitroglycerin has been shown to be effective in improving the condition of patients with hypertensive cardiogenic pulmonary edema 4.
• Nitroglycerin preparations are considered a mainstay of therapy for acute cardiogenic pulmonary edema, along with morphine sulfate, furosemide, and other medications 6.
• The treatment of cardiogenic pulmonary edema often includes diuretics, possibly morphine, and often nitrates, with the goal of early stabilization of oxygenation and ventilation 7.

Mechanisms and Treatment Approaches

• The pathophysiology of cardiogenic pulmonary edema is complex and involves multiple mechanisms, including increased hydrostatic pressure and impaired alveolar fluid clearance 5, 7.
• Treatment approaches for cardiogenic pulmonary edema include reducing venous return, reducing systemic vascular resistance, and providing inotropic support as needed 5.
• The use of newer approaches, such as nesiritide, high-dose vasodilators, milrinone, and vasopressin receptor antagonists, may be considered in the treatment of cardiogenic pulmonary edema, although larger clinical trials are needed to determine their effectiveness 7.

Clinical Evidence and Guidelines

• The management of acute cardiogenic pulmonary edema has historically been based on anecdotal evidence, but recent articles provide evidence-based outcomes that suggest changing standard therapy and using adjunctive medications 8.
• Furosemide, morphine, and nitroglycerin have been the baseline standard for drug therapy in cardiogenic pulmonary edema management, but other treatment modalities may result in improved outcomes and decreased adverse events 8.