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Author: Admin | 2025-04-28
Arteriolar dilatation as well. Prolonged administration of nitroglycerin (>24 hours) may produce tolerance.Sodium NitroprussideSodium nitroprusside is a potent, rapid-acting direct peripheral vasodilator useful in the treatment of severe heart failure and hypertensive emergencies.60 Direct venodilatation causes decreases in right and left ventricular filling (preload), resulting in relief of pulmonary congestion and reduced left ventricular volume and pressure. Arteriolar relaxation causes decreases in peripheral arterial resistance (afterload), resulting in enhanced systolic emptying with reduced left ventricular volume and wall stress and reduced myocardial oxygen consumption.If intravascular volume is normal or high, reduction in peripheral vascular resistance is usually accompanied by an increased stroke volume, minimizing the fall in systemic blood pressure. In the presence of hypovolemia, nitroprusside is likely to cause excessive drop in blood pressure with reflex tachycardia. Hemodynamic monitoring is useful when nitroprusside is used. Left ventricular filling pressure should be optimized and maintained at 15 to 18 mm Hg.Studies have reported improvement in clinical status in patients with low-output states and high systemic vascular resistance refractory to dopamine, although mortality was not reduced.61 Nitroprusside has been reported as particularly useful in severe heart failure caused by the regurgitant valvular lesions of aortic insufficiency and mitral regurgitation.62 Nitroprusside can decrease wall stress and myocardial work in patients with hypertension and acute ischemic heart disease. There is conflicting data about the effects of nitroprusside in patients with acute MI. Some studies indicate an adverse effect in patients treated early after onset,63 contrasting with benefit in others during the same period.64 Nitroglycerin is less likely to lower coronary perfusion pressure (produce coronary steal) and is more likely to increase blood supply to ischemic areas of the myocardium compared with nitroprusside.65 66 67 Before the reperfusion era, nitroglycerin reduced mortality in acute MI more than nitroprusside (45% versus 23%, relative reduction).68 Nitroglycerin is the preferred vasodilator in acute MI, especially when infarction is complicated by congestive heart failure. Nitroprusside may be added when elevated blood pressures are present during acute MI and acute congestive heart failure if nitroglycerin fails to produce optimal levels. Nitroprusside has effects on the pulmonary arterial system. These effects may reverse hypoxic pulmonary vasoconstriction in patients with pulmonary disease (eg, pneumonia, adult respiratory distress syndrome). This may exacerbate intrapulmonary shunting, resulting in hypoxemia.The major complication of nitroprusside is hypotension. Patients may also complain of headaches, nausea, vomiting, and abdominal cramps. Nitroprusside is rapidly metabolized to both cyanide and thiocyanate. Cyanide either is metabolized to thiocyanate in the liver or forms a complex with vitamin B6. Thiocyanate undergoes renal elimination. Patients with hepatic or renal insufficiency and patients requiring >3 μg/kg per minute for more than 72 hours may accumulate cyanide or thiocyanate and should be monitored for signs of cyanide or thiocyanate toxic effects. Cyanide toxicity is detected by the development of metabolic acidosis. When levels exceed 12 mg/dL, thiocyanate toxicity is manifest as confusion, hyperreflexia, and convulsions. Treatment of elevated cyanide or thiocyanate levels includes immediate discontinuation of the infusion. If cyanide levels are extremely elevated and
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