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Chapter 46: Vasodilators

What do vasodilators effect? Some act primarily on primarily on arterioles, some act primarily on veins, and some act on both types of vessels. Action: Direct relaxation of VSM, producing vasodilation of arterioles which decreases afterload.
What are the three vasodilator agents? 1. Hydralazine 2. Minoxidil 3. Nitroprusside
Hydralazine effect what type of vessels? Produce selective dilation of arterioles
Minoxidil effect what type of vessels? Produce selective dilation of the arterioles
Nitroprusside and Prazosin effects what type of vessels? Produce selective dilation of the arterioles and veins
Therapeutic uses of vasodilators: Essential hypertension, Hypertensive crisis Angina pectoris HF MI Others include: pheochromocytoma, PVD, pulmonary arterial HYN, and production of controlled hypotension during surgery.
Adverse effects of vasodilators: Postural Hypotension, Reflex tachycardia, and expansion of blood volume. Place patients at an increased risk of falls.
What is reflex tachycardia? The heart beats faster when there is an unexpected change in BP due to hemorrhage, sweating or diarrhea. When this happens it leads to hypovolemia --> decreased CO= poor tissue perfusion. The SNS is then activated and the HR increases to counteract low BP
What is postural hypotension? A fall in blood pressure brought on by moving from a supine or seated position to an upright position. Decreases venous retrun to the heart by pooling.
What happens with prolonged use of vasodilators? Can cause increase blood volume and patients need a diuretic to counteract this. Causes an increase in aldosterone, decreases renal blood flow (due to reduced arterial pressure), decreases GFR because kidney is able to reabsorb more.
Hydralazine and metabolism Acetylation: some people are rapid acetylators; some are slow acetylators. To avoid hydralazine accumulation in slow acetylators dosages should be reduced
Hydralazine Therapeutic uses: Essential hypertension; Hypertensive Crisis; HF
Adverse affects of Hydralazine: Reflex tachycardia; increased blood volume; and systemic lupus erythematosus-like syndrome. Others: HA, dizziness, weakness, and fatigue (induced hypotension)
Hydralazine drug interactions:Hydralazine + Beta-blocker protection from reflex tachycardia
Hydralazine drug interactions: Hydralazine + Diuretic Prevent Na+ and water retention and expansion of blood volume
Hydralazine drug interactions: Hydralazine + antihypertensive excessive hypotension
Hydralazine drug interactions: Hydralazine + isosorbide dinitrate treatment of HF
Hydralazine dosage: Dosage usually low and gradually increased. Rapid increase can cause excessive hypotension. usual dosage for adults is 25-100mg twice a day. Dosage greater than 200 mg a day should be avoided. IV usual is 20-40mg
What is Minoxidil? produces more intense vasodilation than hydralazine but also causes more severe adverse reactions. Very dangerous and reserved for patients with severe hypertension unresponsive to safer drugs.
Adverse effects of Minoxidil Reflex tachycardia (can be co-treated with a beta-blocker), sodium and water retention (can be so severe is can cause cardiac decomposition; furosemide needed), hypertrichosis, and pericardial effects (can cause cardiac tamponade- pericardicentesis.
Minoxidil dosage: Initial dose 5 mg once a day. Max is 100 mg/day. Loading dose of 5 to 20 mg.
Describe sodium nitroprusside Acts faster than any other vasodilator available. It is the DOC for hypertensive emergencies. Causes vasodilation of venous and arteriolar dilation. Reflex tachycardia is minimal. Can trigger retention of sodium and water (furosemide needed).
Mechanism of action: Nitroprusside Breaks down to nitric oxide activated guanylate cyclase causing vasodilation.
Therapeutic uses of Nitroprusside Hypertensive emergencies
Adverse effects of Nitroprusside: Excessive hypotension: if given too rapidly it will result in HA, palpitations, nausea, vomiting, and sweating; cyanide poisoning: most likely in pt's with liver disease or with low stores of thiosulfate to cyanide detoxifier, thiocyanate toxicity
Dosages of Nitroprusside: Faint brown color is normal; solution can be degraded by light. Initial infusion should be 0.3 mcg/kg/min; max is 10 mcg/kg/min. No other drugs should be mixed with this solution.
Action of drugs that dilate arterioles: Drugs that dilate resistance vessels (arterioles) cause a decrease in cardiac afterload
Actions of drugs that dilate veins: Drugs that dilate capacitance vessels (veins) reduce the force with which blood is returned to the heart, thus reducing preload
Patient Education Teach patients about symptoms of hypotension (lightheadedness, dizziness) and advise them to sit or lie down if these occur. Avoid abrupt transitions from a supine or seated position to an upright position.
Hydralazine: General Selective dilation of arterioles Mechanism unknown Postural hypotension minimal Therapeutic uses Essential hypertension Hypertensive crisis Heart failure
Hydralazine [?] Hydralazine [Apresoline]
Adverse effects of Hydralazine Adverse effects Reflex tachycardia Increased blood volume Systemic lupus erythematosus–like syndrome Headache, dizziness, weakness, and fatigue
Drug interactions of Hyralazine Drug interactions Other antihypertensive agents Avoid excessive hypotension Combined with beta blocker to protect against reflex tachycardia and with diuretics to prevent sodium and water retention and expansion of blood volume
Minoxidil uses: Selective dilation of arterioles More intense dilation than hydralazine, but causes more severe adverse reactions Used for severe hypertension unresponsive to safer drugs
Minoxidil adverse effects: Adverse effects Reflex tachycardia Sodium and water retention Hypertrichosis Pericardial effusion
Sodium Nitroprusside: General Fastest-acting antihypertensive agent Causes venous and arteriolar dilation Administration: IV infusion Onset: Immediate (BP returns to pretreatment level in minutes when stopped) Used for hypertensive emergencies
Sodium Nirtoprusside [Nitropress] Adverse reactions: Adverse effects Excessive hypotension Cyanide poisoning Thiocyanate toxicity
A patient is prescribed hydralazine. What is most important for the nurse to teach the patient? Prevention of reflex tachycardia Hydralazine is usually combined with a beta blocker to protect against reflex tachycardia.
Which patient would most likely be prescribed sodium nitroprusside [Nitropress]? A patient with a hypertensive crisis in the intensive care unit Sodium nitroprusside is used to treat hypertensive emergencies. The medication is administered intravenously, with continuous monitoring of blood pressure
A patient with severe hypertension is prescribed minoxidil. Which medications will the nurse expect to be administered to reduce adverse responses to minoxidil? Furosemide [Lasix] and propranolol [Inderal] Minoxidil may cause adverse responses (for example, reflex tachycardia, expansion of blood volume, pericardial effusion). Minoxidil should be used with a beta blocker plus intensive diuretic therapy.