4: CARDIAC

Published on 16/06/2015 by admin

Last modified 16/06/2015

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ACTIONS

Antihypertensive drugs act on the vascular, cardiac, renal, and sympathetic nervous systems. They also act to lower blood pressure (BP), cardiac output, and peripheral vascular resistance.

SIDE EFFECTS

• ^**Hypotension, sedation, sexual dysfunction^**

• Calcium channel blockers—bradycardia, peripheral edema, constipation

• Beta blockers—bradycardia, decreased atrioventricular (AV) conduction, reduced cardiac contractility, ^†bronchoconstriction^†

NURSING IMPLICATIONS

1. ^*Monitor vital signs.^*

2. ^‡Teach patients about orthostatic hypotension for initial dosing (e.g., get up slowly) and other lifestyle changes—weight reduction, sodium restriction, and daily exercise.^‡

3. ^*Monitor electrolyte, hepatic, and renal serum blood studies.^*

4. ^*Avoid abrupt withdrawal of drug; may cause rebound phenomenon of excessive rise in BP.^*

5. ^*Methyldopa (Aldomet) is the drug of choice for hypertension in pregnancy.^*

Blood pressure is regulated by cardiac output (CO) and peripheral vascular resistance (PVR). Medications that influence either one of these systems lead to blood pressure control. Antihypertensive drugs that influence these systems to lower the blood pressure are angiotensin-converting enzyme (ACE) inhibitors, beta-adrenergic blockers, and calcium channel blockers (CCBs).

ACTIONS

• A—ACE inhibitors block the conversion of angiotensin I to angiotensin II, a vasoconstrictor. This block causes vasodilation and therefore decreases PVR, resulting in a decrease in blood pressure. Aldosterone is also blocked, causing a decrease in sodium and water retention.

• B—Beta-adrenergic blockers block the beta₁-receptors in the heart, which results in decreased heart rate and decreased force of contraction.

• C—CCBs block calcium influx into the beta-receptors, decrease the force of the myocardial contraction, reduce heart rate, and decrease PVR.

USES

• Mild-to-moderate essential hypertension

• Either as separate drugs or frequently in combination with another drug

NURSING IMPLICATIONS

1. ^*Initial drug selection starts with a thiazide diuretic, typically followed by a beta-adrenergic blocker or an ACE inhibitor or CCB.^*

2. ^‡Take medication as prescribed; do not stop abruptly.^‡

3. ^‡Teach patient never to double-up on doses if a dose is missed.^‡

4. ^‡Change positions slowly; watch for postural hypertension.^‡

5. ^‡Avoid over-the-counter medications.^‡

6. ^‡Take caution in hot weather, hot showers, hot tub baths, or prolonged sitting or standing because these may aggravate low blood pressure.^‡

7. ^‡Teach patients about multidrug therapy; instruct them not to discontinue a previous antihypertensive medication when another medication is started.^‡

Beta-Blockers

ACTIONS

Beta₁ action is primarily on the heart—decreases rate, decreases force of contraction, and delays impulse conduction. Beta₂ action is primarily on the heart, but it also blocks receptors in the lungs and can cause bronchoconstriction.