Other Drug Therapies (Vasodilators & Sympathomimetics), Refractory Cardiac Failure And Pulmonary Edema
Effects of Vasodilators
Diuretics and Cardiac glycosides are not the only drugs used for management of Heart Failure. There are others such as Vasodilators and sympathetic stimulating drugs. We'll also discuss emergency situations such as the management of refractory cardiac failure and acute pulmonary edema.
Vasodilators: These drugs reduce the afterload by causing peripheral arteriolar dilatation and reducing venous return by venodilation. Drugs in this group are isosorbide nitrate (40 mg per 6 hours), hydralazine (25-80 mg per 8 hours). Prazosin (2- 7mg) and captopril (25-100 mg thrice daily) which are all given orally. Among these, isosorbide is predominantly a venodilator, hydralazine and captopril are more effective on the arteriolar system, and prazosin has effects on both. These drugs are indicated when cardiac failure is not responsive to diuretics and digoxin. In acute heart failure, infusion of sodium nitroprusside 25-600 ug/min brings about rapid vasodilation and the maintenance dose can be adjusted depending on the response. The effect lasts only as long as the infusion is on. Nitroprusside reduces both preload and afterload. Sodium nitroprusside is contraindicated if the systolic blood pressure is below 100 mmHg. Use of vasodilators produces remarkable improvement in many cases.
Sympathomimetic amines: These are inotropic agents i.e those that improve force of muscle contraction. Dopamine and dobutamine are the common drugs used widely. When infused intravenously at a rate of 10 ug/kg/min, dopamine increases force of cardiac contraction and cardiac output and improves renal blood flow. One ampule of dopamine (200mg) is diluted in 500ml of 5% glucose and given as a slow drip, till the desired effect is achieved. Dobutamine which is a beta-1 stimulant is given as an intravenous infusion in a dose of 2-10 ug/kg/min. The action resembles that of dopamine, but it has the advantage that it does not induce tachycardia. A new drug is amrinone which is a nonglycoside-nonsympathomimetic inotropic agent.
Management of Resistant Cardiac Failure
Refractory Cardiac Failure
Management of resistant cardiac failure (refractory cardiac failure): The term "resistant cardiac failure" is used when the condition does not improve satisfactorily even after instituting all the standard forms of therapy.
Before considering a case of cardiac failure as resistant all causes such as noncompliance with therapy, inadequate rest, excess intake of salt and therapeutic inadequacy should be excluded. Causes of resistance are:
- Severe and advanced Cardiac disease
- presence of complications such as infective endocarditis, thromboembolism or focal sepsis; or
- injudicious use of diuretics.
In such cases the correctable factors have to be rectified and drug therapy is intensified. If these fail, excess fluid and salt can be removed from the body by peritoneal or hemodialysis.
Management of Pulmonary Edema
Acute pulmonary edema
Emergency treatment of acute pulmonary edema is as follows
- Patient is hospitalized and put to rest with a back rest or cardiac table, in the position of maximum comfort.
- The patient is put on oxygen immediately.
- Morphine sulphate 3-5 mg is given intravenously over three minutes and repeated to a total dose of 15-20 mg, at 15 minutes intervals. In less acute cases, the drug can be given intramuscularly in doses of 15-20 mg. Morphine abolishes anxiety, depresses the respiratory centre, allays dypsnea and reduces the adrenergic vasoconstrictor stimuli.
- Diuretic: Furosemide 40mg should be given intravenously. If the effect is not evident in 30 minutes, the dose may be repeated.
- Aminophylline in a dose of 5mg/kg given intravenously slowly is very effective in increasing the cardiac output and relieving bronchospasm. Aminophylline has different actions such as improvement of cardiac output, stimulation of the respiratory centre, bronchodilation and diuresis. Hypotension and anaphylaxis are potential complications. In many cases the effect of aminophylline is dramatic.
- Reduction of preload: Rotating tourniquets applied to the extremities reduce venous return and thus helps in reducing preload. The venous return from three limbs is obstructed at a time and the tourniquets are rotated at 15 minutes intervals. This method of physiological venesection is very effective. Rarely open venesection to remove 300-500ml blood rapidly may be required. Venesection should not be done on hypotensive patients.
- Digitalisation: Rapid digitalisation is done by intravenous injection of 0.5-1mg digoxin when there is the indication.
- Vasodilators such as nitroprusside given intravenously may be required in intractable cases.
Once the emergency is managed successfully, further elective management depends upon the underlying condition.
© 2013 Funom Theophilus Makama