Congestive heart failure (CHF), results from damage or disease which impairs the heart's ability to pump blood efficiently. Because the heart's pumping action can't keep up to meet the body's needs, blood backs up in the blood vessels, creating fluid overload and congestion in the vessels and organs. Heart failure is a chronic disease requiring lifelong management. Fluid overload is its chief symptom. Excess fluid accumulates in the lungs, making breathing difficult, and in the feet and legs, causing swelling. Over time, fluid overload can affect the entire body.
Diuresis
To get rid of the excess water, doctors prescribe medications called diuretics that trigger the kidneys to make large amounts of urine. The kidneys filter the blood and make urine. In CHF, the feedback systems in the body often trigger the kidneys to retain water, even when it is already in excess. Diuretics, also known as water pills, cause the kidney to draw water out of the blood and excrete it in urine. This effect, known as diuresis, reduces fluid overload by increasing urine production. Because their effect is temporary, most patients with CHF take a daily diuretic, and some patients take more than one kind.
Loop Diuretics
Loop diuretics, such as furosemide and bumetanide, are the strongest diuretics. They work by triggering the kidneys to filter salt from the blood and into the urine. Water follows salt, so water leaves the body as urine. These drugs produce more loss of fluid than any other diuretic and are the most frequently prescribed. However, loop diuretics also pull potassium, an important electrolyte, out of the body. Doctors often prescribe a potassium supplement for people taking these diuretics because low potassium levels can cause serious heart arrhythmias. Also, for patients who take digoxin, as well as a loop diuretic, low potassium creates a high risk of digoxin toxicity. Loop diuretics may be taken as pills or given intravenously to patients hospitalized with severe CHF.
Thiazide Diuretics
Thiazide diuretics increase renal excretion of sodium, potassium and water, but to a much lesser degree than the loop diuretics. Because their diuretic effect is relatively mild, they are prescribed for CHF in patients with mild fluid overload. Like the loop diuretics, they cause depletion of potassium which must then be replaced. Hydrochlorothiazide is the most commonly prescribed medication in this group.
Potassium-sparing Diuretics
Potassium-sparing diuretics differ from thiazide and loop diuretics in two key areas: they produce much less diuresis, and instead of causing potassium depletion, they cause potassium retention. For this reason, they are sometimes prescribed with thiazide or loop diuretics in order to obtain a balance of potassium. However, if they are taken alone, they may cause dangerously high levels of potassium. Spironolactone is the most commonly prescribed potassium-sparing diuretic.
Problems with Diuretics
The increased frequency of urination caused by diuretics can continue up to six hours after taking a dose, and many people find this annoying or inconvenient. However, taking diuretics as prescribed by a doctor is key to managing CHF. Patients who stop taking them without a doctor's advice often experience exacerbations of CHF that require hospitalization. On the other hand, diuretics can cause problems when other systems in the body are disrupted. For example, digestive upsets like vomiting or diarrhea cause loss of both water and potassium. In these situations, taking diuretics can lead to dehydration, low blood pressure, and low potassium levels.
References
- Pharmacology for Nursing Care, Richard D. Lehne, 2006
- MayoClinic.com: Furosemide (Oral Route)
- American Heart Association: Heart Failure
- MedicineNet.com: Congestive Heart Failure
