Chapter 41 Diuretics

Three basic kidney functions

1) cleansing of extracellular fluid ECF and maintenance of ECF volume and composition 2) maintenance of acid-base balance 3) excretion of metabolic wastes and foreign substances

Three basic renal processes

1) filtration 2) reabsorption 3) active secretion To cleanse the entire ECF, a huge volume of plasma must be filtered. To maintain homeostasis, practically everything that has been filtered must be reabsorbed-leaving behind only a small volume of urine for excretion.

Adverse impact on ECF with diuretic use

1) hypovolemia 2) acid-base imbalance 3) altered electrolyte levels These effects can be minimized by using short acting diuretics and timing the drug administration so that the kidney is allowed to operate in a drug free manner between periods of diuresis.

Four major categories of diuretic drugs

1)loop diuretics 2)thiazide diuretics 3) osmotic diuretics 4)potassium-sparing agents

Urine output per % of solute reabsorption

1.8L for each 1% of solute reabsorption Kidneys produce 180 L of filtrate a day; a 3% blockade of solute reabsorption will produce 5.4 L of urine a day and reduce body weight by 12 pounds in 24 hours. With only a small blockade of absorption, diuretics can produce a profound effect on fluid and electrolyte composition of the body.

The healthcare provider orders furosemide [Lasix] 20 mg IV twice daily. The medication available is furosemide [Lasix] 10 mg/mL. How many mL will the nurse administer with each dose? 0.5 mL 1 mL 2 mL 4 mL

2ml

Normal serum potassium level

3.5 to 5 mEq/L

The healthcare provider orders mannitol 72 gm infusion over 24 hours. The nurse plans to set the infusion pump for how many grams per hour? 1 gm 2 gm 3 gm 4 gm

3gm

Thiazides

AKA benzothiadiazides effects similar to loop diuretics increase renal excretion of sodium, chloride, potassium, and water. Elevate plasma levels of uric acid and glucose. Principal difference between loop diuretics is maximum diuresis produced by thiazides is substantially lower than loop diuretics. Loop diuretics can be effective when urine flow is decreased, thiazides cannot.

Potassium-sparing diuretics

Can elicit two potentially useful responses: 1)produce a modest increase in urine production 2) produce a substantial decrease in potassium excretion Rarely employed alone to promote diuresis but often used to counteract potassium loss caused by thiazide and loop diuretics because of ability to decrease potassium excretion

The nurse plans to closely monitor for which clinical manifestation after administering furosemide [Lasix]? Decreased pulse Decreased temperature Decreased blood pressure Decreased respiratory rate

Decreased blood pressure

Loop Diuretics (drugs list)

Furosemide Ethacrynic acid Torsemide-only one approved for hypertension Bumetanide

The nurse caring for a patient taking furosemide [Lasix] is reviewing the patient's most recent laboratory results, which are: sodium, 136 mEq/L; potassium, 3.2 mEq/L; chloride, 100 mEq/L; blood urea nitrogen, 15 mg/dL. What is the nurse's best action? Administer Lasix as ordered. Place the patient on a cardiac monitor. Begin a 24-hour urine collection. Hold the Lasix and notify the physician.

Hold the Lasix and notify the physician

The nurse is teaching a patient who has a new prescription for spironolactone [Aldactone]. Which statement by the patient indicates that the teaching was effective? "I will use salt substitutes to lower my sodium intake." "I will increase my intake of foods that are high in potassium." "I will call my doctor if I begin having menstrual irregularities." "I will take this medication at bedtime each evening."

I will call my doctor if I begin having menstrual irregularities

Which of the following statements about mannitol [Osmitrol] are correct? (Select all that apply.) Mannitol cannot be given orally. Mannitol can cause edema. Mannitol can cause renal failure. Diuresis begins in 30 to 60 minutes after administration. Mannitol is a loop diuretic.

Mannitol cannot be given orally Mannitol can cause edema Diuresis begins in 30 to 60 minutes after administration

Reabsorption

More than 99% of water, electrolytes, and nutrients filtered at glomerulus undergo reabsorption. This conserves valuable constituents of the filtrate while allowing wastes to undergo excretion. Reabsorption of solutes (electrolytes, amino acids, glucose) takes place by way of active transport. Water then follows passively. Diuretics work primarily by interfering with reabsorption.

The increase in urine flow that a diuretic produces is directly r/t the amount of sodium and chloride reabsorption that it blocks.

Since the amount of solute in the nephron becomes progressively smaller as filtrate flows from the proximal tubule to the collecting duct, drugs that act early in the nephron have the opportunity to block the greatest amount of solute reabsorption. These produce the greatest diuresis.

The nurse is caring for a patient with heart failure who needs a diuretic. Which agent is likely to be chosen, because it has been shown to greatly reduce mortality in patients with heart failure? Furosemide [Lasix] Hydrochlorothiazide [HydroDIURIL] Spironolactone [Aldactone] Mannitol [Osmitrol]

Sprionolactone

How do diuretics work

block sodium and chloride reabsorption. By blocking the reabsorption of these solutes, diuretics create osmotic pressure within the nephron that prevents the passive absorption of water. Diuretics cause water and solutes to be retained within the nephron and promote the excretion of both

The nurse knows that diuretics mostly affect which function of the kidneys? Cleansing and maintenance of extracellular fluid volume Maintenance of acid-base balance Excretion of metabolic waste Elimination of foreign substances

cleansing and maintenance of extracellular fluid volume

The nurse should monitor for which adverse effect after administering hydrochlorothiazide [HydroDIURIL] and digoxin [Lanoxin] to a patient? Digoxin toxicity Decreased diuretic effect Dehydration Heart failure

digoxin toxicity

Thiazide type diuretics (list of meds)

hydrochlorothiazide, chlorothiazide, methyclothiazide, chlorthalidone, indapamide, and metolazone.

The nurse is reviewing the home medication list with the patient. The nurse recognizes that hydrochlorothiazide is used primarily for which condition? Hypertension Edema Diabetes insipidus Protection against postmenopausal osteoporosis

hypertension

Furosemide

loop diuretic most frequently prescribed loop diuretic blocks reabsorption of sodium and chloride in loop of Henle. 20% of filtered sodium and chloride is normally reabsorbed in the loop of Henle, interfering with reabsorption can produce profound diuresis. Therapeutic uses: reserved for situations that require rapid or massive immobilization of fluid: pulmonary edema associated with CHF; edema of hepatic, cardiac, or renal origin that has been unresponsive to less efficacious diuretics; and hypertension not controlled with other diuretics Adverse effects: severe dehydration; dry mouth; unusual thirst; oliguria; thrombosis and embolism; headache and pain in the chest, calves, or pelvis; hypotension; hypokalemia; ototoxicity Drug interactions: digoxin: loop diuretics promote potassium loss, low potassium presents a greater risk of digoxin induced toxicity and ventricular dysrhythmias increases. Frequent potassium levels should be checked as well as potassium supplements, or potassium-sparing diuretic given. Ototoxic Drug use, especially aminoglycoside antibiotics (gentamicin), concurrent with furosemide increases chances of furosemide-induced hearing loss. These combinations should be avoided. Lithium: excretion of lithium decreases in pt's with low sodium levels. Furosemide can cause lithium to accumulate to toxic levels. Antihypertensive Agents: furosemide can cause hypotension; pt's need to reduce or eliminate use of other hypotensive drugs. NSAID's: NSAID's can reduce the effects of furosemide. The diuretic effect of furosemide results from increasing renal blood flow, NSAID's prevent the increase in renal blood flow and partially blunt diuretic effects.

Which kidney function does a diuretic affect most

maintenance of ECF volume and composition

Loop diuretics

most effective diuretics available. produce more loss of fluid and electrolytes than any other diuretic. known as loop diuretics because their site of action is in the loop of Henle.

Hydrochlorothiazide

most widely used thiazide diuretic. Promotes urine production by blocking the reabsorption of sodium and chloride in the early segment of the distal convoluted tubule. 10% of filtered sodium and chloride normally reabsorb at site where thiazides act, maximum urine flow these drugs can produce is lower than with loop diuretics. Ability to promote diuresis is dependent of kidney function Therapeutic uses: hypertension, edema, diabetes insipidus (excessive production of urine in these pt's, thiazides reduces urine production by 30-50% with the mechanism being unclear); and protection against postmenopausal osteoporosis (promotes tubular reabsorption of calcium. Adverse effects: not ototoxic like loop diuretics. Adverse effects are nearly identical as loop diuretics: hyponatremia, dehydration, hypokalemia, hyperglycemia. Drug interactions: nearly identical to loop diuretics. Can increase the risk of toxicity from digoxin by promoting potassium loss; by lowering BP, thiazides can augment effects of antihypertensive drugs; by promoting sodium loss, can reduce renal excretion of lithium; NSAID's may blunt effects.

Filtration

occurs at the glomerulus. first step in formation of urination. virtually all small molecules present in the plasma undergo filtration (glucose, drugs, electrolytes, amino acids, metabolic wastes). Cells and large molecules remain behind in the blood (lipids and proteins). Each minute the kidney produces 125 ml of filtrate, which adds up to 180 L/day. Total volume of ECF in only 12.5L, kidneys process the equivalent of all the ECF in the body every 100 minutes. The ECF undergoes complete cleansing about 14 times each day.

Mannitol

osmotic diuretic creates an osmotic force that inhibits passive reabsorption of water, increasing urine flow. The degree of diuresis produced is directly r/t the concentration of mannitol in the filtrate. Has no significant effect on the excretion of potassium and other electrolytes. Therapeutic uses: prophylaxis of renal failure; reduction of intracranial pressure; reduction of intraocular pressure. Adverse effects: edema, headache, nausea, vomiting

Spironolactone

potassium sparing diuretic: Aldosterone antagonist blocks the action of aldosterone in the distal nephron. Aldosterone acts to promote sodium uptake in exchange for potassium secretion, inhibition of aldosterone has the opposite effect: retention of potassium and increased excretion of sodium. Diuresis caused by spironolactone is minimal. Effects can take up t 48 hours Therapeutic uses: hypertension and edema. Most commonly used in combination with a thiazide or loop diuretic. In these situations, spironolactone is used to counteract the potassium-wasting effects of more powerful diuretics. In pt's with severe heart failure, spironolactone reduces mortality and hospital admissions from the protective effects of aldosterone blockade in the heart and blood vessels. Adverse effects: hyperkalemia (if serum potassium rises above 5mEq/L, spironolactone should be discontinued); gynecomastia; menstrual irregularities; impotence; and deepening of the voice. Drug interactions: Because of risk of hyperkalemia, caution should be used when combining with potassium supplements, salt substitutes (which contain potassium chloride); or other potassium sparing diuretic. ACE inhibitors, angiotensin receptor blockers, and direct renin inhibitors can elevate potassium levels and be used only when clearly necessary.

Amiloride

potassium-sparing diuretic has actions similar to those of triamterene. inhibit potassium loss by direct blockade of sodium-potassium exchange in the distal nephron. produces modest diuresis. major adverse effect is hyperkalemia

Triamterene

potassium-sparing diuretic: nonaldosterone antagonists. Directly inhibits sodium reabsorption and a reduction in potassium secretion. Sodium excretion is increased and potassium is conserved. Initial responses develop in hours, compared to days for spironolactone. Diuresis is minimal. Therapeutic uses: hypertension and edema. When used alone, triamterene produces mild diuresis. when combined with other diuretics, triamterene augments diuresis and helps counteract the potassium-wasting effects of the more powerful diuretics. Adverse effects: hyperkalemia, nausea, vomiting, leg cramps, dizziness