Nursing care
Diuretics: what to check before you give it
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated September 2026
Short answer
Diuretics increase urine output to reduce fluid volume, treating conditions like heart failure, hypertension, and edema. The nursing priority is electrolytes: loop diuretics like furosemide waste potassium while potassium-sparing agents like spironolactone hold onto it, and the two are frequently combined on purpose rather than by error.
What it does and why it is prescribed
Diuretics act on different segments of the nephron to reduce sodium and water reabsorption, which increases urine output and lowers circulating volume. Loop diuretics like furosemide act on the loop of Henle and produce the most aggressive diuresis, making them the first choice for acute pulmonary edema and decompensated heart failure. Thiazides act on the distal tubule and are more often used for chronic hypertension.
Potassium-sparing diuretics like spironolactone act on the collecting duct by blocking aldosterone, producing a milder diuresis but one that protects potassium rather than depleting it. Spironolactone is prescribed heavily in heart failure with reduced ejection fraction, not just for its diuretic effect but because aldosterone blockade itself slows cardiac remodeling.
Nursing considerations before giving it
Check baseline potassium, sodium, magnesium, and renal function before starting any diuretic, and weigh the patient, since daily weight is the most sensitive marker of fluid status a nurse can obtain. Review the medication list for other drugs that affect potassium, particularly ACE inhibitors, ARBs, and potassium supplements, all of which raise the risk of hyperkalemia when combined with spironolactone.
When furosemide and spironolactone are ordered together, recognize this as a deliberate combination rather than a prescribing error worth questioning. The loop diuretic drives volume off quickly, and the potassium-sparing agent offsets the potassium loss that would otherwise follow, so the pairing lets the patient get aggressive diuresis without the arrhythmia risk of hypokalemia.
What to monitor
Monitor daily weight at the same time each day, intake and output, blood pressure with orthostatic checks, and lung sounds, since diuretic response is judged as much by clinical improvement as by lab values. A weight loss of more than 2 to 3 pounds in a day signals the dose is working; a lack of any weight change over 24 to 48 hours signals it may not be.
Trend potassium closely and in opposite directions depending on the agent: furosemide can drop potassium into the 2s or low 3s within days, while spironolactone can push potassium above 5.0 mEq/L, particularly in patients with reduced kidney function. Watch renal function throughout therapy, since diuretics can precipitate acute kidney injury in a volume-depleted patient, and check for signs of dehydration such as poor skin turgor, dry mucous membranes, and hypotension.
Side effects versus adverse effects
Expected side effects include increased urinary frequency, mild dizziness on standing, and for spironolactone, gynecomastia and menstrual irregularities from its anti-androgen activity. These are uncomfortable but not dangerous and are usually managed rather than treated as reasons to stop the drug outright.
Adverse effects requiring intervention include severe hypokalemia with furosemide, which can precipitate life-threatening ventricular arrhythmias, and severe hyperkalemia with spironolactone, which carries the same arrhythmia risk from the opposite direction. Ototoxicity with high-dose or rapid IV furosemide, and acute kidney injury from volume depletion with either agent, are also adverse effects rather than tolerable side effects.
What to hold for and when to call
Hold furosemide and call for a potassium below 3.0 mEq/L, a systolic blood pressure below 90 mmHg, or signs of significant dehydration, since pushing further diuresis on a volume-depleted patient risks acute kidney injury.
Hold spironolactone and call for a potassium above 5.5 mEq/L, particularly in a patient with reduced renal function or one taking an ACE inhibitor or ARB concurrently. For IV furosemide, hold and slow future infusions for tinnitus or hearing changes, since these signal early ototoxicity that is usually reversible if caught before permanent damage.
Patient teaching
Teach the patient to weigh themselves daily at the same time, in similar clothing, and to call the clinic for a gain of more than 2 to 3 pounds in a day or 5 pounds in a week, since that signals fluid retention before symptoms appear. Advise taking the diuretic in the morning to avoid nighttime awakenings for urination.
For furosemide, teach the signs of low potassium the patient can recognize at home, such as muscle cramps and weakness, and encourage potassium-rich foods unless a supplement or spironolactone is already covering it. For spironolactone, teach patients to avoid potassium supplements and salt substitutes, which are often potassium chloride, since the combination can push potassium dangerously high without any change in diet the patient would think to mention.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our cardiovascular practice questions are the closest set to what this page covers.
Common questions
Why would a patient be on both furosemide and spironolactone?
The combination is intentional, not a duplication of therapy. Furosemide drives strong diuresis but wastes potassium, and spironolactone spares potassium while adding its own benefit in heart failure by blocking aldosterone, so together they achieve effective fluid removal without leaving the patient hypokalemic.
What potassium level should stop a diuretic dose?
For furosemide, hold and notify the provider below 3.0 mEq/L, since that level raises the risk of dangerous ventricular arrhythmias. For spironolactone, hold above 5.5 mEq/L, since potassium-sparing agents can push levels into hyperkalemic range, especially alongside an ACE inhibitor or ARB.
Why does furosemide cause hearing changes?
High-dose or rapid IV furosemide can be ototoxic, affecting the inner ear and causing tinnitus or transient hearing loss. The risk rises with faster infusion rates, so IV doses are typically given slowly, and any reported ringing or hearing change should prompt holding the next dose.
Should patients on spironolactone eat bananas?
Not without caution. Spironolactone already spares potassium, so adding potassium-rich foods, supplements, or salt substitutes on top of it can push levels into a dangerous range, particularly if kidney function is reduced.
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