# Situation: A 64-year-old man with chronic atrial fibrillation and hypertension takes digoxin 0.125 mg and hydrochlorothiazide 25 mg orally every morning. He has no heart failure or kidney disease. He is admitted with generalized weakness, leg cramps, and palpitations. His serum potassium is 2.9 mEq/L (3.5–5.0 mEq/L). The hydrochlorothiazide is held, and he has a peripheral intravenous (IV) catheter in his forearm. Before the potassium infusion is started, the nurse reviews his data: Weight: 70 kg Urine output, 0800 to 1200: 60 mL in total Serum creatinine: 1.1 mg/dL (97 µmol/L) (0.6–1.2 mg/dL) Apical pulse: 92/min, irregular Blood pressure: 122/74 mmHg What should the nurse do?

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> subject: Nursing Practice III — Care of Clients with Problems in Surgery, Oxygenation, Fluid and Electrolytes, Infectious, Inflammatory and Immunologic Response, Cellular Aberrations

## 문제

Situation: A 64-year-old man with chronic atrial fibrillation and hypertension takes digoxin 0.125 mg and hydrochlorothiazide 25 mg orally every morning. He has no heart failure or kidney disease. He is admitted with generalized weakness, leg cramps, and palpitations. His serum potassium is 2.9 mEq/L (3.5–5.0 mEq/L). The hydrochlorothiazide is held, and he has a peripheral intravenous (IV) catheter in his forearm.

Before the potassium infusion is started, the nurse reviews his data:
Weight: 70 kg
Urine output, 0800 to 1200: 60 mL in total
Serum creatinine: 1.1 mg/dL (97 µmol/L) (0.6–1.2 mg/dL)
Apical pulse: 92/min, irregular
Blood pressure: 122/74 mmHg
What should the nurse do?

## 보기

1. Start the infusion at half the ordered rate until urine output improves
2. Hold the infusion and report his urine output to the physician **✔ 정답**
3. Count his apical pulse for 1 full minute, then start the infusion
4. Start the infusion as ordered and recheck his potassium in 4 hours

**정답: 2**

## 해설

IV potassium is excreted by the kidneys and is started only after adequate urine output is confirmed. 60 mL over 4 hours is 15 mL/h, below the minimum of 0.5 mL/kg/h (35 mL/h for 70 kg), so the nurse holds the infusion and reports. A normal creatinine does not make potassium safe when current urine output is low, and a slower rate still delivers potassium the kidneys may not excrete.

## 심화 해설

Why urine output gates IV potassium
Potassium is predominantly an intracellular cation, but the small extracellular fraction is tightly regulated because even modest shifts alter the resting membrane potential of cardiac and skeletal muscle. When potassium is given intravenously, the immediate defense against hyperkalemia is transcellular shift into cells; the definitive defense is renal excretion. A patient who is not making urine cannot reliably excrete an IV potassium load, so the infusion can raise the serum potassium to a dangerous level even when the starting value is low. IV potassium is therefore held until adequate urine output is confirmed, regardless of the serum creatinine.

Interpreting this patient’s urine output
The minimum acceptable urine output for safe potassium replacement is generally 0.5 mL/kg/h. For a 70 kg patient, that threshold is 35 mL/h. This patient produced 60 mL over 4 hours, which is only 15 mL/h. That is well below the minimum, so the kidneys are not currently demonstrating the ability to clear an exogenous potassium load. The urine output is the limiting factor, not the infusion rate or the potassium level itself.

Why a normal creatinine does not override low urine output
Serum creatinine of 1.1 mg/dL reflects the steady-state balance between creatinine production and glomerular filtration over days, not minute-to-minute renal function. Acute reductions in urine output can occur before creatinine rises, so a normal creatinine does not make IV potassium safe when current urine flow is inadequate. Oliguria in this setting may reflect hypovolemia from diuretic-induced sodium and water loss, reduced effective circulating volume, or early renal hypoperfusion. The correct action is to recognize that the kidney’s excretory capacity is currently unproven and to hold the potassium.

Why the other options are unsafe
Starting the infusion at half the ordered rate still delivers potassium into a system that may not excrete it. Slowing the rate reduces the peak serum concentration but does not eliminate the risk of accumulation if renal excretion is impaired. Counting the apical pulse for a full minute is appropriate nursing care for atrial fibrillation, but it does not address the primary safety issue. A pulse of 92/min, irregular, is not a contraindication to potassium replacement; the urine output is. Rechecking potassium in 4 hours is a monitoring step that belongs after the infusion is safely started, not a justification for starting it now.

Clinical reasoning pathway

| Assessment finding | Interpretation | Nursing action |
| --- | --- | --- |
| Urine output 60 mL over 4 h (15 mL/h) | Below 0.5 mL/kg/h minimum for 70 kg patient | Hold IV potassium |
| Serum creatinine 1.1 mg/dL | Normal, but lags behind acute change | Does not override oliguria |
| Serum potassium 2.9 mEq/L | Genuine hypokalemia requiring replacement | Replace only after urine output is adequate |
| Apical pulse 92/min, irregular | Consistent with chronic atrial fibrillation | Count full minute, but not the gating factor |

Watch out! Hypokalemia itself can impair renal concentrating ability and contribute to polyuria, but that does not change the rule: IV potassium is held until urine output is documented at or above the minimum threshold. The physician must be notified so the oliguria can be evaluated and the route or timing of potassium replacement can be reconsidered.

Key point! The safety sequence for IV potassium is: assess renal excretory capacity first, then give potassium, then monitor. Urine output below 0.5 mL/kg/h means the infusion is held and the prescriber is contacted, even when the potassium is low and the creatinine is normal.

## 임상 시나리오

IV Potassium Safety GateCheck urine output before starting the infusion
IV potassium is excreted by the kidneys and is started only after adequate urine output is confirmed. The minimum acceptable output is 0.5 mL/kg/h; for a 70 kg patient this is 35 mL/h.

This patient made 60 mL over 4 hours, equal to 15 mL/h, which is below the threshold. The nurse should hold the infusion and report the urine output to the physician.

CautionA normal serum creatinine does not make IV potassium safe when current urine output is low. A slower infusion rate still delivers potassium the kidneys may not excrete.

## 핵심 개념

- **Minimum urine output for IV potassium** — 0.5 mL/kg/h; for 70 kg patient equals 35 mL/h
- **Oliguria** — Urine output below the minimum needed to excrete an IV potassium load safely
- **Renal excretion of potassium** — The definitive defense against hyperkalemia after IV potassium administration
- **Transcellular shift** — Immediate defense moving potassium into cells after an IV load

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