# Situation: A 70-year-old man with benign prostatic hyperplasia (BPH) has had a weak stream and dribbling for several months. He comes to the emergency room because he has not been able to void for 12 hours. His lower abdomen is tender, a firm, rounded mass is felt above the pubis, and his creatinine is 2.1 mg/dL (186 µmol/L). The physician orders insertion of an indwelling urinary catheter. The catheter drains 1,100 mL. Over the next 4 hours, his hourly urine output is 350, 420, 460, and 480 mL, and his blood pressure falls from 150/90 mmHg to 118/72 mmHg. Which action should the nurse take?

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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 70-year-old man with benign prostatic hyperplasia (BPH) has had a weak stream and dribbling for several months. He comes to the emergency room because he has not been able to void for 12 hours. His lower abdomen is tender, a firm, rounded mass is felt above the pubis, and his creatinine is 2.1 mg/dL (186 µmol/L). The physician orders insertion of an indwelling urinary catheter.

The catheter drains 1,100 mL. Over the next 4 hours, his hourly urine output is 350, 420, 460, and 480 mL, and his blood pressure falls from 150/90 mmHg to 118/72 mmHg. Which action should the nurse take?

## 보기

1. Report the high output and monitor fluids and electrolytes **✔ 정답**
2. Clamp the catheter for an hour to slow the urine flow
3. Limit his oral fluids until the output falls below 200 mL/h
4. Remove the catheter now that the bladder has been drained

**정답: 1**

## 해설

After relief of a long-standing obstruction, the kidneys can excrete a very large volume of urine along with sodium and potassium (post-obstructive diuresis). His output far exceeds normal and his blood pressure is falling, so the nurse reports the output and closely monitors intake and output, vital signs, and electrolytes so that fluids can be replaced as prescribed.

## 심화 해설

Clinical situation

A 70-year-old man with benign prostatic hyperplasia presents with acute urinary retention. After catheter insertion, he drains 1,100 mL immediately, then produces 350, 420, 460, and 480 mL/h over the next 4 hours. His blood pressure drops from 150/90 mmHg to 118/72 mmHg. The correct nursing action is to report the high output and monitor fluids and electrolytes.

Why this is post-obstructive diuresis

Prolonged bladder outlet obstruction from BPH causes upstream pressure to be transmitted to the kidneys. Over time, this leads to impaired renal concentrating ability and accumulation of retained solutes such as urea and sodium. When the obstruction is suddenly relieved by catheterization, the kidneys begin excreting large volumes of dilute urine. This phenomenon is called post-obstructive diuresis. The urine output in this patient — roughly 1.7 L over 4 hours — far exceeds the normal range of approximately 0.5–1 mL/kg/h, confirming a clinically significant diuresis.

Key point! Post-obstructive diuresis is usually self-limited, but it can cause hypovolemia, hypotension, and electrolyte imbalances — particularly hyponatremia and hypokalemia — if fluid and electrolyte replacement does not keep pace with urinary losses.

Interpreting the falling blood pressure

The drop from 150/90 mmHg to 118/72 mmHg is an early warning sign. In the context of massive urine output, this reflects intravascular volume depletion rather than a benign change. Acute kidney injury and its recovery are closely tied to blood pressure regulation. Renal perfusion depends on adequate circulating volume and systemic pressure; when diuresis outpaces replacement, the falling blood pressure signals that the patient is moving toward hypovolemia, which can secondarily impair renal recovery and precipitate further kidney injury [2]. This is why the nurse must not wait for the output to slow on its own.

Why the other options are unsafe

| Option | Rationale for rejection |
| --- | --- |
| Clamp the catheter for an hour | Clamping re-creates obstruction and raises intravesical pressure. It does not address the underlying diuresis and risks re-injury to the bladder and kidneys. |
| Limit oral fluids until output falls below 200 mL/h | Fluid restriction during post-obstructive diuresis can worsen hypovolemia and hypotension. Replacement is guided by output and hemodynamic status, not by an arbitrary output threshold. |
| Remove the catheter now | The bladder was chronically overdistended. Early removal risks incomplete emptying, re-retention, and loss of the ability to accurately measure ongoing output. |

Nursing priorities and monitoring

The nurse should report the high output immediately and then implement close monitoring. Essential parameters include hourly intake and output, vital signs with attention to orthostatic changes, and serum electrolytes — especially sodium and potassium — along with creatinine trends. Fluid replacement is prescribed based on these data, not on a fixed rule. The patient’s elevated creatinine of 2.1 mg/dL (186 µmol/L) indicates pre-existing acute kidney injury from the obstruction; recovery depends on maintaining adequate renal perfusion while the diuresis resolves.

Watch out! A common exam trap is to assume that high urine output always means the kidneys are fully recovered. In post-obstructive diuresis, high output can coexist with worsening hypovolemia and electrolyte loss. The falling blood pressure is the clue that the patient needs active management, not passive observation.References (research sources)

- [2]Renal diseases and blood pressure dysregulation in acute care: Pathophysiology, clinical patterns.Research articleSu YJ. (2026) · DOI: 10.5527/wjn.121561

## 임상 시나리오

Post-Obstructive Diuresis Nursing GuideAfter catheter relief of urinary retention
After relief of prolonged obstruction, the kidneys may excrete very large volumes of dilute urine with sodium and potassium. Urine output above 200 mL/h for several hours or a rapid drop in blood pressure suggests clinically significant post-obstructive diuresis.

Monitor intake and output, vital signs, and electrolytes closely. Report high urine output and hypotension promptly so prescribed fluid and electrolyte replacement can be started.

CautionDo not clamp the catheter or restrict oral fluids. These actions can worsen volume depletion or increase the risk of bladder overdistension and infection.

## 핵심 개념

- **post-obstructive diuresis** — Large-volume urine output with sodium and potassium loss after relief of prolonged urinary obstruction
- **acute urinary retention** — Sudden inability to void, often with a painful, palpable bladder
- **benign prostatic hyperplasia** — Noncancerous prostate enlargement that can obstruct the bladder outlet
- **intravascular volume depletion** — Loss of circulating blood volume, which may present as falling blood pressure
- **creatinine** — Renal function marker that may be elevated in acute kidney injury from obstruction

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