# Situation: A 66-year-old man weighing 70 kg, who had open abdominal surgery 3 years ago, is admitted with colicky mid-abdominal pain, repeated bilious vomiting since yesterday, and no flatus for 12 hours. An abdominal X-ray shows dilated small-bowel loops with air-fluid levels. He is kept nil per os (NPO), a nasogastric (NG) tube is connected to low suction, and intravenous (IV) fluids are started. The unit protocol sets the minimum urine output at 0.5 mL/kg/h, averaged over 4 hours. His hourly urine outputs over the last 4 hours were 40, 34, 28, and 22 mL, and NG drainage over the same 4 hours was 600 mL. How does his output compare with the protocol limit?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630281  
> language: ko  
> subject: Nursing Practice IV — Care of Clients with Problems in Nutrition and Gastrointestinal, Metabolism and Endocrine, Perception and Coordination

## 문제

Situation: A 66-year-old man weighing 70 kg, who had open abdominal surgery 3 years ago, is admitted with colicky mid-abdominal pain, repeated bilious vomiting since yesterday, and no flatus for 12 hours. An abdominal X-ray shows dilated small-bowel loops with air-fluid levels. He is kept nil per os (NPO), a nasogastric (NG) tube is connected to low suction, and intravenous (IV) fluids are started.

The unit protocol sets the minimum urine output at 0.5 mL/kg/h, averaged over 4 hours. His hourly urine outputs over the last 4 hours were 40, 34, 28, and 22 mL, and NG drainage over the same 4 hours was 600 mL. How does his output compare with the protocol limit?

## 보기

1. 31 mL/h, below the 35-mL/h limit **✔ 정답**
2. 31 mL/h, below the 70-mL/h limit
3. 124 mL, above the 35-mL limit
4. 31 mL/h, above the 30-mL/h minimum

**정답: 1**

## 해설

His limit is 0.5 mL/kg/h × 70 kg = 35 mL/h. Total urine over 4 hours is 40 + 34 + 28 + 22 = 124 mL, and 124 ÷ 4 = 31 mL/h, which is below the limit. NG drainage is a fluid loss, not a measure of kidney perfusion; low urine output with large NG losses suggests hypovolemia, so the nurse reports it.

## 심화 해설

The question asks you to compare the patient’s measured urine output against a protocol-defined minimum. The calculation itself is straightforward, but the clinical reasoning behind it is what matters for licensure exams.

First, determine the patient’s individualized minimum urine output. The protocol specifies 0.5 mL/kg/h. For a 70 kg patient, the minimum acceptable hourly urine output is 35 mL/h (0.5 × 70 = 35).

Next, calculate the actual average hourly urine output over the 4-hour window. The recorded hourly outputs are 40, 34, 28, and 22 mL. The total is 124 mL over 4 hours, which averages to 31 mL/h (124 ÷ 4 = 31).

Comparing the two values, 31 mL/h is below the 35 mL/h minimum. This makes option 1 correct.

The NG drainage of 600 mL is a separate piece of data and must not be added to urine output. Urine output reflects renal perfusion and glomerular filtration, while NG drainage represents gastrointestinal fluid loss. NG output is a fluid loss that contributes to hypovolemia, but it is not a measure of kidney function.

The clinical picture is consistent with a small-bowel obstruction. The patient has colicky mid-abdominal pain, bilious vomiting, absent flatus, and radiographic findings of dilated small-bowel loops with air-fluid levels. In bowel obstruction, fluid sequesters into the intestinal lumen, and vomiting or NG suction removes additional fluid from the body. This third-spacing and external loss reduce circulating blood volume, which in turn decreases renal perfusion and lowers urine output.

Watch out! A common error is adding NG drainage to urine output to “make up” the fluid balance. That is incorrect for assessing renal adequacy. Urine output is evaluated on its own against the weight-based minimum.

Key point! A declining hourly urine trend (40 → 34 → 28 → 22 mL) is more concerning than a single low value. Even though the average is 31 mL/h, the downward trajectory suggests worsening hypovolemia and warrants prompt reporting.

The pathophysiologic link between bowel obstruction and oliguria is well established. In intestinal obstruction, fluid accumulates in the bowel lumen and wall, and losses from vomiting or NG suction compound the intravascular volume deficit. As circulating volume falls, renal hypoperfusion leads to reduced urine output. Early recognition of oliguria in a patient with bowel obstruction is a signal of inadequate resuscitation and possible progression toward more severe complications.

| Item | Value | Interpretation |
| --- | --- | --- |
| Protocol minimum | 0.5 mL/kg/h × 70 kg = 35 mL/h | Individualized lower limit |
| 4-hour urine total | 40 + 34 + 28 + 22 = 124 mL | Sum of hourly outputs |
| Average hourly urine | 124 ÷ 4 = 31 mL/h | Below the 35 mL/h limit |
| NG drainage | 600 mL over 4 hours | Fluid loss, not a renal measure |

The correct comparison is 31 mL/h, below the 35 mL/h limit. The NG drainage is a separate fluid loss that helps explain why the patient is hypovolemic, but it does not change the urine output calculation. In a patient with bowel obstruction, oliguria combined with large NG losses indicates that intravascular volume depletion is ongoing and requires continued fluid resuscitation and close monitoring.

## 임상 시나리오

Urine Output Monitoring in Bowel ObstructionAssessing renal perfusion amid GI fluid losses
Calculate the individualized minimum: 0.5 mL/kg/h × 70 kg = 35 mL/h. Average the 4-hour urine total (124 mL) to 31 mL/h, which is below the limit.

NG drainage is a separate GI fluid loss, not a measure of kidney perfusion. Do not add it to urine output.

CautionLow urine output with large NG losses in small bowel obstruction suggests hypovolemia from third-spacing and external fluid loss. Report promptly and anticipate fluid resuscitation.

## 핵심 개념

- **Minimum urine output** — Lowest acceptable hourly urine output, often 0.5 mL/kg/h, used to screen for inadequate renal perfusion
- **Third-spacing** — Fluid shift from intravascular space into interstitial or bowel lumen, reducing effective circulating volume
- **NG drainage** — Gastrointestinal fluid output via nasogastric tube; a fluid loss contributing to hypovolemia, not a renal function measure
- **Small bowel obstruction** — Blockage of small intestine causing colicky pain, bilious vomiting, distension, and air-fluid levels on X-ray
- **Hypovolemia** — Reduced circulating blood volume, often from GI losses and third-spacing, leading to decreased urine output

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