# Situation: A 65-year-old man weighing 68 kg has an open small-bowel resection under general anesthesia. He returns to the surgical ward with a nasogastric tube to low suction and a wound drain. No urinary catheter was placed, and he is kept nothing by mouth (NPO). On the first postoperative day, the nurse totals his 8-hour intake and output: Intravenous (IV) infusion: 100 mL/h for 8 hours IV antibiotic: 2 doses of 50 mL each Nasogastric tube irrigation: 60 mL of normal saline instilled Urine: 480 mL Nasogastric drainage (collected): 250 mL Wound drain: 70 mL What is his fluid balance for the shift?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=629874  
> language: ko  
> 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 65-year-old man weighing 68 kg has an open small-bowel resection under general anesthesia. He returns to the surgical ward with a nasogastric tube to low suction and a wound drain. No urinary catheter was placed, and he is kept nothing by mouth (NPO).

On the first postoperative day, the nurse totals his 8-hour intake and output:
Intravenous (IV) infusion: 100 mL/h for 8 hours
IV antibiotic: 2 doses of 50 mL each
Nasogastric tube irrigation: 60 mL of normal saline instilled
Urine: 480 mL
Nasogastric drainage (collected): 250 mL
Wound drain: 70 mL
What is his fluid balance for the shift?

## 보기

1. +480 mL
2. +60 mL
3. +100 mL
4. +160 mL **✔ 정답**

**정답: 4**

## 해설

Intake: 800 mL IV + 100 mL antibiotic + 60 mL irrigation = 960 mL. Output: 480 mL urine + 250 mL nasogastric drainage + 70 mL drain = 800 mL. Balance: 960 − 800 = +160 mL. Subtracting the 60 mL of irrigant from the nasogastric drainage instead of counting it as intake gives the same result (900 − 740 = +160 mL).

## 심화 해설

Fluid balance calculation

Fluid balance is determined by subtracting total output from total intake over a defined period. The calculation requires careful attention to what actually enters the body versus what leaves it, and to whether certain fluids should be counted on the intake side, the output side, or not at all.

For this patient, intake includes the maintenance IV infusion, the IV antibiotic diluent, and the nasogastric tube irrigant because all three were instilled into the body. Output includes urine, nasogastric drainage, and wound drainage because all three represent fluid leaving the body.

Step-by-step calculation

| Category | Item | Volume |
| --- | --- | --- |
| Intake | IV infusion (100 mL/h × 8 h) | 800 mL |
| Intake | IV antibiotic (2 doses × 50 mL) | 100 mL |
| Intake | NG tube irrigation (normal saline instilled) | 60 mL |
| Intake | Total intake | 960 mL |
| Output | Urine | 480 mL |
| Output | Nasogastric drainage (collected) | 250 mL |
| Output | Wound drain | 70 mL |
| Output | Total output | 800 mL |

Fluid balance = total intake − total output = 960 mL − 800 mL = +160 mL.

Key point! The nasogastric tube irrigant is counted as intake, not subtracted from the nasogastric drainage. However, if a question presents the irrigation volume and the total nasogastric drainage collected, subtracting the irrigant from the drainage and omitting it from intake yields the same net balance. In this case, counting the 60 mL as intake and the full 250 mL as output gives +160 mL. Alternatively, subtracting 60 mL from the 250 mL drainage (190 mL net NG output) and excluding irrigation from intake gives 900 mL intake − 740 mL output = +160 mL. Both methods are mathematically equivalent.

Why accurate fluid balance matters after bowel surgery

Patients undergoing open small-bowel resection are at risk for significant fluid shifts. The surgery itself, the fasting state, and the presence of a nasogastric tube on suction all contribute to ongoing fluid and electrolyte losses. A positive balance of +160 mL over 8 hours is relatively modest and may reflect appropriate postoperative fluid management, but the trend over multiple shifts is more clinically meaningful than any single 8-hour value.

The nasogastric tube removes gastric and upper intestinal secretions, which are rich in sodium, potassium, chloride, and hydrogen ions. Loss of these secretions can lead to hypokalemia, metabolic alkalosis, and volume depletion if not replaced. The wound drain removes serous or serosanguineous fluid from the surgical site, contributing additional protein and electrolyte loss. Urine output is a key indicator of renal perfusion and overall volume status. In this patient, urine output of 480 mL over 8 hours equals 60 mL/h, which is above the commonly cited minimum of 0.5 mL/kg/h. For a 68 kg patient, that threshold is approximately 34 mL/h, so this output suggests adequate renal perfusion at this point.

Watch out! Insensible losses such as evaporation from the respiratory tract and skin are not directly measured in routine intake and output records. They are typically estimated at 500–800 mL/day but are not included in standard shift calculations. This means the true physiologic balance may be slightly less positive than the recorded value.

Common calculation pitfalls

| Error | Result | Why it is wrong |
| --- | --- | --- |
| Forgetting to count the antibiotic fluid as intake | +60 mL | IV medications diluted in fluid contribute to total intake and must be included. |
| Forgetting to count the NG irrigation as intake | +100 mL | Instilled irrigant enters the stomach and is part of intake unless it is fully recovered and subtracted from drainage. |
| Subtracting irrigation from NG drainage but also counting it as intake | +100 mL | This double-counts the irrigant and distorts the balance. Use one method consistently. |
| Counting only urine as output | +480 mL | NG and wound drainage are measurable outputs that must be included. |

The correct answer is +160 mL because all three intake sources and all three output sources are included in the calculation. In clinical practice, the nurse also assesses the character and color of each drainage, monitors for signs of hypovolemia or fluid overload, and correlates the calculated balance with daily weights, vital signs, skin turgor, and laboratory values such as electrolytes and hematocrit.

## 임상 시나리오

Postoperative Fluid Balance CalculationAccurate intake and output recording after abdominal surgery
Calculate balance as total intake minus total output. For this patient, intake was 960 mL and output was 800 mL, giving a balance of +160 mL.

Count NG tube irrigation as intake because it was instilled into the body. Alternatively, subtract the irrigant from total NG drainage and omit it from intake; both methods give the same net balance.

CautionDo not overlook IV medication volumes or drain output; missing either can shift the balance by 100 mL or more and alter fluid management decisions.

## 핵심 개념

- **Fluid balance** — Difference between total fluid intake and total fluid output over a defined period.
- **Intake** — All fluids instilled into the body, including IV fluids, IV medications, and tube irrigants.
- **Output** — All fluids leaving the body, including urine, nasogastric drainage, and drain output.
- **Nasogastric tube irrigation** — Normal saline instilled through an NG tube; counted as intake unless subtracted from total NG drainage.
- **NPO** — Nothing by mouth; all fluid intake must be provided by other routes such as IV.

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