# Situation: A 49-year-old man with acromegaly from a growth hormone–secreting pituitary adenoma undergoes transsphenoidal removal of the tumor. He returns to the surgical ward with nasal packing and an indwelling urinary catheter. Per unit protocol, the nurse reports urine output of more than 250 mL/h for 2 consecutive hours, or a urine specific gravity below 1.005. He is receiving intravenous fluid at 100 mL/h and no diuretic. His hourly results are shown below. 14:00 — 180 mL, specific gravity 1.012 15:00 — 270 mL, specific gravity 1.008 16:00 — 230 mL, specific gravity 1.007 17:00 — 290 mL, specific gravity 1.004 18:00 — 310 mL, specific gravity 1.003 At which time does his record FIRST meet the reporting rule?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630313  
> language: ko  
> subject: Nursing Practice IV — Care of Clients with Problems in Nutrition and Gastrointestinal, Metabolism and Endocrine, Perception and Coordination

## 문제

Situation: A 49-year-old man with acromegaly from a growth hormone–secreting pituitary adenoma undergoes transsphenoidal removal of the tumor. He returns to the surgical ward with nasal packing and an indwelling urinary catheter.

Per unit protocol, the nurse reports urine output of more than 250 mL/h for 2 consecutive hours, or a urine specific gravity below 1.005. He is receiving intravenous fluid at 100 mL/h and no diuretic. His hourly results are shown below.

14:00 — 180 mL, specific gravity 1.012
15:00 — 270 mL, specific gravity 1.008
16:00 — 230 mL, specific gravity 1.007
17:00 — 290 mL, specific gravity 1.004
18:00 — 310 mL, specific gravity 1.003

At which time does his record FIRST meet the reporting rule?

## 보기

1. 15:00
2. 16:00
3. 17:00 **✔ 정답**
4. 18:00

**정답: 3**

## 해설

The rule has two triggers. Output exceeds 250 mL/h for 2 consecutive hours only at 18:00 (290 and 310 mL), because 16:00 broke the run, but the specific gravity falls below 1.005 at 17:00 (1.004), which already meets the rule. Large volumes of dilute urine after pituitary surgery suggest arginine vasopressin deficiency (central diabetes insipidus).

## 심화 해설

Why this question matters

After transsphenoidal pituitary surgery, the posterior pituitary or pituitary stalk can be bruised or have its blood supply disrupted. This impairs secretion of arginine vasopressin (AVP), also called antidiuretic hormone (ADH). When ADH is deficient, the collecting ducts cannot reabsorb water, so the patient excretes large volumes of dilute urine. This condition is central diabetes insipidus (CDI) [1][3]. The reporting rule in this unit is a screening tool for early CDI.

Breaking down the reporting rule

The rule has two separate triggers. The nurse must report if either condition is met.

| Trigger | Criterion | Clinical meaning |
| --- | --- | --- |
| High output | Urine output greater than 250 mL/h for 2 consecutive hours | Suggests the kidneys are losing free water excessively |
| Dilute urine | Urine specific gravity below 1.005 | Indicates the kidneys are not concentrating urine, consistent with ADH deficiency |

Reading the hourly data

The intravenous fluid is running at 100 mL/h and no diuretic is given, so urine output above this infusion rate already suggests the patient is losing free water. However, the rule is not based on intake; it is based on the specific thresholds.

| Time | Urine output | Specific gravity | Meets high-output trigger? | Meets dilute-urine trigger? |
| --- | --- | --- | --- | --- |
| 14:00 | 180 mL | 1.012 | No | No |
| 15:00 | 270 mL | 1.008 | No, only 1 hour above 250 | No, still above 1.005 |
| 16:00 | 230 mL | 1.007 | No, output dropped below 250 | No |
| 17:00 | 290 mL | 1.004 | No, only 1 hour above 250 | Yes, below 1.005 |
| 18:00 | 310 mL | 1.003 | Yes, 290 and 310 mL are 2 consecutive hours above 250 | Yes |

Why 17:00 is the first meeting time

At 17:00, the urine specific gravity drops to 1.004, which is below the threshold of 1.005. This alone satisfies the reporting rule. The high-output trigger is not yet met at 17:00 because the output at 16:00 was only 230 mL, breaking the consecutive run. The two triggers are independent; meeting either one requires the nurse to report. Therefore, the first time the record meets the rule is 17:00.

Watch out! Do not wait for both triggers to be present. The rule uses “or,” not “and.” A dilute urine below 1.005 is enough by itself.

Key point! In the early phase of postoperative CDI, specific gravity may fall before urine output becomes dramatically high. ADH deficiency reduces water reabsorption, so urine becomes dilute first, and the volume rises as the condition progresses [1]. Monitoring specific gravity alongside hourly output allows earlier detection than watching output alone.

Clinical correlation

After pituitary surgery, CDI can be transient because the neurohypophyseal stalk or posterior pituitary may be temporarily stunned or edematous [1][3]. The onset is often within the first 24 hours. In this patient, the progressively falling specific gravity from 1.012 to 1.003 and rising output from 180 mL to 310 mL form a pattern consistent with developing ADH deficiency. The nurse should report at 17:00 so that serum sodium, serum osmolality, and urine osmolality can be checked and desmopressin considered if CDI is confirmed .References (research sources)

- [1]Severe Transient Central Diabetes Insipidus After Pituitary Adenoma Removal With Peak Urine Output of 33.5 L in 24 h.Research articleBhandari G, Chhetri AK, Gyawali R, Thapa D. (2026) · DOI: 10.1155/crie/7516452

- [3]Incidence of Diabetes Insipidus in Postoperative Period among the Patients Undergoing Pituitary Tumour Surgery.Research articleKadir ML, Islam MT, Hossain MM, Sultana S, Nasrin R, Hossain MM (2017)

## 임상 시나리오

Postop Pituitary Surgery Urine MonitoringEarly detection of diabetes insipidus
Report if urine output exceeds 250 mL/h for 2 consecutive hours OR specific gravity falls below 1.005. The specific gravity trigger is met first at 17:00 with 1.004.

Large volumes of dilute urine after pituitary surgery suggest arginine vasopressin deficiency (central diabetes insipidus). IV fluid at 100 mL/h with no diuretic makes output above this rate clinically significant.

CautionDo not wait for the 2-hour output trigger if specific gravity is already below 1.005. Either criterion alone requires immediate reporting.

## 핵심 개념

- **Central diabetes insipidus** — ADH deficiency causing excretion of large volumes of dilute urine after pituitary surgery
- **Arginine vasopressin** — Antidiuretic hormone that promotes water reabsorption in collecting ducts
- **Urine specific gravity** — Measure of urine concentration; below 1.005 indicates dilute urine
- **Transsphenoidal surgery** — Surgical approach to remove pituitary tumors through the nasal cavity

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