# 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. His admission results are shown. Normal ranges are in parentheses. Sodium: 133 mEq/L (135–145) Potassium: 3.0 mEq/L (3.5–5.0) Chloride: 89 mEq/L (98–106) Arterial pH: 7.51 (7.35–7.45) Partial pressure of arterial carbon dioxide (PaCO2): 47 mmHg (35–45) Bicarbonate (HCO3−): 34 mEq/L (22–26) Which process BEST explains this pattern?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630280  
> 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.

His admission results are shown. Normal ranges are in parentheses.
Sodium: 133 mEq/L (135–145)
Potassium: 3.0 mEq/L (3.5–5.0)
Chloride: 89 mEq/L (98–106)
Arterial pH: 7.51 (7.35–7.45)
Partial pressure of arterial carbon dioxide (PaCO2): 47 mmHg (35–45)
Bicarbonate (HCO3−): 34 mEq/L (22–26)
Which process BEST explains this pattern?

## 보기

1. Loss of bicarbonate-rich fluid from a blockage in the colon
2. Lactic acid build-up from reduced blood flow to the bowel wall
3. Rapid breathing from pain that blows off carbon dioxide
4. Loss of gastric acid and chloride through repeated vomiting **✔ 정답**

**정답: 4**

## 해설

The high pH and high HCO3− show metabolic alkalosis, and the slightly raised PaCO2 is respiratory compensation. With low chloride and potassium, this pattern fits a proximal (high) small-bowel obstruction in which vomiting removes hydrogen and chloride ions from the stomach, and potassium is also lost.

## 심화 해설

Interpreting the blood gas
The arterial pH is 7.51 (high), the bicarbonate is 34 mEq/L (high), and the PaCO2 is 47 mmHg (slightly high). A high pH with a high HCO3− is metabolic alkalosis. The raised PaCO2 moves in the same direction as the HCO3− and represents respiratory compensation: the client hypoventilates slightly to retain carbon dioxide and pull the pH back toward normal. With low chloride and low potassium, this pattern fits loss of gastric acid and chloride through repeated vomiting in a high small-bowel obstruction.

Why vomiting causes metabolic alkalosis
Gastric juice is rich in hydrochloric acid. When it is lost through repeated vomiting or nasogastric suction, the body loses hydrogen ions and chloride, and bicarbonate rises. Volume depletion then drives the kidneys to retain sodium, which they do partly by excreting potassium and hydrogen ions, worsening both hypokalemia and alkalosis. Low chloride also limits the kidneys' ability to excrete excess bicarbonate. The result is the classic triad of metabolic alkalosis, hypochloremia, and hypokalemia seen here: chloride 89 mEq/L and potassium 3.0 mEq/L.

| Process | Expected pH | Expected HCO3− | Expected PaCO2 |
| --- | --- | --- | --- |
| Vomiting of gastric contents (high obstruction) | High | High | Slightly high (compensation) |
| Loss of bicarbonate-rich lower intestinal fluid | Low | Low | Low (compensation) |
| Lactic acidosis from bowel ischemia | Low | Low | Low (compensation) |
| Hyperventilation from pain | High | Normal or slightly low | Low |

Why the other processes do not fit
Loss of bicarbonate-rich fluid from the lower intestine tends toward metabolic acidosis, not a high HCO3−. Bowel ischemia produces lactic acidosis with a low pH and low HCO3−; it is a serious complication of obstruction, but these values do not show it. Watch out! Rapid breathing from pain would cause respiratory alkalosis, which would lower the PaCO2; here the PaCO2 is raised, so the primary problem is metabolic, not respiratory.

Nursing implications
Management corrects the cause and the deficits: isotonic saline restores volume and chloride, and potassium is replaced as ordered, after adequate urine output is confirmed. The nurse measures NG output accurately, because continued suction adds to acid and chloride losses, monitors serial electrolytes and cardiac rhythm for hypokalemia, and watches for signs that suggest strangulation, such as fever, rising pain, or a developing metabolic acidosis.

Exam takeaway
Key point! Vomiting or NG suction: metabolic alkalosis with hypochloremia and hypokalemia. Check the direction of pH and HCO3− first; a PaCO2 that moves the same way is compensation.

## 임상 시나리오

Metabolic Alkalosis From VomitingAcid-base pattern in a high bowel obstruction
pH 7.51 and HCO3− 34 mEq/L show metabolic alkalosis; PaCO2 47 mmHg is respiratory compensation.

Repeated vomiting removes hydrogen and chloride ions from the stomach. Volume loss makes the kidneys excrete potassium, causing hypokalemia and hypochloremia.

Replace volume with isotonic saline and potassium as ordered, and record NG output accurately because suction adds to the losses.

CautionA falling pH or bicarbonate, fever, or rising pain may signal bowel ischemia with lactic acidosis. Report these at once.

## 핵심 개념

- **Metabolic alkalosis** — An acid-base disorder with high pH and high bicarbonate, often from loss of gastric acid.
- **Respiratory compensation** — Adjustment of ventilation that changes PaCO2 to move pH back toward normal.
- **Hypochloremia** — A low serum chloride level, common after vomiting or nasogastric suction.
- **Hypokalemia** — A low serum potassium level that can cause weakness and cardiac dysrhythmias.
- **Small-bowel obstruction** — Blockage of the small intestine, often from adhesions after abdominal surgery.

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