# Situation: A 63-year-old man is in the surgical intensive care unit after a major bowel resection. He receives parenteral nutrition (PN) by infusion pump through a central venous catheter and intermittent hemodialysis (HD) through a tunneled dialysis catheter for kidney failure. The nurse is credentialed by the unit to perform arterial puncture. Over 2 days, while he receives oxygen at 4 L/min by nasal cannula, four arterial blood gas samples are drawn from him into heparinized plastic syringes. The laboratory runs plastic syringes at room temperature, and unit policy requires analysis within 30 minutes of the draw. Every sample was capped and labeled with his oxygen setting. - Sample P: air expelled; rolled gently; kept at room temperature; analyzed at 25 minutes - Sample Q: air expelled; rolled gently; placed on ice; analyzed at 50 minutes - Sample R: small air bubble left at the tip; rolled gently; analyzed at 5 minutes - Sample S: air expelled; shaken hard for 30 seconds; analyzed at 10 minutes Which sample was handled correctly and gives a result the team can rely on?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630265  
> language: ko  
> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 63-year-old man is in the surgical intensive care unit after a major bowel resection. He receives parenteral nutrition (PN) by infusion pump through a central venous catheter and intermittent hemodialysis (HD) through a tunneled dialysis catheter for kidney failure.

The nurse is credentialed by the unit to perform arterial puncture. Over 2 days, while he receives oxygen at 4 L/min by nasal cannula, four arterial blood gas samples are drawn from him into heparinized plastic syringes. The laboratory runs plastic syringes at room temperature, and unit policy requires analysis within 30 minutes of the draw. Every sample was capped and labeled with his oxygen setting.
- Sample P: air expelled; rolled gently; kept at room temperature; analyzed at 25 minutes
- Sample Q: air expelled; rolled gently; placed on ice; analyzed at 50 minutes
- Sample R: small air bubble left at the tip; rolled gently; analyzed at 5 minutes
- Sample S: air expelled; shaken hard for 30 seconds; analyzed at 10 minutes
Which sample was handled correctly and gives a result the team can rely on?

## 보기

1. Sample S
2. Sample Q
3. Sample R
4. Sample P **✔ 정답**

**정답: 4**

## 해설

A reliable arterial sample is free of air, capped, labeled with the oxygen delivery, mixed by gentle rolling and analyzed promptly; for plastic syringes at room temperature this unit requires analysis within 30 minutes. Each of the other samples fails one requirement: icing does not rescue a plastic syringe held beyond the time limit, a small bubble alters the gas values even when the sample is run quickly, and vigorous shaking can hemolyze the sample.

## 심화 해설

Requirements for a reliable ABG sample
An arterial blood gas result is only as good as the sample. A reliable sample is free of air, capped, labeled with the oxygen delivery, mixed by gentle rolling, and analyzed promptly. For plastic syringes kept at room temperature, this unit requires analysis within 30 minutes of the draw. Sample P meets every requirement: air expelled, rolled gently, kept at room temperature, and analyzed at 25 minutes.

How each handling error distorts the result
Each of the other samples fails one requirement, and each error changes the values in a predictable way.

| Sample | Handling | Problem |
| --- | --- | --- |
| P | No air, rolled gently, room temperature, 25 min | Correct; result can be relied on |
| Q | No air, rolled gently, iced, 50 min | Exceeds the 30-minute limit; icing does not rescue a plastic syringe held too long |
| R | Small bubble left, rolled gently, 5 min | Air equilibrates with the blood; values shift toward room air |
| S | No air, shaken hard, 10 min | Vigorous shaking can hemolyze the sample |

Why air and delay matter
Watch out! Even a small air bubble matters. Room air has a much higher oxygen and much lower carbon dioxide tension than the blood of most clients, so gas moves between the bubble and the blood: the PaO2 is pushed toward the room-air value and the PaCO2 falls. Fast analysis does not correct this, because equilibration begins at once. With delay, blood cells keep metabolizing, consuming oxygen and producing carbon dioxide and acid, so PaO2 and pH fall and PaCO2 rises. Plastic is slightly permeable to gases, and chilling a plastic syringe does not reliably prevent these changes; ice is used only when the laboratory specifically requires it.

Why mixing must be gentle
The heparin in the syringe must be mixed with the blood to prevent clotting, which is done by rolling the syringe between the palms and gently inverting it. Shaking it hard damages red cells (hemolysis), which can falsely raise potassium and interfere with other measurements on the analyzer. A clotted sample is equally unreliable and may block the machine.

Other essentials
The label records the client's oxygen setting (here 4 L/min by nasal cannula), because PaO2 cannot be interpreted without it, and the client's temperature if required. Before arterial puncture of the radial artery, collateral circulation is checked, and afterward firm pressure is held at the site for at least 5 minutes, longer if the client is anticoagulated. This client receives intermittent hemodialysis, which often involves heparin, so the site is watched for bleeding.

Exam takeaway
Key point! A reliable ABG: no air, capped, labeled with oxygen delivery, gently rolled, and analyzed within the time limit. Icing does not fix a delay, quick analysis does not fix a bubble, and shaking causes hemolysis.

## 임상 시나리오

Handling an ABG SampleWhich sample can the team rely on?
A reliable arterial sample is air-free, capped, labeled with the oxygen setting, rolled gently, and analyzed within the unit's 30-minute limit for plastic syringes.

Sample P meets all criteria. Q was analyzed at 50 minutes; icing does not rescue it. R kept a bubble, which shifts values toward room air. S was shaken hard and may be hemolyzed.

Delay lets cells consume oxygen and produce carbon dioxide, lowering PaO2 and pH and raising PaCO2.

CautionAfter arterial puncture, hold firm pressure for at least 5 minutes, longer in clients receiving anticoagulants such as heparin during hemodialysis.

## 핵심 개념

- **Arterial blood gas** — A test of arterial pH, PaO2, PaCO2, and bicarbonate used to assess oxygenation and acid-base status.
- **Hemolysis** — Rupture of red blood cells, which can falsely raise potassium in a sample.
- **Heparinized syringe** — A syringe containing heparin to prevent the blood sample from clotting.
- **Air bubble contamination** — Air left in a blood gas sample that shifts gas values toward those of room air.
- **PaO2** — Partial pressure of oxygen in arterial blood, interpreted together with the oxygen delivered.

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