# 看護師が、心房細動でワルファリンを服用している成人患者の朝の検査結果を確認している。最新のINRは5.8である。看護師が最初にとるべき行動はどれか。

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=360515&lang=ja  
> language: ja  
> subject: Adverse Effects/Contraindications/Interactions  
> category: PPT

## 問題

看護師が、心房細動でワルファリンを服用している成人患者の朝の検査結果を確認している。最新のINRは5.8である。看護師が最初にとるべき行動はどれか。

## 選択肢

1. 葉物野菜(ほうれん草・ケール)の摂取を増やすよう指導する
2. 拮抗薬としてプロタミン硫酸塩(protamine sulfate)を投与する
3. ワルファリンの次回投与を保留し、医師に報告する **✔ 正解**
4. 処方されたワルファリン用量を継続し24時間後に再評価する

**正解: 3**

## 解説

INR 5.8は、治療域（心房細動では2.0～3.0）を大きく上回っており、出血リスクが高いことを示している。優先すべき行動は、次のワルファリン投与を保留し、ビタミンKの投与や用量調整の指示を安全に受けられるよう医師に報告することである。プロタミン硫酸はヘパリンの拮抗薬であり、ワルファリンではない（ワルファリンの拮抗薬はビタミンKである）。ビタミンKを多く含む食品を長期的に増やすことでINRは低下する可能性があるが、差し迫った出血リスクには対処できない。何の介入もせずに同量を継続すれば、出血リスクがさらに高まる。

## 詳細解説

Clinical Judgment
The core of this question is the bleeding risk indicated by an INR of 5.8, which greatly exceeds the therapeutic range (INR 2.0–3.0). Using the NCJMM framework: Recognize Cues (abnormal INR 5.8) → Analyze Cues (excessive warfarin effect, impending bleeding) → Prioritize (safety-first: hold the medication) → Take Action (report to provider and consider vitamin K or FFP). Any option that implements another intervention without first discontinuing the drug itself violates safety.

Memory Tip
High INR → Hold + Call. If the INR deviates from the therapeutic range by more than 1 point (especially 4 or above), always "hold + report." Warfarin antidote = Vitamin K, Heparin antidote = Protamine — do not confuse them.

KR vs US
Although the same INR target range is applied in Korea, the NCLEX frequently uses the phrase "first action." In this case, you must select the single most urgent intervention directly related to patient safety. In Korean clinical practice, it is common to observe while waiting for a physician's order change, but the NCLEX differs by clearly asking about the nurse's autonomous authority (holding medication and reporting).

## 臨床シナリオ

Clinical Practice Guide
Warfarin monitoring is INR-based. Standard target for atrial fibrillation is INR 2.0–3.0. INR ≥4.5 sharply increases bleeding risk; for INR ≥5.0, standard practice is to immediately withhold the drug and notify the healthcare provider (ACCP Antithrombotic Therapy Guidelines). If bleeding signs are present, consider IV vitamin K + FFP/PCC.

Caution
On the NCLEX, the "first action" must be a single action that immediately ensures patient safety. "Education" or "observation" are usually lower priority. Drug-antidote pairs (warfarin↔vitamin K, heparin↔protamine, opioid↔naloxone) are tested every time, so memorize them.

## 重要概念

- **Warfarin (와파린)** — 비타민 K 길항제 경구 항응고제. 응고인자 II/VII/IX/X 합성을 억제하여 혈전 형성을 막음. 좁은 치료지수 약물로 정기적 INR 모니터링이 필수이며 식이·약물 상호작용에 민감.
- **INR (International Normalized Ratio)** — PT(prothrombin time)를 표준화한 응고 검사 지표. 정상 약 1.0, 항응고 치료 목표는 적응증에 따라 다름(심방세동·기계판막은 2.0–3.0, 급성 정맥혈전은 2.0–3.0). 5.0 이상은 출혈 고위험.
- **Vitamin K (피토나디온, 비타민 K1)** — Warfarin 길항제. 응고인자 II/VII/IX/X 합성을 회복시킴. 경증 INR 상승은 경구 1–5 mg, 출혈 동반 시 정맥 투여 + FFP/PCC 병용. 헤파린에는 효과 없음.

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