一位因心房顫動服用 warfarin 的成人病人，早晨的檢驗結果顯示 INR 為 5.8。護理師應該先採取下列何項措施？

INR 5.8 已大幅超過心房顫動的治療範圍（2.0–3.0），代表出血風險極高。首要措施是暫停下一劑 warfarin 並通知醫師，以便給予維生素 K（phytonadione）或調整劑量。Protamine 為 heparin 的拮抗劑，warfarin 的拮抗劑是維生素 K。多攝取富含維生素 K 的蔬菜雖可長期降低 INR，但無法解除目前的出血風險。維持原劑量並僅觀察將忽略顱內或消化道出血的危險，違反病人安全原則。

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).

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.