A nurse is preparing to administer heparin 5,000 units subcutaneously every 12 hours. The available heparin concentration is 10,000 units/mL. How many mL should the nurse administer per dose?
11 mL
22 mL
30.25 mL
40.5 mL✓ 정답
해설
Using the formula: Dose ordered ÷ Dose available × Volume = 5,000 units ÷ 10,000 units/mL × 1 mL = 0.5 mL. This calculation ensures safe administration of heparin, a high-alert medication.
Core Nursing Explanation
This question tests a fundamental nursing skill: medication dosage calculation. It requires the nurse to accurately determine the volume of a concentrated drug to deliver a prescribed dose, which is critical for patient safety, especially with Key Point!high-alert medications like heparin.
Key Concept Analysis: The core concept is the application of the basic dosage calculation formula. The nurse must reconcile the desired dose (5,000 units) with the available concentration (10,000 units/mL). The standard formula is: (Desired Dose / Dose on Hand) × Volume on Hand = Volume to Administer.
Answer Rationale: Applying the formula step-by-step:
1. Desired Dose: 5,000 units
2. Dose on Hand: 10,000 units
3. Volume on Hand: 1 mL
Calculation: (5,000 units / 10,000 units) × 1 mL = 0.5 × 1 mL = 0.5 mL.
Key Point! This calculation is logical: if 1 mL contains 10,000 units, then 0.5 mL (half of that volume) contains 5,000 units (half of that dose). The correct answer is 0.5 mL.
Distractor Analysis:
Watch out for confusion!
- 1 mL: This is a common error from misplacing the decimal or incorrectly using the formula (e.g., 10,000/5,000). It results in administering a double dose.
- 2 mL: This error might come from inverting the ratio (10,000/5,000 = 2) and forgetting it's a ratio, not a volume in mL. It results in a dangerously high quadruple dose.
- 0.25 mL: This error might stem from dividing 5,000 by 10,000 and getting 0.5, but then incorrectly halving it again. It results in administering only half the prescribed dose, which could be subtherapeutic.
Related Concepts: This calculation is a cornerstone of safe medication administration. For heparin specifically, subcutaneous administration is common for DVT (Deep Vein Thrombosis) prophylaxis. Always double-check calculations and have another nurse verify high-alert medications. Understanding concentration is vital—drugs come in various strengths (e.g., 1,000 units/mL, 5,000 units/mL, 10,000 units/mL).
Concept Summary
- Formula: (Desired Dose / Dose on Hand) × Volume = Volume to Administer.
- Heparin: Anticoagulant, high-alert medication. Subcutaneous dose often for prophylaxis.
- Safety: Independent double-check for high-alert meds is a standard nursing safety procedure.
Anatomy, Physiology & Pharmacology Points
- Heparin Mechanism: Enhances the activity of antithrombin III, which inactivates thrombin and Factor Xa, inhibiting the clotting cascade.
- Administration Site: Subcutaneous heparin is typically injected into the abdomen (at least 2 inches from the umbilicus), avoiding bony areas and scars, to ensure predictable absorption.
- Monitoring: For therapeutic heparin, monitor aPTT (Activated Partial Thromboplastin Time). For prophylactic doses, monitoring is typically not required, but assessment for bleeding is always crucial.
Memory Tips
- Dimensional Analysis: Set up the problem to cancel unwanted units: 5,000 units × (1 mL / 10,000 units) = 0.5 mL. The "units" cancel, leaving "mL."
- Logic Check: "I need 5,000 units. The vial says 10,000 units in 1 mL. 5,000 is half of 10,000, so I need half of 1 mL, which is 0.5 mL." Always perform this sanity check.
High-Frequency NCLEX Topics
Dosage calculation is a guaranteed topic on the NCLEX. The exam tests your ability to perform these calculations accurately under the pressure of a clinical scenario. Common variations include IV drip rate calculations, weight-based pediatric doses, and insulin administration.
Watch Out for Question Variations!
1. Change the Route/Order: "The provider orders heparin 8,000 units subcutaneously. Available is 5,000 units/mL. How many mL?" (Answer: 1.6 mL).
2. Integrate with Lab Values: "A patient's aPTT is 110 seconds on a heparin infusion. The nurse should prepare to administer protamine sulfate. What is the mechanism of action of protamine sulfate?" (It reverses heparin).
3. Priority Action: "After calculating the dose, the nurse's next priority action is to..." (Often: have another RN verify the dose and calculation for this high-alert medication).
Nursing Clinical Practice GuideClinical Scenario: You are a nurse on a medical-surgical unit. Mr. Jones, 68, post-hip replacement surgery, has a physician's order for "Heparin 5,000 units subcutaneously every 12 hours" for DVT prophylaxis. You retrieve a vial labeled "Heparin Sodium Injection, 10,000 USP units/mL."
Nursing Intervention Strategy:
1Assessment & VerificationCheck the patient's allergy status, latest lab values (platelets for HIT - Heparin-Induced Thrombocytopenia), and for any signs of active bleeding. Verify the order using the "Five Rights" (Right patient, drug, dose, route, time).
2Calculation & Safety CheckPerform the calculation as shown. Key Point! For high-alert medications like heparin, always have your calculation and the drawn-up dose independently verified by a second qualified nurse before administration. This is a non-negotiable safety step in most facilities.
3PreparationUse a tuberculin syringe (1 mL syringe with 0.01 mL increments) for accuracy when measuring 0.5 mL. Do not expel the air bubble from the syringe before a subcutaneous heparin injection; it helps seal the track and minimize bruising.
4AdministrationSelect an appropriate site in the abdominal fat pad, at least 2 inches away from the umbilicus. Cleanse with alcohol. Pinch the skin, insert the needle at a 45- or 90-degree angle (based on patient's body fat), inject slowly, wait 10 seconds, then withdraw. Do not massage the site. Apply gentle pressure if needed.
5Evaluation & EducationObserve for immediate adverse reactions. Educate the patient to report any signs of bleeding (bruising, black stools, bleeding gums) or pain/swelling in the legs (possible DVT).
Patient Safety and Precautions:
1ContraindicationsActive major bleeding, history of HIT, severe thrombocytopenia.
2Site RotationRotate injection sites systematically to prevent lipohypertrophy (lumpy tissue) which affects drug absorption.
3Do Not AspirateDo not aspirate before injecting subcutaneous heparin, as this can cause tissue trauma and bruising.
Nursing Procedure & Medication FlowStep-by-Step for Subcutaneous Heparin Administration:
1. Verify order and perform dosage calculation.
2. Gather supplies: Alcohol swab, heparin vial, appropriate syringe (tuberculin syringe for small volumes), needle.
3. Perform hand hygiene and don gloves.
4. Draw up 0.5 mL of heparin (10,000 units/mL) into the syringe. Have a second nurse verify the vial, calculation, and dose in the syringe.
5. Identify the patient using two identifiers.
6. Select and cleanse the injection site.
7. Administer the injection using the correct technique (pinch, insert, inject, wait, withdraw).
8. Discard the syringe/needle in a sharps container immediately.
9. Document: Drug, dose, route, site, time, and the name of the verifying nurse.
A Word from Your Senior Nurse
"Med math can be intimidating, but it's the bedrock of safe nursing. With heparin and other high-alert meds, there is zero room for error. That's why the double-check is your best friend—it's not a sign of weakness, it's the hallmark of a professional, safety-conscious nurse. In clinicals and on the NCLEX, always show your work mentally. Ask yourself, 'Does 0.5 mL make sense for 5,000 units out of a 10,000 units/mL vial?' That logical step will catch most calculation mistakes before they happen. You've got this!"
Heparin — An anticoagulant (blood thinner) that works by potentiating antithrombin III to inhibit clotting factors, primarily used for prophylaxis and treatment of thromboembolic disorders. It is a high-alert medication.
Subcutaneous Injection — An injection administered into the fatty tissue layer between the skin and muscle, allowing for slower, sustained absorption of medication compared to intravenous routes.
Dosage Calculation — The process of determining the correct volume or quantity of a medication to administer based on the prescribed dose and the available concentration of the drug.
High-Alert Medication — Medications that bear a heightened risk of causing significant patient harm when used in error. They require special safeguards like independent double-checks. Examples include insulin, opioids, and heparin.
Tuberculin Syringe — A small syringe, typically 1 mL in capacity, calibrated in 0.01 mL increments. It is used for precise measurement of small medication volumes, such as insulin or subcutaneous heparin.