NORCET 8 Prelims-2025
Pharmacology
Hard
In a 72 kg patient, lorazepam is prescribed at 40 mcg/kg/min to be administered within 15 minutes. The available concentration is 2 mg/mL. How many ml/min of lorazepam should the nurse administer?
Appeared in: NORCET 8 Prelims-2025
Explanation
- The core task is to calculate an IV infusion rate in mL/min.
- First, calculate the total dose in mcg per minute by multiplying the patient's weight by the prescribed dose rate: 72 kg × 40 mcg/kg/min = 2880 mcg/min.
- Next, convert the available drug concentration to the same unit as the dose. Since the dose is in mcg, convert 2 mg/mL to mcg/mL: 2 mg/mL × 1000 mcg/mg = 2000 mcg/mL.
- Finally, divide the total dose rate by the concentration to find the infusion rate in mL/min: 2880 mcg/min ÷ 2000 mcg/mL = 1.44 mL/min.
- Rounding 1.44 to the nearest tenth gives 1.4 mL/min, which matches the correct option.
Why Other Options Were Wrong
- Option B: This rate is too high and results from a calculation error. For example, incorrectly calculating the total dose could lead to this answer.
- Option C: This is an incorrect rounding of the calculated answer (1.44 mL/min). Standard rounding rules dictate rounding down to 1.4.
- Option D: This rate is significantly lower than required and would lead to underdosing the patient. It likely results from a major error, such as dividing the concentration by the dose.
Related Visual
- Visual 1: Infographic: Step-by-step guide to IV drip rate calculation using the formula method, highlighting unit conversion.
- Visual 2: Diagram: A visual aid showing the relationship between mg and mcg (1 mg = 1000 mcg) to emphasize the importance of unit consistency in drug calculations.
Clinical Relevance
- Nursing practice connection: Use the key finding related to IV medication dosage calculation based on body weight and time to guide bedside assessment, documentation, and the next nursing action.
- Accurate dosage calculation is a fundamental and critical nursing responsibility to prevent medication errors and ensure patient safety, especially with high-alert medications like sedatives (lorazepam).
- The 'Six Rights' of medication administration (Right Patient, Right Drug, Right Dose, Right Route, Right Time, Right Documentation) must always be followed. This question specifically tests the 'Right Dose'.
- For precise, low-volume infusion rates like 1.44 mL/min, the use of an electronic infusion pump is mandatory to ensure accurate delivery. Manual regulation via a roller clamp is not safe or reliable for such rates.
How to Approach the Question
- First, identify the question's goal: to find the infusion rate in mL per minute.
- Next, carefully extract all the given numerical values and their units: Patient weight (72 kg), prescribed dose (40 mcg/kg/min), and available concentration (2 mg/mL).
- Recognize that this is a weight-based calculation. Calculate the total dose needed per minute: 72 kg × 40 mcg/kg/min.
- Check for unit consistency between the dose needed (in mcg) and the drug on hand (in mg). Perform the necessary conversion: 2 mg = 2000 mcg.
- Apply the standard formula for infusion rate: Rate = (Dose required / Concentration available).
- Perform the final division and round the answer to the nearest tenth, as suggested by the format of the options.
Concept Tested & Keywords
- Concept Tested: IV medication dosage calculation based on body weight and time.
- Stem keywords: lorazepam, 72 kg, 40 mcg/kg/min, 2 mg/mL, ml/min
- Lead-in keywords: How many
- Clinical cues: Patient weight: 72 kg (indicates a weight-based calculation is required)
- Clinical cues: Dose unit: mcg/kg/min (indicates a rate of infusion calculation)
Question ID
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Practise the full NORCET 8 Prelims-2025
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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