NMC CBT Drug Calculations and Numeracy 3 — Questions and Answers
Question 1: Heparin 25,000 units in 50 mL NaCl to run at 1,200 units/hour. What rate should the syringe pump be set to?
- 1.8 mL/hr
- 2.0 mL/hr
- 2.4 mL/hr (Correct answer)
- 3.0 mL/hr
Correct answer: 2.4 mL/hr
Concentration = 25000/50 = 500 units/mL. Rate = 1200/500 = 2.4 mL/hr.
Step 1: 25000 units/50 mL = 500 units/mL. Step 2: 1200/500 = 2.4 mL/hr. Heparin infusions require regular APTT monitoring (usually every 6 hours initially). The infusion must be clearly labelled and dose changes documented.
Question 2: Prescription: digoxin 125 micrograms daily. Available: 0.25 mg tablets. How many tablets?
- 0.25 tablets
- 0.5 tablets (Correct answer)
- 1 tablet
- 2 tablets
Correct answer: 0.5 tablets
Convert: 0.25 mg = 250 mcg. Calculate: 125/250 = 0.5 tablet (half).
Convert 0.25 mg to micrograms: 0.25 x 1000 = 250 mcg. Calculate: 125/250 = 0.5 (half tablet). Digoxin has a narrow therapeutic index. Check pulse before administration; withhold if below 60 bpm. Signs of toxicity: nausea, visual disturbances, arrhythmias.
Question 3: An insulin infusion of 50 units Actrapid in 50 mL NaCl runs at 4 mL/hr. How many units per hour?
- 2 units/hr
- 4 units/hr (Correct answer)
- 8 units/hr
- 50 units/hr
Correct answer: 4 units/hr
Concentration = 50/50 = 1 unit/mL. At 4 mL/hr: 4 x 1 = 4 units/hr.
50 units/50 mL = 1 unit/mL. Rate x concentration = 4 x 1 = 4 units/hr. Monitor blood glucose hourly. Administer via syringe pump with dedicated IV access. Stop and treat if BG < 4 mmol/L.
Question 4: An 80 kg patient needs gentamicin 5 mg/kg. Available: 80 mg in 2 mL ampoules. How many mL needed?
- 8 mL
- 10 mL (Correct answer)
- 5 mL
- 12 mL
Correct answer: 10 mL
Dose = 5 x 80 = 400 mg. Concentration = 80/2 = 40 mg/mL. Volume = 400/40 = 10 mL (5 ampoules).
Step 1: 5 x 80 = 400 mg. Step 2: 80/2 = 40 mg/mL. Step 3: 400/40 = 10 mL (5 ampoules). Gentamicin requires therapeutic drug monitoring (trough < 1 mg/L for once-daily dosing) and regular renal function monitoring due to nephrotoxicity and ototoxicity risk.
Question 5: Prepare adrenaline infusion: 5 mg in 500 mL NaCl. What is the concentration in micrograms per mL?
- 1 mcg/mL
- 5 mcg/mL
- 10 mcg/mL (Correct answer)
- 100 mcg/mL
Correct answer: 10 mcg/mL
5 mg = 5000 mcg. Concentration = 5000/500 = 10 mcg/mL.
5 mg x 1000 = 5000 mcg. 5000/500 = 10 mcg/mL. This is a standard critical care adrenaline concentration. Must be administered via central line and infusion pump with continuous cardiac monitoring.
Question 6: A portable O2 cylinder contains 340 litres. At 15 L/min for a 60% Venturi mask, how long will it last?
- About 15 minutes
- About 23 minutes (Correct answer)
- About 34 minutes
- About 45 minutes
Correct answer: About 23 minutes
340/15 = 22.67 minutes, approximately 23 minutes.
340 litres / 15 L/min = 22.67 minutes (approximately 23 minutes). This is critically important for patient transfers. Ensure adequate supply for the journey plus a safety margin. A larger cylinder or multiple cylinders may be needed for longer transfers.
NMC CBT Drug Calculations and Numeracy 3
Heparin 25,000 units in 50 mL NaCl to run at 1,200 units/hour.
What rate should the syringe pump be set to?