Clinical refresher
CRNA med math & clinical refresher
CRNA programs and interviews probe whether your medication math and critical-care fundamentals are sharp. This is the refresher — the calculations and concepts you'll be expected to know cold, with worked examples and practice.
Conversions to know cold
The calculations you must know
Volume = (desired dose ÷ available concentration) × volume per unit
Example: Order 40 mg; vial is 80 mg / 2 mL → (40 ÷ 80) × 2 = 1 mL.
Dose = ordered (mg/kg) × weight (kg)
Example: Propofol 2 mg/kg for a 70 kg patient → 2 × 70 = 140 mg.
gtt/min = (volume mL × drop factor gtt/mL) ÷ time in minutes
Example: 1000 mL over 8 h with a 15 gtt/mL set → (1000 × 15) ÷ 480 ≈ 31 gtt/min.
mL/hr = (mcg/kg/min × weight kg × 60) ÷ concentration (mcg/mL)
Example: Norepinephrine 0.1 mcg/kg/min, 80 kg, bag 4 mg/250 mL (= 16 mcg/mL) → (0.1 × 80 × 60) ÷ 16 = 30 mL/hr.
A 1% solution = 10 mg/mL (1 g per 100 mL)
Example: Lidocaine 2% = 20 mg/mL; so 5 mL holds 100 mg.
Practice problems
Work each one on paper first, then check yourself.
1. Order 25 mg; the vial is 50 mg/mL. How many mL do you draw up?
Show the work
25 ÷ 50 = 0.5 mL.
2. Succinylcholine 1.5 mg/kg for a 60 kg patient. What dose?
Show the work
1.5 × 60 = 90 mg.
3. Infuse 1000 mL over 6 h with a 10 gtt/mL set. Rate in gtt/min?
Show the work
(1000 × 10) ÷ 360 ≈ 28 gtt/min.
4. Dopamine 5 mcg/kg/min, 90 kg, bag 400 mg/250 mL (1600 mcg/mL). Rate in mL/hr?
Show the work
(5 × 90 × 60) ÷ 1600 = 27,000 ÷ 1600 ≈ 16.9 mL/hr.
5. How many mg of lidocaine are in 3 mL of a 2% solution?
Show the work
2% = 20 mg/mL → 20 × 3 = 60 mg.
6. Convert 0.5 g to mcg.
Show the work
0.5 g × 1000 = 500 mg × 1000 = 500,000 mcg.
56 more, from infusions to conversions
Drip rates, weight-based doses, concentrations and unit conversions — the shapes that come up most. Each one shows its working.
7. Phenylephrine 100 mcg IV ordered.
Stock: 10 mg in 250 mL. How many mL do you draw?
Show the work
10 mg / 250 mL = 40 mcg/mL. 100 mcg ÷ 40 mcg/mL = 2.5 mL. = 2.5 mL
8. Heparin 18 units/kg/hr for an 80 kg patient.
Bag: 25,000 units in 250 mL. Set the pump rate.
Show the work
18 × 80 = 1,440 units/hr. 25,000 units / 250 mL = 100 units/mL. 1,440 ÷ 100 = 14.4 mL/hr. = 14.4 mL/hr
9. Norepinephrine 0.1 mcg/kg/min for a 70 kg patient.
Bag: 4 mg in 250 mL. Set the pump rate.
Show the work
0.1 × 70 = 7 mcg/min → ×60 = 420 mcg/hr. 4 mg / 250 mL = 16 mcg/mL. 420 ÷ 16 = 26.25 mL/hr. = 26.25 mL/hr
10. Insulin infusion ordered at 6 units/hr.
Bag: 50 units in 100 mL. Set the pump rate.
Show the work
50 units / 100 mL = 0.5 units/mL. 6 ÷ 0.5 = 12 mL/hr. = 12 mL/hr
11. Order: 1.5 mg/kg. Patient weighs 176 lb.
Convert and calculate the dose in mg.
Show the work
176 lb ÷ 2.2 = 80 kg. 1.5 mg/kg × 80 kg = 120 mg. = 120 mg
12. Nitroglycerin 20 mcg/min ordered.
Bag: 50 mg in 250 mL. Set the pump rate.
Show the work
50 mg / 250 mL = 200 mcg/mL. 20 mcg/min × 60 = 1,200 mcg/hr. 1,200 ÷ 200 = 6 mL/hr. = 6 mL/hr
13. Dopamine 5 mcg/kg/min for an 80 kg patient.
Bag: 800 mg in 500 mL. Set the pump rate.
Show the work
5 × 80 = 400 mcg/min → ×60 = 24,000 mcg/hr. 800 mg / 500 mL = 1,600 mcg/mL. 24,000 ÷ 1,600 = 15 mL/hr. = 15 mL/hr
14. Dobutamine 5 mcg/kg/min for a 70 kg patient.
Bag: 250 mg in 250 mL. Set the pump rate.
Show the work
5 × 70 = 350 mcg/min → ×60 = 21,000 mcg/hr. 250 mg / 250 mL = 1,000 mcg/mL. 21,000 ÷ 1,000 = 21 mL/hr. = 21 mL/hr
15. Insulin infusion ordered at 8 units/hr.
Bag: 100 units in 100 mL. Set the pump rate.
Show the work
100 units / 100 mL = 1 unit/mL. 8 units/hr ÷ 1 unit/mL = 8 mL/hr. = 8 mL/hr
16. Heparin bolus 80 units/kg for a 75 kg patient.
How many units do you give?
Show the work
80 units/kg × 75 kg = 6,000 units. = 6000 units
17. Order: 0.5 mg/kg. Patient weighs 220 lb.
Convert and calculate the dose in mg.
Show the work
220 lb ÷ 2.2 = 100 kg. 0.5 mg/kg × 100 kg = 50 mg. = 50 mg
18. Maintenance fluids: 1,000 mL ordered over 8 hours.
Set the pump rate.
Show the work
1,000 mL ÷ 8 hr = 125 mL/hr. = 125 mL/hr
19. Epinephrine 2 mcg/min ordered.
Bag: 4 mg in 250 mL. Set the pump rate.
Show the work
4 mg / 250 mL = 16 mcg/mL. 2 mcg/min × 60 = 120 mcg/hr. 120 ÷ 16 = 7.5 mL/hr. = 7.5 mL/hr
20. Vasopressin 0.04 units/min ordered.
Bag: 20 units in 100 mL. Set the pump rate.
Show the work
20 units / 100 mL = 0.2 units/mL. 0.04 × 60 = 2.4 units/hr. 2.4 ÷ 0.2 = 12 mL/hr. = 12 mL/hr
21. Propofol 25 mcg/kg/min for an 80 kg patient.
Stock: 10 mg/mL. Set the pump rate.
Show the work
25 × 80 = 2,000 mcg/min = 2 mg/min → ×60 = 120 mg/hr. 120 ÷ 10 mg/mL = 12 mL/hr. = 12 mL/hr
22. Amiodarone 1 mg/min ordered.
Bag: 200 mg in 100 mL. Set the pump rate.
Show the work
200 mg / 100 mL = 2 mg/mL. 1 mg/min × 60 = 60 mg/hr. 60 ÷ 2 = 30 mL/hr. = 30 mL/hr
23. Lidocaine 2 mg/min ordered.
Bag: 2 g in 500 mL. Set the pump rate.
Show the work
2 g = 2,000 mg / 500 mL = 4 mg/mL. 2 mg/min × 60 = 120 mg/hr. 120 ÷ 4 = 30 mL/hr. = 30 mL/hr
24. Procainamide 3 mg/min ordered.
Bag: 1 g in 250 mL. Set the pump rate.
Show the work
1 g = 1,000 mg / 250 mL = 4 mg/mL. 3 mg/min × 60 = 180 mg/hr. 180 ÷ 4 = 45 mL/hr. = 45 mL/hr
25. Milrinone 0.375 mcg/kg/min for an 80 kg patient.
Bag: 20 mg in 100 mL. Set the pump rate.
Show the work
20 mg / 100 mL = 200 mcg/mL. 0.375 × 80 = 30 mcg/min → ×60 = 1,800 mcg/hr. 1,800 ÷ 200 = 9 mL/hr. = 9 mL/hr
26. Fentanyl 75 mcg IV ordered.
Stock: 50 mcg/mL. How many mL do you draw?
Show the work
75 mcg ÷ 50 mcg/mL = 1.5 mL. = 1.5 mL
27. Order: 4 mg/kg. Patient weighs 165 lb.
Convert and calculate the dose in mg.
Show the work
165 lb ÷ 2.2 = 75 kg. 4 mg/kg × 75 kg = 300 mg. = 300 mg
28. Nicardipine 5 mg/hr ordered.
Bag: 25 mg in 250 mL. Set the pump rate.
Show the work
25 mg / 250 mL = 0.1 mg/mL. 5 mg/hr ÷ 0.1 mg/mL = 50 mL/hr. = 50 mL/hr
29. Esmolol 50 mcg/kg/min for a 100 kg patient.
Bag: 2.5 g in 250 mL. Set the pump rate.
Show the work
2.5 g = 2,500 mg / 250 mL = 10 mg/mL = 10,000 mcg/mL. 50 × 100 = 5,000 mcg/min → ×60 = 300,000 mcg/hr. 300,000 ÷ 10,000 = 30 mL/hr. = 30 mL/hr
30. Magnesium 2 g ordered over 30 minutes.
Bag: 2 g in 50 mL. Set the pump rate.
Show the work
50 mL over 30 min = 0.5 hr. 50 mL ÷ 0.5 hr = 100 mL/hr. = 100 mL/hr
31. Potassium 20 mEq ordered over 2 hours.
Bag: 20 mEq in 100 mL. Set the pump rate.
Show the work
100 mL ÷ 2 hr = 50 mL/hr. = 50 mL/hr
32. Diltiazem 15 mg/hr ordered.
Bag: 125 mg in 125 mL. Set the pump rate.
Show the work
125 mg / 125 mL = 1 mg/mL. 15 mg/hr ÷ 1 mg/mL = 15 mL/hr. = 15 mL/hr
33. Nitroprusside 2 mcg/kg/min for a 50 kg patient.
Bag: 50 mg in 250 mL. Set the pump rate.
Show the work
50 mg / 250 mL = 200 mcg/mL. 2 × 50 = 100 mcg/min → ×60 = 6,000 mcg/hr. 6,000 ÷ 200 = 30 mL/hr. = 30 mL/hr
34. Labetalol 2 mg/min ordered.
Bag: 200 mg in 200 mL. Set the pump rate.
Show the work
200 mg / 200 mL = 1 mg/mL. 2 mg/min × 60 = 120 mg/hr. 120 ÷ 1 = 120 mL/hr. = 120 mL/hr
35. Cisatracurium 3 mcg/kg/min for a 70 kg patient.
Bag: 20 mg in 100 mL. Set the pump rate.
Show the work
20 mg / 100 mL = 200 mcg/mL. 3 × 70 = 210 mcg/min → ×60 = 12,600 mcg/hr. 12,600 ÷ 200 = 63 mL/hr. = 63 mL/hr
36. Vecuronium bolus 0.1 mg/kg for an 80 kg patient.
How many mg do you give?
Show the work
0.1 mg/kg × 80 kg = 8 mg. = 8 mg
37. Rocuronium bolus 0.6 mg/kg for a 75 kg patient.
How many mg do you give?
Show the work
0.6 mg/kg × 75 kg = 45 mg. = 45 mg
38. A patient weighs 198 lb.
Convert to kilograms. 1 kg = 2.2 lb.
Show the work
198 lb ÷ 2.2 = 90 kg. = 90 kg
39. A patient weighs 60 kg.
Convert to pounds. 1 kg = 2.2 lb.
Show the work
60 kg × 2.2 = 132 lb. = 132 lb
40. Convert 0.4 mg to micrograms.
1 mg = 1000 mcg.
Show the work
0.4 mg × 1000 = 400 mcg. = 400 mcg
41. Convert 250 mcg to milligrams.
1 mg = 1000 mcg.
Show the work
250 mcg ÷ 1000 = 0.25 mg. = 0.25 mg
42. Convert 0.5 g to milligrams.
1 g = 1000 mg.
Show the work
0.5 g × 1000 = 500 mg. = 500 mg
43. Infuse 100 mL over 30 minutes by gravity.
Drop factor: 15 gtt/mL. Find the drip rate.
Show the work
(100 mL × 15 gtt/mL) ÷ 30 min = 1,500 ÷ 30 = 50 gtt/min. = 50 gtt/min
44. A gravity line runs at 90 mL/hr.
Drop factor: 20 gtt/mL. Find the drip rate.
Show the work
90 mL/hr ÷ 60 = 1.5 mL/min. 1.5 × 20 gtt/mL = 30 gtt/min. = 30 gtt/min
45. A 500 mL bag is running at 125 mL/hr.
How many hours will it last?
Show the work
500 mL ÷ 125 mL/hr = 4 hr. = 4 hr
46. A 1,000 mL bag is running at 80 mL/hr.
How many hours will it last?
Show the work
1,000 mL ÷ 80 mL/hr = 12.5 hr. = 12.5 hr
47. A bag holds 500 mg of drug in 250 mL.
What is the concentration in mg/mL?
Show the work
500 mg ÷ 250 mL = 2 mg/mL. = 2 mg/mL
48. A bag holds 4 mg of drug in 250 mL.
What is the concentration in mcg/mL? (1 mg = 1000 mcg)
Show the work
4 mg = 4,000 mcg. 4,000 mcg ÷ 250 mL = 16 mcg/mL. = 16 mcg/mL
49. Ketamine 0.2 mg/kg/hr for an 80 kg patient.
Stock: 10 mg/mL. Set the pump rate.
Show the work
0.2 × 80 = 16 mg/hr. 16 ÷ 10 mg/mL = 1.6 mL/hr. = 1.6 mL/hr
50. Dexmedetomidine 0.4 mcg/kg/hr for a 70 kg patient.
Bag: 200 mcg in 50 mL. Set the pump rate.
Show the work
200 mcg / 50 mL = 4 mcg/mL. 0.4 × 70 = 28 mcg/hr. 28 ÷ 4 = 7 mL/hr. = 7 mL/hr
51. Furosemide 10 mg/hr ordered.
Bag: 100 mg in 100 mL. Set the pump rate.
Show the work
100 mg / 100 mL = 1 mg/mL. 10 mg/hr ÷ 1 mg/mL = 10 mL/hr. = 10 mL/hr
52. Octreotide 50 mcg/hr ordered.
Bag: 500 mcg in 250 mL. Set the pump rate.
Show the work
500 mcg / 250 mL = 2 mcg/mL. 50 mcg/hr ÷ 2 mcg/mL = 25 mL/hr. = 25 mL/hr
53. Argatroban 2 mcg/kg/min for a 90 kg patient.
Bag: 250 mg in 250 mL. Set the pump rate.
Show the work
250 mg / 250 mL = 1 mg/mL = 1,000 mcg/mL. 2 × 90 = 180 mcg/min → ×60 = 10,800 mcg/hr. 10,800 ÷ 1,000 = 10.8 mL/hr. = 10.8 mL/hr
54. Phenylephrine infusion 40 mcg/min ordered.
Bag: 20 mg in 250 mL. Set the pump rate.
Show the work
20 mg / 250 mL = 80 mcg/mL. 40 mcg/min × 60 = 2,400 mcg/hr. 2,400 ÷ 80 = 30 mL/hr. = 30 mL/hr
55. Epinephrine 0.01 mg/kg for a 70 kg patient.
How many mg do you give?
Show the work
0.01 mg/kg × 70 kg = 0.7 mg. = 0.7 mg
56. One unit of PRBCs (300 mL) is ordered over 2 hours.
Set the pump rate.
Show the work
300 mL ÷ 2 hr = 150 mL/hr. = 150 mL/hr
57. Bumetanide 1 mg/hr ordered.
Bag: 5 mg in 100 mL. Set the pump rate.
Show the work
5 mg / 100 mL = 0.05 mg/mL. 1 mg/hr ÷ 0.05 mg/mL = 20 mL/hr. = 20 mL/hr
58. Aminophylline 0.6 mg/kg/hr for an 80 kg patient.
Bag: 500 mg in 250 mL. Set the pump rate.
Show the work
500 mg / 250 mL = 2 mg/mL. 0.6 × 80 = 48 mg/hr. 48 ÷ 2 = 24 mL/hr. = 24 mL/hr
59. Pantoprazole 6 mg/hr ordered.
Bag: 80 mg in 100 mL. Set the pump rate.
Show the work
80 mg / 100 mL = 0.8 mg/mL. 6 mg/hr ÷ 0.8 mg/mL = 7.5 mL/hr. = 7.5 mL/hr
60. Tranexamic acid 10 mg/kg for a 70 kg patient.
How many mg do you give?
Show the work
10 mg/kg × 70 kg = 700 mg. = 700 mg
61. Lidocaine is supplied as a 2% solution.
How many mg are in each mL? (2% = 2 g/100 mL)
Show the work
2% = 2 g / 100 mL = 2,000 mg / 100 mL = 20 mg/mL. = 20 mg/mL
62. D50 is 50% dextrose. How many grams are in a 50 mL amp?
50% = 50 g/100 mL.
Show the work
50% = 50 g / 100 mL = 0.5 g/mL. 0.5 × 50 mL = 25 g. = 25 g
Critical-care quick reference
Interview-ready- CO = HR × SV (normal ≈ 4–8 L/min)
- MAP = DBP + ⅓ (SBP − DBP) — target ≥ 65 mmHg
- SV depends on preload, afterload, and contractility
- Pressors (raise SVR): norepinephrine, phenylephrine, vasopressin
- Inotropes (raise contractility): dobutamine, milrinone, epinephrine
- Dopamine is dose-dependent across receptors
- 1) pH — acidemia < 7.35, alkalemia > 7.45
- 2) PaCO₂ (respiratory) — normal 35–45 mmHg
- 3) HCO₃⁻ (metabolic) — normal 22–26 mEq/L
- 4) Compensation — which system is correcting?
- K⁺ 3.5–5.0 — hyperkalemia → peaked T waves; hypokalemia → arrhythmias
- Na⁺ 135–145 — correct slowly to avoid shifts
- Mg²⁺ and Ca²⁺ matter for rhythm and contractility
Turn knowledge into answers
Clinical questions are a big part of CRNA interviews. Practice articulating your reasoning out loud — browse the clinical question bank, then get feedback from Coach or a full mock with Ana.
For study and interview prep only. Doses, formulas, and reference ranges are summarized for review and may differ by source and institution — always confirm against an authoritative clinical reference and your program's protocols.