Formula sheets, the key method steps for every topic and 6 practice problems, with full solutions at the back.
Which test estimates how much fetal blood has entered the mother's circulation, to guide the dose of anti-D?
One hour after a vaginal birth, the fundus is firm at the umbilicus, but there is a steady trickle of bright red blood. What is the most likely cause?
A prefilled syringe of epinephrine (adrenaline) is labelled 1:10 000 (0.1 mg/mL). The prescription is 1 mg IV in cardiac arrest. What volume V do you give?
A child weighing 8 kg is prescribed 20 mg/kg per dose of an oral suspension that contains 40 mg in 1 mL. What volume V do you give?
A drip runs at 30 gtt/min through a set of 20 gtt/mL. How many millilitres V does the patient receive in 6 hours?
A bag contains 400 mg of a drug in 50 mL and runs at 20 mL/h. How many milligrams per hour D does the patient receive?
Answer: A · Kleihauer–Betke test
The Kleihauer–Betke test (or flow cytometry) measures fetal red cells in maternal blood after a sensitising event such as trauma or birth. The result guides whether extra anti-D is needed.
Answer: A · A tear of the cervix, vagina or perineum
Continuous bright red bleeding with a firm uterus suggests trauma (laceration), which needs inspection and repair. Atony would make the uterus soft, and normal lochia does not flow in a steady stream.
Answer: V = 10 mL
Solution strengths: a percentage strength is grams per 100 mL, so 1% = 1 g/100 mL = 10 mg/mL. A ratio strength 1:1000 means 1 g in 1000 mL = 1 mg/mL; 1:10 000 is 0.1 mg/mL. For a dilution the amount of drug stays the same: C₁·V₁ = C₂·V₂.
US labels now state mg/mL (1 mg/mL = 1:1000; 0.1 mg/mL = 1:10 000). Never give 1 mg/mL epinephrine IV push.
Answer: V = 4 mL
Dose calculation: the amount to give equals what is prescribed divided by what you have, times the quantity it comes in: amount = (desired dose/stock strength) × stock volume. Always keep the units the same (convert g to mg, mg to mcg first) and check that the answer is sensible.
Answer: V = 540 mL
Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.
Answer: D = 160 mg/h
Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.
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