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1Formulas and methods
Maternity & obstetric nursing
Method
Place the woman in time: weeks of pregnancy, stage of labour or day after birth, and decide what is normal at that point.
Look for the patient in danger: the mother, the fetus or the newborn, or more than one of them.
Link the finding to its cause: VEAL CHOP for decelerations, the four Ts for bleeding, BUBBLE-HE after birth.
Choose the action that improves blood flow and oxygen first (side-lying, stopping oxytocin, fundal massage), then escalate.
Dosage calculations
Dose from strength
volume = dose / strength
Weight-based dose
dose = mg/kg × body weight
Tablets
number = dose / tablet strength
Units
1 g = 1000 mg, 1 mg = 1000 mcg
Method
Convert the ordered dose and the stock strength to the same unit.
Use desired over have times quantity: (D/H) × Q.
For weight-based doses, multiply by the weight in kg first, then divide the daily dose by the number of doses.
Estimate first and check that the answer is reasonable.
IV infusion rates
Pump rate
mL/h = volume (mL)/time (h)
Drip rate
drops/min = volume (mL) × drop factor / time (min)
Infusion time
time (h) = volume (mL)/rate (mL/h)
Method
Pump rate in mL/h: volume divided by time in hours.
Drip rate in drops/min: volume × drop factor divided by time in minutes.
For time remaining: volume left divided by the rate.
Round as the question or the equipment requires.
2Practice problems
1.Maternity & obstetric nursingMedium
A woman at 18 weeks asks about safe exercise. Which advice is correct?
AContact sports and scuba diving are safe if she did them before
BModerate exercise like walking or swimming is encouraged
CExercise lying flat on her back is best after 20 weeks
DExercise should be stopped completely during pregnancy
2.Maternity & obstetric nursingHard
A woman at 28 weeks has itching, and her liver tests and bile acids are raised. Which advice is most important?
AReport reduced fetal movements straight away
BStop attending antenatal visits once itching settles
CItching proves the baby is healthy
DTake a hot bath to relieve the itching
3.Dosage calculationsMedium
A patient weighs 15 kg. The prescribed dose is 15 mg/kg per day, given in 3 equal doses. How many milligrams D are given per dose?
15 kg15 mg/kg/day3× per day
D = mg
4.Dosage calculationsHard
The prescription is 610 units of a drug that comes as 1000 units/mL. Draw up the dose in the 1 mL syringe: what volume V do you give?
610 units1000 units/mL
V = mL
5.IV infusion ratesMedium
500 mL was ordered over 6 hours. After 2 hours you find that 380 mL is still in the bag, and the order must still finish on time. To what rate R in mL/h must the pump be reset?
500 mL / 6 hafter 2 h: 380 mL
R = mL/h
6.IV infusion ratesHard
An infusion of 50 mg in 500 mL runs at 15 mL/h. How many micrograms per minute D does the patient receive?
50 mg/500 mL15 mL/h
D = mcg/min
3Solutions
1.Maternity & obstetric nursing
Answer: B · Moderate exercise like walking or swimming is encouraged
Why this is the answer
Moderate exercise is safe and beneficial for most pregnant women. Contact sports, activities with a high fall risk and scuba diving are avoided, as is lying flat on the back for long periods later in pregnancy.
Answer
B · Moderate exercise like walking or swimming is encouraged
2.Maternity & obstetric nursing
Answer: A · Report reduced fetal movements straight away
Why this is the answer
Intrahepatic cholestasis is linked with stillbirth, especially with high bile acids. Women are monitored closely, told to report reduced movements and may be offered birth earlier. Cool baths and emollients ease itching.
Answer
A · Report reduced fetal movements straight away
3.Dosage calculations
Answer: D = 75 mg
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.
Total per day
15·15 = 225 mg
Per dose
D = 225/3 = 75 mg
Answer
D = 75 mg
4.Dosage calculations
Answer: V = 0.61 mL
Drawing up a dose: volume = (prescribed dose/stock strength) × stock volume. Convert to the same units first, then check that the volume fits the syringe and lands on one of its graduations.
Volume
V = 610/1000 = 0.61 mL
On the syringe
On this 1 mL syringe every small line is 0.01 mL.
Answer
V = 0.61 mL
5.IV infusion rates
Answer: R = 95 mL/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.
Original rate
500/6 = 83.33 mL/h
New rate
R = 380/4 = 95 mL/h
Answer
R = 95 mL/h
Many hospitals allow such an adjustment up to 25% without a new order; check local policy.
6.IV infusion rates
Answer: D = 25 mcg/min
Dose-based infusions: concentration = amount of drug in the bag/bag volume. Pump rate (mL/h) = dose per hour/concentration, and dose per hour = mL/h × concentration. Convert per-minute doses to per-hour (× 60) and keep the mass units the same (1 g = 1000 mg, 1 mg = 1000 mcg).