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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
Why is congenital hypothyroidism included in newborn screening?
AIt causes hip dysplasia
BIt causes jaundice that cannot be treated
CEarly treatment prevents brain damage
DIt can only be treated before birth
2.Maternity & obstetric nursingHard
A newborn in the first hours sneezes, has a high-pitched cry, tremors and loose stools. The mother took opioids throughout pregnancy. Which intervention is most appropriate first?
AA quiet, dim room, swaddling and small, frequent feeds
BWithholding feeds until the symptoms settle
CBright lights and frequent handling to keep the baby awake
DGiving naloxone to reverse the opioids
3.Dosage calculationsMedium
How many milligrams of drug m are in 2 mL of a 10% (w/v) solution?
10% w/v2 mL
m = mg
4.Dosage calculationsHard
The prescription is 1200 units of a drug that comes as 10000 units/mL. Draw up the dose in the 1 mL syringe: what volume V do you give?
1200 units10000 units/mL
V = mL
5.IV infusion ratesMedium
Infuse 250 mL over 4 hours with a giving set of 10 gtt/mL. Find the drip rate R in drops per minute. Round to the nearest whole number.
250 mL4 h10 gtt/mL
R = gtt/min
6.IV infusion ratesHard
An infusion of 200 mg in 250 mL runs at 9 mL/h. How many micrograms per minute D does the patient receive?
200 mg/250 mL9 mL/h
D = mcg/min
3Solutions
1.Maternity & obstetric nursing
Answer: C · Early treatment prevents brain damage
Why this is the answer
Untreated congenital hypothyroidism causes poor growth and intellectual disability. Daily levothyroxine started in the first weeks allows normal development.
Answer
C · Early treatment prevents brain damage
2.Maternity & obstetric nursing
Answer: A · A quiet, dim room, swaddling and small, frequent feeds
Why this is the answer
Neonatal abstinence (withdrawal) is managed first with non-drug care: low stimulation, swaddling, skin-to-skin, responsive feeding and rooming-in. Medication is added if scores stay high. Naloxone can precipitate seizures.
Answer
A · A quiet, dim room, swaddling and small, frequent feeds
3.Dosage calculations
Answer: m = 200 mg
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.
Concentration
10% = 10 g/100 mL = 100 mg/mL
Mass of drug
m = 100·2 = 200 mg
Answer
m = 200 mg
4.Dosage calculations
Answer: V = 0.12 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 = 1200/10000 = 0.12 mL
On the syringe
On this 1 mL syringe every small line is 0.01 mL.
Answer
V = 0.12 mL
5.IV infusion rates
Answer: R = 10 gtt/min
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.
Time in minutes
4·60 = 240 min
Drip rate
R = 250·10/240 = 10.42 ≈ 10 gtt/min
Answer
R = 10 gtt/min
At the bedside you round to the nearest whole drop: 10 gtt/min.
6.IV infusion rates
Answer: D = 120 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).