Obstetrics and Paediatrics
Obstetric and paediatric anaesthesia rewards exact numbers. The exam expects you to reproduce dose limits, block recipes, pre-eclampsia thresholds and paediatric formulae without hesitation, and to explain why each number exists.
Obstetrics
- From 20 weeks, aortocaval compression demands left lateral tilt of 15 degrees or manual uterine displacement for every anaesthetic, including induction and resuscitation.
- Spinal for caesarean section: hyperbaric 0.5% bupivacaine 2.2–2.5 mL with fentanyl 15–25 micrograms and optional preservative-free morphine 100–200 micrograms. Treat hypotension with prophylactic phenylephrine 50–100 microgram boluses to preserve uteroplacental perfusion; reserve ephedrine for bradycardia.
- Pre-eclampsia with severe features: blood pressure 160/110 or above, platelets below 100 × 10⁹/L, rising transaminases or creatinine, pulmonary oedema. Give magnesium sulphate 4 g loading then 1 g/h, and labetalol, hydralazine or nifedipine for blood pressure. Neuraxial anaesthesia is acceptable with platelets above 75–80 × 10⁹/L and no coagulopathy.
Paediatrics
- Weight in kg ≈ (age + 4) × 2. Uncuffed tube internal diameter ≈ age/4 + 4.
- Fasting: 2 hours clear fluid, 4 hours breast milk, 6 hours formula or cows' milk, 8 hours solids.
- Suxamethonium 2 mg/kg intravenously (4 mg/kg intramuscularly); atropine 20 micrograms/kg; bradycardia in a child is usually hypoxic in origin.
Worked example
A 3-year-old weighing 15 kg presents for appendicectomy. Choose a 4.5 uncuffed tube, set maintenance fluid at 4-2-1, giving 40 + 10 = 50 mL/h, induce with sevoflurane, and prescribe paracetamol 15 mg/kg = 225 mg. A 4 mg/kg lidocaine dose would be 60 mg.
Traps
Quoting adult drug doses in a child; forgetting to check cuff pressure or to size down; missing neonatal hypoglycaemia; and underestimating blood loss - 100 mL in a 5 kg neonate is 20% of blood volume.