NEW Added to close a syllabus gap — obstetric anaesthesia and analgesia is named in the Clinical Anaesthesiology heading.

Obstetric anaesthesia

Labour analgesia, caesarean section, and the obstetric emergencies — pre-eclampsia, haemorrhage and amniotic fluid embolism.

Labour analgesia

Pain pathways: first stage T10–L1 (visceral, uterine contraction and cervical dilatation); second stage adds S2–S4 (somatic, perineal stretch via the pudendal nerve).
Epidural is the gold standard. Effects: prolongs the second stage, increases instrumental delivery, no increase in caesarean rate, no long-term backache.
Remifentanil PCA is the alternative where epidural is contraindicated — but needs one-to-one midwifery care, continuous SpO₂ and oxygen, because of apnoea risk.
Entonox — 50:50 N₂O/O₂, self-administered, onset ~30 s. Watch the pseudocritical temperature of −6 °C if cylinders are stored cold.

	Spinal	General anaesthesia
Block height needed	T4 to light touch	—
Typical dose	2.0–2.5 ml heavy bupivacaine 0.5% + fentanyl 15 µg + diamorphine	RSI: thiopentone or propofol + suxamethonium or rocuronium
Main risk	Hypotension (up to 80%)	Failed intubation (~1:250, far higher than general population) and aspiration
Prevention	Phenylephrine infusion + fluid co-load + left uterine displacement	Antacid prophylaxis, ramped position, videolaryngoscopy, preoxygenation

Phenylephrine beats ephedrine — ephedrine crosses the placenta and raises fetal metabolic rate, lowering umbilical pH.
Aortocaval compression is significant from about 20 weeks: use 15° left lateral tilt or manual displacement.
Antacid prophylaxis: ranitidine, sodium citrate 0.3 M 30 ml, and metoclopramide.
Awareness risk is higher in obstetric GA — the reasons are light anaesthesia to avoid uterine atony and neonatal depression.

Definition: new hypertension after 20 weeks with proteinuria or other organ dysfunction. Severe: BP ≥160/110, or features such as headache, visual disturbance, epigastric pain, clonus.
HELLP: Haemolysis, Elevated Liver enzymes, Low Platelets.
Magnesium sulphate for seizure prophylaxis and treatment — 4 g load then 1 g/h. Monitor reflexes, respiratory rate, urine output. Calcium gluconate is the antidote.
Magnesium toxicity sequence: loss of tendon reflexes (4–5 mmol/L) → respiratory depression (6–7) → cardiac arrest (>12). It also potentiates non-depolarising blockers.
Check the platelet count and its trend before neuraxial block. Airway oedema makes intubation harder; use a smaller tube.
Avoid ergometrine — it causes severe hypertension.

Uterotonic	Dose	Caution
Oxytocin	5 IU slow IV, then infusion	Rapid bolus causes vasodilation, hypotension and tachycardia
Ergometrine	500 µg IM	Avoid in hypertension and pre-eclampsia; causes vomiting
Carboprost	250 µg IM, up to 8 doses	Contraindicated in asthma — severe bronchospasm
Misoprostol	800 µg PR	Pyrexia, shivering

Causes of PPH — the 4 Ts: Tone (commonest), Trauma, Tissue (retained products), Thrombin (coagulopathy).
Amniotic fluid embolism: sudden hypoxia, hypotension and coagulopathy/DIC, often with seizures and cardiovascular collapse. Diagnosis is clinical and of exclusion; management is supportive with early massive haemorrhage protocol.
The uterus receives about 700–900 ml/min at term (10% of cardiac output) and the uteroplacental bed is maximally dilated and pressure-dependent — so maternal hypotension directly reduces fetal perfusion.