Anaesthetic Choice for Caesarean Section
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Direct answer
Spinal anaesthesia is the technique of choice for caesarean section: a single intrathecal injection of hyperbaric bupivacaine (commonly 10-12.5 mg) with an opioid such as fentanyl (10-25 micrograms) or diamorphine produces a block to at least the T4-T6 sensory level within minutes, keeps the mother awake for delivery, avoids the airway and its obstetric-specific dangers — failed intubation and pulmonary aspiration — and improves neonatal condition compared with general anaesthesia in most settings. Hypotension, its chief physiological toll, is prevented and treated with left uterine displacement, co-loaded intravenous fluid, and phenylephrine (50-100 microgram boluses or an infusion), the current vasopressor of choice for fetal acid-base neutrality. Epidural top-up serves women with a working labour epidural; general anaesthesia is reserved for profound fetal compromise, contraindications to neuraxial block such as coagulopathy or frank sepsis with shock, and urgency where no block exists.
What you must remember
- Spinal recipe: hyperbaric bupivacaine 0.5%, 10-12.5 mg (about 2-2.5 mL), plus fentanyl 10-25 micrograms or diamorphine 300 micrograms; target sensory level T4-T6 (to the nipple or sternum); onset 2-5 minutes; duration roughly 2-3 hours.
- Why awake beats asleep: the pregnant airway is difficult (oedema, full dentition), ventilation is harder (low functional residual capacity), and aspiration risk is high (Mendelson syndrome) — failed intubation runs of the order of 1 in 300-500, many-fold above the general theatre.
- Hypotension protocol: block to sympathectomy plus aortocaval compression drop vascular tone — prophylaxis with at least 15 degrees of left tilt or manual displacement, crystalloid co-load, and phenylephrine 50-100 micrograms titrated to maintain systolic pressure near baseline; ephedrine (tachycardia, fetal acidosis with repeated doses) is second line.
- High spinal and total spinal: ascending block above T4 with respiratory embarrassment — recognise bradycardia, hypotension and dyspnoea; treat with airway support, vasopressors and fluids; it follows excessive dose or barbotage, and must be distinguished from hypotension alone.
- Epidural top-up: for an existing labour epidural, urgent conversion with 10-20 mL of concentrated local anaesthetic (lidocaine 2% with adrenaline or bupivacaine 0.5%) in fractionated doses through a tested catheter, with a test dose to exclude intravascular or intrathecal placement.
- General anaesthesia technique: rapid sequence induction with cricoid pressure, propofol (moderated in shock or severe pre-eclampsia), and succinylcholine 1-1.5 mg/kg, whose short duration suits the difficult airway.
- Neuraxial contraindications: patient refusal, coagulopathy (platelets commonly below about 75-80 × 10^9/L in pre-eclampsia protocols), sepsis, and hypovolaemic shock until resuscitated.
- Pre-eclampsia angle: neuraxial is preferred if platelets permit (avoids pressor surges of laryngoscopy); general anaesthesia in pre-eclampsia risks hypertensive crisis at intubation — blunted with agents such as magnesium continuation, opioids or short-acting antihypertensives before induction.
A decision walk-through
An elective caesarean at 39 weeks in a healthy woman: spinal in the sitting or lateral position at L3-L4, hyperbaric bupivacaine 12 mg with fentanyl, laid supine with left tilt, co-loaded with a litre of crystalloid, phenylephrine infusion running to hold systolic pressure — delivery within 15 minutes of the block, neonate vigorous, mother's partner present. Now the same day's emergency: a term woman with an epidural that has worked well through labour needs a category-2 caesarean for arrest — top up the tested catheter in fractionated doses, aspirating between aliquots. Then the category-1 crash for cord prolapse with no block: preoxygenase, rapid sequence induction with cricoid pressure, incision within minutes — the failed-intubation drill is rehearsed beforehand, never improvised.
Finally, the severe pre-eclampsia case with platelets of 95,000: neuraxial stands, general anaesthesia doubles the intubation-pressor risk — the choice of technique is a risk-benefit arithmetic performed for every single case.
Where students slip
Two classic confusions. First, vasopressor choice: phenylephrine is first line for spinal hypotension (alpha agonism, reflex bradycardia, fetal acid-base neutral), while ephedrine crosses the placenta and repeated doses acidify the fetus — an old teaching reversed by modern trials that candidates still get backwards. Second, the level: a block to T10 (umbilicus) is inadequate for caesarean — intra-abdominal traction and peritoneal pain demand T4-T6; examiners ask "what level?" expecting "nipple/T4-T6". The third, subtler slip is calling general anaesthesia safer for the fetus: apart from true profound compromise where minute-level speed matters, awake regional anaesthesia delivers better neonatal acid-base status and immediate skin-to-skin contact — the default answer is spinal.
Frequently asked questions
Which anaesthetic technique is standard for elective caesarean section?
Spinal anaesthesia — hyperbaric bupivacaine 10-12.5 mg with an intrathecal opioid, targeting a T4-T6 sensory level with the mother awake.
How is spinal hypotension managed?
Left uterine displacement, crystalloid co-load, and titrated phenylephrine 50-100 micrograms (or infusion) to maintain baseline systolic pressure, with ephedrine as second line.
When is epidural top-up used instead of a spinal?
When a functioning labour epidural exists — urgent conversion with fractionated concentrated local anaesthetic through a tested catheter saves the time and risk of a fresh spinal.
Which conditions force general anaesthesia for caesarean?
Patient refusal of neuraxial block, coagulopathy or thrombocytopenia below threshold, sepsis with shock, profound hypovolaemia, and category-1 urgency without an existing block.
Why is the obstetric airway dangerous under general anaesthesia?
Airway oedema and full dentition make intubation harder, functional residual capacity is low, and aspiration risk is high — failed intubation is several-fold commoner than in general surgery.