A parturient at 38 weeks undergoes emergency caesarean section under general anaesthesia for placental abruption. After delivery, uterine atony develops. Oxytocin 5 IU is given as IV bolus. The haemodynamically dangerous direct effect of rapid IV oxytocin bolus is:

• A Coronary vasospasm and myocardial ischaemia
• B Pulmonary hypertension and right heart failure via thromboxane release
• C Severe vasoconstriction and hypertension due to V2 receptor activation
• D Profound vasodilation with hypotension and reflex tachycardia via V1 receptor agonism ✓

Explanation

Rapid IV bolus of oxytocin (particularly doses ≥5 IU) causes significant vasodilation via nitric oxide release and direct vascular smooth muscle relaxation, resulting in profound hypotension, reflex tachycardia, and decreased SVR. In haemodynamically compromised patients (haemorrhage, cardiac disease), this can be catastrophic. Current guidelines recommend slow IV infusion (5 IU over 5–10 minutes) rather than rapid bolus. Oxytocin acts on OT receptors in vascular smooth muscle to release NO; it does not act via V1 or V2 vasopressin receptors at standard doses. Ergometrine (not oxytocin) causes vasoconstriction and is contraindicated in hypertension and cardiac disease.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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