During spinal anaesthesia for lower limb surgery, the block is at T10. Suddenly the patient develops bradycardia to 38 bpm with hypotension and nausea. The most likely cause of bradycardia in this clinical setting is:

• A Block of T1–T4 cardioaccelerator fibres causing loss of sympathetic cardiac innervation
• B Phrenic nerve palsy causing respiratory compromise and vagal activation
• C High spinal spreading to medullary vasomotor centre causing parasympathetic predominance
• D Hypotension-mediated reflex bradycardia via right atrial stretch receptor (Bezold-Jarisch reflex) ✓

Explanation

When spinal anaesthesia causes significant venous pooling and hypotension, right heart venous return diminishes markedly. Empty or near-empty right atrium triggers the Bezold-Jarisch reflex: mechanoreceptors in the inferoposterior left ventricular wall sense decreased preload and paradoxically mediate vagally-mediated bradycardia, hypotension, and nausea. This triad is the hallmark of high sympathectomy with reduced venous return during neuraxial anaesthesia. Cardioaccelerator fibre block (T1–T4) does contribute when block is at that level, but the Bezold-Jarisch reflex explains the triad at T10. High spinal would present with respiratory compromise, not isolated bradycardia.

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

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Written and medically reviewed by the StethoPrep medical team.