Autonomic Dysreflexia — FRCA Final MCQ

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ModerateTrauma & Emergency AnaesthesiaAutonomic DysreflexiaFRCA Final

Six weeks after sustaining a complete C5 spinal cord injury, a 40-year-old man is undergoing rehabilitation. His urinary catheter becomes obstructed and he develops a pounding headache with flushing and sweating above the level of the lesion. His blood pressure is 210/110 mmHg and his heart rate is 48 beats min−1. Which complication best explains this episode?

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Correct answer: B — Autonomic dysreflexia

The diagnosis is **autonomic dysreflexia**. A noxious stimulus below a spinal cord lesion at or above T6—here, bladder distension from an obstructed catheter—causes an uncontrolled spinal sympathetic discharge. Widespread vasoconstriction below the lesion produces severe hypertension. Intact carotid and aortic baroreceptors then increase vagal activity, causing reflex bradycardia, while compensatory vasodilatation and sweating occur above the lesion. The initial hypotension and bradycardia following cervical injury represent neurogenic shock, whereas autonomic dysreflexia develops subsequently and may occur within weeks. Neurogenic pulmonary oedema would predominantly cause respiratory failure. Paroxysmal sympathetic hyperactivity is associated mainly with severe brain injury and usually causes tachycardia. Supraventricular tachycardia is incompatible with the bradycardia, and tamponade causes obstructive hypotension rather than paroxysmal hypertension.

Reference: Cowan H, Lakra C, Desai M. Autonomic dysreflexia in spinal cord injury. BMJ 2020;371:m3596. https://www.bmj.com/content/371/bmj.m3596