Baroreflex Failure

Baroreflex failure is loss of buffering of blood pressure from damage to the afferent baroreflex arc (carotid sinus, glossopharyngeal nerve, nucleus tractus solitarius), causing labile hypertension with sudden surges and hypotension. Causes include neck irradiation, neck surgery (carotid endarterectomy, radical neck dissection), carotid body tumour resection, neck tumours, brainstem stroke or tumour, and familial paraganglioma.

Pathophysiology. Without afferent input, sympathetic outflow is unrestrained, causing extreme hypertension with emotion or stress, and lack of compensation to hypotension.

Labile hypertension with surges over 200 mmHg systolic, severe headache, flushing, sweating, palpitation and tachycardia, followed by falls to normal or low pressure (and bradycardia). Orthostatic intolerance can occur. Emotional stress, neck movement or noise are triggers. It may follow neck treatment by months to years.

Red flags.

• Hypertensive crisis with encephalopathy.
• Persistent severe hypertension after neck surgery or radiotherapy.

Prior neck surgery, radiotherapy or brainstem injury and labile pressure with a raised blood pressure variability. Autonomic testing shows blunted baroreflex gain (absent heart rate responses to phenylephrine and nitroprusside, loss of phase IV overshoot of Valsalva manoeuvre). Plasma noradrenaline is raised during surges. Exclude phaeochromocytoma (plasma metanephrines), thyrotoxicosis, substance use, panic disorder and drug effects. Imaging of the neck and brainstem.

Differential diagnosis.

• Phaeochromocytoma and paraganglioma.
• Autonomic dysreflexia, panic attacks and withdrawal states.
• Essential hypertension with variability and thyrotoxicosis.

Acute surge. Use short acting agents: clonidine 0.1 to 0.2 mg orally, then 0.1 mg hourly (maximum 0.8 mg), or sublingual or oral short acting agents. Intravenous nitroprusside or labetalol for crisis, with ICU monitoring.

Long term. Clonidine 0.1 mg twice daily, increased to 0.3 mg twice daily (or transdermal patch), as the mainstay, with benzodiazepines (diazepam 2 to 5 mg or lorazepam) for stress triggered surges. Add beta blockers cautiously and alpha blockers. Avoid abrupt clonidine withdrawal, which causes rebound hypertension.

Hypotension. Fluids, salt and compression.

Non-drug measures. Stress reduction, relaxation, cognitive behavioural therapy and avoidance of triggers.

Device therapy. Baroreflex activation therapy has been used in selected patients.

Monitoring. Home blood pressure diary, ambulatory monitoring, renal function and cardiac function.

Referral and escalation. Refer to an autonomic or hypertension specialist.