Orthostatic Syncope

Orthostatic syncope is transient loss of consciousness caused by a fall in systolic pressure of 20 mmHg or more, or diastolic of 10 mmHg or more, within 3 minutes of standing, or systolic under 90 mmHg. It reflects volume depletion, drugs or autonomic failure.

• Causes: dehydration, haemorrhage, adrenal insufficiency, diabetes with autonomic neuropathy, Parkinson disease, multiple system atrophy, amyloidosis, vitamin B12 deficiency, alcohol, prolonged bed rest.
• Drugs: diuretics, alpha blockers, vasodilators, nitrates, tricyclic antidepressants, antipsychotics, levodopa, sildenafil.
• Common in older adults and after meals or hot environments.

Loss of consciousness within seconds to minutes of standing, preceded by dizziness, dim vision and weakness, recovery within a minute on lying flat.

• Neck and shoulder aching (coat hanger pain) in autonomic failure.
• Absence of heart rate rise (under 15 beats per minute) suggests neurogenic cause.
• Supine hypertension in autonomic failure.
• Differential diagnosis: reflex syncope, arrhythmia, aortic stenosis, pulmonary embolism, hypoglycaemia, seizure, vertebrobasilar ischaemia, carotid sinus hypersensitivity, anaemia.
• Complications: falls and fractures, head injury, cardiovascular events, supine hypertension, fear of standing, reduced independence.

Measure blood pressure and heart rate supine after 5 minutes then standing at 1 and 3 minutes.

• Haemoglobin, urea, electrolytes, glucose, HbA1c, morning cortisol or short synacthen test where adrenal insufficiency is possible, vitamin B12, thyroid function.
• ECG; echocardiography when cardiac disease suspected.
• Autonomic testing, tilt table, 24 hour blood pressure monitoring in suspected neurogenic orthostatic hypotension.
• Review all medicines.

Restore volume, stop causative drugs, and add non drug and drug measures stepwise.

• Supportive: slow staged standing, avoid prolonged standing, large meals and alcohol; fluids 2 to 3 litres daily and salt 6 to 10 g daily; raise head of bed by 10 to 15 degrees; waist high compression stockings 30 to 40 mmHg or abdominal binder; leg crossing and squatting; small frequent meals.
• Pharmacological: for volume depletion give 0.9 percent sodium chloride 500 mL IV bolus, repeat as needed. Stop or reduce offending drugs. Chronic neurogenic: midodrine 2.5 mg three times daily increasing to 10 mg three times daily (last dose at least 4 hours before bed); fludrocortisone 0.1 mg daily increasing to 0.3 mg daily with potassium and oedema monitoring; pyridostigmine 30 to 60 mg three times daily as add on. Replace hydrocortisone and fludrocortisone if adrenal insufficiency.
• Procedures: none; treat underlying lesion such as bleeding source or anaemia.
• Special groups: pregnancy, left lateral rest and fluids, avoid midodrine and fludrocortisone unless essential; elderly, titrate cautiously and check supine blood pressure; diabetes, treat neuropathy and glycaemia; heart failure, avoid large volume loading.
• Red flags: syncope with chest pain, dyspnoea, melaena or other bleeding, ECG abnormality, supine systolic over 180 mmHg on treatment, progressive neurological signs, recurrent injurious falls.
• Follow-up: review in 2 to 4 weeks with lying and standing pressures; recheck potassium and supine pressure on therapy; advise on driving and heights.