Orthostatic Hypotension

Overview

Also known as postural hypotension, orthostatic hypotension (OH) describes a fall in blood pressure when standing up from sitting or lying down.

OH is defined as a drop in blood pressure of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing.

Pathophysiology

When a healthy person stands up, their blood pools in the veins of the leg, reducing the venous return to the heart and reducing the cardiac output. This leads to the stimulation of baroreceptors and sympathetic activation causing an increase in heart rate, cardiac stroke volume and peripheral vasoconstriction to prevent blood pressure from falling. When these mechanisms fail, orthostatic hypotension can arise.

Epidemiology

• Presentation increases with age, most patients are >70 years
• More prevalent in those with Parkinson’s disease

Causes

• Normal ageing
• Deconditioning due to prolonged bed rest
• Hypovolaemia:
  • Dehydration
  • Excess diuretic use
  • Vasodilators
• Drugs:
  • Beta-blockers
  • Sildenafil
  • Tricyclic antidepressants
  • MAO inhibitors
  • Alpha blockers
  • Levodopa and dopamine agonists
• Neurological:
  • Parkinson’s disease
  • Alcoholic neuropathy
  • Guillain-Barré syndrome
  • Neurosyphilis
  • Multiple system atrophy
• Cardiovascular:
  • Aortic stenosis
  • Arrhythmia
  • Myocardial infarction
  • Heart failure
  • Constrictive pericarditis
  • Cardiac tamponade
• Haematological:
  • Anaemia
• Endocrine:
  • Diabetes mellitus
  • Primary hypoaldosteronism (Addison’s disease)
  • Phaeochromocytoma

Presentation

Patients usually have symptoms after standing from sitting or lying down. The symptoms are a result of inadequate cerebral perfusion due to the blood pressure being too low as the body responds too slowly. They may experience:

• Blurred vision
• Light-headedness
• Nausea
• Weakness
• Syncope or loss of consciousness

Patients may have aggravating factors:

• Early morning – due to not drinking water overnight
• Hot environments – due to vasodilation
• Post-prandial – due to diversion of blood to the gut
• During or after exercise – due to the diversion of blood to muscles

Differential Diagnoses

Vasovagal (neurally-mediated) syncope

• Pre-syncopal symptoms usually present e.g. sweating and nausea, but these may not occur in those with autonomic dysfunction
• Syncope usually intermittent and occurs with specific triggers e.g. prolonged standing, strong emotions, having blood taken
• Patients usually recover rapidly after

Investigations

• Lying and standing/sitting blood pressure is monitored:
  • Patient lies down for 5 minutes
  • Patient sits up/stands up and the blood pressure is recorded immediately, at 1 minute, then at 3 minutes
• If blood pressure measurements are inconclusive, a tilt-table test may be considered.

Management

Management initially is conservative, through managing contributing risk factors (e.g. prescription reviews, drinking enough water, salt ingestion etc.)

• If patients have an inadequate response to conservative management, they may benefit from fludrocortisone.
• Older patients should be screened for postural hypotension before starting medications that may risk worsening or inducing symptoms.
• Patients who are known to have autonomic dysfunction should have regular and careful monitoring of their lying and standing blood pressure.

Patient Advice and Complications

Patient Advice

• Patients should be advised to sit before standing up fully from sitting to avoid symptoms
• Patients should eat small and frequent meals to prevent post-prandial postural hypotension
• Patients should stay well hydrated
• Patients should avoid straining when opening their bowels

Complications

• Falls
• Hypertension when supine
• This may lead to end-organ damage associated with hypertension