Postural hypotension

• Postural (orthostatic) hypotension:

  • Defined as a sustained reduction in systolic BP of at least 20 mmHg or diastolic BP of 10 mmHg that occurs within 3 minutes of standing
  • Significant contributor to morbidity and adverse events in older adults
• Aetiology can be divided into neurogenic and non-neurogenic causes
• Neurogenic causes:

  • Insufficient release of noradrenaline from the sympathetic vasomotor neurons - limits vasoconstriction so that body cannot increase and normalise BP on standing/sitting
  • Most often seen in disorders that cause autonomic dysfunction:
  • Type 2 diabetes mellitus
  • Parkinson's disease
  • Small cell lung carcinoma
  • Amyloidosis
• Non-neurogenic causes:

  • Arises from either hypovolaemia, cardiac failure or venous pooling
  • Cardiac impairment - myocardial infarction and aortic stenosis
  • Reduced intravascular volume - dehydration, adrenal insufficiency
  • States that induce vasodilation - fevers
• Common causative medications:

  • Diuretics
  • Alpha-adrenoceptor blockers e.g. tamsulosin
  • Antihypertensives
  • Insulin
  • Levodopa
  • Tricyclic antidepressants
• Physiology:

  • On standing, blood moves with gravity from within the thorax to below the diaphragm. This shift reduces venous return, which reduces ventricular filling and this preload, decreasing cardiac output
  • Baroreceptors in the aortic arch and carotid sinus detect hypotension - vasoconstriction and compensatory tachycardia
  • Postural hypotension occurs when these mechanisms to regulate blood pressure are impaired - failure of baroreflexes (autonomic failure), volume depletion, end-organ dysfunction
• Susceptibility in older adults:

  • More prone to hypovolaemia - increase in natriuretic peptides and reduction in renin, angiotensin and aldosterone with age
  • Impaired ability to conserve water and sodium, diminished thirst response exacerbates this
  • Baroreflex sensitivity decreases with age
  • Comorbidities such as chronic hypertension and diabetes also result in reduced baroreflex sensitivity
  • Polypharmacy - combination of antihypertensives and diuretics
• Risk factors:

  • Rising quickly after prolonged sitting or lying
  • prolonged motionless standing
  • Time of day - early morning after nocturnal diuresis
  • Dehydration
  • Physical exertion
  • Alcohol intake
  • Carbohydrate-heavy meals
  • Straining during micturition or defecation
  • Fever
• The symptoms of postural hypotension are caused by cerebral hypoperfusion. They include:

  • Dizziness
  • Weakness
  • Confusion
  • Blurred vision
  • Nausea
  • Syncope
• Bedside investigations:

  • Lying and standing BP - measures after lying for at least 5 minutes, immediately on standing and after 3 minutes
  • Heart rate
  • ECG - exclude cardiac causes
• Lab investigations:

  • FBC - may show infection
  • U&Es - may show electrolyte disturbance
  • Random cortisol and short syacthen test - if adrenal insufficiency is suspected
• Imaging:

  • Echocardiogram - if suspecting heart failure or cardiac aetiology
•  management of postural hypotension targets three main physiologic processes:

  • Reducing venous pooling
  • Increasing blood volume
  • Increasing vasoconstriction
• First line management is non-pharmacological measures:

  • Increasing salt and fluid intake - increase circulating blood volume
  • Avoidance of high risk situations - sudden sitting to standing
  • Compression stockings or abdominal binders - reduce venous pooling
  • Physical activity - reduce venous pooling
  • Counter manoeuvres - leg elevation and leg crossing to reduce venous pooling
• Pharmacological management:

  • Fludrocortisone
  • Synthetic mineralocorticoid - expands plasma volume
  • Contraindicated in heart failure, ascites and chronic renal failure
  • Side effects - hypertension and severe hypokalaemia - monitor potassium
  • Midodrine - vasopressor that is useful in neurogenic postural hypotension
• Complications:

  • Significant contributor to falls in older adults
  • Considered an independent risk factor for both mortality and cardiovascular disease