Orthostatic hypotension

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Contents

Introduction

Orthostatic Hypotension (Postural hypotension) is best considered to be a symptomatic fall in blood pressure (BP) when standing. However the diagnosis of symptomatic orthostatic hypotension does not require symptoms at the time a significant drop in blood pressure on standing is measured. The symptoms do not have to be syncope or pre-syncope. It does not necessarily have to be associated in time with a change in posture, although this is usual.

Diagnosis

The history is often suggestive, and symptoms clearly related to a change to upright posture should result in confirmation by lying and standing BPs. Once confirmed, it is important to identify the underlying cause.

In the work up of syncope, a patient should lie supine for at least five minutes, followed by measurements each minute or more frequently after standing for 3 minutes. If the patient is unable to stand for 3 minutes the lowest upright systolic BP should be noted. A decrease in systolic BP of 20mmHg or more, or a decrease to less than 90mmHg systolic is defined as orthostatic hypotension [1]. If the diagnosis can not be established with standard inflatable cuffs, the use of a non-invasive continuous BP monitor is recommended. This equipment is usually used in tilt testing and is in practice much more sensitive and specific than standard manual and automatic apparatus. Continuous BP monitoring can detect profound brief periods of hypotension lasting only a few seconds which are now known to be the cause of much syncope and unexplained falls in the elderly.

Tilt testing using a tilt table may be part of the investigation.

Diagnostic Issues

It is a common problem hard to put in total patient context. For the patient the diagnosis requires symptoms that can be directly related to a postural fall in blood pressure. There are insufficient resources to do continous beat to beat BP monitoring on every patients symptomatic change in posture. There are several clinical research definitions as above which are no use to the patient who faints due to postural hypotension 30 seconds into a head up tilt and has normal BP at 2 minutes. At one extreme it is a known cause of transient ischaemic attacks [2][3] almost certainly underdiagnosed and at another it is easy to confuse with symptomatic cervical/vertebro-basilar/vestibular disease manifest on changing posture.

Underlying Causes

Info bulb.pngIn 1960, Dr. Milton Shy and Dr. Glen Drager described Shy-Drager Syndrome, which is now considered a subclass of multiple systems atrophy, where the symptoms of autonomic failure dominate.

Treatment

  • Identify and address the underlying cause as above.
  • Advice on prevention
    • Gravitational exposure/Mobility
    • Avoiding rapid postural change
    • Adequate salt intake
  • External leg compression (eg support stockings)
  • Volume expansion
    • NSAIDs
    • Fludrocortisone
      • Expands the extravascular body fluid volume
      • Improves alpha-adrenergic sensitivity
  • Sympathetic stimulation & vasoconstriction
    • Midodrine
      • alpha1-adrenergic agonist
      • Causes arterial and venous vasoconstriction

A number of agents might have indications in specific patients such as MAOIs, beta-adrenergic antagonists, ergot alkaloids, clonidine, yohimbine, octreotide, dopamine antagonists, desmopressin, and erythropoietin.

References

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