Hypotension is low fluid pressure which within reason can be a good thing. It is usually used in the sense of blood pressure when unqualified. The other major use of the term is with regard to CSF hypotension. Spontaneous intracranial hypotension is an important underdiagnosed cause of headaches . Ocular hypotension, after say glaucoma surgery can lead to hypotony maculopathy.
Blood pressure hypotension
In the case of blood pressure this is all relative to population mean and that mean for many populations is not at the bottom of the J shaped curve that applies for blood pressure morbidity and mortality. Hypotension that impairs tissue perfusion and is symptomatic needs treatment. Different medical cultures have evolved different criteria for such intervention in symptomatic cases but the criteria for intervention with impaired tissue perfusion tend to be more similar. There does appear to be a chronic fatigue syndrome associated with hypotension which can be more or less objectively diagnosed. The commonest present causes of chronic hypotension is medical therapy or low cardiac output states owing to myocardial damage.
All causes of shock. However when it comes down to it:
- Reduction in cardiac output
- Reduction in blood volume for a given vascular capacitance
- Reduction in myocardial contractiblity
Obstruction of cardiac output is a rare cause
Patient history can be revealing. Consider low salt intake and even more commonly drugs. Note that a patient may have different perceptions as to the likelihood of low blood pressure causing symptoms to an attending doctor and there is considerable medical variation in the objective and subjective interpretation of symptoms and signs associated with hypotension. Symptomatic hypotension can produce non specific malaise, tiredness, syncope or dizziness and of course postural symptoms if there is orthostatic hypotension. A particular organ in a given individual might be more susceptible than usual to the effects of hypotension and thus cause ischaemic symptoms. Thus those with ischaemic heart disease could manifest angina or those with atherosclerotic renal artery stenosis might develop renal failure at blood pressures which do not impair cerebral perfusion. A full physical examination might identify the cause, eg warmth over bowed tibia from Paget's disease, bruit from A-V fistula, murmur of aortic stenosis - rather unlikely not only because if aortic stenosis so severe to cause hypotension there is not enough flow over the aortic valve to generate much noise) .
- Measure BP (lying and standing) to help confirm diagnosis.
- Consider artifact : eg falsely low BP in obese patients measured with wrong cuff size or with proximal arterial narrowing/steal proximal to the measurement.
- Tilt table studies if objective diagnosis chronic fatigue syndrome indicated
- Endocrine function as indicated (Consider Addison's disease)
- Treat underlying cause
- Plasma expansion eg NSAIDs, Fludrocortisone
- Adrenergic agents such as midodrine (note: this drug is licensed in some countries to treat hypotension where the diagnosis has more medical acceptability than the UK)
- ↑ Schievink WI. Misdiagnosis of spontaneous intracranial hypotension. Archives of neurology. 2003 Dec; 60(12):1713-8.(Link to article – subscription may be required.)
- ↑ Galland BC, Jackson PM, Sayers RM, Taylor BJ. A Matched Case Control Study of Orthostatic Intolerance in Children/Adolescents With Chronic Fatigue Syndrome. . 2007 Dec 10.(Epub ahead of print) (Link to article – subscription may be required.)