How Low Can You Go? - Orthostatic Hypotension

One day in clinic, I was scheduled to see a patient with a chief concern of dizziness, syncope and gait imbalance. He had a history of orthostatic hypotension and was being investigated for the underlying etiology. While the patient did not attend his appointment, I though it was an interesting case and a topic I didn’t have much exposure to.

Upon standing, much of our circulating blood volume pools in the lower extremities and splanchnic circulation. As such, decreased venous return leads to decreased cardiac output and blood pressure. In response, baroreceptors in the carotid sinus and aortic arch are activated, generating increased sympathetic outflow and decreased vagal tone. By increasing peripheral resistance, venous return and cardiac output, this baroreflex response helps to maintain blood pressure with positional change. Without an adequate baroreflex response and subsequent sympathetic vasoconstriction, orthostatic hypotension and associated cerebral hypoperfusion occur in response to this autonomic failure.

Orthostatic hypotension is defined as a reduction in systolic BP by at least 20 mmHg or a reduction in diastolic BP by at least 10 mmHg in the first 3 minutes of standing after lying down or sitting. This diagnosis should be considered in any patient presenting with falls, pre-syncope, syncope and dizziness. Prevalence increases with age, as changes of aging are associated with diminished baroreflex response. This presentation can be quite debilitating if not treated, as orthostatic hypotension can limit a patient's mobility, independence and quality of life.

The differential diagnosis for orthostatic hypotension is quite broad, but by considering the work-up for this condition, we can organize our thoughts. When considering the diagnosis of orthostatic hypotension, it is critical to assess intravascular volume status by examining the vitals, JVP, and mucous membranes. Volume depletion can cause orthostatic hypotension, and if symptoms resolve after volume correction, a diagnosis has been made. If the patient is volume replete, consider non-neurogenic causes, including cardiac (CHF, MI, myocarditis, pericarditis, arrhythmia), endocrine (adrenal insufficiency, diabetes insipidus) or infectious (sepsis) etiologies. Another important category to consider is medication side-effect. Medications which can cause orthostatic hypotension include antihypertensives (diuretics, calcium channel blockers), alpha-adrenoreceptor blockers and atypical antipsychotics. If this approach has yielded no diagnosis, consider neurogenic causes which include multiple system atrophy, alcoholic polyneuropathy, diabetic neuropathy and multiple sclerosis.

Treatment of orthostatic hypotension can be very challenging. In addition to treating the underlying cause, some initial non-pharmacologic interventions include encouraging hydration (drinking 2-2.5 litres/day) and increasing intake of salty foods (up to 10g of sodium/day). We can also counsel patients to perform gradual movements with postural change, to allow time for autonomic adaptation. As well, we can prescribe compression stockings and an abdominal binder to reduce peripheral venous pooling.

The only pharmacologic treatment approved for use in orthostatic hypotension is midodrine, a peripheral, selective, direct alpha-adrenoreceptor agonist. Fludrocortisone has also been used, for its mineralocorticoid properties to increase plasma volume. Other agents which may be considered are recommended based on data from small, single-centre trials and include pyridostigmine, desmopressin acetate and erythropoietin.

This diagnosis is an interesting one which requires careful consideration of the pathophysiology responsible.  Overall, the aim of treating orthostatic hypotension is to manage symptoms, through non-pharmacologic and pharmacologic treatment.

-EB- 

References:

Bradley JG, Davis KA. Orthostatic hypotension. American family physician. 2003 Dec 15;68(12):2393-8.

Figueroa JJ, Basford JR, Low PA. Preventing and treating orthostatic hypotension: as easy as A, B, C. Cleveland Clinic journal of medicine. 2010 May;77(5):298.

Freeman R. Neurogenic orthostatic hypotension. New England Journal of Medicine. 2008 Feb 7;358(6):615-24.