57 Hypotension

A number of factors can cause hypotension (low blood pressure). Hypotension is considered less than 95/60 mm Hg in a normotensive adult. However, low blood pressure measurements are always interpreted in the context of a client’s baseline and past blood pressure readings as well as their current health state. Common symptoms associated with hypotension are lightheadedness, loss of consciousness, blurry vision, clammy skin, and fatigue.

Orthostatic Hypotension

Orthostatic hypotension is a drop in blood pressure when the client moves from lying to sitting to a standing position.

Have you ever stood up quickly and felt dizzy for a moment? This is because, for one reason or another, blood is not getting to your brain so it is briefly deprived of oxygen. When you change position from sitting or lying down to standing, your cardiovascular system has to adjust for a new challenge, keeping blood pumping up into the head while gravity is pulling more and more blood down into the legs. The reason for this is a sympathetic reflex that maintains the output of the heart in response to postural change. This sympathetic reflex keeps the brain well oxygenated so that cognitive and other neural processes are not interrupted. Sometimes this does not work properly. If the sympathetic system cannot increase cardiac output, then blood pressure into the brain will decrease, and a brief neurological loss can be felt. This can be brief, such as a slight ‘wooziness’ when standing up too quickly, or could lead to a loss of balance and neurological impairment for a period of time. The name for this is orthostatic hypotension, which means that blood pressure falls below the homeostatic set point when standing. It can be the result of standing up faster than the reflex can occur, which may cause a benign ‘head rush,’ or it may be the result of an underlying cause.

There are two basic reasons why orthostatic hypotension occurs. First, blood volume is too low and the sympathetic reflex is not effective. This hypovolemia may be the result of dehydration or medications that affect fluid balance, such as diuretics or vasodilators. The second underlying cause of orthostatic hypotension is autonomic failure. Several disorders can result in compromised sympathetic functions, ranging from diabetes to multiple system atrophy (a loss of control over many systems in the body), and addressing the underlying condition can improve the hypotension. Orthostatic hypotension is more common with advancing age and can be aggravated by antihypertensive medications.

How to Assess Orthostatic Hypotension

Orthostatic hypotension is assessed by measuring orthostatic or postural blood pressure and pulse changes. This procedure is done by assessing when the client moves from supine to sitting to standing. There are variations in how this procedure is done in terms of timing. Here is a common way to proceed:

1. The client rests supine for three minutes.
2. Take blood pressure and pulse in supine position.
3. The client sits up with feet dangling.
4. Take blood pressure and pulse within two minutes of position change.
5. The client stands up.
6. Take blood pressure and pulse within two minutes of position change.

How to Evaluate the Findings 

Normal variation is a 10 mm Hg decrease in blood pressure from lying to standing and an increase in pulse of 10–15 bpm.

A decrease in blood pressure from lying to standing of systolic ≥ 20 mm Hg or diastolic ≥ 10 mm Hg is identified as orthostatic hypotension.

An increase in pulse from lying to standing of ≥ 20 bpm is identified as orthostatic pulse.

_________________________________________________________________________
The content under the sub-title “Orthostatic Hypotension” was adapted from OER #2 (as noted in brackets above):
© Apr 10, 2017 OpenStax Anatomy and Physiology. Textbook content produced by OpenStax Anatomy and Physiology is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/7c42370b-c3ad-48ac-9620-d15367b882c6@12