Hypotension

Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure.<ref>TheFreeDictionary > hypotension. Citing: The American Heritage Science Dictionary Copyright 2005</ref> Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood<ref name=":0" /> and is indicated by two numbers, the systolic blood pressure (the top number) and the diastolic blood pressure (the bottom number), which are the maximum and minimum blood pressures within the cardiac cycle, respectively.<ref name="cdc.gov">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension.<ref name=":22">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Mayo2009def">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Different numbers apply to children.<ref>Template:Cite journal</ref> However, in practice, blood pressure is considered too low only if noticeable symptoms are present.<ref name="Mayo2009causes">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Symptoms may include dizziness, lightheadedness, confusion, feeling tired, weakness, headache, blurred vision, nausea, neck or back pain, an irregular heartbeat or feeling that the heart is skipping beats or fluttering, sweating, and fainting.<ref name=":22" /> Hypotension is the opposite of hypertension, which is high blood pressure.<ref name=":0">Template:Cite book</ref> It is best understood as a physiological state rather than a disease.<ref name=":0" /> Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.<ref name="cdc.gov"/> Shock is classified based on the underlying cause, including hypovolemic shock, cardiogenic shock, distributive shock, and obstructive shock.<ref>Template:Citation</ref>

Hypotension can be caused by strenuous exercise, excessive heat, low blood volume (hypovolemia),<ref name=":10" /> hormonal changes,<ref name=":15" /> widening of blood vessels,<ref name=":16" /> anemia,<ref name=":17" /> vitamin B₁₂ deficiency,<ref name="Mayo2009causes" /><ref name="B799" /> anaphylaxis,<ref name="Mayo2009causes" /> heart problems,<ref name=":18" /> or endocrine problems.<ref name=":19" /> Some medications can also lead to hypotension.<ref name=":1" /> There are also syndromes that can cause hypotension in patients including orthostatic hypotension,<ref name="Joseph S55–S67"/> vasovagal syncope,<ref name=":4" /> and other rarer conditions.<ref name=":20" /><ref name=":21" />

For many people, excessively low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders.<ref name="Joseph S55–S67">Template:Cite journal</ref>

For some people who exercise and are in top physical condition, low blood pressure could be normal.<ref name="bupalowbloodpressure">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A single session of exercise can induce hypotension and water-based exercise can induce a hypotensive response.<ref>Template:Cite journal</ref>

Treatment depends on what causes low blood pressure.<ref name=":22" /> Treatment of hypotension may include the use of intravenous fluids or vasopressors.<ref>Template:Cite journal</ref> When using vasopressors, trying to achieve a mean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve an MAP of greater than 65 mmHg in adults.<ref name=Hy2017>Template:Cite journal</ref>

Signs and symptoms

For many people, low blood pressure goes unnoticed.<ref name=":22" /> For some people, low blood pressure may be a sign of an underlying health condition, especially when it drops suddenly or occurs with symptoms.<ref name="Mayo2009def" /> Older adults also have a higher risk of symptoms of low blood pressure, such as falls, fainting, or dizziness when standing or after a meal.<ref name=":22" /> If the blood pressure is sufficiently low, fainting (syncope) may occur.<ref name="Joseph S55–S67" />

Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:<ref name="Mayo2009def" />

• confusion
• dizziness or lightheadedness
• feeling tired or weak
• shortness of breath
• irregular heartbeat, feeling that the heart is skipping beats, or fluttering
• chest pain
• fever
• headache
• stiff neck
• severe back or neck pain
• cough with sputum
• prolonged diarrhea or vomiting
• chills
• loss of appetite
• nausea
• dyspepsia (indigestion)
• dysuria (painful urination)
• acute, life-threatening allergic reaction
• seizures
• loss of consciousness
• temporary blurring or loss of vision
• black tarry stools

Causes

Low blood pressure can be caused by low blood volume,<ref name=":10">Template:Cite journal</ref> hormonal changes,<ref name=":15">Template:Cite journal</ref> pregnancy,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> widening of blood vessels, medicine side effects,<ref name=":16">Template:Cite journal</ref> severe dehydration,<ref name="Mayo2009causes" /> anemia,<ref name=":17">Template:Cite journal</ref> vitamin B₁₂ deficiency,<ref name="Mayo2009causes" /> <ref name="B799">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> anaphylaxis,<ref name="Mayo2009causes" /> heart problems<ref name=":18">Template:Cite journal</ref> or endocrine problems.<ref name=":19">Template:Cite journal</ref>

Reduced blood volume, hypovolemia, is the most common cause of hypotension.<ref>Template:Cite journal</ref> This can result from hemorrhage; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia can be induced by excessive use of diuretics.<ref name=":1">Template:Cite journal</ref> Low blood pressure may also be attributed to heat stroke which can be indicated by absence of perspiration, light headedness and dark colored urine.<ref>Template:Cite book</ref>

Other medications can produce hypotension by different mechanisms. Chronic use of alpha blockers or beta blockers can lead to hypotension.<ref name=":1" /> Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.<ref name=":1" />

Decreased cardiac output despite normal blood volume, due to severe congestive heart failure, large myocardial infarction, heart valve problems, or extremely low heart rate (bradycardia), often produces hypotension and can rapidly progress to cardiogenic shock.<ref name=":18"/> Arrhythmias often result in hypotension by this mechanism.<ref name=":18"/>

Excessive vasodilation, or insufficient constriction of the blood vessels (mostly arterioles), causes hypotension.<ref name=":11">Template:Cite journal</ref> This can be due to decreased sympathetic nervous system output or to increased parasympathetic activity occurring as a consequence of injury to the brain or spinal cord.<ref name=":12" /> Dysautonomia, an intrinsic abnormality in autonomic system functioning, can also lead to hypotension.<ref name=":12">Template:Citation</ref> Excessive vasodilation can also result from sepsis,<ref name=":11" /> acidosis, or medications, such as nitrate preparations, calcium channel blockers, or AT1 receptor antagonists (Angiotensin II acts on AT1 receptors). Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents, produce significant vasodilation.<ref>Template:Cite journal</ref>

Lower blood pressure is a side effect of certain herbal medicines,<ref>Template:Cite journal</ref> which can also interact with several medications. An example is the theobromine in Theobroma cacao, which lowers blood pressure<ref>Template:Cite journal</ref> through its actions as both a vasodilator and a diuretic,<ref name="dictbiochem1943">Template:Cite book</ref> and has been used to treat high blood pressure.<ref>Theobromine Chemistry – Theobromine in Chocolate Template:Webarchive. Chemistry.about.com (May 12, 2013). Retrieved on 2013-05-30.</ref><ref name="AJCN">Template:Cite journal</ref>

Syndromes

Orthostatic hypotension

Orthostatic hypotension, also called postural hypotension, is a common form of low blood pressure.<ref name="Joseph S55–S67"/> It occurs after a change in body position, typically when a person stands up from either a seated or lying position.<ref>Template:Cite journal</ref> It is usually transient and represents a delay in the normal compensatory ability of the autonomic nervous system.<ref>Template:Cite journal</ref> It is commonly seen in hypovolemia and as a result of various medications.<ref name="Joseph S55–S67" /> In addition to blood pressure-lowering medications, many psychiatric medications, in particular antidepressants, can have this side effect.<ref>Template:Cite journal</ref> Simple blood pressure and heart rate measurements while lying, seated, and standing (with a two-minute delay in between each position change) can confirm the presence of orthostatic hypotension.<ref name=":3">Template:Cite journal</ref> Taking these measurements is known as orthostatic vitals.<ref name="Joseph S55–S67" /> Orthostatic hypotension is indicated if there is a drop of 20 mmHg in systolic pressure (and a 10 mmHg drop in diastolic pressure in some facilities) and a 20 beats per minute increase in heart rate.<ref name=":3" />

Vasovagal syncope

Vasovagal syncope is a form of dysautonomia characterized by an inappropriate drop in blood pressure while in the upright position.<ref name=":4">Template:Cite journal</ref> Vasovagal syncope occurs as a result of increased activity of the vagus nerve, the mainstay of the parasympathetic nervous system.<ref name=":4" /> Patients will feel sudden, unprovoked lightheadedness, sweating, changes in vision, and finally a loss of consciousness.<ref name=":4" /> Consciousness will often return rapidly once patient is lying down and the blood pressure returns to normal.<ref name=":13" />

Other

Another, but rarer form, is postprandial hypotension, a drastic decline in blood pressure that occurs 30 to 75 minutes after eating substantial meals.<ref name=":20">Merck Manual Home Edition. "Postprandial Hypotension." Last accessed October 26, 2011.</ref> When a great deal of blood is diverted to the intestines (a kind of "splanchnic blood pooling") to facilitate digestion and absorption, the body must increase cardiac output and peripheral vasoconstriction to maintain enough blood pressure to perfuse vital organs, such as the brain.<ref name=":5">Template:Cite journal</ref> Postprandial hypotension is believed to be caused by the autonomic nervous system not compensating appropriately, because of aging or a specific disorder.<ref name=":5" />

Hypotension is a feature of Flammer syndrome, which is characterized by cold hands and feet and predisposes to normal tension glaucoma.<ref name=":21">Template:Cite journal</ref>

Hypotension can be a symptom of relative energy deficiency in sport, sometimes known as the female athlete triad, although it can also affect men.<ref>Template:Cite journal</ref>

Pathophysiology

Blood pressure is continuously regulated by the autonomic nervous system, using an elaborate network of receptors, nerves, and hormones to balance the effects of the sympathetic nervous system, which tends to raise blood pressure, and the parasympathetic nervous system, which lowers it.<ref name=":0" /> The vast and rapid compensation abilities of the autonomic nervous system allow normal individuals to maintain an acceptable blood pressure over a wide range of activities and in many disease states.<ref name=":0" /> Even small alterations in these networks can lead to hypotension.<ref name=":10" />

Diagnosis

Hypotension thresholds (mmHg)<ref>Template:Cite journal</ref>

Office	Ambulatory
	Daytime	Nighttime	24 hours
<110/70	<105/65	<90/50	<100/60

For most adults, the optimal blood pressure is at or below 120/80 mmHg.<ref name=":6"> Template:Cite journal</ref> If the systolic blood pressure is <90 mmHg or the diastolic blood pressure is <60 mmHg, it would be classified as hypotension.<ref name="Mayo2009def" /> However, occasional blood pressure readings below 90/60 mmHg are not infrequent in the general population,<ref name=":8">Template:Cite journal</ref> and, in the absence of some pathological cause, hypotension appears to be a relatively benign condition in most people.<ref name=":8"/> The diagnosis of hypotension is usually made by measuring blood pressure, either non-invasively with a sphygmomanometer or invasively with an arterial catheter (mostly in an intensive care setting). Another way to diagnose low blood pressure is by using the mean arterial pressure (MAP) measured using an arterial catheter <ref name=":14">Template:Cite book</ref> or by continuous, non-invasive hemodynamic monitoring which measures intra-operative blood pressure beat-by-beat throughout surgery. A MAP <65 mmHg is considered hypotension.<ref name=":14" /> Intra-operative hypotension <65 mmHg can lead to an increased risk of acute kidney injury,<ref name="ReferenceA">Walsh, M., Devereaux, P. et al. Relationship between Intraoperative Mean Arterial Pressure and Clinical Outcomes a er Noncardiac Surgery. Anaesthesiology. 2013;119:507-515.</ref> myocardial injury <ref name="ReferenceA"/> or post-operative stroke.<ref>Bijker J., Persoon S., Peelen L., et al. Intraoperative Hypotension and Perioperative Ischemic Stroke a er General Surgery. Anesthesiology. 2012;116(3):658-664.</ref> While an incidental finding of hypotension during a routine blood pressure measurement may not be particularly worrying, a substantial drop in blood pressure following standing, exercise or eating can be associated with symptoms and may have implications for future health.<ref name=":6"/> A drop in blood pressure after standing, termed postural or orthostatic hypotension, is defined as a decrease in supine-to-standing BP >20 mm Hg systolic or >10 mm Hg diastolic within 3 minutes of standing.<ref>Template:Cite journal</ref><ref name=":6"/> Orthostatic hypotension is associated with increased risk of future cardiovascular events and mortality. Orthostatic vitals are frequently measured to assist with the diagnosis of orthostatic hypotension,<ref name=":3" /> and may involve the use of a tilt table test to evaluate vasovagal syncope.<ref name=":13">Template:Cite journal</ref>

Treatment

Treatment depends on what causes low blood pressure.<ref name=":22" /> Treatment may not be needed for asymptomatic low blood pressure.<ref>Template:Citation</ref> Depending on symptoms, treatment may include drinking more fluids to prevent dehydration, taking medicines to raise blood pressure, or adjusting medicines that cause low blood pressure.<ref name=":22" /> Adding electrolytes to a diet can relieve symptoms of mild hypotension, and a morning dose of caffeine can also be effective.<ref name=":7">Template:Cite journal</ref> Chronic hypotension rarely exists as more than a symptom. In mild cases, where the patient is still responsive, laying the person on their back and lifting the legs increases venous return, thus making more blood available to critical organs in the chest and head.<ref name=":7" /> The Trendelenburg position, though used historically, is no longer recommended.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Hypotensive shock treatment always follows the first four following steps. Outcomes, in terms of mortality, are directly linked to the speed that hypotension is corrected.<ref name=":10"/> Still-debated methods are in parentheses, as are benchmarks for evaluating progress in correcting hypotension. A study on septic shock provided the delineation of these general principles.<ref>Template:Cite journal</ref> However, since it focuses on hypotension due to infection, it is not applicable to all forms of severe hypotension.

1. Volume resuscitation (usually with crystalloid or blood products)<ref name=":10"/>
2. Blood pressure support with a vasopressor (all seem equivalent with respect to risk of death, with norepinephrine possibly better than dopamine).<ref>Template:Cite journal</ref> Trying to achieve a mean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve a MAP of greater than 65 mmHg in adults.<ref name=Hy2017/>
3. Ensure adequate tissue perfusion (maintain SvO2 >70 with use of blood or dobutamine)<ref name=":10"/>
4. Address the underlying problem (i.e., antibiotic for infection, stent or CABG (coronary artery bypass graft surgery) for infarction, steroids for adrenal insufficiency, etc...)<ref name=":10"/>

The best way to determine if a person will benefit from fluids is by doing a passive leg raise followed by measuring the output from the heart.<ref>Template:Cite journal</ref>

Medication

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Chronic hypotension sometimes requires the use of medications.<ref>Template:Cite journal</ref> Some medications that are commonly used include Fludrocortisone, Erythropoietin, and Sympathomimetics such as Midodrine and Noradrenaline and precursor (L-DOPS).<ref name="Joseph S55–S67" />

• Fludrocortisone is the first-line therapy (in the absence of heart failure) for patients with chronic hypotension or resistant orthostatic hypotension.<ref name="Joseph S55–S67"/> It works by increasing the intravascular volume.<ref name="Joseph S55–S67"/>
• Midodrine is a therapy used for severe orthostatic hypotension, and works by increasing peripheral vascular resistance.<ref name="Joseph S55–S67"/>
• Noradrenaline and its precursor L-DOPS are used for primary autonomic dysfunction by increasing vascular tone.<ref name="Joseph S55–S67"/>
• Erythropoietin is given to patients with neurogenic orthostatic hypotension and it works through increasing vascular volume and viscosity.<ref name="Joseph S55–S67"/>

Pediatrics

The definition of hypotension changes in the pediatric population depending on the child's age as seen in the table below.

citation

CitationClass=web }}</ref>	Age	Systolic pressure
Term neonates	<60 mmHg
Infants	<70 mmHg
Children 1–10 years	<70 + (age in years x 2) mmHg
Children >10 years	<90 mmHg

The clinical history provided by the caretaker is the most important part in determining the cause of hypotension in pediatric patients.<ref name=":9">Template:Cite journal</ref> Symptoms for children with hypotension include increased sleepiness, not using the restroom as much (or at all), having difficulty breathing or breathing rapidly, or syncope.<ref name=":9" /> The treatment for hypotension in pediatric patients is similar to the treatment in adults by following the four first steps listed above (see Treatment).<ref name=":10"/> Children are more likely to undergo intubation during the treatment of hypotension because their oxygen levels drop more rapidly than adults.<ref name=":9" /> The closing of fetal shunts following birth can create instability in the "transitional circulation" of the fetus, and often creates a state of hypotension following birth; while many infants can overcome this hypotension through the closing of shunts, a mean blood pressure (MBP) of lower than 30 mmHg is correlated with severe cerebral injury and can be experienced by premature infants who have poor shunt closure.<ref>Template:Cite journal</ref>

Etymology

Hypotension, from Ancient Greek hypo-, meaning "under" or "less" + English tension, meaning "'strain" or "tightness".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This refers to the under-constriction of the blood vessels and arteries which leads to low blood pressure.<ref>Template:Cite journal</ref>

See also

• Hypertension

External links

• Curlie.org: Hypotension