Hypotension
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Hypotension is low blood pressure,
especially in the arteries of the left
sided systemic circulation.[1] Blood
pressure is the force of blood pushing
against the walls of the arteries as the
heart pumps out blood. A systolic
blood pressure of less than 90
millimeters of mercury (mm Hg) or
diastolic of less than 60 mm Hg is
generally considered to be
hypotension.[2][3] However, in practice,
blood pressure is considered too low
only if noticeable symptoms are
present.[4]
Hypotension
Specialty Critical care medicine
Hypotension is the opposite of
hypertension, which is high blood
pressure. It is best understood as a
physiological state rather than a
disease. Severely low blood pressure
can deprive the brain and other vital
organs of oxygen and nutrients, leading
to a life-threatening condition called
shock.
For some people who exercise and are
in top physical condition, low blood
pressure is a sign of good health and
fitness.[5] A single session of exercise
can induce hypotension and water-
based exercise can induce important
hypotension response.[6] For many
people, excessively low blood pressure
can cause dizziness and fainting or
indicate serious heart, endocrine or
neurological disorders.
Treatment of hypotension may include
the use of intravenous fluids or
vasopressors. When using
vasopressors, trying to achieve a mean
arterial pressure (MAP) of greater than
70 mm Hg does not appear to result in
better outcomes than trying to achieve
a MAP of greater than 65 mm Hg in
adults.[7]
Signs and symptoms
The primary symptoms of hypotension
are lightheadedness or dizziness.[8]
If the blood pressure is sufficiently low,
fainting may occur.
Low blood pressure is sometimes
associated with certain symptoms,
many of which are related to causes
rather than effects of hypotension:
chest pain
shortness of breath
irregular heartbeat
fever higher than 38.3 °C (101 °F)
headache
stiff neck
stiff neck
severe upper back pain
cough with sputum
Prolonged diarrhea or vomiting
dyspepsia (indigestion)
dysuria (painful urination)
acute, life-threatening allergic
reaction
seizures
loss of consciousness
profound fatigue
temporary blurring or loss of vision
Black tarry stools
Causes
Low blood pressure can be caused by
low blood volume, hormonal changes,
widening of blood vessels, medicine
side effects, anemia, heart problems or
endocrine problems.
Reduced blood volume, hypovolemia, is
the most common cause of
hypotension. This can result from
hemorrhage; insufficient fluid intake, as
in starvation; or excessive fluid losses
from diarrhea or vomiting.
Hypovolemia is often induced by
excessive use of diuretics. Low blood
pressure may also be attributed to heat
stroke. The body may have enough
fluid but does not retain electrolytes.
Absence of perspiration, light
headedness and dark coloured urine
are also indicators.
Other medications can produce
hypotension by different mechanisms.
Chronic use of alpha blockers or beta
blockers can lead to hypotension. Beta
blockers can cause hypotension both
by slowing the heart rate and by
decreasing the pumping ability of the
heart muscle.
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. Arrhythmias
often result in hypotension by this
mechanism.
Some heart conditions can lead to low
blood pressure, including extremely low
heart rate (bradycardia), heart valve
problems, heart attack and heart
failure. These conditions may cause
low blood pressure because they
prevent the body from being able to
circulate enough blood.
Excessive vasodilation, or insufficient
constriction of the resistance blood
vessels (mostly arterioles), causes
hypotension. 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 or of dysautonomia, an
intrinsic abnormality in autonomic
system functioning. Excessive
vasodilation can also result from
sepsis, 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.
Meditation, yoga, or other mental-
physiological disciplines may reduce
hypotensive effects.[9]
Lower blood pressure is a side effect of
certain herbal medicines,[10] which can
also interact with hypotensive
medications. An example is the
theobromine in Theobroma cacao,
which lowers blood pressure[11]
through its actions as both a
vasodilator and a diuretic,[12] and has
been used to treat high blood
pressure.[13][14]
Syndromes
Orthostatic hypotension, also called
postural hypotension, is a common
form of low blood pressure. It occurs
after a change in body position,
typically when a person stands up from
either a seated or lying position. It is
usually transient and represents a delay
in the normal compensatory ability of
the autonomic nervous system. It is
commonly seen in hypovolemia and as
a result of various medications. In
addition to blood pressure-lowering
medications, many psychiatric
medications, in particular
antidepressants, can have this side
effect. 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. Orthostatic hypotension
is indicated if there is a drop in 20
mmHg of systolic pressure (and a 10
mmHg drop in diastolic pressure in
some facilities) and a 20 beats per
minute increase in heart rate.
Vasovagal syncope is a form of
dysautonomia characterized by an
inappropriate drop in blood pressure
while in the upright position. Vasovagal
syncope occurs as a result of
increased activity of the vagus nerve,
the mainstay of the parasympathetic
nervous system .
Another, but rarer form, is postprandial
hypotension, a drastic decline in blood
pressure that occurs 30 to 75 minutes
after eating substantial meals.[15] 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. Postprandial
hypotension is believed to be caused
by the autonomic nervous system not
compensating appropriately, because
of aging or a specific disorder.
Hypotension is a feature of Flammer
syndrome, which is characterized by
cold hands and feet and predisposes to
normal tension glaucoma.[16]
Hypotension can be a symptom of
relative energy deficiency in sport,
sometimes known as the female
athlete triad, although it can also affect
men.[17]
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. 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.
Diagnosis
The diagnosis of hypotension is made
by first obtaining a blood pressure,
either non-invasively with a
sphygmomanometer or invasively with
an arterial catheter (mostly in an
intensive care setting). If the MAP
(Mean Arterial Pressure) is <65mmHg,
this is generally considered
hypotension.[18]
For most adults, the healthiest blood
pressure is at or below 120/80 mmHg.
A small drop in blood pressure, even as
little as 20 mmHg, can result in
transient hypotension.[19]
Evaluation of vasovagal syncope is
done with a tilt table test.
Besides the definitive threshold, an
abrupt fall in systolic blood pressure
around 30 mmHg from one's typical
average systolic pressure can also be
diagnosed with hypotension.[20]
Treatment
The treatment for hypotension depends
on its cause. Chronic hypotension
rarely exists as more than a symptom.
Asymptomatic hypotension in healthy
people usually does not require
treatment. Adding electrolytes to a diet
can relieve symptoms of mild
hypotension. A morning dose of
caffeine can also be effective. In mild
cases, where the patient is still
responsive, laying the person in dorsal
decubitus (lying on the back) position
and lifting the legs increases venous
return, thus making more blood
available to critical organs in the chest
and head. The Trendelenburg position,
though used historically, is no longer
recommended.[21]
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. 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.[22] 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)
2. Blood pressure support with a
vasopressor (all seem equivalent
with respect to risk of death, with
norepinephrine possibly better
than dopamine).[23] 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 mm Hg in
adults.[7]
3. Ensure adequate tissue perfusion
(maintain SvO2 >70 with use of
blood or dobutamine)
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...)
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.[24]
Other
Medium-term (and less well-
demonstrated) treatments of
hypotension include:
Blood sugar control
Early nutrition (by mouth or by tube
to prevent ileus)
Steroid support
Etymology
Hypotension, from Ancient Greek hypo-,
meaning "under" or "less" + English
tension, meaning "'strain" or
"tightness".[25] This refers to the under-
constriction of the blood vessels and
arteries which leads to low blood
pressure.
See also
Dysautonomia
Hypotensive transfusion reaction
Orthostatic intolerance
References
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2013). Retrieved on 2013-05-30.
14. Kelly, Caleb J (2005). "Effects of
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External links
Classification ICD-10: I95 • D
ICD-9-CM: 458 or
more commonly used
796.3 •
MeSH: D007022 •
DiseasesDB: 6539
External resources MedlinePlus:
007278 •
Patient UK:
Hypotension
Hypotension PubMed Health
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