hock is a failure of the cardiovascular system to deliver
enough oxygen and nutrients to meet cellular metabolic
needs. The causes of shock are many and varied, but all
are characterized by inadequate blood flow to body tis-
sues. Here are some of the most common varieties:
H y p o v o le m ic s h o c k
is the result of excessive
fluid loss, resulting in a decrease in the blood
volume. Causes of hypovolemic shock include
hemorrhage, dehydration, burns, excessive
vomiting, persistent diarrhea, and excessive
C a r d io g e n ic s h o c k
is due to ineffective
pumping of the ventricles of the heart, which
reduces cardiac output.
S e p tic s h o c k
is caused by an infection that has
gotten into the bloodstream. As the body reacts
to the infection, chemicals are released that cause
A n a p h y la c t ic s h o c k
happens when there is an allergic reac-
tion in which lots of histamine is released, causing wide-
spread vasodilation.
N e u r o g e n ic s h o c k
is the result of injury to the nervous sys-
tem that interferes with sympathetic nervous system control
of vessel size.
Despite multiple responses by the body to restore blood pressure,
including the neurologic and hormonal responses discussed previ-
ously, with shock the body is unable to restore the blood pressure
to a normal level. If shock persists, cells and organs become dam-
aged, and cells may die unless proper treatment begins quickly.
The signs and symptoms of shock include the following,
which may vary with the severity of the condition:
Systolic blood pressure is lower than 90 mmHg.
Resting heart rate is rapid due to sympathetic stimulation and
increased blood levels of epinephrine and norepinephrine.
Pulse is weak and rapid due to reduced cardiac output and
fast heart rate.
Skin is cool, pale, and clammy due to sympathetic constriction
of skin blood vessels and sympathetic stimulation of sweating.
Mental state is altered due to reduced oxygen supply to the
Urine formation is reduced due to increased levels of aldo-
sterone and antidiuretic hormone (ADH).
The person is thirsty due to loss of extracellular fluid.
The pH of blood is low (acidosis) due to buildup of lactic acid.
The person may have nausea because of impaired blood flow
to the digestive organs from sympathetic vasoconstriction.
Immediate treatment includes keeping the patient warm with a
blanket, elevating the feet above the heart and head to improve
cardiac output, and administering intravenous fluid. It may be
necessary to give medicines to increase blood pressure and
cardiac output (such as epinephrine). Ultimately, blood volume
must be restored by repairing the injury, administering fluids, or
transfusing blood. If the condition is not treated quickly, death
may ensue.
Think Critically!
Explain how elevating the feet
above the heart and head increases cardiac output in a
patient suffering from hypovolem ic shock.
M any p eo ple try to adm inister fluids by m outh to
hypovolem ic sh o ck patients. This is not a recom m ended
or advisable treatm ent. W hy w ould this m ethod of
restoring fluid volum e be ineffective?
beat or two. This important reflex prevents you from faint-
ing every time you stand up. It also helps maintain blood
pressure in other situations (such as exercise and hemor-
rhagic shock, one of several types of shock characterized by
inadequate flow of blood to body tissues—see
W h a t a H ea lth
P rovider Sees).
Maintaining Blood Pressure Is Critical for Survival
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