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P A R T 8
Drugs acting on the cardiovascular system
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Severe hypotension, or shock, is treated with
sympathomimetic drugs that stimulate the
sympathetic system to increase blood pressure.
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Midodrine, an alpha-specific adrenergic stimulant,
is an oral drug used to treat people with orthostatic
hypotension whose lives are considerably impaired by
the fall in blood pressure when they stand.
CHAPTER SUMMARY
■■
The cardiovascular system is a closed system that
depends on pressure differences to ensure the delivery
of blood to the tissues and the return of that blood to
the heart.
■■
Blood pressure is related to heart rate, stroke volume
and the total peripheral resistance against which the
heart has to push the blood.
■■
Peripheral resistance is primarily controlled
by constriction or relaxation of the arterioles.
Constricted arterioles raise pressure; dilated
arterioles lower pressure.
■■
Control of blood pressure involves baroreceptor
(pressure receptor) stimulation of the medulla to
activate the sympathetic nervous system, which
causes vasoconstriction and increased fluid retention
when pressure is low in the aorta and carotid arteries,
and vasodilation and loss of fluid when pressure is
too high.
■■
The kidneys activate the renin–angiotensin–
aldosterone system when blood flow to the kidneys
is decreased.
■■
Renin activates the conversion of angiotensinogen to
angiotensin I in the liver; angiotensin I is converted
by angiotensin-converting enzyme (ACE) to
angiotensin II in the lungs; angiotensin II then reacts
with specific receptor sites on blood vessels to cause
vasoconstriction to raise blood pressure and in the
adrenal gland to cause the release of aldosterone,
which leads to the retention of fluid and increased
blood volume.
■■
Hypertension is a sustained state of higher-than-
normal blood pressure that can lead to damage to
blood vessels, increased risk of atherosclerosis and
damage to small vessels in end organs. Because
KEY POINTS
drugs
; pregnancy or breastfeeding
because of the
potential adverse effects on the fetus or neonate
;
cardiovascular dysfunction; visual problems;
urinary retention; and phaeochromocytoma,
which
could be exacerbated by the effects of the drugs.
■
■
Assess baseline status before beginning therapy
to determine any potential adverse effects
; this
includes body temperature and weight; skin
colour, lesions and temperature; pulse, blood
pressure, orthostatic blood pressure and perfusion;
respiration and adventitious sounds; bowel sounds
and abdominal examination; and renal and liver
function tests.
Implementation with rationale
■
■
Monitor blood pressure carefully
to monitor
effectiveness and blood pressure changes.
■
■
Do not administer the drug to people who are
bedridden, but only to people who are up and
mobile,
to ensure therapeutic effects and decrease
the risk of severe hypertension.
■
■
Monitor heart rate regularly when beginning
therapy
to monitor for bradycardia, which
commonly occurs at the beginning of therapy; if
bradycardia persists, it may indicate a need to
discontinue the drug.
■
■
Monitor the person with known visual problems
carefully
to ensure that the drug is discontinued if
visual fields change.
■
■
Encourage the person to void before taking a
dose of the drug
to decrease the risk of urinary
retention problems.
■
■
Provide comfort measures
to help the person
tolerate drug effects,
including small, frequent
meals; access to bathroom facilities; safety
precautions if CNS effects occur; environmental
controls; appropriate skin care as needed; and
analgesics as needed.
■
■
Provide thorough teaching, including the name
of the drug, dosage prescribed, measures to avoid
adverse effects, warning signs of problems and
the need for periodic monitoring and evaluation,
to enhance knowledge about drug therapy and to
promote compliance.
■
■
Offer support and encouragement
to help the
person deal with the diagnosis and the drug
regimen.
Evaluation
■
■
Monitor response to the drug (maintenance of
blood pressure within normal limits).
■
■
Monitor for adverse effects (hypertension,
dizziness, visual changes, piloerection, chills,
urinary problems).
■
■
Evaluate the effectiveness of the teaching plan
(person can name drug, dosage, adverse effects to
watch for, specific measures to avoid them and the
importance of continued follow-up).
■
■
Monitor the effectiveness of comfort measures and
compliance with the regimen.
