McKenna's Pharmacology for Nursing, 2e - page 476

464
P A R T 5
 Drugs acting on the autonomic nervous system
Prototype summary: Phenylephrine
Indications:
Treatment of vascular failure in
shock or drug-induced hypotension; to overcome
paroxysmal supraventricular tachycardia; to
prolong spinal anaesthesia; as a vasoconstrictor in
regional anaesthesia; to maintain blood pressure
during anaesthesia; topically for symptomatic relief
of nasal congestion and as adjunctive therapy in
middle ear infections; ophthalmically to dilate
pupils and as a decongestant to provide temporary
relief of eye irritation.
Actions:
Powerful postsynaptic alpha-adrenergic
receptor stimulant causing vasoconstriction and
raising systolic and diastolic blood pressure with
little effect on the beta-receptors in the heart.
Pharmacokinetics:
Route
Onset
Duration
IV
Immediate
15–20 mins
IM, SC 10–15 mins
30–120 mins
Topically Very little systemic
absorption occurs
T
1/2
:
47 to 100 hours; metabolised in the tissues and
liver; excreted in urine and bile.
Adverse effects:
Fear, anxiety, restlessness, headache,
nausea, decreased urine formation, pallor.
Care considerations for people receiving
α
-specific adrenergic agonists
Assessment: History and examination
Assess for contraindications or cautions:
any known allergies to the drug
to avoid
hypersensitivity reactions
; presence of any
cardiovascular diseases,
which could be
exacerbated by the vascular effects of these drugs;
thyrotoxicosis or diabetes,
which would lead
to an increase in thyroid stimulation or glucose
elevation
; chronic renal failure,
which could
be exacerbated by drug use
; renal or hepatic
impairment,
which could interfere with drug
excretion or metabolism
;
and current status of
pregnancy and breastfeeding.
Perform a physical assessment to establish
baseline
status before beginning therapy to determine
effectiveness and during therapy to evaluate for
any potential adverse effects.
Assess level of orientation, affect, reflexes and
vision
to monitor for CNS changes related to drug
therapy.
Monitor blood pressure and pulse, assess
peripheral perfusion and obtain ECG, if indicated,
to determine drug effectiveness and evaluate for
adverse cardiovascular effects.
Assess urinary output
to evaluate renal function
and monitor for adverse effects of the drug.
Evaluate person for nausea and constipation
to
assess adverse effects of the drug and establish
appropriate interventions.
Monitor laboratory test results, such as renal and
liver function tests,
to determine drug effects on
renal and hepatic systems.
Implementation with rationale
Do not discontinue the drug abruptly
because
sudden withdrawal can result in rebound
hypertension, arrhythmias, flushing and even
hypertensive encephalopathy and death
; taper
drug over 2 to 4 days.
Do not discontinue the drug before surgery;
document on the person’s chart and monitor blood
pressure carefully during surgery.
Sympathetic
stimulation may alter the normal response to
anaesthesia, as well as recovery from anaesthesia.
Monitor blood pressure, orthostatic blood
pressure, pulse, rhythm and cardiac output
regularly, even with ophthalmic preparations,
to adjust dose or discontinue the drug if
cardiovascular effects are severe.
When giving phenylephrine intravenously, ensure
that an
α
-blocking agent is readily available to
counteract the effects
in case severe reaction
occurs
; infiltrate any area of extravasation with
phentolamine within 12 hours after extravasation
to preserve tissue.
Arrange for supportive care and comfort
measures, including rest and environmental
control,
to decrease CNS irritation
; analgesics for
headache
to relieve discomfort
; safety measures,
such as use of side rails and assistance with
ambulation if CNS effects occur,
to protect the
person from injury
; and protective measures
if
CNS effects are severe.
Provide thorough teaching about drug name, dose
and schedule for administration; technique for
administration if appropriate; measures to prevent
potential adverse effects such as voiding before
taking the drug and use of bowel training activities
if constipation is a problem; safety measures such
as avoiding driving and operating dangerous
machinery if CNS effects occur, and getting up and
down slowly if orthostatic hypotension is an issue;
warning signs of problems; and importance of
monitoring and follow-up.
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