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2.7
Sympathomimetics
2.7.1 Inotropic sympathomimetics
2.7.2 Vasoconstrictor sympathomimetics
2.7.3 Cardiopulmonary resuscitation
The properties of sympathomimetics vary according to
whether they act on alpha or on beta adrenergic recep-
tors.
Adrenaline (epinephrine)
(section 2.7.3)
acts on
both alpha
and beta
receptors
and increases
both
heart rate and contractility (beta
1
effects);
it can cause
peripheral vasodilation (a beta
2
effect) or vasoconstric-
tion (an alpha effect).
2.7.1
Inotropic
sympathomimetics
The cardiac stimulants dobutamine and dopamine act
on beta
1
receptors
in cardiac muscle,
and increase
contractility with little effect on rate.
Dopexamine acts on beta
2
receptors in cardiac muscle
to produce its positive inotropic effect;
and on periph-
eral dopamine receptors to increase renal perfusion; it is
reported not to induce vasoconstriction.
Isoprenaline injection is available from ‘special-order’
manufacturers or
specialist
importing companies,
see
p.
988.
Shock
Shock is a medical emergency associated with a
high mortality.
The underlying causes of shock such as
haemorrhage, sepsis, or myocardial insufficiency should
be corrected. The profound hypotension of shock must
be treated promptly to prevent tissue hypoxia and organ
failure.
Volume replacement is essential
to correct the
hypovolaemia associated with haemorrhage and sepsis
but may be detrimental
in cardiogenic shock.
Depend-
ing on haemodynamic status,
cardiac output
may be
improved by the use of
sympathomimetic inotropes
such
as
adrenaline
(epinephrine),
dobutamine
or
dopamine (see notes
above).
In septic shock,
when
fluid replacement and inotropic support fail to maintain
blood pressure,
the vasoconstrictor noradrenaline (nor-
epinephrine)
(section 2.7.2)
may be
considered.
In
cardiogenic shock peripheral
resistance is
frequently
high and to raise it
further
may worsen myocardial
performance and exacerbate tissue ischaemia.
The
use
of
sympathomimetic
inotropes
and vaso-
constrictors should preferably be confined to the inten-
sive care setting and undertaken with invasive haemo-
dynamic monitoring.
For advice on the management of anaphylactic shock,
see section 3.4.3.
DOBUTAMINE
Indications
inotropic support in infarction,
cardiac
surgery,
cardiomyopathies,
septic shock,
and cardio-
genic shock;
cardiac stress testing (consult product
literature)
Cautions
arrhythmias,
acute myocardial infarction,
acute heart failure,
severe hypotension,
marked
obstruction of cardiac ejection (such as idiopathic
hypertrophic subaortic stenosis);
correct hypovol-
aemia before starting treatment;
tolerance may
develop with continuous infusions longer than 72
hours;
hyperthyroidism; interactions: Appendix 1
(sympathomimetics)
Contra-indications
phaeochromocytoma
Pregnancy
no evidence of harm in
animal
studies—
manufacturers advise use only if potential benefit
outweighs risk
Breast-feeding
manufacturers advise avoid—no
information available
Side-effects
nausea;
hypotension,
hypertension
(marked increase in systolic blood pressure indicates
overdose),
arrhythmias,
palpitations,
chest pain;
dys-
pnoea,
bronchospasm;
headache;
fever;
increased
urinary urgency;
eosinophilia;
rash,
phlebitis;
very
rarely
myocardial infarction, hypokalaemia; coronary
artery spasm and thrombocytopenia also reported
Dose
. By intravenous infusion,
2.5–10 micrograms/kg/
minute,
adjusted according to response
Dobutamine
(Non-proprietary) A
Injection
,
dobutamine (as hydrochloride) 5 mg/mL.
To be diluted before use or given undiluted with
syringe pump.
Net price 50-mL vial = £7.50
Excipients
may include sulphites
Concentrate for intravenous infusion
,
dobutamine
(as hydrochloride) 12.5 mg/mL.
To be diluted before
use.
Net price 20-mL amp = £5.20
Excipients
may include sulphites
DOPAMINE HYDROCHLORIDE
Indications
cardiogenic shock in infarction or cardiac
surgery
Cautions
correct hypovolaemia; low dose in shock
due to acute myocardial infarction—see notes above;
hyperthyroidism; interactions: Appendix 1
(sympathomimetics)
Contra-indications
tachyarrhythmia, phaeochromo-
cytoma
Pregnancy
manufacturer advises use only if potential
benefit outweighs risk
Side-effects
nausea and vomiting,
peripheral vaso-
constriction,
hypotension,
hypertension,
tachycardia
Dose
. By intravenous infusion,
2–5 micrograms/kg/minute
initially (see notes above)
Dopamine
(Non-proprietary) A
Concentrate for intravenous infusion
,
dopamine
hydrochloride 40 mg/mL, net price 5-mL amp = 90p;
160 mg/mL, 5-mL amp = £3.40. To be diluted before
use
Intravenous infusion
,
dopamine hydrochloride
1.6 mg/mL in glucose 5% intravenous infusion,
net
price 250-mL container (400 mg) = £11.69.
Available
from ‘special-order’
manufacturers or specialist
importing companies,
see p.
988
DOPEXAMINE HYDROCHLORIDE
Indications
inotropic support and vasodilator in
exacerbations of chronic heart failure and in heart
failure associated with cardiac surgery
Cautions
myocardial infarction,
recent angina,
hypo-
kalaemia,
hyperglycaemia; correct hypovolaemia
before starting and during treatment, monitor blood
pressure, pulse, plasma potassium, and blood glucose;
hyperthyroidism; avoid abrupt withdrawal; interac-
tions: Appendix 1 (sympathomimetics)
BNF 61
2.7 Sympathomimetics
137
2
Cardiovascular system