- Hypovolemic shock: Dehydration or
Blood Loss
- Treatment includes fluid
infusion to obtain adequate cardiac
preload (filling pressure) without
precipitating pulmonary congestion and
compromising oxygenation.
- Cardiac Failure (Cardiogenic Shock
(pump failure) due to excessive myocardial tissue
loss or arrhythmia
- Cardiac Output obstruction
(pulmonary embolism, aortic dissection,
pericardial tamponade)
- Loss of peripheral vascular tone
(Septic Shock or anaphylaxis)
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Drugs
Used in Treating Shock
a agonists: increase peripheral vascular resistance
- Norepinephrine, phenylephrine,
metaraminol,
mephenteramine and methoxamine may be
used to maintain blood pressure in severe hypotension.
- The objective is to ensure
adequate CNS perfusion.
- The use of these agents
may be indicated if the hypotensive state
is due to sympathetic failure, such as
possibly occurring following spinal
anesthesia or injury.
- In shock due to
other causes, reflex vasoconstriction is
typically intense; adding a agonists may be
harmful by further compromising organ
(e.g. renal) perfusion.
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ß- agonists: increase heart rate and
contractility
Increasing heart rate and contractility
by isoproterenol, epinephrine or
norepinephrine may adversely affect
cardiac performance in damaged
myocardium.
These
agents increase myocardial oxygen
requirements and may induce arrhythmias.
Norepinephrine
by increasing afterload (a receptor activation)
may worsen myocardial performance
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Dopamine and Dobutamine
Dopamine,
(Intropin), at low
concentrations, acts at D1 receptors and
improve myocardial contractility
(positive inotropism).
Dopamine (Intropin) produces
less of an increase in heart rate
compared to isoproterenol and dopamine
dilates renal arteries, promoting better
kidney perfusion.
Dobutamine
(Dobutrex), through complex actions
mediated by a
and ß receptors enhances
contractility without substantially
increasing either heart rate or
peripheral resistance.
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Drugs
in Cardiogenic Shock:
Nitrates, Adrenergic Agonists, Amrinone (Inocor) and Milrinone (Primacor)
- In cardiogenic shock
precipitated by acute myocardial
infarction, salvage of reversibly damaged
myocardial may be accomplished by:
- supplemental
oxygen
- i.v. nitroglycerin (decreasing preload)
- intra-aortic
balloon pump (reducing afterload)
- surgery to repair
valve pathologies or to
revascularize
-
Cardiogenic Shock
may be caused myocardial stunning due to
prolonged cardiopulmonary bypass.
- Dopamine (Intropin) and Dobutamine
(Dobutrex) may be useful as
positive inotropic agents
- Dobutamine
(Dobutrex) may be
preferable because of a
decreased likelihood of
increasing heart rate and
peripheral resistance
(increasing afterload
increases myocardial
work).
- Amrinone (Inocor) and
milrinone (Primacor)
(phosphodiesterase inhibitors)
have positive inotropic effects
that may be useful if other
agents are ineffective.
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