Pharm Ch 29

Drug Therapy for Shock

and Hypotension

CHAPTER 29

KEY TERMS

• Chronotropic effect causing a change in heart rate
• Dromotropic effect causing a change in speed of electrical

conduction in the heart

• Inotropic effect causing a change in myocardial contraction
• Normotensive having normal blood pressure
• Pressor effect that increases blood press

Types of shock

• Hypovolemic shock, the most common type of shock, is caused by

insufficient circulating volume from actual blood loss or relative
loss from fluid shifts within the body.

• Hypovolemic shock may result from hemorrhage, trauma, burns,

and medical conditions such as diabetic ketoacidosis or diabetes
insipidus.

• In children, vomiting and diarrhea are the most typical causal

conditions

Cardiogenic shock

• Cardiogenic shock occurs when the myocardium has lost its ability

to contract efficiently and maintain an adequate cardiac output.

• Cardiogenic shock is seen with myocardial infarction, atrial and

ventricular arrhythmias, and valve or ventricle septal rupture

Obstructive shock

• Obstructive shock may result when any kind of mass or fluid

accumulation and/or blood clot outside of the heart interferes
with the heart’s ability to adequately pump a sufficient quantity
of blood.

• Causes include pulmonary embolism, pulmonary hypertension,

tension pneumothorax, constrictive pericarditis, and restrictive
cardiomyopathy

Distributive or vasogenic shock

• Distributive or vasogenic shock develops from impaired

utilization of oxygen and thus production of energy by the cell.

• It is characterized by massive vasodilation, which results in a

relative hypovolemia.

• Distributive shock can be further divided, depending on cause,

into three subtypes

Distributive shock three subtypes

• Anaphylactic shock, which is due to massive vasodilation caused by release of

histamine in response to a severe allergic reaction.

• Neurogenic shock, which is a result of massive vasodilation of the peripheral

blood vessels from high-level spinal cord injuries. In this injury, sudden loss of
signals from the sympathetic nervous system causes loss of normal muscle
tone in blood vessel walls, leading to decreased systemic vascular resistance
and altered oxygen extraction.

• Septic shock, which is due to massive vasodilation caused by release of

mediators of the inflammatory process in response to overwhelming infection.
Often this kind of shock is associated with gram-negative and gram-positive
bacteria and fungi

STAGES OF SHOCK

TREATMENT OF HYPOTENSION AND SHOCK

• In hypotension and shock, initial efforts involve identifying and treating

the cause when possible.

• It may help to place the patient in a recumbent position; give blood

transfusions, fluids, and electrolytes; and treat infections.

• If these measures are ineffective in raising the blood pressure enough to

maintain perfusion to vital organs such as the brain, kidneys, and heart,
adrenergic drugs may be used.

• The usual goal of drug therapy is to maintain tissue perfusion and a mean

arterial pressure of at least 80 to 100 mm Hg

ADRENERGIC DRUGS

• Three adrenergic receptors (beta1, beta2, and alpha) are targets

of catecholamines, predominately epinephrine and
norepinephrine.

• Adrenergic drugs effects of these drugs work mainly on the heart,

blood vessels, and bronchi.

• Often used as emergency drugs in the treatment of acute

cardiovascular and respiratory collapse

• useful in the treatment of allergic reactions
• Benefit from these drugs include those in need of restoration of

blood pressure in reversing types of hypotensive states.

ADRENERGIC DRUGS

• Adrenergic drugs produce effects similar to those produced by

stimulation of the sympathetic nervous system and therefore have
widespread effects on body tissues

• adrenergic drugs, such as norepinephrine, epinephrine, and

dopamine, are exogenous formulations of naturally occurring
neurotransmitters and hormones.

• adrenergic medications, such as phenylephrine, pseudoephedrine,

and isoproterenol, are synthetic chemical relatives of naturally
occurring neurotransmitters and hormones

Norepinephrine (Levophed)

• serves as the prototype adrenergic drug in the treatment of hypotension and shock.
• has an immediate onset of action with vasopressor duration of 1 to 2 minute
• Action
• Norepinephrine is a pharmaceutical preparation of the naturally occurring

catecholamine norepinephrine.

• alpha-receptor agonist effects and results in potent peripheral arterial

vasoconstriction.

• (As a result, it increases blood pressure more than it increases heart rate, force of

contraction, or cardiac output).

• The drug is useful in cardiogenic and septic shock, but reduced renal blood flow

limits its prolonged use

Norepinephrine

• Use
• Treat severe hypotension and shock that persists after adequate

fluid volume replacement. The drug is recommended as the first-
choice vasopressor for the management of sepsis and septic
shock

• used with caution: geriatric patient population, renal failure,
• Renal system eliminates many adrenergic drugs, including

norepinephrine, and their metabolites. In the presence of renal
disease, these compounds may accumulate and cause increased
adverse effects

Adverse Effects Norepinephrine

• Possible diminished renal perfusion and decreased urine output due to

vasopressor action

• Possible decreased perfusion to the liver, with subsequent liver damage due

to vasopressor action

• Possible irritable cardiac dysrhythmias due to beta1 activity
• Possible increase in myocardial oxygen requirement due to beta1 activity
• Hyperglycemia, hypokalemia, and hypophosphatemia due to beta1 activity
• Severe hypertension and reflex bradycardia
• Limb ischemia due to profound vasoconstriction
• Extravasation at infusion site

BLACK BOX WARNING

• regarding the potential risk of tissue damage with extravasation of

norepinephrine.

• The drug should be infused into a large vein or central line if possible.
• The use of leg veins should be avoided in older adults and in those with occlusive

disorders.

• If extravasation occurs, diluted phentolamine should be injected into the area

with a small-gauge hypodermic needle as soon as possible to prevent sloughing
and necrosis of the tissue

Contraindications

• cardiac dysrhythmias, angina pectoris, hypertension,

hyperthyroidism, and cerebrovascular disease; stimulation of the
sympathetic nervous system worsens these conditions.

• Narrow-angle glaucoma is a contraindication, because the drugs

result in mydriasis, closure of the filtration angle of the eye, and
increased intraocular pressure.

Other Drugs in the Class (ADRENERGIC
DRUGS)

• Epinephrine (Adrenalin) is a naturally occurring catecholamine

produced by the adrenal gland

• increase the pressure by increasing the cardiac index and stroke

volume, as well as systemic vascular resistance and heart rate.

• low doses, epinephrine stimulates beta receptors, which increases

cardiac output by increasing the rate and force of myocardial
contractility.

• Also causes bronchodilation.
• Larger doses act on alpha receptors to increase blood pressure

through vasoconstriction

Epinephrine (Adrenalin)

• Epinephrine is the adrenergic drug of choice for relief of anaphylactic shock,

the most serious allergic reaction

• People susceptible to severe allergic responses should carry a syringe of

epinephrine at all times.

• EpiPen and EpiPen Jr are prefilled, autoinjection syringes for intramuscular

self-administration of epinephrine in emergency situation

• Epinephrine is also used as treatment of cardiac arrest
• Epinephrine is used as an additive to local anesthetics for vasoconstrictive

effects, which include prolonging the action of the local anesthetic drug,
preventing systemic absorption, and minimizing bleeding

Dopamine,

• Dopamine, a naturally occurring precursor of norepinephrine and epinephrine,

functions as a neurotransmitter. Its action is dose dependent and can stimulate
alpha, beta, or dopaminergic receptors, depending on the dose being used.

• Dopamine acts indirectly by releasing norepinephrine from sympathetic nerve

endings and the adrenal gland

• At low doses (1–5 mcg/kg/min), increased renal blood flow and urine output occur

( used for CHF-pulmonary edema)

• Doses greater than 10 mcg/kg/min, stimulation of beta receptors takes place, and

there is an increase in heart rate, myocardial contractility, and blood pressure

• Effects at higher doses(20-30 mcg/kg/min) are tachycardia and increased

pulmonary shunting, as well as the potential for decreased splanchnic perfusion
and increased pulmonary arterial wedge pressure

Dobutamine

• Dobutamine acts on beta1 receptors in the heart to increase the

force of myocardial contraction with a minimal increase in heart
rate

• Dobutamine is most useful in cases of shock that require increased

cardiac output without the need for blood pressure support.

• Caution is warranted when administering the drug in patients with

moderate or severe hypotension (systolic blood pressure less than
80 mm Hg), because the peripheral vasodilation may cause a
further fall in blood pressure

Phenylephrine (Vazculep)

• is a synthetic adrenergic drug that stimulates alpha-adrenergic

receptors to produce vasoconstriction.

• Constricts arterioles and raises systolic and diastolic blood

pressure

• Phenylephrine resembles epinephrine but has fewer cardiac

effects and a longer duration of action.

• Vasoconstriction decreases cardiac output and renal perfusion and

increases peripheral vascular resistance and blood pressure

• excreted primarily in the urine

Phenylephrine (Vazculep

• Phenylephrine may be given to increase blood pressure in

hypotension and shock

• may be used therapeutically to relieve paroxysmal atrial

tachycardia