Drugs for treating shock

Shock

• shock: a syndrome characterized by collapse of the circulatory system

• vital tissues do not receive enough blood to function properly

• cells cannot carry on normal metabolism

Symptoms of shock

• shock is a collection of signs and symptoms, many nonspecific:

• skin: pale, cool, or clammy

• respiratory: breathing rapid and shallow

• CV: low b.p., low cardiac output, weak pulse

• neurologic: restlessness, anxiety, lethargy, confusion

Classification of shock

• 1. cardiogenic

• failure of the heart to pump sufficient blood to tissues

• due to: left heart failure, ischemia, MI, arrhythmias, pulmonary embolism, myocardial/pericardial infection

• 2. hypovolemic

• loss of blood volume

• due to: hemorrhage, burns, profuse sweating, excessive urination, vomiting, diarrhea

• 3. septic

• multiple organ dysfunction as a result of pathogenic organisms in the blood

• due to: widespread inflammatory response to bacterial, fungal or parasitic infections

• 4. anaphylactic

• acute allergic reaction

• due to: severe reaction to allergens (penicillin, nuts, shellfish, animal proteins)

Treatment of shock

• initial treatment includes basic life support while identifying the underlying cause

• maintain ABC of life support: airway, breathing, circulation

• administer fluids/electrolytes and blood products if patient has lost a significant amount of blood

Drug categories in treating shock

• There are 3 categories of drugs that play a role in treating shock:

• vasoconstrictors

• cardiotonic drugs

• fluid replacement agents

Vasoconstrictors used to treat shock

• early stages of shock: body compensates for initial fall in b.p. by ↑ activity of sympathetic nervous system

• this sympathetic activity results in vasoconstriction which:

• ↑ b.p.

• ↑ heart rate and force of myocardial contractions

• Purpose: maintain blood flow to vital organs (heart, brain) and ↓ blood flow to other organs (kidneys, liver)

• Body’s ability to compensate is limited

• Severe hypotension may develop

• vasoconstrictors are used to maintain b. p.

• given IV they immediately raise b. p.

• patients monitored continuously during infusion to avoid HT due to overtreatment

Specific Vasoconstrictors used to treat shock

• 1. epinephrine: a nonselective adrenergic agent

• b.p. rises due to stimulation of alpha1 receptors in smooth muscle of blood vessels

• cardiac output increases due to stimulation of beta1 receptors in heart

• airway opens due to stimulation of beta2 receptors in the bronchi

• 2. norepinephrine (Levarterenol, Levophed) has both alpha and beta1 activity

• 3. methoxamine hydrochloride (Vasoxyl)

selective to alpha receptors

Cardiotonic drugs used to treat shock

• aka inotropic agents

• as cardiogenic shock progresses, the heart begins to fail:

• cardiac output ↓, lowering amount of blood reaching vital tissues and worsening shock

• cardiotonic drugs are used in the treatment of shock to ↑ the force of contraction and increase cardiac output

Specific Cardiotonic drugs used to treat shock

• 1. digoxin (Lanoxin)

• 2. dobutamine (Dobutrex): a beta1 adrenergic agent that is often drug of choice for short term (1/2 life of only 2 min.) treatment of shock

• has the ability to cause heart to beat more forcefully without significantly increasing heart rate

• increase in cardiac output assists in maintaining blood flow to vital organs

• 3. dopamine (Dopastat, Intropin)

• mechanism of action is dependent on dose

• low doses: selectively stimulates beta1 receptors in kidneys that cause vasodilation and an ↑ blood flow to kidneys (used in treating hypovolemic and cardiogenic shock)

• moderate doses: stimulates beta1 receptors, causing heart to beat with more force and increasing cardiac output

• higher doses: stimulates alpha receptors causing vasoconstriction and raising b.p.

Fluid replacement agents used to treat shock

• Used to replace blood or other fluids lost during hypovolemic shock

• Fluid replacement agents are generally placed into the following 3 categories:

• blood, colloids, crystalloids

Blood

• Whole blood indicated for treatment of acute, massive blood loss when there is a need to replace plasma volume and supply RBC’s

Colloids

• Used when up to 1/3 of adult blood volume is lost

• colloids are proteins that stay suspended in the blood for a long period and draw water from the body’s cells and tissues into the blood vessels

• colloids include: normal serum albumin, plasma protein fractions, dextran and hetastarch

Crystalloids

• IV solutions that contain electrolytes in amounts resembling those of natural plasma

• Unlike colloids, crystalloid solutions leave the blood and enter cells

• used to replace fluids lost, and to increase urine output

• include: normal saline, lactated Ringer’s, hyperotonic saline, 5% dextrose in water