Download Unit One: Introduction to Physiology: The Cell and General Physiology

Chapter 24: Circulatory Shock and Its Treatment
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Physiologic Causes of Shock
• Circulatory Shock Caused by Decreased CO
a. Cardiac abnormalities that decrease the ability of the
heart to pump blood
b. Factors that decrease venous return
•
Circulatory Shock That Occurs Without Diminished
CO
a. Excessive metabolic rate
b. Abnormal tissue perfusion pattterns
Physiologic Causes of Shock
• Tissue Deterioration is the End Result of Circulatory
Shock
• Stages of Shock
a. Nonprogressive (compenstated) stage-normal
compensatory mechanisms result in full recovery
b. Progressive stage-without theapy, the shock eventually
results in death
c.
Irreversible stage-all forms of therapy are inadequate
Shock Caused by Hypovolemia-Hemorrhagic Shock
• Relationship of Bleeding Volume to CO and
Arterial Pressure
Fig. 24.1 Effect of hemorrhage on CO and arterial pressure
Shock Caused by Hypovolemia-Hemorrhagic Shock
• Sympathetic Reflex Compensations
• Value of Sympathetic Nervous Reflexes
• Greater Effect of the Sympathetic Nervous Reflexes
in Maintaining Arterial Pressure than in
Maintaining CO
• Protection of Coronary and Cerebral Blood Flow
Progressive and Non-progressive Hemorrhagic Shock
• Non-progressive (Compensated) Shock
If the shock is not severe enough to cause its own
progression, the person eventually recovers. Factors
that allow recovery are the negative feedback
mechanisms that attempt to restore CO and arterial
pressure
Progressive and Non-progressive Hemorrhagic Shock
a. Baroreceptor reflexes
b. CNS ischemic response
c. Reverse stress-relaxation of the circulatory system
d. Increased secretion of renin and the formation of
angiotensin II
e. Increased secretion of vasopressin (ADH)
f. Increased secretion of epinephrine and norepinephrine
g. Compensatory mechanisms that return the blood volume
back toward normal
Progressive and Non-progressive Hemorrhagic Shock
• Progressive Shock-Viscous Circle of Cardiovascular
Deterioration
Fig. 24.3 Different types of “positive feedback” that can lead to progression of shock
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Cardiac Depression
Fig. 24.4 CO curves of the heart at different times after hemorrhagic shock begins
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Vasomotor Failure
• Blockage of Small Vessels
• Increased Capillary Permeability
• Release of Toxins by Ischemic Tissue
• Cardiac Depression Caused by Endotoxin
• Generalized Cellular Deterioration
• Tissue Necrosis in Severe Shock and Acidosis
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Irreversible Shock –Depletion of Cellular Hight Energy
Phosphate Reserves
Fig. 24.6 Failure of transfusion to prevent death in irreversible shock
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Hypovolemic Shock Caused by Plasma Loss
a. Intestinal obstruction
b. Severe burns
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Hypovolemic Shock Caused by Dehydration
a.
b.
c.
d.
e.
•
Excessive sweating
Fluid loss in severe diarrhea or vomiting
Excess loss of fluid by the kidneys
Inadequate intake of fluids and electrolytes
Destruction of the adrenal cortices, with the
loss of aldosterone
Hypovolemic Shock Caused by Trauma
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Neurogenic Shock-sudden loss of vasomotor tone
a. Deep general anesthesia
b. Spinal anesthesia
c. Brain damage
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Anaphylactic Shock and Histamine Shock
a. Release of histamine in immune type reactions,
causing
1. Venous dilation
2. Arteriole dilation
3. Increased capillary permeability
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Septic Shock (bacterial infection)
a. Peritonitis caused by infection from the uterus and
fallopian tubes
b. Peritonitis resulting from rupture of the GI tract
c. Generalized body infection resulting from the
spread of a skin infection (Staph or Strep)
d. Generalized gangrenous infection
e. Infection spreading into the blood from the kidney
or urinary tract
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Special Features of Septic Shock
a.
b.
c.
d.
e.
High fever
Marked vasodilation, especially in infected areas
High cardiac output
Sludging of the blood caused by rbc agglutination
Development of micro-blood clots (disseminated
intravascular coagulation)
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Physiology of Treatment in Shock
a. Replacement therapy with blood and plasma
transfusion
b. Dextran solution as a plasma substitute
c. Sympathomimetic drugs (simulate sympathetic
stimulation)
d. Head down position
e. Oxygen therpay
f. Glucocorticoids
Progressive and Non-progressive Hemorrhagic Shock (cont.)
• Circulatory Arrest-all blood flow stops
a. Usually as a result of cardiac arrest or ventricular
fibrillation
b. Effect on the brain