Flashcards in Chapter 24 - Guyton Deck (21):
What are two factors that can reduce cardiac output and cause circulatory shock?
cardiac abnormalities that decrease the ability of the heart to pump blood; any factor that decreases venous return
How can circulatory shock occur without reduced cardiac output?
excessive metabolism of the body, so that even a normal cardiac output is inadequate; or abnormal tissue perfusion patterns, so that most of the cardiac output is passing through blood vessels besides those that supply the local tissues with nutrition
Three Major Stages of Shock
nonprogressive (compensated) stage, progressive stage, irreversible stage
diminished blood volume
Point of no return for blood loss (cardiac output and arterial pressure = 0).
35-45% blood lost
What is the “last-ditch stand” of the sympathetic reflexes in their attempt to keep the arterial pressure from falling too low?
central nervous system ischemic response
Is the effect of the sympathetic nervous system greater on arterial pressure or cardiac output?
increase the arterial pressure mainly by increasing the total peripheral resistance, which has no beneficial effect on cardiac output; however, the sympathetic constriction of the veins is important to keep venous return and cardiac output from falling too much
The factors that cause a person to recover from moderate degrees of shock are all the ________ feedback control mechanisms of the circulation that attempt to return cardiac output and arterial pressure back to normal levels.
negative (remember positive feedback is typically BAD)
Factors that cause a person to recover from moderate levels of circulatory shock:
baroreceptor reflexes, central nervous system ischemic response, reverse stress-relaxation of the circulatory system, formation of angiotensin by the kidneys, formation of vasopressin (antidiuretic hormone) by the posterior pituitary gland, compensatory mechanisms that return the blood volume back toward normal (absorption of fluid from GI)
How quickly do the sympathetic reflexes kick in after hemorrhage?
30 seconds to 1 minute
Factors that lead to progressive shock.
arterial pressure drop decreases coronary blood flow and depresses heart, diminished blood flow to the brain’s vasomotor center depresses the center (no sympathetics), blockage of small blood vessels (sludged blood), increased capillary permeability (capillary hypoxia), release of toxins by ischemic tissue (endotoxin), generalized cellular deterioration
sudden loss of vasomotor tone throughout the body, resulting especially in massive dilation of the veins - will see venous pooling
Causes of neurogenic shock.
deep general anesthesia, spinal anesthesia, brain damage
__________ is an allergic condition in which the cardiac output and arterial pressure often decrease drastically.
What occurs during anaphylactic shock?
released histamine or histamine-like substance causes increase in vascular capacity because of venous dilation; dilation of the arterioles; greatly increased capillary permeability, with rapid loss of fluid and protein into the tissue spaces (net effect is greatly reduced venous return)
A condition that was formerly known by the popular name “blood poisoning” is now called?
A plasma substitute used when plasma is unavailable?
In which types of shock is sympathomimetic drug therapy effective?
neurogenic and anaphylactic shock
Why is sympathomimetic drug therapy not proved to be very valuable in hemorrhagic shock?
the sympathetic nervous system is almost always maximally activated by the circulatory reflexes already; so much norepinephrine and epinephrine are already circulating in the blood that sympathomimetic drugs have essentially no additional beneficial effect
Other treatments for shock?
head-down position, oxygen therapy, glucocorticoids