Chapter 24 - Guyton

Question 1

What are two factors that can reduce cardiac output and cause circulatory shock?

Answer 1

cardiac abnormalities that decrease the ability of the heart to pump blood; any factor that decreases venous return

Question 2

How can circulatory shock occur without reduced cardiac output?

Answer 2

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

Question 3

Three Major Stages of Shock

Answer 3

nonprogressive (compensated) stage, progressive stage, irreversible stage

Question 4

Hypovolemia

Answer 4

diminished blood volume

Question 5

Point of no return for blood loss (cardiac output and arterial pressure = 0).

Answer 5

35-45% blood lost

Question 6

What is the “last-ditch stand” of the sympathetic reflexes in their attempt to keep the arterial pressure from falling too low?

Answer 6

central nervous system ischemic response

Question 7

Is the effect of the sympathetic nervous system greater on arterial pressure or cardiac output?

Answer 7

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

Question 8

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.

Answer 8

negative (remember positive feedback is typically BAD)

Question 9

Factors that cause a person to recover from moderate levels of circulatory shock:

Answer 9

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)

Question 10

How quickly do the sympathetic reflexes kick in after hemorrhage?

Answer 10

30 seconds to 1 minute

Question 11

Factors that lead to progressive shock.

Answer 11

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

Question 12

Neurogenic shock

Answer 12

sudden loss of vasomotor tone throughout the body, resulting especially in massive dilation of the veins - will see venous pooling

Question 13

Causes of neurogenic shock.

Answer 13

deep general anesthesia, spinal anesthesia, brain damage

Question 14

__________ is an allergic condition in which the cardiac output and arterial pressure often decrease drastically.

Answer 14

Anaphylaxis

Question 15

What occurs during anaphylactic shock?

Answer 15

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)

Question 16

A condition that was formerly known by the popular name “blood poisoning” is now called?

Answer 16

septic shock

Question 17

A plasma substitute used when plasma is unavailable?

Answer 17

dextran

Question 18

In which types of shock is sympathomimetic drug therapy effective?

Answer 18

neurogenic and anaphylactic shock

Question 19

Why is sympathomimetic drug therapy not proved to be very valuable in hemorrhagic shock?

Answer 19

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

Question 20

Other treatments for shock?

Answer 20

head-down position, oxygen therapy, glucocorticoids

Question 21

It is likely that the severe brain damage that occurs from circulatory arrest is caused mainly by permanent blockage of many small blood vessels by _____ ____, thus leading to prolonged ischemia and eventual death of the neurons.

Answer 21

blood clots; rather than acute cerebral hypoxia which was previously thought to cause brain cell death