Shock

Question 1

Definitions

Answer 1

1. inadequate bloodflow leading to tissue damage
2. DO2 decrease compared to VO2(consumption)
3. inadequate cellular energy production due to poor perfusion

poor perfusion/uneven distribution->lower DO2/VO2 ->inadequate cellular energy production

as DO2 decreases, tissues can extract more 02 and keep VO2 constant. up to a certain point - critical DO2 - which is when VO2 starts falling (supply dependent)=tissue hypoxia

Question 2

physiologic causes

Answer 2

Ddecreased CO:
Cardiac abnormalities - cardiomyopathies, valve Dz, toxins
Decrease in venous return-sepsis, anaphylaxis, GDV

Normal CO:
excessive metabolism
abnormal tissue perfusion patterns

Question 3

functional classification

Answer 3

according to Silverstein & Hopper

shock is usually caused by decreased DO2 secondary to 3 main mechanisms:

1. cardiogenic:
   decrease on CO (CHF, tamponade, arrhythmia, od)
2. hypovolemic:
   decreased venous return
   hemorrhage (trauma, coagulation)
   dehydration, neoplasia, burns, internal fluid loss
3. distributive:
   can cause locally decreased DO2 in normal CO
   affects vasoconstriction-resistance
   sepsis sirs anaph obstruction

1-3 are circulatory shock

4. metabolic:
   Hypoglycemia Cyanide toxicity Mitochondrial dysfunction
5. hypoxemic:
   A decrease in oxygen content in arterial blood.
   Anemia Severe pulmonary disease Carbon monoxide toxicity Methemoglobinemia

shock leads to a vicious cycle with deterioration of tissues and CO, until death

Question 4

Shock phases

Answer 4

non progressive (compensatory)-
comp circulatory mechanisms such as raas catecholamines will get animal out of shock without external help, but if primary cause is not removed-animal will deteriorate

progressive-
without help, the animal will deteriorate and die

irreversible-
beyond a certain point, no intervention will help - damage is too severe

Question 5

experiment

Answer 5

dogs bled to a point where arterial pressure was below 45 did not make it. even the ones that made it-the closer to 45, the slower the recovery

the objective is not to reach that threshold

Question 6

compensatory mechanisms

Answer 6

baroreceptors - effective at 50-150 mmhg - low bp lowers their tone

raas - ald affects Distal convulated tubules, collecting ducts
other mechs-intestinal absorbtion, movement of fluids from interstitial to intravascular.
adh and ald - absorption of salt and water in kidney increase in thirst
local vascular paracrin-NO endothelin thromboxan prostacyclin

brain eschemic reponse - BP lower than 50 - last ditch effort - significant symp response

barro - seconds
fluid shift mins
raas hours
kidney days

Question 7

BP

Answer 7

BP is loosly correlated to co drop. both are gone at a loss of 45% of volume

BP not necessarily indicative of level of shock or perfusion - due to reflexes

shock, BP, perfusion - not necessarily correlated - depend on animals response