Introduction to Shock Flashcards
describe shock (2)
- decreased oxygen delivery to tissues
- decreased ability of tissues to utilize delivered oxygen
describe the oxygen delivery equation
DO2 = Q x CaO2
Q is cardiac output
CaO2 is oxygen content (per mL of blood) and is determined by hemoglobin concentration multiplied by oxygen saturation (how many oxygens each hemoglobin molecule holds) plus dissolved oxygen (PaO2)
so CaO2 = 1.34[Hb]SaO2 + 0.003PaO2 (FYI)
describe oxygen content
- amount of hemoglobin:
[Hb] normally 15 g/dl
-reflected as packed cell volume (PCV)
-PCV = Hct and is approx 1/3 [Hb}
describe the relation between SaO2 and PaO2
hemoglobin cannot be saturated with oxygen beyond 100% but at 600mHg, PaO2 (dissolved O2) is so high that total O2 can increase O2 diffusion
once 3 O2s are bound to hemoglobin, it is really hard to get the last 4th! so generally as PaO2 increases, SaO2 increases until 3O2s are bound and then the curve flattens out
describe cardiac output
the amount of blood being pumped out of the heart; composed of
- heart rate: determined by nervous input, medications, hormones
-beats/min - stroke volume: determined by cardiac contractility, blood volume, and vascular tone
-mL/beat
what 2 factors contribute to decreased oxygen delivery
- oxygen delivery factors
a. not enough oxygen in the blood: low O2 content
b. inadequate tools to deliver oxygen: hypovolemia, cardiac disease - tissue usage factors
a. increased metabolic rate: fever, exercise
b. inability to use oxygen: cyanide
describe oxygen delivery to the cells
heart to aorta
arteries to aterioles: increase in area and decrease in flow velocity
at arterioles: greatest resistance, smooth muscle
capillaries: site of gas exchange
describe the anaerobic and aerobic components of cellular respiration
anaerobic:
-glycolysis: less efficient, does not need oxygen!
aerobic:
-mitochondria: normal scenario when oxygen is available
what happens to cellular respiration with low tissue oxygenation?
glycolysis becomes the primary method
-is less efficient
-byproducts are pyruvate which is converted to lactate and H+
-is fast though
-provides energy in tissues with limited oxygen supply: in cases of decreased perfusion and decreased oxygen content
describe lactate
- produced by tissues utilizing anaerobic metabolism
- can cause lactic acidosis: decreased blood pH, severe acidosis can result in dysfunction
- can be measured in the blood:
-venipuncture artifact
how can we estimate the oxygen demand (VO2) of a tissue?
- oxygen extraction ratio:
(CaO2 - CVO2)/CaO2 - normally 20-30% but can increase up to 60-70%
-as long as tissues can pull oxygen out of the blood, will not be in anaerobic metabolism and able to compensate - if blood bypasses the tissues will be artificially high
how does the body compensate to maintain aerobic respiration?
- if DO2 is decreasing to near of below VO2, the body will:
-increase heart rate
-increase stroke volume
-increase OER - it is HARD to change PaO2 quickly without assistance:
-need to increase FiO2 - it is HARD to change [Hb] quickly without assistance
-need a blood transfusion
describe decompensatory shock
- as DO2 dips below VO2:
-some tissues must switch to anaerobic metabolism for lack of O2, resulting in lactate production - polonged decreased DO2 may lead to organ dysfunction
-decreased ATP production means cells cannot maintain gradients so there is decreased nervous transmission in the heart, GI, and brain, resulting in increased intracellular Na+, which causes cellular edema and necrosis may follow
describe the physical exam of compensatory shock versus decompensatory shock
compensatory:
1. tachycardia (usually)
2. tachypnea
3. pink/red mucous membranes
4. normal or elevated blood pressure
decompensatory:
1. bradycardia may develop
2. tachypnea
3. grey/purple mucous membranes
4. hypotension
