Chapter 6: Shock Flashcards
How do you calculate the arterial or venous oxygen content (CaO2 or CvO2)?
CaO2= (HbSaO2 x 1.34) + (PaO2 x 0.003)
CvO2 = (HbSvO2 x 1.34) + (PvO2 x 0.003)
HbSxO2 = saturation (percent of Hb that has an O2 molecule)
1.34 = mL of O2 per g of Hgb
PxO2 = partial pressure
0.003 is the oxygen solubility coefficient at 37 degrees celsius
What is the Fick equation?
The Fick Principle simply states that at rest, the oxygen going into an organ minus the oxygen left out of an organ must equal how much oxygen that organ has used.
VO2 (oxygen uptake) = Cardiac output x (CaO2 - CvO2)
If O2 delivery is adequate, sufficient O2 should remain in venous blood to provide 70% saturation of hemoglobin.
What is meant by an ATLS class 2 hemorrhage?
15-30% blood loss
You see increased HR, RR and decreased pulse pressure
What is an ATLS class 4 hemorrhage defined as?
> 40% loss of circulating blood volume
If not treated, leads to irreversible shock and death
What is the oxygen extraction ratio?
What is the resting global oxygen extraction ratio? (%)
Ratio between oxygen uptake and delivery - expressed as a percentage - it represents the efficacy of the tissue extraction of oxygen from the capillary bed
Resting is 20%
can increase to 60-70% in cases of metabolic demand or a reduction in oxygen delivery
Chemoreceptors in the brain stem are more sensitive to which two things, as opposed to baroreceptors which are more sensitive to oxygen?
Hydrogen ions and carbon dioxide
Why in hemorrhagic shock do you see a decrease in TP and PCV?
Compensatory mechanism - decrease in mean arterial pressure, along with constriction of pre-capillary arterioles leads to a fall in hydrostatic pressure in capillaries with a net shift of body fluids from the interstitial into the IV space
More fluids in IV space = dilution of PCV
A typical acute hemorrhagic shock patient will have PCV and TP of what on presentation?
PCV 35-40%
TP 4.5-5.0g/dl
What is the cutoff for normal lactate?
What is severe hyperlactatemia?
<2 normal
>6 severe
What are the 4 classifications of shock?
Cardiogenic
Hypovolemic (hemorrhagic or non-hemorrhagic (burns, urinary))
Distributive (sepsis, anaphylaxis)
Hypoxic (methemoglobinemia)
What three things influence stroke volume?
Preload, afterload and contractility
What is ATLS class 1 hemorrhage?
Loss of up to 15% of circulating blood volume.
minimal clinical signs, maybe tachycardia.
What is ATLS class 3 hemorrhage?
Loss of 30-40% of circulating volume.
Pale MM, prolonged CRT, arterial hypotension
The constant representing the mL of oxygen carried by 1g of hemoglobin is what?
1.34
