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19 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Definition of hypoxia?
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Hypoxia is inadequate oxygen reaching the tissues
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Definition of hypoxemia?
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Hypoxemia is in adequate oxygen in the arteries
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5 causes of decreased PO2?
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1. Low inspired PO2
2. Normal inspired O2, but low alveolar and arterial PO2(like in hypoventilation) 3. Diffusion limitation of O2 across the lung 4. Cardiovascular shunts 5. Mismatching of ventilation and perfusion(V/Q mismatch) |
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4 types of hypoxia?
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1. Stagnant(blood flow = insufficient supply tissues)
2. Anemic(RBC doesn't pick up O2) 3. Histotoxic (competitive inhibition of O2) 4. Arterial (-emia)(Shunts etc) |
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What is Anemic hypoxia?
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A condition that results from a decrease in the bloods ability to transport O2 to the tissues. The PO2 may be normal but hemoglobin binding is impaired.
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Think about what happens in anemia or CO poisoning.
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What is histotoxic hypoxia?
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It is when cells are poisoned and unable to make proper use of the oxygen.
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What is arterial hypoxemia?
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Arterial PO2 being abnormally low because of a problem with oxygenating the blood.
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Low inspired PO2 and hypoxemia; causes, equation description, and cures?
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This is usually caused by high altitude when the PO2 in the air is lowered because of low Pb.
Described by: PaO2 = PiO2 - PCO2/R What you inspire minus what you breath out. Normally fixed by hyperventilation or breathing pure O2. |
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Hypoventilation and hypoxemia?
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Hypoventilation can cause hypoxemia by reducing the alveolar PO2 and increasing the PaCO2. If you don't adequately ventilate O2 will decrease and CO2 will increase.
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High V/Q is what?
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Higher ventilation than perfusion in the alveoli. The O2 is just wasted but the blood that is there is adequately oxygenated.
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Low V/Q?
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Lower ventilation than perfusion. This means that the blood is not adequately oxygenated. This can occur naturally at the top of the lungs because of gravity.
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V/Q mismatch and hypoxemia and which one can compensate for itself?
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When caused by a low V/Q. The blood can compensate for PCO2 but not for the PO2. This is because the CO2 can be regulated by production of HCO3, but the O2 will not get any higher past its saturation point.
When caused by high V/Q everywhere the body can only compensate by adding more blood to the the lungs. |
Blood will take as much oxygen as it can possibly take, but there is a limit. CO2 can be regulated by unlimited amounts of HCO3.
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What is the V/Q ratio of a shunt?
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Shunts have a V/Q of 0 because they bypass the lungs, they are perfused but not ventilated, meaning they receive no O2.
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How are shunts measured?
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1. Inhale pure O2
2. Take PaO2 past the heart. 3. Any blood bypassing the heart will be easy to recognize |
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Shunt Fraction(Qs/Qt)?
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actual dilution of the capillaries/ max potential dilution of the capillaries.
CapPO2-PaO2/CapPO2-PvO2 Shunting the cops in Italy: the CapPO lost PaO divided by the CapPO losing PvO |
If all the blood were shunted the max potential dilution would equal to mixed venous O2. The whole ratio would be 1.
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Detecting a left to right shunt
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You detect one by finding an abnormally high O2 saturation in the RV or RA.
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Left to right shunts are arteries draining into veins. Right to left shunts are veins draining into arteries.
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Diffusion limited gas exchange
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Total amount of gas across the capillary is limited by the diffusion process. Blood will keep picking up the gas for as long as it is flowing past it. If the PaO2 is small with plenty of air then this must be due to the cell's ability to pick O2 up. CO can measure this limitation
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Cyanosis
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A bluish tint in thin capillary beds due to the presence of at least 5g of deoxyHb. Happens in normal adults when the PaO2 falls below 85% normal values. Peripheral cyanosis can occur because of reduced perfusion to certain tissues,
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Anemic Patients and Cyanosis.
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Anemic patients do not appear cyanotic because they cannot produce enough Hb to get to the necessary amount of deoxyHb. This does not mean that they are getting adequate tissue perfusion it just shows that the color is due to the deeper red hue of deoxyHb.
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