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37 Cards in this Set
- Front
- Back
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absolute shunt
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ventilation decreases with no change in blood flow, the V/Q ratio decreases until it equals 0 when ventilation ceases.
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absolute dead space
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when no CO2 can enter alveolar and no O2 can be taken up by blood
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what is blood flow in absolute dead space
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zero
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what are PO2 and PCO2 in absolute shunt
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40 and 45
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relative dead space
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alveoli with abnormally high V/Q ratios
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what is the significance of blood flow in relative dead space
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it is present, but abnormally low
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relative shunt
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ventilation is present but low
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high V/Q ratio
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blood flow deficiency
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low V/Q
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ventilatory deficiency
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what happens to P (A-a) O2 when a person goes from breathing room air to 100% O2
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it increases to above 50 mmHg
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why does the P (A-a) O2 increase on 100% O2
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because of the way the Hb binds to O2 molecules
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what does low V/Q ratios produce
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hypoxemia
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what are the major causes of hypoxemia due to V/Q imbalances
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1. hypoventilation 2. absolute shunt 3. V/Q mismatch
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what is a normal shunt that would decrease CO2 and PO2
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2%-5%
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causes of general hypoventilation
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muscle paralysis or weakness, drug - induced respiratory center depression
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hypoventilation and hypoxemia tx
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increase ventilation
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what causes a physiological shunt
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any abnormal process that prevents alveolar ventilation...shunted blood cannot take up O2 or release CO2
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examples of physiological shunt
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pneumonia, p. edema, pnemothorax
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why does increasing the amount of oxygen breathed by patients with shunting have little effect on improving arterial oxygenation
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because shunted venous blood cannot contact inspired gas
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tx for intrapulmonary shunting
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restore ventilation to the airless alveoli by means of PEEP & CPAP
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what is the PaCO2 of hypoxic patients
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normal or low
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what can hypoxemia activate
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the peripheral chemoreceptors to increase ventilation to produce hyperventilation and respiratory alkolosis
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COPD patients may be unable to do what if there Is a mismatch in V/Q involving a large number of alveoli
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increase their minute ventilation enough to sustain normal PaCO2
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what is the most common cause of hypoxemia and chronic hypercapnia
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V/Q imbalance
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what may result in cases of high alveolar inflation due to to mechanical ventilation or auto-PEEP
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reduced pulmonary blood flow due to obstruction, low blood pressure, flow, or alveolar over distention
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what is a diagnostic indicator for increased dead space
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alveolar - arterial pressure difference
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what is the basis for the Bohr dead space equation
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increased difference between PaCO2 and PECO2
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what is the Bohr equation used to calculate
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dead space to tidal volume ratio,
VD/VT |
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if minute volyme is measured through VD/VT ratio, what else can be calculated
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alveolar minute volume
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what is the best known index of oxygen transfer efficiency
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A-a gradient
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what is a normal P (A-a) O2 at room air
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about 7-14 mm Hg
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what is a normal P (A-a) O2 when breathing 100% O2
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50-60 mmHg
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what is the arterial - alveolar ratio represent
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the percentage of alveolar PO2 that is transferred to the arterial blood
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which is more stable as the the FiO2 changes
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the a-A ratio
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what is the lower normal limit for
a-A ratio |
0.75
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arterial PO2/FiO2 ratio measures oxygenation. what is normal range
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380-475 (when arterial PO2 is 80 - 100 mmHg on FiO2 of 0.21)
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what affects arterial PO2/FiO2
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changes in arterial PCO2
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