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13 Cards in this Set
- Front
- Back
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What is the definition of hypoventilation?
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Reduced alveolar ventilation resulting in an increase in arterial PCO2.
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What is the etiology of hypoxemia?
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1) low mixed venous PO2 (increased oxygen consumption, low cardiac output)
2) Decreased alveolar PO2 (high altitude, low FiO2, high partial pressure of alternate gas, hypoventilation) 3) Increased A-a O2 gradient (Cardiac shunt, pulmonary shunt, V/Q mismatch, diffusion limitations) 4) Decreased oxygen carrying capacity (low or abnormal hemoglobin, carbon monoxide toxicity) |
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What is the status of PaO2 and PaCO2 when VA/Q is 0.01?
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As V/Q ratio decreases (increased right to left shunting)
PaO2 decreases rapidly and progressively. PaCO2 increases gradually at first and then quite rapidly. |
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Which factors affect the VD/VT ratio?
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Position, age, pulmonary disease, perfusion abnormalities, anticholinergic drugs, general anesthesia, ventilation parameters
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Define dead space
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Dead space is the alveolar ventilation without perfusion or the TV that does not participate in gas exchange.
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What would the V/Q ratio be for an absolute dead space?
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The value for absolute dead space is when V/Q = infinity.
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In normal patients, is most of the physiologic dead space anatomic or alveolar?
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Anatomic dead space extending from the oropharynx to terminal bronchioles in which no gas exchange occurs.
It is 2 ml/kg of Ideal body weight. |
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List some of the causes of alveolar dead space.
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Decreased pulmonary blood flow
Decreased CO Pulmonary embolism (Fat, thrombus, air, or amniotic fluid) Chronic obstructive pulmonary disease (COPD) Positive end-expiratory pressure (PEEP) Intense pulmonary vasoconstriction ARDS (Intense pulmonary vasoconstriction, lung contusion, or pulmonary edema) The most common OR and ICU cause is decreased CO and pulmonary blood flow. |
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Define Vds/Vt. What is the normal value? Can the end tidal CO2 value from the mass spectrometer be used in the formula for Vds/Vt?
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Vds/Vt= Alveolar PCo2-Expired PCO2/Alveolar PCO2
Expired PCO2 is the average PCo2 from the mixture of all expired gas samples over a period of time (not the ETCO2). The alveolar PCO2 is determined by alveolar ventilation and the CO2 production. The normal value is 0.2-0.4 but during PPV it is 0.33-0.5. The mass spectrometer ETCO2 value is not accurate because it includes the gas in the anatomic dead space as well as the gas left in the circuit. |
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Define shunt
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Shunt is lung that is perfused but poorly ventilated.
The ABSOLUTE SHUNT EFFECT is a result of venous admixture and may occur in acute lobar atelectasis, advanced pulmonary edema, postoperative atelectasis, or consolidated pneumonia. |
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What would the V/Q ratio be for an absolute shunt?
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0
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What is the difference between a physiologic shunt and an anatomic shunt?
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physiologic shunt--> 2-5% of CO. The portion of the total CO that returns to the left heart and systemic circulation without receiving O2 in the lung.
Anatomic shunt--> pathophysiological changes like congenital heart disease (PDA, VSD, ASD), right to left intrapulmonary anatomic shunts, or AV malformation in hepatic failure. |
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Define Qshunt/Qtotal.
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Qs/Qt= CcO2-CaO2/CcO2-CvO2
CcO2=oxygen content of end pulmonary capillary blood CaO2=arterial oxygen contents CvO2=mixed venous oxygen content |
