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69 Cards in this Set
- Front
- Back
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What is the henderson-hasselbach equation?
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pH=pKa+Log(base/acid)
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What is the henderson-hasselbach equation in vivo?
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pH=6.1+log([HCO3-]/[0.03 x pCO2]), where 0.03 is the solubility of CO2 in blood
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What is dalton's law?
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Sum of all partial pressures = total pressure (usually 1 atm)
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What is pO2 in the atmosphere?
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159 mmHg
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What is pO2 in the lungs?
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104 mmHg
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What is pCO2 in the atmosphere?
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3 mmHg
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What is pCO2 in the lungs?
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40 mmHg
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what is pH2O in the atmosphere?
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0 mmHg
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What is pH2O in the lungs?
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47 mmHg (@37 C - temp dependent)
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Why does the pO2 drop as air enters the lungs?
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Additional water vapor is added. Because the total pressure stays constant, and pH2O increases, pO2 must decrease
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How is PIO2 calculated?
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(Total Barrometric pressure - pH2O) x FiO2 = (760-pH2O)xFiO2
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How is PAO2 calculated?
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PIO2-(PaCO2/RQ)
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What is RQ?
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CO2 eliminated/O2 consumed. Nml=0.8
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What is the not-test-answer shortcut for PAO2?
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FiO2 x 6
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What is a normal PaO2 on room air?
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85-100 mmHg
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What is an age appropriate PaO2 on room air (M&M)?
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102-age/3
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What is the expected PaO2 for a given FiO2?
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FiO2 x 5
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What does a left shift of the O2/Hb-dissociation curve mean?
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O2 binds more tightly to Hb
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What does a right shift of the O2/Hb-dissociation curve mean?
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O2 binds less tightly to Hb
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What shifts to O2 curve to the left?
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Alkalosis, hypothermia, decreased pCO2, decreased DPG
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What is 2,3-DPG?
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2,3-diphosphoglycerate. Binds to deoxygenated Hb, causing it to unload remaining O2.
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What shifts the O2 curve to the right?
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Acidosis, Hyperthermia, increased pCO2, increased DPG
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What is the p50 of the O2/Hb dissociation curve?
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27 mmHg
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How is the A-a gradient calculated?
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PAO2-PaO2
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What affects A-a gradient?
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R-L shunt, V/Q scatter, mixed-venous O2 tension
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How is A-a gradient related to R-L shunt?
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Directly proportional (larger R-L shunt -> greater A-a gradient)
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How is A-a gradient related to mixed venous O2 tension?
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Inversely: Low MVO2 -> decreased returning O2 in returning blood -> less O2 in arteries, thus increasing A-a gradient
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What is a normal A-a gradient?
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<15 mmHg
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What is the effect of increasing FiO2 on A-a gradient?
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Directly proportional
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What is the formula for CaO2?
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1.34 x Hb x SaO2 + 0.003 x PO2
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What is a normal CaO2?
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16 volumes percent
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What is the formula for DO2?
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DO2=CaO2 x CO
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What is a normal DO2?
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1L/min
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What should DO2 be used to manage?
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Fluid management (also inotropics?)
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What does increasing acidosis in the face of a normal CaO2 suggest?
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Decreased CO. Manage usually w/ increased IVF
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How is VO2 calculated?
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Fick principle: VO2 = CO x (CaO2 - CvO2)
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What is normal VO2?
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200 ml/min
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How is O2ER calculated?
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[CaO2-CvO2]/CaO2
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What is a normal O2ER?
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25%
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What is a normal PvO2?
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40 mmHg
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What causes decreased PvO2?
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Decreased CaO2 (dec. Hb, SaO2), CO, or increased uptake (VO2)
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What is a deadspace unit?
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Ventilated, no perfusion
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What is a shunt unit?
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Perfused, no ventilation
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What is a silent unit?
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No perfusion or ventilation
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List 5 causes of hypoxemia?
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Hypoventilation, Diffusion impairment, shunt, V/Q mismatch, high altitude
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What are the feature of hypoventilation?
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Increased PaO2, decreased gas flow. May be secondary hypoxemia
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How is hypoxia tx'd in a diffusion impairment?
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Increased FiO2
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What are possible intrapulmonary causes of shunt?
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A-V fistulas, pneumonia, ARDS
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What are possible extrapulmonary causes of shunt?
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R->L shunt
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Does increasing FiO2 fix shunt?
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No
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What is the shunt equation?
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Qs/Qt = (CcO2-CaO2)/(CcO2-CvO2)
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How is CcO2 calculated?
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Same as CaO2, using PAO2 and corresponding Sat.
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What is CcO2?
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End-capillary O2
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How bad must a shunt be to be incompatable with spontaneous ventilation?
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>30%
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What level of shunt is acceptable?
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<20%
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What is normal physiologic shunt?
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5%
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What vessels contribute to physiologic shunt?
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Thebesian, Bronchial and pleural vessels
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What is a normal V/Q?
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0.8
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What is normal alveolar ventilation?
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4L/min
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Can V/Q mismatch be corrected w/ increased FiO2?
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Somewhat
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Describe West Zone 1
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High up, PA>Pa -> collapse of blood vesels, perfused but not ventilated
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Describe West Zone 2
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Middle, Pa>PA -> perfusion, also ventilation. Less V/Q mismatch
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Describe West Zone 3
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Lower lungs, Pa and Pv > PA, good perfusion, less ventilation
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What is normal deadspace?
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2 cc/kg
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What is the Bohr equation?
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Vd/Vt =(PaCO2-PEtCO2)/PaCO2
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What is normal deadspace?
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Approx 30% of tidal volume
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What is significantly abnormal deadspace?
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>50% of tidal volume
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Is heparin necessary for an ABG?
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No
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What is the effect of temperature on ABGs?
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As blood cools, CO2 dissolves into the solution, decreasing pCO2
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