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31 Cards in this Set
- Front
- Back
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The effect of increasing the V/Q ratio on PO2 and PCO2
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PO2 increases, PCO2 decreases
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The effect of decreasing the V/Q ratio on the PO2 and PCO2
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PO2 decreases, PCO2 increase
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Alveolar gas equation for oxygen
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PAO2=FIO2(PB-PH2O)-PaCO2/R
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Alveolar gas equation for carbon dioxide
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PACO2=VCO2/(VE-VD)
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Define gas pressure
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The tendency of the gas molecules to move. Movement will stop when there is no pressure gradient. Gas pressures, not content, equilibrate
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Define gas content
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The number of molecules contained in a certain volume
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Factors that increase the affinity of the hemoglobin for oxygen (left shift)
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Decreased temperature, decreased 2,3 DPG, increased pH, CO
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Factors that decrease the affinity of hemoglobin for oxygen (right shift)
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Increased temperature, increased 2,3 DPG, decreased pH
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What is the A-a gradient and what does it mean?
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The A-a gradient is the difference between the alveolar oxygen tension calculated from the alveolar gas equation and the arterial oxygen tension directly measured from the patient. The A-a gradient is an index of the dispersion of V/Q ratios. More dispersion means a higher A-a gradient. Normal lung has a narrow range of V/Q ratios and thus a small A-a gradient.
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How do you calculate the resulting tension when mixing two aliquots of blood for O2 and for CO2
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For O2 you have to convert to content, average the contents and convert back to tension. For CO2 you can directly average the tensions.
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Henderson-hasselbach equation, general and for bicarbinate system
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pH=pK+log(conjugate base/weak acid)
pH=6.1+log(HCO3/.03*PCO2) |
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Acidemia
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pH < 7.36
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Alkalemia
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pH > 7.44
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Hypercapnia
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PaCO2 > 44 mmHg
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Hypocapnia
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PaCO2 < 36 mmHg
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Hyperventilation
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Associated with hypocapnia, not rate of breathing
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Hypoventilation
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Associated with hypercapnia, not rate of breathing
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Tachypnia
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Fast breathing rate (not hyperventilation)
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Repiratory acidosis
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A primary process associated with an increase in PaCO2
- Lowers pH Compensation occurs through renal retention of bicarbonate (takes hours to days) |
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Respiratory alkalosis
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A primary process associated with a decrease in PaCO2
- Raises pH Compensation through renal excretion of bicarbonate |
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Metabolic acidosis
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A primary process associated with a decrease in serum bicarbonate
- lowers pH - compensation through hyperventilation |
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Metabolic alkalosis
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A primary process associated with an increase in serum bicarbonate
- Raises pH - Compensation through hypoventilation |
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Normal pH range
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7.36-7.44
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Normal PCO2
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36-44 mmHg
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Normal PO2 (breathing room air at sea level)
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80-100 mmHg
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Indications of primary respiratory disorder
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Inverse relationship between PCO2 and pH
- in acute disorders (no metabolic compensation) there will be a riciprocal change of 0.08 in pH for every change of 10 mmHg PCO2 |
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Indications of primary metabolic disorder
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Changes in pH and PCO2 are discordant
- Low pH and low PCO2 - the change in pH is of greater magnitude than predicted by the change in PCO2 |
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pH 7.24, PCO2 60 (What type of acidosis?)
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Acute respiratory acidosis
- reciprical change in pH and PCO2 - the changes are proportional (.08 pH inverse to 10 mmHg PCO2) |
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pH 7.24, PCO2 80 (What type of acidosis?)
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Respiratory acidosis with partial metabolic compensation
- reciprocal relationship between pH and PCO2 - change in pH is less than expected for the elevation in PCO2 |
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pH 7.24, PCO2 40 (What type of acidosis?)
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Metabolic acidosis
- low pH with normal PCO2 |
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pH 7.24, PCO2 30 (What type of acidosis?)
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Metabolic acidosis with partial respiratory compensation
- PCO2 and pH are both low |
