Chem 6.2 Blood Gases, pH, and Electrolytes
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Which of the following represents the Henderson-Hasselbalch equation as applied to blood pH? A. pH = 6.1 + log HCO3–/PCO2 B. pH = 6.1 + log HCO3–/(0.03 × PCO2) C. pH = 6.1 + log DCO2/HCO3– D. pH = 6.1 + log (0.03 × PCO2)/HCO3–
B. pH = 6.1 + log HCO3–/(0.03 × PCO2)
What is the PO2 of calibration gas containing 20.0% O2, when the barometric pressure is 30 in? A. 60 mm Hg B. 86 mm Hg C. 143 mm Hg D. 152 mm Hg
C. 143 mm Hg Convert barometric pressure in inches to millimeters of mercury by multiplying by 25.4 (mm/in). Next, subtract the vapor pressure of H2O at 37°C, 47 mm Hg, to obtain dry gas pressure. Multiply dry gas pressure by the %O2 : 25.4 mm/in × 30 in = 762 mm Hg 762 mm Hg – 47 mm Hg (vapor pressure) = 715 mm Hg (dry gas pressure) 0.20 × 715 mm Hg = 143 mm Hg PO2
What is the blood pH when the partial pressure of carbon dioxide (PCO2) is 60 mm Hg and the bicarbonate concentration is 18 millimoles per liter (mmol/L)? A. 6.89 B. 7.00 C. 7.10 D. 7.30
C. 7.10 Solve using the Henderson-Hasselbalch equation: pH = pka + log [base/acid] Pka constant=6.1 Base=HCO2- Acid=dissolved CO2=0.03*PCO2 pH = 6.1 + log 18/(0.03 × 60) = 6.1 + log 18/1.8 pH = 6.1 + log 10. Because log 10 = 1, pH = 7.10
Which of the following best represents the reference (normal) range for arterial pH? A. 7.35 to 7.45 B. 7.42 to 7.52 C. 7.38 to 7.68 D. 6.85 to 7.56
A. 7.35 to 7.45
What is the normal ratio of bicarbonate to dissolved carbon dioxide (HCO3–:DCO2) in arterial blood? A. 1:10 B. 10:1 C. 20:1 D. 30:1
C. 20:1
What is the PCO2 if the DCO2 is 1.8 mmol/L? A. 24 mm Hg B. 35 mm Hg C. 60 mm Hg D. 72 mm Hg
C. 60 mm Hg DCO2 = PCO2 × 0.03 Therefore, PCO2 = DCO2 /0.03
In the Henderson-Hasselbalch expression pH = 6.1 + log HCO3–/DCO2, the 6.1 represents: A. The combined hydration and dissociation constant for CO2 in blood at 37°C B. The solubility constant for CO2 gas C. The dissociation constant of H2O D. The ionization constant of NaHCO3
A. The combined hydration and dissociation constant for CO2 in blood at 37°C
Which of the following contributes the most to serum total CO2 (TCO2)? A. PCO2 B. DCO2 C. HCO3– D. Carbonium ion
C. HCO3–
In addition to NaHCO3, what other substance contributes the most to the amount of base in blood? A. Hgb concentration B. Dissolved O2 concentration C. Inorganic phosphorus D. Organic phosphate
A. Hgb concentration
Which of the following effects results from exposure of a normal arterial blood sample to room air? A. PO2 increased PCO2 decreased pH increased B. PO2 decreased PCO2 increased pH decreased C. PO2 increased PCO2 decreased pH decreased D. PO2 decreased PCO2 decreased pH decreased
A. PO2 increased PCO2 decreased pH increased
Which of the following formulas for O2 content is correct? A. O2 content = %O2 saturation/100 × Hgb g/dL × 1.39 mL/g + (0.0031 × pO2) B. O2 content = PO2 × 0.0306 mmol/L/mm C. O2 content = O2 saturation × Hgb g/dL × 0.003 mL/g D. O2 content = O2 capacity × 0.003 mL/g
A. O2 content = %O2 saturation/100 × Hgb g/dL × 1.39 mL/g + (0.0031 × pO2)
The normal difference between alveolar and arterial PO2 (PAO2–PaO2 difference) is: A. 3 mm Hg B. 10 mm Hg C. 40 mm Hg D. 50 mm Hg
B. 10 mm Hg
A decreased PAO2–PaO2 difference is found in: A. A/V (arteriovenous) shunting B. V/Q (ventilation/perfusion) inequality C. Ventilation defects D. All of these options
C. Ventilation defects Patients with A/V shunts, V/Q inequalities, and cardiac failure will have an increased PAO2-PAO2 difference. However, patients with ventilation problems have low alveolar PO2 as a result of retention of CO2 in the airway. This reduces the PAO2 difference.
The determination of the O2 saturation of Hgb is best accomplished by: A. Polychromatic absorbance measurements of a whole blood hemolysate B. Near infrared transcutaneous absorbance measurement C. Treatment of whole blood with alkaline dithionite prior to measuring absorbance D. Calculation using PO2 and total Hgb by direct spectrophotometry
A. Polychromatic absorbance measurements of a whole blood hemolysate Measurement of oxyhemoglobin, deoxyhemoglobin (reduced Hgb), carboxyhemoglobin, methemoglobin, and sulfhemoglobin can be accomplished by using direct spectrophotometry at multiple wavelengths and the absorptivity coefficients of each pigment at those wavelengths. The O2 saturation is determined by dividing the fraction of oxyhemoglobin by the sum of all pigments. This eliminates much of the errors that occur in the other methods when the quantity of an abnormal Hgb pigment is increase.
Correction of pH for a patient with a body temperature of 38°C would require: A. Subtraction of 0.015 B. Subtraction of 0.01% C. Addition of 0.020 D. Subtraction of 0.020
A. Subtraction of 0.015 The pH decreases by 0.015 for each degree Celsius above the 37°C. Because the blood gas analyzer measures pH at 37°C, the in vivo pH would be 0.015 pH units below the measured pH.
Select the anticoagulant of choice for blood gas studies. A. Sodium citrate 3.2% B. Lithium heparin 100 units/mL blood C. Sodium citrate 3.8% D. Ammonium oxalate 5.0%
B. Lithium heparin 100 units/mL blood
What is the maximum recommended storage time and temperature for an arterial blood gas sample drawn in a plastic syringe? (Storage Time, Temperature) A. 10 min, 2°C-8°C B. 20 min, 2°C-8°C C. 30 min, 2°C-8°C D. 30 min, 22°C
D. 30 min, 22°C
A patient’s blood gas results are as follows: pH = 7.26 DCO2 = 2.0 mmol/L HCO3– = 29 mmol/L These results would be classified as: A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis D. Respiratory alkalosis
C. Respiratory acidosis Imbalances are classified as respiratory when the primary disturbance is with PCO2 because PCO2 is regulated by ventilation. PCO2= DCO2/0.03 or 60 mm Hg (normal 35-45 mm Hg). Increased DCO2 will increase H+ concentration, causing acidosis. Bicarbonate is moderately increased, but a primary increase in NaHCO3 causes alkalosis. Thus, the cause of this acidosis is CO2 retention (respiratory acidosis), and it is partially compensated for by renal retention of bicarbonate.
A patient’s blood gas results are: pH = 7.50 PCO2 = 55 mm Hg HCO3– = 40 mmol/L These results indicate: A. Respiratory acidosis B. Metabolic alkalosis C. Respiratory alkalosis D. Metabolic acidosis
B. Metabolic alkalosis Normal ranges pH: 7.45 PCO2: 35-45mm Hg HCO3-: 22-26mmol/L
Which set of results is consistent with uncompensated respiratory alkalosis? A. pH = 7.70 HCO3 = 30 mmol/L PCO2 = 25 mm Hg B. pH = 7.66 HCO3 = 22 mmol/L PCO2 = 20 mm Hg C. pH = 7.46 HCO3 = 38 mmol/L PCO2 = 55 mm Hg D. pH = 7.36 HCO3 = 22 mmol/L PCO2 = 38 mm Hg
B. pH = 7.66 HCO3 = 22 mmol/L PCO2 = 20 mm Hg
Which of the following will shift the O2 dissociation curve to the left? A. Anemia B. Hyperthermia C. Hypercapnia D. Alkalosis
D. Alkalosis
In which circumstance will the reporting of calculated O2 saturation of Hgb based on PO2, PCO2, pH, temperature, and Hgb be in error? A. Carbon monoxide (CO) poisoning B. Diabetic ketoacidosis C. Oxygen therapy D. Assisted ventilation for respiratory failure
A. Carbon monoxide (CO) poisoning
Which would be consistent with partially compensated respiratory acidosis? A. pH:increased PCO2:increased Bicarbonate:increased B. pH:increased PCO2:decreased Bicarbonate:decreased C. pH:decreased PCO2:decreased Bicarbonate:decreased D. pH:decreased PCO2:increased Bicarbonate:increased
D. pH:decreased PCO2:increased Bicarbonate:increased
Which condition results in metabolic acidosis with severe hypokalemia and chronic alkaline urine? A. Diabetic ketoacidosis B. Phenformin-induced acidosis C. Renal tubular acidosis D. Acidosis caused by starvation
C. Renal tubular acidosis