Chem 6.2 Blood Gases, pH, and Electrolytes Flashcards
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
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
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
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
Which of the following mechanisms is responsible for metabolic acidosis?
A. Bicarbonate deficiency
B. Excessive retention of dissolved CO2
C. Accumulation of volatile acids
D. Hyperaldosteronism
A. Bicarbonate deficiency
Which of the following disorders is associated with lactate acidosis?
A. Diarrhea
B. Renal tubular acidosis
C. Hypoaldosteronism
D. Alcoholism
D. Alcoholism
Which of the following is the primary mechanism of compensation for metabolic acidosis?
A. Hyperventilation
B. Release of epinephrine
C. Aldosterone release
D. Bicarbonate excretion
A. Hyperventilation
The following conditions are all causes of alkalosis. Which condition is associated with respiratory (rather than metabolic) alkalosis?
A. Anxiety
B. Hypovolemia
C. Hyperaldosteronism
D. Hypoparathyroidism
A. Anxiety
Which of the following conditions is associated with both metabolic and respiratory alkalosis?
A. Hyperchloremia
B. Hypernatremia
C. Hyperphosphatemia
D. Hypokalemia
D. Hypokalemia
In uncompensated metabolic acidosis, which of the following will be normal?
A. Plasma bicarbonate
B. PCO2
C. p50
D. Total CO2
B. PCO2
Which of the following conditions is classified as normochloremic acidosis?
A. Diabetic ketoacidosis
B. Chronic pulmonary obstruction
C. Uremic acidosis
D. Diarrhea
A. Diabetic ketoacidosis
In diabetic ketoacidosis, acetoacetate and other ketoacids replace bicarbonate. The chloride remains normal or low, and there is an increased anion gap.
Which PCO2 value would be seen in maximally compensated metabolic acidosis?
A. 15 mm Hg
B. 30 mm Hg
C. 40 mm Hg
D. 60 mm Hg
A. 15 mm Hg
A patient has the following arterial blood gas results:
pH = 7.56
PCO2 = 25 mm Hg
PO2 = 100 mm Hg
HCO3– = 22 mmol/L
These results are most likely the result of which condition?
A. Improper specimen collection
B. Prolonged storage
C. Hyperventilation
D. Hypokalemia
C. Hyperventilation
Why are three levels used for quality control of pH and blood gases?
A. Systematic errors can be detected earlier than with two controls
B. Analytical accuracy needs to be greater than for other analytes
C. High, normal, and low ranges must always be evaluated
D. A different level is needed for pH, PCO2, and PO2
A. Systematic errors can be detected earlier than with two controls
A single-point calibration is performed between each blood gas sample to:
A. Correct the electrode slope
B. Correct electrode and instrument drift
C. Compensate for temperature variance
D. Prevent contamination by the previous sample
B. Correct electrode and instrument drift
In which condition would hypochloremia be expected?
A. Respiratory alkalosis
B. Metabolic acidosis
C. Metabolic alkalosis
D. All of these options
C. Metabolic alkalosis
Given the following serum electrolyte data, determine the anion gap:
Na = 132 mmol/L
K = 4.0 mmol/L
Cl = 90 mmol/L
HCO3– = 22 mmol/L
A. 12 mmol/L
B. 24 mmol/L
C. 64 mmol/L
D. Cannot be determined from the information provided
B. 24 mmol/L
Which of the following conditions will cause an increased anion gap?
A. Diarrhea
B. Hypoaldosteronism
C. Hyperkalemia
D. Renal failure
D. Renal failure
Alcoholism, liver failure, and hypoxia induce acidosis by causing:
A. Depletion of cellular NAD+
B. Increased excretion of bicarbonate
C. Increased retention of PCO2
D. Loss of carbonic anhydrase
A. Depletion of cellular NAD+
Which of the following is the primary mechanism causing respiratory alkalosis?
A. Hyperventilation
B. Deficient alveolar diffusion
C. Deficient pulmonary perfusion
D. Parasympathetic inhibition
A. Hyperventilation
Which condition can result in acidosis?
A. Cystic fibrosis
B. Vomiting
C. Hyperaldosteronism
D. Excessive O2 therapy
D. Excessive O2 therapy
Which of the following conditions is associated with an increase in ionized calcium (Cai) in blood?
A. Alkalosis
B. Hypoparathyroidism
C. Hyperalbuminemia
D. Malignancy
D. Malignancy
Which of the following laboratory results is consistent with primary hypoparathyroidism?
A. Low calcium; high Pi (inorganic phosphorus)
B. Low calcium; low Pi
C. High calcium; high Pi
D. High calcium; low Pi
A. Low calcium; high inorganic phosphorus Pi
Which of the following conditions is associated with hypophosphatemia?
A. Rickets
B. Multiple myeloma
C. Renal failure
D. Hypervitaminosis D
A. Rickets
Rickets can result from dietary phosphate deficiency, vitamin D deficiency, or an inherited disorder of either vitamin D or phosphorus metabolism.
Which of the following tests is consistently abnormal in osteoporosis?
A. High urinary calcium
B. High serum Pi
C. Low serum calcium
D. High urine or serum N-telopeptide of type 1 collagen
D. High urine or serum N-telopeptide of type 1 collagen
Which of the following is a marker for bone formation?
A. Osteocalcin
B. Tartrate resistant acid phosphatase (TRAP)
C. Urinary pyridinoline and deoxypyridinoline
D. Urinary C-telopeptide and N-telopeptide crosslinks (CTx and NTx)
A. Osteocalcin
What role do CTx and NTx play in the management of osteoporosis?
A. Increased urinary excretion is diagnostic of early-stage disease
B. Increased levels indicate a low risk of developing osteoporosis
C. Decreased urinary excretion indicates a positive response to treatment
D. The rate of urinary excretion correlates with the stage of the disease
C. Decreased urinary excretion indicates a positive response to treatment
What role does vitamin D measurement play in the management of osteoporosis?
A. Vitamin D deficiency must be demonstrated to establish the diagnosis
B. Vitamin D is consistently elevated in osteoporosis
C. A normal vitamin D level rules out osteoporosis
D. Vitamin D deficiency is a risk factor for developing osteoporosis
D. Vitamin D deficiency is a risk factor for developing osteoporosis
Which statement best describes testing recommendations for vitamin D?
A. Vitamin D testing should be reserved only for those persons who demonstrate hypercalcemia of an undetermined cause
B. Vitamin D testing should be specific for the 1,25(OH)D3 form
C. Testing should be for total vitamin D when screening for deficiency
D. Vitamin D testing should not be performed if the patient is receiving vitamin D supplementation
C. Testing should be for total vitamin D when screening for deficiency
The serum level of which of the following laboratory tests is decreased in both VDDR and VDRR?
A. Vitamin D
B. Calcium
C. Pi
D. Parathyroid hormone
C. Pi
Which of the following is the most accurate measurement of inorganic phosphorus (Pi) in serum?
A. Rate of unreduced phosphomolybdate formation at 340 nm
B. Measurement of phosphomolybdenum blue at 680 nm
C. Use of aminonaptholsulfonic acid to reduce phosphomolybdate
D. Formation of a complex with malachite green dye
A. Rate of unreduced phosphomolybdate formation at 340 nm
What is the percentage of serum calcium that is ionized?
A. 30%
B. 45%
C. 60%
D. 80%
B. 45%
Which of the following conditions will cause erroneous Cai results? Assume that the samples are collected and stored anaerobically, kept at 4°C until measurement, and stored for no longer than 1 hour.
A. Slight hemolysis during venipuncture
B. Assay of whole blood collected in sodium oxalate
C. Analysis of serum in a barrier gel tube stored at 4°C until the clot has formed
D. Analysis of whole blood collected in sodium heparin, 20 units/mL (low-heparin tube)
B. Assay of whole blood collected in sodium oxalate
Which of the following conditions is associated with a low serum magnesium?
A. Addison disease
B. Hemolytic anemia
C. Hyperparathyroidism
D. Pancreatitis
D. Pancreatitis
When measuring calcium with the complexometric dye o-cresolphthalein complexone, magnesium is kept from interfering by:
A. Using an alkaline pH
B. Adding 8-hydroxyquinoline
C. Measuring at 450 nm
D. Complexing to ethylenediaminetetraacetic acid (EDTA)
B. Adding 8-hydroxyquinoline
Which electrolyte measurement is least affected by hemolysis?
A. Potassium
B. Calcium
C. Inorganic phosphorus
D. Magnesium
B. Calcium
Which of the following conditions is associated with hypokalemia?
A. Addison disease
B. Hemolytic anemia
C. Digoxin intoxication
D. Alkalosis
D. Alkalosis
Which of the following conditions is most likely to produce an elevated plasma potassium?
A. Hypoparathyroidism
B. Cushing syndrome
C. Diarrhea
D. Digitalis overdose
D. Digitalis overdose
Which of the following values is the threshold critical value (alert or action level) for low plasma potassium?
A. 1.5 mmol/L
B. 2.0 mmol/L
C. 2.5 mmol/L
D. 3.5 mmol/L
C. 2.5 mmol/L
Which electrolyte is least likely to be elevated in renal failure?
A. Potassium
B. Magnesium
C. Inorganic phosphorus
D. Sodium
D. Sodium
Which of the following is the primary mechanism for vasopressin (antidiuretic hormone [ADH]) release?
A. Hypovolemia
B. Hyperosmolar plasma
C. Renin release
D. Reduced renal blood flow
B. Hyperosmolar plasma
Which of the following conditions is associated with hypernatremia?
A. Diabetes insipidus
B. Hypoaldosteronism
C. Burns
D. Diarrhea
A. Diabetes insipidus
Which of the following values is the threshold critical value (alert or action level) for high plasma sodium?
A. 150 mmol/L
B. 160 mmol/L
C. 170 mmol/L
D. 180 mmol/L
B. 160 mmol/L
Which of the following conditions is associated with total body sodium excess?
A. Renal failure
B. Hyperthyroidism
C. Hypoparathyroidism
D. Diabetic ketoacidosis
A. Renal failure
Total body sodium excess often occurs in persons with renal failure, congestive heart failure (CHF), and cirrhosis of the liver. When water is retained along with sodium, the result is total body sodium excess, rather than hypernatremia.
Which of the following conditions is associated with hyponatremia?
A. Diuretic therapy
B. Cushing syndrome
C. Diabetes insipidus
D. Nephrotic syndrome
A. Diuretic therapy
Which of the following conditions involving electrolytes is described correctly?
A. Pseudohyponatremia occurs only when undiluted samples are measured
B. Potassium levels are slightly higher in heparinized plasma than in serum
C. Hypoalbuminemia causes low total calcium but does not affect Cai
D. Hypercalcemia may be induced by low serum magnesium
C. Hypoalbuminemia causes low total calcium but does not affect Cai
Which of the following laboratory results is usually associated with cystic fibrosis?
A. Sweat chloride greater than 60 mmol/L
B. Elevated serum sodium and chloride
C. Elevated fecal trypsin activity
D. Low glucose
A. Sweat chloride greater than 60 mmol/L
When performing a sweat chloride collection, which of the following steps will result in analytical error?
A. Using unweighed gauze soaked in pilocarpine nitrate on the inner surface of the forearm
to stimulate sweating
B. Collecting greater than 75 mg of sweat in 30 minutes
C. Leaving the preweighed gauze on the inside of the arm exposed to air during collection
D. Rinsing the collected sweat from the gauze pad using chloride titrating solution
C. Leaving the preweighed gauze on the inside of the arm exposed to air during collection
Which electrolyte level best correlates with plasma osmolality?
A. Sodium
B. Chloride
C. Bicarbonate
D. Calcium
A. Sodium
Which formula is most accurate in predicting plasma osmolality?
A. Na + 2(Cl) + BUN + glucose
B. 2(Na) + 2(Cl) + glucose + urea
C. 2(Na) + (glucose ÷ 18) + (BUN ÷ 2.8)
D. Na + Cl + K + HCO3
C. 2(Na) + (glucose ÷ 18) + (BUN ÷ 2.8)
