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A2 - Chemistry & Immunology - Harr > Chem 6.2 Blood Gases, pH, and Electrolytes > Flashcards

Chem 6.2 Blood Gases, pH, and Electrolytes Flashcards

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1
Q

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–

A

B. pH = 6.1 + log HCO3–/(0.03 × PCO2)

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

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

A. 7.35 to 7.45

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5
Q

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

A

C. 20:1

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6
Q

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

A

C. 60 mm Hg

DCO2 = PCO2 × 0.03
Therefore, PCO2 = DCO2 /0.03

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7
Q

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

A. The combined hydration and dissociation constant for CO2 in blood at 37°C

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8
Q

Which of the following contributes the most to serum total CO2 (TCO2)?
A. PCO2
B. DCO2
C. HCO3–
D. Carbonium ion

A

C. HCO3–

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9
Q

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

A. Hgb concentration

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10
Q

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

A. PO2 increased PCO2 decreased pH increased

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11
Q

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

A. O2 content = %O2 saturation/100 × Hgb g/dL × 1.39 mL/g + (0.0031 × pO2)

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12
Q

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

A

B. 10 mm Hg

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13
Q

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

A

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.

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14
Q

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

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.

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15
Q

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

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.

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16
Q

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%

A

B. Lithium heparin 100 units/mL blood

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17
Q

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

A

D. 30 min, 22°C

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18
Q

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

A

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.

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19
Q

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

A

B. Metabolic alkalosis

Normal ranges
pH: 7.45
PCO2: 35-45mm Hg
HCO3-: 22-26mmol/L

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20
Q

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

A

B. pH = 7.66
HCO3 = 22 mmol/L
PCO2 = 20 mm Hg

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21
Q

Which of the following will shift the O2 dissociation curve to the left?
A. Anemia
B. Hyperthermia
C. Hypercapnia
D. Alkalosis

A

D. Alkalosis

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22
Q

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

A. Carbon monoxide (CO) poisoning

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23
Q

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

A

D. pH:decreased PCO2:increased Bicarbonate:increased

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24
Q

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

A

C. Renal tubular acidosis

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25
Q

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

A. Bicarbonate deficiency

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26
Q

Which of the following disorders is associated with lactate acidosis?
A. Diarrhea
B. Renal tubular acidosis
C. Hypoaldosteronism
D. Alcoholism

A

D. Alcoholism

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27
Q

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

A. Hyperventilation

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28
Q

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

A. Anxiety

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29
Q

Which of the following conditions is associated with both metabolic and respiratory alkalosis?
A. Hyperchloremia
B. Hypernatremia
C. Hyperphosphatemia
D. Hypokalemia

A

D. Hypokalemia

30
Q

In uncompensated metabolic acidosis, which of the following will be normal?
A. Plasma bicarbonate
B. PCO2
C. p50
D. Total CO2

A

B. PCO2

31
Q

Which of the following conditions is classified as normochloremic acidosis?
A. Diabetic ketoacidosis
B. Chronic pulmonary obstruction
C. Uremic acidosis
D. Diarrhea

A

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.

32
Q

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

A. 15 mm Hg

33
Q

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

A

C. Hyperventilation

34
Q

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

A. Systematic errors can be detected earlier than with two controls

35
Q

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

A

B. Correct electrode and instrument drift

36
Q

In which condition would hypochloremia be expected?
A. Respiratory alkalosis
B. Metabolic acidosis
C. Metabolic alkalosis
D. All of these options

A

C. Metabolic alkalosis

37
Q

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

A

B. 24 mmol/L

The anion gap is defined as unmeasured anions minus unmeasured cations in the plasma or serum. It is calculated by subtracting the measured anions (bicarbonate and chloride) from the measured cations (sodium plus’s potassium although some labs ignore the potassium. A normal anion gap is approximately 12 to 20 mmol/L (8-16 mmol/L when potassium is not included).

Anion gap = (Na + K) - (HCO3 + C)
Anion gap = (132 + 4) - (90+22) =24 mmol/L

38
Q

Which of the following conditions will cause an increased anion gap?
A. Diarrhea
B. Hypoaldosteronism
C. Hyperkalemia
D. Renal failure

A

D. Renal failure

39
Q

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

A. Depletion of cellular NAD+

40
Q

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

A. Hyperventilation

41
Q

Which condition can result in acidosis?
A. Cystic fibrosis
B. Vomiting
C. Hyperaldosteronism
D. Excessive O2 therapy

A

D. Excessive O2 therapy

42
Q

Which of the following conditions is associated with an increase in ionized calcium (Cai) in blood?
A. Alkalosis
B. Hypoparathyroidism
C. Hyperalbuminemia
D. Malignancy

A

D. Malignancy

43
Q

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

A. Low calcium; high inorganic phosphorus Pi

44
Q

Which of the following conditions is associated with hypophosphatemia?
A. Rickets
B. Multiple myeloma
C. Renal failure
D. Hypervitaminosis D

A

A. Rickets

Rickets can result from dietary phosphate deficiency, vitamin D deficiency, or an inherited disorder of either vitamin D or phosphorus metabolism.

45
Q

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

A

D. High urine or serum N-telopeptide of type 1 collagen

46
Q

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

A. Osteocalcin

47
Q

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

A

C. Decreased urinary excretion indicates a positive response to treatment

48
Q

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

A

D. Vitamin D deficiency is a risk factor for developing osteoporosis

49
Q

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

A

C. Testing should be for total vitamin D when screening for deficiency

50
Q

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

A

C. Pi

51
Q

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

A. Rate of unreduced phosphomolybdate formation at 340 nm

Inorganic phosphorus is proportional to the rate of absorbance increase at 340 nm when it combines with ammonium molybdate. Colorimetric methods suffer from interferences resulting from the reduction of ammonium phosphomolybdate.

52
Q

What is the percentage of serum calcium that is ionized?
A. 30%
B. 45%
C. 60%
D. 80%

A

B. 45%

Calcium exists in serum in three forms: protein bound, ionized, and complexed (as undissociated salts). Only Cai, is physiologically active. Protein bound and Cai each account for approximately 45% of total calcium, and the remaining 10% is complexed.

53
Q

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)

A

B. Assay of whole blood collected in sodium oxalate

54
Q

Which of the following conditions is associated with a low serum magnesium?
A. Addison disease
B. Hemolytic anemia
C. Hyperparathyroidism
D. Pancreatitis

A

D. Pancreatitis

55
Q

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)

A

B. Adding 8-hydroxyquinoline

56
Q

Which electrolyte measurement is least affected by hemolysis?
A. Potassium
B. Calcium
C. Inorganic phosphorus
D. Magnesium

A

B. Calcium

57
Q

Which of the following conditions is associated with hypokalemia?
A. Addison disease
B. Hemolytic anemia
C. Digoxin intoxication
D. Alkalosis

A

D. Alkalosis

58
Q

Which of the following conditions is most likely to produce an elevated plasma potassium?
A. Hypoparathyroidism
B. Cushing syndrome
C. Diarrhea
D. Digitalis overdose

A

D. Digitalis overdose

59
Q

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

A

C. 2.5 mmol/L

60
Q

Which electrolyte is least likely to be elevated in renal failure?
A. Potassium
B. Magnesium
C. Inorganic phosphorus
D. Sodium

A

D. Sodium

Reduced glomerular filtration coupled with decreased tubular secretion causes accumulation of potassium, magnesium, and inorganic phosphorus. Poor tubular reabsorption of sodium offsets reduced glomerular filtration. Unfiltered sodium draws both chloride and water, causing osmotic equilibrium among filtrate, serum, and tissues. In renal disease, serum sodium is often normal, although total body sodium is increased owing to fluid and salt retention.

61
Q

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

A

B. Hyperosmolar plasma

ADH is released by the posterior pituitary in response to increased plasma osmolality. Normally, this is triggered by release of aldosterone caused by ineffective arterial pressure in the kidney. Aldosterone causes sodium reabsorption, which raises plasma osmolality; release of ADH causes reabsorption of water, which increases blood volume and restores normal osmolality. A deficiency or ADH (diabetes insipidus) results in dehydration and hypernatremia. An excess of ADH (syndrome of inappropriate ADH release [SIADH] results in dilutional hyponatremia. This may be caused by regional hypovolemia, hypothyroidism, central nervous system (CNS) injury, drugs, and malignancy.

62
Q

Which of the following conditions is associated with hypernatremia?
A. Diabetes insipidus
B. Hypoaldosteronism
C. Burns
D. Diarrhea

A

A. Diabetes insipidus

63
Q

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

A

B. 160 mmol/L

64
Q

Which of the following conditions is associated with total body sodium excess?
A. Renal failure
B. Hyperthyroidism
C. Hypoparathyroidism
D. Diabetic ketoacidosis

A

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.

65
Q

Which of the following conditions is associated with hyponatremia?
A. Diuretic therapy
B. Cushing syndrome
C. Diabetes insipidus
D. Nephrotic syndrome

A

A. Diuretic therapy

Diuretics lower blood pressure by promoting water loss. This is accomplished by causing sodium loss from the proximal tubule and/or loop. Addison disease, SIADH, burns, diabetic ketoacidosis, hypopituitarism, vomiting, diarrhea, and cystic fibrosis also cause hyponatremia.

Cushing syndrome causes hypernatremia by promoting sodium reabsorption in the collection tubule in exchange for potassium. Diabetes insipidus and nephrotic syndrome promote hypernatremia by causing water loss.

66
Q

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

A

C. Hypoalbuminemia causes low total calcium but does not affect Cai

67
Q

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

A. Sweat chloride greater than 60 mmol/L

68
Q

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

A

C. Leaving the preweighed gauze on the inside of the arm exposed to air during collection

69
Q

Which electrolyte level best correlates with plasma osmolality?
A. Sodium
B. Chloride
C. Bicarbonate
D. Calcium

A

A. Sodium

70
Q

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

A

C. 2(Na) + (glucose ÷ 18) + (BUN ÷ 2.8)

A2 - Chemistry & Immunology - Harr (18 decks)

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