Anesthesiology.Respiratory Physiology

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  • 1/72 Questions

    The normal FEV1/FVC ratio is

    • 0.95
    • 0.80
    • 0.60
    • 0.50
    • 0.40
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About This Quiz

The organs in the respiratory system make sure that oxygen enters the body and carbon dioxide leaves our body. It is therefore important to ensure that the process goes smoothly when a patient is under anesthesia. Take up the quiz and see how prepared you are for such an event.

Anesthesiology.Respiratory Physiology - Quiz

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  • 2. 

    The most important buffering system in the body is

    • Hemoglobin

    • Plasma proteins

    • Bone

    • HCO3-

    • Phosphate

    Correct Answer
    A. HCO3-
    Explanation
    Buffer systems represent the first line of defense against adverse changes in pH. The HC03- buffer system is the most important system and represents > 50% of the total buffering capacity of the body. Other important buffer systems include hemoglobin, which is responsible for approximately 35% of the buffering capacity of blood, phosphates, plasma proteins, and bone.

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  • 3. 

    The functional residual capacity is composed of the

    • Expiratory reserve volume and residual volume

    • Inspiratory reserve volume and residual volume

    • Inspiratory capacity and vital capacity

    • Expiratory capacity and tidal volume

    • Expiratory reserve volume and tidal volume

    Correct Answer
    A. Expiratory reserve volume and residual volume
    Explanation
    A comprehensive understanding of respiratory physiology is important for understanding the effects of both regional and general anesthesia on respiratory mechanics and pulmonary gas exchange. The volume of gas remaining in the lungs after a normal expiration is called the functional residual capacity. The volume of gas remaining in the lungs after a maximal expiration is called the residual volume. The difference between these two volumes is called the expiratory reserve volume. Therefore, the functional residual capacity is composed of the expiratory reserve volume and residual volume.

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  • 4. 

    The normal vital capacity for a 70-kg man is

    • 1 L

    • 2 L

    • 5 L

    • 7 L

    • 9 L

    Correct Answer
    A. 5 L
    Explanation
    The volume of gas exhaled during a maximum expiration is the vital ca¬pacity. In a healthy adult, the vital capacity is 60-70 mL/kg. In a 70-kg patient, the vital capacity is approximately 5 L.

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  • 5. 

    Reynold's number is an important factor in the determination of

    • O2 transport

    • Surface tension

    • Turbulent vs. laminar flow

    • Physiologic dead-space ventilation

    • Functional residual capacity

    Correct Answer
    A. Turbulent vs. laminar flow
    Explanation
    . Reynold's number is a calculated value that represents the overall ratio of inertial forces to viscous forces during flow. Reynold's number is directly proportional to the density of the substance, the flow velocity of the substance, and the radius of the container through which the substance is flowing, and is inversely proportional to the viscosity of the substance. In general, flow through a long, straight, smooth-walled container becomes turbulent when the Reynold's number is greater than 2,300.

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  • 6. 

    The anatomic dead space in a 70-kg male is

    • 50 mL

    • 150 mL

    • 250 mL

    • 500 mL

    • 700 to 1000 mL

    Correct Answer
    A. 150 mL
    Explanation
    The conducting airways (trachea, right and left mainstem bronchi, and lobar and segmental bronchi) do not contain alveoli and therefore do not take part in pulmonary gas exchange. These structures constitute the anatomic dead space. In the adult, the anatomic dead space is approximately 1 mL/lb or 2 mL/kg. The anatomic dead space increases during inspiration because of the traction exerted on the conducting airways by the surrounding lung parenchyma. In addition, the anatomic dead space depends on the size and posture of the subject.

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  • 7. 

    The P50 for normal adult hemoglobin is

    • 15

    • 25

    • 35

    • 45

    • 50

    Correct Answer
    A. 25
    Explanation
    P50 is the PaO2 required to produce 50% saturation of hemoglobin. The P50 for adult hemoglobin is 26 mm Hg

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  • 8. 

    Each of the following will cause erroneous readings by dual-wavelength pulse oximeters EXCEPT

    • Carboxyhemoglobin

    • Methylene blue

    • Fetal hemoglobin

    • Methemoglobin

    • Nail polish

    Correct Answer
    A. Fetal hemoglobin
    Explanation
    The presence of hemoglobin species other than oxyhemoglobin can cause erroneous readings by dual-wavelength pulse oximeters. Hemoglobin species such as carboxyhemoglobin and methemoglobin, dyes such as methylene blue and indocyanine green, and nail polish will cause erroneous readings. Since the absorption spectrum of fetal hemoglobin is similar to that of adult oxyhemoglobin, fetal hemoglobin does not significantly affect the accuracy of these types of pulse oximeters. High levels of bilirubin have no significant effect on the accuracy of dual-wavelength pulse oximeters, but may cause falsely low readings by nonpulsatile oximeters.

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  • 9. 

    O2 requirement for a 70-kg adult under general anesthesia is

    • 150 mL/min

    • 250 mL/min

    • 350 mL/min

    • 450 mL/min

    • 550 mL/min

    Correct Answer
    A. 250 mL/min
    Explanation
    The O2 requirement for an adult under general anesthesia is 3 to 4 mL/kg/min. The O2 requirement for a newborn under general anesthesia is 7 to 9 mL/kg/min. Alveolar ventilation (VA) in neonates is double that of adults to help meet their increased O2 requirements. This increase in VA is achieved primarily by an increase in respiratory rate as tidal volume (VT) is similar to that of adults. Although CO2 production is also increased in neonates, the elevated VA maintains the PaCO2 hear 38 to 40 mm Hg.

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  • 10. 

    What is the O2 content of whole blood if the hemoglobin concentration is 10 mg/dL, the PaO2 is 60 mm Hg, and the SaO2 is 90%?

    • 10 mL/dL

    • 13 mL/dL

    • 15 mL/dL

    • 18 mL/dL

    • 21 mL/dL

    Correct Answer
    A. 13 mL/dL
    Explanation
    The amount of O2 in blood (O2 content) is the sum of the amount of O2 dissolved in plasma and the amount of O2 combined with hemoglo¬bin. The amount of O2 dissolved in plasma is directly proportional to the product of the blood:gas solubility coefficient of O2 (0.003) and PaO2. The amount of O2 bound to hemoglobin is directly related to the fraction of hemoglobin that is saturated. One gram of hemoglobin can bind 1.39 ml of O2. The mathematical expression of O2 content is as follows:
    O2 content = 1.39 * [Hgb] * SaO2 + 0.003 * (PaO2), where [Hgb] is the hemoglobin concentration (mg/dL), SaO2 is the fraction of hemoglobin saturated with O2, and 0.003 (PaO2) is the amount of O2 dissolved in plasma. The O2 content of blood in this patient is approximately 13 mL/dL.

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  • 11. 

    Which of the following is the correct mathematical expression of Fick's law of diffusion of a gas through a lipid membrane (V   = rate of diffusion, D = diffusion coefficient of the gas, A = area of the membrane, P1 - P2 = transmembrane partial pressure gradient of the gas, T = thickness of the membrane)?

    • V=D*A*T/(P1-P2)

    • V=A*T/D*(P1-P2)

    • V=D*A*(P1-P2)/T

    • V=D*T*(P1-P2)/A

    • V=D*T*A/(P1-P2)

    Correct Answer
    A. V=D*A*(P1-P2)/T
    Explanation
    The rate that a gas diffuses through a lipid membrane is directly proportional to the area of the membrane, the transmembrane partial pres¬sure gradient of the gas, and the diffusion constant of the gas, and is inversely proportional to the thickness of the membrane. The diffusion constant is directly proportional to the square root of gas solubility and is inversely proportional to the square root of the molecular weight of the gas. This is known as Fick's law of diffusion.

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  • 12. 

    During the first minute of apnea, the PaCO2 will rise

    • 2 mm Hg/min

    • 4 mm Hg/min

    • 6 mm Hg/min

    • 8 mm Hg/min

    • 10 mm Hg/min

    Correct Answer
    A. 6 mm Hg/min
    Explanation
    During apnea, the PaCO2 will increase approximately 6 mm Hg during
    the first minute and then 3 to 4 mm Hg each minute thereafter

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  • 13. 

    Which of the following statements correctly defines the relationship between minute ventilation (Ve), dead space ventilation (Vd), and PaCO2?

    • If VE is constant and VD increases, then PaCO2 will increase

    • If VE is constant and VD increases, then PaCO2 will decrease

    • If VD is constant and VE increases, then PaCO2 will increase

    • If VD is constant and VE increases, then PaCO2 will decrease

    • None of the above

    Correct Answer
    A. If VE is constant and VD increases, then PaCO2 will increase
    Explanation
    The volume of gas in the conducting airways of the lungs (and not available for gas exchange) is called the anatomic dead space. The volume of gas in ventilated alveoli that are unperfused (and also not available for gas exchange) is called the functional dead space. The anatomic dead space together with the functional dead space is called the physiologic dead space. Physiologic dead-space ventilation can be calculated by the Bohr dead-space equation, which is mathematically expressed as follows:
    VD/VT = (PaCO2 — PeCO2)/PaCO2,
    where VD/VT is the ratio of physiologic dead-space ventilation (VD) to VT, and the a and e represent arterial and mixed expired, respectively. Of the choices given, only the first is correct. A large increase in physiologic dead-space ventilation will result in an increase in PaCO2

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  • 14. 

    Calculate the Vd/Vt ratio (physiologic dead-space ventilation) based on the following data: PaCO2 45 mm Hg, mixed expired CO2 tension (PeCO2) 30 mm Hg.

    • 0.1

    • 0.2

    • 0.3

    • 0.4

    • 0.5

    Correct Answer
    A. 0.3
    Explanation
    Physiologic dead-space ventilation can be estimated using the Bohr equation
    Vd/Vt= (45mm Hg - 30 mm Hg)/45 mm Hg= 0.33

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  • 15. 

    Each of the following is decreased in elderly patients compared with their younger counterparts EXCEPT

    • PaO2

    • FEV1

    • Ventilatory response to hypercarbia

    • Vital capacity

    • Closing volume

    Correct Answer
    A. Closing volume
    Explanation
    In general, aging is associated with reduced ventilatory volumes and capacities, and decreased efficiency of pulmonary gas exchange. These changes are caused by progressive stiffening of cartilage and replacement of elastic tissue in the intercostal and intervertebral areas, which decreases compliance of the thoracic cage. In addition, progressive kyphosis or scoliosis produces upward and anterior rotation of the ribs and sternum, which further restricts chest wall expansion during inspiration. With aging, the functional residual capacity, residual volume, and closing volume are increased, while the vital capacity, total lung capacity, maximum breathing capacity, FEV1, and ventilatory response to hypercarbia and hypoxemia are reduced. In addition, age-related changes in lung parenchyma, alveolar surface area, and diminished pulmonary capillary bed density cause ventilation/perfusion mismatch, which decreases resting PaO2.

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  • 16. 

    The shift of the CO2-hemoglobin dissociation curve which occurs in response to changes in PaO2 is known as the

    • Fick principle

    • Bohr effect

    • Haldane effect

    • Law of Laplace

    • Le Chatelier principle

    Correct Answer
    A. Haldane effect
    Explanation
    The shift of the CO2-hemoglobin dissociation curve that occurs in response to changes in PaO2 is known as the Haldane effect. Because of this effect, deoxygenated hemoglobin (in peripheral tissues) has a greater affinity for CO2 than does oxygenated hemoglobin.

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  • 17. 

    The degree of transpulmonary shunt can be estimated to equal 1% of the cardiac output for each

    • 10 mm Hg increase in the alveolar-to-arterial difference in O2 tension P(A - a)O2

    • 20 mm Hg increase in the P(A - a)O2

    • 30 mm Hg increase in the P(A - a)O2

    • 40 mm Hg increase in the P(A - a)O2

    • 50 mm Hg increase in the P(A - a)O2

    Correct Answer
    A. 20 mm Hg increase in the P(A - a)O2
    Explanation
    The fraction of the cardiac output shunted through the lungs without exposure to ventilated alveoli (i.e., transpulmonary shunt) can be estimated using the general rule that for every increase in the alveolar-to-arterial difference in O2 tension P(A-a)O2 of 20 mm Hg, there is a shunt fraction of approximately 1% of the cardiac output (i.e., Qs/Qt = P(A-a)O2/20, where Qs/Qt is the shunt fraction)

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  • 18. 

    The predominant stimulus for activation of hypoxic pulmonary vasoconstric­tion is

    • Increased PaCO2

    • Decreased PaCO2

    • Increased PaO2

    • Decreased PAO2

    • None of the above

    Correct Answer
    A. Decreased PAO2
    Explanation
    Hypoxic pulmonary vasoconstriction is a reflex within the lungs that causes regional vasoconstriction of the pulmonary vasculature to reduce blood flow to hypoxic alveoli. This is an important compensatory mechanism for minimizing transpulmonary shunt. The most important stimulus for this reflex is PAO2.

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  • 19. 

    The leftward shift of the oxyhemoglobin dissociation curve caused by hypocarbia is known as the

    • Fick principle

    • Bohr effect

    • Haldane effect

    • Law of Laplace

    • None of the above

    Correct Answer
    A. Bohr effect
    Explanation
    The effects of PaCO2 and pH on the position of the oxyhemoglobin dissociation curve is known as the Bohr effect. Hypercarbia and acidosis shift the curve to the right, and hypocarbia and alkalosis shift the curve to the left. The Bohr effect is attributed primarily to the action of CO2 and pH on erythrocyte 2,3-DPG metabolism.

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  • 20. 

    What is the maximum compensatory increase in serum bicarbonate concen­tration ([HC03-]) for every 10 mm Hg increase in PaCO2 with chronic respiratory acidosis?

    • 1 mEq/L

    • 3 mEq/L

    • 7 mEq/L

    • 10 mEq/L

    • 15 mEq/L

    Correct Answer
    A. 3 mEq/L
    Explanation
    The kidneys respond to chronic respiratory acidosis by conserving bicarbonate (HCO3-) and secreting hydrogen (H+). In respiratory acidosis, there is an immediate hydration of CO2 in plasma to produce HCO3-. This acute process produces approximately 1 mEq/L of HCO3- for every 10 mm Hg increase in PaCO2. Hydration of CO2 in the proximal and distal renal tubules stimulates the secretion of H+ into the urine. This compensatory response requires 12 to 48 hours. The compensatory response to chronic respiratory acidosis is rarely complete such that the pH does not fully return to 7.4. The maximum compensatory increase in serum bicarbonate concentration ([HCO3-]) in response to chronic respiratory acidosis is 3 mEq/L.

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  • 21. 

    The most important mechanism for the transport of CO2 from peripheral tis­sues to the lungs is

    • CO2 dissolved in plasma

    • Carbonic acid

    • Carbaminohemogiobin

    • HC03-

    • (CO3)-2

    Correct Answer
    A. HC03-
    Explanation
    CO2 is transported from the peripheral tissues to the lungs, primarily in the form of HCO3-; there it is eliminated from the body. The conversion of CO2 to HCO3- occurs within erythrocytes and is catalyzed by the enzyme carbonic anhydrase. HCO3- then diffuses out of the cell in exchange for a chloride ion (Cl-) to maintain electrical neutrality. This exchange is called the chloride shift. CO2 is also transported dissolved in blood and bound to proteins as carbamino compounds. Carbamino compounds are formed by the combination of CO2 with terminal amine groups on blood proteins, primarily hemoglobin. This reaction occurs very rapidly without enzymatic catalysts. Approximately 60% of CO2 is transported from peripheral tissues to the lungs in the form of HC03-, 30% in the form of carbaminohemoglobin, and 10% dissolved in plasma.

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  • 22. 

    Each of the following will alter the position or slope of the CO2-ventilatory response curve EXCEPT

    • Hypoxemia

    • Fentanyl

    • N2O

    • Volatile anesthetics

    • Ketamine

    Correct Answer
    A. Ketamine
    Explanation
    Measuring the ventilatory response to increased PaCO2 is a sensitive method for quantifying the effects of drugs on ventilation. In general, all volatile anesthetics (including N2O), narcotics, benzodiazepines, and barbiturates depress the CO2-ventilatory response curve in a dose-dependent manner. The magnitude of ventilatory depression by volatile anesthetics is greater in patients with chronic obstructive pulmonary disease (COPD) than in healthy patients. Thus, it is recommended that arterial blood gases are monitored during recovery from general anesthesia in patients with COPD. Ketamine causes minimal respiratory depression. Typically, respiratory rate is decreased only 2 to 3 breaths/min and the ventilatory response to changes in PaCO2 is maintained during ketamine anesthesia.

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  • 23. 

    Inhalation of CO2 increases Ve by

    • 0.5 L/min/mm Hg increase in PaCO2

    • 1 to 3 L/min/mm Hg increase in PaCO2

    • 3 to 5 L/min/mm Hg increase in PaCO2

    • 5 to 10 L/min/mm Hg increase in PaCO2

    • 10 to 20 L/min/mm Hg increase in PaCO2

    Correct Answer
    A. 1 to 3 L/min/mm Hg increase in PaCO2
    Explanation
    The degree of ventilatory depression caused by volatile anesthetics can be assessed by measuring resting PaCO2, the ventilatory response to hypercarbia and the ventilatory response to hypoxemia. Of these techniques, the resting PaCO2 is the most frequently used index. How¬ever, measuring the effects of increased PaCO2 on ventilation is the most sensitive method of quantifying the effects of drugs on ventilation. In awake, unanesthetized humans, inhalation of CO2 increases minute ventilation (VE) by approximately 1 to 3 L/min/mm Hg increase in PaCO2. Using this technique, halothane, isoflurane, enflurane, and N2O cause a dose-dependent depression of the ventilation.

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  • 24. 

    Which of the following pulmonary function tests is least dependent on pa­tient effort?

    • FEV1

    • FVC

    • FEF800-1200

    • FEF25-75

    • MVV

    Correct Answer
    A. FEF25-75
    Explanation
    Pulmonary function tests can be divided into those that assess ventilatory capacity and into those that assess pulmonary gas exchange. The simplest test to assess ventilatory capacity is the FEV1/FVC ratio. Other tests to assess ventilatory capacity include the maximum midexpiratory flow (FEF25-75), maximum voluntary ventilation (MVV), and flow-volume curves. The most significant disadvantage of these tests is that they are dependent on patient effort; however, since the FEF25-75 is obtained from the midexpiratory portion of the flow-volume loop, it is least dependent on patient effort.

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  • 25. 

    Which of the following statements concerning the distribution of alveolar ventilation (Va) in the upright lungs is true?

    • The distribution of VA is not affected by body posture

    • Alveoli at the apex of the lungs (nondependent alveoli) are better ventilated than those at the base

    • All areas of the lungs are ventilated equally

    • Alveoli at the base of the lungs (dependent alveoli) are better ventilated than those at the apex

    • Alveoli at the central regions of the lungs are better ventilated than those at the base or apex

    Correct Answer
    A. Alveoli at the base of the lungs (dependent alveoli) are better ventilated than those at the apex
    Explanation
    The orientation of the lungs relative to gravity has a profound effect on efficiency or pulmonary gas exchange. Because alveoli in dependent regions of the lungs expand more per unit change in transpulmonary pressure (i.e., are more compliant) than alveoli in nondependent regions of the lungs, Va increases from the top to the bottom of the lungs. Because pulmonary blood flow increases more from the top to the bottom of the lungs than does Va, the ventilation/perfusion ratio is high in nondependent regions of the lungs and is low in dependent regions of the lungs. Therefore, in the upright lungs, the PO2 and pH are greater at the apex, while the PCO2 is greater at the base.

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  • 26. 

    Which of the following statements concerning the distribution of O2 and CO2  in the upright lungs is true?

    • PAO2 is greater at the apex than at the base

    • PACO2 is greater at the apex than at the base

    • Both PAO2 and PACO2 are greater at the apex than at the base

    • Both PAO2 and PACO2 are greater at the base than at the apex

    • The PACO2 is equal throughout the lung

    Correct Answer
    A. PAO2 is greater at the apex than at the base
    Explanation
    The ventilation/perfusion ratio is greater at the apex of the lungs than at the base of the lungs. Thus, dependent regions of the lungs are hypoxic and hypercarbic compared to the nondependent regions.

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  • 27. 

    The vital capacity is composed of the

    • Expiratory reserve volume

    • Inspiratory reserve volume

    • Tidal volume

    • Functional residual capacity

    Correct Answer(s)
    A. Expiratory reserve volume
    A. Inspiratory reserve volume
    A. Tidal volume
    Explanation
    The vital capacity is the volume of gas that can be exhaled during a maximal expiration. It is composed of the inspiratory and expiratory reserve volumes, and the Vt.

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  • 28. 

    An acute increase in PaCO2 of 10 mm Hg will result in an immediate com­pensatory increase in [HCO3-] of

    • 1 mEq/L

    • 2 mEq/L

    • 4 mEq/L

    • 5 mEq/L

    • 7 mEq/L

    Correct Answer
    A. 1 mEq/L
    Explanation
    A prolonged increase in PaCO2 of 10 mm Hg will result in a maximum compensatory increase in [HC03-] of 3 mEq/L. An acute increase in PaCO2 of 10 mm Hg results in an immediate compensatory increase in [HCO3-] of 1 mEq/L. This immediate compensatory increase in [HC03-] is caused by the hydration of CO2 in plasma to produce HCO3-. An acute decrease in PaCO2 of 10 mm Hg will cause an immediate compensatory decrease in [HCO3-] of 2 mEq/L, and a chronic decrease in PaCO2 of 10 mm Hg will cause a maximum compensatory decrease in [HCO3-] of 5 mEq/L.

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  • 29. 

    An increase in PaCO2 of 10 mm Hg will result in a decrease in pH of

    • 0.01 pH units

    • 0.02 pH units

    • 0.04 pH units

    • 0.08 pH units

    • None of above

    Correct Answer
    A. 0.08 pH units
    Explanation
    Respiratory acidosis is present when the PaCO2 exceeds 44 mm Hg. Respiratory acidosis is caused by decreased elimination of CO2 by the lungs (i.e., hypoventila¬tion) or increased metabolic production of CO2. An acute increase in PaCO2 of 10 mm Hg will result in a decrease in pH of approximately 0.08 pH units. The acidosis of arterial blood will stimulate ventilation via the carotid bodies and the acidosis of cerebrospinal fluid will stimulate ventilation via the medullary chemoreceptors located in the fourth cerebral ventricle. Volatile anesthetics greatly attenuate the carotid body-mediated and aortic body-mediated ventilatory responses to arterial acidosis, but have little effect on the medullary chemoreceptor-mediated ventilatory response to cerebrospinal fluid acidosis.

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  • 30. 

    Which of the following acid-base disturbances is the least well compensated?

    • Metabolic alkalosis

    • Respiratory alkalosis

    • Increased anion gap metabolic acidosis

    • Normal anion gap metabolic acidosis

    • Respiratory acidosis

    Correct Answer
    A. Metabolic alkalosis
    Explanation
    The degree to which a person can hypoventilate to compensate for metabolic alkalosis is limited and hence, this is the least well compensated acid-base disturbance. Respiratory compensation for metabolic alkalosis is rarely more than 75% complete. Hypoventilation to a PaCO2 > 55 mm Hg is the maximum respiratory compensation for metabolic alkalosis. A PaCO2 > 55 mm Hg most likely reflects concomitant respiratory acidosis.

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  • 31. 

    Correct mathematical expressions of static lung capacities and volumes include which of the following?

    • Total lung capacity = vital capacity + residual volume

    • Functional residual capacity = expiratory reserve volume + residual volume

    • Inspiratory capacity = inspiratory reserve volume + tidal volume

    • Closing capacity = residual volume + closing volume

    Correct Answer(s)
    A. Total lung capacity = vital capacity + residual volume
    A. Functional residual capacity = expiratory reserve volume + residual volume
    A. Inspiratory capacity = inspiratory reserve volume + tidal volume
    A. Closing capacity = residual volume + closing volume
    Explanation
    The maximum volume of gas that can be inhaled is called the inspiratory capacity. The volume of gas that can be inhaled from the end of a normal inspiration is called the inspiratory reserve volume. Thus, the inspiratory capacity is corn-posed of the VT and inspiratory reserve volume.

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  • 32. 

    The normal arterial-to-alveolar ratio (a/A) is greater than

    • 0.10

    • 0.65

    • 0.75

    • 0.50

    • 0.25

    Correct Answer
    A. 0.75
    Explanation
    Arterial hypoxemia is defined as a decrease in PaO2 below 60 mm Hg. Arterial hypoxemia can be caused by low PO2, hypoventilation, or shunt. Shunt can be caused by a right-to-left transpulmonary or intracardiac shunt, or mismatching of ventilation to perfusion. Diffusion limitation to the passage of O2 from the alveoli to blood has not been documented as a cause of arterial hypoxemia in humans. The degree of shunt can be estimated by calculating the P(A-a)O2 or arterial-to-alveolar (a/A) ratio. It is easier to use the a/A ratio to calculate shunt fraction because the normal range for the P(A-a)O2 changes with the PO2 of inspired gas. The normal a/A ratio should be greater than 0.75.

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  • 33. 

    The mechanism for the compensatory shift of the oxyhemoglobin dissociation curve toward normal in response to chronic (>24 hours) respiratory alkalosis is

    • Increased renal excretion of HCO3-

    • An influx of potassium into red blood cells

    • Altered erythrocyte 2,3-diphosphoglycerate (2,3-DPG) metabolism

    • Decreased sensitivity of the central nervous system to changes in PaCO2

    • None of the above

    Correct Answer
    A. Altered erythrocyte 2,3-diphosphoglycerate (2,3-DPG) metabolism
    Explanation
    The compensatory shift of the oxyhemoglobin dissociation curve toward normal in response to chronic acid-base abnormalities is a result of altered erythrocyte 2,3-diphosphoglycerate (2,3-DPG) metabolism.

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  • 34. 

    What is the PaO2 of air in a patient in Denver, Colorado (assume a baro­metric pressure of 630 mm Hg, respiratory quotient of 0.8, and PaCO2 of 34 mm Hg)?

    • 40 mm Hg

    • 50 mm Hg

    • 60 mm Hg

    • 70 mm Hg

    • 80 mm Hg

    Correct Answer
    A. 80 mm Hg
    Explanation
    PAO2 can be estimated using the alveolar gas equation which is as follows:
    PAO2 = (Pb-47)*FiO2-PaCO2/R, where Pb is the barometric pressure (mm Hg), Fi02 is the fraction of inspired 02, PaCO2 is the arterial CO2 tension (mm Hg), and R is the respiratory quotient.

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  • 35. 

    Which of the following muscles or muscle groups of respiration is not used for inspiration?

    • Diaphragm

    • Internal intercostal muscles

    • External intercostal muscles

    • Scalene muscles

    • Sternomastoids

    Correct Answer
    A. Internal intercostal muscles
    Explanation
    The muscles of expiration are those of the abdominal wall and the internal intercostal muscles. The internal intercostal muscles function to pull the ribs downward and inward, which decreases the volume of the thoracic cavity

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  • 36. 

    The half-life of carboxyhemoglobin in a patient breathing 100% 02 is

    • 5 minutes

    • 1 hour

    • 2 hours

    • 4 hours

    • 12 hours

    Correct Answer
    A. 1 hour
    Explanation
    The most frequent immediate cause of death from fires is carbon monoxide toxicity. Carbon monoxide is a colorless, odorless gas that exerts its adverse effects by decreasing O2 delivery to peripheral tissues. This is accomplished by two mechanisms. First, because the affinity of carbon monoxide for the O2 binding sites on hemoglobin is 240 times that of O2, O2 is readily displaced from hemoglobin. Thus, O2 content is reduced. Second, carbon monoxide causes a leftward shift of the oxyhemoglobin dissociation curve, which increases the affinity of hemoglobin for O2 at peripheral tissues. Treatment of carbon monoxide toxicity is administration of 100% O2. Breathing 100% O2 decreases the half-life of carboxyhemoglobin from 250 minutes to approximately 50 minutes.

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  • 37. 

    The P50 of sickle cell hemoglobin is

    • 19

    • 26

    • 31

    • 35

    • 40

    Correct Answer
    A. 31
    Explanation
    A P50 less than 26 mm Hg defines a leftward shift of the oxyhemoglobin dissociation curve, which means that at any given PaO2, hemoglobin has a higher affinity for O2. A P50 greater than 26 mm Hg describes a rightward shift of the oxyhemoglobin dissociation curve, which means that at any given Pao2, hemoglobin has a lower affinity for O2. Conditions that cause a rightward shift of the oxyhemoglobin dissociation curve are metabolic and respiratory acidosis, hyperthermia, increased erythrocyte 2,3-DPG content, pregnancy, and abnormal hemoglobins, such as sickle cell hemoglobin or thalassemia. Alkalosis, hypothermia, fetal hemoglobin, abnormal hemoglobin species, such as carboxyhemoglobin, methemoglobin, and sulfhemoglobin, and decreased erythrocyte 2,3-DPG content will cause a leftward shift of the oxyhemoglobin dissociation curve.

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  • 38. 

    Which of the following respiratory variables can be measured by simple spirometry?

    • Vital capacity

    • Expiratory reserve volume

    • Inspiratory capacity

    • Residual volume

    Correct Answer(s)
    A. Vital capacity
    A. Expiratory reserve volume
    A. Inspiratory capacity
    Explanation
    Static lung volumes can be divided into those that can be measured by simple spirometry and into those that cannot. The functional residual capacity and residual volume cannot be measured by simple spirometry; however, these two variables can be measured using gas-dilution techniques or body plethysmography

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  • 39. 

    During a normal Vt (500 mL) breath, the transpulmonary pressure in­creases from 0 to 5 cm H2O). The product of transpulmonary pressure and Vt is 2,500 cmH2O-ml. This expression of the pressure-volume relationship during breathing determines what variable of respiratory mechanics?

    • Lung compliance

    • Airway resistance

    • Pulmonary elastance

    • Work of breathing

    • Closing capacity

    Correct Answer
    A. Work of breathing
    Explanation
    The work of breathing is defined as the product of transpulmonary pres¬sure and VT. The work of breathing is related to two factors: the work required to overcome the elastic forces of the lungs and the work required to overcome airflow or frictional resistances of the airways. Volatile anesthetics cause a marked increase in the elastic component of the work of breathing .

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  • 40. 

    The P(A - a)O2 of a patient breathing 100% O2 is 240 mm Hg. The esti­mated fraction of the cardiac output shunted past the lungs without exposure to ventilated alveoli (i.e., transpulmonary shunt) is

    • 5%

    • 12%

    • 17%

    • 20%

    • 34%

    Correct Answer
    A. 12%
    Explanation
    Qs/Qt=P(A-a)O2/20, where Qs is the cardiac output that is shunted past the lungs without exposure to ventilated alveoli, Qt is the total cardiac output, and P(A-a)O2 is the alveolar-to-arterial difference in O2 tension.

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  • 41. 

    Factors that determine the diffusing capacity of the lungs for carbon monox­ide (DLco) include the

    • Area of the alveolar membrane

    • Blood volume of the pulmonary vasculature

    • Thickness of the alveolar membrane

    • Red blood cell hemoglobin concentration

    Correct Answer(s)
    A. Area of the alveolar membrane
    A. Blood volume of the pulmonary vasculature
    A. Thickness of the alveolar membrane
    A. Red blood cell hemoglobin concentration
    Explanation
    The diffusing capacity of the lungs is determined by several processes: 1) diffusion of a gas through the alveolar walls and 2) the rate of reaction of the gas with hemoglobin. The mathematical expression of the diffusing capacity of the lungs is as follows: DL = DM + ( Θ • Vc),
    where DL is the diffusing capacity of the lungs, DM is the diffusing capacity of the alveolar membrane, Θ is the rate (in mL/min) a gas can combine with 1 mL of blood/mm Hg partial pressure of the gas in the blood, and Vc is the volume of blood in the pulmonary capillaries. Thus, DL is determined by the area and thickness of the alveolar membrane, the blood:gas solubility and molecular weight of the gas, the transmembrane partial pressure difference of the gas, pulmonary blood volume, and hemoglobin concentration.

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  • 42. 

    Which of the following will increase the closing capacity?

    • Smoking

    • Obesity

    • Supine position

    • Aging

    Correct Answer(s)
    A. Smoking
    A. Obesity
    A. Supine position
    A. Aging
    Explanation
    The closing capacity is the product of residual volume and the volume remaining in the lung when airway closure occurs (i.e., closing volume). Measurement of the closing capacity is a sensitive test of early small-airway diseases, such as emphysema, asthma, bronchitis, and pulmonary interstitial edema. Smoking tobacco, obesity, aging, and the supine position increase the closing capacity.

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  • 43. 

    A decrease in PaCO2 of 10 mm Hg will result in

    • A decrease in serum potassium concentration ([K+]) of 0.5 mEq/L

    • A decrease in [K+] of 1.0 mEq/L

    • No change in [K+] under normal circumstances

    • An increase in [K+] of 0.5 mEq/L

    • An increase in [K+] of 1.0 mEq/L

    Correct Answer
    A. A decrease in serum potassium concentration ([K+]) of 0.5 mEq/L
    Explanation
    Cardiac dysrhythmias are a common complication associated with acid-base abnormalities. The etiology of these dysrhythmias is related partly to the effects of pH on myocardial potassium homeostasis. As a general rule, there is an inverse relationship between [K+] and pH. For every 0.08 unit change in pH, there is a reciprocal change in [K+] of approximately 0.5 mEq/L.

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  • 44. 

    An increase in [HCO3-] of 10 mEq/L will result in an increase in pH of

    • 0.10 pH units

    • 0.15 pH units

    • 0.20 pH units

    • 0.25 pH units

    • None of the above

    Correct Answer
    A. 0.15 pH units
    Explanation
    There are several guidelines that can be used in the initial interpretation of arterial blood gases that will permit rapid recognition of the type of acid-base disturbance. These guidelines are as follows: 1) a 1 mm Hg change in PaCO2 above or below 40 mm Hg results in a 0.008-unit change in the pH in the opposite direction; 2) the PaCO2 will decrease by about 1 mm Hg for every 1 mEq/L reduction in [HCO3-] below 24 mEq/L; 3) a change in [HCO3-] of 10 mEq/L from 24 mEq/L will result in a change in pH of approximately 0.15 pH units in the same direction.

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  • 45. 

    In the resting adult, what percent of total body O2 consumption is spent do­ing the work of breathing?

    • 2%

    • 5%

    • 10%

    • 20%

    • 50%

    Correct Answer
    A. 2%
    Explanation
    The work required to overcome the elastic recoil of the lungs and thorax, along with airflow or frictional resistances of the airways, contributes to the work of breathing. When the respiratory rate or airway resistance is high, or pulmonary or chest wall compliance is reduced, a large amount of energy is spent in overcoming the work of breathing. In the healthy, resting adult, only 1% to 2% of total O2 consumption is used for the work of breathing.

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  • 46. 

    What is the rate of O2 transported to peripheral tissues in a healthy 70-kg patient with a hemoglobin concentration of 10 mg/dL, a PaO2 of 60 mm Hg, an SaO2 of 90%, and a cardiac output of 5 L/min?

    • 300 mL/min

    • 400 mL/min

    • 500 mL/min

    • 600 mL/min

    • 700 mL/min

    Correct Answer
    A. 600 mL/min
    Explanation
    The amount of O2 transported from the lungs to peripheral tissues is determined by the O2 content and the cardiac output. The mathematical expression of O2 transport is as follows:
    02 transport = CO • 02 content, where CO is the cardiac output (mL/min).
    In this patient, O2 transport is approximately 600 mL/min

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  • 47. 

    A venous blood sample from which of the following sites would correlate most reliably with PaO2 and PaCO2?

    • Jugular vein

    • Subclavian vein

    • Antecubital vein

    • Femoral vein

    • Vein on posterior surface of a warmed hand

    Correct Answer
    A. Vein on posterior surface of a warmed hand
    Explanation
    When arterial sampling is not possible, "arterialized" venous blood can be used to determine arterial blood gas tensions. Because blood in the veins on the back of the hands have very little O2 extracted, the O2 content in this blood best approximates the O2 content in a sample of blood obtained from an artery.

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  • 48. 

    Each of the following will shift the oxyhemoglobin dissociation curve to the right EXCEPT

    • Volatile anesthetics

    • Decreased PaO2

    • Decreased pH

    • Increased temperature

    • Increased red blood cell (RBC) 2,3-DPG content

    Correct Answer
    A. Decreased PaO2
    Explanation
    In addition to the items listed in this question, other factors that shift the oxyhemoglobin dissociation curve to the right include pregnancy and all abnormal hemoglobins such as hemoglobin S (sickle cell hemoglobin). For reasons unknown, volatile anesthetics increase the P50 of adult hemoglobin by 2 to 3.5 mm Hg. A rightward shift of the oxyhemoglobin dissociation curve will decrease the transfer from O2 from alveoli to hemoglobin and improve release of O2 from hemoglobin to peripheral tissues.

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  • 49. 

    Which of the following can cause a rightward shift of the oxyhemoglobin dis­sociation curve?

    • Methemoglobinemia

    • Carboxyhemoglobinemia

    • Rapid transfusion of large amounts of citrate-preserved packed erythrocytes

    • Pregnancy

    Correct Answer
    A. Pregnancy
    Explanation
    During pregnancy, there is an increased production of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells. 2,3-BPG binds to hemoglobin and reduces its affinity for oxygen, causing a rightward shift of the oxyhemoglobin dissociation curve. This shift allows for increased release of oxygen to the tissues, compensating for the increased oxygen demand during pregnancy. Methemoglobinemia and carboxyhemoglobinemia cause a leftward shift of the curve, while rapid transfusion of citrate-preserved packed erythrocytes does not have a significant effect on the curve.

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  • Mar 21, 2023
    Quiz Edited by
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  • Jan 21, 2012
    Quiz Created by
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