chapter 41. quiz 4. Arterial Blood Gas Analysis
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Questions and Answers

What is the most common cause of hypoxemia in the clinical setting?

  • Impairment of diffusion of O2
  • V ̇/Q ̇mismatching (correct)
  • Intrapulmonary shunt
  • Right-to-left shunt

    • What areas in the lung are associated with low end-capillary PO2?

  • Areas with normal V/Q ratio
  • Areas with low V/Q ratio (correct)
  • Areas with intrapulmonary shunt
  • Areas with high V/Q ratio

    • Which factor limits the ability of normal and high V/Q regions to increase O2 content and compensate for low V/Q regions?

  • V/Q mismatch
  • Right-to-left shunt
  • O2Hb dissociation curve plateau (correct)
  • Hypoxemia

    • What occurs in a right-to-left shunt?

    <p>Extreme case of V/Q mismatch</p> Signup and view all the answers

    In healthy awake spontaneously breathing subjects, what is the status of intrapulmonary shunt?

    <p>&lt;1% of cardiac output</p> Signup and view all the answers

    Why does V/Q mismatch result in hypoxemia?

    <p>Limited O2 compensation due to the O2Hb dissociation curve</p> Signup and view all the answers

    What is the normal range for PaO2 in healthy adults breathing room air at sea level?

    <p>80-100 mm Hg</p> Signup and view all the answers

    Which of the following is NOT a physiologic cause of hypoxemia?

    <p>Left-to-right shunt</p> Signup and view all the answers

    How does hypoventilation contribute to hypoxemia?

    <p>By reducing the PAO2</p> Signup and view all the answers

    Which factor can produce hypoxemia by affecting the different steps of O2 transport from the environment to arterial blood?

    <p>hypoventilation</p> Signup and view all the answers

    In which conditions does diffusion limitation play a role in causing hypoxemia?

    <p>In interstitial lung diseases</p> Signup and view all the answers

    Which step of O2 transport to arterial blood is affected by V ̇/Q ̇ mismatch and right-to-left shunt?

    <p>Efficiency of O2 exchange</p> Signup and view all the answers

    which of the following causes explain the majority of hypoxemia in the perioperative setting

    <p>all of the above</p> Signup and view all the answers

    The normal value of PaO2 decreases with ?

    <p>increasing age</p> Signup and view all the answers

    How does an increase in FIO2 affect PaO2 in the presence of a large true right-to-left shunt?

    <p>It has a small effect on PaO2</p> Signup and view all the answers

    What is a possible cause of right-to-left shunt during general anesthesia as mentioned in the text?

    <p>Atelectasis</p> Signup and view all the answers

    In addition to atelectasis, which other pathologic condition can lead to a right-to-left shunt?

    <p>Pneumonia</p> Signup and view all the answers

    What factors determine the effect of a right-to-left shunt on PaO2?

    <p>Magnitude of the shunt, FIO2, and the cardiac output</p> Signup and view all the answers

    What does the shunt fraction equation use to calculate the shunted blood flow in the three-compartment lung model?

    <p>End-capillary O2 content</p> Signup and view all the answers

    In the ideal alveolar gas equation, the ratio of pulmonary CO2 elimination to O2 uptake is represented by which parameter?

    <p>Respiratory quotient (R)</p> Signup and view all the answers

    Under normal diet and metabolic conditions, what value does the respiratory quotient (R) typically have?

    <p>0.8</p> Signup and view all the answers

    Which lung compartment represents regions with ventilation but no perfusion in the three-compartment lung model?

    <p>Dead space compartment</p> Signup and view all the answers

    What does Q ̇S/Q ̇T represent under conditions of FIO2 less than 100%?

    <p>Combination of factors producing hypoxemia</p> Signup and view all the answers

    What is the term used when Q ̇S/Q ̇T is referred to as the calculated estimate of how much hypoxic blood is required to produce the measured arterial oxygen results?

    <p>Venous admixture</p> Signup and view all the answers

    What condition can be caused by the administration of 100% oxygen (FIO2 of 1.0), particularly in compartments with very low V ̇/Q ̇?

    <p>Absorption atelectasis</p> Signup and view all the answers

    In the simplified form of the shunt fraction equation, what does Q s/Q T= (1−SaO2)/ (1 − SvO2) represent?

    <p>Relationship between arterial and mixed venous saturation levels</p> Signup and view all the answers

    What is the purpose of the shunt fraction equation assuming end-capillary blood has an O2 saturation of 100%?

    <p>To calculate the shunt fraction accurately</p> Signup and view all the answers

    Which factor is eliminated when FIO2 is at 100% according to the text?

    <p>Effects of V ̇/Q ̇ heterogeneity</p> Signup and view all the answers

    Why is proper handling of arterial blood gas samples important?

    <p>is important to prevent errors.</p> Signup and view all the answers

    In adult patients during procedures involving deep hypothermic circulatory arrest (DHCA), which management strategy is suggested for increasing the rate and uniformity of cooling?

    <p>pH-stat management</p> Signup and view all the answers

    What is the potential consequence of a delay in analyzing an arterial blood gas sample for 20 minutes at room temperature or 4°C?

    <p>Decline in PaO2</p> Signup and view all the answers

    What issue can arise if an air bubble is present in the sampling syringe during arterial blood gas sample collection?

    <p>decline in PaCO2</p> Signup and view all the answers

    Which strategy is supported for hypothermic circulatory pulmonary bypass (HCPB) in adult patients?

    <p>Alpha-stat management</p> Signup and view all the answers

    What is a limitation of indices of oxygenation based on PaO2?

    <p>They vary with changes in FIO2, PaCO2, Hb, and V ̇O2</p> Signup and view all the answers

    What is an ideal characteristic of an index of oxygenation?

    <p>It should change with changes in lung function</p> Signup and view all the answers

    What is a disadvantage of using indices of oxygenation based on PaO2?

    <p>They are limited in providing a measure of the magnitude of the O2 exchange deficiency</p> Signup and view all the answers

    Why do indices of oxygenation based on PaO2 vary with changes in FIO2?

    <p>Because they are dependent on FIO2</p> Signup and view all the answers

    What is the main purpose of developing less invasive indices of oxygenation?

    <p>To reflect the efficiency of oxygenation using non-invasive measures</p> Signup and view all the answers

    What should an ideal index of oxygenation do when there are changes in extrapulmonary conditions like FIO2?

    <p>Remain constant</p> Signup and view all the answers

    Why is a pulmonary artery catheter needed for measuring SvO2?

    <p>To calculate shunt fraction directly</p> Signup and view all the answers

    What is a main limitation of indices of oxygenation based on PaO2?

    <p>They vary with FIO2, PaCO2, Hb, and O2 consumption</p> Signup and view all the answers

    What does the (A-a)PO2 help to differentiate?

    <p>Hypoventilation and low FIO2 from V ̇/Q ̇ mismatch, shunt, and diffusion limitation</p> Signup and view all the answers

    What is the normal value of the (A-a)PO2 in young adults breathing room air?

    <p>Less than 10 mm Hg</p> Signup and view all the answers

    What happens to the (A-a)PO2 under conditions of decreased FIO2 and hypoventilation?

    <p>It remains unchanged</p> Signup and view all the answers

    What effect does lower temperature have on the solubility of CO2 and O2 in blood?

    <p>Increases solubility</p> Signup and view all the answers

    In blood gas analyzers, As blood from a hypothermic patient is warmed to 37°C by the analyzer lead to

    <p>PaCO2 and PaO2 higher</p> Signup and view all the answers

    What potential benefit does alpha-stat management offer in the management of hypothermic patients?

    <p>Preservation of cerebral autoregulation</p> Signup and view all the answers

    In pH-stat management, why are measurements corrected to the patient’s actual temperature before being used for analysis?

    <p>Because patients are hypothermic, the PaO2 and PaCO2 at the patient’s temperature are lower and the pH higher</p> Signup and view all the answers

    What stands out as a key difference between alpha-stat and pH-stat management during blood gas analysis?

    <p>Temperature corrections</p> Signup and view all the answers

    What is a limitation of the PaO2/FIO2 ratio for characterizing respiratory failure severity?

    <p>Dependence on lung recruitment</p> Signup and view all the answers

    In which condition is the SpO2/FIO2 ratio, also referred to as SF, considered useful?

    <p>respiratory failure</p> Signup and view all the answers

    What does the PaO2/FIO2 ratio not depend on according to the text?

    <p>PAO2</p> Signup and view all the answers

    What values are used as part of the diagnostic criteria for ARDS?

    <p>PaO2/FIO2</p> Signup and view all the answers

    Which ratios show good correlation when SpO2 values are in the range of 80% to 97%?

    <p>PaO2/FIO2 and SF</p> Signup and view all the answers

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