Hypoxemia: Difference between revisions

(Created page with "==Background== *Defined as PaO2 <60 mm Hg **Amount of oxygen available is a function of the arterial oxygen content and blood flow *Occurs in states of low CO, low Hb, or low SaO...")
 
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*Defined as PaO2 <60 mm Hg
*Defined as PaO2 <60 mm Hg
**Amount of oxygen available is a function of the arterial oxygen content and blood flow
**Amount of oxygen available is a function of the arterial oxygen content and blood flow
*Occurs in states of low CO, low Hb, or low SaO2 (arterial oxygen saturation)
*Occurs in states of low CO, low hemoglobin, or low SaO2 (arterial oxygen saturation)
*Relative Hypoxemia
*Relative Hypoxemia
**PaO2 is < expected for given level of inhaled O2 (e.g. PaO2 of 100 on FiO2 100%)
**PaO2 is < expected for given level of inhaled O2 (e.g. PaO2 of 100 on FiO2 100%)
**Can calculate amount of relative hypoxemia by A-a gradient
**Can calculate amount of relative hypoxemia by A-a gradient
***P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy pts)
***P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy patients)


==Pathophysiology==
===Causes===
*Hypoexemia results from any combination of 5 mechanisms
*Hypoventilation
#Hypoventilation
**Always associated with increased PaCO2
##d
**Normal A-a gradient
*Right-to-left shunt
**Occurs when blood enters the systemic arteries with out traversing ventilated lung
***Occurs with pulmonary consolidation, atelectasis
**Hallmark is failure of arterial O2 levels to increase with supplemental O2 (increased A-a)
*V/Q mismatch
**PE, pneumonia, asthma, COPD
**Improves with supplemental O2
**A-a gradient increased
*Diffusion impairment
**Improves with supplemental O2
**A-a gradient increased
*Low inspired O2
**Improves with supplemental O2
**A-a gradient normal


==Work-Up==
===Compensation===
#Increased minute ventilation
#Pulmonary arterial vasoconstriction
#Increased sympathetic tone


==Differential Diagnosis==
{{SOB DDX}}


==DDx==
==Evaluation==
 
 
==Treatment==


==Management==


==Disposition==
==Disposition==


==See Also==
==See Also==
*[[Shortness of breath]]
*[[Hypercapnia]]
==References==
<references/>


==Source==
Tintinalli


[[Category:Pulm]]
[[Category:Pulmonary]]

Revision as of 12:15, 23 October 2021

Background

  • Defined as PaO2 <60 mm Hg
    • Amount of oxygen available is a function of the arterial oxygen content and blood flow
  • Occurs in states of low CO, low hemoglobin, or low SaO2 (arterial oxygen saturation)
  • Relative Hypoxemia
    • PaO2 is < expected for given level of inhaled O2 (e.g. PaO2 of 100 on FiO2 100%)
    • Can calculate amount of relative hypoxemia by A-a gradient
      • P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy patients)

Causes

  • Hypoventilation
    • Always associated with increased PaCO2
    • Normal A-a gradient
  • Right-to-left shunt
    • Occurs when blood enters the systemic arteries with out traversing ventilated lung
      • Occurs with pulmonary consolidation, atelectasis
    • Hallmark is failure of arterial O2 levels to increase with supplemental O2 (increased A-a)
  • V/Q mismatch
    • PE, pneumonia, asthma, COPD
    • Improves with supplemental O2
    • A-a gradient increased
  • Diffusion impairment
    • Improves with supplemental O2
    • A-a gradient increased
  • Low inspired O2
    • Improves with supplemental O2
    • A-a gradient normal

Compensation

  1. Increased minute ventilation
  2. Pulmonary arterial vasoconstriction
  3. Increased sympathetic tone

Differential Diagnosis

Acute dyspnea

Emergent

Non-Emergent

Evaluation

Management

Disposition

See Also

References

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