Hypoxemia: Difference between revisions

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#Pulmonary arterial vasoconstriction  
#Pulmonary arterial vasoconstriction  
#Increased sympathetic tone
#Increased sympathetic tone
==Work-Up==


==DDx==
==DDx==
==Treatment==
==Disposition==


==See Also==
==See Also==
[[Hypercapnea]]


==Source==
==Source==

Revision as of 09:18, 22 July 2011

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 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 pts)

Pathophysiology

Causes

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

Compensation

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

DDx

See Also

Hypercapnea

Source

Tintinalli