Arterial Blood Gasses Flashcards Preview

CVPR: Pulmonary > Arterial Blood Gasses > Flashcards

Flashcards in Arterial Blood Gasses Deck (9)
Loading flashcards...
1

Oxygen "off-loading" characteristics

  • most oxygen is bound to hemoglobin
  • tissues can only use freely-dissolved O2 ==> O2 must unbind from hemoglovin
  • ODC reflects equilibrium between O2 binding and unbinding
    • decreased pH or increased PaCO2 ==> rightward shift of ODC curve
    • rightward shift ==> increased O2 unloading @ tissues (beneficial during exercise)

2

Quantity of O2 delivery/minute = 

  • = CO x concentration of arterial O2 
  • DO2 = Q x CaO2
  • CaO2 = (SaO2 x [Hb] x 1.39) + (0.003 x PaCO2)
    • SaO2 = saturation of hemoglobin
    • 1.39 (ml/gram) = max volume of O2 that can combine w/1 g of hemoglobn 
    • ([Hb] x 1.39) = "oxygen carrying capacity"

3

Hypoxemia definition

  • reduced arterial free oxygen + reduced percent saturation of hemoglobin (SaO2) ==>
  • decreased O2 delivery

4

Oxygen consumption equation

  • =difference between O2 content of arterial and venous blood
  • VO2 = (Q x CaO2) - (Q x CvO2) = Q x (CaO2 - CvO2)
  • Ignoring small dissolved O2 component ==>
    • VO2 = Q x (SaO2 - SvO2) x [Hb] x 1.39

5

Relationship between oxygen tension and transport towards/into tissues [diagram]

6

Measures that asses arterial oxygenation

  1. arterial oxygen tension (PaO2)
  2. oxy-hemoglobin saturation (SaO2)
  3. alveolar-arterial pressure gradient for oxygen
  4. blood oxygen content (CaO2) 

7

Desturation vs. hypoxemia

  • saturation = % hemoglobin occupied (SaO2)
  • hypoxemia = low arterial oxyen tension (PaO2)
  • hypoxemia w/out desaturated: PaO2 < 65 mmHG & SaO2 > 90%

  • desaturation w/out hypoxemia: PaO2 > 65 mmHG & SaO2​ < 90%
     

8

Main causes of hypoxemia (+ major physiologic problem)

  • PaO2 < 80 Torr (<65 Torr @ Denver)
  1. low ambient PO2 in inspired air (altitude)
    • normal A-a gradient
    • problem w/O2 ==> alveoli
  2. hypoventilation: increased alveolar PACO2 ==> decreased PAO2
    • normal A-a gradient

    • problem w/O2​ ==> alveoli
       

  3. diffusion limitation between alveoli and pulmonary capillaries
    • widened A-a gradient
  4. V/Q mismatch

    • widened A-a gradient 



    • responds readily to 100% oxygen  

  5. Shunt

    • widened A-a gradient
      ​ 

    • does not respond to 100% oxygen

9

Main methods of CO2 transport w/in blood

  • Dissolved CO2
  • Bicarbonate ion (HCO3-): Carbonic acid (H2CO3) is converted to water and carbon dioxide via carbonic anyhydrase
    • H2O + CO2 <==> H2CO3 <==> H+ + HCO3-
  • Carbamino acids: bound to proteins (e.g. hemoglobin)