OXYHEMOGLOBIN DISSOCIATION CURVE

1. OXYHEMOGLOBIN DISSOCIATION CURVE Chemeketa Community College

2. Oxyhemoglobin Dissociation Curve Mathematically equates the percentage saturation of hemoglobin to the partial pressure of oxygen in the blood

3. Oxygen hemoglobin dissociation curve

4. Oxy/hemo Curve • The ability of oxygen to bind with and dissociate from hemoglobin • How shifts change affinity

5. Oxy/hemo Curve • 97% O2 on Heme of Hgb • 3% in plasma • 3% is available in anemia • Harmful in toxicity

6. Oxy/hemo Curve • O2 is “loosely” attached to heme • Easily formed and dissolved

7. Oxy/hemo Curve • Heme can carry 4 O2 molecules • Each site is affected by the other 3 • As they bind, space is decreased

8. Oxy/hemo Curve • The more they bind, the easier it becomes to bind

10. Oxy/hemo Curve • Two transfer sites exist • Alveolar-capillary site • Capillary-tissue site

11. O2 Saturation Monitoring • ABGs, pulse oximetry • Venous sats

12. O2 Sat. Monitoring • Does not tell tissue oxygenation • Patient may have tissue hypoxia in spite of monitors

13. Oxy/hemo Curve • Normal curve uses O2 Sats and PaO2 to reflect amount of oxygen available to the tissues

14. Oxy/hemo Curve-Normals • 37 degrees, pH 7.40, PaCO2 40 mm/hg • Deviation causes a shift

15. Oxygen-hemoglobin dissociation curve

16. Oxy/hemo Curve • Upper-flat portion is lungs • Steep portion is tissues • Body can hold 96-97% down to 80 mm/hg

17. Oxy/hemo Curve • Results of tissue transfer- • Venous blood at 63% • At 27 mm/hg the Sat is 50%

18. Changes in Affinity • pH, PaCO2, carbon monoxide, abnormal Hgb., temp, intracellular compounds, 2,3-DPG

19. The Bohr effect • Oxygenated Hgb = stronger acid than deoxygenated Hgb • Change in pH facilitates release of oxygen

20. The Bohr effect • Acid becomes weaker • Blood picks up CO2 • Transports to lungs and process reverses

21. Relationship of hemoglobin saturation and pH

22. Temperature • Decrease causes increased affinity • Shift to left • Increase causes decreased affinity • Shift to right

23. Relationship of hemoglobin sat. and Temperature

24. 2,3 DPG (diphosphoglycerate) • An enzyme that affects binding directly • Competes with oxygen

25. 2,3 DPG (diphosphoglycerate) • More 2,3 DPG =decreased affinity • Less = increased affinity

26. Carbon Monoxide (CO) • CO has > 200 times greater affinity than oxygen • Always causes lower oxygen sats

27. Abnormal Hemoglobin • May have greater or lesser affinity

28. Left Shift • Increased affinity for O2 • At any PaO2, % is higher

29. Left Shift • Easier to “hook-on” • Harder to “un-hook”

30. Left Shift-clinical situations • Alkalosis, hypocapnia, hypothermia • Decreased DPG, CO poisoning • Blood transfusion, fetal Hgb

31. Clinical example • 56 yo woman with ICP elevated • Craniotomy for CVA bleed/ aneurysm • Hyperventilated to vasoconstrict

32. Her ABGs • pH = 7.53, Pa CO2 = 21 mm/hg • PO2 = 118 mm/hg, HCO3 = 17.8 mEq/L • O2 Sat = 99.1%, Temp =37.6

33. What does it mean? • Left shift makes it hard to “un-hook” • Tissue hypoxia must be watched for, even if readings indicate high sats

34. Right shift • Decreased affinity for O2 • At any PO2, sat % is decreased • Harder to “hook-on” • Easy to “un-hook”

35. Clinical situations • Acidosis, hypercapnia, hyperthermia • Elevated DPG • Hyperthyroidism, anemia, chronic hypoxia

36. Clinical example • 25 yo with ARDS • Secondary to staph pneumonia • 100% O2, PPV

37. ABGs • pH = 7.27, PaCO2 = 51.2 mm/hg • PO2 = 40 mm/hg, HCO3 = 23.6 mEq/L • O2 Sat = 76.2%, Temp =39.7

38. Clinical example • Right shift is protective if additional O2 is given

39. Summary • The curve helps us appreciate factors that affect the oxygenation status of critical patients. • http://www.ventworld.com/resources/oxydisso/oxydisso.html • http://en.wikipedia.org/wiki/Arterial_blood_gas

40. Summary • Diseases or treatments shift the curve • Understanding allows for more appropriate interventions