OXYHEMOGLOBIN DISSOCIATION CURVE

1. OXYHEMOGLOBIN DISSOCIATION CURVE Chemeketa Community College

2. Oxygen-hemoglobin dissociation curve

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

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

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

6. 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 harder it becomes to bind

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

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

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

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

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

14. Oxygen-hemoglobin dissociation curve

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

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

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

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

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

20. Relationship of hemoglobin sat. and pH

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

22. Relationship of hemoglobin sat. and Temperature

23. 2,3 DPG (diphosphoglycerate) • An enzyme that affects binding directly • Competes with oxygen

24. 2,3 DPG (diphosphoglycerate) • More 2,3 DPG =decreased affinity • Less = increased affinity

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

26. Abnormal Hemoglobin • May have greater or lesser affinity

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

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

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

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

31. 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

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

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

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

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

36. 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

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

38. Summary • The curve helps us appreciate factors that affect the oxygenation status of critical patients. • http://www.ventworld.com/resources/oxydisso/oxydisso.html

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