"New Perspectives in Blood Gas Measurement, Assessment and Interpretation"

1. "New Perspectives in Blood Gas Measurement, Assessment and Interpretation" William J Malley, M.S., RRT, CPFT

4. “Blood gas and pH analysis has more immediacy and potential impact on patient care than any other laboratory determination.” • National Committee for Clinical Laboratory Standards (NCCLS)

5. OUTLINE • 1) Review pre-analytical ABG issues and consequences of improper technique. • 2) Discuss the value of temperature correction of ABG’s. • 3) Use case studies to highlight some key clinical concepts. • 4) Explore appropriate clinical ABG targets in different clinical scenarios.

7. Interactive

8. Sample Handling

9. Icing blood gas samples Routine arterial blood gases in plastic syringes should be iced if they will be run within 30 minutes. Yes/No

10. Rationale for Icing • To minimize the effect of metabolism of living tissue

11. .No NCCLS. Blood gas and pH analysis and related measurements. C46-A, 2001

12. Icing blood gas samples PaO2 decreased in a linear fashion when measured up to 30 minutes after the blood sample in a plastic syringe had been placed in an ice-water bath. YES/NO

13. Factors which could theoretically impact results: • 1) Metabolism • 2) Diffusion of gases between the sample and the ambient gas • 3) The change in gas solubility due to the temperature decrease

14. No…PaO2 actually increased Liss, HP, Payne, CB. Stability of blood gases in ice and at room temperature. Chest 103:1120, 1993.

15. Icing blood gas samples when also measuring electrolytes Potassium will tend to be higher in iced samples or samples sent through pneumatic tubes. Yes/No

16. Factors which may falsely elevate plasma potassium levels • Hemolysis • Physical Stress on sample • Icing • Pneumatic Tubes

17. Yes

18. Learning Styles “I learn best least from facts and figures and most from pictures and stories!”

20. A 38 y.o. female patient is admitted to the emergency department with severe pneumonia and a temperature of 41oC. • ARTERIAL BLOOD GASES • SaO2 85% • pH 7.30 • PaCO2 41 mm Hg • PaO2 62 mm Hg • [HCO3] 25 mEq/L • (data has been temp corrected to 410C)

21. Oxygenation status of this patient is satisfactory. • Yes/No

23. NO!

24. ARTERIAL BLOOD GASES • SaO2 86% 69% • pH 7.24 7.30 • PaCO2 41 mm Hg 32 mm Hg • PaO2 62 mm Hg 40 mm Hg • [HCO3] 17 mEq/L15 mEq/L • 41oC 37oC

26. A 51 y.o. male with severe leukemia has a blood gas drawn. He is also on a pulse oximeter which is reading 92%. • ARTERIAL BLOOD GASES • SaO2 85% • pH 7.36 • PaCO2 37 mm Hg • PaO2 50 mm Hg • [HCO3] 25 mEq/L

27. The patient must have carboxyhemoglobinemia which is not being picked up by the pulse oximeter. • Yes/No

28. KEY OBSERVATIONS • Pulse oximetry reading is satisfactory. • There is a discrepancy between the pulse oximeter reading and the PaO2 • The patient has leukemia

29. NO Haynes JM, A case of disparity between pulse oximetry measurements and blood gas analysis values, Resp Care 49,1059-60, 2004

31. A 55 year old male patient in the burn unit suffers a cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate. • ARTERIAL BLOOD GASES • SaO2 91% • pH 7.52 • PaCO2 47 mm Hg PaO2 63 mm Hg • [BE] -11 mEq/L

32. BICARBONATE THERAPY • Bicarbonate therapy for metabolic acidosis should be directed primarily at the negative base excess. • YES/NO

33. BICARBONATE THERAPY • May be indicated is metabolic acidosis but is controversial

34. NO

35. A 55 year old male patient in the burn unit suffers a cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate. • ARTERIAL BLOOD GASES • SaO2 91% • pH 7.52 • PaCO2 47 mm Hg PaO2 63 mm Hg • [BE] -11 mEq/L

36. Blood Gas Interpretation • The blood gas reported is impossible. • Yes/NO

37. If you know two of the three acid-base variables (pH- HCO3- PaCO2)you know the third!

38. Arterial Blood Gas • pH 7.55 • PaCO2 40 mm Hg • [HCO3] ?

39. Blood Gas Interpretation • The blood gas reported is impossible. • Yes/NO

40. Yes

42. ARTERIAL BLOOD GASES • SaO2 91% • pH 7.52 • PaCO2 47 mm Hg PaO2 63 mm Hg • [BE] +11 mEq/L

44. A 25 year old female patient arrives in the emergency room in a coma. • ARTERIAL BLOOD GASES • SaO2 85% • pH 7.16 • PaCO2 80 mm Hg PaO2 52 mm Hg • [BE] blood - 4 mEq/L • [HCO3] 28 mEq/L

45. METABOLIC INDICES • It is impossible to have an elevated plasma bicarbonate with a decreased base excess of the blood. • YES/NO

46. METABOLIC INDICES • HYPERCAPNIA CAUSES • Increased bicarbonate via the hydrolysis reaction • Decreased blood base excess because of in vivo – in vitro discrepancies in calculation

47. NO

49. Arterial Blood Gases • pH 7.38 • PaCO2 73 mm Hg • [HCO3] 42 mEq/L • [K] 2.8 mEq/L

50. COPD • This blood gas represents a compensated respiratory acidosis. • YES/NO