1. Clinical Aspect of Interpretation of Blood Gas Analysis For medical students of PUMC Class 1999, Sept. 15, 2003

2. What Does Arterial Blood Gas (ABG) Measure ?

3. Pulmonary function tests are concern with ventilation: the movement of air into and out of the lung

4. MIXED VENOUS BLOOD pH 7.36 PCO 2 46 mmHg PO 2 40 mmHg SO 2 75% pH 7.40 PCO 2 40 mmHg PO 2 95 mmHg SO 2  95% ARTERIAL BLOOD External Respiration Internal Respiration

6. Alveolar Ventilation Equation Inverse relationship between V A and P a CO 2

8. Henderson-Hasselbalch Equation The relationship between pH, P a CO 2 , HCO 3 -

11. Henderson-Hasselbalch Equation The relationship between pH, P a CO 2 , HCO 3 -

12. Case 1: normal

13. Case 1: normal

14. Case 1: normal

15. Case 1: normal

16. Case 1: normal

17. Case 2 Uncompensated Respiratory Acidosis

18. Case 2 Uncompensated Respiratory Acidosis

19. Case2 Uncompensated Respiratory Acidosis

20. Case 2 Uncompensated Respiratory Acidosis

21. Case 3 Compensated Respiratory Acidosis

22. Case3 Compensated Respiratory Acidosis

23. Case 3 Compensated Respiratory Acidosis PEARL: The compensations of either the renal system or the respiratory system can never be complete.

24. Clinically Relevant Parameters (1) Through the years, opinions have changed regarding what are the most clinically relevant parameters. Today, for a nearly complete description of the oxygenation, ventilation, and acid-base status, pH, PaCO 2 , PaO 2 and actual HCO 3 - are generally sufficient.

25. Clinically Relevant Parameters (2) Indeed, the literature or text book contains literally several parameters, i.e. standard HCO 3 - , buffer base (BB), base excess (BE) from in vitro measures. Because intro and in vivo changes in response to hypercapnia are different, their actual clinical benefit is limited. Burton GG, Hodgkin JE, Ward JJ. Respiratory care: A guide to clinical practice. 1997, 260-265.

30. Normal Range of Arterial Blood Gases

31. Interpretation of Arterial Blood Gases

33. Air Contamination of Sample

39. Step 5 Oxygenation? Is P a O 2 within normal limits of 80 to 100 mm Hg? If P a O 2 < 50 mm Hg, severe hypoxemia is present.

40. The Hypoxemic State Hypoxemia is defined as PaO2 < 80 mm Hg while breathing room air. When patients are already on oxygen it is not necessary and may be dangerous to interrupt the oxygen therapy to assess hypoxemia.

41. Step 6 Correlated with clinical picture? Are blood gas results consistent with patient's clinical status?

46. Case 5 A patient referred to PFT Lab. for shortness of breath

47. Case 5 pH 7.28 HCO 3 - 25.8 mEq/L PCO 2 51 mm Hg PO 2 55 mm Hg What is your interpretation?

48. Case 6 A 17 y/o diabetic, entered Emergency with Kussmaul breathing

49. Case 6 Interpretation? pH 7.05 HCO 3 - 5 mEq/L PCO 2 12 mm Hg PO 2 108 mm Hg

50. Case 7 34 y/o female, entered Emergency in coma, drug overdose suspected

51. Case 7 pH 7.15 HCO 3 - 28 mEq/L PCO 2 80 mm Hg PO 2 42 mm Hg What is your interpretation?

52. Case 8 A 63 y/o male, admitted for elective knee surgery

53. Case 8 pH 7.36 BP 122/84 PCO 2 46 mm Hg P 80, regular PO 2 41 mm Hg RR 15/min Preoperative blood gas

55. Summary Since arterial blood gas analysis is the reflection of efficiency or inefficiency of several organ systems, proper interpretation is essential in the care of critically ill patients.