The document discusses arterial blood gas analysis, which provides information on oxygenation, ventilation, and acid-base balance. It outlines the key parameters measured in an ABG test and strategies for interpreting the results, including evaluating for respiratory or metabolic causes of acid-base imbalances and hypoxemia. Several case studies are presented to demonstrate interpreting ABG values in the context of patients' clinical presentations.

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

5. What Information Does Arterial Blood Gas provide? Arterial oxygenation Alveolar ventilation Respiratory/metabolic acid-base balance Carboxyhemoglobin levels

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

7. Arterial Blood Gas Analysis Indications Evaluate adequacy of lung function Ventilation, acid-base status Oxygenation Determine need for supplemental O 2 Monitor ventilatory support Document severity or progression of known pulmonary disease Diagnose the toxicity of CO

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

9. Why the assessment of a single buffer system is adequate despite multiple buffer systems? Bicarbonate buffer system: of primary importance, open system in communication with external environment via kidneys Hemoglobin buffer: of second importance Phosphate buffer system Plasma protein buffer system All buffer systems are linked together through H +

10. Why the assessment of carbonic acid is adequate? Each day our body produces large amount of acid from metabolism. 99% of the total acid is in the form of CO 2 . Only 1% is fixed acid

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.

26. Primary Respiratory Acidosis Initiating event: hypoventilation Resultant effects: CO 2 retention Compensation: HCO 3 - retention via renal system

27. Primary Respiratory Alkalosis Initiating event: hyperventilation Resultant effects: CO 2 elimination Compensation: HCO 3 - elimination via renal system

28. Primary Metabolic Acidosis Initiating event: renal, extrarenal Resultant effects: HCO 3 - deficit Compensation: CO 2 elimination via respiratory system

29. Primary Metabolic Alkalosis Initiating event: renal, extrarenal Resultant effects: HCO 3 - increase Compensation: CO 2 retention via respiratory system

30. Normal Range of Arterial Blood Gases

31. Interpretation of Arterial Blood Gases

32. Interpretation Strategies Step 1 Was the blood gas specimen obtained acceptably? Free of air bubbles and clots? Analyzed promptly and/or iced properly?

33. Air Contamination of Sample

34. Step 2 Did the blood gas analyzer function properly? Was there a recent acceptable calibration of all electrodes? Was analyzer function validated by appropriate quality control?

35. Data Quality in Blood Gases Acceptability criteria of AARC Blood collected anaerobically The specimen adequately anticoagulated A 2-4 ml sample recommended The specimen analyzed in a few minutes, otherwise stored in ice within 1 hour Equipment calibration and quality control The specimen adequately identified

36. Step3 Determine acid-base imbalance The normal limits of pH is 7.35 - 7.45. If below 7.35, acidosis is present; If above 7.45, alkalosis is present. Otherwise look for compensation. Is pH within normal limits?

37. Step 4 the cause of acid-base imbalance? Respiratory? If PCO 2 >45 and pH <7.35, respiratory acidosis. If PCO 2 >45 and pH 7.35-7.45, then compensated respiratory acidosis If PCO 2 <35 and pH >7.45, respiratory alkalosis If PCO 2 <35 and pH 7.35-7.45, then compensated respiratory alkalosis

38. Step 4 the cause of acid-base imbalance? Metabolic? If HCO 3 - <22 and pH <7.35, metabolic acidosis. If HCO 3 - <22 and pH 7.35-7.45, then compensated metabolic acidosis If HCO 3 - >27 and pH >7.45, metabolic alkalosis If HCO 3 - >27 and pH 7.35-7.45, then compensated metabolic alkalosis

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?

42. Case 1 pH 7.35 PCO 2 30 mm Hg HCO 3 - 16 mEq/L What is your interpretation?

43. Case 2 pH 7.45 PCO 2 30 mm Hg HCO 3 - 20 mEq/L What is your interpretation?

44. Case 3 pH 7.55 PCO 2 27 mm Hg HCO 3 - 23 mEq/L PO 2 104 mm Hg Get the plastic bag out!!! What is your interpretation?

45. Case 4 pH 7.30 PCO 2 34 mm Hg HCO 3 - 24 mEq/L Get the technician out!!! What is your interpretation?

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

54. Suggested panic values of ABG pH < 7.20 pH > 7.60 PaCO 2 > 65mmHg (check pH and HCO 3 - to see compensation) PaO 2 < 50mmHg (exception: congenital cardiac malformations) COHb > 20% MetHb > 10%

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.