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1. ABG series ANAS SAHLE , MD DAMASCUSE HOSPITAL

2. MORE FORESTSMORE OXYGENLONGER LIFE

3. Acid-Base Disorders and the ABG 1

4. OUTLINE ACID-BASE DISORDERS HIGH AG METABOLIC ACIDOSIS NORMAL AG METABOLIC ACIDOSIS METABOLIC ALKALOSIS OXYGENATION AXIES A-a GRADIENT

5. ABG - Introduction Blood gas and pH analysis has more immediacy and potential impact on patient care than any other laboratory determination.(National committee for Laboratory Standards). Cornerstone in the diagnosis & management of clinical oxygenation and acid-base disturbances. Of all the concepts employed in the diagnosis and treatment of respiratory disorders, few are more important or less well understood than those of blood gas interpretation.

6. Getting an arterial blood gas sample

11. PCO2

14. Sampling errors -Air contamination Most important change: PaO2 tends to increase towards 158mm Hg, Less significant change: PaCO2 falls, pH rises All air bubbles should be expelled immediately All samples with visually apparent froth should be discarded.

15. Anticoagulant effects 0.05ml of heparin(1,000units/ml) is required to anticoagulate 1 ml of blood. Dead space of a standard 5ml syringe with 22G needle is 0.2ml; i.e. filling the syringe dead space with heparin provides sufficient volume to anticoagulate a 4ml blood sample. Heparin – weak acid equilibrated with room air Initially PaCO2 falls, In extreme dilution pH and bicarbonate falls PaO2 usually unchanged.

16. Time delay - metabolism Samples should be analyzed within 20 min to avoid error. Placing the sample in iced water slows metabolism to 10%.

17. EXPECTED CHANGES IN ACID-BASE DISORDERS From: THE ICU BOOK - 2nd Ed. (1998) [Corrected]

18. Overview of Acid-Base Physiology

19. Henderson-Hasselbalch Equation

20. Renal Regulation of Acid-Base

21. Primary Acid-Base Disorders As dictated by the Henderson-Hasselbalch equation, disturbances in either the respiratory component (pCO2) or metabolic component (HCO3-) can lead to alterations in pH.

22. Compensation When a primary acid-base disorder exists, the body attempts to return the pH to normal via the “other half” of acid base metabolism. Primary metabolic disorder  Respiratory compensation Primary respiratory disorder  Metabolic compensation

23. Compensation (continued)

24. The Arterial Blood Gas (ABG) pH, pCO2, pO2 – Measured directly HCO3-, O2 saturation (usually) – Calculated from pH, pCO2, and pO2

25. Practical Approach 1. Check the pH If the pH < 7.37, acidemia (and at least 1 acidosis) is present. If the pH > 7.43, alkalemia (and at least 1 alkalosis) is present.

26. Practical Approach 2. Check the pCO2 pH < 7.37 and pCO2 < 40  metabolic acidosis pH < 7.37 and pCO2 > 40  respiratory acidosis pH > 7.43 and pCO2 < 40  respiratory alkalosis pH > 7.43 and pCO2 > 40  metabolic alklosis

27. Practical Approach 3. Choose the appropriate compensation formula

28. Practical Approach 4. Determine if the degree compensation is appropriate (If it isn’t, a second acid-base disorder is likely present)

29. Practical Approach 5. Calculate the anion gap Anion gap = [Na+] – ( [Cl-] + [HCO3-] ) If the anion gap is elevated, an elevated gap metabolic acidosis is likely present.

30. Practical Approach 6. If an elevated gap acidosis is present, calculate the delta-delta ratio, to determine if a second metabolic disorder is present. Delta–Delta = Measured anion gap – Normal anion gap Normal [HCO3-] – Measured [HCO3-]

31. Practical Approach 7. If a metabolic acidosis is present, check the urine pH. Urine pH > 6.0 in the setting of an acidosis  Suggests RTA

32. Practical Approach 8. Generate a differential diagnosis If multiple disorders are present, they may be: All related to the same process All independent of one another

33. Differential Diagonsis for Acid-Base Disorders

34. Summary of the Approach to ABGs Check the pH Check the pCO2 Select the appropriate compensation formula Determine if compensation is appropriate Check the anion gap AG=NA – (HCO3 + CL):12 If the anion gap is elevated, check the delta-delta G:G Ratio =Δ AG (12-AG m) HCO3 (24-HCO3 m) If a metabolic acidosis is present, check urine pH Generate a differential diagnosis

36. Gap:gap ratio??

38. AGc=AG +(2,5(4-alb)) Expected PCO2

39. Case 1 A 26 year old man with unknown past medical history is brought in to the ER by ambulance, after friends found him unresponsive in his apartment. He had last been seen at a party four hours prior. ABG: pH 7.25 Chem 7: Na+ 137 PCO2 60 K+ 4.5 HCO3- 26 Cl- 100 PO2 55 HCO3- 25

40. APPROCHE 1 RESPIRATORY ACIDOSIS

41. Case 2 A 67 year old man with diabetes and early diabetic nephropathy (without overt renal failure) presents for a routine clinic visit. He is currently asymptomatic. Because of some abnormalities on his routine blood chemistries, you elect to send him for an ABG. ABG: pH 7.35 Chem 7: Na+ 135 PCO2 34 K+ 5.1 HCO3- 18 Cl- 110 PO2 92 HCO3- 16 Cr 1.4 Urine pH: 5.0

42. APPROCHE 2 Normal AG METABOLIC ACIDOSIS

43. Case 3 A 68 year old woman with metastatic colon cancer presents to the ER with 1 hour of chest pain and shortness of breath. She has no known previous cardiac or pulmonary problems. ABG: pH 7.49 Chem 7: Na+ 133 PCO2 28 K+ 3.9 HCO3- 21 Cl- 102 PO2 52 HCO3- 22

44. APPROCHE 3 RESPIRATORY ALKALOSIS

45. Case 4 A 6 year old girl with severe gastroenteritis is admitted to the hospital for fluid rehydration, and is noted to have a high [HCO3-] on hospital day #2. An ABG is ordered: ABG: pH 7.47 Chem 7: Na+ 130 PCO2 46 K+ 3.2 HCO3- 32 Cl- 86 PO2 96 HCO3- 33 Urine pH: 5.8

46. APPROCHE 4 Pure metabolic Alkalosis

47. Case 5 A 75 year old man with morbid obesity is sent to the ER by his skilled nursing facility after he developed a fever of 103° and rigors 2 hours ago. In the ER he is lucid and states that he feels “terrible”, but offers no localizing symptoms. His ER vitals include a heart rate of 115, and a blood pressure of 84/46. ABG: pH 7.12 Chem 7: Na+ 138 PCO2 50 K+ 4.2 HCO3- 13 Cl- 99 PO2 52 HCO3- 15 Urine pH: 5.0

48. APPROCHE 5 Respiratory Aci+High AG Metabolic Aci

49. Case 6 A 25 year old man with type I diabetes presents to the ER with 24 hours of severe nausea, vomiting, and abdominal pain. ABG: pH 7.15 Chem 7: Na+ 138 PCO2 30 K+ 5.6 HCO3- 10 Cl- 88 PO2 88 HCO3- 11 Cr 1.1 Urine pH: 5.0

50. APPROCHE 6 HIGH AG Metabolic.Acidosis + RESPIRATORY ACIDOSIS

51. Case 7 A 62 year old woman with severe COPD comes to the ER complaining of increased cough and shortness of breath for the past 12 hours. There are no baseline ABGs to compare to, however, her HCO3- measured during a routine clinic visit 3 months ago was 34 mEq/L. ABG: pH 7.21 Chem 7: Na+ 135 PCO2 85 K+ 4.0 HCO3- 33 Cl- 90 PO2 47 HCO3- 34 Urine pH 5.5

52. APPROCHE 7 CHRONIC RES.ACI + NORMAL AG MET.ACI

53. Case 8 A 36 year old man with a history of alcoholism is brought to the ER after being found on the floor of his apartment unresponsive, soiled with vomit, and with an empty pill bottle nearby. ABG: pH 7.03 Chem 7: Na+ 134 PCO2 75 K+ 5.2 HCO3- 19 Cl- 90 PO2 48 HCO3- 20 Urine pH 5.0

54. APPROCHE 8 RES.AC+High AG MET.AC +concomitant M.ALK