The document provides an overview of acid-base disorders and interpreting arterial blood gases (ABGs). It discusses the Henderson-Hasselbalch equation, compensation mechanisms, normal ABG ranges, and a step-by-step approach to analyzing ABGs. This includes checking the pH, pCO2, selecting the appropriate compensation formula, evaluating anion gap, delta-delta ratio, and urine pH to differentiate primary from combined acid-base disorders. Several case examples are then presented and analyzed using this approach.

1. ABG seriesANAS SAHLE , MDDAMASCUSE HOSPITAL

2. MORE FORESTSMORE OXYGENLONGER LIFE

3. Acid-Base Disorders and the ABG 1

4. OUTLINEACID-BASE DISORDERSHIGH AG METABOLIC ACIDOSISNORMAL AG METABOLIC ACIDOSISMETABOLIC ALKALOSISOXYGENATION AXIESA-a GRADIENT

5. ABG - IntroductionBlood 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

10. Blood Gas ReportAcid-Base InformationpH

11. PCO2

12. HCO3 [calculated vs measured]Oxygenation InformationPO2 [oxygen tension]

13. SO2 [oxygen saturation]Normal RangesPaO2 >80mm HgIn supine posture PaO2=109-(0.43 Х age)PaO2=100mmHg in 10 year old child, PaO2 falls approximately 5mmHG for every 10 years upto 90 years.5 mmHg higher in the sitting position that supine position

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

15. Anticoagulant effects0.05ml 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 airInitially PaCO2 falls, In extreme dilution pH and bicarbonate fallsPaO2 usually unchanged.

16. Time delay - metabolismSamples 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 DisordersAs dictated by the Henderson-Hasselbalch equation, disturbances in either the respiratory component (pCO2) or metabolic component (HCO3-) can lead to alterations in pH.

22. CompensationWhen 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 directlyHCO3-, O2 saturation (usually) – Calculated from pH, pCO2, and pO2

25. Practical Approach1. Check the pHIf 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 Approach2. Check the pCO2pH < 7.37 and pCO2 < 40  metabolic acidosispH < 7.37 and pCO2 > 40  respiratory acidosispH > 7.43 and pCO2 < 40  respiratory alkalosispH > 7.43 and pCO2 > 40  metabolic alklosis

27. Practical Approach3. Choose the appropriate compensation formula

28. Practical Approach4. Determine if the degree compensation is appropriate(If it isn’t, a second acid-base disorder is likely present)

29. Practical Approach5. 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 Approach6. 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 Approach7. If a metabolic acidosis is present, check the urine pH.Urine pH > 6.0 in the setting of an acidosis  Suggests RTA

32. Practical Approach8. Generate a differential diagnosisIf 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 ABGsCheck the pHCheck the pCO2Select the appropriate compensation formulaDetermine if compensation is appropriateCheck the anion gap AG=NA – (HCO3 + CL):12If the anion gap is elevated, check the delta-deltaG:G Ratio =Δ AG (12-AG m) \Δ HCO3 (24-HCO3 m)If a metabolic acidosis is present, check urine pHGenerate a differential diagnosis

36. Gap:gap ratio??

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

39. Case 1A 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 1RESPIRATORY ACIDOSIS

41. Case 2A 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 1.4Urine pH: 5.0

42. APPROCHE 2Normal AG METABOLIC ACIDOSIS

43. Case 3A 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 3RESPIRATORY ALKALOSIS

45. Case 4A 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- 33Urine pH: 5.8

46. APPROCHE 4Pure metabolic Alkalosis

47. Case 5A 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- 15Urine pH: 5.0

48. APPROCHE 5Respiratory Aci+High AG Metabolic Aci