1. INTERPRETATION OF ABG ASMAA MOHAMMAD M.D.

2. Interpretation of the ABG  Arterial blood gas analysis is an essential part of diagnosing and managing a patient’s oxygenation status and acid-base balance.  The usefulness of this diagnostic tool is dependent on being able to correctly interpret the results.

3. Now that I have this data, what does it mean? ----- XXXX Diagnostics ------ Blood Gas Report Measured37.0 o C pH7.463 pCO 2 44.4 mm Hg pO 2 113.2mm Hg Na+ 135 mmol / L K+ 3.5 mmol / L Ca++ 0.23 mmol / L Hct 6 % Derived parameters Ca++ 1.2 mmol / L HCO 3 act31.1 mmol / L HCO 3 std30.5mmol / L BE6.6mmol / L O 2 CT14.7mL / dl O 2 Sat98.3% ct CO 2 32.4mmol / L pO 2 (A - a)32.2mm Hg pO 2 (a / A)0.79 THbc 5 gm/dl

4. ----- XXXX Diagnostics ------ Blood Gas Report Measured37.0 o C pH7.463 pCO 2 44.4 mm Hg pO 2 113.2mm Hg Na+ 135 mmol / L K+ 3.5 mmol / L Ca++ 0.23 mmol / L Hct 6 % Derived parameters Ca++ 1.2 mmol / L HCO 3 act31.1 mmol / L HCO 3 std30.5mmol / L BE6.6mmol / L O 2 CT14.7mL / dl O 2 Sat98.3% ct CO 2 32.4mmol / L pO 2 (A - a)32.2mm Hg pO 2 (a / A)0.79 THbc 5 gm/dl ----- XXXX Diagnostics ------ Blood Gas Report Measured37.0 o C pH7.463 pCO 2 44.4 mm Hg pO 2 113.2mm Hg Na+ 135 mmol / L K+ 3.5 mmol / L Ca++ 0.23 mmol / L Hct 6 % Derived parameters Ca++ 1.2 mmol / L HCO 3 act31.1 mmol / L HCO 3 std30.5mmol / L BE6.6mmol / L O 2 CT14.7mL / dl O 2 Sat98.3% ct CO 2 32.4mmol / L pO 2 (A - a)32.2mm Hg pO 2 (a / A)0.79 THbc 5 gm/dl Oxygenation status Acid Base Balance

5. pH HCO3 PCO2

6. Basic Concepts  The pH is a measurement of the acidity or alkalinity of the blood.  It is inversely proportional to the number of hydrogen ions (H+) in the blood.  The pH of a solution is measured on a scale from 1 (very acidic) to 14 (very alkalotic).

7. CO 2 CHANGES pH in opposite direction Primary lesion compensation pH HCO 3 CO 2 METABOLIC ACIDOSIS HYPER VENTILATION BICARB CHANGES pH in same direction LOW pCO 2 LOW pH LOW HCO3 Low Alkali

8. CO 2 CHANGES pH in opposite direction Primary lesion compensation pH HCO3 CO 2 METABOLIC ALKALOSIS HYPO VENTILATION BICARB CHANGES pH in same direction HIGH CO2 HIGH pH HIGH HCO3 High Alkali

9. CO 2 CHANGES pH in opposite direction Primary lesion compensation pH CO 2 HCO3 RESPIRATORY ACIDOSIS HIGH HCO3 LOW pH HIGH pCO2 High CO 2

10. CO 2 CHANGES pH in opposite direction Primary lesion compensation pH CO 2 HCO3 RESPIRATORY ALKALOSIS LOW HCO3 HIGH pH LOW pCO2 Low CO 2

11. Acidic or Alkalotic  pH 7.0  pH 7.9  pH 7.4  pH 7.5  pH 7.3 ACIDEMIA ALKALEMIA NORMAL ALKALEMIA ACIDEMIA (pH: 7.35-7.45)

12. Interpreting pCO2 values  pCO2 of 22  pCO2 of 32  pCO2 of 35  pCO2 of 40  pCO2 of 45  pCO2 of 50 ALKALOSIS NORMAL ACIDOSIS (pCO2=35-45mmHg)

13. Interpreting HCO3 Values  HCO3 of 22  HCO3 of 16  HCO3 of 30  HCO3 of 25  HCO3 of 12  HCO3 of 27 NORMAL ACIDOSIS ALKALOSIS NORMAL ACIDOSIS ALKALOSIS (HCO3=22-26 meq)

14. Steps of interpretation  Step One Identify whether the pH, pCO2 and HCO3 are abnormal. For each component, label it as “normal”, “acid” or “alkaline”. The two matching values determine what the problem is.

15. Steps of interpretation  Step Two If the ABG results are abnormal, determine if the abnormality is due to the kidneys (metabolic) or the lungs (respiratory).

16. PHPCO2HCO3INTERPRETATION 7.305526 ACIDIC NORMAL Respiratory Acidosis 7.504233 ALKALINENORMAL ALKALINE Metabolic Alkalosis

17. PHPCO2HCO3INTERPRETATION 7.313917 ACIDIC NORMAL ACIDIC Metabolic Acidosis 7.503024 ALKALINE NORMAL Respiratory Alkalosis

18. PHPCO2HCO3INTERPRETATION 7.414024 NORMAL Normal ABG 7.54235 ALKALINE NORMAL ALKALINE Metabolic Alkalosis Respiratory Acidosis 7.246524 ACIDIC NORMAL

19. PHPCO2HCO3INTERPRETATION 6.72405 ACIDIC NORMAL ACIDIC Metabolic Acidosis 7.266325 ACIDIC NORMAL Respiratory Acidosis Respiratory Alkalosis 7.521825 ALKALINE NORMAL

20. PH 7.38 PCO2 56 HCO3 35 Normal Alkalosis Acidosis CompensatedAcidosisRespiratory Acidosis when both the pCO2 and HCO3 are abnormal use a single value of 7.40 as “ normal ”

21. Key Concept:  Sometimes, the system that is compensating (respiratory or metabolic) may either have not had sufficient time to correct the situation, or is unable to completely compensate for the degree of abnormality present.

22. pH HCO 3 CO 2 7.20 15 40 7.25 15 30 7.37 15 20 pH HCO 3 CO 2 7.20 15 40 7.25 15 30 7.37 15 20 Un Compensated Partially Compensated Fully Compensated (Attempt+pH abnormal) (pH in normal range) N (No attempt +pH abnormal)

23. Expected changes in pH and HCO 3 - for a 10-mm Hg change in PaCO 2 ACUTE CHRONIC Resp Acidosis pH ↓ by 0.07 pH ↓ by 0.03 HCO 3 - ↑ by 1 HCO 3 - ↑ by 3 - 4 Resp Alkalosis pH ↑ by 0.08 pH ↑ by 0.03 HCO 3 - ↓ by 2 HCO 3 - ↓ by 5

24. Case 1  A diabetic presents with diarrhea and cough. CXR reveals an infiltrate.  pH: 7.31  pCO2: 10  HCO3: 5  Na 123; Cl 99.

25.  Step 1: Acidemic or Alkalemic ? Acidemia  Step 2: Primary respiratory or metabolic ? Metabolic pH: 7.31pCO2: 10 HCO3: 5 Na: 123 Cl: 99

26.  Step 3: Compensation appropriate? pH abnormal: Partially compensated 1.5(HCO3) + 8 = ±2 = pCO2? No, pCO2 less than expected. = additional respiratory alkalosis. pH: 7.31pCO2: 10HCO3: 5Na: 123 Cl: 99 15.5

27.  Step 4: AGMA? AG= Na – (Cl + HCO3) = 12 ± 4 mEq/L 123 – (99 + 5) = 9 pH: 7.31pCO2: 10HCO3: 5Na: 123 Cl: 99

28. Case 2  An alcoholic presents with vomiting.  pH: 7.20  pCO2: 25  HCO3: 10  Na: 130  Cl: 80

29.  Step 1: Acidemic or Alkalemic ? Acidemia  Step 2: Primary respiratory or metabolic ? Metabolic pH: 7.20pCO2: 25 HCO3: 10 Na: 130 Cl: 80

30.  Step 3: Compensation appropriate? pH abnormal: Partially compensated 1.5(HCO3) + 8 = 23 ±2 = pCO2? Yes, pCO2 value is expected. pH: 7.20pCO2: 25HCO3: 10Na: 130 Cl: 80

31.  Step 4: AGMA? AG = Na – (Cl + HCO3) = ± 12 130 – (80 + 10) = 40 AGMA pH: 7.20pCO2: 25HCO3: 10Na: 130 Cl: 80

32. Pulmonary gas exchange

33. Oxygenation pCO2 Indicate ventilation Po2 free oxygen molecules dissolved in plasma O 2 Content of blood: (Hb x1.34x O 2 Sat + 0.003x Dissolved O 2 ) Remember Hemoglobin Oxygen Saturation: ( remember this is calculated …error prone) Alveolar / arterial gradient: ( classify respiratory failure) Blood Gas Report Measured 37.0 0 C pH 7.452 pCO2 45.1 mm Hg pO2 112.3 mm Hg Corrected 38.6 0 C pH 7.436 pCO2 47.6 pCO2 47.6 mm Hg pO2 122.4 pO2 122.4 mm Hg Calculated Data HCO3 act 31.2 mmol / L HCO3 std 30.5 mmol / L B E 6.6 mmol / L O2 ct 15.8 mL / dl O2 Sat 98.4 % ct CO2 32.5 mmol / L pO2 (A -a) 30.2 mm Hg  pO2 (a/A) 0.78

34. OXYGEN PRESSURE: PaO2  Since PaO 2 reflects only free oxygen molecules dissolved in plasma and not those bound to hemoglobin, PaO 2 cannot tell us “how much” oxygen is in the blood; for that you need to know how much oxygen is also bound to hemoglobin, information given by the SaO 2 and hemoglobin content.

35. OXYGEN SATURATION: SaO 2  The percentage of all the available heme binding sites saturated with oxygen is the hemoglobin oxygen saturation (in arterial blood, the SaO 2 ). Note that SaO 2 alone doesn’t reveal how much oxygen is in the blood; for that we also need to know the hemoglobin content.

36. OXYGEN CONTENT: CaO 2 CaO 2 = (Hb x 1.34 x SaO 2 ) + (.003 x PaO 2 ) Neither the PaO 2 nor the SaO 2 provide information on the number of oxygen molecules, i.e., how much oxygen is in the blood. Only CaO 2 (units ml O 2 /dl) tells us how much oxygen is in the blood; this is because CaO 2 is the only value that incorporates the hemoglobin content.

37. Test Your Overall Understanding case 1 A 55-year-old man is evaluated in the pulmonary lab for shortness of breath. His regular medications include a diuretic for hypertension and one aspirin a day. He smokes a pack of cigarettes a day. FIO 2.21HCO 3 - 30 mEq/L pH 7.53%COHb 7.8% PaCO 2 37 mm HgHb 14 gm% PaO 2 62 mm HgCaO 2 16.5 ml O 2 /dl SaO 2 87%

38. OXYGENATION: The PaO 2 and SaO 2 are both reduced on room air. Since P(A-a)O 2 is elevated (approximately 43 mm Hg), the low PaO 2 can be attributed to V-Q imbalance, i.e., a pulmonary problem. SaO 2 is reduced, in part from the low PaO 2 but mainly from elevated Co Hb. The arterial oxygen content is adequate. VENTILATION: Adequate; the patient is neither hyper- nor hypo-ventilating. Case 1 – Discussion

39. ACID-BASE: Elevated pH and HCO 3 - suggest a state of metabolic alkalosis, most likely related to the patient's diuretic; his serum K + should be checked for hypokalemia.

40. Test Your Overall Understanding Test Your Overall Understanding Case 2 A 46-year-old man has been in the hospital two days with pneumonia. He was recovering but has just become diaphoretic, dyspneic, and hypotensive. He is breathing oxygen through a nasal cannula at 3 l/min.

41. Test Your Overall Understanding Test Your Overall Understanding Case 2 pH 7.40 PaCO 2 20 mm Hg PaO 2 80 mm Hg SaO 2 95% Hb13.3 gm% HCO3-12 mEq/L CaO217.2 ml O2/dl %COHb1.0%

42. OXYGENATION: The PaO 2 is lower than expected for someone hyperventilating to this degree and receiving supplemental oxygen, and points to significant V-Q imbalance. The oxygen content is adequate. VENTILATION: PaCO 2 is half normal and indicates marked hyperventilation. Case 2 – Discussion

43.  ACID-BASE:  Normal pH with very low bicarbonate and PaCO 2 indicates combined respiratory alkalosis and metabolic acidosis.  If these changes are of sudden onset, the diagnosis of sepsis should be strongly considered, especially in someone with a documented infection.

44. Test Your Overall Understanding Test Your Overall Understanding Case 3 A 58-year-old woman is being evaluated in the emergency department for acute dyspnea. FIO 2.21 pH 7.19 PaCO 2 65 mm Hg %COHb1.1% PaO 2 45 mm Hg SaO 2 90% Hb15.1 gm% HCO 3 - 24 mEq/L CaO 2 18.3 ml O 2 /dl

45. Case 3 – Discussion OXYGENATION: The patient's PaO 2 is reduced for two reasons - hypercapnia and V-Q imbalance - the latter apparent from an elevated P(A- a)O 2 (approximately 27 mm Hg). VENTILATION: The patient is hypoventilating..

46. Case 3 discussion ACID-BASE: pH and PaCO 2 are suggestive of acute respiratory acidosis plus metabolic acidosis; the calculated HCO 3 - is lower than expected from acute respiratory acidosis alone.

47. Test Your Overall Understanding Test Your Overall Understanding Case 4  A 23-year-old man is being evaluated in the emergency room for severe pneumonia. His respiratory rate is 38/min and he is using accessory breathing muscles.

48. Test Your Overall Understanding Test Your Overall Understanding Case 2 FIO 2.90Na + 154 mEq/L pH 7.29K + 4.1 mEq/L PaCO 2 55 mm HgCl - 100 mEq/L PaO 2 47 mm HgCO 2 24 mEq/L SaO 2 86% HCO 3 - 23 mEq/L %COHb2.1% Hb13 gm% CaO 2 15.8 ml O 2 /dl

49. Case 4 – Discussion OXYGENATION: The PaO 2 and SaO 2 are both markedly reduced on 90% inspired oxygen, indicating severe ventilation-perfusion imbalance. VENTILATION: The patient is hypoventilating despite the presence of tachypnea, indicating significant dead- pace ventilation. This is a dangerous situation that suggests the need for mechanical ventilation.

50. Case 4 – Discussion  ACID-BASE: The low pH, high PaCO 2, and slightly low calculated HCO 3 - all point to combined acute respiratory acidosis and metabolic acidosis. Anion gap is elevated to 30 mEq/L indicating a clinically significant anion gap (AG) acidosis, possibly from lactic acidosis.