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ARTERIAL BLOOD GAS ANALYSIS

ARTERIAL BLOOD GAS ANALYSIS. Arnel Gerald Q. Jiao, MD, FPPS, FPAPP Pediatric Pulmonologist Philippine Children’s Medical Center. Guidelines for Interpreting ABG’S. The body always tries to maintain a normal ph The lungs compensate rapidly; the kidneys compensate slowly

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ARTERIAL BLOOD GAS ANALYSIS

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  1. ARTERIAL BLOOD GASANALYSIS Arnel Gerald Q. Jiao, MD, FPPS, FPAPP Pediatric Pulmonologist Philippine Children’s Medical Center

  2. Guidelines for Interpreting ABG’S • The body always tries to maintain a normal ph • The lungs compensate rapidly; the kidneys compensate slowly • There is no overcompensation. • Consider the underlying disease • Maintain an adequate level of hemoglobin

  3. Bicarbonate-Carbonic AcidBuffer System: CO2 + H2O H2CO3 H+ + HCO3-

  4. Normal Arterial Blood Gas Values pH: 7.35 – 7.45 paCO2: 35 – 45 mm Hg paO2: 80 – 100 mm Hg HCO3: 22 – 26 mEq/L BE/BD: - 2 to + 2 O2 Sat: > 95 %

  5. Clinically Acceptable Levels pH: 7.30 – 7.50 paCO2: 30 – 50 mm Hg paO2 Neonates: 60 – 80 mm Hg 2 months above: 80 – 100 mmHg Decreases with age: Subtract 1 mm Hg from 80 mm Hg for every year past the age of 60

  6. Acidosis:patho- physiologic state where a significant basedeficit is present (HCO3 < 22mEq/L) Alkalosis:patho-physiologic state where a significant baseexcess is present (HCO3 > 26mEq/L) Nomenclature for Clinical interpretation

  7. Mathematical interrelationship among pH, pCO2 and HCO3 • Basis for all Acid-Base interpretation: pH= HCO3/pCO2

  8. Clinical Approach to Interpretation:Steps • Assessment of the pCO2 and pH: ventilatory status and acid-base balance 2. Assessment of Arterial Oxygenation

  9. Step 1 • Classify carbon dioxide tension • Consider pH and determine classification • Consider BE/BD or HCO3 levels and determine classification

  10. Step 1Classification of PaCO2 < 35 mmHg:alveolar hyperventilation (respiratory alkalosis) 35 – 45 mmHg: Normal alveolar ventilation > 45 mmHg:ventilatory failure (respiratory acidosis)

  11. Step 1Three questions to ask: • Is the PaCO2 abnormal? • Is the pH explained by the level of PaCO2? Yes: respiratory No: metabolic • Is the pH: Abnormal: acute/uncompensated Normal: chronic/ compensated

  12. Step 1PaCO2 < 35 mmHg

  13. PCO2 < 35 mm Hg • pH < 7.35 • HCO3 decreased • partly compensated metabolic acidosis

  14. PCO2 < 35 mm Hg • pH 7.35 – 7.45 • HCO3 decreased • chronic respiratory alkalosis

  15. PCO2 < 35 mm Hg • pH > 7.45 • HCO3 normal • acute respiratory alkalosis

  16. PCO2 < 35 mm Hg • pH > 7.45 • HCO3 decreased • partly compensated respiratory alkalosis

  17. PCO2 < 35 mm Hg • pH > 7.45 • HCO3 increased • combined respiratory and metabolic alkalosis

  18. Step 1PaCO2 35 – 45 mmHg

  19. PCO2 35 – 45 mm Hg • pH < 7.35 • HCO3 decreased • acute metabolic acidosis

  20. PCO2 35 – 45 mm Hg • pH 7.35 – 7.45 • HCO3 normal • normal acid-base balance

  21. PCO2 35 – 45 mm Hg • pH > 7.45 • HCO3 increased • acute metabolic alkalosis

  22. Step 1PaCO2 > 45 mmHg

  23. PCO2 > 45 mm Hg • pH < 7.35 • HCO3 normal • acute respiratory acidosis

  24. PCO2 > 45 mm Hg • pH < 7.35 • HCO3 decreased • combined respiratory and metabolic acidosis

  25. PCO2 > 45 mm Hg • pH < 7.35 • HCO3 increased • partly compensated respiratory acidosis

  26. PCO2 > 45 mm Hg • pH 7.35 – 7.45 • HCO3 increased • chronic respiratory acidosis

  27. PCO2 > 45 mm Hg • pH > 7.45 • HCO3 increased • partly compensated metabolic alkalosis

  28. Approximate PaCO2-pH Relationship

  29. Determining Base Excess/ Deficit 1. Determine pCO2 variance: difference between measured pCO2 & 40, move decimal point two places to the left 2. Determine the predicted pH: pCO2 > 40, subtract half pCO2 variance from 7.40 pCO2 < 40, add pCO2 variance to 7.40 3. Estimate BE/BD: Difference between measured and predicted pH Move decimal point two places to right. Multiply by 2/3

  30. Base Excess: measured pH > predicted pHBase Deficit: measured pH < predicted pH pH 7.04 pCO2 76 predicted pH 7.22 7.22 – 7.04 = 0.18 18 x 2/3 = 12 mEq/L (BD) pH 7.21 pCO2 90 predicted pH 7.15 7.21 – 7.15 = 0.06 6 x 2/3 = 4 mEq/L (BE)

  31. Causes of Acidosis Metabolic Diabetes (ketoacidosis) Renal failure (impaired H+ secretion) Diarrhea (loss of base) Tissue hypoxia (lactic acidosis) Respiratory Respiratory insufficiency

  32. Causes of Alkalosis Metabolic Excessive loss of HCl (e.g. pyloric stenosis) Excessive citrate/bicarbonate load Respiratory Hyperventilation (fever, psychogenic)

  33. Treatment Metabolic Acidosis HCO3 administration Empiric: 1-2 meq/kg Calculated: (Desired – actual) x k x KBW = meqs required k = 0.5 - 0.6 (represents fraction of body wt. where material is apparently distributed)

  34. Treatment Metabolic Alkalosis Volume expansion; Cl and K replacement Respiratory Acidosis Inc. RR, PIP, or both Respiratory Alkalosis Dec. RR

  35. Step 2: Assessment of Arterial Oxygenation Evaluation of Hypoxemia Room Air (Patient < 60 y/o): Mild: PaO2 < 80 mmHg Moderate: PaO2 < 60 mmHg Severe: PaO2 < 40 mm Hg

  36. Step 2On Oxygen Therapy: • Uncorrected hypoxemia: PaO2 < 80 mm Hg • Corrected hypoxemia: PaO2 = 80 – 100 mm Hg • Overcorrected hypoxemia: PaO2 > 100 mm Hg

  37. FiO2 (Fractional InspiredOxygen Concentration) • the measurable amount of oxygen received by the patient • 21% - room air • > 21% - supplemental oxygen

  38. Inspired Oxygen to PaO2 Relationship If PaO2 < minimal predicted (FiO2 x 5), the patient can be assumed to be hypoxemic at room air.

  39. Treatment of Hypoxemia For ventilated patients Increase: FiO2 RR PIP PEEP Inspiratory time Flow rate

  40. Exercises pH 7.44 PCO2 40 PO2 99 HCO3 22 BE +2 SaO2 95 FiO2 21%

  41. Exercises pH 7.44 PCO2 40 PO2 99 HCO3 22 BE +2 SaO2 95 FiO2 21% normal acid-base balance with adequate oxygenation

  42. pH 7.36 PCO2 25 PO2 78 HCO3 15 BE -10 SaO2 95 FiO2 35%

  43. pH 7.36 PCO2 25 PO2 78 HCO3 15 BE -10 SaO2 95 FiO2 35% chronic metabolic acidosis with uncorrected hypoxemia

  44. pH 7.24 PCO2 60 PO2 80 HCO3 26 BE -2 SaO2 95 FiO2 60%

  45. pH 7.24 PCO2 60 PO2 80 HCO3 26 BE -2 SaO2 95 FiO2 60% acute respiratory acidosis with corrected hypoxemia

  46. pH 7.55 PCO2 52 PO2 70 HCO3 44 BE +17 SaO2 97 FiO2 90%

  47. pH 7.55 PCO2 52 PO2 70 HCO3 44 BE +17 SaO2 97 FiO2 90% partly compensated metabolic alkalosis with uncorrected hypoxemia

  48. pH 7.19 PCO2 56 PO2 120 HCO3 17 BE -30 SaO2 94 FiO2 45%

  49. pH 7.19 PCO2 56 PO2 120 HCO3 17 BE -30 SaO2 94 FiO2 45% combined metabolic and respiratory acidosis with overcorrected hypoxemia

  50. Thank You!

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