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ARTERIAL BLOOD GAS ANALYSIS

ARTERIAL BLOOD GAS ANALYSIS

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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!