Blood Gas Interpretation

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Blood Gas Interpretation

  1. 1. Blood Gas Interpretation Ayman I. Abou Mehrem, MD Assistant Consultant King Abdulaziz Hospital
  2. 2. Blood Gas Interpretation <ul><li>Components of blood gas (BG) analysis </li></ul><ul><li>Normal arterial BG (ABG) </li></ul><ul><li>Indications for BG analysis </li></ul><ul><li>Abnormalities in ABG </li></ul><ul><li>Stepwise analysis of ABG </li></ul><ul><li>Quiz </li></ul>
  3. 3. Components of BG <ul><li>Measured Values: </li></ul><ul><ul><li>pH </li></ul></ul><ul><ul><li>PaCO 2 </li></ul></ul><ul><ul><li>PaO 2 </li></ul></ul><ul><li>Calculated Values: </li></ul><ul><ul><li>HCO 3 </li></ul></ul><ul><ul><li>O 2 Sat </li></ul></ul><ul><ul><li>BE </li></ul></ul>
  4. 4. Components of BG Blood Gas Oxygenation Ventilation Acid-Base PaO 2 SaO 2 PCO 2 pH HCO 3 -BE
  5. 5. Normal ABG <ul><li>pH 7.35 - 7.45 </li></ul><ul><li>PCO 2 35 – 45 mmHg </li></ul><ul><li>PO 2 70 - 100 mmHg </li></ul><ul><li>SaO 2 ≥ 93 % </li></ul><ul><li>HCO 3 22 - 26 mEq/L </li></ul><ul><li>BE -2 - +2 mEq/L </li></ul>
  6. 6. Normal ABG Is it the same for a preterm baby?
  7. 7. NO Answer
  8. 8. Normal ABG <ul><li>In preterm babies the acid-base balance is a bit different. </li></ul><ul><li>We use usually the term “Acceptable Blood Gas” instead of normal blood gas. </li></ul><ul><li>This is to avoid more aggressive interventions to normalize their blood gas, which may lead to harm. </li></ul>
  9. 9. Target Blood Gas in Neonates * * Goldsmith and Karotkin, Assisted Ventilation of the Neonate, 4 th edition, Saunders 50-80 80-120 50-70 45-65 PaO 2 55-65 30-40 45-55 45-55 PaCO 2 7.35-7.45 7.30-7.50 ≥ 7.25 ≥ 7.25 pH Infant with BPD Term with PPHN 28-40 weeks’ GA < 28 weeks’ GA
  10. 10. Indications <ul><li>Assessment of ventilation and oxygenation status in patients with respiratory disease </li></ul><ul><li>Assessment of acid-base imbalance in sepsis, metabolic, and renal diseases </li></ul>
  11. 11. What may go wrong in ABG? Hypoxia Respiratory Acidosis Respiratory Alkalosis Metabolic Alkalosis Metabolic Acidosis
  12. 12. <ul><li>↓ PaO 2 </li></ul><ul><li>↓ O 2 Saturation </li></ul><ul><li>Causes: </li></ul><ul><ul><li>Respiratory: RDS, Pneumonia </li></ul></ul><ul><ul><li>Cardiac: Cyanotic CHD, CHF </li></ul></ul><ul><ul><li>Abnormal Hemoglobins </li></ul></ul>HYPOXIA
  13. 13. Acid-Base Disorders PaCO 2 HCO 3 pH
  14. 14. <ul><li>Primary acid-base disorders </li></ul><ul><li>Compensation </li></ul><ul><li>Mixed acid-base disorders </li></ul>Acid-Base Disorders
  15. 15. <ul><li>One of the four acid-base disturbances that is manifested by an initial change in HCO 3 - or PaCO 2 </li></ul><ul><li>Types: </li></ul><ul><ul><li>Respiratory acidosis </li></ul></ul><ul><ul><li>Respiratory alkalosis </li></ul></ul><ul><ul><li>Metabolic acidosis </li></ul></ul><ul><ul><li>Metabolic alkalosis </li></ul></ul>Primary Acid-Base Disorders
  16. 16. <ul><li>A primary disorder where the first change is an elevation of PaCO 2 , resulting in decreased pH. </li></ul><ul><li>Causes: </li></ul><ul><ul><li>Airway: e.g. laryngeal edema, severe micrognathia </li></ul></ul><ul><ul><li>Lungs: e.g. RDS, pneumonia </li></ul></ul><ul><ul><li>CNS: respiratory depression due to medications, CNS infection, hemorrhage, etc. </li></ul></ul>Respiratory Acidosis
  17. 17. <ul><li>A primary disorder where the first change is a lowering of PaCO2, resulting in an elevated pH. </li></ul><ul><li>Rare in neonates </li></ul><ul><li>Causes: </li></ul><ul><ul><li>Iatrogenic: for ventilated babies </li></ul></ul><ul><ul><li>Hyperventilation: e.g. urea cycle disorders </li></ul></ul>Respiratory Alkalosis
  18. 18. <ul><li>A primary acid-base disorder where the first change is a lowering of HCO 3 - , resulting in decreased pH. </li></ul><ul><li>Causes: </li></ul><ul><ul><li>Dehydration </li></ul></ul><ul><ul><li>Shock </li></ul></ul><ul><ul><li>Sepsis </li></ul></ul><ul><ul><li>Metabolic disorders </li></ul></ul>Metabolic Acidosis
  19. 19. <ul><li>A primary acid-base disorder where the first change is an elevation of HCO3-, resulting in increased pH. </li></ul><ul><li>Causes: </li></ul><ul><ul><li>Iatrogenic: loop diuretics </li></ul></ul><ul><ul><li>Rare diseases: cystic fibrosis, congenital chloride diarrhea </li></ul></ul>Metabolic Alkalosis
  20. 20. <ul><li>The body tries to overcome either a respiratory or metabolic dysfunction in an attempt to return the pH into the normal range. </li></ul><ul><li>For respiratory disorders (i.e. resp. acidosis or alkalosis) the body develops metabolic compensation through the kidney (i.e. HCO 3 ). </li></ul><ul><li>For metabolic disorders (i.e. metabolic acidosis or alkalosis) the body develops respiratory compensation through the lungs (i.e. CO 2 ). </li></ul>Compensation
  21. 21. <ul><li>Combination of two primary acid-base disorder with different range of compensation. </li></ul><ul><li>Usually happen in patients with chronic diseases or multiple primary pathologies </li></ul>Mixed Acid-Base Disorders
  22. 22. <ul><li>Step One : </li></ul><ul><ul><li>Assess the pH to determine if the blood is within normal range, alkalotic or acidotic. If it is above 7.45, the blood is alkalotic. If it is below 7.35, the blood is acidotic. </li></ul></ul>Steps to ABG Interpretation
  23. 23. <ul><li>Step Two: </li></ul><ul><li>If the blood is alkalotic or acidotic, we now need to determine if it is caused primarily by a respiratory or metabolic problem. To do this, assess the PaCO 2 level. Remember that with a respiratory problem, as the pH decreases below 7.35, the PaCO 2 should rise. If the pH rises above 7.45, the PaCO 2 should fall. Compare the pH and the PaCO 2 values. If pH and PaCO 2 are indeed moving in opposite directions , then the problem is primarily respiratory in nature. </li></ul>Steps to ABG Interpretation
  24. 24. <ul><li>Step Three </li></ul><ul><li>Assess the HCO 3 value. Recall that with a metabolic problem, normally as the pH increases, the HCO3 should also increase. Likewise, as the pH decreases, so should the HCO 3 . Compare the two values. If they are moving in the same direction , then the problem is primarily metabolic in nature. </li></ul>Steps to ABG Interpretation
  25. 25. Steps to ABG Interpretation Primary Acid-Base Disorders (No compensation) ↓ normal ↓ Metabolic Acidosis ↑ normal ↑ Metabolic Alkalosis normal ↓ ↑ Respiratory Alkalosis normal ↑ ↓ Respiratory Acidosis HCO 3 PaCO 2 pH
  26. 26. Steps to ABG Interpretation Partially Compensated Acid-Base Disorders ↓ ↓ ↓ Metabolic Acidosis ↑ ↑ ↑ Metabolic Alkalosis ↓ ↓ ↑ Respiratory Alkalosis ↑ ↑ ↓ Respiratory Acidosis HCO 3 PaCO 2 pH
  27. 27. Steps to ABG Interpretation Fully Compensated Acid-Base Disorders ↓ ↓ normal, but < 7.4 Metabolic Acidosis ↑ ↑ normal, but > 7.4 Metabolic Alkalosis ↓ ↓ normal, but > 7.4 Respiratory Alkalosis ↑ ↑ normal, but < 7.4 Respiratory Acidosis HCO 3 PaCO 2 pH
  28. 28. Steps to ABG Interpretation
  29. 29. Quiz 1 <ul><li>Baby boy, 28 wks GA, admitted 3 hrs ago, intubated initially, given surfactant, then extubated immediately to nasal CPAP, pressure 5 cm H 2 O, FiO 2 0.5. </li></ul><ul><li>ABG now: pH=7.20, PCO 2 =68, PO 2 =40, HCO 3 =22, SaO 2 =85% </li></ul><ul><li>Interpret above blood gas </li></ul>
  30. 30. Quiz 2 <ul><li>Baby girl, born at term by emergency CS, because of cord prolapse and severe fetal distress. She was flat, needed thorough resuscitation (intubation, UVC, 2 doses of epinephrine) </li></ul><ul><li>Now she is 6 hrs old, ventilated, FiO 2 0.3, and had focal seizure. </li></ul><ul><li>ABG: pH=7.15, PCO 2 =30, PO 2 =60, HCO 3 =6, SaO 2 =92% </li></ul><ul><li>Interpret above blood gas </li></ul>
  31. 31. Quiz 3 <ul><li>Hundred day-old baby girl, was born at 27 wks GA, had stormy course. </li></ul><ul><li>Now she is on NC 1 LPM, FiO2 0.3 </li></ul><ul><li>ABG: pH=7.34, PCO 2 =65, PO 2 =60, HCO 3 =33, SaO 2 =92% </li></ul><ul><li>Interpret above blood gas </li></ul>
  32. 32. Quiz 4 <ul><li>Seven day-old, baby boy, born at 29 wks GA. </li></ul><ul><li>He had large PDA, led to pulmonary hemorrhage, which treated conservatively. </li></ul><ul><li>Indomethacin cannot begiven because of Lt side grade 4 IVH, TFI was restricted to 120 ml/kg/d and furosemide was given 1.2 mg q12 hrs. </li></ul><ul><li>ABG: pH=7.47, PCO 2 =40, PO 2 =60, HCO 3 =30, SaO 2 =92% </li></ul>
  33. 33. THANK YOU

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