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ABG 101

ABG 101. Acid-base Terminology. Acidemia : blood pH < 7.35

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ABG 101

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  1. ABG 101

  2. Acid-base Terminology • Acidemia: blood pH < 7.35 • Acidosis: a primary physiologic process that, occurring alone, tends to cause acidemia. Examples: metabolic acidosis from decreased perfusion (lactic acidosis); respiratory acidosis from hypoventilation. If the patient also has an alkalosis at the same time, the resulting blood pH may be low, normal, or high. • Alkalemia: blood pH > 7.45 • Alkalosis: a primary physiologic process that, occurring alone, tends to cause alkalemia. Examples: metabolic alkalosis from excessive diuretic therapy; respiratory alkalosis from acute hyperventilation. If the patient also has an acidosis at the same time, the resulting blood pH may be high, normal, or low.

  3. Why Order an ABG? • Aids in establishing a diagnosis • Helps guide treatment plan • Aids in ventilator management • Improvement in acid/base management allows for optimal function of medications • Acid/base status may alter electrolyte levels critical to patient status/care

  4. The Steps • Start with the pH • Note the PCO2 • Determine compensation

  5. RESPIRATORY ACIDOSIS • pH < 7.35 (Normal: 7.35 - 7.45) CO2 > 45 (Normal: 35 – 45) • a. depression of the Respiratory Center (sedatives, narcotics, drug overdose, CVA, cardiac arrest, MI) • b. Respiratory muscle paralysis (spinal cord injury, Guillian-Barre, paralytics) • c. Chest wall disorders (flail chest, pneumothorax) • d. Disorders of the lung parenchyma (CHF, COPD, pneumonia, aspiration, ARDS) • e. Alteration in the function of the abdominal system (distension)

  6. RESPIRATORY ALKALOSIS • Respiratory Alkalosis: pH > 7.45 (Normal: 7.35 - 7.45) CO2 < 35 (Normal: 35 – 45) • a. Psychogenic (fear, pain, anxiety) • b. CNS stimulation (brain injury, ETOH, early salicylate poisoning, brain tumor) • c. Hypermetabolic states (fever, thyrotoxicosis) • d. Hypoxia (high altitude, pneumonia, heart failure, pulmonary embolism) • e. Mechanical overventilation (ventilator rate too fast)

  7. METABOLIC ACIDOSIS • Metabolic Acidosis pH < 7.35 (Normal: 7.35 - 7.45) HCO3- < 22 (normal: 22 – 26) • a. Overproduction of organic acids (starvation, ketoacidosis, increased catabolism) • b. Impaired renal excretion of acid (renal failure) • c. Abnormal loss of HCO3- (diarrhea, biliary fistula, Diamox) • d. Ingestion of acid (salicylate overdose, oral anti-freeze)

  8. Metabolic Gap Acidosis M - Methanol U - Uremia D - DKA P - Paraldehyde I - INH L - Lactic Acidosis E - Ehylene Glycol S - Salicylate Non Gap Metabolic Acidosis Hyperalimentation Acetazolamide RTA (Calculate urine anion gap) Diarrhea Pancreatic Fistula

  9. Metabolic Alkalosis • pH, HCO3 • PCO2 by 0.7 for every 1mEq/L  in HCO3 • Causes • Vomiting • Diuretics • Chronic diarrhea • Hypokalemia • Renal Failure

  10. Compensated or Uncompensated • Metabolic acidosis: pCO2= 1.5 x HCO3 + (8 + 2) • Metabolic alkalosis: pCO2= 40 +[( HCO3 – 24) x 0.6] +2 • Respiratory Acidosis: HCO3 = (CO2 - 40) (0.3) +24 • Respiratory alkalosis: HCO3 = 24- [(40-pCO2)](0.4)

  11. pH = 7.20 PaCO2 = 36 HCO3- = 14 pO2= 98 O2 sat= 97% • METABOLIC ACIDOSIS • pCO2= 1.5 x HCO3 + (8 + 2) • Uncompensated metabolic acidosis, adequate oxygenation

  12. pH = 7.46 PaCO2 = 33 HCO3- =22pO2= 88 O2 sat = 94% • RESPIRATORY ALKALOSIS • HCO3 = 24- [(40-pCO2)](0.4) • Compensated respiratory alkalosis with adequate oxygenation

  13. pH = 7.35 PaCO2 = 40 HCO3- = 23pO2 = 80 O2sat 95% • NORMAL

  14. pH = 7.20 PaCO2 = 36 HCO3- = 12pO2= 81 O2sat = 76% • VENOUS BLOOD GAS

  15. pH = 7.35 PaCO2 = 33 HCO3- = 18.1 pO2 = 110 O2 sat = 99% • METABOLIC ACIDOSIS • pCO2= 1.5 x HCO3 + (8 + 2) • Compensated Metabolic Acidosis with adequate oxygenation

  16. pH = 7.01 PaCO2 = 21 HCO3- = 10pO2 = 77 O2 sat= 89% • METABOLIC ACIDOSIS • pCO2= 1.5 x HCO3 + (8 + 2) • Compensated Metabolic Acidosis with inadequate oxygenation • Anion gap? • Na 139 Cl 105

  17. pH = 7.57 PaCO2 = 60 HCO3- = 45pO2= 110 O2sat 99% • METABOLIC ALKALOSIS pCO2= 40 +[( HCO3 – 24) x 0.6] +2 • Partially Compensated Metabolic Alkalosis with Respiratory Acidosis with adequate oxygenation

  18. pH 7.20 PCO2 42 HCO318pO2 77 O2 sat 89% • METABOLIC ACIDOSIS • pCO2= 1.5 x HCO3 + (8 + 2) • Combined Metabolic Acidosis and Respiratory Acidosis with inadequate oxygenation

  19. pH 7.45, PCO2 28, HCO3- 20, BE -3, PO2 66 O2 sat 82% • RESPIRATORY ALKALOSIS • HCO3 = 24- [(40-pCO2)](0.4) • Compensated Respiratory Alkalosis with inadequate oxygenation

  20. pH 7.29, PCO2 78, HCO3- 36, BE +7, PaO2 32 O2sat 84% • RESPIRATORY ACIDOSIS HCO3 = (CO2 - 40) (0.3) +24 • Partially Compensated Respiratory Acidosis with hypoxemia

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