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ABG analysis & Acid-Base Disorders

ABG analysis & Acid-Base Disorders. 2012. Outline. Discuss simple steps in analyzing ABGs Calculate the anion gap Calculate the delta gap Differentials for specific acid-base disorders. Steps for ABG analysis. What is the pH? Acidemia or Alkalemia? What is the primary disorder present?

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ABG analysis & Acid-Base Disorders

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  1. ABG analysis & Acid-Base Disorders 2012

  2. Outline • Discuss simple steps in analyzing ABGs • Calculate the anion gap • Calculate the delta gap • Differentials for specific acid-base disorders

  3. Steps for ABG analysis • What is the pH? Acidemia or Alkalemia? • What is the primary disorder present? • Is there appropriate compensation? • Is the compensation acute or chronic? • Is there an anion gap? • If there is a AG check the delta gap? • What is the differential for the clinical processes?

  4. Normal Values

  5. Step 1: • Look at the pH: is the blood acidemic or alkalemic? • EXAMPLE : • 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress • ABG :ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 • ACIDMEIA OR ALKALEMIA ????

  6. EXAMPLE ONE • ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 • Answer PH = 7.23 , HCO3 7 • Acidemia

  7. Step 2: What is the primary disorder?

  8. EXAMPLE • ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5. • PH is low , CO2 is Low • PH and PCO2 are going in same directions then its most likely primary metabolic will check to see if there is a mixed disoder.

  9. Step 3-4: Is there appropriate compensation? Is it chronic or acute? • Respiratory Acidosis • Acute: for every 10 increase in pCO2 -> HCO3 increases by 1 and there is a decrease of 0.08 in pH MEMORIZE • Chronic: for every 10 increase in pCO2 -> HCO3 increases by 4 and there is a decrease of 0.03 in pH • Respiratory Alkalosis • Acute: for every 10 decrease in pCO2 -> HCO3 decreases by 2 and there is a increase of 0.08 in PH MEMORIZE • Chronic: for every 10 decrease in pCO2 -> HCO3 decreases by 5 and there is a increase of 0.03 in PH

  10. Step 3-4: Is there appropriate compensation? Is it acute or chronic ? • Metabolic Acidosis • Winter’s formula: pCO2 = 1.5[HCO3] + 8 ± 2 MEMORIZE • If serum pCO2 > expected pCO2 -> additional respiratory acidosis • Metabolic Alkalosis • For every 10 increase in HCO3 -> pCO2 increases by 6

  11. EXAMPLE • ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5. • Winter’s formula : 17= 1.5 (7) +8 = 18.5 • So correct compensation so there is only one disorder Primary metabolic

  12. Step 5: Calculate the anion gap • AG = Na – Cl – HCO3 (normal 12 ± 2) • AG corrected = AG + 2.5[4 – albumin] • If there is an anion Gap then calculate the Delta/delta gap (step 6). Only need to calculate delta gap (excess anion gap) when there is an anion gap to determine additional hidden metabolic disorders (nongap metabolic acidosis or metabolic alkalosis) • If there is no anion gap then start analyzing for non-anion acidosis

  13. EXAMPLE • Calculate Anion gap • ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5/ Albumin 4. • AG = Na – Cl – HCO3 (normal 12 ± 2) 123 – 97 – 7 = 19 • No need to correct for albumin as it is 4

  14. Step 6: Calculate the different needed formulas • Delta gap = (actual AG – 12) + HCO3 • Adjusted HCO3 should be 24 (+_ 6) {18-30} • If delta gap > 30 -> additional metabolic alkalosis • If delta gap < 18 -> additional non-gap metabolic acidosis • If delta gap 18 – 30 -> no additional metabolic disorders

  15. EXAMPLE : Delta Gap • ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5/ Albumin 4. • Delta gap = (actual AG – 12) + HCO3 • (19-12) +7 = 14 • Delta gap < 18 -> additional non-gap metabolic acidosis • So Metabolic acidosis anion and non anion gap

  16. Metobolic acidosis: Anion gap acidosis

  17. EXAMPLE: WHY ANION GAP? • 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress • ABG :ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 • So for our patient for anion gap portion its due to BUN of 119 UREMIA • But would still check lactic acid

  18. Nongap metabolic acidosis For non-gap metabolic acidosis, calculate the urine anion gap UAG = UNA + UK – UCL If UAG>0: renal problem If UAG<0: nonrenal problem (most commonly GI)

  19. EXAMPLE : NON ANION GAP ACIDOSIS • 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress • ABG :ABG 7.23/17/235 on 50% VM • BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 • Most likely due to the diarrhea

  20. Metabolic alkalosis • Calculate the urinary chloride to differentiate saline responsive vs saline resistant • Must be off diuretics in order to interpret urine chloride

  21. Respiratory Alkalosis

  22. Respiratory Acidosis

  23. Steps for ABG analysis • What is the pH? Acidemic or Alkalemic? • What is the primary disorder present? • Is there appropriate compensation? • Is the compensation acute or chronic? • Is there an anion gap? • If there is a AG, what is the delta gap? • What is the differential for the clinical processes?

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