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LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS

LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS. dr. Husnil Kadri, M.Kes Biochemistry Departement Medical Faculty Of Andalas University Padang. Arterial Blood Gases . Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management

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LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS

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  1. LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS dr. Husnil Kadri, M.Kes Biochemistry Departement Medical Faculty Of Andalas University Padang

  2. Arterial Blood Gases • 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

  3. Logistics • When to order an arterial line -- • Need for continuous BP monitoring • Need for multiple ABGs • Where to place – (with antikoagulant) • A. Radial • A. Femoral • A. Brachial • A. DorsalisPedis • A. Axillary

  4. The Components Desired Ranges: • pH ; 7.35 - 7.45 • PaCO2 ; 35-45 mmHg • PaO2 ; 80-100 mmHg • HCO3 ; 21-27 • O2sat ; 95-100% • Base Excess ; +/-2 mEq/L

  5. Arterial Blood Gases • Reflect oxygenation, gas exchange, and acid-base balance • PaO2 is the partial pressure of oxygen dissolved in arterial blood • SaO2 is the amount of oxygen bound to hemoglobin

  6. Base Excess Definition: The amount of a strong acid (like HCl) needed to bring blood to 7.40. • Assumes 100% oxygenation, 37oC, and pCO2 of 40. Normal = 0 Used to calculate the metabolic component of an acid-base disturbance.

  7. Base Excess calculations Calculated the same way, in practice, as SID: Buffer Base (SID) = HCO3- + A- HCO3 calculated by pH & pCO2 (blood gas machine) A- calculated using pH & hemoglobin (whole blood) OR A- calculated using albumin & phos (plasma) BE = Buffer Base – “expected buffer base” (expected if pH = 7.4 and pCO2 = 40)

  8. Indicators of hypoxaemia and hypoxia

  9. Respiratory Acidosis Respiratory Alkalosis Metabolic Acidosis Metabolic Alkalosis Increased pCO2 >50 Decreased pCO2<30 Decreased HCO3 <18 Increased HCO3 >30 Is it Respiratory or Metabolic?

  10. Compensated or Uncompensated—what does this mean? • Evaluate pH—is it normal? Yes • Next evaluate pCO2 & HCO3 • pH normal + increased pCO2 + increased HCO3 = compensated respiratory acidosis • pH normal + decreased HCO3 + decreased pCO2 = compensated metabolic acidosis

  11. Compensated vs. Uncompensated • Is pH normal? No • Acidotic vs. Alkalotic • Respiratory vs. Metabolic • pH<7.30 + pCO2>50 + normal HCO3 = uncompensated respiratory acidosis • pH<7.30 + HCO3<18 + normal pCO2 = uncompensated metabolic acidosis • pH>7.50 + pCO2<30 + normal HCO3 = uncompensated respiratory alkalosis • pH>7.50 + HCO3>30 + normal pCO2 = uncompensated metabolic alkalosis

  12. Respiratory Hypoventilation Impaired gas exchange Metabolic Ketoacidosis Diabetes Renal Tubular Acidosis Renal Failure Lactic Acidosis Decreased perfusion Severe hypoxemia Causes of Acidosis

  13. Respiratory Hyperventilation due to: Hypoxemia Metabolic acidosis Neurologic Lesions Trauma Infection Metabolic Hypokalemia Gastric suction or vomiting Hypochloremia Causes of Alkalosis

  14. Mixed Metabolic Acidosis and Chronic Respiratory Alkalosis Examples: • Sepsis • Addition of respiratory alkalosis to metabolic acidosis further decreases HCO3- but pH may remain normal • Lactic acidosis plus respiratory alkalosis due to severe liver disease, pulmonary emboli, or sepsis

  15. Mixed Metabolic Alkalosis and Chronic Respiratory Acidosis Examples: • Patient with COPD receiving glucocorticoids or diuretics • pCO2 and HCO3- are increased by both conditions, but pH is neutralized

  16. Mixed Alkalosis, Severe Example: • Postoperative patient with severe hemorrhage stimulating hyperventilation [respiratory alkalosis] plus massive transfusion and nasogastric drainage [metabolic alkalosis]

  17. Mixed Chronic Respiratory Acidosis and Acute Metabolic Acidosis Examples: • COPD [chronic respiratory acidosis] with severe diarrhoea [metabolic acidosis]. pH is too low for pCO2 of 55 mmHg in chronic respiratory acidosis, indicating low pH due to mixed acidosis, but HCO3- effect is offset

  18. Mixed Metabolic Acidosis and Metabolic Alkalosis Examples: • Gastroenteritis with vomiting [metabolic alkalosis] and diarrhoea [metabolic acidosis due to loss of HCO3-]; surprisingly normal findings with marked volume depletion

  19. Serum Values in Acid-Base Disturbances

  20. Serum Values in Acid-Base Disturbances

  21. Summary of Pure and Mixed Acid-Base Disorders Source: Adapted from Friedman HH. Problem-oriented medical diagnosis, 3rd ed. Boston: Little, Brown. 1983

  22. References • Anisman, S. Base Excess & Strong Ion Theories. ppt. 2003. • Klee, V. Arterial Blood Gas Analysis.ppt. 2012. • Perkins, J. ABG Interpretation. ppt. 2012. • Rashid, FA. Respiratory Mechanisms in Acid-Base Homeostasis.ppt. 2005.

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