Arterial Blood Gas (ABG)

 Arterial Blood Gas (ABG): pH/PaCO2/PO2/HCO3- calculated from Henderson-Hasselbach /(O2 saturation) Arterial Blood Gas (ABG)7.40 (7.35-7.45)/ 35-45 mmHg/ 80-100 mmHg/ 23-28 mEq/L/ 95% Mixed Venous Blood Gas (VBG)7.38 (7.33-7.43)/ 45-51 mmHg/ 35-40 mmHg/ 24-28 mEq/L/ 70-75% What can we learn from ABG ? Ventilation – PaCO2Oxygenation – PaO2, SaO2Acid/base status - Metabolic vs respiratoryIs the compensation adequate or as expected ?To reveal a previously undetected metabolic disorder Ventilation info from ABG HYPERventilation -- PaCO2 < 35 mmHg-- Resp compensation, HyperactiveHYPOventilation -- PaCO2 > 45 mmHg-- Resp depression, Weak respiratory muscle Oxygenation info from ABG Look at PaO2, O2 satHypoxemia: -- PaO2 <80 mmHg-- O2 sat< 92%To assess the integrity of Alveolar-arterial oxygen gradient, calculate A-a gradient (Alveolar-arterial Oxygen gradient) Calculate A-a gradient (Alveolar-arterial oxygen gradient) A-a gradient= PAlveolar O2 – Parterial O2= PAO2 – PaO2**PAO2 = (Patm – Pwater) FiO2 – PaCO2/0.8 = (760 mmHg – 47 mmHg) FiO2 – PaCO2/0.8 (FiO2= Fraction of inspired O2= 21% (0.21) if room air)Expected A-a gradient < (Age / 4) + 4If Calculated A-a gradient < Expected A-a gradient, then no problem with transfer of O2 from alveoli to capillaries If Calculated A-a gradient > Expected A-a gradient, then there is problem with transfer of O2 from alveoli to capillaries eg. diffusion defects, V/Q mismatch or R-to-L shunting Acid-base status pH – acidosis vs alkalosisPrimary disorder: Respiratory vs metabolicIs compensation adequate or as expected ?Reveal a previously undetected metabolic disorder Acidosis vs Alkalosis (differentiating the primary disorder) pH is < 7.40 – acidosisPaCO2 > 40 mmHg – Respiratory acidosisSerum HCO3-- < 23 mEq/L – Metabolic acidosis pH is > 7.40 – alkalosisPaCO2 < 40 mmHg – Respiratory alkalosisSerum HCO3-- > 23 mEq/L – Metabolic alkalosis Compensation Respiratory compensation -- Happens immediatelyRenal compensation -- Takes 72 hours Is the compensation adequate or as expected? Is the compensation adequate or as expected ? (acidosis) Metabolic acidosis-- Respiratory compensation. Winter’s formula: PaCO2= 1.5(HCO3-) + 8 (+/-2) Respiratory acidosis-- Acute: Change in HCO3- = 0.1 x change in PaCO2-- Chronic: Change in HCO3- = 0.35 x change in PaCO2 Is the compensation adequate or as expected ? (alkalosis) Metabolic alkalosis -- Respiratory compensation (PaCO2 rarely rises >50 mmHg) -- Change in PaCO2= 0.6 (change in HCO3-) Respiratory alkalosisAcute: Change in HCO3- = 0.2 x change in PaCO2Chronic: Change in HCO3- = 0.5 x change in PaCO2 Calculate Anion Gap for everybody Anion Gap= Na – Cl – HCO3 Correct Anion Gap if low serum albumin Equation of Figge:Corrected Anion Gap = Anion Gap + 2.5 (4.4 – albumin g/dL) (Do NOT correct Na for hyperglycemia when calculating Anion Gap.) Reveal a previously undetected metabolic disorder Calculate an anion gapNormal anion gap= 12 Calculate “delta gap”= Calculated anion gap – normal anion gap Corrected (serum) HCO3 = serum HCO3 + “delta gap” If corrected HCO3 < 23 – additional non-anion gap metabolic acidosisIf corrected HCO3 > 23 – additional metabolic alkalosis Authorjosephplam ID10016 Card SetArterial Blood Gas (ABG) DescriptionArterial Blood Gas (ABG) Updated2010-03-25T06:07:04Z Show Answers