Anion Gap (AG) It is a measure of anions other than HCO3 and Chloride Biochemical Basis: Always: CATIONS = ANIONS 11/18/2018 5:41 PM

AG (Biochemical Basis) Major Cat-ions: Na = 143 mmol/L K = 4 mmol/L Ca = 1.5 mmol/L Mg = 1.5 mmol/L TOTAL CATIONS = 150 mmol/L 11/18/2018 5:41 PM

AG (Biochemical Basis) Major Anions: Cl = 100 mmol/L HCO3 = 27 mmol/L proteins = 15 mmol/L PO3 = 2 mmol/L SO3 = 1 mmol/L Organic Acids = 5 mmol/L TOTAL ANIONS = 150 mmol/L 11/18/2018 5:41 PM

AG =(Na+ K+) - (Cl- + HCO3-) or =Na+ - (Cl- + HCO3-) Range : 7 – 18 mmol/l Cations Anion Gap = - It is a measure of anions other than HCO3 and Chloride Biochemical Basis: Always: CATIONS = ANIONS Anions

Anion Gap: It is only a lab derived index There can Never be an anion gap in any condition because electro- neutrality is always maintained in the plasma 11/18/2018 5:41 PM

AG corrected for low albumin (AG corr) Albumin accounts for about 90% of the mean value AG and albumin is reversely correlated with HCO3 When the level of serum albumin decreases, AG will decrease equally AG is concealed by hypoalbuminemia HCO3 will increase accordingly (low Alb alkalosis)

* coefficient for converting Alb g/L into Alb mmol/L. AG corr Albumin: 40 (35-50) g/L×0.25* = 10 (9-13) mmol/L * coefficient for converting Alb g/L into Alb mmol/L.

Steps in Diagnosis of a Triple Disorder Diagnose Double Disorder Examine AG Examine [HCO3] Example: Double Disorder : Low PCO2+ High [HCO3] (i.e. Resp Alk + Met Alk) Triple Disorder : Low PCO2+ High [HCO3] + AG > 16 (i.e. Resp Alk + Met Alk+ High AG Met Acidosis)

Diagnosis Triple Disorder Metabolic Alkalosis Respiratory Alkalosis High AG Metabolic Acidosis

Steps in Diagnosis of a Triple Disorder Diagnose Double Disorder Examine AG Examine [HCO3] Example: Double Disorder: High PCO2+ [HCO3] higher than the upper limit of compensation (i.e. Resp Acidosis + Met Alk) Triple Disorder: High PCO2+ [HCO3] higher than the upper limit of compensation + AG > 16 (i.e. Resp Acidosis + Met Alk + High AG Met Acidosis)

Diagnosis Triple Disorder Metabolic Alkalosis High AG Metabolic Acidosis Respiratory Acidosis

Other situations of Triple Disorders Combined High AG and Normal AG Met Acidosis in a patient with Resp Alkalosis Low Albumin Met Alkalosis with Met Acidosis and Respiratory Alkalosis

Important Fact Respiratory Acidosis and Respiratory Alkalosis never occur together in the same patient !!!

Delta Ratio Measured anion gap – Normal anion gap (anion gap – 12) The delta ratio is used for the determination of a mixed acid base disorder in an elevated anion gap metabolic acidosis Measured anion gap – Normal anion gap Normal [HCO3-] – Measured [HCO3-]or (anion gap – 12) (24 - [HCO3-])

Delta Ratio Assessment Guideline < 0.4 Hyperchloraemic normal anion gap acidosis 0.4 - 0.8 Renal failure Combined high AG & normal AG acidosis 1 to 2 Uncomplicated high-AG acidosis Lactic acidosis: 1.6 (average value) >2 A pre-existing elevated HCO3 level due to: a concurrent metabolic alkalosis, or a pre-existing compensated respiratory acidosis

Predicted HCO3 If patient's [HCO3] > Predicted [HCO3] Predicted [HCO3] = 24 -[Anion Gap-12] If patient's [HCO3] > Predicted [HCO3] Metabolic acidosis + Metabolic Alkalosis Compensatory response to resp acidosis

If patient's [HCO3] =Predicted [HCO3] Simple Metabolic acidosis If patient's [HCO3] < Predicted [HCO3] Compensatory response to resp alkalosis

Example Blood Gases Electrolytes pH 7.58 PCO2 2.1mmHg HCO3 19mmol/L Na 137 mmol/L K 5.2 mmol/L Cl 89 mmol/L Anion Gap 33 mmol/L Blood Gases pH 7.58 PCO2 2.1mmHg HCO3 19mmol/L

Interpretation of ABG Reports Look at pH Step-1 Examine pH and HCO3 Step 2 PCO2 and HCO3 Step 3 Mobile App e.g. Skyscape (or Equations) Step 4 1. Acidosis, alkalosis, or normal? primary disturbance respiratory or metabolic? 3. primary respiratory disturbance, is it acute or chronic? 4.If metabolic disturbance, is the respiratory system compensating OK 5. If metabolic acidosis, is there an increased anion gap? 6. an increased anion gap metabolic acidosis, are there other derangements? Delta Ratio for Triple Disorders Step 5

Thank you