MLAB 2401: C LINICAL C HEMISTRY K ERI B ROPHY -M ARTINEZ ABG Interpretation

E VALUATING A CID -B ASE D ISORDERS ARMADA acid-base balance made easy in 4 steps 1. A cidosis or Alkalosis? 2. R espiratory disorder? acidosis or alkalosis check pCO 2 M etabolic disorder? acidosis or alkalosis check HCO 3 The one that matches the pH (acidosis or alkalosis), is the primary disorder. 3. A nion Gap? D elta AG? 4. A ssess compensation

S TEP 1: E VALUATE P H Evaluate pH < 7.35 = Acidosis > 7.45 = Alkalosis

STEP 2: T HINK “ROME” To determine whether the disorder is respiratory or metabolic use “ ROME ” R = Respiratory Seesawing (opposite) is pCO 2 less than 35 (alkalosis) or more than 45 (acidosis) O = Opposite [pH & pCO 2 ] M = Metabolic Swinging together o is HCO 3 less than 22 (acidosis) or more than 26 (alkalosis) E = Equal [pH & HCO 3 ]

S TEP 3: A NION G AP (AG) & D ELTA AG Examine AG and Delta AG Anion gap = (Na + K) - (Cl + [HCO 3 ]) (all units mmol/L) Since K is a small number, then... AG = Na+ - (Cl- + HCO 3 -) Delta AG = patient's AG - 12 mEq/L

M ORE ON THE A NION G AP MUDPILES Methanol Uremia of renal failure Diabetes or ketoacidosis Paraldehyde toxicity Isoniazid Lactic acidosis Ethylene glycol Salicylate

S TEP 4: A SSESS C OMPENSATION To assess compensation compare pCO 2 and HCO 3 - to reference range Is the pH normal? Yes Respiratory disorder compensated by kidneys Metabolic disorder compensated by lungs

S TEP 4: A SSESS C OMPENSATION If the pH is still outside the reference range Partial compensation has occurred

A CID -B ASE - P ROBLEM #1 pH = 7.56 pCO 2 = 43 mmHG HCO 3 = 38 mEQ/L pH > 7.45, then alkalosis pH & HCO 3 swinging up, then Metabolic Alkalosis Since pH still high and pCO 2 normal then it is Uncompensated What are some causes of Metabolic Alkalosis?

A CID -B ASE P ROBLEM #2 pH = 7.23 P CO 2 = 57 mmHG HCO 3 = 23 mEQ/L pH < 7.35, then acidosis Bicarb is normal but CO 2 is elevated or opposite of pH so this is Respiratory Acidosis Since the pH is still low and the HCO 3 is normal it is uncompensated What causes Respiratory Acidosis?

pH < 7.35, then acidosis pCO 2 normal but HCO 3 is low or swinging w/ pH so it is Metabolic Acidosis pCO 2 normal so uncompensated What causes Metabolic Acidosis? A CID -B ASE P ROBLEM #3 pH = 7.23 pCO 2 = 45 HCO3 = 19

A CID -B ASE P ROBLEM #4 pH = 7.51 pCO 2 = 29 mmHG HCO 3 = 20 mEq/L pH > 7.45, then alkalosis pCO 2 is low or opposite pH so it is Respiratory Alkalosis Since HCO 3 is low it is partially compensated What causes Respiratory Alkalosis? How is it compensated?

R EFERENCES Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins. Carreiro-Lewandowski, E. (2008). Blood Gas Analysis and Interpretation. Denver, Colorado: Colorado Association for Continuing Medical Laboratory Education, Inc. Jarreau, P. (2005). Clinical Laboratory Science Review (3rd ed.). New Orleans, LA: LSU Health Science Center. Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson. 13