MLAB 2401: CLINICAL CHEMISTRYKERI BROPHY-MARTINEZ

ABG Interpretation

EVALUATING ACID-BASE DISORDERS ARMADA

acid-base balance made easy in 4 steps

1. A cidosis or Alkalosis?2. R espiratory disorder?

acidosis or alkalosis check pCO2

M etabolic disorder? acidosis or alkalosis check HCO3

The one that matches the pH (acidosis or alkalosis), is the

primary disorder.

3. A nion Gap? D elta AG?4. A ssess compensation

STEP 1: EVALUATE PH

Evaluate pH< 7.35 = Acidosis> 7.45 = Alkalosis

STEP 2: THINK “ROME”

To determine whether the disorder is respiratory or metabolic use “ROME”

R = Respiratory Seesawing (opposite) is pCO2 less than 35 (alkalosis) or more than 45 (acidosis)

O = Opposite [pH & pCO2]

M = Metabolic Swinging togethero is HCO3 less than 22 (acidosis) or more than 26 (alkalosis)

E = Equal [pH & HCO3]

STEP 3: ANION GAP (AG) & DELTA AG

Examine AG and Delta AG

Anion gap = (Na + K) - (Cl + [HCO3]) (all units mmol/L)

Since K is a small number, then . . .

AG = Na+ - (Cl- + HCO3-)

Delta AG = patient's AG - 12 mEq/L

MORE ON THE ANION GAP

MUDPILES Methanol Uremia of renal failure Diabetes or ketoacidosis Paraldehyde toxicity Isoniazid Lactic acidosis Ethylene glycol Salicylate

STEP 4: ASSESS COMPENSATION

To assess compensation compare pCO2 and HCO3

- to reference range

Is the pH normal? Yes

Respiratory disorder compensated by kidneys

Metabolic disorder compensated by lungs

STEP 4: ASSESS COMPENSATION

If the pH is still outside the reference range Partial compensation has occurred

ACID-BASE - PROBLEM #1

pH = 7.56pCO2 = 43 mmHG

HCO3 = 38 mEQ/L

pH > 7.45, then alkalosis

pH & HCO3 swinging up, then Metabolic Alkalosis

Since pH still high and pCO2 normal then it is Uncompensated

What are some causes of Metabolic Alkalosis?

ACID-BASE PROBLEM #2

pH = 7.23

PCO2 = 57 mmHG

HCO3 = 23 mEQ/L

pH < 7.35, then acidosis

Bicarb is normal but CO2 is elevated or opposite of pH so this is Respiratory Acidosis

Since the pH is still low and the HCO3 is normal it is uncompensated

What causes Respiratory Acidosis?

pH < 7.35, then acidosis

pCO2 normal but HCO3 is low or swinging w/ pH so it is Metabolic Acidosis

pCO2 normal so uncompensated

What causes Metabolic Acidosis?

ACID-BASE PROBLEM #3

pH = 7.23pCO2 = 45

HCO3 = 19

ACID-BASE PROBLEM #4

pH = 7.51pCO2 = 29 mmHG

HCO3 = 20 mEq/L

pH > 7.45, then alkalosis

pCO2 is low or opposite pH so it is Respiratory Alkalosis

Since HCO3 is low it is partially compensated

What causes Respiratory Alkalosis?How is it compensated?

REFERENCES 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 .

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