Acid-Base Disorders

Use pH, CO2, and HCO3 to determine metabolic vs respiratory acidosis/alkalosis. Calculate anion gap for metabolic acidosis.

Detailed Explanation

Step 1: Look at pH

pH < 7.35 = Acidemia

pH > 7.45 = Alkalemia

Step 2: Primary Disorder

pH and CO2 move OPPOSITE = Respiratory cause

pH and HCO3 move SAME direction = Metabolic cause

Step 3: Compensation

Metabolic: Winter's formula for expected CO2

- Expected CO2 = 1.5 × [HCO3] + 8 ± 2

Respiratory: 10/10/5 rule

Step 4: Anion Gap (for metabolic acidosis)

AG = Na - (Cl + HCO3)

Normal: 8-12

High Anion Gap Metabolic Acidosis (MUDPILES):

Methanol

Uremia

DKA

Propylene glycol

INH/Iron

Lactic acidosis

Ethylene glycol

Salicylates

Normal AG Metabolic Acidosis (HARDASS):

Hyperalimentation

Acetazolamide

RTA

Diarrhea

Addison's

Spironolactone

Saline infusion

Clinical Correlation

DKA presents with high AG metabolic acidosis (glucose breakdown → ketones). RTA causes normal AG acidosis because the kidney loses HCO3 or can't excrete H+.

Memory Trick

"MUDPILES for high gap, HARDASS for normal gap. MUD is the dirty stuff that accumulates."