APPROACH TO ACID BASE DISORDERS

Question 1

Bronsted-Lowry Approach

Answer 1

1. Assess the pH
2. Determine if primarily respiratory (pC02) or Metabolic (HCO3) disorder
3. Determine the degree of compensation
4. In the setting of Metabolic Acidosis:
   a. Calculate Anion Gap
   b. Calculate Delta Delta

Question 2

Acute vs. Chronic Respiratory Acidosis Compensation

Answer 2

Acute:
pC02 10 : HCO3 1

Chronic:
pC02 10 :HCO3 3

Question 3

Acute vs. Chronic Respiratory Alkalosis Compensation

Answer 3

Acute:
pC02 10 :HCO3 2

Chronic:
pC02 10 :HCO3 4

Question 4

Anion Gap

Answer 4

Na - (Cl + HC03)

Question 5

Delta Delta

Answer 5

Delta AG / Delta HC03

(Calculated AG - Expected AG) / (24-HC03)

1-2 = pure AG metabolic acidosis

<1 = AG metabolic acidosis and simultaneous non-AG acidosis

> 2 = simultaneous metabolic acidosis and metabolic alkalosis

Question 6

Investigations AG Metabolic Acidosis

Answer 6

Osmolar Gap

Question 7

DDx: Anion Gap Metabolic Acidosis

Answer 7

Ketoacidosis: DKA, EtoH, Stavation

Uremia: accumulation of organic anions (phosphate, sulfates, urates etc)

Lactic Acidosis: impairment of tissue oxygenation vs. no impairment

Toxic Ingestions: methanol, ethylene glycol, propylene glycol, glutathione depletion

Salicylates

Question 8

Investigations Non-AG Metabolic Acidosis

Answer 8

Urine Net Charge (non-AG MA)

Question 9

Urine Net Charge

Answer 9

(UNa + Uk)-UCl
Normal <0
<0 Suggest loss of GI bicarb
>/1 Suggest renal bicarb loss

Question 10

Respiratory Acidosis DDx

Answer 10

CNS Trauma
Drugs: opiates, benzos, barbituates
Asthma, COPD, Hypoxic Respiratory Failure (late stage)
Neuromuscular Disorder