Acid-Base Disorders

Question 0

What are the causes of metabolic acidosis with an increased anion gap?

Answer 0

• Formic acid from methanol overdose
• Uremia from renal failure
• Ketoacids from DKA or starvation
• Salicylates e.g. aspirin overdose
• Oxalic acid from ethylene glycol (antifreeze) overdose
• Isoniazid
• Lactate from hypotension or hypoperfusion

Question 1

What are the 2 causes of metabolic acidosis with a normal anion gap? How do you distinguish them?

Answer 1

RTA and diarrhea cause normal anion gap (6-12) metabolic acidosis.

Urine anion gap (UAG) is one way to distinguish between them. UAG = Na - Cl. RTA has a positive UAG; diarrhea has a negative UAG.

Question 2

What are the tests and treatments for the causes of increased anion gap metabolic acidosis?

Answer 2

• Methanol toxicity causes an inflamed retina; treated with fomepizole or dialysis.
• Uremia is diagnosed by BUN and Cr; treated with dialysis.
• DKA is diagnosed by acetone level; treated with insulin and fluids.
• Isoniazid toxicity is prevented by B6 supplementation.
• Lactic acidosis is treated by correcting hypoperfusion.
• Ethylene glycol overdose is diagnosed by crystals on UA; treated with fomepizole or dialysis.
• Salicylates are treated by alkalinization of urine.

Question 3

How do you compensate for metabolic acidosis?

Answer 3

Hyperventilate

Question 5

What are the causes of metabolic alkalosis?

Answer 5

• GI loss: vomiting or NG suction
• Increased aldosterone: primary aldosteronism, Cushing syndrome, ectopic ACTH (e.g. small cell CA), volume contraction, licorice
• Diuretics
• Milk-alkali syndrome: high-volume liquid antacids

Question 6

How do you compensate for metabolic alkalosis?

Answer 6

Hypoventilation

Question 7

Describe the findings on ABG in metabolic acidosis

Answer 7

• Decreased pH < 7.4
• Decreased pCO2 indicating respiratory alkalosis as compensation
• Decreased bicarbonate

Question 8

How do metabolic derangements kill patients?

Answer 8

Cardiac arrhythmias

Question 9

What are the causes of respiratory acidosis?

Answer 9

Obstruction:
- COPD/emphysema 
- Sleep apnea / morbid obesity
- Kyphoscoliosis
Hypoventilation or decreased respiratory drive 
- Drowning 
- Opiate or alcohol overdose
- Neuromuscular disease (if diaphragm is affected)

Question 10

What are the causes of respiratory alkalosis?

Answer 10

Anything that causes hyperventilation:

• Anemia
• Anxiety
• Pain
• Fever
• Interstitial lung disease
• Pulmonary emboli

Question 11

How is the pt’s breathing used to distinguish between respiratory acidosis and alkalosis?

Answer 11

Minute ventilation is more precise than respiratory rate.

MV = respiratory rate x tidal volume

Respiratory acidosis: decreased MV
Respiratory alkalosis: increased MV

*Hyperventilation may occur with a small tidal volume, in which case it would not cause alkalosis.

Question 12

Describe the ABG findings for metabolic alkalosis

Answer 12

• Increased pH > 7.4
• Increased pCO2 indicating respiratory acidosis as compensation
• Increased bicarbonate