Acid Base

Question 1

What are the two types of metabolic acidosis?

Answer 1

Elevated Anion Gap (increased acid generation)

Non-anion gap (loss of bicarbonate leading to hyperchloremia)

Question 2

What causes elevated anion gap?

Answer 2

MUDPILES
Metformin/methanol
Uremia (elevated BUN)
Diabetic ketoacidosis
Paraldehyde/propylene glycol
Iron/INH
Lactic acidosis
Ethylene glycol/ethanol
Salicylates

Question 3

What causes non-anion gap?

Answer 3

USED CAR
Ureteral diversion (fistula)
Sodium chloride administration
Exogenous acid
Diarrhea

Carbonic anhydrase inhibitors
Ammonium chloride
Renal tubular acidosis

Question 4

What is a normal anion gap?

Answer 4

3-11

Question 5

What does an abnormal anion gap indicate?

Answer 5

High anion gap indicates acidosis

Question 6

Metabolic acidosis expected pco2
What if it’s less?
What if it’s more?

Answer 6

Expect pco2 decrease:
[ HCO3 * 1.5 + 8 ] plus or minus 2

Decreases More: Underlying respiratory acidosis
Decreases Less: Underlying metabolic alkalosis

Question 7

How to treat metabolic acidosis

Answer 7

Sodium bicarbonate
Need half your body weight times deficit in mEq

ie 0.5 * 60 kg * (24-14) = 300 mEq

Question 8

Metabolic alkalosis expected pco2
What if it’s less?
What if it’s more?

Answer 8

Increases by: 40 + 0.7 (Pt’s HCO3 - Normal) plus or minus 5

Increases more: Underlying respiratory acidosis
Increases less: Underlying respiratory alkalosis

Question 9

How to treat metabolic alkalosis

Answer 9

Withhold diuretic
Hydration with chloride-containing solution
Anti-emetic

Severe cases:
Carbonic anhydrase inhibitor (acetazolamide 500 mg)

Question 10

Respiratory acidosis expected HCO3
What if it’s less?
What if it’s more?

Answer 10

Expected INCREASE:

Acute 24 + 0.1 (pt’s Pco2-normal) plus or minus 3
Chronic 24 + 0.4(pt’s Pco2-normal) plus or minus 4

More: Underlying metabolic alkalosis
Less: Underlying metabolic acidosis

Question 11

How to treat respiratory acidosis?

Answer 11

Bronchodilators for COPD
Decrease dose or reverse sedative medications (e.g. naloxone for opiate-induced respiratory depression)
Increase mechanical ventilation rate

Typically avoid
Alkali therapy may worsen acidosis (e.g. cardiac arrest)
Carbonic anhydrase inhibitors may worsen acidosis

Question 12

What is the expected HCO3 in respiratory alkalosis
What if it’s less?
What if it’s more?

Answer 12

Expect to see decrease
Acute: 24 - 0.2 (normal - pts co2)
Chronic: 24 - 0.4 (normal - pts co2)

If it decreases more: underlying metabolic alkalosis
Less: underlying metabolic acidosis

Question 13

How to treat respiratory alkalosis

Answer 13

Sedatives for anxiety (or breathe into paper bag)
Analgesics for pain
Decrease mechanical ventilation rate
Treatment of salicylate toxicity