Acid-base disorders

Question 1

Approach to acid-base disorders

Answer 1

1. Identify the primary disturbance (ROME: Respiratory Opposite (pH vs. pCO2), Metabolic Equal (pH vs. HCO3-))
2. Evaluate compensation. If compensation is not appropriate, a second acid-base disorder is likely present. Compensation occurs in the SAME direction as the primary disturbance (HCO3- change is not as dramatic as CO2)
3. Calculate Plasma Anion Gap (AG)
4. If AG elevated, compare increase in AG with decrease in HCO3-
5. Calculate Osmolar Gap

Question 2

Compensation in metabolic acidosis

Answer 2

for every 1 mmol/L decrease in HCO3-, pCO2 should decrease by 1 mmHg

Question 3

Compensation in metabolic alkalosis

Answer 3

for every 10 mmol/L increase in HCO3-, pCO2 should increases by 5-7 mmHg

Question 4

Compensation in respiratory acidosis

Answer 4

for every 10 mmHg increase in pCO2, HCO3- should increase by 1 (acute) or 3 (chronic) mmol/L

Question 5

Compensation in respiratory alkalosis

Answer 5

for every 10 mmHg decrease in pCO2, HCO3- should decrease by 2 (acute) or 5 (chronic) mmol/L

Question 6

How do you calculate the anion gap & what is its normal range?

Answer 6

AG = [Na+] – ([HCO3-] + [Cl-])

Baseline = 12
Rnage= 10-14

Question 7

What can cause increased anion gap metabolic acidosis?

Answer 7

KARMEL

• KETOACIDOSIS
• Toxins (ASA, methanol, ethylene glycol)
• RENAL FAILURE
• LACTIC ACIDOSIS

Question 8

What can commonly cause non-anion gap metabolic acidosis?

Answer 8

• Diarrhoea

- Renal tubular acidosis

Question 9

How do you calculate the osmolar gap?

Answer 9

osmolar gap = measured osmolality – calculated osmolality*

*calculated osmolality (GUN2) = (2 x [Na+]) + [urea] + [glucose] (all units are in mmol/L)

Question 10

What is the normal osmolar gap and what does increased osmolar gap indicate?

Answer 10

-normal osmolar gap 10, consider: methanol poisoning, ethylene glycol poisoning, OR another cause of acidosis plus ethanol ingestion