Question 1

What is the expected compensation for metabolic alkalosis?

Accepted Answer

Winter's formula does not apply to metabolic alkalosis. The expected compensation for metabolic alkalosis is pCO₂ = 0.7 × HCO₃⁻ + 20 ± 5, with compensation limited to a maximum pCO₂ of 55 mmHg.

Question 2

Can Winter's formula be used in chronic metabolic acidosis?

Accepted Answer

Yes, the formula applies to both acute and chronic metabolic acidosis. In chronic renal failure and RTA, the compensation may be at the upper end of the expected range.

Question 3

What if the measured pCO₂ is lower than Winter's predicts?

Accepted Answer

A lower-than-predicted pCO₂ indicates a concurrent respiratory alkalosis, which may be caused by sepsis, pulmonary embolism, pain, or mechanical hyperventilation in an intubated patient.

Question 4

What is the minimum achievable pCO₂ in metabolic acidosis?

Accepted Answer

The maximum ventilatory response typically achieves pCO₂ of 10–12 mmHg. Healthy young adults can transiently reach values as low as 8 mmHg. A pCO₂ <10 with metabolic acidosis suggests a primary respiratory alkalosis is present.