Winter's formula calculates how much respiratory compensation(change in PaCO₂) is expected for a metabolic acidosis, helping determine whether breathing is compensating appropriately or a separate respiratory problem is also present.
It's one of the clearest teaching examples of how the lungs and kidneys work together to control blood pH, and it's essential for correctly interpreting an ABG in a patient with a metabolic acid-base problem.
If the measured PaCO₂ falls within the expected range, respiratory compensation is appropriate. A higher PaCO₂ means a concurrent respiratory acidosis; a lower one means a concurrent respiratory alkalosis.
Expected PaCO₂ = (1.5 × HCO₃⁻) + 8, plus or minus 2 mmHg.
No — Winter's formula is specific to metabolic acidosis. Metabolic alkalosis uses a different expected-compensation relationship.