Winters Formula Calculator For Metabolic Acidosis

Winters formula explained

In cases of metabolic acidosis, medical professionals may be required to evaluate PCO₂ compensation in connection with the level of bicarbonate [HCO₃^-].

The Winters formula calculator provides the lower and upper values of partial CO₂ pressure in mmHg:

Expected pCO₂ = 1.5 x HCO₃^- + 8 +/- 2

Which means that the creation of a compensation interval between 1.5 x HCO₃^- + 6 and 1.5 x HCO₃^- + 10.

The rule is that for every 1 mEq/L reduction of plasma bicarbonate, there is a 1.2 mmHg PCO₂ reduction, but only to a minimum of 10 - 15 mmHg.

The clinician should compare the patient’s data with the computed value:

■ If the value retrieved from patient data is included in the computed interval, then respiratory compensation is adequate;

■ If the patient’s value is higher than interval, this is indicative of primary respiratory acidosis;

■ If the patient’s value is lower than interval, this is indicative of primary respiratory alkalosis.

To be exact, where respiratory alkalosis is suspected, Winters formula should be adapted to the following:

PCO₂ = 0.7 x HCO₃^- + 20 +/- 5 mmHg meaning the interval between 0.7 x HCO₃^- + 15 and 0.7 x HCO₃^- + 25.

When is compensation required

The formula developed by Dr Winters is suitable for cases where the level of respiratory compensation needs to be adapted for the patient to recover from acidosis.

These results are used in the analysis of acid base disorders along with the anion gap.

In metabolic acidosis, the bicarbonate reduction may result even in extracellular imbalances and loss of bicarbonate in urine.

The body responds by attempting to restore the PCO₂/HCO₃^- ratio which means a reduction of what is seen as excess PCO_2.

The physiological mechanism is based on signals from the low arterial pH that stimulate chemoreceptors in charge with respiration.

Therefore, an increase in alveolar ventilation takes place, which sometimes leads to Kussmaul type respiration.

Original source

Asch MJ, Dell RB, Williams GS, Cohen M, Winters RW. Time course for development of respiratory compensation in metabolic acidosis. J Lab Clin Med. 1969; 73(4):610-5.

Validation

Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. Ann Intern Med. 1967; 66(2):312-22.