# Winter's formula

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"Winter's Formula",[1] named for Dr. R.W. Winters,[2] is a formula used to evaluate respiratory compensation when analyzing acid-base disorders and a metabolic acidosis is present.[3][4] It can be given as

$P_{CO_2} = (1.5 \times HCO_3^-) + 8 \pm 2$,

where HCO3- is given in units of mEq/L and PCO2 will be in units of mmHg.

Winter's formula gives an expected value for the patient's PCO2; the patient's actual (measured) PCO2is then compared to this.
If the two values correspond, respiratory compensation is considered to be adequate.
If the measured PCO2 is higher than the calculated value, there is also a primary respiratory acidosis.
If the measured PCO2 is lower than the calculated value, there is also a primary respiratory alkalosis.