Winter’s Formula Calculator
Calculate expected PaCO₂ using Winter’s Formula for metabolic acidosis. Determine appropriate respiratory compensation in acid-base disorders.
Step 1: Blood Gas Parameters
Winter’s Formula
Expected PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2 mmHg
Used to assess respiratory compensation in metabolic acidosis
Step 2: Clinical Context & Options
Normal Blood Gas Values
pH: 7.35-7.45
PaCO₂: 35-45 mmHg
HCO₃⁻: 22-26 mEq/L
Base Excess: -2 to +2
Winter’s Formula Results
Expected PaCO₂ for Respiratory Compensation
Clinical Interpretation
Interpretation Guide
If measured PaCO₂ equals expected: Appropriate respiratory compensation
If measured PaCO₂ > expected: Concomitant respiratory acidosis
If measured PaCO₂ < expected: Concomitant respiratory alkalosis
Winter’s Formula applies only to primary metabolic acidosis.
| HCO₃⁻ (mEq/L) | Expected PaCO₂ (mmHg) | Clinical Context | Common Causes |
|---|
Winter’s Formula Details
Winter’s Formula: Expected PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2 mmHg
Where:
• HCO₃⁻ = Serum bicarbonate concentration (mEq/L)
• 1.5 = Multiplier derived from empirical data
• 8 = Constant offset (mmHg)
• ± 2 = Acceptable range for adequate compensation
Alternative formulas:
• 1.2 × HCO₃⁻ + 2 (for mixed disorders)
• Pediatric: 1.5 × HCO₃⁻ + 6-10 (age-dependent)
Example Calculation
Example: DKA with HCO₃⁻ = 10 mEq/L
Using Winter’s Formula:
1.5 × 10 + 8 =
15 + 8 = 23 mmHg
Range: 21-25 mmHg
Interpretation:
If measured PaCO₂ is 22 mmHg: Appropriate compensation
If measured PaCO₂ is 30 mmHg: Concomitant respiratory acidosis
If measured PaCO₂ is 18 mmHg: Concomitant respiratory alkalosis
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