Acid-Base & ElectrolytesEvidence-Based Golden Standard
Winter's Formula & Respiratory Compensation Suite
Calculates expected respiratory compensation (PaCO₂) in primary metabolic acidosis to diagnose concurrent primary respiratory acidosis or alkalosis.
Expected PaCO₂ (mmHg) = (1.5 × HCO₃⁻) + 8 ± 2
In kPa: Expected PaCO₂ = (0.2 × HCO₃⁻) + 1.07 ± 0.27
Published Clinical Benchmark Cases
Clinical Parameters & Inputs
Unit: mEq/L
mEq/L
Unit: mmHg
mmHg
Computed OutputAppropriate Respiratory Compensation
24 – 28mmHg
Diagnostic Interpretation
Actual PaCO₂ (26 mmHg) is within the expected compensatory range (24 – 28 mmHg). The respiratory center is appropriately compensating for the metabolic acidosis.
Calculation Breakdown
Mean Expected PaCO₂
(1.5 × 12) + 8 =26 mmHg (3.47 kPa)
Permissible Compensation Range (± 2 mmHg)
26 - 2 to 26 + 2 =24 – 28 mmHg (3.2 – 3.73 kPa)
Clinical Comparison
Actual PaCO₂ = 26 mmHg vs Range 24 – 28 mmHg =Appropriate Respiratory Compensation
Clinical Decision Pearls
- Winter's formula is only valid when the primary disorder is Metabolic Acidosis (HCO3 < 22).
- If PaCO2 exceeds expected compensation, evaluate airway patency, work of breathing, and prepare for possible mechanical ventilatory support.
- In mixed DKA and salicylate toxicity, salicylate stimulates the medullary respiratory center driving PaCO2 lower than predicted by Winter's formula alone.
Limitations & Confounders
- Requires 12-24 hours of sustained metabolic acidosis for maximal full respiratory compensation to reach equilibrium.
- PaCO2 cannot physiologically drop below ~10-12 mmHg even with maximal hyperventilation.
Evidence & Citations
- Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. Ann Intern Med. 1967;66(2):312-322.