🧪 Expected Compensation (PaCO₂ / HCO₃)
UseWhen to use: ABG review when Winter’s (metabolic acidosis) is not the question.
StrataValues outside the expected band suggest a second primary acid-base disorder.
LimitsWhen not to use: replacing full ABG interpretation. · Pitfall: using chronic rules in acute-only change. · Pair with Winter’s for metabolic acidosis.
SourceClassic acid-base compensation teaching equations
This-shift next steps
After scoring: open the scene pack, peer scores, and the matching pathway. Local reference — no HIS write.
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Methodology · worked example, guidelines & full notes
Compensation teaching bands.
When to use
When to use: ABG review when Winter’s (metabolic acidosis) is not the question.
How it works
Met alk: PaCO₂≈0.7×HCO₃+20 (±5); chronic resp acid: HCO₃≈24+0.35×(PaCO₂−40); chronic resp alk: HCO₃≈24−0.5×(40−PaCO₂).
Key points
- Compensation teaching bands.
- Mixed-disorder clue.
- Next: AG / BE / Winter.
References
- Classic acid-base compensation teaching equations
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Disorder | Chronic respiratory acidosis → expected HCO₃ |
|---|---|
| HCO₃⁻ | 36 mmol/L |
| PaCO₂ | 55 mmHg |
→Expected HCO₃29.3mmol/L
- Formula：HCO₃ ≈ 24 + 0.35×(PaCO₂−40)
- Measured − expected HCO₃：+6.8 mmol/L
- Cue：HCO₃ off chronic band — consider mixed disorder or acute-on-chronic change.
| Disorder | Metabolic alkalosis → expected PaCO₂ |
|---|---|
| HCO₃⁻ | 36 mmol/L |
| PaCO₂ | 55 mmHg |
→Expected PaCO₂45mmHg
- Formula：0.7×HCO₃ + 20 (±5)
- Band：40–50 mmHg
- Measured PaCO₂：55 mmHg
Verification & sources · governance
FAQ
Frequently asked questions
- Does Expected Compensation (PaCO₂ / HCO₃) upload patient data? Where is it calculated?
- Calculation runs locally in the browser; inputs and results are not uploaded. For licensed clinicians only; interpret with history, investigations and local protocols — not a diagnosis or prescription.
- How is Expected Compensation (PaCO₂ / HCO₃) calculated in practice? Can you show a worked example?
- Inputs: Disorder Chronic respiratory acidosis → expected HCO₃, HCO₃⁻ 36 mmol/L, PaCO₂ 55 mmHg → Result: Expected HCO₃ 29.3 mmol/L（Formula: HCO₃ ≈ 24 + 0.35×(PaCO₂−40), Measured − expected HCO₃: +6.8 mmol/L, Cue: HCO₃ off chronic band — consider mixed disorder or acute-on-chronic change.） Inputs: Disorder Metabolic alkalosis → expected PaCO₂, HCO₃⁻ 36 mmol/L, PaCO₂ 55 mmHg → Result: Expected PaCO₂ 45 mmHg（Formula: 0.7×HCO₃ + 20 (±5), Band: 40–50 mmHg, Measured PaCO₂: 55 mmHg）