RespiratoryPathophysiology

Blood Gas Interpreter

Enter a blood gas to identify the primary acid–base disorder, whether it is compensated, and the type and adequacy of compensation — with anion gap and the caveats specific to arterial, capillary, and venous samples.

Reference (arterial): pH 7.35–7.45, PCO₂ 35–45 mmHg, HCO₃ 22–26 mEq/L. Leave HCO₃ blank to derive it from pH and PCO₂. Add Na and Cl to compute the anion gap.

Sample type

Arterial — the reference standard for pH, PCO₂, and oxygenation.

Henderson–Hasselbalch: HCO₃ = 0.03 × PCO₂ × 10^(pH − 6.1).

Winter's formula (expected PCO₂ in metabolic acidosis) = 1.5 × HCO₃ + 8 ± 2.

Compensation rules are estimates; correlate with the clinical scenario and trends.

Frequently asked questions

How do I tell a respiratory from a metabolic problem?

Compare the pH direction with the pCO₂ and HCO₃. Winters' formula checks whether respiratory compensation for a metabolic acidosis is adequate.

Can I use a capillary or venous gas?

Capillary and venous gases approximate pH and pCO₂ but not oxygenation; an arterial sample is needed for an accurate pO₂.

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