Blood Gas Analyser

ABG/VBG acid-base, oxygenation, anion gap, Stewart/SIG, osmolality, and narrative interpretation support.

For education and clinical decision support only. Verify calculations and local policy before use.

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Related documents
Boston approach & compensation rules

Acute/chronic respiratory and metabolic compensation rules, including Winter formula.
Winter formula: expected PaCO2

Expected respiratory compensation in metabolic acidosis.
Expected PaCO2 in metabolic alkalosis

Summary of metabolic alkalosis and expected respiratory compensation.
Albumin-corrected anion gap - Figge

Albumin correction for anion gap interpretation.
Expected anion gap with albumin

Expected AG and interpretation caveats.
Delta ratio and delta gap interpretation

Mixed HAGMA/NAGMA interpretation support.
Fencl-Stewart bedside approach

SIDa, SIDe and strong ion gap background.
Arterial-venous differences for pH and PCO2

Educational context for VBG-to-ABG estimates.
Siggaard-Andersen/Zander base excess methods

Standard base excess equation background.
Alveolar gas equation and A-a gradient

PAO2 and A-a gradient calculation background.
A-a ratio overview

Oxygenation ratio interpretation and limitations.
Berlin ARDS definition and P/F thresholds

P/F threshold context for ARDS severity.
Calculated osmolality and osmolar gap

Calculated osmolality and osmolar gap context.
Balanced crystalloids vs saline - SALT-ED

Education context for chloride load and balanced fluids.
Feedback

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Inputs
Venous → arterial offsets (editable)
≈ −0.67 kPa
Educational approximations. PaO₂ is not inferred from venous samples.
Timing of the respiratory disturbance, not just the current presentation.
Preserve analyser type, e.g. BE(B); comparison with estimates only.
Shown beside calculated gaps; convention must be checked.
Normal ~ 7.35–7.45
Normal: 4.7–6.0 kPa (35–45 mmHg)
Normal: 22–26
Optional (oxygenation)
Used for corrected + expected AG & Stewart
Used in Stewart SIDe
Sea level ≈ 760 mmHg (101.3 kPa)
If lab uses mg/dL, convert ≈ mg/dL ÷ 4.6
Optional clinical context

Unknown stays unknown. These entries support educational differentials; do not enter identifiers.

Unit toggle converts gas pressures only. Concentrations remain in mmol/L (albumin in g/L).
Stewart: SIDa = (Na + K + 2Ca + 2Mg) − (Cl + Lactate). SIDe = 2.46×10⁻⁸×PaCO₂(mmHg)/10−pH + Albg/L×(0.123·pH−0.631) + Phos×(0.309·pH−0.469). SIG = SIDa − SIDe.
Interpretation
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Expected Compensation (Boston + Winter’s) Metabolic & respiratory rules
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Anion Gap, Delta AG, Delta Ratio & Delta–Delta Albumin-corrected AG & expected AG
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Stewart (SID) SIDa / SIDe / SIG
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Base Excess (BE) Siggaard–Andersen / Van Slyke
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Oxygenation (Alveolar Gas, A–a, P/F) PAO₂, gradients & ratios
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Osmolality & Osmolal Gap Calculated vs measured
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Visuals
Strong ions (SIDa)
SIDe components
Osmolality components
Clinical synthesis and unifying possibilities
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Clinical caution
This tool supports clinical reasoning and education. It does not replace clinical judgement, local protocols, or specialist advice.

Summary

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