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Blood Gas Analyser

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

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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

Report issues with this proforma. Do not include patient identifiers.

Inputs
Venous → arterial offsets (editable)
≈ −0.67 kPa
Educational approximations. PaO₂ is not inferred from venous samples.
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
Unit toggle converts gas pressures only. Concentrations remain in mmol/L (albumin in g/L).
Stewart: SIDa = (Na + K + Ca + Mg) − (Cl + Lactate). SIDe = 2.46×10⁻⁸×PaCO₂(mmHg)/10−pH + Albmmol/L×(0.123·pH−0.631) + Phos×(0.309·pH−0.469). SIG = SIDa − SIDe.
Interpretation
Enter values and click Calculate.
Run a calculation to view the step-by-step explainer.
Expected Compensation (Boston + Winter’s) Metabolic & respiratory rules
  • No results yet.
Anion Gap, Delta Ratio & Delta Gap Albumin-corrected AG & expected AG
  • No results yet.
Stewart (SID) SIDa / SIDe / SIG
  • No results yet.
Base Excess (BE) Siggaard–Andersen / Van Slyke
  • No results yet.
Oxygenation (Alveolar Gas, A–a, P/F) PAO₂, gradients & ratios
  • No results yet.
Osmolality & Osmolal Gap Calculated vs measured
  • No results yet.
Visuals
Strong ions (SIDa)
SIDe components
Osmolality components
Charts appear when enough data are present.
Clinical caution
This tool supports clinical reasoning and education. It does not replace clinical judgement, local protocols, or specialist advice.