Acid-Base & Blood Gas
Every acid-base & blood gas calculator on CalcEngines — unit converters, derived indices and interpretive tools, each with its formula, a worked example and the reference intervals it is judged against.
22 calculators in this section
- A-a Gradient CalculatorCalculate the alveolar-arterial oxygen gradient to distinguish hypoxaemia from V/Q mismatch or shunt from hypoxaemia caused by hypoventilation alone.
- Albumin-Corrected Anion Gap CalculatorCorrect the anion gap for hypoalbuminaemia, which lowers the measured gap and can hide a clinically significant high-anion-gap acidosis.
- Alveolar Gas Equation Calculator (PAO₂)Calculate alveolar pO₂ from FiO₂, PaCO₂, atmospheric pressure and respiratory quotient — the reference value the A-a gradient is built on.
- Anion Gap CalculatorCalculate the serum anion gap from sodium, chloride and bicarbonate — with the interval that belongs to this formula, not the one the textbooks printed before ion-selective electrodes.
- Arterial Blood Gas InterpreterRead a whole arterial blood gas rather than one number from it: pH, pCO₂ and bicarbonate together name the primary disorder, say whether it is acute or chronic, and test the compensation against the published expected range — where a value outside that range means a second disorder, not over-compensation.
- Arterial Oxygen Content (CaO₂) CalculatorCalculate CaO₂ from haemoglobin, saturation and pO₂ — and see why anaemia costs far more oxygen content than a modest desaturation.
- Base Excess Calculator (Standard Base Excess)Standard base excess from pH and bicarbonate by the Siggaard-Andersen form of the Van Slyke equation — the measure of how much metabolic acid or base is present independent of the respiratory component, which is exactly what bicarbonate alone cannot tell you.
- Bicarbonate Deficit CalculatorEstimate the bicarbonate needed to reach a target level, and see why bicarbonate replacement remains a genuinely controversial therapy.
- Delta Ratio Calculator (Delta Gap)Classify a high-anion-gap acidosis as pure or mixed by comparing the rise in the anion gap against the fall in bicarbonate.
- Expected pCO₂ in Metabolic Alkalosis CalculatorCheck whether the measured pCO₂ shows appropriate respiratory compensation for a metabolic alkalosis — the mirror of Winter's formula, which belongs to metabolic acidosis and must not be used here.
- Henderson-Hasselbalch CalculatorCalculate pH from bicarbonate and pCO₂ using the equation blood gas analysers themselves rely on.
- Lactate Unit ConverterConvert blood lactate between mg/dL, mmol/L, µmol/L and mg/L, with the 2 and 4 mmol/L thresholds, the sampling artefacts that invent a high result, and why clearance beats any single value.
- Oxygen Delivery (DO₂) CalculatorCalculate DO₂ from oxygen content and cardiac output, and see why chasing a supranormal target does not help.
- Oxygen Extraction Ratio CalculatorThe fraction of delivered oxygen the tissues take up, from arterial and venous oxygen content. A rising extraction ratio means delivery is failing to meet demand — the physiological question behind lactate and ScvO₂ monitoring.
- PaO₂/FiO₂ (P/F) Ratio CalculatorCalculate the P/F ratio, the oxygenation criterion in the Berlin definition of ARDS severity.
- pCO₂ Unit Converter (mmHg to kPa)Convert arterial pCO₂ from mmHg to kPa, using the same factor as pO₂, with the type 2 respiratory failure threshold.
- pO₂ Unit Converter (mmHg to kPa)Convert arterial pO₂ from mmHg to kPa — the commonest source of confusion when reading a blood gas from another country.
- Raised Lactate Interpreter: Type A, Type B or D-LactateWork out why a lactate is raised. Enter the lactate and the context — hypotension or vasopressors, infection, hypoxia, metformin, salbutamol, propofol, liver failure, thiamine risk, cancer, a recent seizure, short bowel — and the page separates type A (hypoperfusion or hypoxia) from type B causes and flags D-lactic acidosis, which the standard assay cannot detect. It applies the Sepsis-3 septic shock threshold and the Surviving Sepsis remeasurement advice.
- Strong Ion Difference CalculatorApparent strong ion difference by the Stewart physicochemical approach — the account of acid-base balance that explains why the bicarbonate moved rather than recording that it did, and that predicts the acidosis large-volume saline causes. A second lens, not a replacement for the anion gap and base excess.
- VBG vs ABG InterpreterYou have a venous gas. Can you act on it, or do you need an arterial one? That depends entirely on what you are trying to establish, so this page asks. It deliberately does not convert a venous pCO₂ to an arterial one — the limits of agreement are about ±20 mmHg, which makes a point estimate dishonest. For the one value that is worth converting, see the venous to arterial blood gas converter.
- Venous to Arterial Blood Gas ConverterA peripheral venous gas is a good screen for pH and bicarbonate and a poor substitute for an arterial pO₂ — venous oxygen tells you nothing about oxygenation. This converts the one value the evidence supports converting, and says plainly why it will not convert the others.
- Winter’s Formula CalculatorCheck whether the measured pCO₂ shows appropriate respiratory compensation for a metabolic acidosis, or a second acid-base disorder.