Blood Gas Interpreter Calculator

Arterial blood gas interpretation is really two separate assessments run side by side: an acid-base assessment built from pH, pCO2, and HCO3-, and an oxygenation assessment built from pO2 alone. This calculator keeps that separation exactly as clean as the textbook framework does -- pO2 has no influence at all on Acid-Base Status or Compensation, and pH, pCO2, and HCO3- have no influence on Oxygenation Status, across every value each input can take. On the acid-base side, a pH below 7.35 is frankly acidotic and above 7.45 is frankly alkalotic, but the primary disturbance is not read off pH alone: a fully compensated disorder can pull pH back inside the 7.35-7.45 range while pCO2 and HCO3- still show a clear primary derangement plus a compensatory response, so this calculator also uses which side of the 7.40 midpoint pH sits on to identify the primary driver even when pH itself has normalized. It then checks pCO2 (above 45 mmHg is a respiratory driver) and HCO3- (below 22 mEq/L or above 26 mEq/L is a metabolic driver) to decide whether the primary disturbance is respiratory, metabolic, or mixed, and separately grades Compensation as none, partial, or full: full compensation means the opposing value (HCO3- for a respiratory disorder, pCO2 for a metabolic one) has moved enough that pH sits back within 7.35-7.45 while the primary derangement persists; partial compensation means the opposing value is moving in the corrective direction but pH is still outside that range.

This calculator uses these threshold-based rules rather than a quantitative Winter's formula (the expected pCO2 for a given HCO3- in metabolic acidosis) and does not calculate an anion gap, so it should be read as a directional teaching aid, not a substitute for full ABG interpretation against those formulas. On the oxygenation side, pO2 alone sorts the result into normal (80 mmHg or above), mild, moderate, or severe hypoxemia, with lower pO2 always mapping to an equal or worse classification across this calculator's full 20-600 mmHg range. The calculator also accepts a Base Excess value, but it is not currently used in any of the three classifications -- Acid- Base Status, Compensation, and Oxygenation Status are all determined without reference to it, so it should be read as supplementary context rather than as an input that changes the result.