LogHCO3003pCO2

LogHCO3003pCO2 refers to the base-10 logarithm of the ratio between bicarbonate concentration and dissolved carbon dioxide in blood, represented by the expression [HCO3-] / (0.03 × pCO2). This form appears in the Henderson-Hasselbalch equation used in physiology to relate bicarbonate and carbon dioxide to blood pH: pH = pKa + log10([HCO3-] / (0.03 × pCO2)). Here pKa for carbonic acid at body temperature is about 6.1, and 0.03 is the CO2 solubility coefficient in plasma (mmol/L per mmHg). The ratio is dimensionless because [HCO3-] is in mmol/L and pCO2 is in mmHg, with the 0.03 factor converting the dissolved CO2 to the same units.

Interpretation and use: The log ratio increases as bicarbonate rises relative to dissolved CO2. Clinically, the value helps distinguish metabolic from respiratory contributions to acid-base status. An elevated bicarbonate or a reduction in pCO2 (hyperventilation) can raise the ratio, while metabolic acidosis lowers it. The ratio is not the pH itself, but a derived quantity that summarizes the balance of metabolic and respiratory components.

Example: If [HCO3-] = 24 mmol/L and pCO2 = 40 mmHg, 0.03 × pCO2 = 1.2; the ratio is 24 / 1.2 = 20, and log10(20) ≈ 1.30. Limitations include temperature sensitivity (pKa varies with temperature), measurement variability, and the fact that it is a simplified representation of complex acid-base dynamics.