Arterial Blood pH Calculator

This calculator is rooted in the Henderson-Hasselbalch equation adapted for physiological plasma. The math demonstrates the relationship between blood pH, bicarbonate concentration ($HCO_3^-$, measured in mEq/L), and partial pressure of arterial carbon dioxide ($PaCO_2$, measured in mmHg). The core formula is: pH = 6.1 + log10 ( HCO3 / ( 0.0308 * PaCO2 ) ), where 6.1 represents the pKa of carbonic acid under physiological conditions, and 0.0308 is the solubility coefficient of carbon dioxide in blood plasma.

Imagine a patient in the intensive care unit with a bicarbonate level ($HCO_3$) of 24 mEq/L and a partial pressure of arterial carbon dioxide ($PaCO_2$) of 40 mmHg. First, multiply the $PaCO_2$ by the solubility coefficient: 40 * 0.0308 = 1.232. Next, divide the bicarbonate by this product: 24 / 1.232 = 19.48. Then, find the base-10 logarithm of that result: log10(19.48) = 1.289. Finally, add this value to the pKa constant: 6.1 + 1.289 = 7.389, which rounds to a normal arterial blood pH of 7.39.

Always cross-reference your calculated pH with a full arterial blood gas (ABG) panel to account for clinical context like oxygen saturation and patient history. Ensure your units are correct before entering data ($HCO_3$ in mEq/L or mmol/L, and $PaCO_2$ in mmHg). Remember that a single calculated value is a snapshot in time; trending values over hours is far more valuable for managing acute care patients.