Arterial Blood pH Calculator

Arterial blood pH reflects the balance between the metabolic component, represented by bicarbonate, and the respiratory component, represented by dissolved carbon dioxide. This calculator uses the Henderson-Hasselbalch equation: pH equals 6.1 plus the base-10 logarithm of bicarbonate divided by 0.03 times PaCO2. Bicarbonate is entered in milliequivalents per liter and arterial carbon dioxide pressure is entered in millimeters of mercury. With typical values of 24 mEq/L and 40 mmHg, the equation gives approximately 7.40 under standard clinical conditions. A calculated pH from 7.35 through 7.45 is generally described as the normal arterial range. A value below 7.35 indicates acidemia, while a value above 7.45 indicates alkalemia. These labels describe the direction of the blood pH at that moment; they do not by themselves identify the primary disorder. Low bicarbonate may point toward a metabolic acidifying process, high PaCO2 toward a respiratory acidifying process, high bicarbonate toward a metabolic alkalinizing process, and low PaCO2 toward a respiratory alkalinizing process. Real acid-base interpretation requires all arterial blood gas values and the clinical context. Compensation can move bicarbonate or PaCO2 in the opposite direction from the primary disturbance, and mixed disorders can produce a near-normal pH despite major abnormalities. Clinicians often compare measured compensation with expected rules such as Winter's formula, review the anion gap, and consider oxygenation, lactate, electrolytes, kidney function, medications, and the timing of ventilation changes. A laboratory analyzer directly reports pH with a sensitive electrode. The calculated value may differ slightly because of rounding, sample handling, temperature, unit assumptions, or because reported bicarbonate itself may be calculated. Never delay urgent assessment to use this tool. Severe pH disturbance can be life-threatening, and an unexpected arterial blood gas result requires prompt review by a qualified clinician. This calculator is intended for education and a mathematical cross-check, not diagnosis or independent treatment.