Arterial Blood pH Calculator
Estimate arterial blood pH from bicarbonate and PaCO2 using the Henderson-Hasselbalch equation.
Arterial Blood pH and the Henderson-Hasselbalch Equation
Arterial blood pH reflects the balance between acids and bases in blood. This calculator estimates pH from bicarbonate (HCO₃⁻) and arterial carbon dioxide partial pressure (PaCO₂) using the Henderson-Hasselbalch equation. For broader acid-base analysis, see the Acid Base Calculator and Anion Gap Calculator.
pH Formula
$$pH = 6.1 + \log_{10}\left(\frac{HCO_3}{0.0308 \times PaCO_2}\right)$$
Bicarbonate is entered in mEq/L (equivalent to mmol/L) and PaCO₂ in mmHg. Normal arterial pH is 7.35 to 7.45.
Acidosis vs Alkalosis
pH below 7.35 indicates acidemia (acidosis); above 7.45 indicates alkalemia (alkalosis). Determining whether the disturbance is respiratory or metabolic requires comparing PaCO₂ and HCO₃⁻ to their normal ranges alongside the calculated pH.
Frequently Asked Questions
What is normal arterial blood pH?
Normal arterial pH ranges from 7.35 to 7.45. Venous pH is typically 0.03 to 0.05 units lower due to higher dissolved CO₂.
What are normal PaCO₂ and bicarbonate values?
Normal PaCO₂ is 35–45 mmHg and normal bicarbonate is 22–26 mEq/L in adults.
Why use 0.0308 in the formula?
0.0308 is the solubility coefficient of CO₂ in plasma at 37 °C, relating PaCO₂ to dissolved carbonic acid in the Henderson-Hasselbalch equation.
Can this calculator diagnose the type of acid-base disorder?
This tool calculates pH only. Full ABG interpretation requires assessing whether PaCO₂ and HCO₃⁻ are primary or compensatory changes.
Is venous blood pH the same as arterial?
No. Venous blood is more acidic. Use arterial values for this calculator; for venous estimates see dedicated venous pH tools.
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