Henderson–Hasselbalch pH
Provide arterial bicarbonate (HCO₃⁻) and PaCO₂ to calculate arterial blood pH and hydrogen ion concentration. Useful for cross-checking arterial blood gas reports or performing quick acid-base assessments.
Estimated arterial pH
7.401
Hydrogen ion concentration
39.7 nEq/L
Normal arterial pH (7.35–7.45)
How to Use This Calculator
Obtain arterial blood gas values
Use arterial bicarbonate and PaCO₂ from the same blood gas sample for accurate estimation.
Enter values in standard units
HCO₃⁻ in mEq/L (or mmol/L) and PaCO₂ in mmHg. The calculator uses the Henderson–Hasselbalch equation.
Interpret results in clinical context
Compare with measured pH, assess acid-base disorders, and evaluate compensation using other calculators if needed.
Formula
pH = 6.1 + log₁₀ (HCO₃⁻ ÷ (0.03 × PaCO₂))
[H⁺] (nEq/L) = 10^(9 − pH)
Derived from the Henderson–Hasselbalch equation assuming dissolved CO₂ = 0.03 × PaCO₂.
Full Description
The Henderson–Hasselbalch equation relates pH to bicarbonate and carbon dioxide in blood, elucidating the balance between metabolic (HCO₃⁻) and respiratory (PaCO₂) components. While arterial blood gas analysers report pH directly, this calculation is useful for bedside checks, acid-base teaching, and estimating changes after therapy. Use results alongside clinical assessment, anion gap analysis, and compensation calculations to diagnose complex acid-base disorders.
Frequently Asked Questions
How accurate is Henderson–Hasselbalch?
It closely approximates arterial pH when bicarbonate and PaCO₂ are accurate. Deviations occur with significant measurement error or non-standard conditions.
Can I use venous values?
Venous bicarbonate is similar to arterial, but venous PaCO₂ differs. For venous blood gases, convert to arterial equivalents before calculating.
Why compute hydrogen ion concentration?
Hydrogen ion concentration in nEq/L offers an intuitive view of acidemia/alkalemia severity and aids in teaching physiology.
How does temperature affect the equation?
The constants assume 37 °C. In hypothermia or hyperthermia, arterial blood gas analysers provide temperature-corrected values.