Learning Objective:
Understand and apply the Henderson–Hasselbalch equation to calculate blood pH using bicarbonate concentration and arterial .

Formula:

Explanation:

• = plasma bicarbonate concentration (mEq/L)
• = partial pressure of CO₂ in arterial blood (mm Hg)
• 0.03 = solubility constant of CO₂ in blood (mmol/L·mm Hg)

This equation relates pH, bicarbonate (metabolic component), and CO₂ (respiratory component) — forming the foundation of acid–base balance assessment.

Concept Summary:

• ↑ → Metabolic alkalosis
• ↓ → Metabolic acidosis
• ↑ → Respiratory acidosis
• ↓ → Respiratory alkalosis

Example:

Given:

✅ Answer: Normal extracellular pH = 7.4