ConverterHub

Alveolar Gas Equation Calculator

Find alveolar oxygen pressure and the A–a gradient.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

The alveolar gas equation — PAO2 = FiO2 × (Patm − PH2O) − (PaCO2 / R) — calculates the partial pressure of oxygen inside the alveoli. Combined with a measured arterial PaO2, it produces the A–a gradient, a key diagnostic value in pulmonology and critical care for assessing how well oxygen is diffusing from the lungs into the blood.

Physicians, respiratory therapists and medical students use it to distinguish the causes of low blood oxygen: the A–a gradient stays normal when hypoxemia is caused by simple hypoventilation, but rises when the real problem is a ventilation-perfusion mismatch, a shunt, or a diffusion defect.

This calculator takes FiO2, PaCO2, measured PaO2 and atmospheric pressure (or altitude), and returns the calculated PAO2 and the resulting A–a gradient.

Was this helpful?

Comments (0)

  • Be the first to comment.

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators