Gas Exchange & Oxygenation

Oxygen delivery starts in the alveolus and ends at the mitochondria — these calculators track every step. From the alveolar gas equation and A-a gradient that localize the failure, to CaO₂ and DO₂ that quantify what reaches the tissues, this set covers the full oxygenation chain used daily in the ICU, ED, and pulmonary clinic.

13 calculators available

A-a Gradient

Alveolar-to-arterial oxygen gap — tells hypoventilation apart from a lung transfer problem.

a/A Ratio

Arterial oxygen as a fraction of alveolar oxygen — steadier than the A-a gradient across FiO₂ changes.

PF Ratio (PaO₂/FiO₂)

Grades hypoxemia severity — the core metric for diagnosing and staging ARDS.

Oxygenation Index (OI)

Combines mean airway pressure with the PF ratio — used in severe failure and ECMO decisions.

Arterial Oxygen Content (CaO₂)

Total oxygen carried per deciliter of arterial blood — why hemoglobin matters as much as PaO₂.

Venous Oxygen Content (CvO₂)

Oxygen left in the blood after tissues extract what they need.

Oxygen Consumption (VO₂)

How fast the body uses oxygen, from the Fick principle.

Oxygen Delivery (DO₂)

Total oxygen the heart pumps to the body each minute.

Pulmonary Shunt Fraction (Qs/Qt)

Fraction of blood passing the lungs that never picks up oxygen.

FiO₂ from Nasal Cannula Flow

Estimates delivered oxygen percentage from nasal cannula flow rate.

PaO₂ Correction for FiO₂

High-FiO₂ rule of thumb for whether oxygenation matches the oxygen given.

In-Flight PaO₂ Estimation

Predicts blood oxygen at cabin altitude to assess fitness to fly.

Alveolar Oxygen Pressure (PAO₂)

The alveolar gas equation on its own — expected oxygen inside the alveoli.