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Alveolar Gas Equation & A-a Oxygen Gradient Calculator

The Alveolar Gas Equation calculates the partial pressure of oxygen within the alveoli of the lungs.

Calculated Result
99.7 mmHg

Alveolar Oxygen Tension (PAO2)

PAO2 in kPa

13.30 kPa

Dry Inspired Oxygen Tension

149.7 mmHg

Respiratory Exchange Ratio R

0.8

Calculation Breakdown

  1. Calculate dry gas partial pressure accounting for 37°C water vapor (47 mmHg)P_dry = 760 - 47 = 713 mmHg
  2. Apply alveolar gas equation PAO2 = FiO2 · (Patm - 47) - (PaCO2 / R)PAO2 = 0.21 * 713 - (40 / 0.8) = 99.7 mmHg

PAO2 vs Inspired Oxygen Fraction (FiO2)

Interactive visualization based on your current inputs

mmHg
0.016633249766321% (Room Air)35% (Nasal Cannula)50% (Venturi Mask)100% (Non-Rebreather)FiO2PAO2 (mmHg)

What Is the Alveolar Gas Equation (PAO2) Arterial Oxygen Tension Calculator?

The alveolar gas equation computes the ideal partial pressure of oxygen in pulmonary alveoli to identify ventilation-perfusion mismatching and shunt pathology.

How Does the Alveolar Gas Equation (PAO2) Arterial Oxygen Tension Calculator Work?

The calculation evaluates user-provided measurements using recognized domain equations, converts between measurement units, and adjusts for real-world efficiency factors.

Alveolar Gas Equation (PAO2) Arterial Oxygen Tension Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

P_A\text{O}_2 = F_i\text{O}_2 (P_{\text{atm}} - 47) - \frac{P_a\text{CO}_2}{R}

Inspired gas is fully saturated with body-temperature water vapor (47 mmHg at 37°C) before reaching the gas-exchange alveoli.

How to Use the Alveolar Gas Equation (PAO2) Arterial Oxygen Tension Calculator

  1. Enter your primary measurements in the input fields above.
  2. Select your preferred units (e.g. metric or imperial) if applicable.
  3. Review or adjust operational assumptions such as field efficiency.
  4. Click Calculate to instantly generate the full results breakdown and visual chart.
  5. Use the Reset button at any time to clear the form and test a new scenario.

Step-by-Step Example Calculation

Room Air Sea Level Healthy Adult

Input Values:

fio2Fraction:0.21
barometricPressureMmhg:760
paco2Mmhg:40
respiratoryQuotient:0.8

Understanding Your Result

Your calculated result represents the realistic operational capacity or baseline output under the specified conditions. Comparing theoretical and effective outputs reveals the direct impact of turns, overlap, and practical downtime.

Factors That Affect the Result

Field terrain, operator experience, equipment maintenance, overlap margin, and weather conditions can significantly influence real-world output.

When Should You Use This Calculator?

Use this calculator whenever you need quick, verified estimates for job planning, budgeting, equipment sizing, or project timelines.

Assumptions & Limitations

  • Saturated water vapor pressure is fixed at 47 mmHg under normal body temperature (37°C).

Frequently Asked Questions

Calculation Accuracy & Reference Note

This calculator implements verified, deterministic mathematical equations based on published standards. Results should be treated as professional engineering estimates; always verify critical operations with local equipment manuals and site inspections.

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