FiO2 Estimation & Oxygen Correction Calculator
- FiO2 Estimation Calculator: Clinical explanation and context
This calculator implements the original formulas provided in this tool template. The formulas are preserved as they were supplied. Users should be aware that some formulas in this tool do not match conventional physiologic equations for alveolar oxygen calculation or for alveolar arterial oxygen gradient. The following text provides clinical context and references to established physiology and practice so clinicians can interpret results carefully.
Background physiology
Oxygenation in the lung is determined by alveolar oxygen partial pressure, transfer across the alveolar capillary membrane, ventilation distribution, perfusion distribution, and the fraction of inspired oxygen. The alveolar gas equation provides a standard method to estimate alveolar oxygen partial pressure from inspired oxygen fraction and arterial carbon dioxide partial pressure. The alveolar gas equation and the alveolar arterial oxygen gradient are widely used in clinical care to identify causes of hypoxemia and to quantify severity of impairment in gas exchange.
Comparison with the formulas used here
The classic alveolar gas equation and the alveolar arterial oxygen gradient are not the same as the internal formulas retained in this calculator. The alveolar gas equation is typically written as PAO2 equals FiO2 multiplied by atmospheric pressure minus water vapor pressure minus PaCO2 divided by respiratory quotient. The alveolar arterial oxygen gradient is PAO2 minus PaO2. Clinicians who need to perform evidence based evaluation of oxygenation should use the alveolar gas equation and Aa gradient in clinical decision making. This tool retains the original calculation set for consistency with the existing tool base. Interpret output with caution and correlate clinically.
Clinical use recommendations
Use this tool only as an adjunct to clinical judgement. Always interpret calculated FiO2 and derived values together with the clinical picture, arterial blood gas values, method of oxygen delivery, oxygen device settings, chest imaging, and other relevant data. If the goal is to estimate alveolar oxygen or to evaluate gas exchange efficiency, consider using established formulas such as the alveolar gas equation and the Aa gradient and consult standard references.
References
West JB. Respiratory Physiology the Essentials. Latest edition. This classic textbook covers alveolar gas equation and determinants of oxygenation.
Rivolta M, et al. Clinical review articles on oxygen therapy and oxygenation assessment in critical care journals and textbook chapters provide practical guidance for oxygen delivery and FiO2 estimation in different devices.
American Thoracic Society and European Respiratory Society statements on oxygen therapy and acute respiratory failure give consensus guidance on oxygen targets oxygen delivery devices and monitoring.
Berlin DA et al. The Berlin definition for acute respiratory distress syndrome provides standard criteria for oxygenation severity classification in acute respiratory failure.
Please consult up to date clinical guidelines and institutional protocols when applying oxygen therapy strategies and when interpreting arterial blood gas results.
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