# Alveolar - arterial (A-a) Gradient > Medical calculator for alveolar-arterial oxygen gradient and PaO2/FiO2 ratio. (iPhone/iPad app by Satish Deopujari.) - Source: https://appshunter.io/ios/app/alveolar-arterial-a-a-gradient/id996385661 (this page in markdown: same URL + `.md`) - Developer: [Satish Deopujari](https://appshunter.io/developer/1180072702) - Category: Medical, Education - Price: Free - Rating: 5.00/5 from 1 App Store ratings · 9 written reviews indexed - Age rating: 17+ - Requires: iOS 8.0 · 16 MB - Languages: American English - Released: 2015-07-24 - Data updated: 2026-07-08 - Monetization: free - User reviews in markdown: https://appshunter.io/ios/app/alveolar-arterial-a-a-gradient/id996385661/reviews.md ## What is Alveolar? A-a oxygen gradient — The alveolar - arterial (A-a) oxygen gradient is a measure of oxygen transfer across alveolar capillary membrane (“A” denotes alveolar and “a” denotes arterial oxygenation). It is the difference between the amount of the oxygen in the alveoli. PAO2 = Alveolar oxygen tension PaO2 = Arterial oxygen tension A-a oxygen gradient = PAO2 - PaO2. PaO2 is derived from ABG while PAO2 is calculated. PAO2 = (FiO2 x [Patm - PH2O]) - (PaCO2 ÷ R) FiO2 is the fraction of inspired oxygen (0.21 at room air). Patm is the atmospheric pressure (760 mmHg at sea level). PH2O is the partial pressure of water (47 mmHg ). PaCO2 is derived from ABG , and R is the respiratory quotient. (The respiratory quotient is approximately 0.8 at normal physiological state) A-a gradient varies with age and can be estimated from the following equation, assuming the patient is breathing room air. A-a gradient = 2.5 + 0.21 x age in years A-a gradient increases with higher FiO2. PaO2/FiO2 ratio — The PaO2/FiO2 ratio is a measure of oxygen transfer across the alveolar capillary membrane . Normal PaO2/FiO2 ratio is 300 to 500 mmHg, with values less than 300 mmHg indicating impaired gas exchange and values less than 200 mmHg indicates severe hypoxemia . Concept By: Dr. Satish Deopujari Dr Vivek Shivhare Disclaimer: This app is based on equations available publicly in Medical domain.  The information contained on this app is intended for educational purposes only. It does not constitute medical advice. You should consult a physician regarding medical diagnosis or treatment. ## Key features - Alveolar-arterial oxygen gradient calculation - PaO2/FiO2 ratio calculation - Formulas for PAO2 and A-a gradient - Educational explanations of respiratory measurements - Supports room air and variable FiO2 ## Recent user reviews (9 of 9) All indexed reviews: https://appshunter.io/ios/app/alveolar-arterial-a-a-gradient/id996385661/reviews.md ### 5/5 — Dr j vegad *2015-08-09, version 1.0.3* Simply awesome. Makes highly technical issue reasonably simple ### 5/5 — User friendly app *2015-08-08, version 1.0.3* This app is extremely useful. ### 5/5 — A-a Simplified *2015-08-07, version 1.0.3* Great app...... It will make life easy for intensive care physicians. That's what technology is for- to make life easier. ### 3/5 — Simplified app for Neonatal Intensivist *2015-08-03, version 1.0.3* Neat and clean look. Nice use of blue - red colours hue demonstrating the Oxygen saturation. ### 5/5 — Fantastic app!! *2015-08-02, version 1.0.3* Working up a patient with hypoxemia couldn't have got simpler! A fantastic app at ur service to get the alveolar arterial gradient within seconds. Perfect for use in ICUs. ### 5/5 — Dr Anil Jain *2015-07-27, version 1.0.3* Excellent application for students, nurses and teachers in critical care units. Congratulations Dr deopujari for developing such a wonderful programme. ### 5/5 — Awesome app! *2015-07-25, version 1.0.3* Wonderfully designed productive app for PICU & NICUs. Need some more like these for the practicing Paediatricians and Neonatologists. ### 5/5 — Special moment *2015-07-24, version 1.0.3* This is the only application in the App Store which has simplified the way ABG and other calculations are done . My heartiest congratulations to the developers team and the man behind this Dr Satish Deopujari sir , the gem of our city nagpur !! ### 5/5 — A-a gradient......!!!! *2015-07-24, version 1.0.3* A splendid app for all intensivist...!!! A thought provoking app... Understand what we were doing for O2 status, will now change the concept..!!! ## Frequently asked questions about Alveolar ### What is the A-a gradient calculator app? The A-a gradient calculator app is a tool designed to help users compute the alveolar-arterial oxygen gradient (A-a gradient) and the PaO2/FiO2 ratio. It utilizes established medical formulas for these calculations. ### How does the A-a gradient calculator app work? The app uses provided inputs such as arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), and fraction of inspired oxygen (FiO2) to calculate the A-a gradient and PaO2/FiO2 ratio. It also offers an age-based estimation for the A-a gradient on room air. ### Is the A-a gradient calculator app free to use? Yes, the A-a gradient calculator app is available for free. It does not require any payment for download or usage of its features. ### What devices support the A-a gradient calculator app? The A-a gradient calculator app is supported on iPhone, iPad, and iPod devices. It is designed for iOS users. ### What is the age rating for the A-a gradient calculator app? The app has an age rating of 17+. This indicates that it is intended for mature users, likely due to its medical context. ### When was the A-a gradient calculator app last updated? The A-a gradient calculator app was last updated on March 24, 2016. The latest version available is 1.0.5. ### Does the A-a gradient calculator app have ads? No, the A-a gradient calculator app does not contain advertisements. Users can utilize its features without encountering any ads. ### What is the user rating for the A-a gradient calculator app? The A-a gradient calculator app has a rating of 5.0 stars based on one user review. This suggests a very positive reception from its users. ## Version history (last 3 releases) ### 1.0.5 — 2016-03-24 This app has been updated by Apple to display the Apple Watch app icon. Bug fixes and enhancements. ### 1.0.4 — 2015-11-06 iOS9 support Add/update/delete feature for patient records Minor fixes ### 1.0.3 — 2015-07-24 No release notes. ## Apps similar to Alveolar | App | Rating | Price | Category | | --- | --- | --- | --- | | [Meducator - Medical AI](https://appshunter.io/ios/app/meducator-medical-ai/id1659157660) | 4.8 (23) | Free | Medical | | [ImmerseRx mNSCLC Immunotherapy](https://appshunter.io/ios/app/immerserx-mnsclc-immunotherapy/id1640327940) | 5.0 (1) | Free | Medical | | [Verifie Health](https://appshunter.io/ios/app/verifie-health/id1594121580) | — | Free | Medical | | [TOKA Surgery Simulator](https://appshunter.io/ios/app/toka-surgery-simulator/id1589939900) | 2.0 (6) | Free | Medical | | [misTMJ](https://appshunter.io/ios/app/mistmj/id1592838220) | — | Free | Medical | | [MiMed Pharmacy](https://appshunter.io/ios/app/mimed-pharmacy/id1639863000) | 5.0 (1) | Free | Medical | ## More apps by Satish Deopujari - [ODC Tutor](https://appshunter.io/ios/app/odc-tutor/id993661003) - [Complete ABG](https://appshunter.io/ios/app/complete-abg/id993718869) - [Medical MCQs](https://appshunter.io/ios/app/medical-mcqs/id1011714896) - [ETCO2 Tutor](https://appshunter.io/ios/app/etco2-tutor/id1047646888) - [Rx Pediatric Dehydration](https://appshunter.io/ios/app/rx-pediatric-dehydration/id1051199730) All apps by Satish Deopujari: https://appshunter.io/developer/1180072702 ## Related topics [satish deopujari](https://appshunter.io/ios/topics/satish-deopujari) --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-08.*