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A-a Gradient   ExpectedAaG = 2.5 + (0.21 * Age) MeasuredAaG = (FIO2 * (pAtm - pH2O)) - (pCO2 / RespQuot) + (pCO2 * FIO2 * (1 - RespQuot) / RespQuot) - paO2   Input:   Age   mo yr Patient Temp   degC degF Elevation   cm ft in micm mm m nm yd Percent Inspired O2   %O2 fractionO2 litresO2 p CO2   Pascal atm bar cmH2O cmHg ftH2O gm/sqcm inH2O inHg kPa mbar mmHg psi torr Resp Quot   % fraction ratio p aO2   Pascal atm bar cmH2O cmHg ftH2O gm/sqcm inH2O inHg kPa mbar mmHg psi torr Results:   Expected AaG   Pascal atm bar cmH2O cmHg ftH2O gm/sqcm inH2O inHg kPa mbar mmHg psi torr Measured AaG   Pascal atm bar cmH2O cmHg ftH2O gm/sqcm inH2O inHg kPa mbar mmHg psi torr   Decimal Precision: 0 1 2 3           Notes High A-a gradients are associated with oxygen transfer / gas exchange problems. These are usually associated with alveolar membrane diseases, interstitial diseases or V/Q mismatch. Hypoxemia in the face of a normal A-a gradient implies hypoventilation with displacement of alveolar O2 by CO2 or other substance. The FIO2 (fraction of inspired oxygen) is equal to the Percent Inspired O2 / 100. In this calculator, pATM is estimated by elevation above sea level using this formula: pAtm = 760 * eTo(Elevation / -7000) pH2O is dependent on body temperature and calculated with the following formula: pH2O = 47 * eTo((Patient Temp - 37) / 18.4) The equation for expected A-a gradient assumes the patient is breathing room air; therefore, it is less accurate at higher percentages of inspired oxygen.   Related Results            Pull down to select a related equation and transfer values in common a/A Ratio     [ p_CO2, Resp_Quot, p_aO2 ] Amikacin Dosing to Produce Desired Peak and Trough Levels     [ Age ] Amikacin Level Prediction from Maintenance Dosing     [ Age ] Aminoglycoside Clearance Estimate     [ Age ] AUC Dose Calculation for Carboplatin (Calvert formula)     [ Age ] Blood Pressure Percentiles for Boys (2 - 17 years)     [ Age ] Blood Pressure Percentiles for Girls (2 - 17 years)     [ Age ] Body Mass Index Percentiles for Boys (2 - 20 years)     [ Age ] Body Mass Index Percentiles for Girls (2 - 20 years)     [ Age ] Creatinine Clearance Estimate by Cockcroft-Gault Equation (SI units)     [ Age ] Creatinine Clearance Estimate by Cockcroft-Gault Equation     [ Age ] Creatinine clearance estimate for changing serum creatinine     [ Age ] Diabetes Risk Score (Type 2)     [ Age ] Framingham 10 Year Risk of General Cardiovascular Disease (2008 paper)     [ Age ] Gentamycin Dosing to Produce Desired Peak and Trough Levels     [ Age ] Gentamycin Level Prediction from Maintenance Dosing     [ Age ] Glomerular Filtration Rate Estimate by Abbreviated MDRD Study Equation (SI units)     [ Age ] Glomerular Filtration Rate Estimate by Abbreviated MDRD Study Equation     [ Age ] Glomerular Filtration Rate Estimate by Quadratic Equation     [ Age ] Glomerular Filtration Rate Estimation using the MDRD Equation (SI units)     [ Age ] Glomerular Filtration Rate Estimation using the MDRD Equation     [ Age ] Harris-Benedict Estimation of Basal Energy Expenditure     [ Age ] Height for Age Percentiles for Boys (2 - 20 years)     [ Age ] Height for Age Percentiles for Girls (2 - 20 years)     [ Age ] Hepatitis C Fibrosis Prediction Score     [ Age ] Infant Head Circumference for Age Percentiles (< 36 months)     [ Age ] Infant Length for Age Percentiles (< 36 months)     [ Age ] Infant Weight for Age Percentiles (< 36 months)     [ Age ] Lung Cancer One Year Risk Estimation (for smokers 50-75 years old)     [ Age ] Osteoporosis Risk Assessment by Composite Linear Estimate (ORACLE score)     [ Age ] Osteoporosis Risk SCORE (Simple Calculated Osteoporosis Risk Estimation)     [ Age ] Osteoporosis Self Assessment Tool for Men     [ Age ] Osteoporosis Self Assessment Tool for Women     [ Age ] paO2 / FIO2 Ratio (for MODS Calculation)     [ p_aO2 ] Peak Expiratory Flow Prediction     [ Age ] PELD Score for End-Stage Liver Disease (patients less than 12 years old)     [ Age ] PFT Adjusted Predicted Values for Men MultiCalc     [ Age ] PFT Adjusted Predicted Values for Women MultiCalc     [ Age ] PFT Predicted Values for Boys MultiCalc     [ Age ] PFT Predicted Values for Girls MultiCalc     [ Age ] PFT Predicted Values for Men MultiCalc     [ Age ] PFT Predicted Values for Women MultiCalc     [ Age ] Renal Artery Stenosis Prediction Rule     [ Age ] Solitary Pulmonary Nodule Malignancy Risk     [ Age ] Stroke Risk in Diabetes Type 2 UKPDS 60     [ Age ] Stroke Risk in Patients 55-84 Years Old (Framingham data)     [ Age ] Systolic Murmur Significance Probability     [ Age ] Tobramycin Dosing to Produce Desired Peak and Trough Levels     [ Age ] Tobramycin Level Prediction from Maintenance Dosing     [ Age ] Total Body Water (BIA formula)     [ Age ] Total Body Water in Men (Johansson formula)     [ Age ] Total Body Water in Men (Watson formula)     [ Age ] Total Body Water in Women (Johansson formula)     [ Age ] Total Daily Energy Requirement Estimate     [ Age ] Vancomycin Dosing to Produce Desired Peak and Trough Levels     [ Age ] Vancomycin Level Prediction from Maintenance Dosing     [ Age ] Volume of Distribution of Urea     [ Age ] Weight for Age Percentiles for Boys (2-20 years)     [ Age ] Weight for Age Percentiles for Girls (2-20 years)     [ Age ] WHO Assessment of Malnutrition in Boys 0 to 2 Years Old     [ Age ] WHO Assessment of Malnutrition in Boys 2 to 5 years Old     [ Age ] WHO Assessment of Malnutrition in Girls 0 to 2 Years Old     [ Age ] WHO Assessment of Malnutrition in Girls 2 to 5 years Old     [ Age ]       References Kanber GJ, King FW, Eshchar YR, et. al. The alveolar-arterial oxygen gradient in young and elderly men during air and oxygen breathing. Am Rev Respir Dis. 1968 Mar;97(3):376-81. Mellemgaard K. The alveolar-arterial oxygen difference: its size and components in normal man. Acta Physiol Scand. 1966 May;67(1):10-20.     Legal Notices and Disclaimer   All information contained in and produced by the MedCalc 3000 system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER. Click here for full notice and disclaimer.   MedCalc 3000 is Copyright © 1998-2008 Foundation Internet Services, LLC    [Build 237646 v9.1]