About the

Oxygen Status Algorithm

Windows® program for calculation and interpretation of pH and blood gas data

The Oxygen Status Algorithm (OSA) calculates the Acid Base Status and the Oxygen Status of the blood and displays the results in the Acid Base Chart, the Oxygen Graph, the Blood Gas Map, and the Oxygen Consumption Diagram. It also produces a Laboratory Diagnosis, a printed Status Report, and Cumulated Report. It also allows predicting consequences of different therapeutic actions.

It is intended for laboratories using a combined blood pH-pCO2-pO2 and O2-CO-Met-Hemoglobin analyzer. It calculates a series of derived quantities, e.g. the extracellular hydrogen ion excess (ctH+Ecf), the total physiological veno-arterial shunt fraction (Fva), the half-saturation tension (p50), and the oxygen extraction tension (px), and thereby enhances the diagnostic potential of the pH-blood gas analyzer. OSA stores data in a TAB delimited ASCII text file.

The program is useful in the pre- and postgraduate teaching of respiratory physiology and acid-base balance.


1. The measured data (all input values) must be of high precision and accuracy to allow valid calculations.

2. Values for pO2a and/or pO2Alv should not be applied if the estimated functional v-a shunt (Fva) is negative.

3. Values for p50, cDPG, and px should not be applied if the measured oxygen saturation is above 0,97. If the imprecision of the measured oxygen saturation is higher than 0,001 this limit should be reduced to 0,95 or less.

4. Values for p50 and px should not be applied if the estimated 2,3-diphosphoglycerate concentration (cDPG) is less than 1 or higher than 9 mmol/L, unless the result is verified by direct independent measurement of the cDPG, or can be explained by the presence of a hemoglobin variant with abnormal hemoglobin-oxygen affinity.

5. User of the program has full responsibility for data quality and patient safety.

6. Author is neither responsible for errors in the Oxygen Status Algorithm, nor any economical loss or damage to hardware or software resulting from use of the program.

Program versions

The OSA program is developed by Prof. O.Siggaard-Andersen and Ph.D. M.Siggaard-Andersen, Denmark. It was originally distributed in DOS version 2.0 by Radiometer Copenhagen. DOS version 3.0 with on-line capabilities was distributed by the author. The present version is Windows version 1.0 written in Delphi 5 code. The program itself is a single compiled file (OSA.exe). The program and the algorithm are copyright 1994, 1999, 2003 by O.Siggaard-Andersen. The source code is available upon request.


The help system consists of five HTML documents:

1. AboutOSA.htm, the present text on program versions, etc.

2. OsaManual.htm, on how to use of the program.

3. OsaTextbook.htm, on the Acid-Base and Oxygen Status of the Blood, with descriptions of the graphical displays, all the equations, and a systematic list of all the acid-base and oxygen related quantities.

4. OsaAnthologyOnBE.htm, on the Base Excess concept.

5. OsaBibliography.htm

The five documents are compiled into one file (OSA.chm), using Microsoft HTMLHelp version 1.2. To install HTMLHelp version 1.2 run the HHUPD.EXE program found in the updates directory. HHUPD.EXE is redistribution of Microsoft’s original file and subject to Microsoft’s licensing conditions.


The common controls DLL must be of version 4.02 or newer to ensure correct display of all visual control elements. To update the DLL and associated files download and install the newest version of Internet Explorer from Microsoft.


M.Siggaard-Andersen, M.Sci.,Ph.D., and my colleagues Ivar H. Gøthgen, Dr. Med. Sci., Niels Fogh-Andersen, Dr. Med. Sci., and Peter D. Wimberley , Dr. Med.Sci., have been most helpful in the development of the program. I am grateful to all who have shown an interest and helped me with comments and suggestions.

2005 March 10


Olaf Poulsens Vej 7
DK-2920 Charlottenlund, Denmark