Manual (revised 2005-03-10)

Oxygen Status Algorithm

The Oxygen Status Algorithm opens with a Data Page with default values.

Fill in all the yellow fields guided by the advice in Hints and Status Line.

Input must be ended with TAB or ENTER to be effective.

Input Fields are yellow, Output Fields white.

Popup Hints for labels show quantity names.

Popup Hints for data fields show reference values.

The Status Line at the bottom of the page gives the same information and in addition the limits of input.

The program automatically calculates and updates the output fields upon completion of each input field. This may temporarily cause odd values for calculated quantities until all input variables have been entered.

Some of the fields may be either input or output depending upon the selection made in the pull down menu ‘Input’.

Several output fields may be unhidden (or hidden) by left clicking the label.

Extensive help is available by selecting menu ‘Help’ or by pressing F1.

Title Line

at top of page shows icon, name of program, and name of any opened data file.

Status Line

gives information on current input: quantity name, reference values, and input limits, i.e. limits for calculations. Current page number and total number of pages in the current ‘data book’ are shown in the lower right corner.


pop up when the cursor is above Labels or Data Fields.

Labels show quantity symbols, - hints quantity names.
Data Fields show keyed-in or calculated values, - hints reference values.

Hidden Values

are toggled on/off by left clicking the Label. In order to make the Data Page less crowded, only essential quantities are permanently shown.

F1 Key

also called Help Key, opens this Manual on the page relevant for the current input or menu item.

PrtScr Key

Pressing PrtScr gives snapshot of the whole screen.

Pressing Alt-PrtScr gives a snapshot of the active window, for example one of the diagrams.

The snapshot is placed in the Clipboard and may be pasted into any document, e.g. a Word document. The latter may then be printed. These are standard Windows procedures.


Pull down menus:
File – Page – Input – View – Print – Help.

Press Alt to see the key letters for access.

File Menu

•   Open ...: an OSA file (*.OSA) as specified in an ‘Open Dialog Box’.

A check is performed and a message may appear: ‘Invalid OSA file, incorrect header’.
The name of the file is shown in the title line.

   Save: data in an OSA file (*.OSA) in TAB delimited ASCII format.
If a file is already open the data is saved to that file.
If no file is open, a ‘Save Dialog Box’ asks for a file name.

   Save as ...: specified in a 'Save Dialog Box'.

   Setup ...: opens a window with options for units of quantities: fractions as decimal number or percent, pressure and tension as kPa or mmHg, gas concentrations as mM or mL/dL, and hemoglobin concentrations as mM or g/dL. The choices are automatically saved in a file (osa.ini) and employed by the program until changed by the user.

Page Menu

   New, append: new page with default data at the end of the book.

   New, insert: new page with default data after the current page.

   Previous: page, same as PgUp.

   Next: page, same as PgDn.

   First: page.

   Last: page.

   Copy: current page for later pasting. This function is useful when a venous sample corresponding to an arterial is to be keyed in.

   Paste: previously copied page on to the current page (overwriting). Usually you would paste on to a new page (added or inserted).

   Delete: current page from the book.

   Update all pages: by recalculation using the current input menu selections. The purpose of this option is to allow changes of input values in an OSA file using any text editor or spreadsheet and afterwards calculate values using the OSA algorithm. For example, 300 lines (pages) of normal values may be created in Excel by copying one line (page). Then the values for pO2T may be changed stepwise from 1 to 300 (kPa). The file is saved as a text file (*.osa), OSA is started and menu ‘Input > pO2T, cDPG’ is selected. The file (book) is opened, menu ‘Page > Update all pages’ is clicked and the book is saved. When the file is reopened in Excel you have a table of corresponding pO2 and sO2 values, i.e. a table of the oxygen dissociation curve.

Input Menu

allows selection of input variables. The color of the data field changes from white to yellow when the field is selected to be input.

Acid-base calculations, four options:

   pHm, pCO2m: measured pH and pCO2 are input variables by default. Output is ctH+, cHCO3, etc. pHT and pCO2T are also output provided TPt is entered.

   pCO2T, ctH+Ecf: pCO2 at patient temperature and hydrogen ion excess of extracellular fluid become input variables. Output is pH, cHCO3, etc. This mode is useful for predicting the effect of a change in pCO2 due to altered ventilation or the effect of a change in base excess due to infusion of acid or base.

   pHT, pCO2T: pH and pCO2 at patient temperature become input variables. Useful when these values have been measured with intravascular sensors at patient temperature.

   pHT, ctCO2P: pH at patient temperature and concentration of total carbon dioxide in the plasma become input variables. A classical type of calculation before the pCO2 electrode was developed.

Oxygen calculations, six options:

   pO2m, sO2m: measured pO2 and oxygen saturation are input variables by default. Output is cDPG, p50, and Fva, the latter provided FO2dI is entered. pO2T and sO2T are also output provided TPt is entered.

   Fva, cDPG: the veno-arterial shunt fraction and the 2,3-diphosphoglycerate concentration become input variables, useful for predicting the effect of an altered inspired oxygen fraction or altered pCO2, when the pulmonary function (Fva) and the position of the oxygen binding curve (cDPG) are unchanged.

   pO2m, cDPG: measured pO2 and concentration of 2,3-diphosphoglycerate becomes input variables, useful for calculation of the oxygen saturation at a given pO2 when the position of the oxygen dissociation curve (i.e. cDPG) is known.

   pO2T, cDPG: same as previous except with pO2 at patient temperature as input variable.

   sO2m, cDPG: the measured oxygen saturation and concentration of 2,3-diphosphoglycerate become input variables, useful for calculation of the pO2 at a given oxygen saturation when the position of the oxygen dissociation curve (i.e. cDPG) is known.

   sO2T, cDPG: same as previous except with sO2 at patient temperature as input variable.

View Menu

   Acid Base Chart: displays pH, pCO2, and ctH+Ecf, with reference areas for classical acid-base disturbances.

   Oxygen Graph: displays the blood oxygen binding curve with pO2, ceHb, p50, and px.

   Blood Gas Map: displays the arterial pO2 and pCO2 and the alveolar pO2 as a function of pCO2 (alveolar air equation).

   All Three: displays all three diagrams simultaneously.

   a + v Display: is a scheme of arterial and venous data together for comparison when both have been measured and for input for Cardiac Output, patient mass, and height. When the latter values are available the oxygen consumption rate and energy production rate are displayed.

   Critical Diagram: displays the relationship between the venous pO2 and the oxygen consumption rate.

   Diagnosis: is a laboratory diagnosis solely based on the measured and calculated laboratory data.

Print Menu

   Status report ... : shows a print preview of the current patient data summarized in one A4 page. The Acid-Base Chart and the Oxygen Graph are shown at the top of the page. The results are shown in a table in relation to the reference values: decreased values to the left, normal values within the reference interval, and increased values to the right. The ‘laboratory diagnoses’ are appended. Printing is started by selecting the local menu Print.

   Cumulated report … : shows a print preview of a cumulated report with one line for each sample and with only the most essential data.

   Printer setup: allows selection of printer from the standard Windows dialog box.

Help Menu

   ? Cursor Help: the cursor turns into a question mark, and when placed over a label or data field, a click on the left mouse button opens the Textbook on the relevant page. Exceptions are the Patient Identification Panel and the Sample Identification Panel where Cursor Help opens the User Manual.
Note: pressing the function key F1 opens the User Manual on the page relevant for the current cursor position.

   Manual: present document.

   Textbook: on the ‘Acid-Base and Oxygen Status of the Blood’ with special emphasis on a graphical presentation.

   About OSA: info pages on OSA program versions, user responsibilities, etc.

Patient Identification Panel

The top panel contains input fields for patient identification. These fields may be empty, except information needed for reference values: age, age unit, and sex, where default is 20 y F (female).

   Patient name: preferably in the order of last name, first name(s) middle name(s).

   Pt ID: must be unique in order to obtain Cumulated Reports. If the first 6 characters of Pt ID is a date of the format, ddMMyy, the program assumes that this is the patient birth date and patient age is calculated.
If Pt ID is a valid Danish Central Person Registry number of the form ddMMyy:nnnn, the program calculates patient age and sex. The last digit is even for women, uneven for men. (The separator in the CPR number may be a space, -, or :).

   Birth date: if entered as ddMMyy, patient age is calculated.

   Age: patient age is needed to display appropriate reference values as hints for the data fields. The age is automatically calculated if the first 6 characters of the Patient ID field represent a date or if the patient birth date is entered. If no age is entered a default value of 20 y is used.

   Age unit: may be years (y), months (m), weeks (w), or days (d). (Days of prematurity (negative number) or postmaturity (positive number) may be entered. Press Ctrl-F to calculate FHbF). (Not yet implemented).

   Sex (F or M): needed for display of appropriate reference values.

   Patient address: may be the hospital address, i.e. ward and room number.

   Diagnosis and comments: will appear on the printed Status Report.

Sample Identification Panel

   Sample date and time: of creation of the page is default. Current date and time are inserted by double clicking the field or when exiting an empty field.

   Sample Nr: may be any accession number or other type of identification, or empty. When the program is online with the analyzer the number will be the analyzer sample ID number.

   Type of blood: choices are arterial, capillary, mixed venous, central venous, or peripheral venous. If the blood is ‘venous’ then irrelevant quantities (e.g. Pamb, FO2dI) disappear from the Oxygen Panel.

   Respiration: choices are ‘spontaneous’ and ‘artificial’ ventilation. If ‘artificial’ ventilation is chosen the pCO2 value is flagged with an ‘R’ (for respirator) in the Cumulated Report.

Temperature Panel

   TPt: it is important to enter an accurate patient temperature to obtain a valid calculation of pCO2Alv, pO2Alv, and Fva. The latter is the most important indicator of pulmonary dysfunction. Ignoring patient temperature reduces the value of performing an arterial blood gas analysis. Entering a patient temperature different from the measurement temperature automatically unhide the fields for pH, pCO2, sO2 and pO2 at patient temperature. If patient temperature equals the measurement temperature these fields are hidden (but may be unhidden by left mouse click). Entering a question mark (?) in the field returns a default value of 37 °C and a question mark is added in the printed Status Report and the Cumulated Report.

   Tm: the temperature of measurement rarely differs from 37 °C, hence this field is hidden by default. Left clicking the label opens the field for input.

Acid-Base Panel

H+ related quantities (left column)

pHm, pHT and ctH+Ecf may be either input or output, depending upon the choice in menu  ‘Input’. All other are output, except cAlb (concentration of albumin in the plasma) and VB/VEcf (fraction of blood in the extended extracellular fluid, i.e. including erythrocytes). Usually, the latter two are unknown (not measured by the blood gas analyzer) and the default values are employed. Anyway they have minor influence upon the calculated values.

CO2 related quantities (right column)

pCO2m, pCO2T, and ctCO2P may be either input or output, depending upon the choice in menu ‘Input’. All other are output.

Oxygen Panel

Concentration scale (left)

The left scale shows hemoglobin and oxygen concentrations.

Quantities which account for a fall in concentration along the scale are interspaced: FCOHb, FMetHb, sO2, and cdO2.

ctHb, FCOHb, and FMetHb are always input, whereas sO2m and sO2T may be either input or output, depending upon the choice in menu ‘Input’. All the rest are always output.

Pressure scale (right)

The right scale shows quantities related to oxygen pressures and represents the so-called ‘oxygen cascade’.

Quantities which account for a fall in pressure along the scale are interspaced: FO2dI, RQ, and Fva. cDPG and FHbF, which affect the p50, are placed next to it.

When the blood is venous several quantities are irrelevant and therefore hidden: Pamb, FO2dI, pO2hI, RQ, pO2Alv, Fva.

Pamb, FO2dI, RQ, and FHbF are always input, whereas Fva, pO2Tm, pO2T, and cDPG may be either input or output, depending upon the choice in menu ‘Input’.

   Pamb: ambient barometric pressure is usually measured by the blood gas analyzer; if not, a separate barometer must be read.

   FO2dI: is important to enter with the correct value; otherwise the calculated Fva may be misleading. If the patient receives supplementary oxygen and the composition of the gas mixture or the flow rate of pure oxygen is known then the FO2dI may be roughly estimated using the Tables in the Textbook. If FO2dI is unknown, enter a question mark or a zero; then Pamb, FO2dI, pO2hI, RQ, pO2Alv, and Fva are all irrelevant and therefore hidden.

   RQ: the respiratory quotient, the CO2/O2 exchange ratio, is by default 0,85. When corresponding arterial and mixed venous blood has been analyzed, the arterio-venous RQ value is calculated from the arterio-venous ctO2 and ctCO2 differences. A repeat calculation may then be done with this calculated RQav value, probably resulting in a minor change in the calculated RQav. In rare cases the respiratory RQ value is known from expiratory gas monitoring.

   FHbF: the fraction of fetal hemoglobin is rarely known. In adults the default value is 0,005. In newborn infants a value of 0,80 may be employed. Estimation of FHbF on the basis of the age of the newborn and days of prematurity or postmaturity is not yet implemented.

a + v Display

The a+v Display is shown when ‘View > a+v Display’ is selected. It displays a scheme of blood circulation for comparison of arterial and venous pO2, ctO2, pCO2, ctCO2, and pH. The veno-arterial differences in ctCO2 and ctO2 are shown as well as the calculated RQ. If not both arterial and corresponding venous blood are available then only values for the actual blood sample are shown.

If the current page shows the arterial sample and the following page the corresponding venous sample then the more accurate venous cDPG replaces the arterial, and the arterial sO2 value is recalculated on the basis of pO2 and cDPG. For ctHb, FCOHb, and FMetHb the mean values of the arterial and venous values are employed. In case of mixed venous or central venous blood, the estimated total physiological shunt fraction (Fva) is recalculated, using the actual DctO2av value.

The venous point is displayed in the arterial graphs and pO2v is printed in the arterial Status Report and the Cumulated Report.

Hints pop up for labels (quantity name) and data fields (reference values).

Left clicking under the title line opens this Manual at the present description.

Clicking the ‘?’ button in the upper right corner changes the cursor into a question mark and clicking on a label or data field opens the Textbook on the relevant page.

Cardiac Output Panel

at bottom of a+v Display

   Q: once cardiac output is entered (liter/min), the field for patient mass (weight) is opened for input, and oxygen consumption rate and oxidative energy rate (power) are shown.

   m: once body mass  is entered (kg), the field for patient height is opened for input.

   h:  once patient height is entered (cm), patient surface area (m2) is calculated from weight and height with the Du Bois Equation. If m and h are not specified the default value for A is 1.8 m2. When surface area is calculated, values are related to surface area:  areic cardiac output (cardiac index), areic oxygen consumption rate, and areic power. Clicking areic cardiac output or areic oxygen consumption rate show values relative to normal mean values according to patient age and sex.


The Acid Base Chart, Oxygen Graph, Blood Gas Map, and Critical Diagram are shown when clicking the menu ‘View > respective diagram’. Clicking ‘View > All Three’ show the first three diagrams. They may be moved, resized, maximized, minimized, or closed.

As soon as an input value has changed in the Data Page, the diagrams are updated.

In order to display the venous values in an arterial diagram, first select the menu ‘View > a + v Display’. If the following page contains the corresponding venous data, the arterial and venous data are combined and displayed. If the current page contains the venous data, first page up to the arterial page.

The coordinates at the cursor position are shown in red. In the Acid Base Chart, cHCO3 at the cursor position is also displayed. There are popup hints for labels and marks.

Left clicking under the title of the diagram opens the Textbook on the relevant page.


The diagnoses, selected with menu ‘View > Diagnosis’, are laboratory diagnoses, i.e. translations of the laboratory results into plain language. For example, a low blood pH is called acidaemia, a high pCO2 is called hypercapnia, and a high ctH+Ecf is called metabolic acidosis. It is not possible to specify any of these as acute or chronic, primary or secondary (compensatory). This requires more clinical information about the patient history.

Print Previews

Before printing a Status Report or a Cumulated Report, choosing menu ‘Print > Report’, a print preview is displayed and actual printing must be activated by selecting the local menu ‘Print’.

End of Manual