Siggaard-Andersen nomogram

This point is taken up again later in the chapter because the haemoglobin concentration appears on the Siggaard-Andersen nomogram. 

SECTION 4.2 THE SIGGAARD-ANDERSEN NOMOGRAM FOR THE PARAMETERS OF ACID-BASE STATUS... 

This section considers the Siggaard-Andersen nomogram for reading off the parameters of acid base status such as the base excess. It has previously been noted that, although the PCO2 and [HCOj"] values for a sample of arterial blood define a point on the chart of acid-base status, they do not by themselves provide enough information to identify the magnitude of the base excess, total... 

Figure 4.10. An example of the use of the Siggaard-Andersen nomogram. Arterial blood from a patient had a PcOj of 71 mmHg and a pH of 7.34 this is plotted as point A. The blood sample was then equilibrated with a gas mixture containing CO2 at a partial pressure of 40 mmHg the pH was then 7.54, giving point B. These points are joined by the straight line shown in bold. This allows us to read off the base excess and the buffer base values.

This last formula allows one to calculate the normal buffer base from values read from the Siggaard-Andersen nomogram. This normal buffer base value is then identified on the part of the buffer base curve against which is plotted the haemoglobin subscale and the haemoglobin is read off. 

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