Normal blood line

Figure 3.1. Bicarbonate concentration as a function of PCO2. The normal blood line is shown and the oblique line representing a normal extracellular hydrogen ion concentration. Point N is a typical point representing normal acid-base status. Arrow NA indicates the change accompanying uncompensated respiratory acidosis and arrow AB indicates renal compensation.

In a patient in whom there is a sudden rise in the alveolar partial pressure of carbon dioxide, the change in composition of the patient s arterial blood is represented in Figure 3.1 as a move from the normal, represented by point N, along the normal blood line to point A. The increase in the x coordinate represents the rise in the PCO2 of the patient s arterial blood. The increase in the y coordinate represents the rise in bicarbonate concentration the move to a new isohydric contour reflects the increase in hydrogen ion concentration. These changes in composition of the arterial blood are summarized in Table 3.1 Column A. 

Figure 4.2. Graph to show the regions of the acid-base status plot corresponding to positive and to negative base excess. The unshaded area around the normal blood line gives an approximate indication of the variations in base excess to be found in a normal healthy population.

Figure 4.3. A. Normal blood the normal blood line is plotted with axes as indicated below and to the left. The full arrows show the value of the [HCOj j at the relevant PtU2. Above each full arrow is a dashed arrow indicating the concentration of non-bicarbonate buffer base. The two arrows together indicate the magnitude of the total buffer base. B. A similar plot for anaemic blood.

In the initial stages of a disturbance of acid-base physiology, the condition is uncompensated, which essentially means that chemical buffering alone is operating. At this stage therefore, there is only one component to the disorder. This component is respiratory in respiratory disorders and metabolic in metabolic disorders. In the respiratory disorder the subject moves along the normal blood line. The partial pressure of carbon dioxide is abnormal but the base excess, the measure of metabolic component, is zero. This is shown in Table 4.4A. For an uncompensated metabolic disorder (Table 4.4C), it is the... 

C. Blood from a patient with an uncompensated respiratory alkalosis would yield a point lying on the normal blood line . 

B. Ingestion of a large amount of ammonium chloride would result in a change which would be represented by moving along the normal blood line . 

D. No. The point would lie below the normal blood line. 

E. Yes. Any point above the normal blood line has an increased value of total buffer base. 

B. No. This produces a metabolic acidosis the point representing the subject s arterial blood moves down from the normal blood line. 

E. No, because the point representing the blood is above the normal blood line, so reducing the PcOj to 40 mmHg brings the blood along its blood line which is higher than normal. So the at a PcOj of 40 mmHg would be below normal. 

C. Yes, because [HCOj ] is low in the presence of high PCO2 the point representing his blood must fall well below the normal blood line . 

With the help of the normal blood line, describe and explain ... 

Define the standard bicarbonate for blood and explain how it is measured give a typical normal value. Show this point on the normal blood line . 

From the preceding, and in relation to the graph of the normal blood line , define the terms base excess. Define base deficit and describe how it can be regarded as a negative base excess . 

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