ACIDOSIS 41 



THE MEASUREMENT OF THE RESERVE ALKALINITY 



1. Titration Methods 



There are several methods by which the reserve alkalinity of the blood 

 may be measured. The simplest in theory consists in seeing how much 

 standard acid must be added to a measured quantity of blood plasma in 

 order to reach the neutral point as judged by change in tint of some 

 indicator. The indicators employed (e. g., methyl orange) are such as 

 change their tints at H-ion concentrations that are well to the acid side 

 of neutrality (i. e., at a high C H or low P H ). To bring the plasma to this 

 point of neutrality the added alkali will need to neutralize, not only the 

 bicarbonate of the plasma, but other acid-binding substances as well. 

 This will give us a false impression of the acid-binding powers of the 

 plasma, since, at the normal C H of the blood, proteins do not absorb acids 

 to anything like the extent they do at higher degrees of C H . Another 

 objection to the method is that the proteins interfere with the sensitive- 

 ness of the indicators. 



The objections can be removed by determining the end point electro- 

 metrically or by indicators that change tint at about P H 7. The most 

 practical way is to determine the change in CH produced by adding a 

 known volume of standard acid to blood plasma. The resulting change 

 in CH will then be greater the less the alkaline reserve. In the electro- 

 metric method irregularities that might be caused by variable amounts 

 of carbonic acid in the blood to start with are best controlled by removing 

 the C0 2 from the plasma after adding the standard acid. The procedure 

 therefore consists in mixing 1 c.c. plasma with 2 c.c. N/50 HC1 in a small 

 separating funnel, which is then evacuated so as to remove the C0 2 , 

 after which the fluid is transferred to a hydrogen electrode and CH 

 measured (see page 29). In normal blood this should be 10 5 - 6 (P H 5.6). 

 In acidosis, where there is a depleted alkaline reserve, the 2 c.c. of acid 

 will cause a much greater change in CH in diabetic blood to below 5 

 or lower. 



The technic involved in the above method is, however, too exacting for 

 routine clinical work. For such purposes the colorimetric method of Levy 

 and Rowntree may be employed. 



THE METHOD OF LEVY AND ROWNTREE. IS A test tube made of hard 

 ("nonsol") glass of about 20 c.c. capacity, containing about a gram of 

 powdered neutral potassium oxalate, is filled with newly drawn blood, 

 immediately stoppered and placed on ice. Quantities of 2 c.c. each of 

 the blood are then placed in a series of seven small (nonsol) test tubes 

 and allowed to stand for five to six minutes in order to permit a narrow 



