ALKALI RESERVE 143 



ALKALI RESERVE 



Indirect Method. Index of Add Excretion in Urine 

 Method of Fitz and Van Slyke 1 



Principle. The method depends upon the determination of 

 the rate of excretion of acid (NHs+ titratable acid) from which 

 the plasma carbon dioxide capacity is calculated. 



Procedure. Collect the urine for twenty-four-hours (or if 

 desired for a period of 1 or 2 hours during which the subject 

 ingests neither food nor water). In the latter case the urine col- 

 lection should not be too soon after a meal. Measure, carefully, 

 the volume of the urine and determine its ammonia content 

 according to the method given on page 42 and the titratable acid 

 according to the method given on page 21. Obtain the body 

 weight of the patient. 



Calculation. The plasma bicarbonate may be calculated by 

 substitution in the following equation: 



Plasma Carbon Dioxide Capacity = 80 5 \ . 



* W 



D = Rate of excretion per twenty-four hours. 

 W = body weight in kilograms. 



(The value 80 represents the maximum normal value of plasma 

 bicarbonate. Under such a condition the titratable acid and 

 ammonia excretion tend to approach zero.) 



The value D is equal to the product VC, in which V is the 

 twenty-four-hour volume (if the urine is collected for only one 

 or two hours its volume is, of course, multiplied by 24 or 12 as 

 the case may be) expressed in liters, and C the sum of the ammonia 

 (expressed as c.c. of N/10 NHa per liter of urine) plus the titratable 

 acid (expressed as c.c. of N/10 acid per liter of urine). For prac- 

 tical purposes the acid excretion may, without going through the 

 calculation of the formula, be interpreted directly into terms of 

 clinical severity of acidosis, as indicated in the table on page 144, 

 e.g., an excretion exceeding 27 c.c. of N/10 ammonia plus titratable 

 acid per kilo indicates acidosis, which usually becomes critical in 

 severity if the excretion approaches 100 c.c. per kilo. 



1 Fitz and Van Slyke: Jour. Biol. Chem., 1917, 30, 389. Van Slyke: Ibid. 

 1918, 33, 271. Barnett: Ibid., 1918, 33, 267. 



