Nitrogen balance

The balance of nitrogen in the body( the difference between the amount of nitrogen consumed and released) is one of the widely used indicators of protein metabolism. In a healthy person, the rates of anabolism and catabolism are in equilibrium, so the nitrogen balance of is zero. In case of trauma or stress, for example, with burns, nitrogen consumption decreases,

and nitrogen losses increase, resulting in a negative nitrogen balance in the patient. Upon recovery, the nitrogen balance should become positive as a result of protein production with food. The study of nitrogen balance provides more complete information about the condition of a patient who has metabolic needs in nitrogen. Estimation of nitrogen excretion in critical patients allows to judge the amount of nitrogen lost as a result of proteolysis.

Two methods for measuring nitrogen loss in urine are used to estimate nitrogen balance:

■ measurement of urea nitrogen in daily urine and calculation method for determining total nitrogen loss;

■ Direct measurement of total nitrogen in daily urine.

Total nitrogen includes all protein metabolites that are excreted in the urine. The amount of total nitrogen is comparable to the nitrogen of the digested protein and accounts for approximately 85% of the nitrogen supplied with food proteins. Proteins contain an average of 16% nitrogen, therefore, 1 g of isolated nitrogen corresponds to 6.25 g protein. Determination of the daily excretion of urea nitrogen in urine allows us to estimate satisfactorily the nitrogen balance( AB) value with the maximum possible recording of the protein intake: AB = [supplied protein( g) / 6.25] - [daily nitrogen urea nitrogen( g) + 3], wherethe number 3 reflects the approximate loss of nitrogen with feces, etc.

This indicator( AB) is one of the most reliable criteria for evaluating the protein metabolism of the body. It allows you to timely identify the catabolic stage of the pathological process, evaluate the effectiveness of nutrition correction and the dynamics of anabolic processes. It was found that in cases of correction of the expressed catabolic process it is necessary to bring AB with the help of artificial nutrition to + 4-6 g / day. It is important to monitor the excretion of nitrogen day by day.

Direct determination of total nitrogen in the urine is preferable to urea nitrogen, especially in critical patients. The release of total nitrogen in urine is normally 10-15 g / day, its percentage is distributed as follows: 85% - urea nitrogen, 3% - ammonium, 5% - creatinine, 1% - uric acid. Calculation of AB by total nitrogen is carried out according to the following formula: АБ = [received protein( g) / 6.25] - [daily losses of total nitrogen( g) + 4].

Determination of total nitrogen in the urine during the initial catabolic stage should be done every other day, and then once a week.

An important criterion, complementing all the above, is the definition of urinary excretion of creatinine and urea.

Creatinine excretion reflects the metabolism of muscle protein. Normal excretion of creatinine with daily urine is 23 mg / kg for men and 18 mg / kg for women. With the depletion of muscle mass, there is a decrease in the excretion of creatinine in the urine and a decrease in the caffeine-growth index. The hypermetabolic response that occurs in most patients with urgent conditions is characterized by an increase in the total metabolic expenditure, which accelerates the loss of muscle mass. In such patients in a state of catabolism, the main task of maintenance nutrition is to minimize muscle loss.

Urea excretion in the urine is widely used to evaluate the effectiveness of parenteral nutrition using amine nitrogen sources. Reducing the excretion of urea in urine should be considered an indicator of stabilization of trophic status.

The results of laboratory tests allow us to identify risk groups for the development of complications caused by malnutrition and inflammatory reactions in critically ill patients, in particular, by calculating the Prognostic Inflammatory and Nutritional Index( PINI) according to the following formula[Ingenbleek Y., Carpenter YA, 1985]: PINI = [Acid a1-glycoprotein( mg / l) xCPB( mg / l)] / [albumin( g / l) xpalalbumin( mg / l)].According to the PINI index, the risk groups are distributed as follows:

■ below 1 - healthy;

■ 1-10 - low risk group;

■ 11-20 - high risk group;

■ more than 30 - critical condition.