M Phadke, S Menon, M Gore
burns, hyper metabolic state, nitrogen balance, nutritional support, thermal injury
M Phadke, S Menon, M Gore. Study Of Nitrogen Balance In Thermally Injured Patients. The Internet Journal of Emergency and Intensive Care Medicine. 2007 Volume 11 Number 1.
A study was undertaken to determine the protein metabolism and nitrogen balance in moderately burned patients (30-60% TBSA) and to find the efficacy of various food supplementations in recovering the nitrogen balance. The total protein and albumin, the markers of protein status were seen to improve in patients throughout the four weeks of follow up after protein supplementation. At admission, these components were found to be lower than the reference levels. The protein content of the supplements was determined by a chemical method. Total nitrogen excretion per day was established by the values of various non-protein parameters like urea, uric acid, creatinine and amino acid nitrogen. The nitrogen output showed a considerable decline in the passing weeks, which correlated with an increase in dietary protein supplementation. There was also an improvement in the nitrogen balance which showed a shift from the negative towards a positive value by a constant infusion of high protein supplements.
Thermal and related injuries continue to be the major cause of disability and death in India. The most affected are those who are socio-economically challenged 8 . The largest groups of burned patients are women and young children.
The importance of nutritional support in the condition of trauma and injury was first quoted by Stanley M Levenson, in 1954. Following a burn injury, a rise in metabolic rate occurs, usually one to two days after the injury. Extensive catabolism of muscle protein is a feature in this post-burn period 26,28,38,39 . The amino acid released by the muscle protein catabolism form an amino acid pool, which is utilized for gluconeogenesis, protein synthesis and wound repair.
Burn like any other form of stress or injury, immediately initiates the metabolic response to the trauma. The response is characterized by an acute catabolic reaction, which precedes the metabolic process of recovery and repair. This metabolic response to trauma was divided in to an ebb and flow phase by Cuthbertson. 4 . The ebb phase typically lasts for twelve to twenty four hours post injury. Immediately after injury the most frequent form of shock is hypovolemic shock, which results from the loss of blood and extra cellular fluid 41 . The other main markers for the ebb phase are lactic acidosis along with decreased levels of cardiac output, oxygen consumption, blood pressure, metabolic rate and body temperature.
The flow phase follows the ebb phase and can be divided in to,
The catabolic phase with fat and protein mobilization associated with increased urinary nitrogen excretion and weight loss, and
An anabolic phase with restoration of fat and protein stores, and weight gain.
In the flow phase, the body is hyper metabolic, causing an increase in cardiac output, oxygen consumption, glucose production, metabolic rate and body temperature 5,6,7,9,29.
Nitrogen balance: Nitrogen balance is the difference between dietary nitrogen intake and excretion and is widely used as an index of protein requirements. In the case of burn patients, the catabolic process exceeds the anabolic process and more nitrogen is excreted than ingested, resulting in a negative nitrogen balance. Negative nitrogen balance can be more serious in children than adults because growth is compromised.
Nutritional support: Since the nutritional effect of hyper metabolic response manifest primarily as exaggerated energy expenditure and massive nitrogen loss, nutritional support should be directed primarily toward provision of calories to match energy expenditure and of nitrogen to replace or support body protein loss. Carbohydrate primarily in the form of glucose appears to be the best source of non-protein calories in the thermally injured patients. The combination of glucose with nitrogen containing nutrients improves nitrogen balance and allows more calories to be utilized for the restoration of nitrogen balance than would be the case if either nutrient group were used alone.
The aim of the present study was to determine the protein metabolism and the nitrogen balance in thermally injured patients through various biochemical parameters.
Materials And Methods
The patients included in the study were from the Burns Unit of Lokmanya Tilak Municipal Medical College and General Hospital Sion, Mumbai, India.
Fasting blood and 24 hour urine samples were collected from the patients on the day of admission and followed at the 1 st week, 2 nd week and 3 rd week. The blood was collected in EDTA containers and 24 hour urine samples were collected in 5ml 5% Thymol which was used as a preservative 10 .
The various biochemical parameters estimated from the plasma and 24 hour urine samples were as follows
The formulae used for calculating the nitrogen balance for the patients was:
[Where the factor 2 was added to the measured 24 hour urinary nitrogen output to account for the average skin sloughing and fecal losses (9-s)] 10 .
With the help of dietician the patient's calorie and protein content were recorded through a 24 hour recall method, using National Institute of Nutrition (NIN) 42 charts and also L.T.M.M.C diet section charts.
The high protein supplements given to the patients were in the form of Milk formula,
The protein content in the various supplements was estimated using a modified Micro-kjeldahl method 18 . The Micro-Kjeldahl method is still the reference method used for the determination of total protein. 100 mg of the food samples were digested using a digestion mixture. The digest was loaded in a Markham Still Apparatus. The ammonia released was absorbed in a boric acid solution containing Methyl Red and Bromocresol Green indicators. This was titrated against a standard acid to find the nitrogen content. The protein content of the food product was then calculated from the nitrogen values.
The patients were separated in to two groups depending upon the Total Burn Surface Area (TBSA).
Group I : 30-44 %
Group II : 45-60 %
In the present study immediately after the burn trauma, the hyper metabolic status obtained was evidenced through parameters like plasma total protein and plasma albumin which decreased considerably as compared to the normal values in both the group of patients. Simultaneously, the breakdown products of protein catabolism viz. amino acids as the first phase and urea as the second phase increased significantly as reflected by both plasma and urine values (Table 1, 2, 3 and 4). Plasma albumin is a protein with many functions, one of them being a supplier of calories in the condition of needs. Only plasma albumin values are considered as an index of nutritional status of a person. Decreased albumin value which also brings down the total protein content is a clear indicator of body protein utilization for energy purposes. Albumin values have gradually been built over a period of four weeks thereby also increasing total protein values.
The nitrogen balance calculated immediately after admission in both the group showed a very high negative status. This status had shifted towards a zero balance over the weeks with constant protein supplementation along with the patient's normal diet. But as obvious from the values, the status had not reached a positive value even after 4 weeks post burn injury. (Table 5 & 6). The rate of improvement of the nitrogen balance was not similar for the entire 4 week follow up period in the two groups. It was found to be appreciably slower in the last week of the follow up period. Most of the patients who were burned, were of lower socio-economic strata, thereby might have had a nitrogen balance slightly on the negative side which was further reduced due to hyper metabolic responses following a burnt injury. This would be a probable cause for the inefficiency of the patient in attaining a positive nitrogen balance even after four weeks of protein supplementation.
As regards the urine analysis, the nitrogen load was seen to be very high. Total nitrogen excretion per day was established by the values of various non-protein parameters like urea, uric acid, Creatinine and amino acid nitrogen (nitrogen output). The surplus presence of these compounds represents a temporary imbalance between anabolism and catabolism 25 . The nitrogen output showed a considerable decline in the passing weeks which correlated with an increase in dietary protein supplementation (Table 3 & 4). The evidence of high urinary urea nitrogen output indicated a high level of protein breakdown in to amino acids. The ammonia released during deamination was converted in to urea. The kidney, in turn, excretes urea 10 .
The nutritional support given to all patients were in terms of high protein diets along with their regular food. Initial high protein intake given parenterally, was later found to drop slightly once the patient started ingesting the food themselves. It again went up gradually as their injuries started healing to some extent and there was a slight betterment in their physical condition, thereby able to ingest more food.
The recommended amount of calorie intake and protein supplement both depended upon the Curreri formula 11,12 .With the patients on a high protein diet, the rise in the levels of plasma total protein and plasma albumin were recorded and their effect was seen with the drop in the levels of urinary urea nitrogen and urinary total amino acid nitrogen. This decline in the levels of urinary urea nitrogen and urinary total amino acid nitrogen were of high importance in relation to the nitrogen balance. There was a marked change in the nitrogen balance values in the period of 4 weeks. The level reached close to zero with the passing weeks which coincided with an increase in the protein intake.
This study thus proves that for an improvement in the nutritional status of the patient, as judged by their nitrogen balance, can be brought about through adequate calorie and protein supplementation immediately post burn.
The burn patients went into a hyper metabolic state immediately after burn trauma, as clearly evidenced by decreased total protein, albumin content and increased excretion of urea, uric acid, creatinine and total amino acid nitrogen. They went in to a negative nitrogen balance.
To improve the nitrogen balance status, protein supplementation was started on the 3 rd to 4 th day post-burn. This was found to be effective to bring a drastically negative value of nitrogen balance towards a balanced state over a period of four weeks. This proves an early supplementation of high protein diet during the post-burn period is a requirement to improve the nitrogen balance status.