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Volume: 2 Issue: 2 June 2022


Nonprotein Calorie-to-Nitrogen Ratio at Flow Phase in Patients With Major Burn Injuries


OBJECTIVES: Protein is the only nutrient that provides nitrogen, and nitrogen has important roles in metabolism, wound healing, and recovery of burns. During burn injuries, metabolic states are similar to other higher metabolic stress clinical conditions and are classified as the ebb (early), flow (second), or anabolic (third) phase, depending on time postinjury, with the early phase from injury to 48 hours, the second phase from 48 to 72 hours, and the third phase up to 1 year. In burn patients, the flow phase is crucial because nutrient substrates are utilized, requiring patients to have a high calorie and high protein diet along with standard micronutrients supplements, with recommendations defining a 100:1 to 150:1 calorie-to-nitrogen ratio for patients with major burns. Most patients require additional protein if they have open wounds. Here, we evaluated effects and outcomes of nonprotein calorie-to-nitrogen ratio in high-calorie and high-protein diets in patients with major burns seen at our center.
MATERIALS AND METHODS: Our retrospective study included 54 male and female adult patients (18-60 years of age) with 20% to 60% total burn surface area burn injury who had reached our hospital within 12 hours of injury from 2017 to 2021. After primary clinical management and resuscitation, all patients received nutritional care, with monitoring of nonprotein calorie-to-nitrogen ratio. Outcome measures included length of hospital stay, recovery of wounds, and final outcome.
RESULTS: Nonprotein calorie-to-nitrogen ratio was maintained at 93:1 during the flow phase of metabolism in all patients. Maintenance of this ratio was significantly correlated with positive measures of wound healing, length of stay, and final outcome.
CONCLUSIONS: The nonprotein calorie-to-nitrogen ratio has important roles in the early phase of higher metabolic stress conditions in patients with burns. Maintaining a ratio of at least 100:1 ratio can result in better outcomes for patients.

KEY WORDS: Burns metabolism, Flow phase, Nutrition, Recovery, Wound healing



Patients with major burn have significant alterations in their metabolism, with 4-fold higher levels than under normal conditions. Higher metabolism is known as hypermetabolism. Metabolic changes have been classified into 3 different phases depending on the hours postinjury. The early phase within 24 to 48 hours does not bring changes in nutrient utilization as the body tries to maintain hemodynamic stability. The second phase, known as the flow phase, occurs after 48 hours of injury; during this phase, patients require support by optimum nutrient supplements. The flow phase is especially crucial in high metabolic stress conditions like burns, where the higher nutritional demand is meant for recovery, wound healing, and infection prevention.
Nutrients provide energy; on the basis of their quantitative requirement in the daily diet of healthy individuals, they are classified into macronutrients and micronutrients. Macronutrients are major sources of energy and include carbohydrates, proteins, and fats. Among these, only proteins are a nitrogenous source; therefore, proteins have an important role in most metabolic activities and hormonal regeneration. In burn patients, proteins help in wound healing and recovery. It is a crucial substance for burn patients because of the patient s hypermetabolic status. A high calorie and high protein diet is recommended to fulfill this higher metabolic demand, and a calorie-to-nitrogen ratio of 100:1 to 150:1 is recommended according to previous research and critical care nutrition guidelines.1-4
During the initial 48 to 72 hours of burn injury, patients with burn injuries require optimum levels of nutrients to cope with the higher metabolic demand so that they can have faster recovery of wounds. During this flow phase, the maintenance of positive nitrogen balance is important for wound healing and overall outcome in patients with severe burns. In this study, we analyzed nonprotein calorie-to-nitrogen ratio and its impact on outcomes of burn patients seen at our center, including its effect on wound healing, duration of hospital stays, and survival rate. These results can be helpful for recommendations in future burn nutrition guidelines. Such data are not available for Asian populations of patients with major burns.


Study design and setting

This retrospective observational study was conducted at our burn unit (Choithram Hospital and Research Centre), which is a tertiary care multispeciality hospital in central India, from 2017 to 2021. Ethical approval was obtained from our institutional ethical committee at Choithram Hospital and Research Centre (Indore, India).

Study population

The study population included 54 adult patients (18 to 60 years of age) who arrived within 12 hours of burn injury with 20% to 60% of total burn surface area (TBSA). Male-to-female patient ratio was 1.07:1. Patients with or without any comorbidity, clinically stable at the time of hospitalization, and with no significant respiratory issues or inhalational injury were included. Patients who did not fulfill the above criteria were excluded.

Nutrition screening and assessment

At the time of admission, included patients had been screened by a nutritional risk screening tool (NRS2002), which provides information on the patient s premorbid nutritional status and was also to formulate the subsequent nutritional care process.
Hospital staff conducted nutritional assessments with structured forms that included documentation of all anthropometric, biochemical, clinical, and dietary parameters. Anthropometric assessments included weight, height, ideal body weight, clinical details (including percent TBSA, type of burn, depth of burn), and dietary recall using previous 24 hours of food intake.

Nutrient calculation (energy estimation) and prescription

Further nutritional requirements were calculated using the Curreri formula and protein by 1.5 g/kg body weight, with additional calculations based on wound protein losses wherever applicable (Table 1). Wound protein losses were calculated by using a body surface area calculation based on height, weight, and percent TBSA. Calorie-to-nitrogen ratio was calculated by using the 24-hour diet recall with nitrogen conversion factor of 6.25 g of protein. Patients without diabetes were provided diet with 70% carbohydrates and 30% fats to fulfil their nonprotein calorie requirements, whereas patients with diabetes were provided 60% carbohydrates and 40% fats from nonprotein calories. Patients also received micronutrients (500 mg vitamin C twice per day along with vitamin E, zine, selenium, and 1 multivitamin tablet).

Route of nutrition provision

Patients received the estimated nutrients through various routes of feeding, depending on their condition and acceptability. The oral route was always the preferred route of feeding, and the enteral route was used if patients could not tolerate the oral route or for exceptional situations, such as patients who required neck grafts. Some patients received nutrients through both the oral and enteral routes to achieve optimum nutrient delivery.

Nutritional monitoring and reassessment

To achieve optimum nutrient requirements, dieticians and nursing staff closely monitored nutrition provision in patients. Patients were also observed for other gastrointestinal symptoms, such as loose stools, vomiting, abdominal distension, and constipation. If changes were required, they were made accordingly, including for patients on enteral feeds (Ryles tube aspiration), and tolerance of food was monitored.

Wound healing status

Wound healing status was checked by observations of color of wound, granulation, smell, and fluid discharge from the wound site. Wound healing was classified as good wound healing or poor wound healing. Wounds that showed no bleeding, no swelling, no redness, absence of any fluid collection and puss discharge, and no foul smell for over 1 week to 10 days of duration were considered to have good healing status. Wounds with signs of bleeding, increase in pain and swelling, foul smell, and/or thick grayish or clear fluid discharge from the incision site until day 10 were considered to have poor wound healing status.

Nonprotein calorie-to-nitrogen ratio

Nonprotein calorie-to-nitrogen ratio was measured by calculating total calories. Protein calories were subtracted from total calories to calculate nonprotein calories. Further conversion of protein to nitrogen was done by multiplying a factor of 6.25 to the amount of protein in grams. Nonprotein calorie-to-nitrogen ratio is important in burns because sufficient amounts of nitrogen are required through nutrition provision for wound healing and acceptance of the grafted skin. It is also important in prevention of muscle loss and wasting during high metabolic stress conditions like burns.

Data collection

Data were collected in a well-structured format, which was prepared on the basis of the ABCD method of nutritional assessment, which included anthropometric parameters (weight, height, ideal body weight), biochemical and clinical parameters, and dietary history. A trained dietician and dietetic interns performed the complete nutritional care process and documented it in the tool.


Sociodemographic characteristics

The mean age of study patients was 31.8 ± 9.39 years, with male-to-female patient ratio of 1.07:1. Of the included patients, 90.7% were married, 51.9% were educated, 59.3% were employed, and 61.1% belonged to the lower middle income group (Table 2).

Food habits

Among the 54 included patients, none had food allergies. Among the patients, 24 were vegetarian (44.4%), 24 were nonvegetarian (44.4%), and 6 were ovo-vegetarian (11.1%).

Premorbid nutritional status

At the time of hospitalization, 68.5% (n = 37/54 patients) were undernourished, 18.5% (n = 10/54) were well nourished, and 13.0% (n = 7/54) were overweight. Of note, most patients were malnourished; however, this observation was not significantly associated with patient outcome.

Nutritional assessment

Nutrition assessment is crucial to initiate the effective nutrition care process. In patients with burn injuries, measuring weight or true weight without fluid overload was important for nutrition calculation. To investigate the nutritional requirements, we observed that the mean weight of study patients was 58.37 ± 13.44 kg and the mean height was 162.42 cm. We found that current weight and ideal body weight (60.64 kg) did not greatly differ.

Clinical characteristics

We observed that 38 patients had flame burns, 3 had scald burns, 13 had electrical burn, and none had chemical and other burns. Results for degree of burn at admission are shown in Table 3.

Nutritional provisions

The mean calories provided to study patients was 2967.8 ± 509 kcal/day, and the mean protein level was 156.7 ± 39.99 g/day, with a mean ratio of nonprotein calorie-to-nitrogen ratio of 93:1, which favored maintenance of positive nitrogen balance during the flow phase of burn injury. Mode of feeding among study patients was 59.3% oral (n = 32), 9.3% enteral (n = 5), and 31.5% oral and enteral (n = 17).

Outcome variables

The outcome variables that we analyzed in the study patients included wound healing status, length of hospital stay, changes in weight, mortality and survival, and nitrogen balance (Table 4). All patients were provided optimum nutrition support, with 70% maintaining positive nitrogen balance and 30% not having positive nitrogen balance.

Analysis of outcome variables and their association by chi-square test

We investigated associations between different variables and outcomes by chi-square test (Table 5), with P < .05 indicating significant difference. We found no significant difference between weight loss or any changes in weight with age of patients. Similarly, we found no significant correlation between wound healing status and patient age. Age of patient was also not significantly associated with positive nitrogen or negative nitrogen ratio and final outcome of patient in terms of survival and death. Patient sex was not associated with wound healing outcomes, weight loss, positive nitrogen ratio, or final outcome of patients in terms of survival or death (P > .05).
Food habits of study patients had no significant effect on wound healing rate, weight loss, nitrogen ratio, or patient survival rate (P > .05). Nutrition status also had no significant effect on wound healing rate, weight change, nitrogen ratio, or survival rate of patients.
Type of burn in study patients was not significantly associated with wound healing rate, weight changes, nitrogen ratio, or mortality rate. Degree of burn had no significant effect on wound healing rate, weight changes, nitrogen ratio, or mortality rate in study patients.
The percent TBSA in study patients was significantly associated with wound healing rate (P < .05). Weight loss or no change in weight was also found to be significantly associated with wound healing rate (P < .05). Furthermore, percent TBSA in study patients was associated with positive nitrogen ratio (P < .05). Patients in the 20% to 40% TBSA group had significantly higher survival rate than patients in the 41% to 60% TBSA group (P < .05).
Feeding route in study patients showed significant associations with wound healing rate. Patients who had oral route of feeding had significantly better wound healing rate (P < .05) than patients who either had enteral route feeding alone or combined oral and enteral feeding route. However, feeding route had no significant association with change in weight of patients (P > .05). Feeding route was also significantly associated with nitrogen ratio and was higher among patients who received oral route feeding (P < .05) than patients who had enteral route or combined oral and enteral route feeding. Furthermore, feeding route had a significant effect on the final outcome of patients, with patients who had oral route of feeding having a higher survival rate than patients who had either enteral route alone or combined oral and enteral route (P < .05).


Research in burn management has shown that management of nutritional and metabolic estimates in burn patients plays a vital role. Wound healing is a complex and dynamic process that requires an optimum nutritional status for the rapid inflammatory phase to promote collagen production, to enhance fibroblast proliferation and fast granulation, and to increase wound tensile strength for improved wound healing outcomes. Nutritional status is a fundamental aspect for optimal wound healing, resulting in decreased length of hospital stay, minimized health care costs, and reduced postoperative infections and complications. Within nutritional support, management of nonprotein calorie-to-nitrogen balance is crucial, and various guidelines have recommended a ratio of 100:1 to be maintained to compensate for changes in patients with high metabolic stress, including patients with severe burn injuries.
In the present study, we found that our patients had nonprotein calorie-to-nitrogen ratio maintenance of 93:1 to fulfil the increased requirement of nutrients, which is especially needed during the flow phase of metabolic stress. Similar to previous data, we found an association between wound healing rate and percent TBSA, with higher percent TBSA meaning lower probability of survival. A similar association between percent TBSA was reported by Kagan and associates.5
Our study revealed that patients who had oral feeding had a better wound healing rate, positive nitrogen balance, and better survival rate than patients who received nutrients enterally or combined oral and enteral feeding. Similar findings were reported previously.6
The present study did not consider the nutritional status before burn injury because of difficulty in obtaining these data. There also was no follow-up of patients once good wound healing was shown and after discharge, even in those patients with wound relapses and poor wound healing at home. Despite these limitations, this study provided baseline information that patients with positive nonprotein calorie-to-nitrogen ratio had better rate of wound healing, fewer days in the hospital, and better survival, similar to that reported by de Oliveira and associates.7


In the present study, we found that nonprotein calorie-to-nitrogen ratio maintained at 93:1 was able to fulfill the increased requirement of nutrients, especially during the flow phase of metabolic stress. Maintenance of this ratio was vital for overall improvement of patient outcomes.


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Volume : 2
Issue : 2
Pages : 51 - 56

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From the 1Department of Dietetics, the 2Department of Research and Statistics, and the 3Department of Burn and Plastic Surgeries, Choithram Hospital and Research Center, Interburns Training Center, Indore, India
Acknowledgements: The authors have not received any funding or grants in support of the presented research or for the preparation of this work and have no declarations of potential conflicts of interest. The authors are grateful to the Choithram Hospital and Research Centre Indore for providing infrastructure and supporting this study.
Corresponding author: Pratibha Sharma, Department of Dietetics, Choithram Hospital and Research Center, Interburns Training Center, Indore, India 452014
Burn Care and Prevention 2022/2: 51-56