Use of indirect calorimetry in the nutritional management of burned patients

Weight changes and patterns of weight measurements in hospitalized burn patients: a contemporary analysis

Background

Severe burn is associated with significant changes in body weight due to resuscitation volumes, fluid shifts, a hypermetabolic state, prolonged bed rest, and caloric intake. Our goal was to quantify and describe trends in weight change in patients with burns of all severities under modern treatment conditions and to identify the time points at which these changes occur.

Methods

An institutional review board-approved chart review was conducted of acute burn patients treated at an American Burn Association-verified regional burn center from February 2016 to November 2016. Patients were then divided into three groups based on percent of total burn surface area (%TBSA) burn: 1–19%, 20–39%, and ≥ 40%. Weight was expressed as percent change of weight from baseline. Regression analysis was conducted on percent weight changes for each TBSA group.

Results

We identified 197 burn patients with a length of stay (LOS) of ≥ 7 days. Of the study cohort, 149 had TBSA burn of 1–19%, 27 had TBSA burn of 20–39%, and 21 had TBSA burn of ≥ 40%. All groups had a majority of White male, non-Hispanic patients with mean ages between 40 and 42 years. Burn patients with > 20% TBSA burn had a median increase in weight above baseline of approximately 5 to 8% likely due to resuscitation fluids within the first week of hospitalization. Weight loss below baseline often did not exceed 10% and was more pronounced as LOS increased, mostly in patients with > 20% TBSA burn. Whereas patients with 1–19% TBSA burn on average returned to baseline weight at last measurement, patients with 20–39% TBSA and ≥ 40% TBSA burn continued a decline in weight at 4 weeks (r² = 0.57 and 0.55, respectively) on the same trajectory.

Conclusions

Burn patients with > 20% TBSA burn had an increase in weight above baseline of up to 8%, likely due to resuscitation fluids within the first week of hospitalization. Weight loss below baseline often did not exceed 10% and was more pronounced as LOS increased, mostly in patients with > 20% TBSA burn. Therefore, our patients on average, lost body weight to a lesser extent than the maximum mean loss of 22% of pre-burn weight reported prior to modern treatment conditions.

Nutrition and metabolism in burn patients

Severe burn causes significant metabolic derangements that make nutritional support uniquely important and challenging for burned patients. Burn injury causes a persistent and prolonged hypermetabolic state and increased catabolism that results in increased muscle wasting and cachexia. Metabolic rates of burn patients can surpass twice normal, and failure to fulfill these energy requirements causes impaired wound healing, organ dysfunction, and susceptibility to infection. Adequate assessment and provision of nutritional needs is imperative to care for these patients. There is no consensus regarding the optimal timing, route, amount, and composition of nutritional support for burn patients, but most clinicians advocate for early enteral nutrition with high-carbohydrate formulas.

Nutritional support must be individualized, monitored, and adjusted throughout recovery. Further investigation is needed regarding optimal nutritional support and accurate nutritional endpoints and goals.

Nutrition and metabolism in burn patients

Severe burn causes significant metabolic derangements that make nutritional support uniquely important and challenging for burned patients. Burn injury causes a persistent and prolonged hypermetabolic state and increased catabolism that results in increased muscle wasting and cachexia. Metabolic rates of burn patients can surpass twice normal, and failure to fulfill these energy requirements causes impaired wound healing, organ dysfunction, and susceptibility to infection. Adequate assessment and provision of nutritional needs is imperative to care for these patients. There is no consensus regarding the optimal timing, route, amount, and composition of nutritional support for burn patients, but most clinicians advocate for early enteral nutrition with high-carbohydrate formulas. Nutritional support must be individualized, monitored, and adjusted throughout recovery. Further investigation is needed regarding optimal nutritional support and accurate nutritional endpoints and goals.

Influence of inhalation injury on energy expenditure in severely burned children

OBJECTIVE

Determine the effect of inhalation injury on burn-induced hypermetabolism in children.

DESIGN

Prospective study comparing hypermetabolism (i.e., resting energy expenditure and oxygen consumption) in burned children with and without inhalation injury during acute hospitalization.

SETTING

Single pediatric burn center.

PATIENTS

Eighty-six children (1-18 years) with ≥40% total body surface area burns were stratified to two groups: no inhalation injury and inhalation injury.

INTERVENTIONS

None.

MAIN MEASUREMENTS AND RESULTS

Inhalation injury was diagnosed based on bronchoscopic evaluation. At admission, PaO2:FiO2 ratios (an index of respiratory distress) were significantly higher in patients with no inhalation injury than in patients with inhalation injury. No differences were detected in resting energy expenditure or percent of the predicted basal metabolic rate between groups. Additionally, oxygen consumption did not significantly differ between groups.

CONCLUSIONS

Inhalation injury does not augment the burn-induced hypermetabolic stress response in children, as reflected by resting energy expenditure and oxygen consumption.

Practical guidelines for nutritional management of burn injury and recovery

Nutrition practice in burn injury requires a multifaceted approach aimed at providing metabolic support during a heightened inflammatory state, while accommodating surgical and medical needs of the patient. Nutritional assessment and determination of nutrient requirements is challenging, particularly given the metabolic disarray that frequently accompanies inflammation. Nutritional therapy requires careful decision making, regarding the safe use of enteral or parenteral nutrition and the aggressiveness of nutrient delivery given the severity of the patient's illness and response to treatment. With the discovery that specific nutrients can actually alter the course of disease, the role of nutrition support in critical illness has shifted from one of preventing malnutrition to one of disease modulation. Today the use of glutamine, arginine, essential fatty acids, and other nutritional factors for their effects on immunity and cell regulation is becoming more common, although the evidence is often lagging. An exciting dichotomy exits, forcing nutrition support specialists to make responsible choices while remaining open to new potential helpful therapeutic options.

Comparison of Measured Resting Energy Expenditure Versus Predictive Equations in Pediatric Burn Patients

Many equations have been developed to estimate resting energy expenditure (REE) in thermally injured patients. A consensus has not been reached on the accuracy of these equations in children. The purpose of our study was to compare three predictive equations: Harris Benedict x 2 multiplier (HB x 2), Mayes (MG), and the WorId Health Organization x 2 multiplier (WHO x 2) with measured resting energy expenditure x I.3 multiplier (MREE x 1.3) in pediatric burn patients. MREE was measured by open-circuit indirect calorimetry in 10 burned children (6 boys, 4 girls) aged 2 to 10 years with TBSA burn ranges from 35% to 97%. MREE x 1.3 was compared with values obtained by HB x 2, MG, and WHO x 2 predictive equations. When comparing MREE x 1.3 with all three equations, significant differences were found when compared with HB x 2 and MG, but there were no significant difference between MREE x 1.3 vs WHO x 2. The HB x 2 and MG equations overpredicted MREE x 1.3 by 29% and 19%, respectively. Many predictive equations have been developed to predict energy expenditure in burns, but their accuracy in predicting MREE x 1.3 is variable. A larger study comparing/contrasting predictive equations and resting energy expenditure measured by indirect calorimetry is needed to improve the prediction of energy needs in burned children.

Immune modulating nutrition support for a patient with severe toxic epidermal necrolysis

Toxic epidermal necrolysis (TEN) is a rare but serious condition with a high mortality rate, whose clinical features resemble major thermal injury. Nutritional substrates which can affect the immune response have been shown to benefit burned and critically ill patients but there is a lack of data in the TEN literature. A case study is presented of a 63-year-old female admitted to our burn unit with extensive skin and mucosal involvement. Immune modulating artificial nutrition support was given initially via the parenteral route and then the nasogastric route. Maintenance of the patient's nutritional status and clinical outcome suggest that there may be a role for this type of intervention in TEN.

Caloric requirements in patients with necrotizing fasciitis

Patients with necrotizing fasciitis (NF) and other soft tissue infections are often treated in burn centers due to the extent of wound care and surgical intervention needed. Sepsis and surgery increase metabolic needs and may limit oral intake and necessitate enteral (TEN) or parenteral (TPN) nutrition. We reviewed the records of patients admitted with necrotizing fasciitis or surgical soft tissue infections from January 1993 to June 1998 who had indirect calorimetry (IC) measurements performed. Records were also reviewed for surgical/medical management and nutritional intervention. Twenty-six patients were admitted with 17 of these having IC measurements (133 total IC measurements). The IC group had more surgeries (mean 4.9 versus 2.7) and 82% required mechanical ventilation (mean 17.9 days). Energy expenditure showed a moderate but significant increase in energy needs (mean 23.8 kcal/kg/day, 124% BEE) with large variations (10.7-42.4 kcal/kg/day, 60%-199% BEE) in individual energy requirements. Caloric intake averaged 73% of needs based on IC (range 53%-104%). Nearly all patients (94%) required TEN (82%) and/or TPN (41%) nutrition for a mean of 24 days (range 1-68 days). NF presents a broad range of metabolic and surgical needs. Our data indicates patients with NF have increased energy requirements and suggests provision of calories at 124% basal or 25 kcal/kg actual wt/d; but due to the large individual variation, routine assessment using IC is recommended. Clinicians need to recognize the likely need for nutritional support and possibly lengthy clinical course for these patients.

Audit of successful weight maintenance in adult and paediatric survivors of thermal injury at a UK regional burn centre

BACKGROUND

Thermal injury is associated with significant weight loss, particularly of lean body mass. Weight loss increases the risk of morbidity and increased length of stay (LOS). Appropriate nutrition support can improve these outcomes. The aim of this audit was to evaluate the success of nutrition intervention in minimizing weight loss in adults and children with thermal injury.

METHOD

Patients referred for nutrition support were monitored for weight change during their inpatient care episode. Sixty cases met the study criteria. Admission and discharge weight profiles were identified. The degree of weight loss was calculated. Comparison was made to a recognized standard of acceptable weight loss.

RESULTS

On admission five (13.2%) adults were found to be clinically underweight. All children were within the acceptable weight percentile range. Adults demonstrated higher (mean +/- SD) percentage weight loss (8.1 +/- 6.0%) than children (4.7 +/- 4.5%). About 76.7% of all cases met the standard used. More children (95.5%) met the standard than adults (65.8%).

CONCLUSIONS

Most subjects maintained weight within an acceptable limit during the inpatient episode. Children appeared particularly successful at weight maintenance. Reasons are multifactorial and warrant further investigation.

Burns

During the past 20 yrs, as burn care has evolved as a specialty of surgery, survival and outcome quality have soared. Public expectations for survival and long-term outcomes are at previously unprecedented levels. These changes are the result of a number of advances in aspects of burn care that have occurred in parallel and have fostered increasing regionalization of this resource-intensive activity into fewer specialized centers. These are complex hospitalizations and can be divided into four phases: initial evaluation and resuscitation, initial wound excision and biological closure, definitive wound closure, and rehabilitation and reconstruction.

[Metabolic problems and nutrition in burns]

Metabolic changes with burns patients are enormous. The loss of skin substance and the necessity of its reconstruction are at the origin of this exceptional situation. In this context of major aggression with important metabolic alteration the nutritional needs are considerable. To assure a tissue reconstruction, nutrition is as important as the fight against infection. The authors make the point on the quantity needs and the quality needs. They raise up the perspectives concerning immunonutriments and note the importance of enteral administration. As a conclusion, they insist on the fundamental role of the clinical aspect, in the survey of nutritional state.

Energy expenditure and caloric balance after burn: increased feeding leads to fat rather than lean mass accretion

OBJECTIVE

Resting energy expenditure (REE) is commonly measured in critical illness to determine caloric "demands" and thus nutritive needs.

SUMMARY BACKGROUND DATA

The purpose of this study was to 1) determine whether REE is associated with clinical outcomes and 2) determine whether an optimal caloric delivery rate based on REE exists to offset erosion of lean mass after burn.

METHODS

From 1995 to 2001, REE was measured by indirect calorimetry in 250 survivors of 10 to 99%TBSA burns. Caloric intake and REE were correlated with muscle protein catabolism, length of stay, ventilator dependence, sepsis, and mortality. From 1998 to 2000, 42 patients (>60%TBSA burns) received continuous enteral nutrition at a spectrum of caloric balance between 1.0x REE kcal/d -1.8x REE kcal/d. Serial body composition was measured by dual energy x-ray absorptiometry. Lean mass, fat mass, morbidity, and mortality were determined.

RESULTS

REE/predicted basal metabolic rate correlated directly with burn size, sepsis, ventilator dependence, and muscle protein catabolism (P <.05). Declining REE correlated with mortality (P <.05). 2) Erosion of lean body mass was not attenuated by increased caloric balance, however, fat mass increased with caloric supply (P <.05).

CONCLUSION

In surviving burned patients, caloric delivery beyond 1.2 x REE results in increased fat mass without changes in lean body mass. Declining energy expenditure appears to be a harbinger of mortality in severely burned patients.

[Systemic complications of extended burns]

Burns covering more than 10% of the total body surface area (TBSA) are responsible for systemic perturbations which, in very severe cases, can represent a vital risk and, in all cases, affect the wound evolution. Among these general perturbations, fluid volume and electrolyte changes, leading eventually to burn shock, have the most dramatic consequences. Burn shock is, still to day, a vital risk and can also, in case of inadequate early fluid resuscitation, results in secondary morbidity and mortality. Fluid replacement during the very first hours after injury represents certainly a key point of the management of severe burn cases. Estimation of resuscitation fluid needs during this period is frequently underestimated. For adult, we recommend, during the first hour, a minimum of one liter for all severe injuries and two liters if the injury exceeds 50% of TBSA. Pulmonary injuries due to smoke inhalation are frequent, about 25% of patients hospitalized in burn units, and responsible for numerous death at site of house fires. In burn units, about 25% of hospitalized patients have pulmonary injuries in relation with smoke inhalation. This population has a high mortality rate increasing with the area of the skin injury and with age. Patients with inhalation injury need more resuscitation fluids, are subject to pneumonia and necessitate frequently mechanical ventilation. Parameters of the mechanical ventilation have to be choice to avoid barotrauma. Severe burn patients are submitted to a very high metabolic level. This can leads to a deep nutritional deficit responsible for an immunological suppression. It is then of major importance to provide an adequate nutritional support. It is also necessary to fight against the stress and to put the patient in a warm environment. Finally, infection is the most frequent and the most severe complication of burn injuries. Everything have to be done to avoid bacteriological contamination including architecture, equipment's, care procedure, nutritional support, types of wound dressing and most importantly surgery. Surgical procedures have to be done as earliest as possible to excise necrosis and cover the wound.

A comparison of renal phosphorus regulation in thermally injured and multiple trauma patients receiving specialized nutrition support

To compare phosphorus intake and renal phosphorus regulation between thermally injured patients and multiple trauma patients, 40 consecutive critically ill patients, 20 with thermal injury and 20 with multiple trauma, who required enteral tube feeding were evaluated. Phosphorus intakes were recorded for 14 days from the initiation of tube feeding which was started 1 to 3 days postinjury. Serum for determination of phosphorus concentrations was collected at days 1, 3, 7, and 14 of the study period. A 24-hour urine collection was obtained during the first and second weeks of nutrition support for urinary phosphorus excretion, fractional excretion of phosphorus, renal threshold phosphate concentration, and phosphorus clearance. Average total daily phosphorus intake during the 14-day study for thermally injured patients and multiple trauma patients was 0.99+/-0.26 mmol/kg/d vs 0.58+/-0.21 mmol/kg/d, respectively, p < .001. Serum phosphorus concentration on the third day of observation was significantly lower in the thermally injured group than those with multiple trauma (1.9+/-0.8 mg/dL vs 3.0+/-0.8 mg/dL, p < or = .01). A trend toward hypophosphatemia in the thermally injured group persisted by the seventh day of feeding (2.7+/-1.2 mg/dL vs 3.3+/-0.6 mg/dL, p < or = .04). Differences in urinary phosphorus excretion was not statistically significant between the thermally injured and multiple trauma groups (271+/-213 mg/d vs 171+/-181 mg/d for week 1, and 320+/-289 mg/d vs 258+/-184 mg/d for week 2, respectively). Urinary phosphorus clearance, fractional excretion of phosphorus, or renal threshold phosphate concentrations were also not significantly different between thermally injured and multiple trauma patients. During nutrition support, serum phosphorus concentrations are lower in thermally injured patients compared with multiple trauma patients despite receiving a significantly greater intake of phosphorus. Renal phosphorus regulation does not significantly contribute to the profound hypophosphatemia observed in thermally injured patients when compared with multiple trauma patients during nutrition support.

Pharmacological nutrition after burn injury

Burn patients develop pathophysiological alterations, which include extensive nitrogen loss, malnutrition, markedly increased metabolic rate and immunologic deficiency. This predisposes burn patients to frequent infections, poor wound healing, increased length of hospitalization and increased mortality. The nutritional support requires high protein and high energy diets preferably administered enterally soon after injury. The effects of increased dietary components such as glutamine, arginine and (n-3) fatty acids and related compounds have been evaluated in burn victims. These components, when supplied in quantities two to seven times of those in normal diets of healthy persons, appear to have beneficial pharmacological effects on the pathophysiological alterations associated with burns. However, the efficacy of immune-enhancing diets remains to be convincingly shown.

Accuracy of 30-minute indirect calorimetry studies in predicting 24-hour energy expenditure in mechanically ventilated, critically ill patients

BACKGROUND

There is no consensus regarding the optimal duration of measurement or time of day to perform indirect calorimetry (IC). Energy expenditure (EE) varies at different times of day and with different activity levels. We sought to assess the variability of EE in mechanically ventilated patients over a 24-hour period and the accuracy of 30-minute IC studies in predicting the 24-hour energy expenditure (EE24).

METHODS

The study was a prospective comparison between the resting EE obtained by 30-minute measurement of IC and EE values obtained from 24-hour measurements. Tests were performed in the Medical Intensive Care Unit (MICU) of a tertiary care, university hospital. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured for 24 hours in eight ventilated patients. Measurements were made every 3 minutes and used to calculate 30-minute and 24-hour oxygen consumption values. EE24 was calculated using the modified Weir equation. Each 30-minute interval was compared with the value obtained from the 24-hour measurement.

RESULTS

Three hundred forty-one of 384 30-minute intervals remained for analysis. Average EE24 measured was 1490 +/- 486 kcal/d. Average EE24 predicted by extrapolation from 30-minute studies was 1501 +/- 503 kcal/d, with a mean difference of 0 +/- 209 kcal/d from the measured 24-hour values (range: -1068 to +585 kcal/d). Thirty-minute studies were within 20% of 24-hour measurements for 89% of intervals. The difference between 24-hour and 30-minute studies correlated with changes in minute ventilation (VE), heart rate, systolic blood pressure, and breath rate from their 24-hour means (p < .001). The mean error of EE estimate was greatest between 3 and 11 PM (p < .001).

CONCLUSIONS

We conclude the following: (1) EE in MICU patients is variable; (2) 30-minute IC studies predict measured EE24 acceptably well for clinical purposes; and (3) accuracy is maximized if a 30-minute study is performed between 11 PM and 3 PM, and when Ve, heart rate, systolic blood pressure, and breath rate are near the day's average.

Energy Needs Are Poorly Predicted in Critically Ill Elderly

Changes in energy expenditure with age have been described, but this physiology is not routinely considered when managing critically ill elderly patients. To allow us to avoid the potential problems associated with underfeeding or overfeeding the critically ill elderly population, with approval of the human studies committee and appropriate consent from legal guardians, 25 critically ill patients over 65 years of age requiring mechanical ventilation underwent expired gas indirect calorimetry. If they had a pulmonary artery catheter in place for clinical reasons, reverse-Fick indirect calorimetry was also performed. Data obtained by indirect calorimetry was compared with commonly applied equations for predicting energy expenditure by statistical methods of correlation and limits of agreement. These 25 patients had an average age of 74 ± 1.23 (standard error of the mean) and an average APACHE II score of 15. Predictive equations correlated poorly with measured resting energy expenditure, and although they showed reasonable bias, they were imprecise in their estimation of resting energy expenditure. These data suggest that energy expenditure in critically ill, mechanically ventilated elderly patients is highly variable. Although generally overestimating energy needs, currently available equations for predicting energy expenditure in this population are associated with significant bias and imprecision, which may lead to both overfeeding and underfeeding. Although these equations may be suitable as a basis of initiating nutritional support, energy provisions should ideally be guided by indirect calorimetry.

Nutritional management of patients with gastrointestinal fistulas

Nutritional support plays a key and integral role in the management of patients with gastrointestinal fistulas. It needs to be instituted early to minimize erosion of body cell mass, to prevent further physiologic deterioration of the patient, and to initiate repletion in an otherwise malnourished patient. Furthermore, it allows for rest of the gastrointestinal tract and facilitates healing of the fistula.

Evaluation of predicted and measured energy requirements in burned children

OBJECTIVE

The energy predictions of nine calculations for pediatric patients were compared with measured resting energy expenditure (MREE) by means of indirect calorimetry to determine the optimal means of energy projection in the burn population younger than 3 years of age.

METHODOLOGY

Nutritional sufficiency and maintenance of preburn weight were factors in the confirmation of energy needs. Demographic factors were also studied: preburn weight, percent burn, percent third-degree burn, and age. Group 1 consisted of 24 patients younger than 3 years of age (range = 7 months to 2.6 years) with a percent burn of 30.6 +/- 2.0 and percent third-degree burn of 21.9 +/- 2.6. Group 2, consisting of 24 patients 5 to 10 years old matched by percent burn and percent third-degree burn, was included to determine whether differences between actual and projected needs were evident in older, prepubescent patients.

STATISTICAL ANALYSIS

Analysis of variance was used to ascertain the most reliable multiplier for MREE needed to maintain at least 95% of preburn weight at discharge while ensuring adequate nutrition. Multiple regression analysis was used to determine the relationship between energy requirement and body weight, percent burn, and age.

RESULTS

An additional 30% of MREE provided a consistent ratio of actual energy intake to required intake. MREE x 1.3 was used as a guide to study the existing calculations. For both groups, the four equations that predicted energy in healthy children most often underestimated MREE x 1.3, whereas the five formulas for children with burns tended to overpredict energy. Regression analysis yielded two new sets of equations using age, preburn weight, and percent burn (< 3 years = Mayes 1 [r2 = .71], 5 to 10 years = Mayes 3 [r2 = 70] or percent third-degree burn (< 3 years = Mayes 2 [r2 = .68], 5 to 10 years = Mayes 4 [r2 = .67]).

CONCLUSIONS

The application of a 30% factor to MREE is supported in burn patients younger than 10 years of age. Standard energy projections do not provide an accurate assessment of energy needs in the pediatric burn population; thus, two sets of equations that more closely predict energy needs are proposed.

Resting metabolic rate in subjects with paraplegia: the effect of pressure sores

OBJECTIVE

To determine the overall effect of paraplegia and pressure sores on resting metabolic rate.

DESIGN

Unblinded, case-control study using a convenience sample.

SETTING

Hospital primary care setting.

PATIENTS

Fourteen individuals with paraplegia and pressure sores (PS-Para), 24 with paraplegia in good health (NPS-Para), and 23 non-spinal cord injury (SCI) controls.

MAIN OUTCOME MEASURES

The planned outcome measures consisted of resting metabolic rate, percent of predicted resting metabolic rate, resting metabolic rate per kilogram body weight, and resting metabolic rate per meter squared body surface area. Post hoc analyses were used to identify the effect of completeness of lesion, smoking, and pressure sores on percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight.

RESULTS

Percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight were significantly higher in the PS-Para group than in the NPS-Para or control groups (115% +/- 4% vs 100% +/- 2% or 107% +/- 2%, p < .05) and (25.9 +/- 1.2 vs 21.4 +/- 0.6 or 22.5 +/- 0.4 kcal/kg, p < .05, respectively). The resting metabolic rate per meter squared body surface area was significantly higher in the PS-Para group than in NPS-Para group (973 +/- 39 vs 874 +/- 20kcal/m2, p < .05). In the PS-Para group, current smokers had significantly higher resting metabolic rate per kilogram body weight than nonsmokers (27.3 +/- 1.7 vs 24.0 +/- 1.4kcal/kg, p < .01). Controlling for the effects of smoking in a multiple regression model, those in the PS-Para group had significantly (p < .001) greater percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight than those in the NPS-Para group.

CONCLUSIONS

These findings indicate that individuals with SCI may have a decreased percent of predicted resting metabolic rate and those with pressure sores may have a hypermetabolic state. This hypermetabolic state is significantly higher than that resulting from smoking. Because ordinary prediction equations for energy expenditure may not be accurate when applied to subjects with paraplegia and pressure sores, quantification of energy needs by indirect calorimetry is recommended.

Heart rate and metabolic response to burn injury in humans

BACKGROUND

Although frequently done, estimating the energy requirements of individual burn patients without measuring their resting metabolic rate is a less than satisfactory method of evaluation.

METHODS

We tested whether heart rate, which relates to the energy expenditure during physical activity, is also associated with postburn hypermetabolism (calculated as percentage increase of resting metabolic rate above the predicted normal fasting resting metabolic rate). Twenty-three patients [12 men and 11 women, aged 38 +/- 13 years (mean +/- SD); weight, 71.6 +/- 14.8 kg; body mass index, 25.4 +/- 3.6; total burn surface area, 35.3 +/- 17.8% (percentage of body surface)] were studied weekly for 3 weeks after an overnight fast.

RESULTS

Measured resting metabolic rates and heart rates were 2016 +/- 497 kcal/d, 101 +/- 13 bpm (n = 19); 2231 +/- 485 kcal/d, 107 +/- 13 bpm (n = 18); and 1903 +/- 598 kcal/d, 99 +/- 14 bpm (n = 11) for weeks 1, 2, and 3, respectively. Postburn hypermetabolism was +36% +/- 19%, +55% +/- 27%, and +36% +/- 35% in the first, second, and third week, respectively. In each week postburn hypermetabolism correlated with heart rate (r = 0.65, p = .003; r = 0.69, p = .001; and r = 0.80, p = .002, respectively). Only in the second week did postburn hypermetabolism correlate with total burn surface area (r = 0.52, p = .02); there was no correlation with body temperature. In a multiple regression analysis, predicted resting metabolic rate, heart rate, and total burn surface area together explained 77% of all of the variance observed in the 48 fasting resting metabolic rates that were measured in the study (r2 = 0.77, p < .0001), and each of these variables also had a significant partial correlation with fasting resting metabolic rates (r2 = 0.45, p < .0001; r2 = 0.29, p < .0001; and r2 = 0.03, p < .03, respectively).

CONCLUSIONS

In burn patients, variability in heart rate is associated with a significant part of postburn hypermetabolism variability. Therefore, heart rate may be considered a useful variable to be used for the evaluation of the energy requirements of severely burned patients.

Predictors of total parenteral nutrition-induced lipogenesis

OBJECTIVE

To evaluate the incidence and cause of parenteral nutrition-induced lipogenesis.

DESIGN

Retrospective patient review.

SETTING

A 40-bed predominantly surgical ICU.

PATIENTS

One hundred forty patients receiving central venous nutrition and mechanical ventilatory support.

INTERVENTIONS

Indirect calorimetry was used to determine patient's measured energy expenditure (MEE) and respiratory quotient (RQ). Additionally total caloric intake (TCAL), glucose infusion rate, basal energy expenditure (BEE), estimated stress factor, and calculated energy expenditure (CEE) were assessed in each patient.

MEASUREMENTS AND MAIN RESULTS

Net fat synthesis was found as RQs exceeded 1 in 47 percent of patients. Statistically significant differences in oxygen consumption, CO2 production, measured energy expenditure, total and carbohydrate caloric intake, and glucose infusion rate were found between groups of patients with an RQ < or = or > 1. Seventy-three percent of patients with glucose infusion rates > 4 mg/kg-min had RQs > 1.

CONCLUSIONS

Net fat synthesis was found in a surprisingly large number of critically ill patients receiving central venous nutrition. Many of these patients received carbohydrate calories in excess of their measured energy expenditure, even though it appeared that they needed this level of caloric intake by clinical assessment. The high carbohydrate total parenteral nutrition (TPN) solutions with lipids provided only for prevention of essential fatty acid depletion resulted in an unacceptably high incidence of fat synthesis. The results suggest that caloric intake may be optimized in critically ill patients using indirect calorimetry. When calorimetry is not available, a total caloric intake of up to 140 percent of the BEE with glucose infusion rates not exceeding 4 mg/kg-min and fats providing 40 to 60 percent of calories will meet the energy requirements of most critically ill patients without forcing the RQ > 1.

The metabolic effects of thermal injury

Major thermal injury is associated with extreme hypermetabolism and catabolism as the principal metabolic manifestations encountered following successful resuscitation from the shock phase of the burn injury. Substrate and hormonal measurements, indirect calorimetry, and nitrogen balance are biochemical metabolic parameters which are useful and more readily available biochemical parameters worthy of serial assessment for the metabolic management of burn patients. However, the application of stable isotopes with gas chromatography/mass spectroscopy and more recently, new immunoassays for growth factors and cytokines has increased our understanding of the metabolic manifestations of severe trauma. The metabolic response to injury in burn patients is biphasic wherein the initial ebb phase is followed by a hypermetabolic and catabolic flow phase of injury. The increased oxygen consumption/metabolic rate is in part fuelled by evaporative heat loss from wounds of trauma victims, but likely also by a direct central effect of inflammation upon the hypothalamus. Although carbohydrates in the form of glucose appear to be an important fuel source following injury, a maximum of 5-6 mg/kg/min only is beneficial. Burn patients have accelerated gluconeogenesis, glucose oxidation, and plasma clearance of glucose. Additionally, considerable futile cycling of carbohydrate intermediates occurs which includes anaerobic lactate metabolism and Cori cycle activity arising from wound metabolism of glucose and other substrates. Similarly, accelerated lipolysis and futile fatty acid cycling occurs following burn injury. However, recent evidence suggests that lipids in the diet of burned and other injured patients serve not only as an energy source, but also as an important immunomodulator of prostaglandin metabolism and other immune responses. Amino acid metabolism in burn patients is characterized by increased oxidation, urea synthesis, and protein breakdown which is prolonged and difficult to reduce with current nutritional therapy. However, the current goal of nutritional support is to optimize protein synthesis. Specific unique requirements may exist for supplemental glutamine and arginine following burn injury but further research is needed before enhanced branched chain amino acids supplements can be recommended for burn patients. Recent research investigations have revealed the importance of enteral feeding to enhance mucosal defense against gut bacteria and endotoxin. Similarly, research has demonstrated that many of the metabolic perturbations of burns and sepsis may be due, at least in part, to inflammatory cytokines. Investigation of their pathogenesis and mechanism of action both at a tissue and a cellular level offer important prospects for improved understanding and therapeutic control of the metabolic disorders of burn patients.

Nutritional support in the critically ill surgical patient

Aggressive nutritional support in the critically ill surgical patient is essential if improved outcome is to be realized. An understanding of the metabolic alterations of trauma and sepsis provides the foundation for a nutritional prescription for the individual patient. Careful nutritional assessment; titration of fluid, electrolytes, and micronutrients; provision of adequate calories and nitrogen to meet metabolic needs; and the selective use of specialized formulations are important components of nutritional management in the ICU.

Altered gastric emptying in the head-injured patient: relationship to feeding intolerance

Most patients with moderate to severe head injury initially do not tolerate enteral feedings postinjury. This intolerance is more prolonged than that found in patients suffering other types of trauma. The authors prospectively evaluated 12 patients with moderate to severe head injury (Glasgow Coma Scale score between 4 and 10) throughout their hospitalization for liquid gastric emptying as a possible mechanism for intolerance to enteral feeding. During Week 1, the majority of patients displayed a delay in gastric emptying. Patients also displayed an abnormal biphasic response (gastric emptying faster than normal during the early stage but prolonged later). By Week 2, many patients still had delayed and abnormal biphasic responses to gastric emptying. By Week 3, an improvement was observed with the majority of patients exhibiting rapid gastric emptying, but delays and abnormal biphasic responses were still seen. Patients who initially had rapid or normal gastric emptying tolerated full-strength full-rate feedings significantly earlier compared with those who experienced delayed gastric emptying (8.5 +/- 0.5 days vs. 13.7 +/- 3.2 days, p less than 0.001). All patients tolerated full-strength full-rate feedings by Day 16 postinjury (range 7 to 16 days) except the two patients who displayed delayed gastric emptying for prolonged periods of time (mean 25 days). This is the first study to longitudinally evaluate gastric emptying following head injury. The authors suggest that patients with moderate to severe head injury often experience alterations in gastric emptying which may affect their ability to tolerate enteral feedings.

Nutrition for adult burn patients: a review

Adequate nutritional support is an important aspect of burn therapy. To accomplish this goal, nutrition assessment must be conducted, with particular attention given to the determination of energy and macronutrient needs. Providing these nutrients by the enteral route is recommended.

Nutritional monitoring of a pediatric burn patient

The pediatric burn patient presents a particular challenge nutritionally. Nutritional reserves are limited, and excesses are often poorly tolerated. Ongoing monitoring is essential for discovering at an early stage the dynamic shifts in energy, protein, and other nutrients that may be occurring. Adequate enteral intake may be difficult to achieve as a result of repeated holding of feedings on surgery days and gastrointestinal tolerance problems such as poor gastric emptying and abdominal distention. This case report illustrates techniques, such as the nutritional assessment record and parenteral nutrition evaluation form, which may assist the clinician in optimizing the nutritional management of the patient.

Factors contributing to increased energy expenditure in thermal injury: a review of studies employing indirect calorimetry

In summary, a remarkably close agreement exists for the mean MEE measured in 28 studies of severe burn trauma. This is especially surprising given the variability in sample sizes, measurement techniques, study designs, and DPBs studied. The mean MEE calculated from the data published in these reports is listed in the final column of Table I. For more than 450 cases, an unweighted MEE is 2750 +/- 85 kcal/day. For those studies prior to 1980, the mean MEE exceeds 3000 kcal/day in eight of 14 reports vs only two of 14 published after 1980. Even so, the mean MEE for the pre-1980 reports differs by only 200 kcal/day (2960 +/- 120, n = 14). The accepted notion that the degree of elevation in MEE is in proportion to the % BSAB up to about 60% BSAB is useful in a general sense but must be applied with caution. The recent studies, which include proportionately more burns exceeding 80% BSAB, suggest an elevation in MEE in these cases. Nevertheless, a physiologic plateau apparently exists at or slightly below 2 x normal RMR at the peak of MEE. The magnitude of the MEE response results from an undefined interaction among several factors of which some have been examined while others such as inflammatory mediators are only beginning to receive study. The contributions to reduction in MEE from interventions to control cardiac output and peripheral cooling, core temperature, evaporative water (heat) loss, and substrate cycling have been reviewed. The importance of indirect calorimetry in patient care is highlighted by the large variability in similarly injured individuals and in the unexplained component of regression analyses.(ABSTRACT TRUNCATED AT 250 WORDS)

Total energy expenditure in burned children using the doubly labeled water technique

Total energy expenditure (TEE) was measured in 15 burned children with the doubly labeled water technique. Application of the technique in burned children required evaluation of potential errors resulting from nutritional intake altering background enrichments during studies and from the high rate of water turnover relative to CO2 production. Five studies were discarded because of these potential problems. TEE was 1.33 +/- 0.27 times predicted basal energy expenditure (BEE), and in studies where resting energy expenditure (REE) was simultaneously measured, TEE was 1.18 +/- 0.17 times REE, which in turn was 1.16 +/- 0.10 times predicted BEE. TEE was significantly correlated with measured REE (r2 = 0.92) but not with predicted BEE. These studies substantiate the advantage of measuring REE to predict TEE in severely burned patients as opposed to relying on standardized equations. Therefore we recommend that optimal nutritional support will be achieved in convalescent burned children by multiplying REE by an activity factor of 1.2.

Nutritional support in the critical care setting (Part 1)

Over the past two decades nutritional support has rapidly become an integral part of the medical care of critically ill patients. As scientific evidence accumulates supporting the important role of underlying nutritional status in determining the eventual outcome of many illnesses, aggressive nutritional intervention has become commonplace in our medical and surgical ICUs. However, nutritional support, particularly parenteral alimentation, is expensive and associated with important morbidity and even mortality. Furthermore, definite evidence of its clinical efficacy under certain specific conditions is often lacking and in need of properly done prospective studies. This review summarizes the basic principles of nutrition as applied to the critically ill patient in the clinical setting. Special emphasis is on practical considerations regarding cost, efficacy (or lack thereof), and potential advantages, disadvantages, and risk of complications of each proposed approach.