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

Estimates of resting energy expenditure using predictive equations in adults with severe burns: A systematic review and meta-analysis

BACKGROUND

Many equations to estimate the resting energy expenditure (REE) of patients with burns are currently available, but which of them provides the best guide to optimize nutrition support is controversial. This review examined the bias and precision of commonly used equations in patients with severe burns.

METHODS

A systematic search of the PubMed, Web of Science, Embase, and Cochrane Library databases was undertaken on June 1, 2023, to identify studies comparing predicted REE (using equations) with measured REE (by indirect calorimetry [IC]) in adults with severe burns. Meta-analyses of bias and calculations of precisions were performed in each predictive equation, respectively.

RESULTS

Nine eligible studies and 12 eligible equations were included. Among the equations, the Toronto equation had the lowest bias (26.1 kcal/day; 95% CI, -417.0 to 469.2), followed by the Harris-Benedict equation × 1.5 (1.5HB) and the Milner equation. The Ireton-Jones equation (303.4 kcal/day; 95% CI, 224.5-382.3) acceptably overestimated the REE. The accuracy of all of the equations was <50%. The Ireton-Jones equation had the relatively highest precision (41.2%), followed by the 1.5HB equation (37.0%) and the Toronto equation (34.7%).

CONCLUSION

For adult patients with severe burns, all of the commonly used equations for the prediction of REE are inaccurate. It is recommended to use IC for accurate REE measurements and to use the Toronto equation, 1.5HB equation, or Ireton-Jones equation as a reference when IC is not available. Further studies are needed to propose more accurate REE predictive models.

Early Hypermetabolism is Uncommon in Trauma Intensive Care Unit Patients

BACKGROUND

Classic experiments demonstrating hypermetabolism after major trauma were performed in a different era of critical care. We aim to describe the modern posttraumatic metabolic response in the trauma intensive care unit (TICU).

METHODS

This prospective observational study enrolled TICU mechanically ventilated adults (aged ≥18) from 3/2018-2/2019. Multiple, daily resting energy expenditure (REE) measurements were recorded. Basal energy expenditure (BEE) was calculated by the Harris-Benedict equation. Hypometabolism was defined as average daily REE < 0.85*BEE and hypermetabolism defined as average daily REE > 1.15*BEE. Demographics, interventions, and clinical outcomes were abstracted. Descriptive statistics and multivariable logistical regression models evaluating demographics with the outcome variable of hypermetabolism for the first 3 days ("sustained hypermetabolism") were performed, along with group-based trajectory modeling (GBTM).

RESULTS

Fifty-five patients were analyzed: median age was 38 (28-56) years; 38 (69%) were male; body mass index (kg/m² ) was 28 (26-32); and Injury Severity Score was 27 (19-34), with (38 [71%] blunt, 8 [15%] penetrating, 7 [13%] burn) injury mechanism. Overall, 19 (35%) had hypermetabolism on day 1 ("immediate hypermetabolism"), and 11 (21%) had sustained hypermetabolism for the first 3 days. Logistic regression analysis identified penetrating mechanism (adjusted odds ratio [AOR], 16.4; 95% CI, 1.9-199.6; p = .015), burn mechanism (AOR, 11.1; 95% CI, 1.3-116.8; p =.029), and maximum temperature (AOR, 4.2; 95% CI, 1.3-20.3; p= .041) as independent predictors of sustained hypermetabolism. GBTM identified 4 nutrition phenotypes, with 2 hyperconsumptive phenotypes associated with increased risk of malnutrition at discharge.

CONCLUSION

Only a minority of injured patients is hypermetabolic in the first week after injury. Elevated temperature, penetrating mechanism, and burn mechanism are independently associated with sustained hypermetabolism. Hyperconsumptive phenotype patients are more likely to develop malnutrition during hospitalization.

Prospective Study on Energy Expenditure in Patients With Severe Burns

BACKGROUND

Nutrition therapy is recognized as one of the most significant treatment aspects for burn patients. However, data were limited regarding the actual nutrition practices in patients with severe burn injury. This study aims to explore the measured energy expenditure (MEE) changes in severe burn patients and to evaluate the precision of commonly used predictive formulas for estimating predictive energy expenditure (PEE) in burn patients.

METHODS

A prospective multicenter trial was conducted in the intensive care units in the hospitals enrolling the severely burned patients. Data on MEE and PEE were collected and analyzed.

RESULTS

Forty-three patients were enrolled from 3 hospitals. All the patients had severe burns. MEE was measured by metabolic cart, and the MEE on the seventh day after severe burns was as high as 65 kcal/kg, which was 267% of the basal metabolic rate. The presence of hypermetabolism was sustained throughout the 21-day afterburn and decreased gradually to 34 kcal/kg thereafter until 4 weeks after injury. Wound percentage after skin-grafting therapy, time course of burn injury, the existence of severe sepsis, and blood infection were significantly associated with higher MEE. Compared with PEE and MEE, Toronto formula could estimate patients' energy requirements with more accuracy; Curreri and Pennisi formula both significantly overestimated the patient's energy expenditure, whereas underestimation occurred with the Harris-Benedict formula.

CONCLUSIONS

Severe burn patients were hypermetabolic at the early stage and sustained this status over a long time. The Toronto formula was the unbiased method to predict energy expenditure.

Use of Predictive Equations for Energy Prescription Results in Inaccurate Estimation in Trauma Patients

BACKGROUND

Overfeeding and underfeeding are associated with poor clinical outcomes. In the absence of indirect calorimetry (IC), the Society of Critical Care Medicine/ASPEN recommend prescribing 25-30 kcal/kg. The Harris-Benedict equation (HBE) multiplied by a stress factor is commonly applied in critically ill patients. We describe the difference between estimated and actual energy needs in critically injured patients.

METHODS

From March to November 2018, we collected demographics and energy needs determined by continuous IC (started within 4 days) in intubated adults. Ideal or adjusted body weight was used for 25-30 kcal/kg, and HBE was multiplied by a 1.3 stress factor (1.3HBE). Daily requirements up to 14 days, extubation, or death were calculated using all 3 methods and compared with IC.

RESULTS

Fifty-five subjects were included. Median age was 38 [27-58] years, 38 (69%) were male, body mass index was 28 [25-33] kg/m² , and Acute Physiology and Chronic Health Evaluation II score was 17 [14-24] Mechanism of injury was blunt (38, 69%), penetrating (9, 16%), and burn (8, 15%). By day 14, compared with measured energy requirements by IC, the other methods could result in a cumulative 1827-kcal (+7%) surplus (1.3HBE), a 1313-kcal (-5%) deficit (25 kcal/kg), or a 3950-kcal (+14%) surplus (30 kcal/kg) per patient over a median 9 days.

CONCLUSION

In critically injured patients, predictive equations for energy needs do not account for dynamic metabolic changes over time and could result in underfeeding or overfeeding. Adjusting daily prescription based on continuous IC may result in better individualized treatment.

Update on metabolism and nutrition therapy in critically ill burn patients

Major burn injury triggers severe oxidative stress, a systemic inflammatory response, and a persistent hypermetabolic and hypercatabolic state with secondary sarcopenia, multiorgan dysfunction, sepsis and an increased mortality risk. Calorie deficit, negative protein balance and antioxidant micronutrient deficiency after thermal injury have been associated to poor clinical outcomes. In this context, personalized nutrition therapy with early enteral feeding from the start of resuscitation are indicated. Over the last four decades, different nutritional and pharmacological interventions aimed at modulating the immune and metabolic responses have been evaluated. These strategies have been shown to be able to minimize acute malnutrition, as well as modulate the immunoinflammatory response, and improve relevant clinical outcomes in this patient population. The purpose of this updating review is to summarize the most current evidence on metabolic response and nutrition therapy in critically ill burn patients.

Impact of decreasing energy intakes in major burn patients: A 15-year retrospective cohort study

BACKGROUND & AIMS

Nutritional therapy is particularly important after major burn injury and specific nutritional guidelines have been developed. The study aimed at evaluating the impact of the changes in our nutritional practice, general compliance with the guidelines and potential consequences.

METHODS

Retrospective analysis of prospectively collected data in burn patients requiring intensive care (ICU) between 1999 and 2014.

INCLUSION CRITERIA

admission on day 1, full treatment and length of ICU stay >7 days. Four periods (P) were defined by protocol changes (P1: 1999-2001, P2: 2002-2005, P3: 2006-2010, P4: 2011-2014). Collected data: demographic and nutritional data, infectious complications, weights, CRP and prealbumin concentrations during the first 21 days.

RESULTS

240 patients were included (median age 43 years, burned area 25%). Measured energy expenditure (MEE) was stable through all periods but the prescribed caloric target decreased significantly, and below MEE (P1: 33 kcal/kg, IQR 7, P4: 28 kcal/kg, IQR 8, p < 0.001). Energy delivery ended decreasing below 30 kcal/kg/day (P1: 30 kcal/kg, IQR 23, P4: 25 kcal/kg, IQR 12, p < 0.001). Protein intakes increased due the use of high protein solutions and glutamine (P1: 1.04 g/kg, IQR 0.90, P4: 1.26, IQR 0.99, p < 0.001). Weight loss by day 21 increased significantly according to area under the curve (P1: 701, IQR 38, P2: 722, IQR 51, P4: 689 IQR 63, p = 0.02). Prealbumin levels decreased with energy decrease (P1: 150 mg/L, IQR 110, P4: 80 mg/L, IQR 70, p = 0.003).

CONCLUSIONS

The observed reduction of the energy delivery <30 kcal/kg was associated with a supplemental weight loss and lower prealbumin concentrations.

Metabolic Support of the Thermally Injured Patient

Nutrition Support Pharmacist features issues pertinent to the practice of clinical pharmacy in the area of nutritional support. The column is edited by Dr. Roland Dickerson, Professor of Pharmacy, University of Tennessee Health Science Center; Memphis, TN. Address correspondence to Dr. Roland N. Dickerson, University of Tennessee Health Science Center, 26 South Dunlap St., Memphis, TN 38163.

This article provides a summary of our approach to the nutritional management of the thermally injured patient. However, it must be pointed out that there are other alternative effective evidence-based approaches to managing this problematic patient population. There are numerous exceptions to the above outlined guidelines that the astute clinician must be able to identify. However, for the beginning reader, this approach will provide a sound foundation upon which to build their practice in the management of these difficult patients.

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.

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.

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.

Veno-venous continuous renal replacement therapy for burned patients with acute renal failure

From 1995 to 1998, 12 burned patients with acute renal failure (ARF) were treated by veno-venous continuous renal replacement therapy (CRRT) at the Burn Unit of Hôtel-Dieu de Montréal. Their mean (+/-SD) age was 51+/-12 years, and the mean burned surface covered 48.6+/-15.8% of total body surface area. All patients were mechanically ventilated and presented evidence of sepsis. The mean delay before occurrence of ARF was 15+/-6 days and ARF was mainly related to sepsis and hypotension. Main reasons for CRRT initiation were azotemia and fluid overload. A total of 15 CRRT modalities were applied (12 continuous veno-venous hemodiafiltration, CVVHDF; two continuous veno-venous hemofiltration, CVVH; and one continuous veno-venous hemodialysis, CVVHD) over 14+/-13 days. For CRRT, nine patients received heparin and three were not anticoagulated. Mean values for dialysate and reinjection flow rates were 1134+/-250 ml/h and 635+/-327 ml/h, respectively. Admission weight was 78.8+/-12.7 kg with a mean weight gain before CRRT initiation of 10.0+/-5.8 kg and a mean weight loss during CRRT of 8.9+/-5.5 kg. Nine patients received enteral plus parenteral nutrition, and three, parenteral nutrition only; the total caloric intake was 31.5+/-7.0 kcal/kg/day and protein intake, 1.8+/-0.4 g/kg/day. The normalized protein catabolic rate (nPCR) was evaluated at 2.28+/-0.78 g/kg/day during CRRT. The mortality rate was 50%. The six survivors all recovered normal renal function with four of them requiring intermittent hemodialysis for short periods. In conclusion, veno-venous CRRT is particularly well suited for this selected population allowing smooth fluid removal and aggressive nutritional support.

1999 Jonathan E. Rhoads lecture. Isotopic metaprobes, nutrition, and the roads ahead

The 1999 Jonathan E. Rhoads lecture, delivered by Vernon R. Young at the annual meeting of American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.), San Diego, February 2, 1999, with the printed version coauthored with Alfred M. Ajami, is concerned with the application of isotopic probes and how, in particular, they may be used as diagnostic tools to enhance the role of nutrition in the comprehensive medical management of the patient. Following a brief review of the early uses of stable isotopes in metabolic research we consider the present and possible future application of stable isotope probes. The concept of a "gateway" enzyme in a discrete biochemical pathway and how the flow of substrate through this step might be assessed by giving a "metaprobe" is developed. The specific and desirable structural requirements of the metaprobe are considered. A number of examples are given that further exploit the concepts of "underground" metabolism and of metabolic "hijackers." It is our view that we are on the verge of a new era where, for the many pragmatic and exciting reasons discussed, stable isotope probes will find and increasing use in the practice of clinical medicine and in the preventive and public health areas.

The metabolic basis of the increase of the increase in energy expenditure in severely burned patients

BACKGROUND

Severe burn trauma is characterized by an elevated rate of whole-body energy expenditure.

APPROACH

In this short review, we have attempted to assess the metabolic characteristics of and basis for the persistent increase in energy expenditure during the flow phase of the injury. We consider some aspects of normal energy metabolism, including the contribution of the major adenosine triphosphate (ATP)-consuming reactions to the standard or basal metabolic rate. Rate estimates are compiled from the literature for a number of these reactions in healthy adults and burned patients, and the values are related to the increased rates of whole-body energy expenditure with burn injury.

RESULTS

Whole-body protein synthesis, gluconeogenesis, urea production, and substrate cycles (total fatty acid and glycolytic-gluconeogenic) account for approximately 22%, 11%, 3%, 17%, and 4%, respectively, of the burn-induced increase in total energy expenditure.

CONCLUSIONS

These ATP-consuming reactions, therefore, seem to explain approximately 57% of the increase in energy expenditure. The remainder of the increase may be due, in large part, to altered Na(+)-K(+)-ATPase activity and increased proton leakage across the mitochondrial membrane.

Muscle strength in individuals with healed burns

OBJECTIVE

To quantify the long-term effects of burns on muscle strength and to investigate the impact of the initial severity of the trauma on muscle strength.

DESIGN

Cross-sectional study comparing individuals with healed burns to nonburned control individuals matched for age, gender, body mass index, and physical activity level.

SETTING

Subjects were selected from the data bank of a burn center of a large Montreal teaching hospital and tested in a university laboratory.

PATIENTS

Thirty subjects (mean age, 36.3 +/- 11.5 yrs) with second- and third-degree burns covering 15% to 75% of total body surface area (TBSA) (mean, 35.5% +/- 15.9%) were evaluated more than 1 year after discharge (mean, 37.3 +/- 20.4 months; range, 15 to 92 months). Thirty unburned subjects were recruited from the community at large.

MAIN OUTCOME MEASURE

Maximal torque, work, and power developed by the elbow and knee flexors and extensors.

RESULTS

Subjects with burns of > 30% of TBSA produced significantly less torque, work, and power in the quadriceps than control subjects (15.2% to 20.5% depending on velocity [p < .05]). The ability to develop muscle power at the elbow was also compromised in the severely burned subjects (19.2% in extension and 18.7% in flexion [p = .07]) at the faster velocities. No differences were observed between controls and patients with small burn injuries (TBSA of < 30%).

CONCLUSION

Patients who had severe burns (TBSA of > 30%) had weaker muscles even years after the trauma, suggesting either an inability to fully recover or insufficient rehabilitation.

Continuous haemofiltration and haemodiafiltration for acute renal failure in severely burned patients

Among 970 burned patients admitted between April 1987 and September 1994, 16 (1.6 per cent) presented acute renal failure requiring dialytic support and were treated by continuous renal replacement therapy as first-line modality. Their mean burned surface area was 58.0 +/- 5.7 per cent. Acute renal failure mainly occurred in the second week following admission in relation to sepsis and nephrotoxic drugs. Four types of continuous renal replacement therapy were performed: continuous arteriovenous haemofiltration and haemodiafiltration (CAVH and CAVHDF) and continuous venovenous haemofiltration and haemodiafiltration (CVVH and CVVHDF). Compared to 33 critically ill patients without burns also treated for acute renal failure by continuous haemofiltration or haemodiafiltration during the same period, the mean duration of therapy was longer for the burned patients (24.2 +/- 9.4 vs. 5.3 +/- 0.8 days). Although mean urine outputs and ultrafiltration rates were similar for both groups, fluid administration was higher for burned patients (8.2 +/- 0.7 vs. 3.3 +/- 0.2 l/day). Total weight loss during therapy was significantly greater in burned patients (12.6 +/- 3.6 vs. 6.8 +/- 1.0 kg), in relation to longer treatment period. Bleeding complications were more frequent in burned patients (56 vs. 15 per cent). Mortality rates were similar in both groups (82 vs. 82 per cent). In conclusion, when aggressive initial fluid resuscitation is applied following burn injury, the occurrence of acute renal failure is low, delayed and multifactorial. Since they are haemodynamically well tolerated and provide a good metabolic and volaemic control, continuous renal replacement therapies appear to be useful modalities for burned patients with acute renal failure. However, as bleeding complications are more frequent, careful monitoring is necessary.

Improved clinical status and length of care with low-fat nutrition support in burn patients

BACKGROUND

The optimal amount and type of fat in the nutrition support of burned patients have not been determined. The aim of this study was to test low-fat nutritional solutions, with or without fish oil, on protein metabolism, morbidity, and length of care in severely burned adults.

METHODS

In a prospective randomized clinical trial, 43 patients were assigned to one of the following groups: control (35% fat), low-fat solution (ie, 15% of total calories as fat), low-fat with fish oil, given for 30 days. Nitrogen balance, urinary 3-methylhistidine excretion, urinary cortisol, and clinical status were measured daily. Corticosteroid-binding globulin and total and free serum cortisol were measured every 3 days.

RESULTS

Compared with controls, patients on low-fat support had fewer cases of pneumonia: 3/24 vs 7/13 (p = .02), better respiratory and nutrition status, and shorter time to healing: 1.2 vs 1.8 days/% burned area (p = 0.01). There was no difference in nitrogen balance between groups, and 3-methylhistidine excretion was higher and serum free cortisol was lower in log-fat--fed patients than in controls. There was no difference between the two low-fat groups in any of the parameters measured.

CONCLUSIONS

This study showed that low-fat nutrition support decreases infectious morbidity and shortens length of stay in burn patients. Fish oil does not seem to add clinical benefit to low-fat solutions. In addition, this study provides the first evidence that nutrition intervention modulates cortisol-binding globulin and the concentration of free circulating cortisol after a severe stress.

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.

Nutrition support in critical illness

Sepsis, shock, multiple trauma, and burns are often associated with altered metabolism characterized by severe catabolism, wasting of the lean body mass, immune dysfunction, and compromised wound healing. Nutrition support is one of the mainstays in the management of these critically ill patients and is aimed at minimizing these complications. The purpose of this article is to compare stress hypermetabolism and starvation metabolism, to review current recommendations for the provision of energy and substrate to the critically ill patient, and to review pertinent literature regarding enteral vs parenteral nutrition. Finally, this article will provide a brief overview of new and future therapies with emphasis on specific substrates and growth factors and the potential for their use in the critically ill patient.

Thermogenic response to feeding in severely burned patients: relation to resting metabolic rate

Energy expenditure (EE) was measured one to five times by indirect calorimetry for 1 h after an overnight fast, and for 2 h after starting feeding in 19 severely burned patients (TBSA > 20 per cent) for a total of 36 tests. Twelve tube-fed volunteers served as controls. Thermogenic response to feeding (TRF) was calculated as the percentage of energy intake and hypermetabolism as the percentage of values obtained with the Harris-Benedict formula (%HB). Measured energy expenditure values were compared with values given by three predicting formulae. TRF was present in 10 out of the 33 measurements. Fasting EE was not different between the tests with and without TRF, but %HB was different between the two groups: 121.1 +/- 25.8 vs 157.8 +/- 32.0 per cent (tests with and without TRF, respectively (P < 0.01)). TRF was always absent when %HB was higher than 50. When TRF was present it was not statistically different from the control values. None of the three predicting formulae gave values within 10 per cent of the measured values in more than 25 per cent of the patients. We conclude that TRF is suppressed in burned patients with marked hypermetabolism, and that EE measured in the fed state reflects resting expenditure accurately in these patients. In addition, EE cannot be predicted from existing formulae.

Use of indirect calorimetry in clinical nutrition

The tremendous variability in resting energy expenditure makes efforts to predict caloric requirements difficult. Indirect calorimetry has provided a valuable tool in assessing energy expenditure, evaluating the way in which the body uses nutrient fuel, and designing nutritional regimens that best fit the clinical condition of the patient. The many indirect calorimetric instruments available vary in their application to clinical nutrition. The best metabolic studies are achieved by controlling the testing environment, accounting for the many clinical factors that may affect measurements, and eliminating potential sources for error. Although indirect calorimetry would seem to reduce the likelihood of complications from overfeeding, its greatest effect may be in cost savings by avoiding unnecessary nutritional support and in providing a means for clinical research.