Substrate oxidation and the contribution of protein oxidation to energy expenditure after severe head injury

The ratio of energy expenditure to nitrogen loss in diverse patient groups--a systematic review

BACKGROUND & AIMS

The ratio of energy expenditure to nitrogen loss respectively of energy to nitrogen provision (E/N) is considered a valuable tool in the creation of an enteral or parenteral formulation. Specific E/N ratios for parenteral nutrition (PN) have not yet been clearly defined. To determine the range of energy expenditure, nitrogen (protein) losses, and E/N ratios for various patient groups, we performed a systematic review of the literature.

METHODS

Medline 1950-2011 was searched for all studies on patients or healthy controls reporting energy expenditure and nitrogen loss at the same time.

RESULTS

We identified 53 studies with 91 cohorts which comprised 1107 subjects. Mean TEE ± standard deviation (SD) was 31.2 ± 7.2 kcal/kg BW/day in patients (n = 881) and 35.6 ± 4.3 kcal/kg BW/day in healthy controls (n = 266). Mean total protein loss (TPL) was 1.50 ± 0.57 g/kg BW/day in patients and 0.94 ± 0.24 g/kg BW/day in healthy controls. A non-linear significant correlation was found between TPL and the E/N ratio.

CONCLUSION

The E/N ratio is not a constant value but decreases continuously with increasing protein loss. These variations should be considered in the nutritional support of patients.

Modified hormonal effects on fat metabolism after severe head injury in children

Previous studies within our research group have indicated that the hormonal influences on whole body energy expenditure may be modified in severely head-injured children. The aim of this study was to examine plasma concentrations of nonesterified fatty acids (NEFA) and the hormonal and metabolic mediators which influence these to determine whether there is a similarly modified effect on fat metabolism. A total of 64 serial measurements were made in 21 fasting severely head-injured children aged 2-15 y (Glasgow Coma Score < or = 8) who were receiving neurointensive care. Circulating NEFA, ketone bodies, and lactate concentrations were analyzed using microenzymatic or electrochemical techniques. Plasma concentrations of adrenaline and insulin were measured using radioenzymatic and RIA techniques, respectively. Net fat oxidation rates were determined using indirect calorimetry. Plasma NEFA concentrations showed a significant positive relationship with both net fat oxidation rates (p = 0.02) and log ketone body concentrations (p = 0.008), indicating that NEFA concentrations were significantly related with utilization. When compared with reference values for normal resting adults, 59 (92%) adrenaline measurements were elevated, whereas only 8 (12%) NEFA values lay above the reference range. Surprisingly, between children, there was a significant negative relationship between NEFA and adrenaline concentrations, even after allowing for the effects of insulin and lactate (p = 0.015). Both plasma NEFA and adrenaline concentrations were significantly related with Glasgo Coma Score (p = 0.04, p = 0.007, respectively), the most severely injured children having the lowest NEFA and highest adrenaline concentrations. The mechanisms underlying these metabolic changes may be related to the severity of head injury and may involve changes in triglyceride/NEFA cycling and/or peripheral effects on adrenergic receptors. If children are to be treated effectively after trauma, it is important to discover the mechanism of these changes which must reflect a fundamental alteration in metabolism.

Measured energy expenditure and plasma substrate and hormonal changes after severe head injury

The influence of head trauma on the pattern of response to injury has been studied. Metabolic and hormonal data from brain injured patients over 20 days following injury were compared with an existing data base from non-head-injured patients and control subjects. The results demonstrated elevated concentrations of plasma glucose, lactate, non-esterified fatty acids (NEFA), cortisol, glucagon and insulin above that of control values in both groups after injury. Head injury as a separate factor did not affect the concentrations of any of these plasma substrates and hormones independently of its contribution to the Injury Severity Score (ISS). However, plasma catecholamine concentrations were higher in the head injured initially and at 7 days after injury. All head-injured patients showed an increase in metabolic rate (above predicted values) at some stage after injury. It should be noted, however, that there were some features of head injury (and its treatment) such as paralysis, ventilation and fasting which were not matched in the non-head-injured group. It was concluded that the metabolic changes occurring after head injury are similar to those occurring after extracranial injury and that therapeutic intervention has a major effect on the level of energy expenditure seen in these patients.