Catabolic effect of dexamethasone in patients with major head injuries

Controversies in the determination of energy requirements

To avoid any negative outcomes associated with under- or overfeeding it is essential to estimate nutrient requirements before commencing nutrition support. The energy requirements of an individual vary with current and past nutritional status, clinical condition, physical activity and the goals and likely duration of treatment. The evidence-base for prediction methods in current use, however, is poor and the equations are thus open to misinterpretation. In addition, most methods require an accurate measurement of current weight, which is problematic in some clinical situations. The estimation of energy requirements is so challenging in some conditions, e.g. critical illness, obesity and liver disease, that it is recommended that expenditure be measured on an individual basis by indirect calorimetry. Not only is this technique relatively expensive, but in the clinical setting there are several obstacles that may complicate, and thus affect the accuracy of, any such measurements. A review of relevant disease-specific literature may assist in the determination of energy requirements for some patient groups, but the energy requirements for a number of clinical conditions have yet to be established. Regardless of the method used, estimated energy requirements should be interpreted with care and only used as a starting point. Practitioners should regularly review the patient and reassess requirements to take account of any major changes in clinical condition, nutritional status, activity level and goals of treatment. There is a need for large randomised controlled trials that compare the effects of different levels of feeding on clinical outcomes in different disease states and care settings.

Catabolic effect in premature infants with early dexamethasone treatment

To evaluate the catabolic effects of dexamethasone therapy on protein metabolism, amino acid concentrations and urinary 3-methylhistidine (3MH) were measured in 28 premature infants who were included in a double-blind controlled study using early dexamethasone therapy in the prevention of bronchopulmonary dysplasia. Fifteen infants received dexamethasone (0.5 mg/kg/day i.v.) and 13 infants received normal saline as control. Heparinized venous blood samples for amino acid analysis were obtained before the study and again at day 5 after starting the study. Urinary 3MH was measured on days 1, 3, 5, 7, 14, 21, and 28 of treatment. A substantial increase in amino acid concentrations was observed in infants receiving dexamethasone. Alanine, glutamine, citrulline, ornithine and cystine concentrations increased twofold or more. The 3MH:creatinine ratio was increased in the treated group. These metabolic effects were most likely due to an increase in protein catabolism.

Observations on the patterns of 24-hour energy expenditure changes in body composition and gastric emptying in head-injured patients receiving nasogastric tube feeding

BACKGROUND

Although intolerance to nasogastric feeding is commonly observed after head injury, quantitative measurements of gastric emptying are lacking. Concepts about energy requirements are limited by the lack of long-term measurements of total energy expenditure.

METHODS

Six male subjects with severe head injury had their gastric emptying measured by the phenol red technique. N and energy balances were measured by classic balance techniques, which included continuous indirect calorimetry for up to 24 hours (days 3 to 5). Measurements of body composition were made on days 3 to 5 and 12 to 19 (4 subjects only).

RESULTS

The subjects lost a mean of 9.8 kg of which 2.3 kg was estimated to be due to fat (equivalent to -14 g N/d and -1690 kcal/d). On days 3 to 5, basal metabolic rate (BMR) was 130% to 135% of predicted. The low dietary intake (650 kcal and 4.2g N/d) was associated with negative energy (-1710 +/- 520 kcal/d) and N balances (-19 +/- 5 g N/d). Gastric emptying was delayed twofold (days 3 to 5) compared with controls (p < .001) and was associated with significant regurgitation of feed into the mouth (16 of 31 saliva samples contained glucose at a concentration of > 0.5 mmol/L compared with control values of < 0.2 mmol/L.

CONCLUSIONS

The large negative energy balance in the subjects studied was largely due to the inadequate nasogastric feeding, which was associated with a twofold reduction in the rate of gastric emptying and frequent regurgitation of feed. The large negative N balance and the high contribution of protein oxidation to total energy expenditure (25% to 28%) was predominantly due to the injury sustained and immobility. An increase in BMR is not necessarily associated with increased total energy expenditure or energy requirements.

Changes in the plasma aminogram of parenterally fed infants treated with dexamethasone for bronchopulmonary dysplasia

A substantial increase in the plasma concentration of most amino acids was observed in 59 preterm infants with chronic lung disease soon after the initiation of dexamethasone therapy. The size of increase appeared to be dose related. This phenomenon is likely to be the result of steroid induced protein catabolism. Interestingly, neither phenylalanine nor tyrosine concentrations were significantly increased.

Catabolic effect of dexamethasone in the preterm baby

Most babies treated with dexamethasone for bronchopulmonary dysplasia exhibit an appreciable rise in the blood urea concentration, from a mean of 2.3 mmol/l before steroid to a mean of 7.1 mmol/l after. In order to discover whether this was primarily the result of increased protein catabolism, nitrogen balance studies before and after the start of dexamethasone were performed and a mean deficit in nitrogen retention of 158 mg/kg/24 hours was found. Similarly the urinary 3-methylhistidine (3MH):creatinine ratio before and after the commencement of dexamethasone treatment in a group of preterm babies was measured. It was found that there was a substantial increase in 3MH excretion after dexamethasone: from a mean 3MH:creatinine ratio of 46 in the week before steroids to a mean ratio of 77 in the week after. As 3MH emanates almost exclusively from the breakdown of actin in skeletal muscle cell, this finding implies the loss of muscle tissue. It was also found that the babies were in less positive nitrogen balance after dexamethasone, to a degree which is significant relative to their protein reserves. The long term consequences of a period of increased catabolism are not yet known but the authors suggest caution in the use of dexamethasone, at least in babies with milder degrees of bronchopulmonary dysplasia in whom the ratio of benefit to risk may be less favourable.

Penetrating craniocerebral trauma

The authors review the pathophysiology of penetrating and perforating cranial wounds. Radiologic evaluation includes computed tomography and angiography. Operative technique and perioperative critical care are discussed, with special emphasis on the control of the intracranial pressure. Other problems such as fluid and electrolyte disorders and nutrition are discussed in relation to neurosurgery.

Parenteral nutrition for marrow transplant recipients: evaluation of an increased nitrogen dose

The use of total parenteral nutrition in bone marrow transplant (BMT) recipients is well recognized. These patients as a result of treatment with chemotherapy and immunosuppressive agents undergo catabolic stress. The metabolic effect of an increased nitrogen dose during total parenteral nutrition (TPN) was studied in 28 BMT patients. Patients were given TPN formulas providing a nitrogen intake of either 267 +/- 44 mg of N/kg/d or 330 +/- 60 mg of N/kg/d. Total calories, nonprotein and protein, were held constant at 40 kcal/kg/d for all patients. Data was collected for three periods posttransplant beginning at 3 days posttransplant through day 16. Both study TPN formulas improved patient weight and TIBC values over baseline. Nitrogen balance (NB) values were not significantly different at any study period. However, an overall group effect favored the H-N formula (p less than 0.01). BMT patients undergo catabolic stress which was reflected by average values of 24-hour urine urea nitrogen increasing from 8.1 +/- 4 g/d at baseline to 19.8 +/- 7.2 g/d at period 3 (p less than 0.01). The H-N formula did not differentially increase blood urea nitrogen or serum creatinine levels. Metabolic cart measures also showed no increase in metabolic rate, oxygen consumption, carbon dioxide production, or percent contribution of protein to total metabolic expenditure. Providing a caloric intake of 40 kcal/kg/d was excessive, where 30 to 35 kcal/kg/d would meet metabolic demands. Pertinent clinical outcomes including length of stay, relapse rate, and survival were monitored, but no conclusions could be drawn in this study. The H-N formula was more effective in reducing loss of lean body mass without causing detrimental metabolic effects in BMT patients.