80]. Although none of these therapies are now routine, they are becoming more widespread. Recommendations for their routine use will need to await larger controlled trials to demonstrate efficacy.

Application: The patient presented previously was started on oxandrolone oral supplementation, 10 mg twice daily, as an anabolic agent. He also received propranolol, 15 mg orally/enterally every 6 hours, with the dose titrated to achieve a 25% reduction in heart rate from post-burn injury baseline.

Monitoring nutrition support

Most patients with major burns who require nutrition support have a prolonged course, particularly because their metabolic demands remain above baseline even after wound coverage is complete. During the course of healing and convalescence from burn injury metabolic demands fluctuate significantly, displaying the classic “ebb and flow” pattern first described by Cuthbertson in 1930 [81], and also responding to changes in clinical status. Therefore, great importance is placed upon use of appropriate monitors of nutritional status.

Although a variety of methods exist for monitoring adequacy of nutritional support, validation of traditional tools used for monitoring nutritional status has not occurred in critically ill patients [3]. This lack of a “gold standard” is further complicated by the heterogeneity of burn patients’ metabolic status and the associated variability in the findings from these methods. Therefore, employing a combination of clinical course, wound healing and objective measures, and an overall focus on trends optimizes monitoring [5]. Notably, neither the Canadian Clinical Practice guidelines nor the SCCM/ASPEN nutrition guidelines address monitoring of nutrition support once initiated [3, 82].

Optimal monitoring of nutritional status

Various laboratory values have been suggested as potential surrogates for nutritional status, including the serum proteins transthyretin, c-reactive protein (CRP), retinol-binding protein (RBP), and transferrin. The relevance of measuring these pro-

teins depends upon the extent of metabolic stress and alters with the patient’s progression through injury recovery. Serum albumin levels become profoundly depressed with burn injury and are slow to recover even with provision of adequate nutrition. Further, serum albumin levels have no apparent correlation with nitrogen balance in burn patients, nor does supplementation of albumin to maintain serum levels have any evident clinical benefit [83, 84]. Transthyretin (prealbumin) has been considered as another surrogate, although levels also decrease precipitously following burn injury. Transthyretin levels do demonstrate consistent improvement as healing from burn injury occurs, as well as a weak association with nitrogen balance [83, 85]. However, no causality in those relationships has been established. Retinol-binding protein and transferrin have failed to demonstrate a relationship with nitrogen balance or any other indicator of nutritional adequacy [83]. Based upon the limited value of visceral proteins in monitoring nutritional status following burn injury, current recommendations consistently indicate that they should only be used in conjunction with other measures [25, 42, 83, 86]. Perhaps most importantly, none of these markers has demonstrated predictive capability for outcomes in burn patients, calling into question their validity as a surrogate for nutritional status; these may instead simply be a marker of severity of illness [87, 88].

The elevated protein demands associated with burn hypermetabolism imply relevance for nitrogen balance monitoring in assessing nutritional adequacy. Unfortunately, urinary urea nitrogen (UUN) has been best evaluated in children with major burns and has been demonstrated to be inaccurate[86]. This unreliability may be primarily present in patients with exceptional hypercatabolic responses[25]. Further, protein losses through wounds complicate the calculation of nitrogen balance. In spite of these limitations, measurement of UUN and calculation of nitrogen balance on a weekly basis allows estimation of nitrogen catabolism and modification of protein goals based upon trends[5, 25].

Indirect calorimetry (IDC) estimates energy expenditure by either oxygen consumption or carbon dioxide production; it also provides a means of estimating the composition of fuels that are being