Nutrition support for the burn patient

Background

Nutrition support represents a critical component in the care of the acutely burned patient. Management of nutritional demands mandates attention to the unique hypermetabolic state that results from major burn injury; this pathophysiology results in loss of lean body mass, increased fat accretion and protein wasting, and impaired wound healing. Historically, failure to address these problems in victims of major burn injury often resulted in a fatal degree of inanition and death from infection and heart failure within a few weeks of injury [1, 2]. Current understanding and appreciation of burn hypermetabolism is still imperfect, but methods exist to support the patient throughout the critical period of muscle wasting and metabolic demand while healing occurs. Thus, the goal of nutrition support in the burn patient is to ameliorateand hopefully optimizethe deranged metabolism resulting from burn injury and permit successful closure of the burn wound and resolution of the hypermetabolic state.

This chapter will review current knowledge of burn metabolism and nutrition with an emphasis on evidence-based literature. In doing so, it must be appreciated that much of our knowledge of nutritional support is extrapolated from studies in other patient populations, particularly trauma and critical care. The reader is referred to excellent recent reviews and practice guidelines on this subject [3, 4]; more lim-

Marc G. Jeschke et al. (eds.), Handbook of Burns

ited guidelines have also been published specifically for burns [5, 6]. It is noteworthy that recommendations from North America regarding burn patient nutrition differ from those published in Europe [7], which illustrates the differences which can arise in interpreting the limited data available in this population. Thus, much of this information requires careful interpretation and leaves a number of important controversies in the care of burn patients unresolved.

Case presentation

A 26-year-old healthy man (85 kg) was transferred to the burn center after he was injured in a propane gas flash explosion. He sustained approximately 48% TBSA burn injury, including face and neck, anterior arms and legs, and most of his anterior torso. His burn is a combination of fulland partialthickness injury. Due to his facial burns and concern for inhalation injury, he was intubated prior to transport. His burn shock resuscitation proceeded normally; at 12 hours post-injury the clinician wished to determine what should be done about nutrition support for this patient.

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Patient selection: Timing and route of nutritional support

While all people require nutrition, not all patients require formal nutritional support. Patients with limited injuries who are anticipated to eat normally within 3–5 days will tolerate this short period of inadequate nutrition. However, these inferences can be wrong and more seriously injured patients should not be “permitted to fail” before beginning nutritional support. This case patient clearly fits this category: he was intubated and may be unable to take anything by mouth for many days. His major burn will unquestionably require more metabolic support than he could reasonably eat and even a few days of starvation would produce significant muscle wasting. Most experts would agree that nutrition should absolutely be started within the first three days of injury [8], and preferably within the first 24–48 hours [3].

How early is early? Debate continues over the value of “early” nutritional support, defined as that started within 24 hours of injury. Some studies have shown that intestinal feeding begun within 12 hours of injury – even in patients subjected to abdominal surgery – can be tolerated, and may reduce infectious complications [9]. However, providing this nutrition can be difficult; burn patients are prone to early ileus, and ongoing burn shock is associated with splanchnic hypoperfusion. Feedings are often poorly tolerated, leading to frequent interruptions, inadequate delivery of nutrients, and increasing the risks of serious complications such as aspiration and intestinal necrosis. Recent trials have confirmed these findings and found no major advantage to such early enteral nutrition in burn patients [10, 11]. A more reasonable goal is to institute nutrition by 48 hours post-burn with the goal of achieving full nutritional maintenance within 3–5 days.

Enteral vs. Parenteral? The superiority of enteral nutrition (EN) is universally acknowledged. Parenteral nutrition (PN) is expensive. Complications associated with intravenous access (pneumothorax, line sepsis) and major metabolic complications, including hypoand hyper-glycemia, are both more common and more severe than those seen with enteral nutrition. Overall infections are also more common in ICU populations given PN [12]. In addition, EN directly nourishes bowel mucosa, pre-

venting mucosal atrophy and preserving normal gutassociated immune and inflammatory status [13]. The enteral route is thus clearly preferred over PN for shortand long-term nutritional support for all critically-ill patients [3, 7].

There is less agreement, however, on the possible value of PN in two situations: as a supplement to “bridge” patients during the initial institution of EN or as “rescue” therapy in patients who cannot tolerate adequate (or sometimes any) enteral support. In some trials in burn patients, PN supplementation was associated with increased mortality compared to patients given even limited EN [14, 15], suggesting that PN should be avoided at all costs. However, this has not been supported in a meta-analysis of criti- cally-ill patients [16]. Current guidelines restrict initial PN use to patients who are anticipated to be unable to tolerate EN for at least 7 days. However, once PN is begun, it should be maintained until patients can take at least 60% of required calories enterally [3]. Some burn authorities routinely use PN to supplement EN during the “ramp-in” phase of nutrition, and whenever tube feedings are interrupted by surgery, technical problems, or intolerance [5]. This can lead to smoother institution of enteral feedings, and fewer interruptions for distension, diarrhea, and other problems. With these few exceptions, however, EN should be the preferred – and usually the only– method of nutrition required for burn patients.

Gastric vs. small bowel? Another disagreement surrounds the best location for placement of enteral feeding tubes. Many patients tolerate feeding directly into the stomach. Large-diameter gastric tubes can be placed by nurses immediately and used for decompression and medications as well as nutrition. However, gastric ileus is common in burn patients, leading to distension and risking aspiration. Intestinal feeding is often better tolerated and may be continued to the time of and during surgery [17]. Enteric feeding tubes require skilled placement and are easily displaced; tubes also clog easily, and these technical complications can lead to delayed initiation and frequent interruptions in nourishment. There is some evidence that aspiration is more common with gastric feedings [18], but this is disputed [19]. In recent meta-analyses no differences in mortality or aspiration rates were found between gastric and small bowel feedings, but the latter took significantly long-