82	M.G. Jeschke

Gut complications may be life threatening: in addition to the already mentioned ACS and constipation, the patients may develop Ogilvie syndrome, ischemic and non-ischemic bowel necrosis, and intestinal hemorrhage. A careful tight supervision of bowel function with daily examinations is therefore mandatory, particularly in perioperative periods with intraoperative hemorrhage leading to hypovolemia, which exposes the patient to gut hypoperfusion and their threatened complications.

Stress ulcer prophylaxis is mandatory, usually by H2-blockers (ranitidine) or proton pump inhibitors since the bleeding risk is elevated in burn injuries and may be life threatening.

6.3.4.2 Micronutrients and Antioxidants

Critically ill burned patients are characterized by a strong oxidative stress, an intense inßammatory response, and a hypermetabolic state that can last months. Trace element (TE) deÞciencies have repeatedly been described. The complications observed in major burns such as infections and delayed wound healing can be partly attributed to TE deÞciencies [47, 48]. Plasma TE concentrations are low as a result of TE losses in biological ßuids, low intakes, dilution by ßuid resuscitation, and redistribution from plasma to tissues mediated by the inßammatory response. The large exudative losses cause negative TE balances. Intravenous supplementation trials show that early substitution improves recovery (IV doses: Cu 3.5 mg/day, Se 400Ð 500 mcg/day, Zn 40 mg/day), reduces infectious complications (particularly nosocomial pneumonia), normalizes thyroid function, improves wound healing, and shortens hospital length of stay. The mechanisms underlying these improvements are a combination of antioxidant effects (particularly of selenium through restoration of glutathione peroxidase activity) and also immune (Cu, Se, Zn) and anabolic effects (Zn particularly).

High vitamin C requirements after major burns were identiÞed already in the 1940s and have been conÞrmed since then. Very interesting studies by Tanaka et al. in 2000 and Kremer in 2010 demonstrated that high doses of vitamin C administered during the Þrst 24 h after a major injury reduced the capillary leak, probably through antioxidant mechanisms, resulting in signiÞcant reductions in ßuid resuscitation requirements [49, 50].

6.3.5Renal

Acute renal failure (ARF) is a major complication of burn injury. The incidence of ARF in burned patients ranges from 1.2 to 20 % and the incidence of ARF requiring renal replacement therapy (RRT) from 0.7 to 14.6 % [8, 51Ð53]. Although ARF is relatively rare, early diagnosis is important, as the mortality of burn patients with manifest ARF has been reported around 50 % [51]. Applying the RIFLE classiÞcation to burn patients, Coca et al. found that the incidence of acute kidney injury was 27 %, and it carried with it a mortality rate of 73 % in the patients with the most severe acute kidney injury (requiring dialysis).

6 Critical Care of Burn Victims Including Inhalation Injury	83

Burn-related ARF can be divided into early and late ARF, depending on the time of onset with each having different etiologies [53, 54]. Early ARF occurs during the Þrst 5 days postburn, and its main causes are hypovolemia, hypotonia, and myoglobinuria. Prevention focuses on early aggressive ßuid resuscitation and escharotomies/fasciotomies. Late ARF begins more than 5 days postburn and is usually multifactorial (generally caused by sepsis and/or nephrotoxic antibiotics) [54]. Regardless of the cause, there is strong evidence that renal replacement therapy (RRT) should be instituted as early as possible in burn patients with renal dysfunction before the traditional criteria for RRT have been established. Further to the discussion of RRT is the choice in mode of delivery. CRRT (continuous renal replacement therapy) offers several potential advantages in the management of severe acute renal failure in burn patients. It is slow and continuous, consequently allowing for very efÞcient metabolic clearance and ultraÞltration of ßuids while minimizing hemodynamic compromise, thus allowing for ongoing optimization of ßuid and metabolic management. Hemodialysis is surely a viable option if the patient tolerates it. In children, an alternative is peritoneal dialysis with placement of a Tenckhoff catheter.

6.3.6Hormonal (Thyroid, Adrenal, Gonadal)

In the postburn state, pronounced hormonal and metabolic changes take place [3, 6], starting immediately after injury. There is a tremendous increase in stress hormones after major burns, the increase being particularly marked during the Þrst 2Ð3 weeks, but the alterations will persist for months and even years [37]. In response to the afferent stimuli from the burn wound, an intense sympathoadrenal response is elicited. Catecholamine secretion contributes to arterial pressure maintenance and also to a massive increase in cardiac afterload. The concentration of epinephrine and norepinephrine remains elevated for several days after injury and contributes to the integrated neuroendrocrine stress response. Cortisol increases markedly, and the intensity of the response is modulated by optimization of pain control with good analgesia [6, 37]. As with many other hormones, the circadian rhythm also changes. Aldosterone levels increase for several days. ACTH response frequently parallels the cortisol levels and tends to be elevated for a few weeks. The increase in plasma rennin activity and aldosterone persists for several weeks.

A patient suffering from infection/sepsis or persistent hypotension should be considered for possible adrenal insufÞciency. The current guidelines call for a baseline cortisol level, and if that level is low, an ACTH challenge test should be performed to rule out insufÞciency. If an adrenal insufÞciency is present, low dose cortisol should be given.

Glucagon concentration is also increased after burn injury, contributing heavily to the hypermetabolic response, while insulin tends to remain within normal values, being paradoxically normal while plasma glucose concentration is elevated.

The thyroid axis exhibits major abnormalities in the patients with major burns. The most constant Þnding is a Òlow T3 syndromeÓ: TSH is generally normal, with