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Sepsis and septic shock are associated with both a relative and an absolute intravas-cular volume deficit []. The absolute volume deficit occurs with fever, and includes perspiration and increased insensible loss, vomiting, diarrhea, and volume loss by drains or sequestration. The relative volume deficit is due to vasodilatation, venous pooling, and alterations in the endothelial barrier. The functional disturbances induced by sepsis are reflected by increased blood lactate concentrations, oliguria, coagulation abnormalities, and altered mental state.

Adequate volume restoration in the hypovolemic patient appears to be essential to stave non-compensatory, irreversible shock and subsequently to avoid development of multiple organ dysfunction syndrome. Vigorous optimization of the circulation is a prerequisite in the management of such patients. This maneuver is aimed at guaranteeing stable macro- and micro-hemodynamics, while avoiding excessive fluid accumulation in the interstitial tissue. The choice of fluid for this purpose engenders considerable controversy and there is still a dispute over the beneficial and adverse effects of each fluid type.

Acute renal failure is a common complication of critical illness [, ]. Of all intensive care unit (ICU) admissions, 15–20% develop acute renal failure and 4–6% require some form of renal replacement therapy []. Causes of acute renal failure include direct renal toxicity due to medication or radiocontrast agents, hypovolemic hypotension, and shock. Acute renal failure frequently accompanies sepsis — its incidence varies from 20% in patients with moderate sepsis to >50% in patients with septic shock [, ]. Acute renal failure carries a high mortality rate, in particular in patients with sepsis — in patients with acute renal failure alone mortality is 45 %; in patients with acute renal failure and sepsis, mortality is reported to be as high as 70% []. The most frequently used form of renal replacement therapy is continuous venovenous hemofiltration (CVVH), an expensive and laborious treatment. CVVH, however, permits efficient control of fluid balance and azotemia in ICU patients with acute renal failure [].

Infection is a common problem in the intensive care unit (ICU). Severe sepsis and septic shock are conditions at the end of the spectrum of human response to infection. Acute renal failure is increasingly seen as part of the multiple organ dysfunction syndrome, which is the most frequent cause of death in patients admitted to the ICU. However, severe sepsis and septic shock are the primary causes of the multiple organ dysfunction syndrome. In the past decades, continuous renal replacement therapy (CRRT) has been widely employed as an extracorporeal blood purification method in the management of septic patients with or without acute renal failure in the ICU, because it offers several advantages over conventional intermitant hemodialysis and peritoneal dialysis [].

Interest in intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) as causes of significant morbidity and mortality among the critically ill has increased exponentially over the past decade [, ]. Given the prevalence of elevated intra-abdominal pressure (IAP) as well as earlier detection and appropriate therapeutic management of IAH and ACS, significant decreases in patient morbidity and mortality have been achieved in recent years.

The intestine is characterized by a large mucosal surface, a complex vascular system, a variable anatomy, a dense neuronal network, a complex mesenteric lymphatic system, and an important gut-associated lymphoid tissue (GALT). Defining intestinal failure starts with the recognition of gut function (Table 1). Intestinal failure may be chronic or acute, may be intrinsic (direct insult to the gut) or extrinsic, with hemodynamic, septic, or pharmacological causes (as in the case of the opioid bowel syndrome). Intestinal failure involves motility disorders, alteration of the barrier function (increased permeability), and decreased absorption capacity. This chapter will focus on conditions observed in the critically ill patient.

One of the most important goals of therapy in critically ill patients is restoring and maintaining adequate perfusion and oxygenation of vital organs in the recovery from a variety of disruptive processes, such as circulatory failure in myocardial infarction, sepsis, and trauma. The gastrointestinal tract is generally regarded as significant in the development of shock and multiple organ failure (MOF) as a consequence of loss of its barrier function against luminal bacteria and bacterial products, such as endotoxin in hypoxic conditions. Insufficient blood flow to the splanchnic organs is believed to be the essential mechanism []. Translocation of bacteria and endotoxin to the lymphatic and portal system is a first step towards distant organ damage. The gut and liver macrophages (Kupffer cells) are important as a first barrier against spread of translocated bacteria and endotoxins to the bloodstream.

After severe injury, such as thermal injury, a variable degree of liver injury is present and it is usually related to the severity of the thermal injury. Fatty changes, a very common finding, are reversible and their significance depends on the cause and severity of accumulation []. However, autopsies of burned children who died have shown that fatty liver infiltration was associated with increased bacterial translocation, liver failure, and endotoxemia, thus delineating the crucial role of the liver during the post-burn response []–[]. In a recent study in 102 children, 41 females and 61 males with a total body burn size of 58 ±2% and third degree burns in 45 ± 2 %, we found that liver size and weight significantly increased during the first week post-burn (+85 ±5%), peaked at 2 weeks post-burn (+126 ± 19%), and was increased by +89 ± 10% at discharge. At 6, 9, and 12 months the liver weight was increased by 40 – 50 % compared to predicted liver weight. In addition, liver protein synthesis was impaired for a 6-month period with a shift from constitutive hepatic proteins to acute phase proteins []. Liver enzymes were significantly elevated over the first 3 weeks post-burn, normalizing over time. These findings indicate that the hepatic acute phase response perseveres for a longer time period than previously thought [, ].

The adult liver weighs around 1500 g and lies mainly in the right upper quadrant of the abdomen, immediately beneath the diaphragm []. The liver is the most commonly injured intra-abdominal organ and is found to be damaged in 30% of patients undergoing laparotomy for penetrating injuries and in 15–20% of laparotomies for blunt injuries [].

Acute liver failure is a syndrome manifest by the rapid cessation of hepatic function in previously normal individuals. The rate of decline in function dictates the manner in which the syndrome manifests and influences the outcome. The etiology of the insult to the liver is the main influence on the rate of progression and the likelihood of spontaneous recovery [].