**1. Introduction**

Acute pancreatitis (AP) is defined by an inflammation of the pancreas, where several organs and other systems are involved with a potential immune response in a severe course [1] with a consecutive augmented release of hydrolytic enzymes, cytokines, and toxins, which may result in failure of several systems. Hypermetabolism is observed with a negative nitrogen balance and also augmented metabolism [2–6]. Global incidence of AP ranges from 13 to 45 cases per 100,000 population with a global estimate of 33.74 cases per 100,000 population, causing an uneven burden across the globe. Gallstones (40%–70%) and alcohol (25%–35%) are two of the most common etiologies [7–10]. AP occurs frequently with a mild clinical course. However, when necrotizing pancreatitis is observed, mortality rises up to 15% of cases [11]. When infection of pancreatic necrosis is present, organ failure or both, mortality rises to 30% [12]. Also, severe pancreatitis can cause sustained hyperglycemia, producing diabetes [13, 14]. Interventions (i.e., surgical, endoscopic, and radiological) are frequently used in some patients with AP [15], requiring nutritional support [6].

Clinical therapy in AP differs according to the severity of the disease. Therefore, adequate identification of patients with mild, moderate, or severe AP (SAP), who need nutritional support, is of great importance. Atlanta classification authors defined and stratified the severity of AP [16]: Mild AP is described with absence of organ failure or local complications; moderate-severe AP with transient organ failure and/or local complications; and SAP when persistent organ failure is observed with more than 48 hours, which usually have an ominous prognosis [16]. The first step of the clinical approach of AP consists of close monitoring of vital signs, general support with vigorous fluid resuscitation, pain relief, nutrition, correction of metabolic disorders, identification of complications, and prevention of recurrence [17]. Most of the patients have a mild course of the disease with good prognosis in most cases, but near 15% of cases develop complications (local and systemic). Local complications are mainly pancreatic pseudocyst, acute necrotic collection, acute peripancreatic fluid collection, and walled-off necrosis; systemic complications are defined as multi-organ failure or as an exacerbation of a preexisting condition [18]. A mean of 15–20% of AP patients will course a severe form of the disease, but mortality is present in only 2–3% of patients because of complications [19, 20].
