[Preoperative fasting of 8 hours or 2 hours: what does evidence reveal?].

Insulin resistance is a transitory phenomenon of the metabolic response to trauma. In uncomplicated operations it lasts for 2-4 weeks postoperatively, and is directly related to the magnitude of the injury. The fasting status caused by conventional fasting protocols aggravates this resistance and may induce hyperglycemia. Conventional preoperative fasting time may aggravate this resistance and increment the elevation of glycemia especially because it is frequently longer than the expected 6-8h and may reach 10-16 hs. Additionally, overnight fasting may cause variable degrees of dehydration depending on the extension of the fasting period. Recently, various societies of anesthesia and nutrition have changed their guidelines to propose a reduction of preoperative fasting to 2h with clear fluids containing carbohydrates. These new protocols (ACERTO, ERAS) are based on the safety of this routine as consistently demonstrated by various randomized trials and a meta-analysis.