There has been many evidence that deficiency in energy and protein take-in are associated with poor outcome in critical patients. To reach an adequate amount of energy and protein is critical in patients with respiratory failure and with mechanical ventilation, as it prevents muscle dystrophy and thus prevents ICU acquired weakness, leading to a better outcome in the end. Enteral Nutrition is preferred as it prevents gut dysfunction in respiratory failure patients, and may prevent further infection. But there are many challenge in implement a good enteral nutrition therapy, and energy or protein deficiency is common in patient with respiratory failure. There have been many protocols aiming at reaching enough enteral nutrition for ICU patients, most of which are based on a background of western and developed countries. The investigators developped a enteral nutrition protocol based on an unique cultural background of eastern developing country, trying to help the ICU patients reaching nutrition target, so that the patients may have better outcome.