Objective To observe different effects of cyclic and continuous nutrition infusion on serum nutritional indicators, peripheral white blood cell counts (WBC), arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2) and acute physiology and chronic health evaluation Ⅲ (APACHE Ⅲ ) score in patients with mechanical ventilated respiratory failure (MVRF).Methods A cross-over and self-controlled trial was conducted in 48 patients with MVRF treated in a medical intensive care unit during December 2006 to June 2009, and continuous nutrition (group A) and cyclic nutrition (group B) were infused respectively for patients of the two groups.Serum levels of albumin (ALB), pre-albumin (PA), transferrin (TR), PaO2, PaCO2, WBC and APACHE Ⅲ score were measured for the patients with 24-hour continuous nutrition (group A) and 16-hour cyclic nutrition (group B)infusion.Effects of the two nutritional therapies were compared.Results After nutrition infusion, serum levels of ALB, PA and TR were (34±3)g/L, (196±28)mg/L and (2.1±0.3 ) g/L in group A, and (35 ±4) g/L, (198 ±25) mg/L and (2.0 ±0.4) g/L in group B, respectively; and PaO2 and PaCO2levels were (92 ± 12) mm Hg ( 1 mm Hg =0.133 kPa) and (42 ± 10) mm Hg in group A, and (91 ±9)mm Hg and (42 ± 10) mm Hg in group B, respectively.WBC and APACHE Ⅲ score were ( 11.8 ± 1.7) ×109/L and 38 ±7 in group A, and ( 12.6 ± 1.2) × 109/L and 40 ±6 in group B, respectively.Significant difference in serum levels of PA and TR was found between the two groups (PPA =0.019 and PTR =0.013),while there was no significant difference in other indictors between the two groups.Conclusions 24-hour continuous nutrition infusion for patients with MVRF can obviously improve their serum levels of PA and TR,but has no effect on serum level of ALB, PaO2, WBC and APACHE Ⅲ score in critical ill patients, as compared to those with 16-hour cyclic nutrition infusion.