BACKGROUND: Nutrition guidelines recommendations differ on the use of parenteral nutrition (PN), and existing clinical trial data are inconclusive. Our recent observational data show that amounts of energy/protein received early in the intensive care unit (ICU) affect patient mortality, particularly for inadequate nutrition intake in patients with body mass indices (BMIs) of <25 or >35. Thus, we hypothesized increased nutrition delivery via supplemental PN (SPN)?+?enteral nutrition (EN) to underweight and obese ICU patients would improve 60-day survival and quality of life (QoL) versus usual care (EN alone).METHODS: In this multicenter, randomized, controlled pilot trial completed in 11 centers across four countries, adult ICU patients with acute respiratory failure expected to require mechanical ventilation for >72 hours and with a BMI of <25 or =35 were randomized to receive EN alone or SPN?+?EN to reach 100% of their prescribed nutrition goal for 7 days after randomization. The primary aim of this pilot trial was to achieve a 30% improvement in nutrition delivery.RESULTS: In total, 125 patients were enrolled. Over the first 7 post-randomization ICU days, patients in the SPN?+?EN arm had a 26% increase in delivered calories and protein, whereas patients in the EN-alone arm had a 22% increase (both p?0.001). Surgical ICU patients received poorer EN nutrition delivery and had a significantly greater increase in calorie and protein delivery when receiving SPN versus medical ICU patients. SPN proved feasible to deliver with our prescribed protocol. In this pilot trial, no significant outcome differences were observed between groups, including no difference in infection risk. Potential, although statistically insignificant, trends of reduced hospital mortality and improved discharge functional outcomes and QoL outcomes in the SPN?+?EN group versus the EN-alone group were observed.CONCLUSIONS: Provision of SPN?+?EN significantly increased calorie/protein delivery over the first week of ICU residence versus EN alone. This was achieved with no increased infection risk. Given feasibility and consistent encouraging trends in hospital mortality, QoL, and functional endpoints, a full-scale trial of SPN powered to assess these clinical outcome endpoints in high-nutritional-risk ICU patients is indicated-potentially focusing on the more poorly EN-fed surgical ICU setting.TRIAL REGISTRATION: NCT01206166.