Nutrition in the critically ill patient
Authors:   , Koekkoek Wilhelmina Aria Christina 
Published: March 2023

Critically ill patients may lose one kilogram muscle mass per day in the first ten days of intensive care unit (ICU) admission. This profound loss of muscle mass is likely to contribute to the long term impairment in physical function observed in many ICU survivors. Optimal nutritional support during and after ICU admission is important as it has been associated with improving clinical outcomes. Ideally, nutritional support reduces the loss of muscle mass in the early phases of ICU admission and later on encourages muscle anabolism and recovery leading to better functional outcomes.
This thesis consists of four parts focused on different aspects of optimizing nutritional support in critically ill patients. In part one we investigated how to estimate the optimal caloric target for patients during ICU admission. We compared different methods to estimate the energy expenditure and tried to identify factors that influence energy expenditure in critically ill patients.
The second part focuses on the optimal macronutrient composition and nutritional dose in the first week of ICU admission. In the PROTINVENT study we observed a time-dependent effect of protein intake in critically ill patients with the lowest 6-month mortality found when increasing protein intake from <0.8g/kg/day on day 1-2 to 0.8-1.2g/kg/day on day 3-5 and >1.2g/kg/day after day 5. In another study, we focused on the incidence of refeeding hypophosphatemia and the association of caloric intake with clinical outcomes. In 36,8% of patients refeeding hypophosphatemia was observed. Within this patient group a reduced 6-month mortality risk for low caloric intake (<50% of target) was seen compared with normal intake, adjusted Hazard Ratio 0.39, (95% CI 0.16–0.95, p = 0.037). In patients without refeeding syndrome no significant difference in 6-month mortality risk was observed between low or normal caloric intake.
Macro- and micronutrient supplements are the focus of interest of the third part of this thesis. We present an extensive review of antioxidant mechanisms, antioxidant status and effects of supplementation of antioxidant vitamins and trace-elements in critically ill patients. In addition, we performed a prospective cohort study on the blood micronutrient concentrations in the first week of ICU admission in the absence of micronutrient supplementation. Most mean micronutrient levels were significantly lower in the ICU patients compared to the healthy controls (selenium, β-carotene, vitamin C and E). Furthermore, micronutrient levels did not normalize during the first week even though progressive enteral tube feeding, containing vitamins and trace elements, was administered. Finally, we performed a systematic review and meta-analysis of 24 trials studying the effects of enteral fish oil supplementation on clinical outcomes in critically ill patients. Enteral fish oil supplementation cannot be recommended for critically ill patients as strong scientific evidence for improved clinical benefits could not be found.
In part four new developments and insights in critical care nutrition between 2015-2018 are described. Finally, the main findings of this thesis are discussed, including a practical approach to provide proteins and calories during the phases of critical illness and convalescence, and specific suggestions for further research.