Fundamental determinants of protein requirements in the ICU

Currently, feeding the ICU patient is highly discussed. Energy feeding has been the topic of randomized studies, but protein feeding has not. Study results are contradictory on early feeding; however, little is known about early protein requirement. What is this protein requirement based on, therefore what are the fundamental determinants?

Recent studies have addressed the importance of protein feeding and/or muscle (protein) wasting in critically ill patients. Targeted feeding has been shown to improve protein balance in one study, and infection rate in one study. Low muscle mass that is already present during ICU admission has been shown to be related to higher mortality, in two studies. Four studies have related muscle wasting to (protein) feeding strategies with very diverse results: Two small studies have reported no advantage [n = 15, computed tomography] or negative impact (n = 62, ultrasound, 50% sepsis patients) of protein on muscle wasting. Two studies, one small (n = 33, computed tomography) and one very large (n = 1372, Subjective Global Assessment), have reported a positive impact of (early) feeding on muscle wasting.

Fundamental to adequate protein feeding in critically ill patients, at least 1.2 g protein/kg per day, is targeted energy feeding using indirect calorimetry. The level of protein requirement is related to fat free mass or muscle mass, which makes sex and BMI also relevant. Targeted early protein feeding is found to improve short-term outcome, reduction of muscle wasting and hospital mortality. Long-term outcome of protein feeding has not been studied. However, targeted protein feeding may be harmful in sepsis patients. Up to now, we lack biomarkers that provide caregivers with an instrument to increase protein feeding up to the individual protein requirement of the critically ill patient.