Citrulline: just a biomarker or a conditionally essential amino acid and a pharmaconutrient in critically ill patients?

Low plasma citrulline levels have been associated with a reduction of functional gut mass in various clinical situations. In critically ill patients, citrulline variations are tricky to interpret because of sepsis, vascular abnormalities, and multiple organ failure. In the previous issue of Critical Care, Ware and colleagues made an important contribution by demonstrating that very low citrulline levels are associated with acute respiratory distress syndrome. This association may be due to a decrease in citrulline availability or citrulline overconsumption for nitric oxide synthesis but also may result from an arginine deficiency syndrome. In any case, the results of this study reinforce the rationale for a study of citrulline supplementation in critically ill patients.