Identification of fluid overload in critically ill children: fluid status, the missing vital sign

Fluid overload, defined as a state of pathologic fluid excess or positive fluid balance, is increasingly recognized as a deleterious state in critically ill infants and children. Fluid overload is common, and mounting evidence shows that it is associated with increased mortality, organ dysfunction, and prolonged need for mechanical ventilation. Despite studies showing adverse outcomes associated with fluid overload, awareness of fluid overload remains limited, especially in small children and infants. Fluid overload as a biomarker and vital sign in the clinical setting has also not been routinely adopted despite its link with morbidity and mortality, and it remains underrecognized by providers. In this review, we first discuss the definition of fluid balance and fluid overload, then briefly review existing data on associations of fluid overload with outcomes in critically ill infants and children. We then consider existing and new data on recognition of fluid overload in critically ill children and infants before closing with the need for better awareness of fluid overload, and a discussion of future research directions and gaps in the field.