RESUMO
OBJECTIVES: Concise definitive review of the physiology of IV fluid (IVF) use in critically ill patients. DATA SOURCES: Available literature on PubMed and MEDLINE databases. STUDY SELECTION: Basic physiology studies, observational studies, clinical trials, and reviews addressing the physiology of IVF and their use in the critically ill were included. DATA EXTRACTION: None. DATA SYNTHESIS: We combine clinical and physiologic studies to form a framework for understanding rational and science-based use of fluids and electrolytes. CONCLUSIONS: IVF administration is among the most common interventions for critically ill patients. IVF can be classified as crystalloids or colloids, and most crystalloids are sodium salts. They are frequently used to improve hemodynamics during shock states. Many recent clinical trials have sought to understand which kind of IVF might lead to better patient outcomes, especially in sepsis. Rational use of IVF rests on understanding the physiology of the shock state and what to expect IVF will act in those settings. Many questions remain unanswered, and future research should include a physiologic understanding of IVF in study design.