Abstract
Intravenous fluid therapy is the most common intervention received by acutely ill patients. Historically, saline (0.9% sodium chloride) has been the most frequently administered intravenous fluid, especially in North America. Balanced crystalloid solutions (e.g., lactated Ringer's, Plasma-Lyte) are an increasingly used alternative to saline. Balanced crystalloids have a sodium, potassium, and chloride content closer to that of extracellular fluid and, when given intravenously, have fewer adverse effects on acid-base balance. Preclinical research has demonstrated that saline may cause hyperchloremic metabolic acidosis, inflammation, hypotension, acute kidney injury, and death. Studies of patients and healthy human volunteers suggest that even relatively small volumes of saline may exert physiological effects. Randomized trials in the operating room have demonstrated that using balanced crystalloids rather than saline prevents the development of hyperchloremic metabolic acidosis and may reduce the need for vasopressors. Observational studies among critically ill adults have associated receipt of balanced crystalloids with lower rates of complications, including acute kidney injury and death. Most recently, large randomized trials among critically ill adults have examined whether balanced crystalloids result in less death or severe renal dysfunction than saline. Although some of these trials are still ongoing, a growing body of evidence raises fundamental concerns regarding saline as the primary intravenous crystalloid for critically ill adults and highlights fundamental unanswered questions for future research about fluid therapy in critical illness.