Other than the administration of oxygen, crystalloid resuscitation fluids are the most common intervention administered to the majority of hospitalized patients. These fluids may be used as a life saving measure to re-establish hemodynamic stability, for rehydration, and to replace losses and maintain intravascular volume in the surgical setting. In the province of Ontario alone, approximately 1 million patients per year will receive one or both of these resuscitation fluids during their hospital admission. The two most common usual care resuscitation crystalloid fluids are Normal Saline and Ringer's Lactate and until recently there was no evidence to suggest that one crystalloid fluid was clinically superior to the other. However, the safety of Normal Saline is now being questioned due to its high chloride content and its association with the development of hyperchloremic metabolic acidosis. Studies in healthy volunteers and observational studies in the critically ill and surgical patient populations have associated saline with an increased risk of acute renal injury and requirement for dialysis, post-operative infections, death and increased resource and blood transfusion use. The evidence base is currently weak given that the majority of studies are observational and suffer from methodological weaknesses including confounding by indication, selection bias, and inability to disentangle the effects of a specific fluid due to interaction of co-interventions administered. As such, several authors and editorials have called for adequately powered randomized controlled trials with clinically relevant outcomes to determine if Ringer's Lactate is indeed superior to Normal Saline for resuscitation.

Given their widespread use, small differences in clinical outcomes between crystalloid resuscitation fluids are highly relevant. Furthermore, small absolute differences in important clinical outcomes translate into significant savings to hospitals and the health care system. To illustrate, if death and hospital re-admissions were each reduced by an absolute 0.5%, this would translate to approximately 2500 lives saved and savings of 10 million dollars to the Ontario health care system. Hence, in collaboration with the Canadian Critical Care Trials Group, the Crystalloid FLUID Choices for Hospitalized Patients (FLUID) trial will examine whether Ringer's Lactate as compared to Normal Saline reduces clinically important outcomes such as death, and hospital re-admissions - outcomes that are particularly relevant to hospitals and the health care system. This proposal is a large pragmatic cluster cross-over comparative effectiveness trial that will be conducted in both academic and community centres in Ontario. It will involve waivers of consent and a novel design making use of provincially available health administrative data through the Institute of Clinical Evaluative Sciences (ICES) to facilitate all data collected in the trial. The trial will answer this fundamental fluid resuscitation question with much less cost in comparison to an individual patient randomized controlled trial. It will help build expertise and capacity for future trials of similar design in the province of Ontario and throughout Canada. However, prior to embarking on a large-scale trial, it is imperative to conduct a pilot trial to determine feasibility and optimize the trial design.