OBJECTIVE: The National Institute for Health and Care Excellence\'s (NICE) Guideline for Maintenance Fluid Therapy in Adults in Hospital is widely used, but the recommendations have not been evaluated properly. In this study, we investigated whether the recommendation of providing 25-30 mL/kg/day of fluid and 1 mmol/kg each of sodium and potassium is sufficient for human needs.
METHODS: First, we calculated the distribution of fluid between the extracellular fluid volume (ECV) and intracellular fluid volume (ICV) during a cross-over infusion experiment where 12 volunteers received 25 mL/kg/day of either a high-sodium (154 mmol/L) or low-sodium (54 mmol/L) solution over 48 h. Second, urine samples from 719 volunteers and clinical patients were used to quantify their renal water conservation and excretion of sodium and potassium. Third, retrospective analysis of a diet study was used to extrapolate how large the fluid intake and the electrolyte excretion likely had been in the 719 volunteers and hospital patients who delivered urine.
RESULTS: The high-sodium fluid maintained the ECV but the ICV had decreased by 1.3 L after 48 h. The low-sodium fluid resulted in a volume deficit of 1.7 L that equally affected the ECV and the ICV. Regression equations based on the diet study suggested that the daily intake of water in the 719 subjects averaged 2.6 L and that 2 mmol/kg of sodium and 1 mmol/kg of potassium was excreted.
CONCLUSIONS: The NICE guideline recommends too little water and sodium for a human to adequately maintain the ECV and ICV.
BACKGROUND: EudraCT 2016-001846-24 and ISRCTN 12215472.

Background: Dehydration appears prevalent, costly and associated with adverse outcomes. We sought to generate consensus on such key issues and elucidate need for further scientific enquiry. Materials and methods: A modified Delphi process combined expert opinion and evidence appraisal. Twelve relevant experts addressed dehydration\'s definition, objective markers and impact on physiology and outcome. Results: Fifteen consensus statements and seven research recommendations were generated. Key findings, evidenced in detail, were that there is no universally accepted definition for dehydration; hydration assessment is complex and requires combining physiological and laboratory variables; \"dehydration\" and \"hypovolaemia\" are incorrectly used interchangeably; abnormal hydration status includes relative and/or absolute abnormalities in body water and serum/plasma osmolality (pOsm); raised pOsm usually indicates dehydration; direct measurement of pOsm is the gold standard for determining dehydration; pOsm >300 and ≤280 mOsm/kg classifies a person as hyper or hypo-osmolar; outside extremes, signs of adult dehydration are subtle and unreliable; dehydration is common in hospitals and care homes and associated with poorer outcomes. Discussion: Dehydration poses risk to public health. Dehydration is under-recognized and poorly managed in hospital and community-based care. Further research is required to improve assessment and management of dehydration and the authors have made recommendations to focus academic endeavours. Key messages Dehydration assessment is a major clinical challenge due to a complex, varying pathophysiology, non-specific clinical presentations and the lack of international consensus on definition and diagnosis. Plasma osmolality represents a valuable, objective surrogate marker of hypertonic dehydration which is underutilized in clinical practice. Dehydration is prevalent within the healthcare setting and in the community, and appears associated with increased morbidity and mortality.