Hyperosmolar dehydration (HD) is defined by low total body water and elevated serum osmolality (above 300 mOsm/kg) and reflects a deficit in hypo-osmolar fluid most often as free water [1]. It differs from hypovolemia, which is a condition with a reduction in extracellular fluid volume (water and salt) [2,3]; HD is common in patients admitted to the hospital. Depending on the method of assessment, the reported prevalence of HD is 25%‐43% in admitted older adults [4,5], 58% in patients admitted with sepsis [6], and 36% in patients admitted with stroke [7]. Regardless of the patient group, HD is associated with adverse outcomes. This includes increased incidence of delirium, functional decline, prolonged hospital stays, higher readmission rates, and increased mortality [6,8,9].

Diagnosis of HD is challenging. Clinical signs such as reduced skin turgor and postural hypotension have poor sensitivity and specificity [10]. Direct measurement of serum osmolality is accurate but is often not routinely performed due to cost [11]. Both increased BUN (blood urea nitrogen) and the BUN/creatinine ratio are used as proxies for HD [11]. Increased sodium can also be used as a proxy measure, as it is a major contributor to serum osmolality; however, HD is independently associated with increased mortality even after adjusting for sodium [12,13], providing an indication that elevated sodium is only part of the problem. A validated osmolarity equation based on routine biochemistry (sodium, potassium, glucose, urea) offers a feasible screening alternative [14,15].

Current clinical guidelines often do not distinguish clearly between subtypes of low fluid status, such as HD and hypovolemia, resulting in uncertainty in treatment decisions [16,17]. Theoretically, HD represents a free water deficit and should be treated with oral water or hypotonic parenteral fluids like 5% glucose. Conversely, hypovolemia is generally managed with isotonic fluids [2]. Guidelines recommending treatment for HD lack solid references to support their recommendation [11,18,19]. The lack of clear differentiation and clinical evidence behind treatment recommendations in guidelines makes it challenging to implement targeted fluid therapy strategies for the treatment of HD [11,18-20].

Despite an increase in studies on HD [21], our preliminary search indicates a heterogeneous evidence base on the treatment of HD. Inconsistent definitions, diagnostic criteria, and outcome measures limit meaningful comparisons across studies and hinder the development of evidence-based treatment guidelines [11,18,22-24]. A scoping review is warranted to map the existing evidence and identify gaps in current knowledge.

The objective is to identify and summarize existing studies on the treatment of HD in adults and to map the current evidence, highlight gaps in the literature, and guide future research.

Which hydration treatments have been evaluated for adults with biochemically confirmed HD in a hospital setting?

The review question is structured using the PCC (Population, Concept, Context) framework as per the Joanna Briggs Institute (JBI) manual for scoping reviews. Table 1 presents the PCC elements and the corresponding sub-questions that will guide data extraction and synthesis.

We will include studies of adult populations admitted to the hospital with and treated for HD, regardless of admission diagnosis; HD must be biochemically confirmed.

Eligible concepts comprise treatment for HD, including oral, subcutaneous, or intravenous fluid therapy. Reports focusing solely on hypovolemia without laboratory evidence of hyperosmolarity will be excluded. Reports on patients without suspected reduced total body water will also be excluded (eg, iatrogenic hypernatremia).

Only studies conducted in hospital wards (any specialty) and emergency departments will be considered, irrespective of country or language.

We will include interventional, observational, qualitative studies, reviews, and case reports. Texts, opinion papers, and sources without direct patient data will be excluded.

Studies will be excluded if they meet any of the following criteria:

The following databases will be searched: MEDLINE (PubMed), Embase (Ovid), Scopus, and the Cochrane Central Register of Controlled Trials. Additional searches will include gray literature sources (eg, trial registries, dissertations, conference abstracts). Reference lists of included articles and relevant reviews will also be screened.

The search followed the three-step JBI approach. An initial exploration search in MEDLINE and Embase was conducted to identify keywords and index terms related to hyperosmolar dehydration and fluid therapy. These terms were combined into a comprehensive strategy and adapted for all databases. No restrictions on publication date or language were applied, and translation support was used when required. All search dates, strategies, and results have been documented. In addition, backward and forward snowballing was undertaken to identify further relevant studies beyond those retrieved in the initial database searches. The search strategy was developed in collaboration with a health sciences librarian, and the complete PubMed search string is presented in Table 2.

All retrieved references will be imported into Covidence (Covidence systematic review software, Veritas Health Innovation, Melbourne, Australia, accessed 2026), where duplicates will be removed. Prior to full screening, a pilot test on a small sample of studies will be conducted to ensure that both reviewers apply the eligibility criteria consistently. Following this, two reviewers will independently screen all titles and abstracts. Full texts of potentially eligible studies will then be assessed in duplicate, with reasons for exclusion documented. Disagreements will be resolved through discussion or, if necessary, by a third reviewer. The entire selection process will be illustrated in a PRISMA-ScR flow diagram.

Data will be extracted independently by two reviewers using a predefined charting form. Extracted variables will follow the PCC framework (Population, Concept, Context) and include study characteristics, participant demographics, diagnostic criteria, intervention details (type, route, dosage, setting), comparators (if any), outcomes (including biochemical, clinical, and health care utilization outcomes), and key findings. The predefined data extraction form is provided in Table 3.

Variations in biochemical definitions and cutoff values of HD across studies will be extracted and reported as part of the evidence mapping.

As suggested by recent work [27], large language models such as ChatGPT-4o may also be explored as a supplementary tool to support the data extraction process. ChatGPT will only be used in addition to the two reviewers as a kind of third reviewer. Use and prompts will be at the discretion of the individual reviewer. All extracted data will be independently verified by human reviewers, and all final decisions will be made by the research team.

Findings will be summarized descriptively, focusing on the key outcomes identified in the PCC framework. Quantitative data, such as participant numbers, intervention types, and clinical outcomes, will be presented in tables to allow comparison across studies. Qualitative information, including study design and narrative outcomes, will be organized thematically.

The extracted data will be grouped into the following categories:

These categories will be mapped to identify patterns and evidence gaps. Joanna Briggs Institute (JBI) scoping review methodology [25] and guidance from PRISMA-ScR [26] will be used to ensure a transparent synthesis. Narrative synthesis will be combined with visual presentation (charts, tables) where appropriate.

This scoping review aims to provide a comprehensive mapping of available evidence on hydration treatment in adults with HD in hospital settings. Based on preliminary searches, we expect the literature to be heterogeneous in terms of both the definition of HD and treatment approaches to the condition. Moreover, we anticipated that the evidence base was limited, especially regarding studies directly comparing different hydration strategies and their clinical outcomes. Thus, the review will highlight gaps in the literature that hinder standardization of clinical practice.

While dehydration in older adults has been widely studied and found to be associated with adverse clinical outcomes such as mortality, functional decline, and hospitalization [8,22-24,28], significantly fewer studies have focused specifically on HD as a separate clinical condition [18]. In clinical practice, and in current guidelines, HD is not consistently differentiated from other subtypes of fluid deficits, such as hypovolemia. This is especially evident in relation to treatment recommendations for HD [16,20]. This lack of clarity leads to variation in clinical practice and uncertainty about the choice of fluid. Mapping the existing evidence is therefore timely and relevant.

This review has several important strengths. It will be conducted according to a predefined protocol and in accordance with the PRISMA-ScR guidelines, which support a systematic and transparent methodological framework. In addition, all relevant published literature on the topic will be considered, allowing for a comprehensive narrative synthesis of the available evidence. Nevertheless, some limitations must be acknowledged. Specifically, no formal risk-of-bias assessment will be performed for the included studies. Moreover, because the review is limited to biochemically verified HD in hospitalized adults, the findings may have limited applicability to patients in other clinical settings or children.

By mapping available evidence and gaps in current knowledge, this review may help guide future interventional research, particularly in relation to standardized definitions, outcome measures, and treatment guidelines for HD.

The results of the review are expected to be disseminated through a peer-reviewed publication and in relevant clinical and academic forums. The aim is to ensure that the findings are accessible to both researchers and clinicians and may contribute to ongoing discussions about hydration management in hospitalized adults.

This scoping review will map the available evidence on treatment approaches for HD in adult hospital and emergency patients. The findings will identify which therapeutic strategies have been studied, highlight inconsistencies in definitions and reporting, and reveal evidence gaps that can guide future research.