The purpose of the project is to validate the performance of a wearable bioimpedance sensor (Re:Balans®) for monitoring hydration status. The study includes hospitalized patients aged 65 years or older who are admitted to the hospital with suspected dehydration. Data will be collected continuously throughout the hospital stay using one sensor placed on the back, one on the upper arm, and one on the front of the thigh. Sensor measurements will be compared with multiple reference methods for assessing hydration status, including blood tests, body weight and fluid balance charts. Agreement with these reference measures will form the basis for the performance evaluation.

The anticipated benefit of the project is the validation of a novel, user-friendly, and non-invasive tool for hydration monitoring, with the aim of improving patient care, preventing complications, and reducing the need for hospital readmissions.

The study aims to evaluate how well a wearable bioimpedance sensor (Re:Balans®) tracks changes in hydration status in hospitalized patients. The objective is to validate the sensor's ability to provide continuous, non-invasive monitoring of fluid balance, which may improve the management and treatment of patients at risk of dehydration or fluid overload. Such a solution could also help reduce the need for hospital admissions and in-person follow-up visits.

The investigation is designed as a prospective cohort study in which patients are followed throughout their hospital stay, typically lasting 3-7 days. Participants will wear three sensors, placed on the upper back, upper arm, and anterior thigh. The sensors automatically perform measurements every minute during the study period.

At baseline and during daily follow-up visits, several assessments of hydration status will be performed. These include body weight measurements, blood tests, and whole-body bioimpedance measurements. In a subgroup of patients, ultrasound assessment of the inferior vena cava will also be performed. The combined results from these assessments will serve as reference measures to determine whether the patient's hydration status has changed over time.

At hospital discharge, the assessments are repeated, the sensors are removed, and participants complete a short questionnaire regarding their experience with the device. In addition, fluid balance data (fluid intake and output) will be collected retrospectively from medical records to allow comparison between the sensor measurements and routine clinical monitoring methods. Relevant clinical information obtained as part of standard patient care will also be recorded if considered important for the assessment of hydration status.

Inclusion Criteria:

• Age ≥ 65 years
• Planned fluid management due to presumed dehydration
• Expected duration of hospital stay ≥ 3 days

Exclusion Criteria:

• Known allergies or skin sensitivities to electrode hydrogel and/or acrylic adhesives
• Implantable pulse generators such as pacemakers and defibrillators, and/or use of other electrical medical equipment for which an interaction effect with the investigational device cannot be ruled out.
• Scheduled MRI
• Scheduled diathermy
• Breached skin at device application areas (upper back, anterior thigh and upper arm)
• Unconsciousness
• Critically ill (presence of acute organ dysfunction requiring intensive monitoring and management)
• Any medical or psychiatric condition, which in the opinion of the investigator precludes participation
• Incapable of giving informed consent

The study population consists of hospitalized patients aged 65 years or older who are admitted with suspected dehydration and are planned to receive fluid therapy. Participants may have varying underlying medical conditions and comorbidities that could influence hydration status during their hospital stay.