This study will evaluate the risk of adverse effects of intravenous hydration compared to subcutaneous hydration. Half of the patients will receive hydration by the subcutaneous route the other half by the intravenous route. In the subsequent 24 hours period the patients will be monitored for any sign of adverse effects.

Adequate hydration is essential to humans, and is tightly regulated in the healthy adult by in- and output (i.e. thirst and urine production). This regulation is often hampered in the geriatric patient due to a decreased sensation of thirst and impaired kidney function. The risk of dehydration increases rapidly in the acutely ill geriatric patient with the growing fluid demand of fever and reduced ability to self-hydrate due to fatigue. Dehydration will often aggravate an acute illness creating a vicious circle. External rehydration is essential to stop or even prevent this downward spiral. Adequate hydration can be maintained or achieved by two different routes: oral intake or parenteral infusion. When oral hydration is insufficient, intravenous (IV) fluid infusion is the commonly used route. However, subcutaneous (SC) infusion of fluid, also known as hypodermoclysis, is an alternative route.

Several studies have compared SC hydration to IV hydration with the main outcome being laboratory test of hydration or subjective assessment scores. They all found similar effects on laboratory markers of hydration, which align with the theory of mass conservation. They also found a similar incidence of side effects between IV and SC hydration as secondary outcomes. The main drawback of these studies is methodological shortcomings. The lack of blinding introduces a large risk of bias on subjective outcome such as assessment scores and grading of side effects. Furthermore, the largest of the studies had a third of their patients switch groups diluting the result. A recent Cochrane review on achieving parenteral hydration found that the quality of included trials was low and future trials should prospectively register, have secure allocation concealment, adequate sample sizes and should be reported according to established standard.

This study will examine if subcutaneous (SC) hydration is a safe alternative to intravenous (IV) hydration in the geriatric patient in the Emergency Department, Acute Assessment Unit or Orthopedic Ward of Aalborg University Hospital. This will be achived by preforming an assessor-blinded, non-inferior, randomized controlled trial.

Relevant participants (see Eligibility Criteria) arriving at Aalborg University Hospital will be enrolled after informed consent. Baseline measurements will be obtained, and the participants will be randomized (1:1) to either intravenous or subcutaneous hydration. A sham setup will be use so both an intravenous access and a subcutaneous access will be visible on the patient, but only one of them will be active. For the next 24 hours the participants will regularly be evaluated by a nurse blinded to infusion for the presence of adverse effects.

Inclusion Criteria:

1. Medical patients admitted to Acute Assessment Unit (AAU). (All internal medicine patients are admitted here first, except highly specialized patients (e.g. ketoacidosis or severe cardiology conditions).
2. Orthopedic hip fracture patients admitted to the orthopedic ward.
3. Patients admitted to short term care.
4. Prescription of 0.5-2 liters of parenteral fluid over the next 24 hours.

Exclusion Criteria:

1. Red triage tag (severe ill patients)
2. Prescription of IV antibiotics or other treatment administrate intravenous
3. Severe dehydration (fluid requirements over 2 liters over 24 hours)
4. Known strict fluid restriction (cannot receive ½ liters of fluid infusion)
5. Severe general edema
6. Unable to give informed consent

All of the individual participant data collected during the trial, after deidentification. Data sets will only be share where anonymity of included participants can be insured.

Beginning 6 months and ending 5 years following article publication.

Data will be shared upon reasonable request.

To achieve assessor/care provider blinding, all participants will receive a sham needle (opposite of the randomization). This will not pierce the skin but just lay on top of the skin. Both the randomized and the sham needle will be covered by non-woven swabs before placement of the dressing. Both the active and the sham device is connected to an infusion set. The infusion tubes will be tangled at the top, just below the roller ball and drop counter. The entanglement will be covered by opaque dressing. This way it cannot be know which infusions tube is connected to the fluid bag, while it is still possible to control the infusion speed.