Hypodermoclysis is a method of infusing fluid into subcutaneous tissue that is an alternative to administering intravenous fluids (Sasson and Shvartzman [321]). Subcutaneous fluids can be given to maintain adequate hydration in patients with mild or moderate dehydration (Scales [324], Walsh [361]) and have been shown to be as effective as the intravenous route for replacing fluid and electrolytes (Barton et al. [19], Barua and Bhowmick [20], Luk et al. [178]). The use of this route is generally limited to palliative care and elderly patients (Scales [324], Walsh [361]). It is not recommended for patients needing rapid administration of fluids, and is also contraindicated in patients with clotting disorders or who have problems with fluid overload (such as those with cardiac failure) (Mei and Auerhahn [196], Walsh [361]).

A volume of 1000–2000 mL can be given over 24 hours; this can be given as a continuous infusion, over a number of hours (such as overnight) or as intermittent boluses (Moriarty and Hudson [220], Scales [324], Walsh [361]). More than one site can be used if greater volumes are required. It is recommended that electrolyte‐containing fluids such as 0.9% sodium chloride or dextrose saline be used, although 5% glucose has also been used (Hypodermoclysis Working Group [139], Sasson and Shvartzman [321]).

Advantages of this route include the following:

Side‐effects of subcutaneous fluid administration include pain, bruising, local oedema, erythema and local inflammation, which can be reduced by changing the site of the infusion (Mei and Auerhahn [196], Scales [324]).

Hyaluronidase is an enzyme that temporarily increases the permeability of subcutaneous connective tissue by degrading hyaluronic acid and has been shown to increase the dispersion and absorption of co‐administered molecules (Thomas et al. [349]). It can be given as a subcutaneous injection before commencing fluids or added to infusion bags (Sasson and Shvartzman [321]). A randomized study compared absorption and the side‐effects of administration of subcutaneous fluids with and without hyaluronidase. No significant differences were found although patients not receiving hyaluronidase showed an increase in the size of the limb in which the fluid had been administered, but no differences in pain or local discomfort were found so no clear benefit to the use of hyaluronidase was demonstrated (Constans et al. [43]). Most agree that it is not necessary to use hyaluronidase if the infusion rate is 1 mL/min or less (Mei and Auerhahn [196]).

Subcutaneous infusion may be the route of choice in patients with problems such as vomiting, diarrhoea or dysphagia, and in those who are unable to tolerate drugs by the oral route. Some patients with bowel obstruction whose gut absorption may be impaired may also benefit. Subcutaneous infusion is also commonly used for patients who are dying and no longer able to manage medication orally (Dickman et al. [70], Dychter et al. [83], Menahem and Shvartzman [197], Ostendorf [277]). Continuous subcutaneous infusion of insulin is used in a small number of diabetic patients, particularly when adequate control cannot be achieved with multiple daily insulin doses. Such patients need to be under the care of a multidisciplinary team familiar with the use of such infusions (NICE [240]).

Infusions of a single drug, such as an antiemetic or analgesic, do not generally cause problems with drug stability. The drug should be diluted with a suitable diluent (sodium chloride is recommended for most drugs) and given over 12–24 hours (Dickman et al. [70]). The use of a combination of drugs can be problematic; there is anecdotal evidence regarding combinations of drugs but not many pharmaceutical studies have confirmed compatibility. Combinations of up to four drugs have been reported; however, if compatibility is uncertain, it may be best to use a second syringe pump. It is also important to ensure that the diluent used is compatible with all the drugs in the infusion. It is recommended that infusions are not exposed to direct sunlight or to increased temperatures as drug instability may result (Dickman et al. [70]). Hyaluronidase may be used to enhance the pharmacokinetics of drugs such as subcutaneous morphine (Menahem and Shvartzman [197], Thomas et al. [349]).

The subcutaneous route can be used in the palliative care setting for parenteral hydration. The decision to commence subcutaneous fluids is individual and the decision process should involve the patient (if possible), their family and/or carers, and the multiprofessional team (Bruera et al. [34]). The overall comfort and wellbeing of the patient should be central to the decision (Gabriel [101]), as the evidence to support the use of the subcutaneous route for this purpose is limited (Bruera et al. [34]).

Choice of infusion site should be based on both thickness of subcutaneous tissue and patient convenience. Sites recommended for subcutaneous infusion of drugs or fluids are the lateral aspects of the upper arms and thighs, the abdomen, the chest and the scapulae (Walsh [361]). If the patient is ambulant then the chest or abdomen are the preferred sites, but the patient should be included in the decision‐making process wherever possible (Dickman et al. [70]). The following areas should not be used:

In general, an infusion site need not be changed for at least 72 hours, unless there is a local reaction to the infusion (Dickman et al. [70]).

Accurate documentation of the site, rate, flow, start time and drugs used is imperative in order to avoid confusion and errors among staff (Dickman et al. [70], Dougherty [75], MHRA [208], Quinn [292], Sasson and Shvartzman [321]). Sites and tubing will need to be changed every 1–4 days.

At the start of the infusion, record the date, time, start volume, infusion rate setting and name of the person setting up the infusion. Checks should subsequently be carried out at a frequency determined by the type of infusion and the patient's condition; however, at minimum, checks should be carried out 15 minutes and 1 hour after the initial set‐up and thereafter a minimum of every 4 hours. Additionally, the device must be checked at the start of each shift and when setting up an infusion.

The following should be taken into account when performing a check: