Thomas Latter, said to be the founding father of intravenous infusions in the UK, put IV therapy to good use to treat dehydration during the cholera epidemic in the 1830s. Infusions of salt and glucose solutions directly into the bloodstream have since been a significant factor in improving outcomes for patients worldwide.

The emergence of the silicone chip in the 1980s saw a plethora of medical infusion devices released into the NHS in an attempt to control the rate of flow, and offer the user a series of alarms and functions to help deliver the medication as intended. Today, sophisticated devices with built-in software, drug error libraries and Wi-Fi capabilities are available, but are all these devices required for all infusion therapies?

Subcutaneous infusions

A less obtrusive and safer alternative is the administration of medication directly into the tissue. Skin is the largest organ of the human body and has three main layers. The lowest layer (hypodermis or subcutaneous) consists of loose connective tissue, lymphatic vessels, elastic fibres and fat, and plays an important role in cushioning the skeleton, homeostasis and recirculation of interstitial or extracellular fluid.

A subcutaneous infusion of fluid into this layer is used in the treatment and management of many health conditions such as hydration, nausea/vomiting and pain. The technique allows the body to absorb the infusion slowly, compared with intravenous infusions, which act more rapidly.

There may be as much as 3L of fluid circulating in tissue, which is shifted back to the circulatory system via absorbtion and the lymphatics, albeit at a slower rate than intravenously. This allows for slower absorption of fluids and medication, and is a preferred route for small-dose injections and symptom control, and pain management in palliative care.

Lymphatic system

The lymphatic system acts as the body’s defence mechanism, and helps shift fluids (lymph) from tissues and redistributes them back to the circulatory system. Lymph nodes located throughout the body help drain and redistribute fluids. The skin needs to be breached and the hypodermis accessed with a needle or cannula) to allow fluid and medications to be administered.

Although subcutaneous therapy in the UK remains an important and effective method for basic solutions and fluids, it seems to fall in and out of favour. Some infusion pump manufacturers allow them to be used for subcutaneous infusions, while others specifically exclude their devices from being utilised for this technique.

Using gravity

The subcutaneous method of infusing fluids uses one of the oldest phenomena: gravitational forces. A simple administration set with roller-clamp, in-line filter and fluid drip-chamber is all that is needed to deliver the medication. A fluid bag (or container) attached to the administration set is connected to a small needle in the subcutaneous tissue space. By raising the fluid bag approximately 1.5m above the patient, a ‘hydrostatic pressure’ of 110mmHg (millimetres of mercury) is exerted on the fluid in the administration set and this allows the fluid to flow.

Three main factors that affect this flow are height, density (or viscosity of the fluid) and the diameter of the cannula or needle. Doubling the length of the cannula will halve the flow, while doubling the diameter of the cannula will result in a 16-fold increase in flow.

"As long as fluid can be administered at a controlled rate, this method is an effective and relatively safe method of infusion."

The flow rate is controlled by adjusting the roller clamp to obtain a flow in ‘drops per minute’. The prescribed infusion (millilitre per hour) must be converted into drops per minute and this depends on the giving set drip factor (Table 1). This ‘drip factor’ (the number of drops per millilitre of fluid) will determine the final flow rate (Table 2). Outside influences such as temperature can affect plastic components and change their characteristics (known as creep). Positional factors, such as sitting the patient up in bed, may also alter the dynamics and pressures in the circuit, sometimes stopping the flow.

While intravenous therapy can be used to administer a vast range of fluids and medication, subcutaneous therapy is limited to a select number of infusions. As long as fluid can be administered at a controlled rate; this method is an effective and relatively safe method of infusion. Fluids and solutions that match the biological make-up of the tissue are safest, and prescribers need to be aware of fluid osmolarity, pH values and their effect on the tissue site; as a result, only a few solutions can be safely administered using this technique. Recent studies have examined antibiotics and simpler compounds, but the issue of balancing safety, risk, speed of delivery and possible absorption errors at the infusion site remain to be overcome.

How to do it

Fluid replacement is mostly given by gravity and low-rate infusions by an electronic pump that precisely controls the dosage of drugs. The administration sets are usually attached to a winged infusion set, which consists of a needle sheathed with a plastic coating and generally placed at a 45° angle into the subcutaneous layer of skin. Modern safety needles allow the removal of the needle, leaving the plastic cannula in position. The access site is covered with a transparent, semi-permeable dressing to hold it in place, keeping contamination out and allowing moisture vapour transfer while providing a window for observation. The advantages of this type of medication delivery include:

  • it can be used for patients who are unable to take oral or rectal medication and have poor venous access or thrombosed veins
  • it can be used for mild rehydration and thirst management
  • it is less invasive and reduces the risk of infection at the injection site
  • no risk of air embolism in blood vessels
  • the sites can be rotated simply
  • it can be performed at home, allowing the patient to leave the hospital setting
  • it is suitable for patients who are drowsy, semi-comatose or comatose
  • increased comfort, avoiding the need for repeated injections
  • when attached to an ambulatory pump, it allows patient mobility.

The disadvantages are:

  • it cannot be used to treat severe dehydration; no more than 3L in a 24-hour period
  • it cannot be administered where there is lymphoedema or oedema, or where there is poor skin integrity
  • it may cause abscess formation at the entry site
  • pain and or infection at the site
  • any adjustment of height of infusion bag will affect the rate of flow
  • it is not suitable for shock
  • it is not for titrating accurate dosages
  • it is contraindicated for use in heart
  • and renal failure.

Doctors are required to prescribe fluids or medication to be given via this route, however, any healthcare professional trained in hypodermoclysis can set up an infusion. Suitable sites used in hypodermoclysis include: abdomen, upper arm, outer area of thighs, scapula region and pectoral areas. Equipment needed include: the prescription, fluid/medication, an administration set, a subcutaneous infusion set/needle, a clear dressing, skin preparation, a sharps bin and gloves.


Prepare by first talking to the patient and relatives explaining the procedure, why you are doing it and how it will be managed, then gain consent. Where the patient is unable to give consent, consent must be obtained from relatives or significant others.

Next, wash your hands and gather the equipment needed in a sterile/clean environment (if working in a community setting, a sterile environment will not always be possible). Put on personal protective equipment such as gloves and aprons. Prepare the infusion using a non-touch aseptic technique and take to the patient. Remember to wash your hands before and after each patient contact.

"Gravity control offers the simplest form of infusion therapy if used properly."

Check the patient details and then prepare the area of skin where the subcutaneous infusion will be inserted with whatever solution the hospital policy recommends. Insert the subcutaneous needle following the manufacturer’s procedure, then cover with a sterile, semi-permeable, clear dressing. Remember to time, date and document these actions in the patient’s notes. While performing this procedure, explanation to the patient is required at all times.

To begin the infusion, the rate has to be calculated and the method depends on whether gravity or an infusion pump is used. A pump can be programmed to deliver the rate, however, this method is not always recommended as high-volume infusion pumps are usually licensed for intravenous infusions. If the gravity method is used, then the rate is calculated by counting the drips using a formula.

What next?

Despite articles outlining the benefits and simplicity of subcutaneous fluid infusions to treat mild to moderate dehydration, it still remains limited in use and application.

Molloy and Gunje (1992) asked users to reconsider this therapy, but it isn’t clear if this has been taken up by healthcare establishments in any great numbers today. Donnelly (1999) added to the debate and the release of the Hypodermoclysis Working Group recommendations (1998) raised the profile of this relatively safe technique. Nevertheless, it still lags behind IV therapy as a method for simple saline and glucose infusions. The advent of safety needles and the European sharps directive (2010/32/EU) will help reduce the occurrence of needlestick injuries, improve operator safety, and increase patient comfort, so organisations may look at hypodermoclysis as a safe and effective alternative.

"Prescribers and clinical staff have an alternative to the sometimes complex and long-winded process when using mechanical infusion pumps."

Scales (2011) outlined the importance of education and highlighted the difficulties in detecting dehydration in patients. Risk factors, warning signs, physiological and psychological aspects to consider, and a targeted training programme needs to include all these elements before organisations embark on replacing IV therapy with this infusion technique. Effective mouth care, regular observations and knowing the patient should not be overlooked. Pressure from family members to address their loved ones’ ‘thirst’ can influence decisions to start subcutaneous fluids when they may not be needed, and this will be a difficult issue to overcome.

Barton et al (2004) highlighted the financial savings of this technique and introduced the notion of antibiotic therapy. Although the use of infusion pumps to administer subcutaneous therapy is reserved for small syringe pumps and symptom control, gravity infusions are more than adequate to deliver an effective treatment for basic fluid replacement in certain patient groups. Lee et al, 2012, suggested that as much as 6% of staff time can be spent dealing with alarms on infusion pumps for IV fluids. Further benefits include ease of use, cost-effectiveness, and being less prone to interruption from alarm and machine error.

Factors that can affect the decision to use this method can be a lack of understanding of its use, versatility and simplicity. Gravity control offers the simplest form of infusion therapy if used properly. Training courses, raising awareness and benefits may help revive this easy-to-use and effective infusion therapy. Prescribers and clinical staff have an alternative to the sometimes complex and long-winded process when using mechanical infusion pumps, which have functions and alarms that can often go unnoticed or be ignored.

The use of subcutaneous therapy to aid symptom control (such as pain, nausea and vomiting) is well established and continues to be accepted within healthcare, albeit in very low volumes in syringes (20-30ml per 24 hours) compared with fluid replacement (1,000-3,000ml per 24 hours). Using medications ‘off-licence’ (where drugs are added together in syringes and administered subcutaneously instead of IV for which they were intended) is also accepted within limits, and local policies and protocols go some way to coordinating the delivery of these medications.

A basic list of fluids, safety cannula, improved cannula dressings and a cultural shift may be all that is required to revive this therapy concept, but it remains to be seen if recent austerity measures will affect decisions to proceed, or if safety legislation will open the discussion to look at whether gravity and hypodermoclysis will come back in favour