By the end of this section, you should know how to:

Revision of the anatomy and physiology of the cardiovascular system, with special reference to the circulation of the blood, and body fluids

An intravenous infusion is the introduction of prescribed sterile fluid into the blood circulation; it may be indicated for the following reasons:

Using an aseptic technique, the competent practitioner chooses a suitable vein site for access, body hair should be clipped as necessary and the site cleansed with antiseptic lotion such as a chlorhexidine and alcohol-based solution, which is allowed to dry fully before the skin is punctured (Pellowe et al 2004). Shaving body hair is no longer recommended as it has been suggested that it can increase bacterial colonisation of the skin (Royal College of Nursing 2003). A topical preparation of local anaesthetic, i.e. Emla cream, can be applied to the skin surface approximately 2 hours prior to the procedure, or Ametop, which can be applied 10 minutes before the procedure (Scales 2005).

A sterile cannula is inserted into the vein so that the prescribed infusion fluid can enter the patient’s blood circulation. The infusion fluid flows into the cannula through an administration set that will have been primed ready for use. The cannula is secured in position and covered by a sterile dressing. The flow of infusion fluid is maintained, and the containers of fluid replaced as prescribed, until the intravenous infusion is discontinued (Royal College of Nursing 2003).

The most commonly prescribed fluids are:

normal saline (sodium chloride 0.9%)

dextrose 5% in water

Ringer’s lactate/Hartmann’s solution

plasma or plasma expanders, e.g. Haemaccel or Gelofusine

blood (see ‘Blood transfusion’, p. 47)

parenteral nutrients (see ‘Parenteral nutrition’, p. 240).

Most prescribed fluids are commercially prepared in sterile containers, being labelled ‘FOR INTRAVENOUS INFUSION’. They may also be prepared by the hospital pharmacy. The containers used for these preparations are frequently soft plastic bags protected by an outer covering (see the manufacturer’s instructions), although glass bottles or semi-rigid plastic containers (Polyfusors) are still used for some preparations.

Various cannulae (Fig. 21.1) are available and are prepared commercially in sterile packs. Size 18–14 gauge can be used for the administration of fluids very quickly such as in a resuscitation event. However, smaller gauge cannulae are preferred, as they cause less damage to the inner vessel wall. A gauge 22 would be sufficient size to deliver maintenance therapy as it can deliver up to 42 ml min^—1 or 2.5L h^—1, (Scales 2005). Those chosen by the competent practitioner have an inner needle surrounded by a plastic cannula. The needle is withdrawn once the vein has been punctured, allowing blood to flow back. Once the cannula is safely in situ, the infusion fluid is connected and the cannula secured in position. Some cannula packs include an accompanying syringe, e.g. Medicut. Small winged needles are used for access to scalp veins in babies and young children, and for elderly patients who have fragile veins.

Administration sets are commercially prepared in sterile packs. The set contains specialised sterile tubing with, at one end, a rigid trocar protected by a sterile sheath. At the other end is a similarly protected Luer connector nozzle. Towards the trocar end, the tubing widens into a drip chamber. An adjustable roller clamp surrounds the tubing below the drip chamber, which allows the flow of fluid to be regulated at the prescribed flow rate. Blood administration sets include a filter and should be changed at the end of transfusion or at 24 hours (Royal College of Nursing 2003). Simple administration sets are available without a filter, for the infusion of crystalloid fluids (Fig. 21.2). These should be changed every 72 hours (Royal College of Nursing 2003).

A specialised administration set is used for infusions when a volumetric infusion pump is not available and a more accurate control of flow rate is needed. The burette can also be used to mix and administer drug infusions, which should be infused over short periods of time. They are also particularly important in reducing the risk of fluid overload when infusions are prescribed for babies or young children. The burette set has a calibrated drip chamber with one roller clamp above and one roller clamp below. The drip chamber is filled with the amount of fluid prescribed in millilitres per hour, and this amount of fluid is infused during 1 hour. The flow rate will depend on the drop factor and the amount prescribed (see the manufacturer’s instructions). For the infusion to continue, the drip chamber has to be refilled as prescribed each time it has emptied.

Some volumetric infusion pumps are used with specific sterile cassettes (e.g. Accuset) as well as a normal administration set so that an accurate flow of fluid can be maintained during the infusion. When primed and connected, these can be set to infuse fluid within a range of 1–999 ml h^—1. Other volumetric infusion sets simply use a specifically adapted administration set. The infusion is controlled by a column of electronically controlled rollers that adjust the flow rate as required, constantly monitoring the rate, total volume infused and infusion pressure. This equipment must be mechanically serviced as per the manufacturer’s guidelines and local policy.

Syringe pumps are used to deliver drug infusions over a prescribed period of time. Patient controlled analgesia (PCA) is delivered via a syringe pump (Fig. 21.3).