Administration of an infusion over a set time period, either as a one-off dose or repeated at specific time intervals, is referred to as an intermittent infusion. An intermittent infusion of medicine is often a compromise between a bolus injection and continuous infusion. It achieves high plasma concentrations rapidly to ensure clinical efficacy yet reduces the risks of adverse reactions associated with rapid administration.

Many medicines are given as intermittent infusions, including gentamicin, metronidazole and Pabrinex.

At UCLH intermittent infusions are defined as any infusion given over longer than 5 minutes but less than 24 hours. Most infusions are given over an hour, although large-volume fluids, e.g. 1 L compound sodium lactate, are usually given over 8 hours.

Intravenous administration of a fluid or medicines over 24 hours is referred to as a continuous infusion. The infusion may be repeated over a period of days. Large volumes (i.e. 250–1000 mL) or small-volume infusions (e.g. 50 mL) may be delivered continuously.

Advantages

• May be used to maintain a constant therapeutic concentration of a medicine. For example, some centres may use constant infusions of antibiotics to maintain high blood levels.
  
• Allows the infusion rate of a medicine to be accurately titrated according to patient response. Morphine infusions for pain control may be adjusted according to the patient’s pain and also their level of sedation and respiratory rate. Insulin infusions are titrated according to blood glucose.
  
• Allows administration of medicines with a short elimination half-life to be given, e.g. adrenaline infusions are used to improve the strength of cardiac contraction in critical care.
  
• If the solutions are dilute they may be less irritating than bolus administration.

Disadvantages

• May be complicated to prepare. May require complex calculations and multiple transfers of medicine/fluids to produce a solution with the correct concentration.
  
• Requires the practitioner to be competent in the use of infusion equipment including syringe and volumetric pumps and administration sets.
  
• During administration the practitioner will need to monitor the infusion to ensure it is running into the patient. This can be very time consuming if an infusion regularly stops.
  
• Greater risk of microbial and particulate contamination (compared to bolus administration) because of the complexity of preparation.
  
• Greater risk of infection (compared to bolus administration) as the solutions are used for up to 24 hours, in which time microbes may grow in infusion fluids (particularly those containing glucose or fats, e.g. intravenous nutrition).
  
• The infusion occupies the VAD continuously. If the patient requires multiple medicines or fluids, more than one infusion may need to be given down the same lumen of a VAD leading to compatibility issues: before two infusions are given via the same lumen it must be confirmed they are compatible.
  
• Large volumes of fluid may cause fluid overload in some patients.
  
• Greater risk of pharmaceutical problems, such as drug degradation in solution and drug interaction with the infusion equipment.

ANTT is fundamental to the safe administration of injectables. Infection, as a result of poor aseptic technique when preparing injectables, or when handling a vascular access device, places a huge burden on healthcare systems. Infection from this route can be severe as microbes are introduced directly into the patient’s bloodstream, quickly leading to systemic infection, significant morbidity and high rates of mortality. All practitioners must use ANTT every time an injectable is administered to a patient.

ANTT is an evidence-based method for standardising the aseptic technique of healthcare workers. It is a simple, efficient and logical approach which is the same for peripheral and central line access and for all patients. In IV therapy the focus is on avoiding microbial contamination of the ‘key parts’ at all the preparation and administration stages.

Key parts are those parts of the equipment that come into direct or indirect contact with the liquid infusion.