Infusion therapy - requirements for flow control

Joanna Ford

February 2009 (updated 2014)

Introduction

Infusion rates can be regulated in a variety of ways. Simple devices use gravity to provide pressure and infusion rates are controlled fairly coarsely with methods such as roller clamps, where rates are calculated visually by counting  drops per minute. In other cases, electronic pumps are used to administer infusions which are designed to accurately control the volume of fluid/medication and the timing of administration. The most common types of electronic pumps are volumetric pumps (for medium to  large volumes of fluids) and syringe pumps (for small volume, low flow rate infusions that can be administered continuously or as bolus injections). Specialist pumps include those for patient controlled analgesia (PCA pumps), anaesthetics and sedation (anaesthetic pumps) and pumps in community situations (ambulatory pumps) (MHRA 2003). 

Administration sets with 'flow regulators' are also available. These sets usually possess dials which can be set to a fixed flow rate and are claimed to allow more 'control' than other manual methods such as roller clamps which have been shown to vary their flow rates due to an effect known as  'plastic creep' ¹.  SMTL investigated 6 different administration sets with flow regulators over a range of flow rates in 2006, and found that they were often inaccurate and risked potential fluid overload in many cases (Hughes 2006). More details are available in the appendix.

A wide range of infusion pumps have been evaluated by the Bath Institute of Mechanical Engineering which are available on the CEP website.

With the range of administration methods and devices available, there is a need for clear guidance regarding what should be used in different circumstances. This report summarises guidance currently available in this area, and poses questions which may form the basis for a discussion within Wales on whether further guidance and/or changes in practice are necessary.

Royal College of Nursing-Standards for infusion therapy, 2005 *

*please note that at the time of updating this document, the above standard was temporarily unavailable on the RCN web site as it was being updated (personal communication).

Choice of device is dependent upon:

• length of treatment 
• type of medication/fluid
• whether therapy is being conducted at home or in hospital

The devices used and methods for infusing different medication or solutions are dependent on local procedures and policies.

Circumstances for using electronic flow

Note: all IV pump devices are collectively referred to as electronic flow devices in the RCN guidance document

• Must use for central venous access infusion when possible
• Use for all paediatric infusion
• Use for all parenteral nutrition
• When using for arterial infusion, use high pressure pump
• When using for vesicant medication, use low pressure pump
• A syringe drive can be considered for sub-cutaneous infusion
• When using for epidural administration, the user should pre-set limits for the maximum infusion rate and bolus size prior to procedure
• When using pumps for high risk drugs, use system with anti-free flow protection

Circumstances for using manual flow

• Manual flow should be suitable for most infusions
• Flow should achieve accurate delivery with minimal deviation from manufacturers guidelines (this presumably means that the flow rate should be within limits recommended by the manufacturers of the device)
• Use a standard administration set for the sub-cutaneous gravity feed of fluids and solutions

MHRA (previously known as the MDA) Device bulletin-infusion systems, 2013

Training should include criteria for the selection of infusion devices and associated disposables for any given therapy

Recommendations

• Gravity controllers suit lower risk applications including fluid replacement therapy (definition of 'lower risk' not defined)
• Syringe pumps are the preferred choice for infusions of low volume and low flow rate (definitions not provided)
• Volumetric pumps are best suited for infusions with medium to high flow rates and large volumes. ( 'medium' and 'high' flow rates are not defined but it is stated that these pumps work satisfactorily at flow rates as low as 5 ml/h and are most suited to category B and C therapies (see following table)

The following information has been taken from a table in appendix 1 of the device bulletin. It categorises different types of therapy and stipulates parameters that the infusion equipment should possess when used for that purpose.

NPSA

The NPSA have produced a range of safety alerts that provide guidance  promoting the safer administration of medicines (see Safety alerts) . These cover appropriate labelling of syringes and IV cannulae for different purposes (injectable medication and oral liquid medicines) to prevent confusion and misuse, as well as the importance of training and risk assessment. However, no specific information about the choice of administration device is provided. Specific guidance around the use of administration equipment includes the following:

• Use a 'double checking 'system and dose checking software in 'smart' infusion pumps and syringe drivers (Patient safety alert 20, 'Promoting safer use of injectable medicines')
• The label, colour and design of epidural infusion pumps and syringe drivers, and the infusion systems they are attached to should clearly identify them (Patient safety alert 21, 'Safer practice with epidural injections and infusions'.)

Welsh Risk Pool

The Welsh Risk Pool does not produce any guidance in this area (personal communication).

Medusa-Intravenous guide

The Medusa system is an electronic database which provides information for clinical staff regarding the correct administration of IV medication. This includes stating whether an infusion falls into the category of therapy A, B or C (in accordance with MDA classification described previously). All NHS Trusts and Health Boards in Wales have access to this system.

Feedback from medical device/IV pump trainers in Wales

General feedback from a number of  IV pump trainers in the Welsh NHS have indicated that there is wide variation in practice across Wales. Trusts and Health Boards have developed their own policies regarding infusion  therapy and have different categories and labelling systems which they use to make clinical choices in this area.

Conclusion

The following points summarise this investigation into administration of infusions:

• practice varies between workplaces
• there may be occasions when pumps are used unnecessarily
• it is possible that some models of gravity administration sets with flow regulator dials are not delivering fluid/medication at the flow rate indicated on the dial.
• clear advice regarding the administration equipment recommended for different types of fluid/medication delivery would be useful

¹ Since writing this document, an additional part to the ISO 8536 guidance (part 14 entitled 'Clamps and flow-regulators for transfusion and infusion equipment without fluid contact') has been drafted and is due for publication later in 2014.

Bibliography

Hughes G.  Regulated Infusion set flow rate investigation. 2007 Technical report no. 06/1949/1. The Surgical Material Testing Laboratory.

Royal College of Nursing. July 2003. Standards for Infusion therapy RCN guidance document.

Appendix - Flow Control Assessments

In 2006, SMTL tested a range of administration sets with 'flow regulator dials' in order to investigate plastic creep and accuracy of flow rates. Administration sets were set up with IV cannula, suspended bags of saline were connected to them and the flow dial set at specific rates. Saline was collected in a beaker and weighed over time to measure accuracy of flow. A similar test was carried out over night with a data logger attached to the balance in order to investigate the possibility of plastic creep over longer periods of time. Flow regulator dials were set at ranges from 5 to 250 ml/h and sets were tested at both 1 meter and 0.5 meter hydrostatic head. The table below summarises actual flow rates measured for 5 different sets whose regulator dials were set to either 250 or 125 ml/hr (standard deviations not included). More results are available in the full report.

Results demonstrated inaccuracies in flow rate, some actual flow rates being far greater than the rate the device was set to. This indicates that these devices have the potential to cause fluid overload which could have adverse patient consequences. No evidence of plastic creep (indicated by a reduction in flow rate over time) was observed with any of the devices. Please refer to the full SMTL report for further details (report number 06/1949/1).