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Published on 1 November 2007

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Devices for continuous subcutaneous infusions

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Andrew Dickman
MSc MRPharmS

Senior Clinical Pharmacist

Marie Curie Palliative Care Institute

Pharmacy Department
The Cardiothoracic Centre

Liverpool
UK

E: andrew.dickman@mariecurie.org.uk

Continuous subcutaneous infusion (CSCI) is an effective method of drug administration that is commonly encountered in palliative care.[1] When the oral route is no longer available, the use of a CSCI is the preferred method of drug administration to maintain symptom control. A syringe driver, or pump, is used to deliver a CSCI. Such portable battery-operated devices were first described in 1978 when they were used to deliver desferrioxamine for the treatment of thalassaemia in children.[2] Shortly after this, the use of CSCIs in the context of palliative care was soon described.[3]

The Medicines and Healthcare products Regulatory Agency (MHRA) has received reports of incidents involving syringe drivers and pumps, which have resulted in patient harm or death.[4] In an attempt to reduce these incidents, the MHRA issued guidance on infusion devices, which included recommendations on important safety features (see Table 1).

[[HPE35_69]]

There are also International Standards, issued by the IEC (International Electrotechnical Commission) and adopted into British Standards to which infusion devices should attain. One such standard that is pertinent to syringe drivers, or pumps, is IEC 60601-2-24, which includes particular requirements for the safety of infusion pumps and controllers.

This article describes four devices that are presently used to deliver CSCIs in the UK.

They each have an array of advantages and disadvantages.

Devices available
Smiths Medical MS26 and MS16A
The Smiths Medical (formerly SIMS Graseby) MS26 and MS16A are presently the most commonly encountered syringe drivers used for the delivery of CSCIs in the UK.

Until recently, these were the only devices available and pre-date the MHRA recommendations and International Standards. It is therefore of no surprise that these devices fail to meet these requirements. Nonetheless, they are simple to use but are very similar in appearance (see Figure 1) and fatal errors, due to incorrect identification have been reported to the MHRA. Although the devices are coloured differently, and are clearly labelled on the front, the most commonly encountered issue relates to confusion between model and delivery rates.

[FIGURE 1]

The flow rate is determined in the same way on both devices, that is, in millimetres of syringe travel over time (MS16A delivers at a rate of millimetres/hour; MS26 delivers at a rate of millimetres/24hours); it is the length of liquid within the syringe, not the volume, that determines the rate of delivery with these syringe drivers. The rate is set by simply turning two screws on the front of the device.

Since the rate of infusion is determined by length, it allows for greater flexibility in the choice of brand and size of syringe. The maximum length than can be infused is 60 mm, but syringes of varying sizes can be attached with 35 ml being the largest; this equates to a maximum volume of approximately 25 ml.

Many palliative care services have adopted one syringe driver (commonly the MS26) in order to reduce the risk of error.

Advantages

  • Simple to use.
  • Lightweight.
  • Wide variety of brands of syringe can be used.
  • Cheap to run (one 9 V PP3 battery lasts for up to 50 infusions).

Disadvantages

  • Devoid of safety features that would be expected from current technology; it fails to comply with IEC 60601-2-24.
  • Fails to comply with any of the safety features that the MHRA considers to be important for infusion devices (see Table 1).
  • Rate can be changed simply, even during the infusion.
  • Flimsy syringe attachment.
  • The MS26 has a “boost” button which delivers a wholly inadequate dose. If the boost button is held down for a period of 10 seconds, an alarm does sound; however, there is no lockout. Consequently, the entire contents of the syringe could be delivered within a matter of minutes.
  • Time to alarm upon occlusion is considered to be too long.
  • Available alarms are rudimentary: occlusion (poor response, with a long time to alarm), end of syringe and boost button (alarms if boost button depressed for 10 seconds).
  • No audible alarm for low battery.
  • If the syringe is not fitted correctly, or is tampered with, there will be no alarm and the device will continue to work.
  • It is difficult to check correct delivery during the infusion, without detaching the syringe.
  • There is the occasional need for complicated, 12-hourly infusions due to the restriction imposed by syringe size.
  • Micrel MP Daily
  • The MP daily (see Figure 2) is very similar to the MS26, in that it delivers the length of liquid within the syringe, not the volume, over a 24 h period. It is, however, more sophisticated with definite improvements over the MS drivers.

[FIGURE 2]

Advantages

  • No boost facility.
  • More secure and robust syringe attachment.
  • Variety of brands of syringe can be used; 30 ml syringes can be comfortably attached, with the total volume of infusion approaching 22 ml, dependent upon brand.
  • Infusion rates are set electronically. They can be easily fixed, limited, or zoned. If the infusion rate is limited, upper and lower limits are applied thereby restricting the rate to a specified range. If the limits are identical, the infusion rate is fixed. If the infusion rate is zoned, the user is alerted to rate settings outside the specified limits.
  • Once started, the infusion rate cannot be altered (unless the device is turned off and on again).
  • A range of alarms/warnings to alert the user; for example occlusion alarm, low battery (one infusion remaining), depleted battery, end of plunger travel (ie, syringe empty; this is set to silence by default), system malfunction.
  • Batteries (six AAA) last for up to 50 infusions (slightly more expensive than the MS26).

Disadvantages

  • It fails to comply with IEC 60601-2-24.
  • Fails to comply with all of the safety features that the MHRA considers to be important for infusion devices (see Table 1).
  • Time to alarm upon occlusion is considered too long.
  • It is difficult to check correct delivery during the infusion, without detaching the syringe.
  • If the syringe is not fitted correctly, or is tampered with, there will be no alarm, the device will continue to work and siphoning may occur.
  • There is the occasional need for complicated, 12-hourly infusions due to the restriction imposed by syringe size.

McKinley T34
The T34 syringe pump (see Figure 3) differs from the previously mentioned syringe drivers in that the delivery rate is based on volume, rather than length. It potentially has a larger application than the above syringe drivers given the additional safety features discussed below. It is more sophisticated and complicated than the other syringe drivers, but it is inherently safer. A 50 ml syringe will fit comfortably on the device, allowing a volume of up to 38 ml to be infused, dependent upon brand.

[FIGURE 3]

Advantages

  • Complies with all the safety features that the MHRA recommends and IEC 60601-2-24 proposes as essential.
  • Device will not work unless the syringe is attached securely.
  • Infusion rate cannot be altered once the device is infusing.
  • No bolus facility.
  • Detects the syringe size automatically – the user has to simply confirm the brand.
  • Determines the rate of infusion automatically
  • Includes history logging – a record of infusion activity is maintained, including a record of button pressing and syringe displacement, which can be viewed at a later date.
  • Occlusion alarm is more rapid than the other syringe drivers.
  • Reduced likelihood of complicated 12-hourly infusions as a larger volume of fluid can be infused.
  • If new brands of syringe become available, their physical properties can easily be entered into the pump memory.

Disadvantages

  • Most expensive of the three syringe drivers to run; one 9 V PP3 battery lasts for only 3–4 daily infusions.
  • Setting or rate changing is complicated if used outside usual configuration.

Conclusion
The Micrel MP Daily offers a simple and safer alternative to the MS26/MS16A syringe drivers. However, it fails to meet all the MHRA safety features, or satisfy IEC 60601-2-24.

However, the McKinley T34 fulfils all of the MHRA specifications and also satisfies the requirements of IEC 60601-2-24.

References
1. Wilcock A, Jacob JK, Charlesworth S, et al. Drugs given by a syringe driver. Palliat Med 2006;20(7):661-4.

2. Graham F, Clark D. The syringe driver and the subcutaneous route in palliative care. J Pain Symptom Manage 2005;29:32-40.

3. Russell PS. Analgesia in terminal malignant disease. Br Med J 1979;1(6177):1561.

4. DoH. Hazard MDA HN9506: Graseby Medical MS16, MS16A and MS26 ambulatory pumps. London: Department of Health; 1995.



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