The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [580]
Advantages and disadvantages of volumetric pumps
These pumps are able to overcome resistance to flow by increased delivery pressure and do not rely on gravity. This generally makes the performance of pumps predictable and capable of accurate delivery over a wider range of flow rates (MHRA 2010b).
The pumps also incorporate a wide range of features, including air-in-line detectors, variable pressure settings and comprehensive alarms such as end of infusion, keep vein open (KVO, where the pump switches to a low flow rate, for example 5 mL/h, in order to continue flow to prevent occlusion of the device) and low battery. Many have a secondary infusion facility, which allows for intermittent therapy, for example antibiotics. The pump is programmed to switch to a secondary set and, when completed, it reverts back to the primary infusion at the previously set rate. The changing hospital environment has led to an increased demand on volumetric pumps, which in turn has resulted in the development of multichannel and dual-channel infusion pumps. These may consist of two devices with an attached housing or of several infusion channels within a single device (Hadaway 2010).
The disadvantages are that these are usually relatively expensive and often dedicated administration sets are required. The use of the wrong set could result in error even if the pump appears to work. Some are complicated to set up, which can also lead to errors (MHRA 2010b).
Syringe pumps
Syringe pumps (Figure 13.30) are low-volume, high-accuracy devices designed to infuse at low flow rates. The plunger of a syringe containing the substance to be infused is driven forward by the syringe pump at a controlled rate to deliver it to the patient (MHRA 2010b).
Figure 13.30 The Alaris GH syringe pump.
Syringe pumps are useful where small volumes of highly concentrated drugs need to be infused at low flow rates (Quinn 2008). The volume for infusion is limited to the size of the syringe used in the device, which is usually a 60 mL syringe, but most pumps will accept different sizes and brands of syringe.
These devices are calibrated for delivery in millilitres per hour (Weinstein and Plumer 2007).
Advantages and disadvantages of syringe pumps
Syringe pumps are mains and/or battery powered, are usually easy to operate, and tend to cost less than volumetric pumps. The alarm systems are becoming more comprehensive and include low battery, end of infusion and syringe clamp open alarms. Most of the problems associated with the older models, for example free flow, mechanical backlash (slackness which delays the start-up time of the infusion) and incorrect fitting of the syringe, have been eliminated in the newer models (MHRA 2010b, Quinn 2008). The risk of free flow is minimized by the use of an antisiphonage valve which may be integral to the administration set (Pickstone 1999). Despite the use of an antisiphonage valve, the clamp of the administration set must still be used (MHRA 2010b). Where mechanical backlash is an issue and there is a prime or purge option, this should be used at the start of the infusion to take up the mechanical slack (Amoore et al. 2001).
Specific patient preparations
Selecting the appropriate infusion device for the patient
The nurse has a responsibility to determine when and how to use an infusion device to deliver hydration, drugs, transfusions and nutritional support, and how to select the appropriate device (Figure 13.31) in order to manage the needs of the patient. The following factors should be considered when selecting an appropriate infusion delivery system (Quinn 2008).
Figure 13.31 Decision tree for selection of infusion device. MHRA (2010b).
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Risk to the patient of:
(a) overinfusion
(b) underinfusion
(c) uneven flow
(d) inadvertent bolus
(e) high-pressure