Testing the Surefuser: A Disposable Subcutaneous Infusion Pump

Transcription

1 SHORT COMMUNICATION Testing the Surefuser: A Disposable Subcutaneous Infusion Pump Clare Huppatz, Deborah Parker, Ian Maddocks ABSTRACT Objective: To assess the accuracy of a new mechanical infusion pump, Nipro Surefuser. Setting: Daw House, a hospice unit located at Repatriation General Hospital, Daw Park, South Australia. Method: Three Surefuser infusion devices were assessed on the bench top over a three-day period. A flowcontrol tubing was chosen that would deliver 50 ml of 0.9% sodium chloride in 72 hours at a rate of0.7 mli h. Devices were fitted with extension tubing and a 25- gauge butterfly needle. One Surefuser device was attached to a healthy volunteer for a three-day trial. The infused volume was indirectly measured every 12 hours throughout the trials and the ambient temperature was also recorded. Results: Mean flow rates for the three Surefuser devices assessed on the benchtop were 0.63 muh, 0.71 ml/h and ml!h. Temperatures for these trials ranged between 18.3 C and 28.6 C. The mean flow rate of the Surefuser device attached to the volunteer was 0.88 ml!h. Conclusions: The manufacturer claims that the Surefuser is accurate within ±10%, at a constant temperature of 32 C. The average rates as measured on the benchtop support this claim. It is unclear what the effect of temperature was on the infusion rate, although it appeared to make only a minor difference. The Surefuser is simple to operate and convenient to work with. The accuracy is acceptable in palliative care and future studies should be trialed in a clinical setting. The major drawback is the cost - a single, disposable unit costs approximately $ AustJ Hosp Pharm 1998; 28: INTRODUCTION Continuous subcutaneous infusion of opiates is an important alternative route for managing chronic pain. For patients unable to take oral medication, administration via continuous subcutaneous infusion is less traumatic than other methods, such as IV, IM and PR, and avoids the peaks and troughs associated with bolus doses. Continuous subcutaneous infusion can: o decrease side effects and increase pain control; 1-3 o decrease nursing time for drug administration; and o be used in both hospital and home. The Daw Park Hospice offers continuous subcutaneous infusions to patients with chronic cancer pain. The infusion pump currently used is the Graseby pump MS26 which is powered by a battery with a screw driving the syringe plunger at an adjustable and predetermined rate in mm/h. Using 10 ml, 20 ml or 30 ml syringes, the pump allows a range of volumes up to 22 ml. The pump is calibrated with speed settings of0-99 mm/h and accuracy of +5%. To set the Graseby MS26, the syringe is filled with the required volume and then inserted in the syringe trough of the syringe driver. If required, bolus doses of drug can be delivered by pressing the boost button. The approximate cost of the Graseby MS26 is $ This study tested a new pump, the Nipro Surefuser (Figure 1). The Surefuser is a balloonstyle disposable infusion device with a predetermined volume and flow rate. Disposable devices have several advantages over battery-powered devices such as the Graseby. They are lightweight, self-powered and easy to use. Furthermore, many can accommodate larger volumes of medication and be operated for longer infusion times. Few reports have evaluated the efficacy of disposable infusion devices. Kaye commented on several problems commonly observed with their use. 5 All problems related to a prolonged infusion time, which can be affected by temperature, viscosity and Clare Huppatz, 3rd Year Medical Student Deborah Parker, BA, MSocSc Ian Maddocks, MD, FRACP, DTM&H Daw House Hospice Repatriation General Hospital Daw Park, South Australia Address for correspondence: Deborah Parker Research Officer Flinders University of Soutb Australia 700 Goodwood Rd, Daw Park SA Debbie.Parker@flinders.edu.au The Australian Journal of Hospital Pharmacy Volume 28, No. 4,

2 Figure 1. The Nipro Surefuser solubility of the drug used, and patient factors (such as site patency). In general, the infusion rates for disposable devices vary within ± 15% of the labelled flow rate, compared with only ±5% for many battery-powered devices. 6 Veal et al. evaluated the accuracy on the bench top, of six different types of disposable infusion devices. 6 None of the pumps tested delivered 100% of the volume expected to be infused over the 60-minute test period, and many showed extremely variable infusion rates throughout the trial. The pump showing the least variability in flow rate was a balloon-style pump, called the Homepump (manufactured by Block Medical, USA). While the Homepump was the most accurate, the authors reported a major disadvantage with its use- the device is difficult to fill and often needs an automated filling apparatus. Reekie et al. evaluated another balloon-style disposable infusion device, thetravenol Infusor (manufactured by Travenol Laboratories Ltd, Norfolk, UK). 7 Clinical trials conducted on 62 patients showed 72% of the infusers to be accurate within ±10% of the specified flow rate. The researchers acknowledged that a major contributing factor to this variability was temperature, rather than manufacture defects. The Travenol Infusor was robust, lightweight and self-powered. However, the authors concluded that its use is limited by the fixed flow-rate tubing (only available in 2 muh) and cost (approximately per single disposable device). Clearly there is a need to continue testing new disposable infusion devices as they appear on the market. Disposable infusion devices need to be accurate, economical and practical, both for patients and nursing staff. This study focused on the accuracy of the Nipro Surefuser. Surefusers are currently available in Japan from Nipro for 4500 (approximately $53.00) per single unit, and are available in Australia from Tuta Laboratories. Description of the Surefuser The Surefuser device comprises an outer plastic container that houses a reservoir balloon made from refined natural rubber. The outer plastic container is 140 mm long x 40 mm wide. The reservoir can hold 50 ml of medication and is connected, via Luerlock, to an infusion line. The solution is forced through the infusion line by pressure created within the expanded rubber reservoir. Throughout the infusion the reservoir maintains an average pressure of480mmhg. The flow rate is determined by a coiled pressure reducer made of vinyl chloride tubing (flow-control The Australian Journal of Hospital Pharmacy Volume 28, No. 4,

3 tubing). The pressure reducer is housed in a plastic casing within the infusion line and as it is temperature sensitive, it is recommended that this is attached to the patient's skin. The Surefuser is filled with medication through a one-way valve filling port, requiring the use of a 50 ml or 60 ml syringe. The Surefuser device can deliver 50 ml of solution, over various infusion times ranging from 11.9 hours to 7 days, depending on the type of infusion line chosen. The infusion lines available have flow-control tubing at set rates of 4.2 muh, 2.1 muh, 1.0 muh, 0. 7 muh, 0.4 muh and 0.3 muh. Each complete Surefuser device is wrapped in sterile packaging, and is intended for single use only. The manufacturer claims that the Surefuser is accurate within± 10% when used with 0. 9% sodium chloride at an ambient temperature of 32 C. The infusion rate varies according to the temperature and viscosity of the solution used. The infusion rate does not significantly vary according to the height difference between the device and infusion site. It has been reported that the infusion rate will increase by 3% when the infusion device is 60 em above the infusion site. Storage of the Surefuser for extended periods of time may cause some deterioration to the rubber reservoir- it has been reported that the infusion speed decreases by 6% in 2 years. 8 METHOD Testing Technique Three Surefuser devices, each with infusion line, extension tubing and a 25-gauge butterfly needle, were set up for benchtop assessment. The devices were used with flow-control tubing of 0. 7 muh and were trialled over a three-day (72-hour) period using 50 mlof0.9% sodium chloride. The volume of sodium chloride in the rubber reservoir was extracted and recorded at 12-hour intervals throughout the infusion. The extracted fluid was reinserted into the reservoir after measurement. The ambient temperature was measured and recorded continuously during the experiment. To estimate the accuracy of the Surefuser when attached to a person, a trial was conducted with the device attached to a healthy volunteer. The device was set up as for the bench top assessment and the coiled pressure reducer was taped to the chest of the volunteer. The volume of 0. 9% sodium chloride in the rubber reservoir was extracted and recorded at 12-hour intervals throughout the infusion. The skin temperature of the volunteer was not measured. RESULTS Bench Tests Pump 1 infused 50 ml of0.9% sodium chloride in 67.5 hours (mean rate: 0.74 muh) at an ambient temperature of25.9 C (±2.34 C). Pump 2 infused 50 ml of sodium chloride in 80 hours (mean rate: 0.63 muh) and pump 3 infused 50 ml of sodium chloride in 70 hours (mean rate: 0.71 muh). For pumps 2 and 3 the ambient temperature was C (±3.1 C). Table 1 shows the flow rate calculated for each 12-hour interval. While the average rate for each pump over 72 hours is within an accuracyof±10%, all pumps infused at a rate outside this limit for some of the infusion. The range of flow rates was 0.54 muh to 0.83 muh, providing an accuracy of -22.8% to +18.6%. Volunteer Trial The Surefuser attached to the healthy volunteer infused 50 ml ofo. 9% sodium chloride in 56.5 hours, a mean rate of0.88 muh. The results for each 12- hour interval are shown in Table 1 (temperature of pump operation was not measured). Table 1. Results ofbench test and volunteer trial ofsurefuser Infusion time (h) Mean rate in muh (Mean temperature C) Pump I Pump 2 Pump 3 Volunteer trial (28.6) 0.66 (21.8) 0.75 (21.8) (22.1) 0.63 (18.3) 0.67 (18.3) (26.1) 0.54 (23.8) 0.67 (23.8) (26.1) 0.54 (22.0) 0.67 (22.0) (28.6) 0.60 (27.0) 0.75 (27.6) 1.0* 61-end of infusion 0.80 (25.2)* 0.71 (23.7)t 0.80 (23. 7)* Mean rate 0.74 (25.9) 0.63 (22.9) 0.71 (22.9) 0.88 * Rate calculated for 7.5 h; t rate calculated for 20 h; *rate calculated for 10 h. The Australian Journal of Hospital Pharmacy Volume 28, No. 4,

4 DISCUSSION The average infusion rates over the entire infusion for the three Surefuser devices bench tested with 0. 9% sodiumchloriderangedfrom 0.63 mljh to 0.74 mu h. This result is consistent with the manufacturer's claim of an accuracy range of±10%. However, the infusion rates fluctuated throughout the infusion, from 0.54 muh to 0.83 muh. This represents a variation of -22.8% to+ 18.6%. Such a fluctuation in medication doses may not present too great a clinical problem in a palliative care setting where a wide range of dosage for narcotics for advanced cancer is usual. 4 However, certain aspects of our study design may have unduly influenced the flow rate and these could be avoided or minimised in a clinical setting. The effect of temperature changes throughout the test period and our method of measuring the volume remaining may have changed the outcome significantly. The Surefuser is designed to operate at an ambient temperature of32 C. Flow speed will decrease by 18% at 25 C and increase by 22% at 37 C. 1 Our results show the effect of operating the pump at average ambient temperatures of22.9 C and 25.9 C. We observed a decrease in overall rate of 4.3% at 22.9 C and an increase of5.7% at 25.9 C.This represents a net change in flow rate of 10% over only 3 C. While this appears to be quite significant, caution must be taken with its interpretation. From the results in Table 1, it is evident that the changes in flow rate for each 12-hour period are not consistent with the temperature changes. For example, pump 1 had a flow rate of0.75 muh for the first 12 hours when the average temperature was 28.6 C. The rate increased to 0.83 muh for the next 12 hours even though the temperature decreased to an average of 22.1 C. Further studies need to be conducted, preferably in constant temperature environments, before any conclusions can be drawn about the effect of temperature on rate of flow. To gauge the flow rate, we extracted the volume of fluid remaining in the balloon every 12 hours. After measurement the fluid was returned (by injection) into the balloon, thus re-stretching the membrane. It is quite possible that this method altered the pressure in the balloon and hence changed the flow rate. The results in Table 1 do not show a dear pattern and it is not possible to tell how much this influenced flow rate. Future studies on the Surefuser and other balloon-style infusion devices should use alternative methods for measuring flow rate, such as weighing the infusion device. One Surefuser was attached to a healthy volunteer to estimate the accuracy of operating it at skin temperature (approximately 32 C). The exact skin temperature of the volunteer was not measured, although this would have been desirable. From the results, it appears that the Surefuser is less accurate when attached to a person than when sitting on a bench. The infusion rate was inaccurate by +25.7%. There maybe a number of reasons for this increase in flow rate and without further trials, no conclusions can be drawn. Movement may have caused increased pressure within the balloon, thus increasing the rate of the infusion. Another factor may have been the skin temperature of the volunteer. As the volunteer was very active during the day, her skin temperature may have been greater than 32 C. Further clinical trials are necessary to determine which factors are important with the use of the Surefuser in a clinical setting. The flow control tubing has been calibrated by the manufacturer to operate using 0. 9% sodium chloride. It is unclear what the effect of using solutions with different viscosities may be. However, in a palliative care environment, commonly used drugs given subcutaneously for treatment of cancer pain, such as morphine and midazolam, have viscosities which are the same as 0.9% sodium chloride and will therefore have no impact on the infusion rates. 4 The loading and operation of the Surefuser device was simple and convenient. Filling the device with medication could be quickly and easily done by nursing staff inexperienced with the operation of balloon-style pumps, by following the simple directions provided by the manufacturer. Once filled, the pump could be easily attached by the patient or a caregiver to the patient's site or extension tubing. It is small and lightweight (37 g), allowing patients freedom of movement, and requires no monitoring during the infusion. Being a mechanical device it requires no external power and as it is disposable, the Surefuser does not require any maintenance or servicing. During this study several potential problems were identified. The Surefuser has no alarm to signal malfunction, nor does it have a suitable gauge to allow the rate and progression of the infusion to be checked. Once the medication reservoir has been filled, the dose and rate of infusion cannot be changed, nor can a bolus dose be administered. This restricts the use of the Surefuser to stable medication regimens, and does not allow for any unforeseen problems, such as breakthrough pain. The Surefuser's biggest drawback is its cost. The price (approximately $61.00) for a single disposable unit makes it unaffordable for routine use in a hospice where most patients require continuous in- The Australian Journal of Hospital Pharmacy Volume 28, No.4,

5 fusion. The Surefuser may be a useful option for centres, such as nursing homes, that require a subcutaneous infusion device only occasionally and do not wish to purchase the alternatives. CONCLUSION The Surefuser is a simple-to-operate and convenient disposable subcutaneous infusion pump. Bench tests support the manufacturer's claim that the Surefuser is accurate within ± 10% at a constant temperature of32 C. Several attributes, e.g. inadequate safety features such as no alarm to signal malfunction and an inability to monitor or change the infusion rate, mean that the Surefuser is unlikely to replace the current battery-operated infusion pump routinely used in palliative care settings. In addition, the Surefuser is expensive to use on a continuous basis as is usually required in a palliative care setting. Further trials in a clinical setting are recommended before the Surefuser can be recommended for use in Australia. Acknowledgments The authors are grateful to Dr Suzuki, Chief of Anesthesiology, Matsue Co-op General Hospital, Izumo, Japan, for the Surefuser pumps and Flinders 2000 for financial support. References 1. Coyle N, Mauskop A, Maggard J, Foley KM. Continuous subcutaneous infusions of opiates in cancer patients with pain. Oncol Nurs Forum 1986; 13(4): Ventafridda V, Spoldi E, Caraceni A, Tamburini M, De Conno F. The importance of continuous subcutaneous morphine administration for cancer pain control. Pain Clinic 1986; 1(1): Sheehan AP. Continuous subcutaneous infusion of morphine. Oncol Nurs Forum 1986; 13(4): Maddocks I, Hamblin VA, Parker D, Sellars N. Evaluation of a spring-driven syringe infusion pump in palliative care. Aust J Hosp Pharm 1994; 24: Kaye T. Prolonged infusion times with disposable elastomeric infusion devices. Am J Hosp Pharm 1994; 51: Veal DF, Altman CE, McKinnon BT, Fillingim 0. Evaluation of flow rates for six disposable infusion devices. Am J Health Syst Pharm 1995; 52: Reekie RM, Carter KB, Owen H. A disposable device for infusion analgesia. Anaesthesia 1986; 41: Miyazaki T, Noda H, Tsujikawa H, Kawamoto S. Development of disposable microcontinuous infuser: new improvements. Pain Research 1992; 7(2): First submitted: October 1995 Resubmitted: May 1998 Accepted: June 1998 New addresses The new address for The Australian Journal of Hospital Pharmacy is: ajhp@shpa.org.au The Journal welcomes the submission of manuscripts via or on disk (see Manuscript Checklist on page 298 of this issue). SHPA also has a new address and all enquiries and correspondence should be directed to: shpa@shpa.org.au The Australian Journal of Hospital Pharmacy Volume 28, No. 4,