To the Editor:—
The breakdown or dysfunction of syringe pumps can present a serious threat to patient safety when they are used to administer high concentrations of narcotic, vasopressor, or depressor drugs. I report an experience in which the power supply circuit and syringe size sensory were damaged— apparently a result of leakage of intravenous infusion fluids into the housing of the pump.
My institute has had 19 anesthesia syringe pumps (Graseby 3500; Graseby Medical LTD, Watford, Hertfordshire, UK) in service for 4 yr or more, and these have been used exclusively for continuous infusion of Propofol. In recent periodic checks of all units, corrosion in the syringe size sensory springs was found in three syringe pumps, and damage to the power supply by short circuit was found in one. Figure 1shows a corroded syringe size sensory spring. Because residual liquid or white crystal was found on the bottom of the housing between the syringe size sensor and the power supply circuit board, it is evident that intravenous infusion fluids had infiltrated into the housing from the narrow space between the main body and the syringe plunger, thus causing both corrosion of the spring and a short circuit of the power supply. Infusion fluid occasionally falls onto the syringe pumps because we usually attach them to the infusion stand during surgery. So, this kind of medical instrument should be waterproof by design. The instruction manual for this syringe pump does state in the Specifications section that its electrical safety category is “drip proof IPX1,” which guarantees protection against a 10-min exposure to artificial rain of 3–5 mm/min from a 50-cm height. 1Therefore, it is anomalous that dripping intravenous infusion fluids should result in the observed problems. Although short circuit of the power supply simply results in infusion interruption, corrosion in the syringe size sensory spring is a severe problem, because it may cause incorrect recognition of syringe size, resulting in an unpredictable drug infusion rate.
I suggest that the syringe size sensory spring be made from a material that is not corroded by the electrolytes included in the infusion fluids, and that the seal between the main body and the syringe plunger be improved. In this case, the Japanese sales agent was unable to distinguish between the possibilities of a structural defect and an assembly problem after checking the faulty syringe pumps. To prevent recurrence of these problems, Graseby Medical and the Japanese sales agent suggested I install a syringe cover normally used with another of Graseby's products with patient-controlled analgesia function that has a common housing. I accepted this suggestion at the time, but it is notable that such a modification potentially constitutes a warranty violation and exposure to legal problems. At any rate, the improved water resistance is expected to prevent this type of accident in the future.