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J. D. Pitcher, III, C. A. McCannel; Fluidic Properties of a Portable Vitrectomy Device. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3611.
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A battery powered, 23 gauge, guillotine-style vitrectomy cutter system using manually controlled syringes for aspiration and infusion is now available. The fluidic properties of this device have not been characterized. This project attempts to quantify parameters of syringe plunger pull and flow rate to optimize settings for use in patient care.
Syringes of three different volumes (3 mL, 6 mL, and 12 mL) were connected to a pressure transducer designed to provide voltage output (Ryobi Inc., Hiroshima, Japan), which was correlated with a calibrated standard curve to determine pressure level. A spring-loaded digital scale (Extech Instruments, Waltham, MA) was used to draw back on the plunger with 0.1, 0.2, 0.3, 0.5, 0.6, and 0.7 kg and vacuum pressure was recorded at each interval. Similar levels of plunger pull force were sustained while measuring flow rate through the Intrector system (Insight Instruments Inc., Stuart, FL) by recording the time needed to drain 0.25 ml of water. This was repeated seperately for each level of pull force with the vitrectomy cutter at 600 cycles/minute and in the off position. Trials with ophthalmology resident subjects were carried out to determine reasonable sustainable pull force on a syringe over a 3 minute period. The optimal combination of plunger pull and syringe was then used to determine flow rate of egg white (to simulate vitreous) through the system.
Syringes with smaller lumens attained higher levels of vacuum pressure and flow for a given pull force. Increasing pull force resulted in higher levels of water flow through the vitrectomy system. Using the cutter did not affect flow rate of water but flow of egg white could only be achieved with the cutter in the on position. Residents most comfortably sustained plunger pull of 0.7 kg for 3 minute intervals. At this level, a 3 mL syringe achieved egg white flow rate of 4 microliters/sec of egg white through the cutter-enabled vitrector.
Portable vitrectomy devices can use syringes to generate vacuum. Different sized syringes obtain varying levels of flow for a given plunger pull force. Guillotine cutting is necessary to aspirate egg white, which was used to simulate vitreous. Residents can comfortably maintain plunger pull of 0.7 kg, which results in flow of 4 microliters/sec through the portable vitrectomy system. Surgeons should consider individual clinical situations including length of procedure and desired flow rate before selecting syringe size.
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