What problems have you had with using force gauges with the 3X00 series Joe?
We find they are useful for checking consistency of force/occlusion threshold, limiting the maximum force produced by the syringe drivers, which is ultimately what has the potential to generate damaging pressures at the cannula when an occlusion occurs. We try to ensure consistency by running-in the mechanics to minimise losses in the mechanism and calibrate without syringe-induced losses hopefully, if anything, to give an overestmate rather than an underestimate of the equivalent occlusion pressure that could be attained when in use.
In syringe manfacturing standards the variation allowed in syringe stiction is something equivalent to 3kgf I think so I can't see how calibration using a syringe is reliable unless the syringe is well lubricated to reduce stiction to a negligible value and a standard extension line is used.
Without use of a force gauge we've found it very difficult to setup 3300's for use with pre-filled syringes - the operators suffer with nuisance alarms if we use wet setup since inconsistencies at calibration cause problems. I think Jim Lefever at the MHRA has suggested, as I have previously mentioned being described in a letter published in a journal, that increasing the force is a way reduce the incidence of nuisance alarms on these pumps.
We set to 5kgf (tolerance 4.5kgf to 5.5kgf in the Graseby manual) and our nuisance alarms due to occlusion disappeared. Anyhing lower than 4.7kgf caused occlusion alarms - I assumed/have established that variability in the syringe stiction was the predominant factor along with the relatively fixed characteristics in the line/anti-syphon valve. We couldn't have reliably measured/examined/set these maximum acceptable occlusion thresholds without the force gauge.
When measured, carefully, using wet setup and well lubricated BD50 syringe this force equates to pressure values that are within the equivalent Graseby specification at occlusion. If a "sticky" syringe is fitted then the pressure losses will be higher thus occlusion pressure measured at the cannula will tend to be lower. This is safer, in my view, than calibrating occlusion thresholds with a "typical", potentially "sticky", syringe, at a particular pressure value, given a particuar syringe characteristic, then when a "loose" syringe is fitted in use then there is the potential for higher occlusion pressures, above the maximum acceptable value, to be generated.
My thinking is that if the maximum force generated by the pump is consistent at a value that produces equivalent, acceptable, occlusion pressure thresholds (for a given syringe type/line) via calibration using a force measurements then it's better than setting occlusion alarms using a wetsetup that's inconsistent and unpredictable (using a syringe/line setup that gives unpredictable results). Worst thing that can happen is you get nuisance occlusion alarms - this is more acceptable than excessive occlusion pressures than could cause injury.
Repeatable wet setup calibration is only possible, in my view, if you measure stiction (a rough test can be done by releasing the syringe actuator under pressure and seeing what residual pressure is indicated on the test manometer, at rest, after the plunger is forced back out of the syringe body - and this is only a guide) or reduce it to a minimum by lubricating the syringe well. Either way the stiction then needs to be added to the pressure measured at occlusion to give an indication of the potential pressure that could be generated given an ideal stictionless syringe - however this still does not include the pressure gradient in the line (that is probably negligible as occlusion is approach and flow approaches zero, anyhow).
The problem is always going to be finding the occlusion pressure to force relationship for typical syringes used on these pumps and the pressure gradients in the line at different rates, with different viscosity of fluids and various check-valve/cannula-gauge/anti-syphon arrangements. A selection of sizes and manufacturers syringes may be used in different hospitals so this may complicate the issue. Perhaps I need to go on a 3X00 refresher course to se how it is done these days.
