Section 10 • Delivery Rate Accuracy
57
SECTION 10 - DELIVERY RATE ACCURACY
The ambIT
®
PIB
v1.5
pumps are pseudo-continuous, positive displacement pumps. This means
that the pump infuses a specific amount of fluid (0.050 ml) each revolution. The cassette is the
pumping mechanism and the pump is the driver. The pump counts the number of revolutions
and time between revolutions. For each milliliter (ml) to be infused the pump needs to infuse
twenty (20) 0.050 ml shots. The shots or revolutions are spread out over the desired time period
to create the correct infusion rate. For a one (1) ml/hr infusion, one of the twenty (20) shots
occur every three minutes. This means that volumetric or flow-rate accuracy is dependent on
three major things:
1.
The volume infused each time the cassette makes a revolution
22
.
2.
The time between each revolution
23
.
3.
The counting and displaying of revolutions (i.e., the display shows the correct infusion
history information).
The easiest way to test all three items is to connect a cassette to the pump and verify that the
pump readout and the amount pumped are the same. It was the objective of the volumetric
accuracy testing to show that the pump was volumetrically accurate for minimum (0.1 ml/hr),
maximum (20 ml/hr) and median (10 ml/hr) basal flow rates, as well as over the full range of
bolus/dose volumes by testing 0.1 ml, 25 ml, and 50 ml boluses/doses.
The cassettes and pumps were set up as described in the clinician manual (see set up of fluid
reservoir, cassette and pump on inside front cover) using a collapsible medication bag (Summit
MediBag). A second fluid reservoir (Summit MediBag) was used to represent the patient and
collect the output from the pump. Catheters
24
and needles
25
were used to simulate the back
pressure that would normally be seen during an infusion. Volumetric accuracy was determined
by weighing the inlet bag before the infusion started and then again after the infusion was
complete. The difference in weight was converted into volume, based on density. The volume
removed from the inlet-fluid reservoir was compared to the reading on the pump display to
determine the pump’s accuracy.
As a positive displacement pump, the pressure generated by the pump changes as necessary
to provide the set flow rate. If the pump is programmed per guidelines set by the drug
manufacturer and/or by following appropriate clinical practice, the volume infused by the
pump will be within the range tolerated by the body of the patient.
The Perifix
®
catheter was chosen as the test catheter because of the gauge size and because
the three outlet holes provided a greater back pressure than an open-ended catheter (IV) or a
multi-hole (> three hole) fenestrated catheter. The needles were used to show that with very
low back pressure the volumetric accuracy is not affected.
22 It is important to note that the volume infused each time the cassette makes one (1) revolution is independent of the pump
and is completely dependent on the cassette.
23
The timing was validated during the software development and validation. The volumetric accuracy testing verified the
timing for the three flow rates and three bolus/dose volumes.
24
B.Braun Perifix
®
epidural catheters 20-gauge were used. Perifix
®
is a trademark of B.Braun.
25 20-gauge EFD ultra dispensing tips.
