Is it OK to Infuse Several Animals at Once with a Multi-syringe Pump?

Some laboratory syringe pumps have a built-in two-syringe rack; others can accommodate racks so that one pump can push four, six or even 10 syringes at the same time. Syringe pumps can be expensive, so it’s tempting to have a pump that can multi-task. What are the downsides?

There are four big ones, and we will discuss them here so that you can decide if the tradeoffs are worth it.

1. No pressure sensor or occlusion alarm. At Instech we believe that any time you are infusing a live animal in an experiment that has a chance of an occlusion, you must have a pump that will prevent dangerous pressures - anything over 20-30 PSI - from building up. Ideally the pump will have a pressure monitor as well so that you can see when pressures are starting to rise, letting you take action before the alarm is tripped. Without this you are flying blind, risking animal safety, ruptures of your infusion lines, and the accuracy of your data.
   
   To sense an occlusion the pump needs to monitor the force it takes to push an individual syringe. This is not possible with a multi-syringe pump. These pumps are designed for the enormous forces required to drive multiple large syringes with viscous solutions. For example, the Harvard PHD Ultra pumps can generate 75lbs of force. When one of the syringes on a rack is occluded, all of the pump's force will be brought to bear on that syringe. If it's a 1mL syringe that's 2800 PSI; even a 10mL syringe will generate 300 PSI with this pump, enough to rupture almost any infusion set.
   
   For us, this is by far the biggest tradeoff, and the reason we have designed our new model 400 syringe pump to hold only one syringe.

2. If one animal has a problem, all animals suffer. If you do have to step in to stop the pump because of an issue with one animal, you are stopping it for all, which may impact your data, and possibly force you to rerun the experiment.

3. Difficult to run weight-based infusions. Many doses are specified in mL/kg/hr. If you are using a multi-syringe pump, all your animals will get the same volume at the same rate, so unless your animals all weigh the same you will be compromising on dose accuracy. In theory you could vary the concentration in each syringe, but the labor to do this and added chance of error will quickly outweigh the savings on the pump.

4. Varying or larger than needed dead volumes. Invariably some cages are closer to the multi-syringe pump than others, so you will either have infusion lines of different lengths or you’ll have to pick a single length based on the furthest cage. If you have varying lengths you’ll need to pay attention to the way you prime the lines so that the timing of your doses are consistent, and this gets particularly difficult if you are changing syringes mid-study from test article to saline, for example, or one dose to another. If you have a longer line than necessary you could be wasting precious test article. The best set up is to have one pump per animal, as close as possible to the cage to minimize dead volume.

How much will you save by using a multi-syringe pump? Here is a chart comparing Harvard Apparatus pumps to the Instech model 400 with 2026 prices.

In summary, you need to decide whether the lower upfront cost of a multi-syringe pump is worth sacrificing the other benefits over all the studies you will conduct with the pump.