IV Pumps

IV Pumps are machines that deliver liquid medications through a needle into a patients veins. These are usually rugged little machines capable of withstanding a lot of abuse. Preventive Maintenance normally consists of measuring flow rate, delivery accuracy, proximal and/or distal occlusion pressure. To the biomedical technician we are generally concerned with setting up whatever analyzer we use and monitoring the numbers we get. We program the pump for 10 ml and our analyzer says we got 9.96 ml. All other tests have passed and we’re good to go. For those who would like to know a little more about what some of the terms used with IV pumps mean read on.

Occlusion pressure occurs when the IV delivery tubing gets twisted, clogged or otherwise kinked preventing flow. There are two places where the delivery tube can get messed up. The first is upstream between the IV solution bag and the pump itself. This is called the proximal area of the pump. The most common reason for proximal occlusions is a tubing clamp that was overlooked during setup. The next one is called the distal area and is between the pump and patient. This area is more critical than the first for several reasons.

Because this end is physically attached to the patients vein it is necessary that the IV needle is securely attached to the patient. The human cardiovascular system operates at a specific pressure. The heart is pumping blood through our bodies under fairly substantial pressure. We are also pumping fluid in from the IV pump. The IV pump must be able to recognize when the pressure in the vein is dangerously critical. Every IV pump has a specified area of pressure that will activate an alarm and shut the pump mechanism off instantly.

One thing most IV pumps cannot do well is detect infiltration of fluid. Infiltration is a medical term describing when fluid leaks into surrounding tissue of the body. There are numerous physiological conditions with a patient that can make them more susceptible to infiltration. Basically what is happening is that the fluid is being pumped into the body at a specific baseline pressure and the infiltration occurs at a small pressure. As an example assume we have a garden hose spraying water. If we insert a small sponge into the hose it will quickly absorb the water before becoming saturated and letting it escape.

The human body tissue is acting as a sponge during infiltration and slowing the infused solution down as it enters the vein. There is a pressure differential going on but if the IV pump is set at a low infusion rate of say 10 ml/hr the body tissue may be able to absorb this at a fast enough rate that the IV pump does not recognize the resultant back pressure. No alarm may occur because the occlusion alarm pressure setting has not been reached. This applies directly to the sensitivity of the pump pressure transducer.

Another term used with IV pumps is VTBI which stands for Volume To Be Infused. This is simply how much you want to pump through the machine. Rate is another term which is fairly self explanatory: How fast do you want it to pump? Titrate is a term used when a cassette is loaded with an additional syringe of different medication. For example a bag of Sodium is the primary delivery agent and on top of the cassette a syringe full of glucophage or other drug is added. Titrate literally means to add one solution to another in specific increments while monitoring the outcome and looking for a specific reaction. In this case the reaction expected would be lowering the blood sugar level to the patient to a level determined by the physician, once the proper mixture rate has been determined through the titrate function. Most IV pumps also have a back-prime function which allows the user to prime the cassette and remove all air bubbles before attaching it to the patients catheter.

Common ailments in the biomedical shop usually take the form of mechanically broken parts. Cassette doors get snapped off, AC plugs get yanked out of the wall instead of being gently removed which separates wires in the end of the plug, and of course every biomeds favorite complaint “I accidentally dropped it”. I have seen this on defective stickers attached to every type of equipment not just IV pumps. Sometimes I have read it and wonder “OK, they dropped it…but down which elevator shaft or from what 4th floor window did they drop it?” Battery power not working is another complaint. More often than not it’s because the pump was not plugged in long enough to recharge the batteries.

I like those kind of fixes, plug it in to the power strip on my desk and return it the next morning after a 30 to 45 minute check on battery power only. Find an empty closet and plug it in to recharge from the test I just gave it. Pump mechanisms do occasionally fail and have to be replaced. Depending on the manufacturer this can be a simple thirty minute job or a half day affair. I don’t think there is a biomedical technician anywhere that hasn’t wished that just once the engineers that design this stuff would have to work on them.