Electromechanical pumps

Last updated: Friday, March 05, 2021

Compared to gravity infusion, electromechanical pumps enable drugs and fluids to be administered with more precise control. They are required in a range of scenarios such as when using drugs with a short half-life (e.g. noradrenaline, heparin), a narrow therapeutic margin (e.g. phenytoin) and those where a variable infusion rate may be required (e.g. insulin). Some are intended to be used at the bedside, whilst others are designed to be worn on the patient enabling them to move around.

Safety features of electromechanical pumps include alarms to detect resistance to flow (e.g. if the intravenous administration line becomes blocked) and to alert the user when the infusion has finished. Some may also be pre-programmed with the usual administration rate for a range of drugs (a 'drug library') to try to avoid errors arising from manual entry; you may hear these called 'SMART' pumps. 

In practice you are most likely to encounter syringe pumps, volumetric pumps and elastomeric pumps

1. Syringe pumps
The plunger of the syringe is pushed forward by the pump at the programmed rate
These are used in a range of patients such as those requiring critical care in hospital to those with a palliative illness living at home. They are intended to deliver small infusion volumes at low rates, typically from around 5mL up to 60mL at less than 10mL/hour. 

The prescribed medicine(s) is drawn up into a syringe and this is placed in the pump. The pump then pushes the plunger of the syringe forward in tiny increments delivering the contents to the patient. At higher flow rates, the administration of the infusion appears to be continuous, maintaining steady plasma levels of the drug. At very low flow rates such as those used in neonates, these small incremental movements mean that the drug is not delivered smoothly and plasma levels of the drug may rise and fall. This matters for drugs with short half-lives such as inotropes where these fluctuations in plasma levels may be clinically significant. 

In a critical care setting syringe pumps may be used to deliver a range of medicines including inotropes and anaesthetics. Care is required when syringes are replaced to ensure that adequate plasma levels of the drug are maintained. This is especially important for drugs with short half-lives, again such as inotropes. If you are not working in critical care, you may see syringe pumps being used to administer drugs such as insulin, heparin and furosemide.

You can read more about the use of syringe pumps ('syringe drivers') in a palliative setting in the Palliative care topic. 

2. Volumetric pumps
A peristaltic pump delivering a large volume infusion
There are several types of volumetric pump; the one used most commonly is a peristaltic pumpThey are designed to deliver large infusion volumes (e.g. 50 to 3000 mLs) at medium to high rates (e.g. 5 to 50mL/hour) The infusion container is hung above the patient, and an administration set is attached. The administration line is then fed through the pump, and a series of rollers 'squeeze' the line to push the infusion fluid to the patient. 

They are commonly used to administer infusion fluids with additives (e.g. potassium chloride) and drugs (e.g. vancomycin, amiodarone) in adults and older children. They are used in neonates but syringe pumps should be used when strict control over administration rate is required.

3. Elastomeric pumps 
These are single use non-electronic pumps. They are generally designed for patients to use at home as they are small and portable. They are used to deliver medicines where accuracy of the administration rate is less critical such as with antibiotics and chemotherapy. They vary in size from around 100mL to 500mL. The pump contains an elastomeric balloon (surrounded by a protective cover) that is stretched when filled with the medicine. As the balloon deflates the drug is pushed out and into the patient. A 'flow restrictor' on the administration set controls the infusion flow rate.

Electromechanical pump calculations
With electromechanical pumps the rate of administration may be expressed in various formats including mL/hr, mg/kg/hr and micrograms/kg/min. 
For example, a 70kg patient is prescribed dopamine 10 micrograms/kg/min through a central intravenous administration line. The concentration of the infusion to be given is 400mg in 100mL 5% glucose. 

Firstly calculate the dose of dopamine the patient requires per minute
70kg x 10 micrograms/kg/min = 700 micrograms per minute
Then convert the concentration of the dopamine infusion to micrograms per mL
400mg in 100mL = 4mg in 1mL = 4000 micrograms in 1mL
Finally calculate the rate of the infusion
700 micrograms per minute/4000 micrograms per 1mL = 0.18mL/min
Now over to you. 
Your 60kg patient is prescribed dobutamine 20 micrograms/kg/min. The infusion concentration is 5mg/mL. Calculate the administration rate in mL per minute.  Click to reveal the answer.
Firstly calculate the dose  required per minute 
60kg x 20 micrograms/kg/minute = 1200 micrograms per minute
Then convert the concentration of the infusion to micrograms per mL
5mg in 1mL = 5000 micrograms in 1mL
Finally calculate the rate of the infusion
1200 micrograms per minute/5000 micrograms per mL = 0.24mL/min

The calculated administration rate is entered into the infusion pump.

Safety concerns with infusion devices 
The MHRA receives many reports of incidents involving infusion pumps, with a significant amount resulting in patient harm or death. The majority of serious problems relate to over-infusion of drugs and user error is often a contributing factor. Training on infusion devices is essential, as well as rationalising the infusion devices used within an organisation and having a centralised equipment library.