Syringe Pump Working Principle


Proper medication is the key to fast recovery, and yet we tend to be negligent with our doses and medication schedule. In some cases, small and continuous doses of specific medicines have shown significant improvement in the condition of the patient, as compared to discontinuous supply. However, achieving that would take an increase in the staff and a lot of precision which cannot be achieved by humans. To solve this problem, syringe pumps were developed as a modification of infusion pumps. These syringe pumps are known to administer accurate and controlled continuous doses of the medication to the patient. Their application is not just limited to humans but animals as well. It is also used to feed a sick newborn for whom, intra-venous passage would be dangerous. These devices have revolutionized the field of medication delivery and continue to do so with further technological advancements.

What is a Syringe Pump?

A syringe pump is a motorized device that is designed to accurately control the continuous delivery of drugs or fluid at a predetermined rate from a syringe by inserting the plunger steadily. They contain a maximum volume of 50 ml and therefore are used to deliver the medications at a small hourly volume. This volume usually ranges from 3-6 ml per hour. For more significant hourly volumes to be administered, an infusion pump is used. It also helps to keep the syringe steady on the body of the pump unit so that the motor is the only moving component. It is very rarely used for the withdrawal of fluids as well and has various versions ranging from manual to fully automated, where all the actions are performed in a sequence by the machine itself. They are widely used for medical and research purposes.

A Brief History

Syringe pumps have been in use for more than 50 years, but they were originally developed as a modification of the infusion pumps for controlled delivery of small amounts of drugs. Christopher Wren was the pioneer of the idea who invented the first infusion pump in 1658. He faced a lot of technical limitations with the initial designs and the government was not supportive of his ideas as well. This slowed down the development of these pumps thereafter until the new prototypes started emerging in the 19th century. In 1950, an infusion pump was used for the first time, for the chemotherapy of a patient.

Between the 1970s and 1980s, smaller and more practical ambulatory pumps came into the market that became popular with patients because of their portability and wearability. It was around that time when the idea of a smaller syringe pump was popularised in the market for hospital and research use. Dean Kamen invented an ambulatory pump for diabetic patients for insulin administration, and that was a major breakthrough for infusion pumps. These pumps were smaller and more cost-effective.

The late 1980s and 1990s saw a fast-paced development in the infusion pump industry. With computerized pump advancements and a decrease in pump size, efficient enhancements were made.

Computerized pump advancements, efficiency enhancements, and pump miniaturization in the 1980s and 1990s increased infusion devices’ use in research. In particular, combining ambulatory technology with PC communications helped researchers identify and troubleshoot problematic pump performance. Researchers were able to diagnose problems with pumps by combining ambulatory technology and PC communications.

The early 2000s saw the development of ‘Smart Pumps’ and automatic features that increased accuracy, controlling the dosage and remote programming. These syringe pumps have increased patient safety and broadened their usage in the domain of research.

Parts of the Syringe Pump

The parts of a syringe pump vary according to the model and the manufacturer of the pump, but the most commonly found components are as follows:

Syringe Pump

  • Syringe Retainer Bracket: helps to hold the ‘Syringe Barrel Flange’ in place so that it does not move the barrel while the fluid is being administered. The barrel flange is the wide area at the end of the barrel of the syringe as shown in the diagram below.

  • Syringe Holder Block: It is a V-shaped notch where the string is placed.
  • Syringe Clamp: holds the string tightly in the holder block so that it does not move when the pressure is applied. The clamp has to be lifted to place the syringe and secured after.
  • Control Panel: contains programming controls to adjust the rate of infusion and other functions of the pump. It also contains some LED indicators to describe the status of the machine.
  • User Interface: Displays all the information about the amount and the rate of the infusion set by users.
  • Drive Screw: It is also known as the lead screw. This screw is driven by the pump motor and passes through a brass nut block inside the pusher block. Its function is to push and pull the pusher block and consequently, the syringe plunger flange as well.
  • Pusher Block: captures the syringe’s plunger flange. It is linked to the drive screw that guides its movement and is supported by the guiding rods.
  • Guide Rod: There are two guide rods in a syringe pump, one on each side. Using guide rods prevents the pusher block from skewing under mechanical loads.
  • End Plate: Provides support for the drive screw and the guide rods.
  • Anti-Siphon Plate: The syringe has a tendency to withdraw the plunger when under vacuum pressure. The anti-siphoning plate prevents that from happening.
  • Anti-Siphon Plate Adjustment Knob: The plunger flange of the syringe is tightened with the adjustment knob.
  • Syringe Retainer Thumbscrew: They are two on each side of the machine and secure the Syringe Retainer Bracket.
  • Drive Nut Button: This button is connected to the brass nut block which is guided by the drive screw. It prevents mechanical and electrical damage to the pump.
  • Pump Motor: A micro DC or ‘Stepper motor’ is used for the syringe pump. Its function is to drive the plate, pushing the plunger which administers the fluid from the syringe.
  • Power Switch: To turn the pump ON/OFF.

Syringe Pump Working Principle

The basic working principle of a syringe pump is that it converts the rotary motion of the motor in the pump to the reciprocating motion of the piston of the syringe. The syringe, which works on Boyle’s Law principle is fit into the syringe pump. The motor of the syringe pump drives the movement of the piston, guided by its driver, a screw rod, and the reciprocating screw. The screw is connected to the piston in the syringe. The syringe contains the medication to be administered. In the automatic versions, the pressure and rate are set according to the dose set, and hence the motor only acts on that amount, leading to smooth pulsating pressure. This is called the ‘Thread Row Mechanism’ because of the interconnection of all the parts of the machine driving one another.

How to Operate a Syringe Pump

  • Start by placing the syringe pump on a clean level surface.
  • Take the prepared syringe that is loaded with the required amount of drug solution.
  • Release the knobs and the clamps/locks before inserting the syringe.
  • Keep the piston of the syringe over the side lock and adjust the syringe till you hear a click.
  • Lock the syringe into place by securing all the clamps and knobs.
  • Connect the pump to the power supply and turn it on.
  • Enter the flow rate using the number keys on the control panel and select the direction of the flow.
  • Connect the feeder tube to the patient before pressing ‘Start’.
  • Connect the feeder pipe to the stopcock.
  • Press start, then document the time and quantity with which the infusion was started.

Types of Syringe Pumps

  • Single Syringe Pumps: These pumps control one syringe at a time and can be used either to infuse or withdraw fluid continuously, or provide a pulse flow. This pump is ideal for more complex multi-step dosing and has a multimode operation.

  • Double Syringe Pumps: These contain two syringes used for the precise delivery of two different but mixed solutions. It can also be used for administering an emulsion of two immiscible liquids. Dual syringe pumps can also be used to deliver only one solution when they are combined with check valves and solvent reservoirs. The two syringes can work independently of each other. It is further possible that one syringe is used to infuse while the other is used to withdraw the fluid simultaneously.

According to another classification, they are also categorized as:

  • Medical Syringe pump: This syringe pump is used in hospitals to deliver controlled amounts of medications to patients. They can also be used for in vivo diagnosis. It comes with a lot of safety features like a wide range of alarms to prevent any injury to the patient from air bubbles or other possible hazards.

  • Research Syringe Pump: These devices are used in research laboratories where accurate but small amounts of fluid are required. The OEM module syringe pump and high-pressure syringe pump are some examples of Research syringe pumps. They also have an option for pulseless flow but are not fit for patient use.

Advantages of the Syringe Pump

  • Avoids any fluctuations and provides a continuous flow of medication that can greatly affect the health of the patient.
  • The pressure and time of the administration of the drug can be set, and hence it gives more control to the practitioner.
  • They are very precise and can deliver really small volumes as well which would be difficult to do manually.
  • They can be connected to computers to maintain a record of the infusion procedure.
  • High-viscosity fluids can also be delivered with ease.
  • They are widely useful in the research field in precisely dosing systems, or in accurately delivering reagents, mixing minuscule volumes, and adding traces of specific chemicals during the experiment.
  • Beneficial for patients who cannot take oral medications or those who are disabled in mobility.
  • Effective patient care with an inbuilt heater for temperature control.
  • It is very economical
  • Useful in providing nutrition to sick newborn children

Limitations of the Syringe Pump

  • The user interface problem may result in failure to maintain the infusion record.
  • It is prone to electrical and mechanical failures.
  • In some devices, there is no fluid overload indication, which can be potentially dangerous.
  • Lack of flow continuity can lead to delays in the treatment or therapy.
  • Syringe pumps have low volume capacity. A separate infusion pump has to be used if large volumes have to be administered.

Maintenance of the Syringe Pumps

  • The contact services should be cleaned properly with a clean and dry cloth.
  • The lead screw and the guide rods should be free of any debris.

  • Lubricants should be applied regularly along the lead screw and guide rod.
  • No air bubbles should be left in the connecting pipes
Tanu Neb
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