Processing of a summary of basic principles to the automated infusion technology with the juxtaposition of technical parameters of frequently used infusion pumps

Essay 2009 25 Pages

Medicine - Biomedical Engineering



Automated Infusion Technology

Hydrostatic pressure

Automated Infusion

Gravity feed infusion with infusion or drip control

6 Infusion pumps with peristaltic feed

8 Infusion pumps with volume chamber

Syringe pumps

Comparison of different automated infusion pumps


Table list

List of Illustration

Formula symbol and explanation

Hydrostatic pressure

The hydrostatic pressure is the pressure generated by the weight force of a fluid. Hydrostatic pressure plays a major role within the scope of infusion technology. A typical area of application is for gravity feed infusions. During the course of a gravity feed infusion, the intravenous solution is administered into the human bloodstream by means of the pressure of a water column (intravenous solution). The hydrostatic pressure generated relates to a force which is applied to a cross- section area. In the case of hydrostatic pressure, the force equates to the weight force of the fluid. As a result, hydrostatic pressure is also referred to as the gravitational pressure of the fluid.

The equation for determining the hydrostatic pressure is:

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Figure A.1 [1]

Illustration of the hydrostatic pressure using the example of gravity feed infusion.

Figure A.1 illustrates the application of hydrostatic pressure for an infusion in a vein in the arm of a patient lying down. The hydrostatic zero point corresponds to the zero point of the right-hand arterial. The distance “h” relates to the height difference between the indwelling cannula and top fill level of the infusion bottle.

The pressure “p” relates to the pressure at the indwelling cannula or the pressure needed in order to administer the intravenous solution. To apply the infusion, it must be greater than the counter pressure applied by the blood vessel (venous pressure).

During administration of a gravity feed (drip) infusion, the cross-section area or pressure area of the intravenous tube has no function. The pressure is purely dependent on the height difference and the density of the intravenous solution.

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p = pressure in the fluid column (intravenous solution)

F = force (weight force)

m = mass of the fluid (intravenous solution)

g = gravitational acceleration

A = cross-section area (intravenous solution)

h = height of the fluid column

ρ = density of the fluid (intravenous solution)

The cross-section surface on which the fluid column acts is omitted when considering the hydrostatic pressure (hydrostatic paradox). The equation verification above clearly indicates that the height difference is the decisive parameter with regard to the altering the pressure of gravity feed infusions.

If the intravenous solution should be administered in a blood vessel, the hydrostatic pressure must be greater than the venous pressure. The average pressure in the large veins near the heart is referred to as the central venous pressure (CVP).

It corresponds, approximately, to the average pressure in the right-hand arterial. This pressure is dependent on the stretch resistance of the venous system and, in particular, on the size of the blood volume.

This pressure is measured by means of a central venous catheter which enables the average venous pressure in the right-hand arterial to be established by an indirect measurement of the blood volume. The height of the right-hand arterial is identical to the hydrostatic zero point.

The average venous pressure in an arm vein of a healthy patient in a lying position is specified in most literature at 4 to 7 mm Hg [2].

The hydrostatic pressure of the gravity feed infusion must overcome this pressure in order for the intravenous solution to flow into the bloodstream.

Average vein pressure

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Figure A. 2 [2]

Illustration of the venous pulse and average venous pressure at the vena jugularis of a patient in a lying position.

The shape of the venous pulse reflects the trend of the pulse pressure in the right artery.

The average blood pressure in the arterial system is composed of a hydrostatic and a hydrodynamic part. The hydrodynamic part (also referred to as the dynamic pressure) results from the relatively high flow velocity in excess of 100 cm/s to max. 1 m/s (aorta) [2] [3].

Within the venous system, on the other hand, the hydrodynamic part of the pressure can be ignored due to the low average flow velocity of 0.05 cm/s [1]. The average venous blood pressure is mainly a result of the function of blood being filled to the low pressure system and is sometimes referred to as the average fill pressure.

By applying the equation (1.19) for hydrostatic pressure previously described, the suspension height of an infusion bottle or bag (Figure A.1) can be calculated for gravity feed infusions.

If it is necessary to feed an infusion against an average venous pressure of 7 mm Hg, a minimum height difference of approx. 100 mm is necessary in an ideal situation (no transition resistance).

However, if it is necessary to feed an infusion against an arterial pressure of 70 mm Hg, a minimum height difference of approx. 1000 mm is necessary in an ideal situation (no transition resistance). These height differences were calculated with an intravenous solution density of 1 g/cm3 and a gravitational acceleration of 9.81 m/s2.

The suspension height of the infusion bottle or bag can be selected between 800 mm and 1500 mm. To ensure a reliable overpressure for gravity feed, the infusion bottle is normally held 900 mm above the insertion point in the vein. These height specifications have proven successful in everyday use in clinics.

The specifications take any possible accumulative transition and flow resistances (tube system, valves, indwelling cannula, etc.) into account.

If larger volumes of an intravenous solution must be administered in a relatively short time, a much higher working pressure is required. In order to achieve these pressures, gravity feed infusions are highly restricted due to the suspension heights necessary for the bottles or bags.

Automated infusion

The use of automated infusion equipment provides a situation where it is not only possible to increase the infusion pressure but also to adjust, administer and monitor the velocity and volume of the infusion. Predefined parameters can be continuously and automatically monitored and, in the event of fluctuations, an acoustic and/or visual warning can be issued.

A major advantage of automated infusion systems is the increased safety of the patient due to various automatic monitoring sensors (air, feed pressure). Since intensive manual infusion monitoring can be dispensed with through implementation of semi-automatic and electronic monitoring equipment, human resources (nursing staff) can be deployed for other important tasks within the everyday running of a clinic.

Automated infusion systems are generally arranged according to their application technology. The most frequently used infusion equipments are:

- Gravity feed infusion (drip feed) with infusion control
- Infusion pumps with rotating peristaltic feed
- Infusion pumps with linear peristalsis
- Infusion pumps with volume chamber
- Syringe pumps.

Another method of arrangement is according to the type of regulation of the infusion. A distinction is made between two relevant methods:

- Drip-controlled infusion
- Volume-controlled infusion.


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Title: Processing of a summary of basic principles to the automated infusion technology with the juxtaposition of technical parameters of frequently used infusion pumps