This publication discuss different automatic infusion techniques and their basics. Different parameter of automatic infusion techniques are shown and listed in a summary table.
CONTENTS
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
Bibliography
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
Frequently asked questions
What is the main topic discussed in this document?
This document discusses automated infusion technology, including hydrostatic pressure, different types of infusion pumps, and their applications.
What is hydrostatic pressure and why is it important in infusion technology?
Hydrostatic pressure is the pressure generated by the weight of a fluid. In infusion technology, particularly in gravity feed infusions, it's the force that drives the intravenous solution into the bloodstream. The pressure depends on the height of the fluid column (intravenous solution) and the density of the solution.
How is hydrostatic pressure calculated?
The hydrostatic pressure is calculated using the formula: p = ρ * g * h, where p is the pressure, ρ is the density of the fluid, g is the gravitational acceleration, and h is the height of the fluid column.
What is the central venous pressure (CVP) and why is it relevant?
The central venous pressure (CVP) is the average pressure in the large veins near the heart, approximately equal to the pressure in the right-hand arterial. It represents the stretch resistance of the venous system and is influenced by blood volume. When administering infusions, the hydrostatic pressure must be greater than the venous pressure for the solution to flow into the bloodstream.
What is the typical height for suspending an infusion bottle in gravity feed infusions?
The suspension height for an infusion bottle or bag in gravity feed infusions is typically between 800 mm and 1500 mm. Clinically, a height of 900 mm above the insertion point in the vein is commonly used to ensure reliable overpressure and account for transition and flow resistances.
What are the advantages of using automated infusion equipment?
Automated infusion equipment offers several advantages, including increased infusion pressure, adjustable velocity and volume, continuous monitoring, and automatic alerts for fluctuations. It also enhances patient safety through monitoring sensors (air, feed pressure) and reduces the need for intensive manual monitoring, allowing nursing staff to focus on other tasks.
What are the different types of automated infusion equipment mentioned in the document?
The document mentions several types of automated infusion equipment, including gravity feed infusion with infusion control, infusion pumps with rotating peristaltic feed, infusion pumps with linear peristalsis, infusion pumps with volume chamber, and syringe pumps.
What are the two main types of regulation for infusion?
The two main types of regulation for infusion are drip-controlled infusion and volume-controlled infusion.
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- Dipl.-Ing. [FH] Thomas Lekscha (Author), 2009, Processing of a summary of basic principles to the automated infusion technology with the juxtaposition of technical parameters of frequently used infusion pumps, Munich, GRIN Verlag, https://www.grin.com/document/121775
