Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-09-07
2002-04-09
Sykes, Angela D. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S067000, C604S225000, C604S224000, C222S309000, C222S390000
Reexamination Certificate
active
06368314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to the monitoring of the pressure of a product fluid to be administered in dosed amounts during infusion or injection.
2. Description of the Related Art
During infusion or injection of a product fluid, the exact dosing of the administered product is of large importance, especially upon dosed administration to humans. If the administration is largely automated, as, for example, in insulin treatment with portable infusion pumps, monitoring of the proper product administration is desired, if not a must. A significant possibility for the monitoring is the monitoring of the product fluid pressure, since during proper functioning of the mechanical and electronic components of an infusion or injection apparatus, a proper product administration can be inferred as long as the fluid pressure remains within a preselected pressure range. Upon noncompliance, an occlusion or leakage in the fluid guide system can be inferred. Leakages and occlusions present a risk, especially during the automated administration of active substance solutions in the medical or veterinary field because of the danger of non-detection or detection too late.
Infusion pumps wherein the pressure of the product fluid to be administered is monitored in order to detect blockages in the fluid guiding system are known, for example, from U.S. Pat. No. 4,562,751, and WO 96/27398. These two references relate to infusion pumps wherein a product fluid is conveyed from a container containing the product by displacement by means of a piston. The piston is linearly displaceable in the container and is driven by a spindle drive positioned parallel to a displacement axis of the piston. A spindle drive element is mounted in the housing of the infusion pump for rotation around its longitudinal axis and supported for displacement in direction of its longitudinal axis. A nut which acts as a driven member and moves on the spindle is secured in the housing against rotation and coupled with the piston in such a way that it moves the piston along during its own linear displacement.
With its free end on one end surface, the spindle according to U.S. Pat. No. 4,562,751 engages a thrust switch which upon exceeding of a threshold pressure stops the pump. This threshold pressure is reached when the piston is not moveable in the container or only with excessively large force. In such a case, the spindle because of its rotation in the nut, moves opposite the displacement direction of the piston and against the thrust switch.
It is mentioned in WO 96/27398 as a disadvantage of such type of pressure monitoring that upon use of such a high pressure limit switch, an occlusion is not indicated in time, since, first, several product dosages, which should have been administered in series, must so to speak accumulate in order to build up the threshold pressure for the switch. The WO 96/27398 suggests the use of a force sensor instead of the use of a high pressure limit switch, which force sensor outputs a signal which is proportional to the measured force and, thus, the fluid pressure in the container. The pressure monitoring consists of detecting the fluid pressure by the force sensor at two different points in time by measuring of the reaction force exerted by the piston during its advance in the container, and comparing the two signals output by the force sensor with one another. Therein a first measurement takes place during administration of the product fluid and a second measurement later before administration of the subsequent product dose. If a preselected difference between the two signals is not reached, an occlusion is indicated and an alarm signal activated. If the difference exceeds the preselected signal difference, this then indicates that the pressure in the container has fallen, and that product fluid is in fact administered in the required manner. This type of pressure monitoring takes substantial time. Furthermore, only occlusions are detectable.
SUMMARY OF THE INVENTION
It is an object of the invention to enable a pressure monitoring of a product fluid to be administered in dosed amounts during infusion or injection wherein malfunctions are detected as quickly and reliably as possible.
The invention is based on a monitoring of the pressure of a product fluid to be administered in dosed amounts during infusion or injection wherein the product fluid is dispensable or dispensed from a container by advancing a piston received in the container. The product fluid is understood to be especially a liquid solution of an active substance. The container is received in a housing or formed by the housing itself. As measure of the fluid pressure, a reaction force is measured which is exerted by the piston during advancement and is fed to a control for a drive of the piston. The control compares this measured reaction force with a preselected reference force and controls the drive of the piston in accordance with the comparative results resulting therefrom.
In accordance with the invention, the reference force is a nominal value for the reaction force and a direct nominal/actual comparison is carried out between the measured reaction force and its nominal value. This at least one nominal value is stored and can always be recalled by the control for the purpose of the nominal/actual comparison for comparing it with the actual reaction force measured during a dispensing operation, especially an administration or priming. The reaction time in case of a malfunction determined during the monitoring can be held as short as possible by the control making the direct comparison between the actually measured reaction force and its nominal value, i.e., measuring the difference between nominal and actual.
Preferably, the control only monitors or controls the actual reaction force and only in the case where a preselected maximum admissible difference between nominal and actual is exceeded reacts with the shutdown of the drive and appropriately also with the activation of an alarm. Apart from this consideration in accordance with the invention, the control as part of the drive control can also start a program as is done by conventional controls.
In an especially preferred embodiment, a valve is positioned in the path of the product fluid between the outlet of the container and the exit location, for example, the forward end of an infusion needle, said valve causing a predefined pressure drop. The pressure drop is preferably selected so that a leaking of product fluid from the container because of gravity is safely prevented during all conditions occurring during the practical use of the device. For the construction and positioning of such a valve, reference is made to German Patent Application No. 197 23 648, the disclosure of which is herewith incorporated. The valve is preferably positioned as closely as possible to the exit location of the product fluid in order to include the whole fluid conducting system into the leakage monitoring. If the valve is positioned in the flow path of the product fluid immediately after the container outlet, which corresponds to another preferred embodiment, leakage between the piston and the valve can still be detected.
Additionally acting forces can be neglected compared to the valve action. That reaction force which results based on the nominal value for the pressure drop of valves of a valve model series is used as the nominal value. The control is adjusted to this nominal value by the manufacturer. The permissible range for the actual reaction force is preselected such that it corresponds to that range of the reaction force which results from the spread of the nominal value for the pressure drop of the valves of the model used. The spread range around the nominal value is upwardly and downwardly extended in order to also consider deviations of other components, for example, the drives used. However, the valve deviation is here also foremost the determining factor. To build the corresponding threshold values regarding an occlusion and a leakage, the deviati
Imhof Erich
Kipfer Urs
Disetronic Licensing AG
Dorsey & Whitney LLP
Sykes Angela D.
Thisse Jeremy
LandOfFree
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