Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Patent
1991-08-14
1993-09-14
Rosenbaum, C. Fred
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
604 66, 604 67, 604154, 604155, 128DIG1, 128DIG12, A61M 3100, A61M 3700
Patent
active
052444619
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to infusion pumps adapted to receive a syringe containing a fluid for infusion via an infusion line, the syringe plunger being displaceable by a suitable drive means, for example an electric motor.
When an infusion pump is in use, particularly in medical applications, it is important that any abnormal increase in pressure in the infusion line should rapidly cause the infusion to cease. Prior art units have either incorporated means, such as a switch, linked to the mechanical drive system and responsive to an unacceptable infusion line pressure, communicated via back-pressure upon the syringe plunger, to operate an electromechanical switch to disable the drive means; or have incorporated a pressure detector in the infusion line acting to produce a signal to disable the drive means in the event of an unacceptable infusion line pressure. The disadvantages of the prior art systems are as follows:
1. in the case of the electromechanical switch coupled to the mechanical drive system, switching is usually slow owing to the need for significant mechanical travel of the system to operate the switch; and
2. in the case of the infusion line pressure sensor, for medical applications the sensor must either be sterilised or replaced for each new infusion duty, as syringes and infusion lines are most usually disposable items.
It is an object of the present invention to provide an infusion pump in which these disadvantages are at least alleviated and preferably substantially overcome.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided an infusion pump comprising a plunger-depression member arranged in use to depress the plunger of a syringe, drive means arranged to effect controlled axial movement of the plunger-depression member and to drive an indicating member, clutch means arranged to disengage when the back-force on the plunger-depression member exceeds a predetermined value thereby allowing the motion of the driven indicating member to cease, and motion-sensing means arranged to detect cessation of motion of the indicating means and to produce an output which disables the drive means.
The clutch means may either be in the direct line of drive from the drive means to the syringe plunger, or may be interposed between the direct line of drive and an associated motion sensing means. In the first case, disengagement of the clutch means decouples the drive means from the plunger depression member; and in the second case disengagement of the clutch means decouples the drive means from the driven indicating member.
Disabling the drive means is of course sensible in any case, even though they may be decoupled from the plunger-depression member, for safety reasons.
The motion indicating member may comprise a rotating disc, preferably a toothed or otherwise segmented disc the speed of rotation of which is indicative of the speed of movement of the plunger-depression member and thus the rate of infusion. Conveniently, the output of the motion-sensing means when the indicating member is moving is fed back to a control means, the control means being arranged to control the speed of the drive means to effect infusion at a desired rate. Thus, the output signal provided by the motion-sensing means may be compared with the expected value that would be produced if the infusion were proceeding at the desired rate and any error in the actual output signal from the motion-sensing means may be used by the control means to make appropriate adjustment to the speed of the drive means.
Adjustment means, for example an adjusting screw, may be provided by which the clutch may be arranged to disengage at different back-forces on the plunger-depression member.
The drive means may comprise a motor arranged to rotate a lead screw about an axis, the plunger-depression member being connected to a lead-screw engaging member whereby rotation of the lead-screw causes axial movement of the lead screw engaging member and thus the plunger-depression member.
In such a
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Bockelman Mark
Graseby Medical Limited
Rosenbaum C. Fred
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