Abstract:
An infusion device with safeguards for protecting a patient from inappropriate infusion during a malfunction comprises a pump, an electronic controller for controlling the pump, and a mechanical stop facility for stopping the pump by mechanically blocking pump motion. The stop facility periodically requires resetting by the controller to continue infusion.

Description:
REFERENCE 
     This application claims priority to European Patent Application No. EP 08 001 688.4 filed Jan. 30, 2008, which is hereby incorporated by reference. 
     FIELD 
     The invention refers to an infusion device comprising a pump and an electronic controller for controlling the pump. Such infusion devices are used to deliver insulin or other medication to a patient. 
     BACKGROUND 
     The accuracy of medication delivery is critical, since minor differences in medication quantity can dramatically affect the health of a patient. Thus, safeguards must be designed into the delivery system to protect the patient from over or under delivery of medication. For example, in the case where insulin is administered via an infusion device to a diabetic patient, excessive insulin delivery could cause complications due to hypoglycaemia, and possibly even result in death. Therefore, controlled delivery with safeguards against over delivery of medications is required for infusion devices. 
     Safeguards against over delivery have been incorporated into electronic controllers of infusion pumps in varying ways. For example, the controller may comprise a microprocessor that monitors motor current consumption to detect a malfunction or utilize sensors for occlusion detection or the like. However, a malfunction of the controller itself, for example a direct short from the power source to the pump motor, might cause the pump motor to drive continuously and deliver all the medication contained in the infusion system over a short period and thereby cause severe over delivery. 
     To guard against such a malfunction US 2002/0071225 A1 teaches to provide infusion devices with a safety circuit system that this designed to cause a disconnection of a drive motor of the pump when the controller fails. 
     To increase the operational safety of infusion devices it is also known to use solenoid actuators or stepper motors to drive the infusion pump. Although in this way the risk of a continued infusion in case of a controller failure may be significantly reduced, solenoid actuators or stepper motors are rather expensive and not nearly as energy efficient as DC motors. Large energy consumption is a serious disadvantage as larger and heavier batteries are required which is incompatible with the standard design objective to make infusion devices small, compact and light-weight. 
     SUMMARY 
     It is therefore an object of embodiments of the invention to provide a cost and energy efficient way to improve the safety of ambulatory infusion devices. 
     An infusion device according embodiments of the invention has a mechanical stop facility for stopping the pump by mechanically blocking pump motion. Such a mechanical stop facility can be used to reliably stop an infusion even if the pump motor is still powered due to a failure of the electronic controller. The stop facility can block pump motion by positive locking, although friction locking may also be used. An especially simple and yet reliable way of stopping an infusion is a stop facility that stops the pump by mechanically locking a driveshaft, e.g. by means of a locking plate. 
     Significantly increased safety may be achieved if the stop facility is configured such that it periodically requires resetting by the controller to continue an infusion. For example, resetting of the mechanical stop facility may comprise moving a locking member out of an engagement position. Another possibility is a stop facility that comprises a reversing transmission and two limit stops which periodically require a reversing of rotation. Such a stop facility may be reset by reversing the direction of rotation of the reversing transmission. 
     A stop facility that periodically requires resetting by the controller to continue an infusion ensures that in the case of a failure of the controller pump motion is blocked after a rather short time as a faulty controller will fail to reset the stop facility. Therefore, over dosing is limited to the amount that can be infused in the time period between resets, i.e. the time between the last reset and the stopping action of the stop facility when the required reset does not occur. 
     It is possible to configure the stop facility in such a way that it has to be reset in fixed time intervals, which may be anything from a few seconds to several minutes. The stop facility can also be configured in such a way that it has to be reset after a drive shaft or other rotating part of the pump has rotated by a predetermined angle of rotation, for example a half turn or a full turn. Periodically resetting refers in such a device to a rotation period or any fraction thereof which depending on current infusion rates may take a variable length of time. For example, the stop facility may block pump motion by engaging a rotating mechanical element, e.g. a protrusion or a recess, for positive locking. The stop facility can comprise a spring biased locking member. The spring forces the locking member into a positive locking engagement with a suitable counterpart, a recess for example. The counterpart may be fixed to the drive shaft or some other rotating part of the pump. For resetting the stop facility, the locking member has to disengage which may be done by an actuator, e.g. a solenoid, controlled by the electronic controller. 
     In some embodiments, the stop facility comprises at least two locking members which alternately block pump motion. Resetting the stop facility may then be done by moving one of the locking members to disengage from locking engagement which activates at least one other locking member so that it will block pump motion after a preset period. For example, an actuator may be used for resetting locking elements in such a way that the actuator, e.g. a winding core, moves between two positions and thereby always pushes either one of two locking members away from a rotating mechanical locking element like a locking plate. Hence, by moving one locking member to disengage from a locking engagement the other locking member is no longer pushed away from the locking element and may engage it as soon as it has rotated far enough. The locking members may be spring biased to readily engage the locking element. 
     The pump can be a peristaltic pump. Peristaltic pumps enable a precise dosing even at very low infusion rates. Especially well suited is a rotary peristaltic pump, although other pumps may also be used. Preferably the peristaltic pump comprises a rotor with at least four, preferably at least five, annularly arranged compressing elements for acting in peristaltic fashion on a flexible tube conveying a liquid to be infused. Then, at least one of the uniformly distributed compressing elements will always reliably compress the tube and thereby close it. Hence, whenever the pump is stopped, no liquid flow can occur. 
     The pump motor can be a DC motor as such motors are efficient and inexpensive although other motors may also be used. 
     The stop facility can cause disconnection of the motor if it is not reset within a preset time. For example the stop facility may upon blocking pumping motion actuate a time delayed switch which will disconnect the motor if no corrective action is taken by the controller within the preset time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages of embodiments of the invention are illustrated in the following by means of exemplary embodiments and by making reference to the appended drawings. Identical and corresponding parts of the embodiments are denoted by the same reference numbers. In the figures: 
         FIG. 1  shows schematically an exemplary embodiment of an infusion device according to the invention; and, 
         FIG. 2  shows schematically a second exemplary embodiment of an infusion device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows schematically an embodiment of an infusion device. The infusion device comprises a peristaltic pump  1  acting on a flexible tube  2  to pump a liquid to be infused, for example insulin. The peristaltic pump  1  has a rotor  3  with more than four compressing elements  4 , and in some embodiments more than five compressing elements  4 , which act in peristaltic fashion on the flexible tube  2  supported by an arcuate pump bed  10 . Stopping the rotor  3  blocks liquid flowing through to the tube  2  as there is always at least one compressing element  4  pressing on the tube  2  and thereby closing it. In the example shown the rotor  3  of the peristaltic pump  1  has eight compressing elements  4 . 
     The rotor  3  of the peristaltic pump  1  is driven by a DC-Motor  5  via a transmission  6  and a drive shaft  7 . The DC motor  5  is controlled by an electronic controller  8 , for example a microprocessor, that monitors by means of a sensor  9  rotation of the rotor  3  and thereby the infusion rate. 
     The infusion device shown in  FIG. 1  comprises a mechanical stop facility for stopping the pump  1  by mechanically blocking pump motion. The stop facility comprises a locking plate  11 , which is connected to the drive shaft  7 , and a locking member  12  which interacts with the locking plate  11 . In order to lock the drive shaft  7  the locking member  12  engages a recess of the locking plate  11 . The locking member  12  is biased by spring  13  against the locking plate  11 . 
     When the locking member  12  has engaged the locking plate  11 , the drive shaft is locked and the stop facility has to be reset by the controller  8  to continue an infusion. Only after the stop facility has been reset, further pumping motion is possible. 
     In the example shown, the controller  8  resets the stop facility by means of an actuator  14 , for example a solenoid. In order to reset the stop facility, the actuator  14  moves the locking member  12  out of its engagement position in which it protrudes into the recess of the locking plate  11 . 
     If the locking plate  11  has only one recess and the stop facility comprises only one locking member  12 , such a resetting is required every full turn of the drive shaft  7 . However, it is also possible to use several locking members  12  and/or several recesses such that a recess is engaged by a locking member  12  more often. In the example shown, two locking members  12  which alternately block pump motion are arranged opposite each other such that the stop facility has to be reset every half turn of the drive shaft  7 . 
     In the example shown, there is only one recess to be engaged by the locking members  12 . However, it is also possible to use a plurality of locking elements, e.g. recesses of a locking plate. Then the stop facility has to be reset more often. If two locking members  12  are to be used alternately, the locking elements, e.g. recesses, should be arranged in such a way that the locking members  12  cannot engage at the same time. 
     Both locking members  12  are reset by the same actuator  14 . Resetting the stop facility by moving one of the locking members  12  to disengage from positive locking engagement activates at least one other locking member  12  so that it will block pump motion after a preset period which is in the example shown a half turn of the locking plate. Activation of a locking member  12  is achieved by movement of the actuator  14  which by moving to disengage one locking member  12  frees the other so that it can engage a rotating locking element, which is in the example shown a recess of the locking plate  11 . 
     When the stop facility stops the pump  1  by locking the drive shaft  7  it also causes a disconnection of the drive motor  5  to avoid unnecessary power consumption. Disconnection of the drive motor  5  may be achieved by a switch which may be actuated by movement of the locking member  12 , for example. Preferably, such a switch is temporally delayed after locking of the pump  1  to ensure that the drive motor  7  is only disconnected in case of a failure of the controller  8 , i.e. when the stop facility is not reset with a predetermined time, for example a few seconds or less. 
       FIG. 2  shows schematically another embodiment of an ambulatory infusion device. This device also comprises a rotary peristaltic pump  1  which is driven via a drive shaft  7  by a DC-Motor  5  controlled by a controller  8 . The infusion devices shown in  FIGS. 1 and 2  differ with respect to the stop facility for stopping the pump by mechanically blocking pump motion. 
     The stop facility of the device shown in  FIG. 2  comprises a reversing transmission  15  which connects the motor  5  to the drive shaft  7 . The reversing transmission comprises two parallel shafts  21 ,  22  which rotate in opposite directions. The shafts are driven by the motor  5  via a gear wheel  23  which meshes with gear wheel  24  fixed to shaft  21  and gear wheel  25  fixed to shaft  22 . Gear wheels  24  and  25  are arranged on opposite sides of gear wheel  23  such that they rotate in opposite directions. 
     A ratchet and pawl mechanism  26   a  is fixed to shafts  21 . The ratchet and pawl mechanism  26   a  interacts with a gear wheel  27  which can turn relative to shaft  21 . When the shaft  21  rotates in a first direction, e.g. clockwise in the example shown, the ratchet and pawl mechanism  26   a  causes the gear wheel  27  to rotate with the shaft  21 . However, rotation of the shaft  21  in opposite direction, e.g. counter clockwise, is not transmitted to the gear wheel  27 . 
     Likewise, ratchet and pawl mechanism  26   b  interacts with a gear wheel  28  which can turn relative to shaft  22 . However, the ratchet and pawl mechanisms  26   a  and  26   b  are active in opposite direction. Hence, in the example show the ratchet and pawl mechanism  26   b  transmits counter-clockwise rotation of the shaft  22  to the gear wheel  28 , whereas clockwise rotation of the shaft  22  is not transmitted to the gear wheel  28 . 
     As the gear wheel  27  meshes with gear wheel  28  which in turn meshes with gear wheel  29  fixed to the drive shaft, the ratchet and pawl mechanisms  26   a ,  26   b  ensure that gear wheel  29  and therefore the drive shaft  7  always rotate in the same direction regardless of the directions of rotation of shafts  21 ,  22  and gear wheel  23 . 
     The reversing transmission drives the drive shaft  7  always in the same direction. Hence, resetting of the stop facility by reversing rotation causes the drive shaft to continue to turn and thereby to pump liquid through the tube  2  in the direction of the arrows shown. 
     As can be seen in  FIG. 2 , gear wheel  24  of the reversing transmission  15  has a locking structure, for example a groove  17 , which is engaged by a pin  18 . During an infusion the pin  18  moves along the locking structure  17  until it reaches a limit stop, in the example shown an end of the groove  17 , which acts as a locking member. Once this happens, an infusion is stopped as further pump action, i.e. further rotation of the gear wheel  24  in the same direction, is blocked by the pin  18  engaging the limit stop. 
     To continue an infusion, the controller  8  has to reset the locking mechanism which in the example shown is done by reversing the direction of rotation of the motor  5 . Reversing rotation causes the pin  18  to move back along the locking structure  17  until it reaches the limit stop at the other end of the groove. Then the motor  5  has to change direction of rotation again. 
     The reversing transmission  15  drives the drive shaft  7  always in the same direction. Hence, resetting of the stop facility by reversing rotation causes the drive shaft to continue to turn and thereby to pump liquid through the tube  2  in the direction of the arrows shown. 
     Thus, embodiments of the infusion device are disclosed. One skilled in the art will appreciate that the teachings can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the invention is only limited by the claims that follow.