Abstract:
A delivery tube is inhibited from unintended withdrawal from an infusion pump which has an internal occlusion clamp that clamps the delivery tube to prevent the free flow of fluid through the tube, by overlapping a blocking lip from a compression edge of the occlusion clamp with a restraint surface of an anvil against which the tubing is compressed and by overlapping a blocking projection from the restraint surface with the compression edge. Inhibition is also achieved by positioning an obstruction protrusion adjacent to the compression edge and the blocking lip to resist the application of exterior physical force to force the occlusion clamp from an occluding position to a non-occluding position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation in part of U.S. application Ser. No. 12/852,116, filed Aug. 6, 2010 by the inventors hereof, for an invention titled “Infusion Pump and Slide Clamp Apparatus and Method.” The present invention is assigned to the assignee of previous application Ser. No. 12/852,116. The subject matter of previous application Ser. No. 12/852,116 is incorporated herein by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to prohibiting the free flow of medicinal fluid into a patient from a delivery tube of an intravenous tubing set used with an infusion pump. More particularly, the present invention relates to a new and improved apparatus and method which uses a slide clamp to release the delivery tube from the infusion pump and simultaneously occlude a delivery tube, thereby ensuring that the delivery tube is occluded whenever the delivery tube is removed from the infusion pump. 
       BACKGROUND OF THE INVENTION 
       [0003]    Intravenous tubing sets are commonly used with an infusion pump to deliver fluid medications directly into the bloodstream of a patient. Fluid, such as glucose or saline, is mixed or dissolved with a medical substance in a bag, and a delivery tube conducts the medicinal fluid from the bag into a needle or other connector which delivers the fluid into a vessel, typically a vein, of the patient. The bag is suspended above the patient so that the force of gravity acting on the fluid causes the fluid to flow through the delivery tube. 
         [0004]    A ramp valve and a drip chamber are sometimes included in-line with the delivery tube to control the flow rate of the fluid. Although the ramp valve is useful and sufficiently accurate for some applications, it is not a fully reliable metering device. Variations in the height or head of fluid in the bag cause variations in the fluid flow rate through the delivery tube. Variations in the height of the fluid in the bag occur naturally as the fluid flows from the bag, and also occur when a pole stand which supports the bag above the patient is adjusted in height. In addition, the use of a ramp valve does not typically provide the degree of precision in fluid delivery necessary in many medical situations. 
         [0005]    For those medical applications which require precise metering of the medicinal fluid delivered to the patient, infusion pumps are used to precisely control the amount of fluid delivered. A portion of the delivery tube is clamped or connected in the infusion pump, and the infusion pump is operated by electrical power to deliver the fluid at a precise rate. In most cases, infusion pumps are peristaltic in operation. The flexible delivery tube is compressed or pinched at two spaced-apart locations to capture a predetermined volume of fluid in the tube between the pinch points. The pinched locations are mechanically advanced at a predetermined timed rate. This wave-like movement repeats and creates a very precise flow of fluid over time. 
         [0006]    When the infusion pump is stopped, the tube remains pinched together by the pumping mechanism to occlude the tube. No fluid can flow to the patient when the pump is stopped and the tube remains within the infusion pump. In some infusion pumps, the peristaltic pinching action occurs with respect to a door on the pump. When the door is closed, the closed door provides a working surface against which the delivery tube is pinched during the peristaltic action. When the door is opened, the delivery tube is no longer pinched because the working surface separates from the delivery tube. Opening the door under these circumstances creates the possibility of the medicinal fluid free-flowing into the patient. 
         [0007]    To prevent the fluid from free-flowing when the door is open, infusion pumps typically include an internal occlusion clamp which pinches the delivery tube to occlude the delivery tube. Such internal occlusion clamps become effective when the door is opened. When the door is closed, the internal occlusion clamp is moved to a non-occluding position. Moving the internal occlusion clamp to the non-occluding position when the door is closed allows peristaltic movement of the fluid through the delivery tube by the peristaltic or other internal pumping mechanism. 
         [0008]    It is necessary to remove the delivery tube from the infusion pump. Of course to do so, the door must be open to gain access to the delivery tube. Opening the door results in the internal occlusion clamp clamping the delivery tube, making it very difficult or impossible to remove the delivery tube from the infusion pump. Under these circumstances, the infusion pump must include some provision for releasing the internal occlusion clamp even though the door is open. With the delivery tube removed from the infusion pump, there is no restriction on the gravity flow of fluid from the bag through the delivery tube into the patient. Even short times of unrestricted gravity flow can introduce potentially dangerous amounts of the medicinal fluid into the bloodstream of the patient, since the flow rate through the operating infusion pump is typically much less than the gravity-induced free flow rate when the delivery tube is not restricted. 
         [0009]    Occasionally when it is necessary to remove the delivery tube from the infusion pump, the tubing set may remain connected to the patient, giving rise to the possibility that the fluid will free-flow by gravity into the patient in an uncontrollable manner. The potential for gravity-induced free flow of fluid into the patient occurs when it is necessary to exchange one infusion pump for a different infusion pump in the case of mechanical failure of an infusion pump. Another circumstance which may give rise to gravity-induced free flow of fluid into the patient is when two bags are connected to a single tubing set and the fluid has been delivered from one of the bags. Under such circumstances, the delivery tube from the empty bag must be removed from the infusion pump and the delivery tube from the full bag substituted within the infusion pump. Under these exemplary circumstances, the fluid may flow from the bag into the patient. 
         [0010]    To prevent overdosing the patient when the delivery tubing is removed from the infusion pump and the delivery tubing is still connected to the patient, manual clamps are usually located on the delivery tube external to the infusion pump. Closing such an external clamp prior to removing the tubing from the infusion pump avoids the free flow of fluid into the patient. Such an external clamp may be the ramp valve or a similar roll or slide clamp. However, the success of this procedure depends on the attending medical personnel closing the external clamp. Although unusual, medical personnel may become distracted and fail to close the external clamp. Medical personnel which do not have the necessary level of experience and training may simply fail to recognize the need to close the external clamp when the delivery tube is removed from the infusion pump while the delivery tube remains connected to the patient. Executing the necessary sequence of closing the external clamp before removing the delivery tube from the infusion pump may also increase the risk that relatively inexperienced medical personnel may make a mistake in the sequence of actions required. 
         [0011]    Because of the potential for human error when using an infusion pump, certain medical standards and accreditation organizations require that infusion pumps have built-in, automatic anti-free flow capabilities. Such anti-free flow capabilities prevent the free flow of fluid through the delivery tube when the delivery tube is removed from the infusion pump or when the door to the pump is open and the peristaltic constrictions can no longer occlude the delivery tube. Such anti-free flow capability is intended to overcome the natural possibility of inadvertent human failure to clamp the delivery tube externally whenever the tubing set is removed from the infusion pump or whenever the infusion pump is manipulated in such a way that free flow through the delivery tube becomes possible. 
         [0012]    A number of previous automatic anti-free flow mechanisms have been employed in infusion pumps. Some of those anti-free flow mechanisms are subject to unintended manipulation in such a way that the delivery tube can be removed from the infusion pump without occluding the delivery tube, thereby defeating the anti-free flow capability. Other anti-free flow mechanisms are more reliable. Regardless of the level of success in preventing gravity flow, almost all of the previous infusion pumps which possess anti-free flow capability are of considerably increased cost and complexity. The increased complexity has also increased the risk of mechanical failure, with the attendant possibility of downtime of the equipment leading to the unavailability of the equipment. The increased complexity also creates an increased risk of successfully defeating the anti-free flow capability, out of a lack of knowledge of the proper functionality of the system or from good faith attempts to remove the delivery tube under appropriate circumstances but using inappropriate techniques. 
         [0013]    One such popular infusion pump which incorporates anti-free flow capabilities requires a slide clamp to be inserted into the pump whenever the delivery tube is loaded into the pump. The slide clamp is captured by the internal operating mechanism of the infusion pump when the door is closed, and the slide clamp becomes part of the occlusion clamp operating mechanism. Sensors within the pump detect the presence of the slide clamp as a condition for operating the pump. A complicated arrangement of moving parts within the pump moves the slide clamp relative to the delivery tube to open the delivery tube to the flow of fluid as a part of operating the internal occlusion clamp. The delivery tube is occluded when the delivery tube is forced into a narrow portion of a V-shaped notch in the slide clamp, thereby pinching the side walls of the tube together. The delivery tube is opened to the flow of fluid when the slide clamp is moved in the opposite direction where the delivery tube extends through the wide portion of the V-shaped notch. 
         [0014]    A variety of other types of anti-free flow mechanisms are also used in infusion pumps, but these other types of anti-free flow mechanisms do not employ slide clamps. These other types of pumps and anti-free flow mechanisms have had varying degrees of success in preventing inadvertent and intentional human action from overriding the intended anti-free flow capability. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention uses a slide clamp as an external manual actuator for releasing or opening an internal occlusion clamp within the infusion pump to an open position, to permit removing the delivery tube from the infusion pump. Manually manipulating the slide clamp to release the internal occlusion clamp simultaneously moves the delivery tube into the narrow end of a slot in the slide clamp, thereby preventing the free flow of fluid through a delivery tube whenever the internal occlusion clamp is opened. Thus, the simple expedient of manually manipulating the slide clamp to release the internal occlusion clamp to the open position has the effect of simultaneously occluding the delivery tube and thereby achieving anti-free flow functionality. The slide clamp does not become part of the internal operating mechanism of the infusion pump. When the door of the infusion pump is closed, the door interacts with a peristaltic pump to occlude the tubing, so closing the door also releases the internal occlusion clamp without requiring the presence of the external slide clamp within the infusion pump. Medical personnel must manually move the external slide clamp relative to the delivery tube to deliver fluid to the patient, even after the internal occlusion clamp opens and the infusion pump commences operation. Requiring manual movement of the slide clamp relative to the delivery tube before the pump can operate is a further safety aspect of the invention which prevents unintended fluid delivery to the patient. 
         [0016]    These features of the invention reduce the number of moving parts of the infusion pump, reduce the cost of the pump because of its simpler construction, make the operation of the pump simpler and safer by avoiding the necessity of performing a sequence of complicated steps to occlude and release the delivery tube, thereby enhancing safety by requiring intentional, manual action on the part of medical personnel to deliver fluid to the patient, and permitting medical personnel with less training and experience to successfully operate the infusion pump in a safe and effective manner. 
         [0017]    One aspect of the invention involves an infusion pump to regulate the flow of medicinal fluid delivered through a delivery tube to a patient. The infusion pump has an internal occlusion clamp which occludes the delivery tube and prevents free flow of the fluid through the delivery tube when in an occluding position and which opens the delivery tube to allow the flow of fluid through the delivery tube when in a non-occluding position. A first portion of the delivery tube is located within a tubing channel. An anvil is located on one side of the tubing channel, and the anvil has a restraint surface facing the tubing channel and against which the delivery tube is compressed and occluded when the occlusion clamp is in the occluding position. A compression edge of the occlusion clamp faces the tubing channel on the opposite side of the tubing channel from the restraint surface. The compression edge moves into adjacency with the restraint surface to compress and occlude the delivery tube between the compression edge and the restraint surface when the occlusion clamp is in the occluding position. The compression edge moves away from the restraint surface to open the delivery tube when the occlusion clamp is in the non-occluding position. A blocking lip extends from the compression edge toward the restraint surface, and at least one blocking projection extends from the restraint surface toward the compression edge. The blocking lip overlaps the restraint surface and the blocking projection overlaps the compression edge to inhibit removal of the delivery tube from between the compression edge and the restraint surface when the occlusion clamp is in the occluding position. 
         [0018]    Another aspect of the invention involves an infusion pump for regulating the flow of medicinal fluid delivered through a delivery tube to a patient. The infusion pump has an internal occlusion clamp which occludes the delivery tube and prevents free flow of the fluid through the delivery tube when in an occluding position and which opens the delivery tube to allow the flow of fluid through the delivery tube when in a non-occluding position. The infusion pump comprises a tubing channel in which a first portion of the delivery tube is located. An anvil is located on one side of the tubing channel, and the anvil has a restraint surface facing the tubing channel and against which the delivery tube is compressed and occluded when the occlusion clamp is in the occluding position. A compression edge of the occlusion clamp faces the tubing channel on the opposite side of the tubing channel from the restraint surface. The compression edge moves into adjacency with the restraint surface to compress and occlude the delivery tube between the compression edge and the restraint surface when the occlusion clamp is in the occluding position. The compression and edge moves away from the restraint surface to open the delivery tube when the occlusion clamp is in the non-occluding position. A front panel has an opening from which a portion of the compression edge extends outward from the front panel. An obstruction protrusion is located adjacent to the opening and extends outward from the front panel a distance at least equal to the distance which the portion of the compression edge extends outward from the front panel. The obstruction protrusion resists the application of exterior physical force on the portion of the compression edge to inhibit unintended forced movement of the occlusion clamp from the occluding position toward the non-occluding position. 
         [0019]    A further aspect of the invention pertains to a method of preventing free flow of fluid through a delivery tube of an infusion tubing set used with an infusion pump to regulate the flow of fluid delivered to a patient. The infusion pump has an internal occlusion clamp which occupies an occluding position for occluding the delivery tube within a tubing channel located within the infusion pump when the tubing channel is accessible to a user of the infusion pump, or which occupies a non-occluding position for opening the delivery tube to allow fluid flow through the delivery tube when the delivery tube within the tubing channel is not accessible to the user of the infusion pump. The delivery tube is occluded by pinching the delivery tube between a restraint surface of an anvil of the infusion pump and a compression edge of the occlusion clamp. Removal of the delivery tube from between the restraint surface and the compression edge when the occlusion clamp is in the occluding position is inhibited by extending a blocking lip from the compression edge across the delivery tube and overlapping the restraint surface with the blocking lip and by extending a blocking projection across the delivery tube and overlapping the compression edge with the blocking projection. 
         [0020]    Other subsidiary aspects of the invention involve separating the blocking lip and each blocking projection from one another to it with sufficient to insert the delivery tube between the blocking lip and the blocking projection and into the tubing channel when the occlusion clamp is in the non-occluding position, positioning at least one obstruction protrusion adjacent to the blocking lip and the compression edge to resist the application of exterior physical force on the blocking lip and compression edge to force the occlusion clamp from the occluding position toward the non-occluding position, and positioning the blocking lip interdigitally between the spaced apart blocking projections when the occlusion clamp is in the occluding position, among other things. 
         [0021]    A more complete appreciation of the present invention and its scope may be obtained from the accompanying drawings, which are briefly summarized below, from the following detailed description of a presently preferred embodiments of the invention, and from the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a perspective view of an infusion pump and a slide clamp which incorporate the present invention, shown with a front door of the infusion pump in a closed position and the slide clamp attached to a delivery tube of an infusion tubing set. 
           [0023]      FIG. 2  is a perspective view similar to  FIG. 1 , shown with the front door of the infusion pump in an open position. 
           [0024]      FIG. 3  is a perspective view similar to  FIG. 2 , showing the slide clamp moving into a position which will simultaneously release an internal occlusion clamp of the infusion pump and occlude the delivery tubing. 
           [0025]      FIG. 4  is an enlarged partial perspective view of a portion of the infusion pump and the slide clamp moving into the position shown in  FIG. 3 . 
           [0026]      FIG. 5  is an enlarged partial perspective view of a portion of the infusion pump with the slide clamp and the delivery tube in the position shown in  FIG. 3 . 
           [0027]      FIG. 6  is an enlarged partial perspective view similar to  FIG. 5 , showing the position of the slide clamp upon simultaneously releasing the internal occlusion clamp and occluding the delivery tube. 
           [0028]      FIG. 7  is an enlarged partial perspective view of the front door of the infusion pump shown in  FIG. 2 , with components of a peristaltic pump of the infusion pump shown an exploded relationship. 
           [0029]      FIG. 8  is an enlarged partial perspective view of components of the peristaltic pump of the infusion pump which interact with the delivery tubing of the tubing set, when the delivery tube is retained in the infusion pump as shown in  FIG. 1 . 
           [0030]      FIG. 9  is an enlarged partial perspective view of components of the internal occlusion clamp of the infusion pump, in the position when the door is opened as shown in  FIG. 2 . 
           [0031]      FIG. 10  is a enlarged partial perspective view similar to  FIG. 9 , in the position when the slide clamp releases the occlusion clamp. 
           [0032]      FIG. 11  is an enlarged partial perspective view similar to  FIG. 10 , in the position where the internal occlusion clamp is opened by closure of the front door as shown in  FIG. 1 . 
           [0033]      FIG. 12  is an enlarged partial perspective view of a slidable lock of the internal occlusion clamp, also shown in  FIGS. 9-11 . 
           [0034]      FIG. 13  is an enlarged perspective view of a portion of a front panel of the infusion pump as shown in  FIG. 5 , illustrating an alternative configuration of an anvil with which an internal occlusion clamp interacts, and also illustrating obstruction protrusions adjacent to the internal occlusion clamp, all shown with the delivery tube removed from the pump. 
           [0035]      FIG. 14  is a view similar to  FIG. 13 , with the delivery tube positioned between the anvil and the internal occlusion clamp in a tubing channel of the infusion pump. 
           [0036]      FIG. 15  is a view similar to  FIG. 14  showing the delivery tube compressed and pinched between a restraint surface of the anvil and a compression edge of the occlusion clamp, with the two spaced apart blocking protrusions of the anvil interdigitating with a blocking lip of the occlusion clamp. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    An infusion pump  10  and a slide clamp  12  which embody the present invention are shown in  FIG. 1 . The infusion pump  10  precisely meters a flow of medicinal fluid  14  through an intravenous tubing set  16  to a patient (not shown). The tubing set  16  includes a flexible and collapsible bag  18  which stores the fluid  14 , and a delivery tube  20  which conducts the fluid  14  from the bag  18  to a connector  22 . The connector  22  connects to a needle (not shown) inserted into a vessel, typically a vein of a patient, or to a complementary connection of a conventional vessel access device attached to the patient. A conventional ramp or roller clamp  23  is connected to the delivery tube  20  to constrict the delivery tube  20  and thereby control the cross-sectional size of an opening through the delivery tube through which the fluid  14  flows. The roller clamp  23  will typically be moved to a non-restricting position when the infusion pump  10  is in operation, because the infusion pump meters the flow of fluid  14  through the delivery tube  20 . 
         [0038]    The slide clamp  12  is retained around the delivery tube  20 , preferably at a position midway between the bag  18  and the connector  22 . As shown in  FIGS. 4 ,  5  and  10 , the delivery tube  20  extends through a rounded opening  24  in the slide clamp  12 . The opening  24  has a diameter approximately equal to or very slightly smaller than an exterior diameter of the delivery tube  20 . The position of the slide clamp  12  along the delivery tube  20  is adjustable by sliding the slide clamp  12  along the length of the delivery tube  20  while the delivery tube  20  is located in the opening  24 . The close size relationship of the opening  24  and the diameter of the tube  20  frictionally maintains the slide clamp  12  at a desired position along a length of the delivery tube  20 . When in the rounded opening  24 , the delivery tube is not occluded to inhibit the flow of fluid. An occluding slot  26  extends rearwardly from the non-occluding opening  24 . The slot  26  converges to create narrow transverse width into which the delivery tube  20  is forced when the delivery tube is occluded, as shown in  FIG. 6 . When the delivery tube  20  is forced into the slot  26 , the sidewall of the delivery tube  20  is pinched together, thereby occluding the delivery tube  20  and preventing the flow of fluid  14 . A trapezoid-shaped release tab  28  ( FIGS. 4 ,  5  and  10 ) extends forward from a front or distal end of the slide clamp  12  at a position which is adjacent to and distal of the non-occluding opening  24 . 
         [0039]    A front door  30  is pivotally attached to a main body  32  of the infusion pump  10 , as shown in  FIGS. 1 ,  2  and  3 . A vertically-extending tubing channel  34  is located within a front panel  36  of the main pump body  32 . The tubing channel  34  is accessible to receive a portion of the delivery tube  20  when the front door  30  is opened as shown in  FIGS. 2 and 3 . A conventional peristaltic pump  38  is located within the tubing channel  34  to compress and pinch the delivery tube  20  with the wavelike motion to move the fluid  14  through the delivery tube  20  when the door  30  is closed. The rate at which the peristaltic pump  38  operates controls the rate of flow of the fluid  14  through the delivery tube  20 . The flow rate is programmed by attending medical personnel with the use of a conventional graphic interface  40  located on the exterior of the door  30 . 
         [0040]    The peristaltic pump  38  prevents the gravity-induced free flow of fluid  14  through the delivery tube  20  when the infusion pump is not operating, so long as the door  30  is closed. To prevent gravity-induced free flow of fluid  14  through the delivery tube  20  when the door  30  is opened, a compression edge  42  of an internal occlusion clamp  43  ( FIGS. 9-11 ) compresses the delivery tube  20  against a stationary anvil  44  attached to the panel  36 , thereby occluding the delivery tube when the door  30  is open. Closing the door  30  causes the internal occlusion clamp  43  to move the compression edge  42  away from the anvil  44  and open the delivery tube  20  to the fluid flow by operation of the peristaltic pump  38 . When the door  30  is closed and the peristaltic pump  38  is not in operation, the peristaltic pump  38  blocks the flow of fluid  14  through the delivery tube  20 . 
         [0041]    A significant aspect of the present invention is using the slide clamp  12  as an actuator to release or open the internal occlusion clamp  43  while simultaneously moving the delivery tube  20  into the occluding slot  26 , thereby pinching and occluding the delivery tube  20  with the slide clamp  12  when the occlusion clamp  43  is released or opened. In this manner, gravity-induced free flow of fluid  14  through the delivery tube  20  is prevented when the delivery tube  20  is released from the infusion pump. The anti-free flow requirements established by regulatory agencies and organizations are satisfied, by occluding the delivery tube with the slide clamp  12  at the same time that the slide clamp  12  is used as an actuator to release or open the internal occlusion clamp  43 . 
         [0042]    To remove the delivery tube  20  from the infusion pump  10  after having opened the door  30 , the slide clamp  12  is manually positioned to insert the release tab  28  into an access opening  46  in the front panel  36  of the main body  32 , as is understood by reference to  FIGS. 3-6 . Two tube supports  48  extend outward from the front panel  36  at locations above and below the access opening  46 . Concave contact areas  50  ( FIG. 4 ) are formed in the forward portions of the tube supports  48  at locations transversely centered about the access opening  46 . As the release tab  28  of the slide clamp  12  is moved into the access opening  46  ( FIG. 5 ), the delivery tube  20  is carried by the slide clamp  12  into a position where the delivery tube  20  above and below the slide clamp  12  contacts the contact areas  50 . Further inward movement of the slide clamp  12  ( FIG. 6 ) causes the release tab  28  to release or open the internal occlusion clamp  43  while the contact areas  50  hold the delivery tube  20  stationary and force the delivery tube  20  into the occluding slot  26  of the slide clamp  12 . Thus, the inward movement of the slide clamp  12  simultaneously forces the delivery tube  20  into the occluding slot  26  of the slide clamp  12  while the slide clamp  12  releases the internal occlusion clamp  43 . Once the internal occlusion clamp  43  has been released, the delivery tube  20  can be removed from the tubing channel  34  in the main body  32  of the infusion pump  10  because the compression edge  42  and the anvil  44  separate from one another. Gravity induced free flow of fluid through the removed delivery tube  20  is prevented by the occlusion from the slide clamp  12 . 
         [0043]    Projections  52  are formed on opposite sides of the front edge of the release tab  28 , as shown in  FIGS. 4 ,  5  and  10 . The projections  52  fit into guide channels  54  formed in the tube supports  48  on opposite sides of the access opening  46 . The projections  52  maintain the alignment of the release tab  28  within the access opening  46 , to assure that the insertion of the slide clamp  12  positions the portion of the delivery tube  20  above and below the slide clamp in the contact areas  50 . Such positioning assures that the further insertion of the slide clamp  12  into the access opening  46  moves the delivery tube into the occluding slot  26 . The projections  52  also maintain the release tab  28  in position to release or open the internal occlusion clamp  43 . 
         [0044]    A proximal or rear wedge-shaped portion  56  of the slide clamp  12  is significantly thicker than the remaining forward portions of the slide clamp  12 . The thickness of the slide clamp  12  through the region of the occluding slot  26  and the release tab  28  is generally uniform. The wedge-shaped portion  56  increases in thickness beginning at a position approximately proximal of the proximal end of the occluding slot  26 . The wedge-shaped rear portion  56  is intended to be grasped between the first and second fingers of the user, while the thumb of the user contacts the rear surface of the wedge-shaped portion  56 . The delivery tube  20  is located in front of the first and second fingers, and the thumb pushes the slide clamp  12  into the access opening  46 . This configuration assists the user in manipulating the slide clamp  12  when inserting the release tab  28  into the access opening  46 . The main body  32  of the infusion pump  10  may be held stationary by the user to counter the forces of pushing the slide clamp  12  to release the occlusion clamp  43  and to force the delivery tube  20  into the occluding slot  26  of the slide clamp  12 . 
         [0045]    The peristaltic pump  38  is formed by a linear array of cam follower plungers  58  ( FIG. 8 ) located in the tubing channel  34  and by a spring-loaded backplate  60  ( FIGS. 8 ,  2  and  3 ) that is attached to an inner surface  62  of the door  30 . The delivery tube  20  is loaded into the infusion pump  10  by positioning a portion of the delivery tube  20  within the tubing channel  34  as shown in  FIG. 2 . The spring-loaded backplate  60  presses the delivery tube  20  against contact edges  63  of the cam follower plungers  58  when the door  30  is closed, as shown in  FIG. 8 . The cam follower plungers  58  alternately and sequentially extend the contact edges  63  toward and away from the backplate  60  during operation of the peristaltic pump  38  to create an occlusion in the delivery tube  20  and move that occlusion sequentially through the peristaltic pump  38 . One or more occlusions of the portion of the delivery tube within the peristaltic pump  38  exists due to this action. Operating in this manner, the peristaltic pump  38  continuously and controllably meters the fluid  14  through the delivery tube  20  toward the connector  22  and into the patient. 
         [0046]    Each contact edge  63  of each of the cam follower plunger  58  moves forward and backward in the tubing channel  34  while pressing against the delivery tube  20  due to the action of a cam lobe  64  attached eccentrically to a shaft  66 , as understood from  FIG. 8 . One cam lobe  64  is associated with each cam follower plunger  58 . The cam lobe  64  is located within a rectangularly shaped opening  68  formed in the structure of each cam follower plunger  58 . An electrical motor (not shown) rotates the shaft  66 , causing the cam lobe  64  to rotate with the shaft  66 . Due to its eccentric position on the shaft  66 , the cam lobe  64  rotates into contact with a front surface  70  of the opening  68  to push the cam follower plunger  58  forward with the contact edge  63  against the delivery tube  20 . Continued rotation of the shaft  66  causes the eccentric surface of the cam lobe  64  to push against a rear surface  72  of the opening  68 , thereby moving the cam follower plunger  58  and the contact edge  63  rearwardly. The side surfaces  74  of the opening  68  may also contact the cam lobe  64  and cause the cam follower plungers  58  to pivot slightly from side to side. Attaching the separate cam lobes  64  at different rotationally displaced positions on the shaft  66  in sequence causes the wave-like sequential action of contact edges  63  of the cam follower plungers  58  against the delivery tube  20  from with rotation of the shaft  66 . 
         [0047]    The spring loaded backplate  60  is confined within a retaining area  76  formed in the inner surface  62  of the door  30 , as shown in  FIG. 7 . Two or more springs  78  push the backplate  60  away from the door  30  and against a pair of retaining lips  80  which extend from the inner surface  62  and which form part of the retaining area  76 . The backplate  60  withdraws into the door  30  from an extended position as shown in  FIGS. 2 ,  3  and  8 , when enough pressure is exerted on the exterior face or working surface of the backplate  60  by the portion of the delivery tube  20  compressed by the contact edges  63  of the cam follower plungers  58 , to overcome the force exerted by the springs  78 . The spring loaded backplate  60  supplies sufficient force against the delivery tube  20  to allow the contact edges  63  to occlude the delivery tube  20  when each cam follower plunger  58  is in its forwardmost position. 
         [0048]    The door  30  of the infusion pump  10  must be closed for the peristaltic pump  38  to operate. A sensor (not shown) detects whether or not the door  30  is closed and allows the operation of the peristaltic pump  38  only when the door  30  is closed. At least one contact edge  63  of one cam follower plunger  58  is always occluding the delivery tube  20  when the door  30  is closed, whether or not the peristaltic pump  38  is operating. Since the delivery tube  20  is always occluded when the door  30  is closed, the fluid  14  is prevented from flowing freely by gravity through the delivery tube  20  when the door  30  is closed. 
         [0049]    To prevent the the free flow of the fluid  14  through the delivery tube  20  when the door  30  is opened, the occlusion clamp  43  moves into a clamping or occluding position shown in  FIG. 9  from an open or released position shown in  FIGS. 10 and 11 . The compression edge  42  of the occlusion clamp  43  presses the delivery tube  20  against the anvil  44  to occlude the delivery tube when the occlusion clamp  43  is in the clamping position. A blocking lip  82  extends from the compression edge  42  around the delivery tube  20  and across the gap between the compression edge  42  and the anvil  44  and slightly overlaps the anvil  44 , as shown in  FIGS. 4 and 9 , to prevent the forcible removal of the delivery tube  20  from between the compression edge  42  and the anvil  44  when the occlusion clamp  43  is in the clamping position. 
         [0050]    The occlusion clamp  43  includes a lever  84  which pivots about a pivot point  86  to establish the clamping position ( FIG. 9 ) and the open position ( FIGS. 10 and 11 ). A lever lock mechanism  88  ( FIG. 12 ) holds the lever  84  in the open position when the slide clamp  12  releases the occlusion clamp  43  when the door  30  of the infusion pump  10  is open. The lever  84  is biased into the clamping position by a bias spring  89  connected between an arm  90  of the lever  84  and a connection point  92  within the main body  32  of the infusion pump  10 . Another arm  94  of the lever  84  extends on the opposite side of the pivot point  86  and locates the compression edge  42  at a position for interaction with the anvil  44 . The other arm  94  also locates a release surface  96  ( FIG. 9 ) formed on the lever arm  94  at a location which is directly behind the access opening  46  ( FIG. 4 ) in the front panel  36  of the main body  32 . The bias spring  89  forces the compression edge  42  toward the anvil  44  and forces the release surface  96  toward the access opening  46 . 
         [0051]    The lever  84  is similar to a lever used in an internal occlusion clamp of a prior art infusion pump, except for the blocking lip  82  and the release surface  96 . In the conventional infusion pump, the blocking lip  82  is not used. Without the blocking lip  82 , the delivery tube can be forcibly removed from between the compression edge  42  and the anvil  44 . In the prior art infusion pump, the release surface  96  does not exist but instead a portion of the lever  84  continues forward and extends outside of the front panel  36 . The portion of the lever which extends forward from the front panel terminates in a contact, which is manually depressed by finger pressure of the user to open or release the internal occlusion clamp after the door has been opened. 
         [0052]    The lever lock mechanism  88  includes a plunger  98  which moves between a retracted position shown in  FIG. 11  and an extended position shown in  FIGS. 9 and 10 . A spring  100  extends from within a recess in the plunger  98  to contact a surface of the main body. The spring  100  biases the plunger  98  toward the lever arm  94 . A retaining edge  102  of the plunger  98  extends in front of and past the release surface  96  on the lever arm  94 . The retaining edge  102  of the plunger  98  holds the lever  84  to establish the open position of the occlusion clamp  43 . The release tab  28  of the slide clamp  12  contacts the release surface  96  of the lever arm  94  through the access opening  46 , and further insertion force applied to the slide clamp  12  pivots the lever  84  sufficiently so that the retaining edge  102  of the plunger  98  extends in front of the release surface  96 . With the plunger  98  in the extended position with the retaining edge  102  overlapping the release surface  96 , the lever  84  is pivoted so that the occlusion clamp  43  is in the open position. The bias spring  89  supplies enough pivoting force on the arm  84  to maintain sufficient frictional contact between the release surface  96  and the retaining edge  102  to hold the occlusion clamp  43  in the open position. 
         [0053]    Once the plunger  98  is in the extended position with the retaining edge  102  overlapping the release surface  96 , the occlusion clamp  43  can only be released by closing the door  30 . Releasing the occlusion clamp  43  is accomplished by moving the plunger  98  to a retracted position where the retaining edge  102  is withdrawn from contact with the release surface  96 , thereby allowing the lever arm  94  to pivot slightly forward. 
         [0054]    Moving the plunger  98  to the retracted position is accomplished by two release projections  104  which protrude from the inner surface  62  of the door  30  ( FIGS. 2 and 3 ). As the door  30  is closed from the open position ( FIG. 2 ), the door release projections  104  extend through openings  108  in the front panel  36  of the main body  32  and contact upper and lower portions of a slide pin  110  which extends vertically upward and downward from the plunger  98  ( FIGS. 11 and 12 ). Ramp surfaces of the door release projections  104  contact the slide pin  110 , and move the plunger to the retracted position by camming action as the door  30  closes. 
         [0055]    A door release tab  114  extends from the inner surface  62  of the door  30  into the access opening  46  when the door is closed. The door release tab  114  contacts the release surface  96  of the lever arm  94 , and holds the lever  84  in the position to release and open the occlusion clamp  43  when the door  30  is closed, as shown in  FIGS. 10 and 11 . 
         [0056]    The retaining edge  102  of the plunger  98  is moved laterally to the side of the release surface  96 , so that upon opening the door  30 , the plunger  98  does not prevent the lever  84  from pivoting to the occluding position. The plunger  98  of the lever lock mechanism  88  does not prevent the lever  84  from pivoting into the position to occlude the delivery tube  20  after the door  30  has been closed and when the door is opened. The plunger  98  of the lever lock mechanism  88  holds the lever  84  in the open position only after the slide clamp  12  has been used as an actuator to release the occlusion clamp  43  to its open position. 
         [0057]    A door latch lever  116  is pivotally connected to the door  30 , as shown in  FIGS. 1-3 . The door latch lever  116  locks the door  30  to the body  32  when the lever  116  is pivoted into the closed position ( FIG. 1 ). Pivoting the door latch lever  116  in the opposite direction unlocks the door  30  and allows it to open to the open position ( FIG. 2 ). An arc shaped portion  118  of the door latch lever  116  extends into a recess area  120  formed on a front panel  36  of the main body  32 . The arc shaped portion  118  engages a latch pin  122  which extends across a portion of the recess area  120 . Pivoting movement of the door latch lever  116  causes the arc shaped portion  118  to move relative to the latch pin  122  and pull the door  30  firmly against the front panel  36  of the main body  32 . Pivoting the door latch lever  116  in the opposite direction opens the door by releasing the arc shaped portion  118  from the latch pin  122 . 
         [0058]    To release the occlusion clamp  43  from occluding the delivery tube  20  ( FIGS. 6 ,  10  and  11 ), the slide clamp  12  is orientated horizontally and positioned such that the release tab  28  of the slide clamp  12  is adjacent to the access opening  46 , as understood from  FIGS. 4 and 5 . The projections  52  of the slide clamp  12  extend into the guide channels  54  ( FIG. 5 ). The release tab  28  is forced into contact with the release surface  96  of the lever arm  94  while portions of the delivery tube  20  immediately above and below the slide clamp  12  move into contact with the concave contact areas  50  ( FIG. 5 ) of the tube supports  48 , as shown in  FIGS. 6 ,  10  and  11 . The thick rear wedge-shaped portion  56  of the slide clamp  12  is pushed by force from the users thumb while the slide clamp  12  is maintained in alignment between the tube supports  48  by the projections  52  in the guide channels  54 . As the release tab  28  of the slide clamp  12  moves forward while in contact with the release surface  96  of the lever arm  94 , the lever  84  pivots into the position where the retaining edge  102  of the plunger  98  extends in front of and overlaps with the release surface  96  to thereby hold the lever  84  and establish the open position of the occlusion clamp  43  simultaneously while the portion of the delivery tube  20  within the slide clamp  12  is forced from the non-occluding opening  24  into the occluding slot  26 . The simultaneous occurrence of these two events effectively maintains, and transfers, the location of the occlusion from the occlusion clamp  43  to the slide clamp  12 . 
         [0059]    After the delivery tube  20  has been occluded by the slide clamp  12  in the manner described, any further use of the delivery tube will require the user to manually move the slide clamp  12  relative to the delivery tube  20  so that the delivery tube extends through the non-occluding opening  24 . Even if the delivery tube is inserted into the infusion pump and the infusion pump is operated, there will be no fluid flow through the delivery tube until the delivery tube  20  is moved into the non-occluding opening  24  of the slide clamp  12 . This requirement establishes the necessity for an additional safety-related manual action before fluid will flow through the delivery tube. 
         [0060]    Since use of the slide clamp  12  is required to release the delivery tube  20  from the occlusion clamp  43 , there is a reduced or eliminated possibility that a free flow condition through the delivery tube  20  will occur when the delivery tube  20  is removed from the infusion pump  10 . The infusion pump  10  as shown and described in relation to this invention is simpler in operation and construction than previously known anti-free flow infusion pumps. The infusion pump  10  and slide clamp  12  combination is also less costly to manufacture, and allows their use together in the manner which makes it relatively easy and straightforward to train medical personnel in the proper and safe use of the equipment. 
         [0061]    Another form of the anvil  44 , shown in  FIGS. 13-15 , further inhibits or prevents to the forcible removal of the delivery tube  20  from tubing channel  34  under circumstances where the delivery tube  20  should not be removed for safety reasons. A pair of spaced apart blocking projections  124  and  126  extend outward away from and beyond a restraint surface  125  on the anvil  44  against which the delivery tube  20  is compressed. The blocking projections  124  and  126  extend in the direction of the internal occlusion clamp  43 . The blocking projections  124  and  126  extend slightly into and partially across the tubing channel  34  when the occlusion clamp  43  is in the open position ( FIGS. 13 and 14 ). The blocking protrusions  124  and  126  are vertically spaced apart a sufficient distance to permit the blocking lip  82  and the portion of the compression edge  42  adjacent to the blocking lip  82  to move between the projections  124  and  126  when the occlusion clamp  43  moves into the closed position ( FIG. 15 ). 
         [0062]    The blocking lip  82  also extends outward away from and beyond the compression edge  42  ( FIGS. 4 ,  9 - 11  and  15 ) in the direction of the anvil  44 . The blocking lip  82  also extends slightly into and partially across the tubing channel  34  when the occlusion clamp is in the open position ( FIGS. 13 and 14 ). Insertion of the delivery tube  20  into the tubing channel  34  is accomplished by slightly compressing the delivery tube  20  with finger pressure to reduce its diameter sufficiently to pass between the opposing ends of the blocking lip  82  and the blocking projections  124  and  126 . 
         [0063]    In the closed position ( FIG. 15 ), the blocking lip  82  and a portion of the compression edge  42  adjacent to the blocking lip  82  are located between the blocking projections  124  and  126 . In this manner, the blocking lip  82  is interdigitated with the blocking projections  124  and  126 . The terminal ends of the blocking projections  124  and  126  are located behind the compression edge  42  of the occlusion clamp, and the terminal end of the blocking lip  82  is located beyond the restraint surface  125  ( FIGS. 13 and 14 ) of the anvil  43 . The terminal ends of the blocking projections  124  and  126  therefore overlap the compression edge  42  of the occlusion clamp  43 , and the terminal end of the blocking lip  82  overlaps the restraint surface  125  of the anvil  44 . 
         [0064]    The overlapping and interdigitated relationship between the blocking lip  82  and the blocking projections  124  and  126  eliminates any clear access space where the delivery tube  20  could be pulled or otherwise forced from between the compression edge  42  and the restraint surface  125 . The interdigitated and overlapping relationship requires the occlusion clamp  43  to be forced away from the anvil  44  by a significant distance to obtain enough space for removal of the delivery tube  20 , because the terminal ends of the projections  124  and  126  extend from the restraint surface and the terminal end of the lip  82  extends from the compression edge  42 . Moving the occlusion clamp  43  such a significant distance requires overcoming significant internal resistance within the pump  10  to such movement, and the extent of such movement and the internal resistance created by such movement should alert the person attempting such an improper tubing removal that his or her action is incorrect, leading the person to stop such action. However, when the occlusion clamp  43  is intentionally and appropriately separated from the anvil  44  during normal movement to the open position, there is enough space to remove the tubing  20  by compressing it within your pressure between the terminal ends of the blocking protrusions  124  and  126  and the blocking lip  82 . 
         [0065]    Another improvement which also inhibits or prevents unintended forcible removal of the delivery tube  20  from tubing channel  34  is accomplished by two obstruction protrusions  128  and  130 . The obstruction protrusions  128  and  130  extend outward from the front panel  36  of the pump  20  on opposite sides of an opening  132  in the front panel  36  through which a portion of the occlusion clamp  43  extends forward. As shown in  FIGS. 13 and 14 , the obstruction protrusions  128  and  130  extend forward from the front panel  36  to the same location as the end of the occlusion clamp  43  from which the blocking lip  82  extends, when the occlusion clamp is in either the open position ( FIGS. 13 and 14 ) or in the closed position ( FIG. 15 ). 
         [0066]    The obstruction protrusions  128  and  130  prevent a user from applying inward thumb or finger pressure on the end of the occlusion clamp  43  from which the blocking lip  82  extends. Inward thumb or finger pressure toward the front panel  36  on the end of the occlusion clamp  43  at the blocking lip  82  will tend to force the occlusion clamp  43  from the closed position ( FIG. 15 ) toward the open position ( FIGS. 13 and 14 ), as can be understood by reference to  FIGS. 9-11 . The pivot point  86  of the lever  84  of which the occlusion clamp  43  is a part, is located to the left (as shown) of the end of the occlusion clamp  43  from which the blocking lip  42  extends. If force is applied directly inward toward the front panel  36  on the end of the occlusion clamp  43 , a counterclockwise moment (as shown) on the lever  84  will be created. If this counterclockwise moment is sufficient, the lever  84  will rotate sufficiently counterclockwise (as shown) to separate the compression edge  42  from the anvil  44 , thereby tending to move the occlusion clamp to the open position ( FIGS. 13 and 14 ). 
         [0067]    The obstruction protrusions  128  and  130  block inward thumb or finger pressure from moving the end of the occlusion clamp  43  (as understood from  FIGS. 9-11 ), thereby preventing any significant separation of the compression edge  42  from the restraint surface  125 . The blocking lip  82  therefore remains in the overlapping relationship with the blocking projections  124  and  126  to prevent the unintended removal of the delivery tube  20  from the tubing channel  34 . 
         [0068]    The blocking projections  124  and  126  and the obstruction protrusions  128  and  130  are effective in preventing users which lack the proper training, presence of mind, or understanding, from defeating the inherent safety functionality and intended use features of the pump  20 . The blocking projections  124  and  126  and the obstruction protrusions  128  and  130  are straightforwardly incorporated into the pump  20  without requiring significant changes in the other components of the pump. 
         [0069]    A presently preferred embodiment of the present invention and many of its improvements have been described with a degree of particularity. This description is of a preferred example of implementing the invention, and is not necessarily intended to limit the scope of the invention. The scope of the invention is defined by the following claims.