Absorption-based optical sensor for detecting infusion pump cassette

An infusion pump has an optical cassette detection system for determining whether or not a cassette of an administration tubing set is properly loaded in the pump. Operation of the pump may be enabled or disabled based on a determination of the cassette detection system. The cassette detection system includes a light emitter and a corresponding photosensitive detector aligned along an optical axis, and window carried by the cassette. When the cassette is properly loaded in the pump, a light beam from the emitter enters the window, where a portion of the beam is absorbed and another portion of the beam is transmitted for receipt by the detector. The detector signal is evaluated by signal evaluation electronics to determine if the cassette is loaded. The determination may be based on an expected attenuation of the light beam corresponding to a predetermined light absorptance property of the window.

FIELD OF THE INVENTION

The present invention relates generally to infusion pumps for controlled delivery of liquid food and medications to patients. More specifically, the present invention relates to a sensor system in an infusion pump for detecting the presence or absence of a cassette by which an administration tubing set is operatively connected to the pump.

BACKGROUND OF THE INVENTION

Programmable infusion pumps are used to carry out controlled delivery of liquid food for enteral feeding and medications for various purposes, for example pain management. In a common arrangement, an infusion pump receives a disposable administration set comprising a cassette removably received by the pump and flexible tubing connected to the cassette for providing a fluid delivery path through the pump.

The cassette itself may be intended for use with a particular infusion pump model or models, and/or with tubing having predetermined properties. In this regard, the cassette may include safety features that are designed and manufactured according to specifications determined at least in part by the intended infusion pump model and/or administration set tubing. The safety features of the cassette may cooperate with corresponding features on the matching pump, and may be manufactured according to size tolerances related to tubing diameter and flexibility. For example, the cassette may have an anti-free flow mechanism for protecting the patient from uncontrolled fluid delivery. The anti-free flow mechanism may take the form of an external pinch clip occluder actuated when the cassette is properly loaded in the pump and a door of the pump is closed. Alternatively, the anti-free flow mechanism may take the form of an internal “in-line occluder” that resides within the flow passage of the tubing, wherein a flow passage is only opened when the cassette is properly loaded in the pump and the pump door is closed.

The cassette may provide additional safety features beyond free flow protection. For example, the cassette may be matched to the pump to maintain a desired volumetric accuracy of the pump, and to ensure correct function of occlusion and air-in-line sensors used to trigger safety alarms.

In view of the safety importance of the cassette, it is desirable to provide means to detect whether or not a matching cassette is properly loaded in the pump as a precondition to enabling pump operation.

SUMMARY OF THE INVENTION

In accordance with the present invention, an infusion pump in which an administration set is removably received is provided with an optical detection system for determining whether or not a cassette of the administration set is properly loaded in the pump. In an embodiment of the present invention, operation of the pump is disabled if a cassette is not properly loaded in the pump.

The optical cassette detection system comprises an optical emitter mounted to the pump and arranged to emit a light beam directed along an optical axis, and a photosensitive detector mounted to the pump and arranged to receive the light beam along the optical axis. The cassette detection system further comprises a window carried by the cassette. The window is arranged to intersect the optical axis at a location between the optical emitter and the photosensitive detector when the cassette is properly loaded in the pump. The window absorbs a portion of the light beam and transmits another portion of the light beam. The transmitted portion of the light beam is received by the photosensitive detector. The photosensitive detector generates a detector signal representing an intensity of light received thereby.

The detector signal is evaluated by signal evaluation electronics to determine if the detector signal level is within an expected range, indicating presence of the cassette. The signal evaluation electronics may be in communication with a pump controller, wherein the pump controller is programmed to disable pump operation unless a cassette is present as determined by the optical cassette detection system.

The window may be made to have a predetermined absorptance with respect to a wavelength band of the light beam. In the context of the present specification, and as understood by persons skilled in the art of optical systems, “absorptance” means the ratio of the absorbed radiant or luminous flux to the incident radiant or luminous flux. By way of illustrative example, a window having an absorptance of 60% will absorb 60% of the beam energy and transmit the remaining 40% of the beam energy. Where the window has a known predetermined absorptance, the signal evaluation electronics can check for an expected attenuation indicated by reduction in the detector signal level from before a cassette is loaded to after a cassette is loaded.

In an embodiment of the invention, the window includes a light entry surface and a light exit surface parallel to the light entry surface, and the window is integrally formed with the cassette in a one-piece molded part made of transparent plastic or translucent plastic. The thickness of the window from light entry surface to light exit surface may be controlled, and the plastic may be doped with a constituent, to achieve a predetermined absorptance.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows an infusion pump10in which an administration set12is removably received. Administration set12includes a cassette14, which is shown by itself inFIG. 2. Cassette14may include an input connector16, an upstream loop connector18in flow communication with input connector16, a downstream loop connector20, and an output connector22in flow communication with downstream loop connector20. Administration set12may further include inflow tubing24having one end mated to input connector16and an opposite end (not shown) connected to a fluid source, and outflow tubing26having one end connected to output connector22and an opposite end (not shown) connected to a patient. Finally, administration set14may further include a pumping segment of tubing28having one end mated to upstream loop connector18and an opposite end mated to downstream loop connector20.

In the illustrated embodiment, pump10is a rotary peristaltic pump having a rotor30, wherein pumping segment28is wrapped around rotor30and is engaged by angularly spaced rollers on rotor30as the rotor rotates to provide peristaltic pumping action forcing liquid through the tubing of administration set12. As may be understood by reference toFIG. 1, when rotor30rotates in a counter-clockwise direction, liquid is moved from inflow tubing24through input connector16and upstream loop connector18to pumping segment28, and then from pumping segment28through downstream loop connector20and output connector22to outflow tubing26. Although the present invention is described in the context of a rotary peristaltic pump, the invention is not limited to this type of infusion pump. The invention may be practiced with any type of infusion pump that receives an administration set having a cassette.

Cassette14may include an in-line occluder32which may be incorporated into downstream loop connector20. In-line occluder32prevents flow when pump door34is open. An actuator36on an underside of pump door34engages pumping segment28in a manner which opens a flow path around occluder32when door34is closed.

Reference is now made toFIGS. 3A and 3B. Cassette14includes a tab38depending downwardly from a ribbed thumb portion40of the cassette. In the present embodiment, tab38is a generally planar tab that is sized for receipt within a corresponding slot42in pump10. Slot42may be provided at a location on pump10between the upstream and downstream portions of pumping segment28, and tab38may be provided on an underside of thumb portion40. For example, slot42may be midway between the upstream and downstream portions of pumping segment28and may be elongated in a direction aligned with the rotation axis of rotor30, and tab38may be midway between one side of cassette14having input connector16and upstream loop connector18and the other side of cassette14having downstream loop connector20and output connector22. In this symmetrical arrangement, cassette14is easily centered in pump10relative to rotor30during installation of administration set12. In an embodiment of the invention, the width of slot42is 2.6 mm and the width of tab38is 1.7 mm.

Pump10includes an optical cassette detection system50operable to detect whether or not cassette14is properly loaded in pump10with cassette tab38present in slot42. Cassette detection system50includes an optical emitter52, which may be mounted to pump10on one side of slot42, and a photosensitive detector54, which may be mounted to pump10on an opposite side of slot42. In the illustrated embodiment, detector54is aligned with emitter52along an optical axis58passing through slot42. Detector54generates a signal, for example a current or voltage signal, having a level corresponding to the intensity of light received by the detector. Cassette detection system50further includes a window55carried by cassette14. In accordance with the present invention, window55is arranged on cassette14to intersect optical axis58at a location between optical emitter52and photosensitive detector54when cassette14is properly loaded in pump10. In the embodiment shown herein, emitter52and photosensitive detector54are each mounted in pump10adjacent to slot42, and window55is part of tab38, however other configurations and arrangements are possible.

Cassette detection system50may also include signal processing electronics56connected to photosensitive detector54for receiving an electronic signal generated by detector54and evaluating the signal. Signal processing electronics56may be in communication with a pump controller60, whereby operation of pump10may be controlled based on an evaluation of the detector signal.

As best seen inFIG. 3B, window55may include a light entry surface62normal to optical axis58, and a light exit surface64also normal to optical axis58. Window55may be integrally formed with tab38or with cassette14as a whole, wherein surfaces62and64are formed as external surface features of the molded part. For example, cassette14may be molded from transparent or translucent optical grade plastic that is doped with a constituent or otherwise provided with a desired absorptivity (internal absorptance per unit length). Possible doping constituents include, but are not limited to, ROMBEST® HT 555, VIBATAN® PE IR Absorber 00535, and Polytechs IR 67. The thickness of window55from entry surface62to exit surface64may be specified in conjunction with the absorptivity of the window material to achieve a desired absorptance value for window55as a whole.

When cassette14is not loaded in pump10, the light beam from emitter52passes directly to detector54with negligible beam attenuation because window55is not present. As a result, detector54generates a relatively high signal level, referred to herein as a “baseline signal,” when cassette14is not loaded. When cassette14is properly loaded in pump10, window55absorbs a portion of the light beam from emitter52and transmits another portion of the light beam. As will be understood, the transmitted portion of the light beam is received by photosensitive detector54. Consequently, when cassette14is loaded in pump10, the level of the signal generated by detector54is reduced somewhat relative to the baseline signal.

Window55may have a predetermined absorptance with respect to a wavelength band of the light beam that is greater than 0% (no absorption) and less than 100% (complete absorption). The baseline detector signal will be reduced according to a predetermined ratio by properly loading cassette14in the infusion pump10, wherein the predetermined ratio is greater than 0% and less than 100%. The predetermined ratio may correspond to the predetermined absorptance of window55in one of two ways. First, if dark current and noise are eliminated from the detector signal by system calibration such that the entire detector signal varies proportionally with changes in the intensity of received light, then the reduction ratio will correspond directly with the absorptance of window55. For example, if the absorptance of window55is 75%, then a 75% reduction in the detector signal level relative to the baseline signal level is expected. Second, if dark current and noise are not eliminated from the detector signal such that the detector signal has a fixed component that does not vary proportionally with changes in the intensity of received light and a variable component that does vary proportionally with changes in the intensity of received light, then only the variable component of the detector signal will be reduced by introduction of window55. In this latter case, the reduction ratio will correspond indirectly with the absorptance of window55according to the following relation:
REDUCTION RATIO=ABSORPTANCE×((BASELINE−DARK)/BASELINE)
For example, if the detector signal has a fixed level of 20 units under dark conditions and a baseline level of 100 units, and the absorptance of window55is 75%, then loading of the cassette will cause an expected reduction of the signal level from 100 units down to 40 units. In this example, the overall reduction ratio is 60% and corresponds indirectly with the window absorptance, taking into account a fixed dark signal component. Under either scenario, a predictable reduction in the detector signal is associated with proper loading of cassette14.

Signal processing electronics56evaluates the signal from detector54to determine if cassette14is properly loaded in pump10. The signal processing and evaluation may be completely analog, or the detector signal level may be converted to a digital value and compared to a threshold in a digital comparator circuit. As illustrated inFIG. 4, operation of pump10may be enabled or disabled based on the determination made by signal processing electronics56.

In block100, a routine is executed at pump startup to read and store the signal level of detector54when there is no cassette loaded and emitter52is OFF (the so-called “dark” of fixed detector signal level), and to read and store the baseline signal level of detector54when there is no cassette loaded and emitter52is ON. A calibration of the detector signal may be executed as part of the startup routine as indicated by block102to eliminate effects of the fixed dark signal component. After startup, the level of the detector signal is read in block104to ascertain loading of a cassette. In block106, the signal level may be evaluated to determine if it is in an acceptable range based on the predetermined baseline signal level and the absorptance of window55. For example, if the baseline signal is 100 units and the expected reduction ratio directly corresponds to a window absorptance of 75%, then the acceptable range may be a range that includes 25 units plus or minus a variability tolerance, for example plus or minus 5 units. Under this example, the acceptable signal level range would be from 20 units to 30 units. If the measured signal level falls in the acceptable range, proper loading of a cassette is indicated and flow branches to block108, wherein pump operation is enabled by pump controller60. However, if the signal level is outside of the acceptable range, flow branches to block110and pump operation is disabled by pump controller60.

Emitter52may be a light-emitting diode (LED) or other light source, and photosensitive detector54may be a photodiode or other photosensitive element capable of generating an electrical signal in response to incident light. Emitter52and detector54may be chosen to operate within predetermined wavelength bands. For example, where window55is made to absorb light in an infrared wavelength band, emitter52may be chosen to emit light in that infrared band, and detector54may have a spectral responsivity substantially confined to that infrared band. Alternatively, emitter52may be a narrow band emitter, for example a laser diode. Likewise, detector54may have a spectral responsivity across a relatively wide wavelength band that includes the emission wavelength band. Emitter52and detector54may be optically coupled by light outside the visible spectrum, e.g. infrared or ultraviolet light. While not shown, emitter52and detector54may have lenses, fiber optics, or other optical elements associated therewith for collimating, focusing, and/or directing the beam.

Tab38on cassette14provides structure that may be used for carrying window55and positioning the window in optical cassette detection system50. A wide variety of tab arrangements and optical detection system configurations are of course possible. The centered arrangement of a thin tab38on the underside of cassette14, and the use of a thin slot42in pump10, takes advantage of the tab and slot as a means for guiding and centering the cassette14during installation. Moreover, the cassette detection system50is hidden within the pump and is inconspicuous to users. Emitter52and detector54may be recessed slightly from the surface of slot42behind respective transparent barriers (not shown) to keep dirt and fluid away from the emitter and detector.

While the invention has been described in connection with exemplary embodiments, the detailed description is not intended to limit the scope of the invention to the particular forms set forth. The invention is intended to cover such alternatives, modifications and equivalents of the described embodiment as may be included within the spirit and scope of the invention.