Abstract:
A blood parameter measurement cassette or other device is configured to control incidental liquid discharged during the device&#39;s calibration process. The cassette includes optical sensors which are chemically responsive to blood constituents and require calibration with a blood parameter monitoring device prior to use in a medical procedure. During the calibration process, an incidental amount of a liquid may be expelled from the cassette. The present invention is directed towards controlling the expelled liquid by absorbing it using an absorbent material disposed on the exterior of the cassette&#39;s main body. The absorbent material thereby prevents the liquid from causing detrimental effects to the monitoring and calibration equipment used in conjunction with the cassette. The scope includes additional embodiments wherein the inventive concept is applied to other fluid-handling medical devices that require venting of gases.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to controlling liquid discharged from a blood parameter measurement cassette or other device during venting of the device while calibrating it by passing calibration gas through the device, and more generally to controlling incidental liquid discharged during a venting process of fluid-handling medical devices. 
         [0005]    2. Description of the Related Art 
         [0006]    Medical devices are often used during certain surgical procedures when various characteristics or parameters of blood are monitored in real time. For example, during open heart surgery the surgeon and other members of the surgical team often monitor the pH of the patient&#39;s blood as well as the concentration of certain blood gases such as carbon dioxide and oxygen. Measurement of blood parameters is often accomplished using optical sensors installed in a cassette connected to an extracorporeal blood circuit in fluid communication with the vascular system of the patient. 
         [0007]    For best results, the optical sensors of blood parameter measurement systems require calibration before use. One calibration technique, described in U.S. Pat. No. 5,997,818 to Hacker which is incorporated herein by reference in its entirety, involves bubbling calibration gases through a sterile liquid in the cassette chamber to calibrate the optical sensors to a blood parameter monitoring device. The calibration gas is vented to atmosphere after bubbling through the liquid. An incidental vestige of liquid may expel from the chamber along with the calibration gas as it is vented from the chamber to the atmosphere. 
         [0008]    Expelled liquid is undesirable since it may migrate into sensitive areas of the blood parameter monitoring device components and potentially cause negative effects to the electronic or optical equipment. However, the current state of the art allows incidental amounts of liquid to be expelled and potentially affect the monitoring and calibration equipment used in conjunction with the cassettes. 
         [0009]    From a broader perspective, many medical devices that receive a liquid flow require a venting process before the device is used in a medical procedure to remove air or other gases that may be contained within the interior of the device. If the gas is not removed prior to use, the safety and/or efficacy of the medical procedure may be negatively affected. For example, gas bubbles inside a medical device may collect in the area of highest elevation within the device and impede the liquid flow thereby reducing the performance of the device. In addition, the gas could be inadvertently injected into a patient, resulting in known health risks. 
         [0010]    Generally, whenever medical devices require a venting process to remove internal gases from a liquid, some potential exists for an incidental amount of the liquid to discharge from the device along with the gas. Discharged liquid related to venting can be problematic in the medical setting because of issues such as blood borne pathogens, cross-contamination of substances, slip and fall injuries, damage to sensitive equipment, and other safety concerns. A means for controlling the liquid discharged caused by a venting process would be beneficial to patients and practitioners in the medical setting. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention in one aspect concerns an improved blood parameter measurement cassette. The cassette includes optical sensors which are chemically responsive to blood constituents during a medical procedure. The sensors require calibration prior to use in a procedure. During the calibration process, an incidental amount of a liquid may be expelled from the cassette, as described below. The present invention is directed towards controlling the expelled liquid to prevent it from causing detrimental effects to the monitoring and calibration equipment used in conjunction with the cassettes. 
         [0012]    The main body of a blood parameter measurement cassette has a longitudinal axis that is oriented substantially vertically during the calibration process. In the vertical orientation, cassettes have a first port at their lower end, and a second port at their upper end. Between the upper and lower ports resides a middle chamber containing a liquid buffer solution that facilitates the calibration process. The cassette manufacturer furnishes the cassettes with the liquid pre-installed in the middle chamber. 
         [0013]    The cassette has a fitting coupled to the second port. The fitting is movable between a first closed position and a second venting position. While in the venting position an egress path is defined by the space between the cassette&#39;s main body and the fitting. The egress path is used during the calibration process to allow calibration gas to flow or vent from inside the cassette to the atmosphere. 
         [0014]    During the calibration process, the first port is used as a calibration gas inlet port for connection to a source of calibration gas from a calibrator device. The second port is used as a gas outlet port for venting the calibration gas to atmosphere. As the calibration gas vents from the cassette, it may induce an incidental amount of the liquid to expel from the main body through the gas outlet port. 
         [0015]    In order to control the expelled liquid, an absorbent material member is disposed on the periphery of the main body of the cassette at least partially in the egress path. During the calibration process the absorbent material permits calibration gas to vent to atmosphere but absorbs and retains the liquid expelled from the cassette&#39;s main body in association with the venting of the calibration gas. The absorbent material thereby mitigates the detrimental effects that may be caused by the liquid if it were to come in contact with the monitoring and calibration equipment used in conjunction with the cassettes. 
         [0016]    The present invention is also directed to other fluid-handling medical devices that have a fitting used for venting air or other gases from their interior to atmosphere. These medical devices may exhibit an adverse discharge of liquid during the venting process. An absorbent material member disposed on the exterior of the medical device at least partially in the egress path of the gas and liquid will allow gas to vent to atmosphere while absorbing liquid. The detrimental effects of the discharged liquid generated during a venting process will thereby be mitigated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a prior art blood parameter measurement cassette. 
           [0018]      FIG. 2  is a perspective elevation view illustrating the coupling of a cassette to a probe and the insertion of the cassette/probe combination into a calibrator. 
           [0019]      FIG. 3  is a perspective view of a cassette having an absorbent material as in the present invention. 
           [0020]      FIG. 4  is a longitudinal cross-sectional view of the upper end of a cassette in the venting position showing details of the fitting used for venting the cassette and the placement of the absorbent material on the periphery of the main body. 
           [0021]      FIG. 5  is a longitudinal cross-sectional view of the upper end of a cassette in the closed position showing details of the fitting used for venting the cassette and the placement of the absorbent material on the periphery of the main body. 
           [0022]      FIG. 6  is a flowchart illustrating the steps of a method of calibrating a blood parameter measurement cassette and collecting liquid discharged during venting. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    A prior art blood parameter measurement cassette  10  for measuring one or more parameters of blood is illustrated in  FIG. 1 . Cassette  10  broadly includes main body  12  with optical sensor(s)  14  and fitting  26 . 
         [0024]    Main body  12  includes an elongated casing having wall sections defining an elongated, internal, flow-through middle chamber  16  that extends along the longitudinal axis of main body  12 . Main body  12  further includes lower end  18  having a first or inlet port  20  for admitting fluid into middle chamber  16  and upper end  22  having a second or outlet port  24  (shown in  FIG. 4 ) for allowing fluid to exit middle chamber  16 . Optical sensor(s)  14  for measuring one or more parameters of blood may include a potassium sensor, a pH sensor, a carbon dioxide sensor, and an oxygen sensor that are arranged in an aligned, spaced-apart relationship on an interior surface along the longitudinal axis of middle chamber  16  as further described in U.S. Pat. No. 5,997,818 to Hacker. 
         [0025]    Fitting  26  has an internal threaded section that matingly receives an external threaded section disposed at upper end  22  of main body  12 . The threaded engagement of fitting  26  to main body  12  enables fitting  26  to be movable with respect to main body  12  between a first closed position and a second venting position. In a preferred embodiment, fitting  26  is a luer connector type fitting. 
         [0026]    In reference to  FIG. 2 , the optical sensor  14  calibration procedure will now be explained. Prior to actual use of blood parameter measurement cassette  10  for a medical procedure, optical sensor(s)  14  must be calibrated with a blood parameter monitor device (not shown). Cassette  10  comes from the cassette manufacturer with a sterile liquid buffer solution in middle chamber  16 . The calibration process involves mixing and dissolving gases having known concentrations of oxygen and carbon dioxide with the liquid. Sensor(s)  14  detect the partial pressures of the oxygen and carbon dioxide in the liquid and send corresponding signals to the monitoring device via probe(s)  204 . Since the concentrations of oxygen and carbon dioxide within the calibration gas are known by the monitoring device, the monitoring device can establish calibration factors to thereby reconcile any differences between the known and measured values. The calibration factors are used during the subsequent medical procedure wherein the optical sensors having been calibrated are utilized. 
         [0027]    As  FIG. 2  shows, calibration of cassettes  10  is performed by a system comprising calibrator  200  having supplies of known gases and one or two probes  204  in communication with a blood parameter monitor device (not shown). Cassettes  10  are specially designed to be mechanically coupled with probes  204  so as to ensure the cassette&#39;s optical sensor(s)  14  are properly adjacent to coordinating fiber optic bundles in probes  204  when in the coupled relationship with cassette  10 . After coupling is cassettes  10  to probes  204 , the combination is inserted into calibrator  200 . First port  20  of cassette  10  is positioned to mate with source of calibration gas  202  in calibrator  200  as the probe/cassette combination is inserted into calibrator  200 . This connection ensures source of calibration gas  202  is in fluid communication with cassette  10 . 
         [0028]    During calibration, cassettes  10  are oriented in an upright, preferably vertical position as shown in  FIG. 2 . Middle chamber  16  contains enough volume of sterile liquid to ensure all optical sensors  14  are in contact with liquid. 
         [0029]    Fitting  26  is then partially unthreaded by rotating fitting  26  relative to main body  12  in an arc about the longitudinal axis of main body  12 . During such motion, fitting  26  is moved from a first closed position to a second venting position for venting the gas to atmosphere. Loosening of the fitting  26  relative to main body  12  creates an egress path to enable calibration gas to flow from main body  12  to the atmosphere. 
         [0030]    A supply of calibration gas can then begin flowing. The gas flows from source of calibration gas  202 , through the cassette&#39;s first port  20 , into middle chamber  16 , i.e. bubbling through the liquid, through second port  24  (shown in  FIG. 4 ), through the space between fitting  26  and upper end  22  of main body  12 , and out to atmosphere. The gas supply creates gas bubbles as it flows up through the liquid in main chamber  16 . The gas bubbles burst as they emerge from the upper surface of the liquid in main chamber  16 . The bursting of the gas bubbles may cause a vestige of liquid to be entrained with the gas flow as it proceeds towards venting from cassette  10 . In prior art devices, this vestige of liquid could make its way completely out of cassette  10  and come to rest on surfaces of probes  204  or calibrator  200 . This liquid may be detrimental to the electronics or optics of probes  204  or calibrator  200 . When the calibration process is complete, fitting  26  is returned to its closed position. The probe/cassette combination is then removed from calibrator  200  and is ready for actual use in a medical procedure with a blood parameter monitoring device. 
         [0031]      FIG. 3  shows the improved blood parameter measurement cassette  10  of the present invention. Absorbent material member  30  is disposed at least partially in the is egress path of the venting gas and accompanying vestige of liquid. Absorbent material  30  will absorb liquid but allow the gas to flow away from cassette  10  to atmosphere. Absorption of the liquid by absorbent material  30  will prevent the liquid from detrimentally affecting the monitoring and calibration equipment used in conjunction with the cassettes. 
         [0032]    In a preferred embodiment, absorbent material  30  is comprised of a strip of medical grade gauze, such as Stratex material from DelStar Technologies, Inc. of Middletown, Del. The strip of absorbent material  30  is wrapped around the outer periphery of main body  12  to substantially surround it. In this embodiment absorbent material  30  may be affixed to main body  12  by use of a medical grade adhesive. In another embodiment absorbent material  30  may be comprised of a stretchable ring of absorbent material. The stretchable ring of absorbent material  30  will have an unstretched inner diameter that is smaller than the outer diameter of main body  12  at the location where the ring is disposed. This diametrical relationship creates an interference fit and the elasticity of the ring of absorbent material will retain it in the proper location. The stretchable ring of absorbent material  30  may be installed by simply stretching it over upper end  22  of the cassette and positioning it at the proper position on the outer periphery of main body  12  as shown in  FIG. 3  (e.g., prior to the installation of fitting  26  onto main body  12 ). 
         [0033]      FIG. 4  is a longitudinal cross-section view of the cassette&#39;s upper end  22  and fitting  26 . Fitting  26  is shown in the second venting position. In this view, the main body&#39;s second port  24  can be visualized. As shown, fitting  26  has internal threaded portion  36  that matingly receives external threaded portion  38  of upper end  22  of main body  12 . Egress path  28  is defined by the space between the cassette&#39;s upper end  22  and fitting  26 . Absorbent member  30 , shown in cross-section, is disposed on the outer periphery of main body  12  at least partially in egress path  28  and adjacent to annular flange  32  which is disposed on the exterior periphery of main body  12  adjacent to threaded portion  38  of upper end  22 . Fitting  26  includes annular shoulder  34  disposed on the interior periphery of the fitting&#39;s lower end. The outer diameter of flange  32  is slightly larger than the inner diameter of shoulder  34 . This diametrical relationship results in a physical interference between the main body&#39;s flange  32  and fitting&#39;s shoulder  34  and functions as a stop in order to prevent detachment of fitting  26  from main body  12 . However, the flexible materials of fitting  26  and shoulder  34  allow fitting  26  to be removed and/or replaced from main body  12  by overcoming the interference fit with the application of a small amount of manual force. 
         [0034]      FIG. 5  is a longitudinal cross-section view of the cassette&#39;s upper end  22  and fitting  26 . Fitting  26  is shown in the closed position. This view illustrates that at least a portion of the space occupied by absorbent material  30  when fitting  26  is in the venting position (shown in  FIG. 4 ) is preserved when fitting  26  is alternately located in the closed position. This preservation of space enables absorbent material  30  to substantially retain the liquid it absorbed during the calibration venting process when fitting  26  was in the open or venting position (i.e. it is not squeezed out). The retention of the liquid in absorbent material  30  thereby prevents the problems associated with liquid contamination of probes  204  or calibrator  200  as described above. 
         [0035]      FIG. 6  is a flow chart describing a method of collecting a liquid discharge generated by a venting process of a blood parameter measurement cassette during calibration. Step  300  consists of physically coupling the cassette to a blood parameter monitor probe. Next, as shown in step  310 , the probe/cassette combination is placed into the calibrator device. The cassette&#39;s lower port must be positioned to engage with the calibrator&#39;s gas supply nozzle to enable calibration gas flow from the calibrator to the cassette. Then the cassette&#39;s fitting will be opened to its venting position as stated in step  320 . Step  330  is the injection of calibration gas into the cassette by bubbling the calibration gas through the liquid located inside the middle chamber of the cassette. Step  340  describes the venting to atmosphere of the calibration gas as it egresses from the cassette through the space between the cassette&#39;s upper gas outlet port and the fitting. This space is also known as the egress path. As stated above, is some vestige liquid may be expelled with the venting gas, and step  350  refers to the collection of this vestige liquid by means of absorption by the absorbent material disposed at least partially in the egress path of the venting gas. Step  360  refers to the termination of the calibration gas flow after the phase of the calibration process requiring gas flow has been completed. Next, the fitting is returned to its closed position as shown in step  370 . Lastly, in step  380 , the probe/cassette combination is removed from the calibrator and is ready for actual use in a medical procedure with a blood parameter monitoring device. 
         [0036]    While the invention has been described in reference to a preferred embodiment comprising a blood parameter measurement cassette, it should be understood by those skilled in the art that the essence of the invention may be applied to other fluid-handling medical devices as well. In addition, various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed herein, but that the invention will include all embodiments falling within the scope of the claims.