Abstract:
A surgical cassette having a chamber for fluidly coupling to a source of vacuum in a surgical console and a bubble breaking structure disposed within the chamber. The cassette protects the source of vacuum from liquid.

Description:
FIELD OF THE INVENTION 
     The present invention generally pertains to a surgical cassette for use with microsurgical systems, and more particularly to such cassettes for use with ophthalmic microsurgical systems. 
     DESCRIPTION OF THE RELATED ART 
     During small incision surgery, and particularly during ophthalmic surgery, small probes are inserted into the operative site to cut, remove, or otherwise manipulate tissue. During these surgical procedures, fluid is typically infused into the eye, and the infusion fluid and tissue are aspirated from the surgical site. The types of aspiration systems used, prior to the present invention, were generally characterized as either flow controlled or vacuum controlled, depending upon the type of pump used in the system. Each type of system has certain advantages. 
     Vacuum controlled aspiration systems are operated by setting a desired vacuum level, which the system seeks to maintain. Flow rate is dependent on intraocular pressure, vacuum level, and resistance to flow in the fluid path. Actual flow rate information is unavailable. Vacuum controlled aspiration systems typically use a venturi or diaphragm pump. Vacuum controlled aspiration systems offer the advantages of quick response times, control of decreasing vacuum levels, and good fluidic performance while aspirating air, such as during an air/fluid exchange procedure. Disadvantages of such systems are the lack of flow information resulting in transient high flows during phacoemulsification or fragmentation coupled with a lack of occlusion detection. Vacuum controlled systems are difficult to operate in a flow controlled mode because of the problems of non-invasively measuring flow in real time. 
     Flow controlled aspiration systems are operated by setting a desired aspiration flow rate for the system to maintain. Flow controlled aspiration systems typically use a peristaltic, scroll, or vane pump. Flow controlled aspiration systems offer the advantages of stable flow rates and automatically increasing vacuum levels under occlusion. Disadvantages of such systems are relatively slow response times, undesired occlusion break responses when large compliant components are used, and vacuum can not be linearly decreased during tip occlusion. Flow controlled systems are difficult to operate in a vacuum controlled mode because time delays in measuring vacuum can cause instability in the control loop, reducing dynamic performance. 
     One currently available ophthalmic surgical system, the MILLENIUM system from Storz Instrument Company, contains both a vacuum controlled aspiration system (using a venturi pump) and a separate flow controlled aspiration system (using a scroll pump). The two pumps can not be used simultaneously, and each pump requires separate aspiration tubing and cassette. 
     Another currently available ophthalmic surgical system, the ACCURUS® system from Alcon Laboratories, Inc., contains both a venturi pump and a peristaltic pump that operate in series. The venturi pump aspirates material from the surgical site to a small collection chamber. The peristaltic pump pumps the aspirate from the small collection chamber to a larger collection bag. The peristaltic pump does not provide aspiration vacuum to the surgical site. Thus, the system operates as a vacuum controlled system. 
     In both vacuum controlled aspiration systems and flow controlled aspiration systems, the liquid infusion fluid and ophthalmic tissue aspirated from the surgical site are directed into an aspiration chamber within a surgical cassette. In vacuum controlled aspiration systems, the aspiration chamber in the surgical cassette is fluidly coupled to a source of vacuum within a surgical console. It is important to protect the source of vacuum from liquid, while maintaining the ability to aspirate air from above the partially liquid-filled aspiration chamber. In the past, hydrophobic filter media were incorporated into the fluid line between the vacuum source and aspiration chamber to provide such protection. However, such filter media delayed air flow and correspondingly increased the fluidic response time of the surgical system. In addition, large air chambers or long fluid paths have been incorporated into conventional ophthalmic surgical systems to reduce the likelihood of liquid reaching the source of vacuum. However, such added volumes of air increased the fluidic response time of the surgical system due to an increased amount of a compressible fluid in the system. 
     Accordingly, a need continues to exist for an improved method of protecting a source of vacuum in the aspiration system of a microsurgical system from liquid. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a surgical cassette. The surgical cassette includes a chamber for fluidly coupling to a source of vacuum in a surgical console and for containing a volume of air, and a bubble breaking structure disposed within the chamber. 
     The volume of air comprises entrained liquid. The bubble breaking structure has a geometry that facilitates breaking of air bubbles so that the entrained liquid is removed from the air and does not pass to the source of vacuum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and for further objects and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram illustrating aspiration control in a microsurgical system; 
         FIG. 2  is a front, perspective view of a body of a surgical cassette showing a bubble breaking structure according to a preferred embodiment of the present invention; 
         FIG. 3  is a front view of the surgical cassette body of  FIG. 2 ; 
         FIG. 4  is a rear view of the surgical cassette body of  FIG. 2 ; 
         FIG. 5  is an enlarged, fragmentary, front, perspective view of body of a surgical cassette showing a bubble breaking structure according to a second preferred embodiment of the present invention; and 
         FIG. 6  is an enlarged, fragmentary, front, perspective view of body of a surgical cassette showing a bubble breaking structure according to a third preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention and their advantages are best understood by referring to  FIGS. 1-6  of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
     Microsurgical system  10  includes a pressurized gas source  12 , an isolation valve  14 , a vacuum proportional valve  16 , an optional second vacuum proportional valve  18 , a pressure proportional valve  20 , a vacuum generator  22 , a pressure transducer  24 , an aspiration chamber  26 , a fluid level sensor  28 , a pump  30 , a collection bag  32 , an aspiration port  34 , a surgical device  36 , a computer or microprocessor  38 , and a proportional control device  40 . The various components of system  10  are fluidly coupled via fluid lines  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56 , and  58 . The various components of system  10  are electrically coupled via interfaces  60 ,  62 ,  64 ,  66 ,  68 ,  70 ,  72 ,  74 , and  76 . Valve  14  is preferably an “on/off” solenoid valve. Valves  16 - 20  are preferably proportional solenoid valves. Vacuum generator  22  may be any suitable device for generating vacuum but is preferably a vacuum chip or a venturi chip that generates vacuum when isolation valve  14  and vacuum proportional valves  16  and/or  18  are open and gas from pressurized gas source  12  is passed through vacuum generator  22 . Pressure transducer  24  may be any suitable device for directly or indirectly measuring pressure and vacuum. Fluid level sensor  28  may be any suitable device for measuring the level of a fluid  42  within aspiration chamber  26  but is preferably capable of measuring fluid levels in a continuous manner. Pump  30  may be any suitable device for generating vacuum but is preferably a peristaltic pump, a scroll pump, or a vane pump. Microprocessor  38  is capable of implementing feedback control, and preferably PID control. Proportional controller  40  may be any suitable device for proportionally controlling system  10  and/or surgical device  36  but is preferably a foot controller. 
     System  10  preferably utilizes three distinct methods of controlling aspiration, vacuum control, suction control, and flow control. These methods are more fully described in co-pending U.S. application Ser. No. 11/158,238 filed Jun. 21, 2005 and co-pending U.S. application Ser. No. 11/158,259, both of which are commonly owned with the subject application and are incorporated herein by reference. 
     In each of these methods, vacuum may be provided to surgical device  36  and aspiration chamber  26  via fluid lines  50 ,  56 , and  58 . Aspiration chamber  26  fills with fluid  42  aspirated by surgical device  36 . Fluid  42  includes liquid infusion fluid as well as aspirated ophthalmic tissue. 
     As shown best in  FIGS. 2-4 , a surgical cassette  100  has a body  102  including aspiration chamber  26  and aspiration source chamber  104 . A cover, which is fluidly sealed to the front side of body  102 , is not shown for purposes of clarity. A pinch plate, which is fluidly sealed to the rear side of body  102 , is not shown for purposes of clarity. Aspiration source chamber  104  preferably has a small volume relative to aspiration chamber  26 . An entry  106  fluidly couples aspiration chamber  26  and aspiration source chamber  104 . A port  108  fluidly couples aspiration source chamber  104  and fluid line  50 . As discussed hereinabove, fluid line  50  is fluidly coupled to vacuum generator  22 . An entry  110  fluidly couples aspiration chamber  26  and fluid line  56 . An entry  112  fluidly couples aspiration chamber  26  and fluid line  52 . Aspiration source chamber  104  includes a bubble breaking structure  114 . Bubble breaking structure  114  preferably includes a first appendage  114   a  extending from an internal wall of aspiration source chamber  104  and a second appendage  114   b  extending from an internal wall of aspiration source  104 . Appendages  114   a  and  114   b  preferably have a thin, planar geometry and are preferably disposed in an opposing manner relative to one another. The distal ends of appendages  114   a  and  114   b  are preferably angled downward toward aspiration chamber  26 . Body  102  is preferably molded from a plastic material. Aspiration chamber  26 , aspiration source chamber  104 , entry  106 , port  108 , entry  110 , entry  112 , and bubble breaking structure  114  are preferably integrally molded into body  102 . 
     As shown best in  FIG. 1 , liquid  42  is present in aspiration chamber  26 , and air  43  is present in aspiration chamber  26  above liquid  42 . When the surgical system supplies vacuum to aspiration chamber  26 , some liquid  42  is mixed with air  43 , typically on or in air bubbles, and is aspirated through entry  106  into aspiration source chamber  104 . As such bubbles pass through entry  106 , they contact appendage  114   a , appendage  114   b , and/or the internal surface of aspiration source chamber  104 . Such contact breaks the bubbles, and any entrained liquid falls back into aspiration chamber  26  via entry  106 . The downward angling of appendages  114   a  and  114   b  facilitates the flow of liquid back into aspiration chamber  26 . 
       FIG. 5  shows a bubble breaking structure  115  according to a second preferred embodiment of the present invention. Bubble breaking structure  115  includes a body  116  that shields port  108  from bubbles or other entrained liquid in aspiration source chamber  104 . Body  116  preferably has a generally U-shaped geometry. Body  116  has an upper end  118  disposed just below internal wall  120  of aspiration source chamber  104  which allows passage of air into port  108 . As bubbles pass around bubble breaking structure  115  toward upper end  118 , they contact the internal surface of aspiration source chamber  104  and/or bubble breaking structure  115 . Such contact breaks the bubbles, and any entrained liquid falls back into aspiration chamber  26  via entry  106 . 
       FIG. 6  shows a bubble breaking structure  130  according to a third preferred embodiment of the present invention. Bubble breaking structure  130  is preferably an appendage extending from top internal surface  132  of aspiration chamber  26 . Bubble breaking structure  130  preferably has a thin, planar geometry. The distal end of bubble breaking structure  130  is preferably angled downward toward the bottom of aspiration chamber  26 . As bubbles or other entrained liquid pass near entry  106 , they contact the internal surface of aspiration chamber  26  and/or bubble breaking structure  130 . Such contact breaks the bubbles, and any entrained liquid falls back into aspiration chamber  26 . The downward angling of structure  130  also prevents upward flow of liquid through entry  106 . 
     The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. For example, the surgical cassette of the present invention may include a first bubble breaking structure in the aspiration source chamber and a second bubble breaking structure in the aspiration chamber. 
     It is believed that the operation and construction of the present invention will be apparent from the foregoing description. While the apparatus and methods shown or described above have been characterized as being preferred, various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the following claims.