Method and apparatus for thermal emulsification

[0002] 1. Field of the Invention

[0003] The present invention relates to a medical device that can remove tissue with a bolus of heated fluid.

[0004] 2. Background Information

[0005] There has been developed a medical procedure commonly referred to as phacoemulsification (“phaco”) that is performed to remove a cataracteous lens. A phaco procedure typically involves the steps of creating an incision in the cornea and inserting an ultrasonically driven tip that breaks the lens. The tip extends from a handpiece which is held by the surgeon. The handpiece is coupled to an irrigation line and an aspiration system. The irrigation line provides an irrigation fluid to the anterior chamber of the cornea. The aspiration system pulls the irrigation fluid and emulsified lens from the cornea.

[0006] Phacoemulsification with an ultrasonic tip typically requires the breaking of the lens into relatively large pieces before emulsification into fragments that can be irrigated. Having to break the lens can be time consuming and may lead to complications in the procedure. It has been found that the lens tissue can be emulsified with a heated liquid. The heated liquid must be introduced into the cornea without burning surrounding corneal tissue such as the epithelium. Burning the epithelium may impair the vision of the patient.

[0007] U.S. patent application Ser. No. 08/755,622 U.S. Pat. No. 5,865,790 discloses a device which can emulsify lens tissue with a heated fluid. The device includes a cannula that can be inserted into the cornea. The cannula has an inner channel that is coupled to an irrigation system. A passive heating element is located within the inner channel at a distal end of the cannula. The passive heating element creates heat within the fluid under an isenthalpic process. The generation of heat occurs within the anterior chamber of the cornea at a location away from the epithelium. The heat generated by the passive heating element disclosed in the '622 application is a continuous process. It may be desirable to provide a non-continuous process. For example, it may be desirable to generate a series of heated fluid slugs or a series of heated and non-heated fluid slugs that are directed onto the lens.

[0008] The amount of heat generated by the passive element is a function of the pressure drop across the element. The pressure drop is a function of the velocity of the fluid. The heat generated and the corresponding temperature of the irrigation fluid used to emulsify the tissue can be varied by changing the flowrate of the fluid through the cannula. Unfortunately, varying the flowrate must be upstream from the distal end of the cannula. Varying the flowrate upstream introduces a time delay between the change command and the response of the system. It may be desirable to varying the temperature essentially instantaneously. It would therefore desirable to provide a hydro-emulsifier that can generate discrete slugs of heated fluid and can quickly vary the temperature of the heated slugs.

[0009] One embodiment of the present invention includes a medical device that can emulsify tissue with a heated fluid. The device may include an active heating element that is located within an inner channel at a distal end of a cannula. The cannula is adapted to be inserted into tissue such as a cornea. The active heating element can provide heat to a fluid that flows through the inner channel.

[0010] FIG. 1 is an end view of an embodiment of a cannula of the present invention;

[0011] FIG. 2 is a cross-sectional view taken at line 2—2 of FIG. 1, showing an active heating element located within an inner channel of the cannula;

[0012] FIG. 3 is an end view of an alternate embodiment of the cannula;

[0013] FIG. 4 is a schematic showing a medical system which can deliver fluid and energy to the cannula and active heating element, respectively;

[0014] FIG. 5 is a cross-sectional view of an alternate embodiment of a cannula with an optical heating element;

[0015] FIG. 6 is a cross-sectional view of an alternate embodiment of a cannula with a radio frequency heating element;

[0016] FIG. 7 is a cross-sectional view of an alternate embodiment of a cannula with an ultrasonic heating element.

[0017] Referring to the drawings more particularly by reference numbers, FIGS. 1 and 2 show a cannula 10 of the present invention. The cannula 10 can deliver heated fluid that may emulsify tissue. For example, the cannula 10 can be inserted into a cornea and the heated fluid may emulsify a cataracteous lens. Although use in an ophthalmic procedure is described, it is to be understood that the cannula 10 can be used to emulsify other tissue. For example, the present invention can be used to emulsify tissue in a “liposuction” procedure.

[0018] The cannula 10 may include a first sleeve 12 that is located within an inner channel 14 of a second sleeve 16. The second sleeve 16 may be located within the inner channel 18 of a third sleeve 20. The diameter of the third sleeve 20 may be approximately 1.5 millimeters (mm), small enough to be inserted through an incision in a cornea 22. The sleeves 12, 16 and 20 may be constructed from either a metal or plastic material that will not collapse under the pressure of the cornea at the incision. An irrigation fluid may flow through the inner channel 18 of the third sleeve 20. The irrigation fluid and emulsified tissue may be aspirated through the inner channel 14 of the second sleeve 16.

[0019] The irrigation fluid may also flow through an inner channel 24 of the first sleeve 12. An active heating element 26 may be located within the inner channel 24 at the distal end of the sleeve 12. The heating element 26 transfers heat to irrigation fluid that flows through the inner channel 24 to raise the temperature of the fluid. The fluid is typically heated to a temperature that will emulsify tissue. By way of example, the fluid may be heated to a temperature of approximately 180 Fahrenheit (°F).

[0020] In one embodiment, the heating element may be an electrically resistive member connected to a current source (not shown) by a pair of wires 28 and 30. One of the wires 28 may extend through the inner channel 24. The other wire 30 may extend along the outer surface 32 of the first sleeve 12 and through an opening 34 to the active heating element 26. Although FIG. 2 shows one type of wire arrangement, it is to be understood that the wires 28 and 30 may be routed in a different manner. For example, both wires 28 and 30 may extend along the outer surface 32 of the first sleeve 12. If the first sleeve 12 is constructed from a metal material the wires 28 and 30 may be coated with an insulative material. If the first sleeve 12 is constructed from a dielectric material such as plastic, the wires 28 and 30 may be plated onto the sleeve 12 with known plating techniques.

[0021] The active heating element 26 converts current to thermal heat that is then transferred into the fluid. The heating element 26 may be porous so that the irrigation fluid can flow therethrough, wherein the element 26 functions as a micro-heat exchanger. Locating the heating element 26 at the distal end of the sleeve 12 provides a hydro-emulsifying device that can heat the fluid downstream from the corneal tissue. This reduces the amount of heat that is transferred into the cornea at the point of incision.

[0022] By way of example, the heating element 26 may be constructed from a sintered stainless steel UNS number 316. The sintered steel may have a porosity that also filters out particulates in the irrigation fluid. As another embodiment, the heating element 26 may be a non-porous resistive element that is smaller than the diameter of the inner sleeve 26 so that the irrigation fluid can flow past the element 26.

[0023] The cannula 10 may have an orifice 36 which has an inlet channel 38 and a tapered outlet 40 that creates a collimated stream of heated irrigation fluid. The orifice 36 can focus the heated fluid onto the tissue that is to be emulsified.

[0024] The orifice 36 may be separated from the heating element 26 by a space 42. The space 42 may define a volume or bolus of heated water that is directed onto the tissue by the orifice 36. As an alternate embodiment, the cannula 10 may have a filter at the location of the heating element 26 and a heating element 26 within the space 42 so that the irrigation fluid is filtered and then heated before flowing through the orifice 36.

[0025] FIG. 3 shows an alternate embodiment of a cannula 10′, wherein the first sleeve 12 and second sleeve 16 are both located within the inner channel 18 of the third sleeve 20. The cannula 10 may further have a fiber optic cable 44 that transmits light to illuminate the surgical site. The cannula 10′ may further have a temperature sensor 46 to sense the temperature of the irrigation fluid at the distal end of the sleeves.

[0026] FIG. 4 shows an embodiment of a medical system 50. The system 50 includes a handpiece 52 which has a cannula 10 or 10′. The handpiece 52 can be held by a surgeon performing a surgical procedure such as the removal of a cataract. The handpiece 52 is connected to a console 54. The console 54 may contain a driver circuit 56 that is connected to the handpiece 52 by an electrical cable 58. The driver circuit 56 may provide a current to the active heating element 26 shown in FIG. 2. The driver circuit 56 may include a power supply that periodically provides a pulse of power to the active heating element. By way of example, the driver circuit 56 may provide enough electrical power to heat 5-500 micro-liters of irrigation fluid, 100° F., within one second. To accomplish this result the power supply may provide a pulse at 3-6 volts, at a current between 0.5 to 10 amps, for a time duration between 0.1 to 100 milliseconds.

[0027] The console 54 may also have a bolus generator 60 that is coupled to the inner channel of the first sleeve by a tube 62. The generator 60 creates a bolus or pulse of fluid that flows into the first sleeve and across the active heating element. The driver circuit 56 may be synchronized with the bolus generator 60 so that power is provided to the active heating element when the bolus of fluid reaches the heating element.

[0028] It is preferable to construct the tube 62 from a material that will not significantly expand when subjected to the increase in pressure that results from the creation of the fluid bolus by the generator 60. By way of example, the tube 62 may be constructed from a polyether ether ketone (P.E.E.K.) material wrapped with a KEVLAR material or a metal material.

[0029] The bolus generator 60 may include a diaphragm pump 64 that is actuated by a solenoid 66. The pump 64 may be in fluid communication with a reservoir 68 of irrigation fluid. The solenoid 66 may be activated by a solenoid driver circuit 70. The driver circuit 70 may periodically activate and de-active the solenoid 66 which causes a pump chamber within the pump 64 to expand and contract. When the pump chamber expands irrigation fluid flows into the chamber through a one-way valve 72. When the pump chamber contracts the irrigation fluid flows out of the chamber through a one-way valve 74 and into the cannula 10 or 10′. The flow of fluid from the reservoir 68 to the pump 64 may be controlled by a pinch valve 76. Although a solenoid is shown and described, it is to be understood that the pump 64 may be driven by other means such as a piezoelectric or magneto-strictive transducer(s).

[0030] The reservoir 68 may also be coupled to the inner channel of the third sleeve by a tube 78 and a pinch valve 80. The inner channel of the second sleeve may be coupled to a peristaltic pump 82 by a tube 84. The pump 82 may pull irrigation fluid and emulsified tissue through the second sleeve. The driver circuit 56, solenoid driver circuit 70 and/or the pump 82 may be coupled to a foot pedal 86 which allows the surgeon to vary the flowrate of fluid and/or the number of fluid pulses per time that are provided to the cannula.

[0031] Referring to FIGS. 1, 2 and 4, in operation the surgeon may insert the cannula 10 or 10′ through tissue such as a cornea and into a cataracteous lens. Irrigation fluid is allowed to flow through the inner channel 18 of the third sleeve 24. The bolus generator 60 can periodically generate a bolus of fluid that flows into the inner channel 24 of the first sleeve 12. The bolus is heated by the heating element 26 and directed by the orifice 36 into or onto the tissue. The heated bolus of fluid impinges and emulsifies the tissue. The irrigation fluid and emulsified tissue is then aspirated through the inner channel 14 of the second sleeve 16 by the peristaltic pump 82. As one embodiment, the system 50 may create a heated bolus of fluid that is followed by a non-heated bolus of fluid. The series of heated bolus followed by non-heated bolus can be repeated many times.

[0032] FIG. 5 is an alternate embodiment of a cannula 100 which has an optical heating element. The cannula 100 may include a light source 102 that is coupled to an optical fiber 104 which extends through an inner channel 106 of a first sleeve 108. The light source 102 emits light that is transmitted by the fiber 104 onto an orifice 110. The wavelength of the light, and the material of the orifice 110 are such that the light is absorbed by the orifice material. The absorbed light heats the orifice 110. The heat is transferred to fluid that flows through an opening 112 in the orifice 110. By way of example, the light source 102 may be an xeon flash lamp or a laser.

[0033] FIG. 6 is an alternate embodiment of a cannula 120 which has a radio frequency heating element. The cannula 120 may include a radio frequency (RF) generator 122 that is connected to a coil 124. The coil 124 is located adjacent to an orifice 126 at the end of a sleeve 128. The generator 122 provides an alternating electrical current to the coil 124 which generates an electric field. The orifice 126 provides a resistance to the electric field wherein there is heat generated in the orifice 126. The heat is transferred into fluid that flows through an opening 130 in the orifice 126.

[0034] FIG. 7 is an alternate embodiment of a cannula 140 which has an ultrasonic heating element. The cannula 140 includes an ultrasonic generator 142 that is coupled to a sleeve 144. The generator 142 can ultrasonically drive the sleeve 144. The cannula 140 may have an orifice 146 that creates an acoustic impedance which results in the generation of heat in the orifice 146. The heat is transferred into fluid that flows through an opening 148 in the orifice 146. The ultrasonic movement of the sleeve 144 may also assist in emulsifying tissue.

[0035] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.