Surgery – Instruments – Heat application
Reexamination Certificate
1999-08-13
2003-09-30
Cohen, Lee (Department: 3739)
Surgery
Instruments
Heat application
C606S030000, C606S031000
Reexamination Certificate
active
06626901
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to instruments and methods for sealing and joining or cutting tissue. The instruments of the present invention are especially intended for use during either conventional open surgery or endoscopic or laparoscopic surgery.
BACKGROUND OF THE INVENTION
Hemostasis, or blood clotting, can be obtained by the activation of a naturally occurring biological pathway known as the coagulation cascade. The pathway can be activated by tissue injury. This injury can come from mechanical, chemical thermal sources. This natural biological pathway results in the conversion of freely flowing blood to a blood clot. Several biological elements are involved in the coagulation cascade, including tissue proteins, mainly fibrin and thrombin. Cells such as platelets and red and white blood cells are also involved.
During surgery, hemostasis can also be achieved by direct denaturization of the proteins found in the blood. Denaturization of a protein means that its characteristic three dimensional structure is altered without actually breaking up the protein. This direct denaturization is a purely physico-chemical process in which the denatured proteins bond together, forming an amorphous mass of protein which is comparable to a naturally occurring clot. How does denaturing a protein cause it to stick together with neighboring proteins? Proteins generally have a complex three-dimensional structure. A protein is actually a chain of smaller molecules called peptides, which peptides may have side-chains which contain a molecular group which can attract a molecular group on another side chain. The main protein chain is looped and folded on itself in a complex way which results in the three-dimensional structure characteristic of the protein. This looping and folding occurs because of an intra-molecular attraction between side-chains of the peptides. This attraction between side-chains is generally of the “hydrogen bond” or electrostatic type. The attraction which holds the peptides together along the main chain is a covalent bond. When a protein is denatured, it loses its normal three-dimensional structure. As a result of this unfolding of the protein molecule, the side-chains on the peptides, instead of facing “inward” to fold up the protein chain are now able to bond to side chains from proteins which are neighbors. This inter-molecular bonding results in the formation of a lump of denatured protein. This process is not dependent on the activation of the biological cascades of the natural clotting mechanism, but it is a purely physico-chemical process. For hemostasis, the tissue proteins which must be denatured are chiefly those in blood such as hemoglobin and albumin but also include structural proteins such as those found in the wall of blood vessels or in other anatomical structures.
One of the best ways to denature a protein is to heat it up to a temperature high enough to cause the intra-molecular hydrogen bonds to break, but which is not high enough to break the much stronger peptide-peptide covalent bonds along the main chain. A prime example of this process is the heating up of the clear part of an egg until it turns white. This white color means that the original clear protein has been denatured.
Heat which is delivered to tissue proteins may start out as electrical energy, light energy, radiowave energy, or mechanical (vibrational or frictional) energy. As far as the tissue is concerned, it does not matter what the original source of the original energy is, as long as it gets converted in some fashion to heat.
For example, if the source of the energy is a laser, then the light energy is absorbed by molecules in the tissue whose absorption spectrum matches the wavelength of the laser light being used. Once the light energy is absorbed, heat is produced, and the physico-chemical process of protein denaturation is achieved. Any sort of light energy will have this effect, if its wavelength is such that it can be absorbed by the tissue. This general process is called photocoagulation. The advantage of using a laser is that since its output is monochromatic, one can selectively heat certain tissue elements which have the right absorption spectrum, while sparing other tissue elements for which the laser light is not absorbed. This principle is used commonly in ophthalmology. Another advantage of using a laser is that its coherent and collimated beam can be very tightly focused on very small targets. If one does not care about spatial precision or selective photocoagulation of only certain tissue elements, then it is perfectly possible to coagulate tissue by using a very bright but otherwise ordinary light.
If the source of energy is electrical currents flowing through the tissue, the process is called “electrosurgery”. What happens here is that the current flowing through the tissue heats up the tissue because the tissue has resistance to the flow of electricity (“Ohmic heating”). In the case of ultrasonic coagulation, the rapid vibration of the ultrasonic element induces heating in essentially the same fashion as the production of fire by rubbing sticks together (although the rate of vibration is much much higher and the process is more controllable).
Since it is heat that denatures and coagulates proteins, why go to all the trouble of starting with a laser or an electrosurgery unit? Why not just use a very simple source of heat, such as a resistance wire or, even simpler, a hot piece of metal? In antiquity, “cautery” via a hot piece of iron was used to staunch bleeding wounds. The problem with this approach is not efficacy, it is control and containment of the amount and extent of tissue which is cauterized or injured.
In fact, the development of “electrocautery” in the late 1920's by Professor of Physics William T. Bovie was spurred by the desire (of the pioneering neurosurgeon Dr. Harvey Cushing) to have a more controllable and refined means of producing heat in tissues than possible by using a large piece of heated metal. Electrocautery uses very high frequency alternating electrical current, since it was found that these high frequencies did not cause tetanic (“Galvanic”) stimulation of muscle tissue which occurs when direct current or low frequency current is used. To avoid muscular stimulation, it is necessary to use alternating currents with very high frequencies, about several hundred thousand cycles-per-second. This high frequency falls in the range of the AM radio band, which is the reason why many electrical instruments such as monitors used in the OR will register interference when electrocautery is activated. There are many potential problems stemming from the use of such high frequencies, including difficulty in controlling stray currents which can injure patients and interfere with pacemakers and computer equipment. Electrocautery has been refined over the past fifty years, but it still represents a rather round-about way of getting tissue to heat up.
Numerous instruments are known which coagulate, seal, join, or cut tissue. For example, there are electrosurgical instruments, both monopolar and bipolar, which use high frequency electrical current that passes through the tissue to be coagulated. The current passing through the tissue causes the tissue to be heated, resulting in coagulation of tissue proteins. In the monopolar variety of these instruments, the current leaves the electrode and after passing through the tissue, returns to the generator by means of a “ground plate” which is attached or connected to a distant part of the patient's body. In a bipolar version of such an electro-surgical instrument, the electric current passes between two electrodes with the tissue being placed or held between the two electrodes as in the “Kleppinger bipolar forceps” used for occlusion of Fallopian tubes.
There are many examples of such monopolar and bipolar instruments commercially available today from companies including Valley Lab, Cabot, Meditron, Wolf, Storz and others worldwide. A new development in
Co Fred H.
Hermann George D.
Howell Thomas A.
Kucklick Theodore R.
Mollenauer Kenneth H.
Cohen Lee
Dippert William H.
Reed Smith LLP
The Trustees of Columbia University in the City of New York
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