Surgery – Miscellaneous – Methods
Reexamination Certificate
1999-07-26
2001-02-13
Dvorak, Linda C. M. (Department: 3739)
Surgery
Miscellaneous
Methods
Reexamination Certificate
active
06186147
ABSTRACT:
The current invention relates to apparatus for use in the electrosurgical field and in particular in relation to the provision of apparatus for cutting body tissue and/or coagulation such as is required in, for example, endoscopic surgery which is increasingly common.
When using apparatus of this type to, for example, cut parenchymal organs the surgeon wishes to obtain efficient heamostasis either as a result of coagulation to a greater or lesser depth as the cut is being made or as a result of partial coagulation of the bleeding vessels once the cut is completed. The efficiency with which the bleeding can be stopped depends upon the intensity of thermal coagulation; and the greater the depth of coagulation inside the tissue, the greater the heamostatic effect. At the same time however it must be ensured that no more tissue suffers thermal damage during cutting and coagulation than is absolutely necessary in order to obtain the desired effect as the damage caused is irreparable. This is an important consideration as increasingly, higher output currents are used to cut. As the higher currents and hence power is provided so the risk of electric current channelling along unseen or obscured body organs adjacent the cutting area is increased and can cause damage to vital anatomical structures and increase the risk of peripheral burns to the patient.
For many years work has been undertaken in an attempt to provide apparatus which allows accurate high powered cutting and coagulation of the body tissue and fluids and which has a minimum risk to the patient upon whom the surgery is performed and also to the surgeon and/or apparatus operator.
In general, when an electrode, which acts as a cutting tool, contacts body tissue an electric arc or spark is created which causes a zone of thermal necrosis to be created beneath and around the area of contact. As the current is applied it passes through individual cell membranes in the patient causing the same to be vapourised and the cut to be created.
One known group of apparatus type is known as monopolar apparatus which utilises an electrode which forms the cutting and coagulation tool and through which an alternating current of, for example, between 300 kHz and 1 mHz flows. When the electrode is held at a distance from the body no current flows and no cutting action occurs but as the electrode is brought closer to the body tissue a spark will jump across the gap to the tissue if, for example, the voltage is between 1000 to 10000 volts peak to peak.
This apparatus is provided with a separate return electrode which must have a sufficiently large area to minimise the heating effect caused by the current passing through the patient and prevent tissue surface burns. Typically therefore the return electrode is required to be in the form of a plate upon which the patient lies. These plates can be disposable but in any case are relatively expensive. Thus, in this type of apparatus, relatively high powered cutting currents can be obtained but there are inherent risks to the patient who does, in effect, form part of the electrical circuit and is therefore exposed, sometimes dangerously, to burns and tissue damage caused by contact with the plate. In an attempt to minimise the problem the resistance of the return electrode plate is monitored but this tends to be a reactive rather than a proactive monitoring technique which does not monitor the condition of the patient body tissue and therefore does not eliminate the risk to the patient. Thus the monopolar cutting system, although widely used, has many deficiencies which, if they are not to cause damage to the patient, are required to be carefully monitored with additional expensive apparatus.
An alternative group of apparatus is the bipolar cutting apparatus which utilises two electrodes which contact the tissue to be cut and coagulated in close proximity to each other. One electrode operates to supply power to cut and coagulate the tissue and the other acts as a return electrode with the current density on both electrodes being kept the same. In this apparatus it is not necessary to have a return or dispersive electrode in the form of a plate and therefore the patient is safer but known bipolar apparatus cannot generate sufficient power to allow fast, efficient high powered cutting such as that required for procedures such as Trans Urethral Resection of the Prostate in Urology and Transcervical Resection of the Endometrium in Gynaecological Surgery.
A further type of apparatus is disclosed in patent document U.S. Pat. No. 5,334,193 which addresses the problem of applied cutting power in electrosurgical use and also discloses in discussing prior art documents how apparatus can be provided to have cut off or alarm thresholds to prevent continued power supply when potentially damaging operating conditions are sensed. However the prior art does not provide for the continued monitoring and analysis and alteration of the power supple during the operation of the apparatus. The document U.S. Pat. No. 5,334,193 discloses the ability to monitor the impedance of the body tissue but only as a means of determining whether the calculations undertaken in respect of the other data received in the form of the active and return current signals are valid and should be applied to the overall control parameters of the apparatus and/or whether the measurements should be taken more or less frequently. The impedance values are not used in the setting of the control parameters in this patent but as a further check of the operation of the apparatus.
Thus the known apparatus systems have many disadvantages and further general disadvantages are that the systems can cause interference to other equipment in the theatre namely anaesthetic apparatus, video monitoring equipment, pacemakers fitted to patients and, due to the system operation, and the presence of currents through the body tissue non conductive cutting fluids are required to be used such as glycine which is toxic and, if absorbed in too great a quantity by the patient, can render them seriously ill or even kill them.
The aim of the current invention is to provide apparatus for the cutting and/or coagulation of body tissue and organs which can provide a controlled output power supply and with sufficient power to allow all required operations to be performed yet minimise the equipment required to be used.
The current invention, in a first aspect, provides apparatus for electrosurgical use to cut and/or coagulate body tissue, said apparatus comprising an electrical generator and control means connected to a tool, said tool selectively operable to provide cutting and/or coagulation via a tip formed at an end thereof, and including first and second electrodes in connection with said tip and in turn said body tissue and characterised in that the control means includes means for measuring the phase angle and the modulus of the impedance indicative of the body tissue and regulates the power supply to the tool dependent on said measurements to ensure that the optimum cutting power is supplied at each instant.
Typically upon the starting of the operation of the apparatus the same current waveform is provided along the power supply and feedback electrodes until the measured impedance alters and this arrangement ensures that the tissue under the influence of the tip is prevented from leaking to areas other than adjacent to the tip.
The electrodes are preferably provided as part of the tool and the control means is operated to allow power to be carried to the tool tip and the measurement of the phase angle and the modulus of the impedance feedback to be received and measured by the control means.
Typically the current supplied is only exposed at the tip of the tool and therefore there is no risk of damage to tissue or organs with which any other part of the tool comes into contact.
Thus the impedance of the body tissue adjacent the tip of the tool can be monitored by the control means.
Typically the control means includes a means for receiving the phase angle and the modulus of the
Dvorak Linda C. M.
Kearney R.
Nuvotek Limited
Woodard Emhardt Naughton Moriarty & McNett
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