Medical electronic apparatus has been employed for many years for many types of diagnosis and treatment. One field in which there has been considerable growth recently is electrosurgery, in which a suitable generator provides a high frequency, high voltage current which is transmitted to a small surgical electrode having a thin knife-like tip to be applied to a patient. The patient sits or lies on a patient plate and is grounded thereto, with the plate being connected by a further conductor back to the generator. The relatively extremely small area of contact by the electrode with the patient provides an intense current in a highly localized area, producing a cutting action. The current passes through the patient's body to the patient plate where the area of contact is so great that no burning effect occurs.
For cutting purposes, the generator is activated to produce a continuous sine wave signal. However, the same instrument may be used to apply to the wound after cutting in order to produce coagulation. For this purpose the generator may be selectively activated to produce a pulsing signal which produces the desired results. Switching means are available for the operator to selectively control an activating means for causing the generator to produce the desired type of current.
In the operating room, a surgeon would like to use the electrosurgical device in a fashion similar to that in which he uses a standard sharp scalpel. The surgeon typically grips the scalpel like a pencil with index finger guiding and hear the cutting tip for precise control. Currently available electrosurgical hand instruments, called "pencils", are not readily gripped this way, because the mode switches are positioned far from the cutting tip, toward the rear of the instrument. This requires the surgeon to grip the pencil far back on the handle in order to have the index finger positioned to activate the mode buttons, resulting in awkward feel and loss of precise control. An additional disadvantage of electrosurgical pencils is the possibility of inadvertent activations of the mode switches by pressures being applied to the unit. If this occurs when the tip is in contact with the patient or with conductive items, a serious burn can result. Another drawback to the use of electrosurgical pencils has been that many surgeons still desire to use a sharp scalpel for incision-making, with coagulation being achieved by the electrosurgical pencil. This requires the surgeon to continually switch from one instrument to the other.
Electrosurgical pencils with a rocker switch for selection of mode of operation are disclosed in U.S. Pat. No. 4,228,800 to Degler, Jr., et al, U.S. Pat. No. 3,648,001 to Anderson, et al, U.S. Pat. No. 4,443,935 to Zamba, et al, and U.S. Pat. No. 3,801,766 to Morrison, Jr. As is typical among such devices, the pencil in each is connected to an electrosurgical generating apparatus by a cable comprising three conductors: a first signal line, a second signal line, and a common line which serves not only to return the selected control signal to the generator, but also to deliver current to the scalpel electrode. Thus, all three conductors are maintained at high voltage, with the control signal conductors differing in voltage slightly from the common conductor so that a relatively small current will serve to select the mode of operation desired.
U.S. Pat. No. 3,720,896 to Beierlein discloses a magnetic slide switch with three positions, and appears to provide electrical isolation when in the center position. U.S. Pat. No. 4,463,759 to Garito, et al. also provides electrical isolation.