ELECTRIC EQUIPMENT 11 Cryosurgical Systems

CRYOSURGICAL SYSTEMS

Cryotherapy, the application of extreme cold to tissues and is a useful technique for the destruction of tissues. It is characterized by minimal bleeding or pain in the postoperative period. Cryosurgical systems are well established in many surgical specialities including:

•    General surgery,

•    Gynecology,

•    Dermatology,

•    Neurology, and

•    Urology.

     The first practical equipment for the control and maintenance of extreme low temperature in surgery was produced in 1962. The apparatus was not very sophisticated and used liquid nitrogen to achieve low temperature in the region of –196 degree Celsius. This very low temperature was subsequently found to exceed requirements, and Amoils developed a more simple apparatus which used nitrous oxide or carbon dioxide to achieve temperatures in the region of –70 degree Celsius. The design principles established by Amoils (Fig. 2.6) are still used in modern cryosurgical equipment which employs high-pressure, non-syphon cylinders of N2O and CO2.

•    Cryosurgical systems consist of flexible tubing connecting the gas flow control unit to a cryoprobe or working tip which comprises two concentric tubes

•    The inner tube delivers nitrous oxide or carbon dioxide at pressures between 4,000 kPa and 6,000 kPa to a narrow orifice in the end

•    The sudden expansion of this gas through the ‘Joule- Thompson Orifice’, produces a rapid drop in temperature of the probe surface forming an ice ball

•    The expanded gas is then returned at atmospheric pressure along the outer tube

•    Some cooling along the shaft of the probe occurs and can be a disadvantage, for example in neurosurgery

•    To overcome this, Spembley manufacture a probe which employs a reversed gas flow. This design enables the incoming gas to be carried to the probe tip via the outer of the two concentric tubes; it is allowed to expand through an annular orifice, being finally released through the central tube.

•    The incoming gas acts as an insulating barrier and the cooling is confined to the probe tip.

          Cryosurgery has been useful in the treatment of early skin cancer. It is being explored in the treatment of prostate, liver and bone.

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ELECTRIC EQUIPMENT 10 Laser Eye protection

Guidelines to Eye Protection during Laser Surgery

•     Ensure that everyone in the laser room is wearing the appropriate eye protection before activating the laser. The eye wear should have the laser wavelength protection and optical density of the lens material inscribed on it.

•     A special lens cover can be placed over the eyepiece of an endoscope to protect the physician’s eye from laser back­scatter. Remember that the physician’s other eye will be unprotected.

•     Everyone in the laser room should wear eye protection during laser endoscopic procedures.

•     An automatic lens shutter can be connected to a microscope head to provide eye protection for persons viewing the procedure through the microscope.

•     When general anesthesia is used, cover the patient’s closed eye with moistened gauze pads. When the patient is awake, place the appropriate glasses or goggles on the patient. Explain the need for eye protection to the patient.

•     During laser surgery near the eye, a special laser eye shield may be placed directly on the anesthetized eye surface.

•     Ensure that the appropriate protective eyewear is available at all entrances to the laser room for anyone entering the area.

•           When storing protective eyewear, guard against scratches and mishandling. Scratches on the lenses may decrease their effectiveness.

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ELECTRIC EQUIPMENT 9 Lasers

LASERS

Laser light is a part of the light spectrum which has been collimated and made coherent so that the waves travel in the same direction in parallel. This beam now carries laser energy measured in Joules and the energy delivered is proportionate to the exposure measured in seconds. The principle of laser generation has been shown in the figures above. New laser systems have been introduced into use. The five components of a system are:

•     Laser head

•     Excitation source

•     Ancillary components

•     Control panel

•     Delivery system.

      The Table 2.1 summarises the characteristics of those in use in surgery.

•     A laser is an instrument equipped to produce a parallel beam of high intensity light which can be focussed on a very small spot 

•     The development of surgical lasers during the last decade has made a significant contribution to microsurgery

•     Used with an operating microscopes or fiberscopes a wide range of microsurgical procedures have now become possible, for example:

      a.   Sutureless microvascular anastomosis.

      b.   Excision of the posterior capsule of the lens through the transparent cornea.

      c.   Coagulation of bleeding peptic ulcers using a flexible gastroscope.

•     In laser surgery, the light beam heats the target tissue and causes:

      a.   Thermal tissue destruction.

      b.   First with local edema.

      c.   Then denaturation of protein.

      d.   Contraction of tissue due to alteration of fibrous tissue protein.

      e.   And finally boiling of cell water and vaporization.

      f.    Generally, low energy exposure results in coagulation of blood vessel.

      g.   Higher energy exposure produces a precise incision by vaporization of the tissue at the focal point.

            It is important that eye protection be worn during procedures

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ELECTRIC EQUIPMENT 8 Surgical Cautrey

Surgical Cautery

•     Electric cautery is used to destroy superficial skin lesions. The wire tip is raised to red heat by means of an electric current

•     This heated cautery point is then applied to the tissue area to cause tissue death through coagulation

•     The current source may be a low-voltage battery or trans­former connected the mains, although the transformer is preferable, as the output is more constant than that of a battery

•     The transformer has a rheostat knob which may be adjusted to alter the voltage applied to the platinum point

•     The cautery must not be used any hotter than at red heat, as too high a current will cause rapid burning out of the cautery wire and reduce its life span

•     The cautery point are various sizes and shapes (Fig. 2.4) are mounted in a heat-resisting handle to which are connected two wires

•     These wires are then connected to the transformer which must be switched off at the wall socket

•     The cautery must be connected to the cautery terminals

•     After connecting the wires the transformer may then be switched on.

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ELECTRIC EQUIPMENT 7 surgical diathermy safety

Safety

Responsibility

The surgeon using the diathermy must realize his overall responsibility, and check the alarm wiring and patient plate before use.

Safety Measures

Alarms

Monopolar diathermy depends on the patient plate for its safety. All diathermy machines in use will alarm when switched on if the plate is not connected to the machine. Safe practice demands rigid adherence to correct procedures:

•     First the patient plate is connected to the patient

•     The return lead is connected to the plate

•     The diathermy machine is switched on 

•     The plate continuity alarm will sound

•     Then is the return lead connected to the diathermy machine.

•     Thus silencing the continuity alarm

•     The plate should be sited close to the operation

•     Diathermy current is moving away for ECG and other monitoring electrodes

•     The area under the plate should have a good blood supply to remove any heat generated

•     All plates must have good skin contact

•     Shave hairy skin and ensure the plate is not kinked or crinkled.

Patient

•     The patient should not touch earthed metal objects such as drip stands, uninsulated ‘screens’, and parts of the operating table

•     Check the dial settings before use

•     If a spirit-based skin preparation fluid is used, ensure it has all evaporated

•     Only the surgeon wielding the active electrode should activate the machine

•     Always replace the electrode in an insulated quiver after use

•     If diathermy performance is poor, carefully check the patient plate and lead rather than increase the dial settings.

 

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ELECTRIC EQUIPMENT 6 Surgical Diathermy

Surgical Diathermy

Surgical diathermy is an equipment that generates a high- frequency current. The patient is connected to a large contact electrode. The other electrode is small.

•     when the current is passed through the patient’s body between two electrodes, the effect is to produce a concen­tration of current at the smaller electrode in the hand of the surgeon

•     As the surgeon applies his ‘live’ (small) electrode to the tissues, the current passes through the touched tissue cells and owing to the tissues electrical resistance, heat is generated at this small contact point (Fig. 2.3A)

•     The effect is localized because with monopolar system the current from the‘live’(small) electrode spreads out in the patient’s body and travels to the ‘indifferent’ electrode which is a large electrode placed in contact with the patient’s body (thigh or sacrum)

•     A high density of current occurs only immediately beneath the live electrode because further away (except under fault conditions) the current density is too small to have any heating effect.

             The purpose of the indifferent large surface electrode is to provide a surface of sufficient area to avoid any heat effects at this site.

•     This is because the indifferent electrode is in contact with hundreds or even thousands more cells than the live electrode which results in a correspondingly lower density of current in each cell

•     If the electrode is applied correctly as described below, negligible heat is generated in this area

•     The commonest types of indifferent electrode is a flexible metal plate. The thin flexible metal plate electrode can either be placed under the patient’s body (sacrum) or carefully bandaged round the thigh to ensure even wide contact with the skin

•     It is unnecessary to use electrode jelly, though if the patient is hairy, shaving beforehand is advisable—as hair acts as an electrical resistance

•     If the patient’s skin is dry, moistening with water or saline and can be used with advantage before applying the plate.

•     Replace a plate electrode which becomes buckled otherwise areas of irregular contact with the skin result which could allow points of high current density and risk of burns

•     The electrode is connected to the high frequency electrosurgical unit indifferent or earth terminal by a heavy insulated wire.

      With bipolar system the surgeon’s instrument, usually in the form of a forceps, combines both electrodes so that current flows down both limbs of the forceps and thus only through the tissue gripped between the tips of the forceps, thereby eliminating the need for an indifferent electrode

 

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Electric equipment 5 defibrillators

Defibrillators

Defibrillator allows the application of electrical stimulus to the heart to convert a ventrical fibrillation to a sinus rhythm and it is called defibrillation .

•     It may be mains or battery operated and can apply the shock through the chest wall or via electrodes placed directly in contact with the walls of the heart.

•     When switched on, the defibrillator charges a condenser to a maximum energy of 320 J for external application, and 20 to 50 J using internal electrodes.

•     The level of stored energy output can be continuously controled between 5 and 320 J and this energy is released in a pulse lasting about 3 milliseconds.

•     In the case of atrial fibrillation the defibrillator is coupled with an electrocardiograph so that the defibrillation discharge is delivered in synchronization, normally 40 milliseconds delay after the peak of the R wave of the patient’s ECG.

•           Although different makes of defibrillator vary slightly in the method of operation, basically the same technique is used. The cardiac recorders defibrillator when used in an emergency the instructions are printed on the side of the lid.

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