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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ELECTRIC EQUIPMENT 4 Care of equipment(low voltage)

Care of Low Voltage Equipments

In order that an extra low-voltage circuit may function well all connections must be kept clean, dry and free from corrosion.

•     After sterilization, heat processed apparatus must be dried before storing away.

•     Good contact of the connections must be maintained and loose contacts repaired immediately by the electrician when they are detected.

•     Lamps must be tightly screwed in position.

•     And the current source should, if possible, remain fairly constant. Therefore, batteries must be replaced before they are exhausted. Batteries left too long in the metal case tend to sweat, especially in humid atmospheres, causing corro-sion and the discharge of power. All batteries not in actual use should be stored under dry conditions.

Rechargeable Battery Packs

Rechargeable nickel-cadmium batteries are being used as accessory of medical equipments. These are expensive and have a limited life, although are electrically safe.

•     Rechargeable batteries are capable of delivering a very high current on discharge, so should not be shorted, as this might result in sparking. Another feature is that their life is extended by regular discharging and recharging

•     Thus, any piece of equipment containing rechargeable batteries should be regularly switched on and regularly recharged

•           They can fail without warning, back-up batteries for essential pieces of equipment are required.

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ELECTRIC EQUIPMENT 3

•     Electronic microchips and integrated circuits are generally very hard wearing and will withstand rough handling; they also operate at low voltages so are relatively safe, but they respond badly to high temperatures. Overheating should therefore be avoided, and ventilation openings left uncovered  with these safeguards, they should give good service

•     Low-voltage battery equipments are generally safe and may even be designed to work in damp or humid conditions.

      A considerable amount of electric equipments in the operat-ing department use extra low-voltage current. These include :

•     Laryngoscopes,

•     Bronchoscopes,

•     Cystoscopes and

•     Head lamps.

•     Generally, an extra low-voltage circuit
used in apparatus for use in theater may range from 1.5 V for endoscopes to 10 V for a surgeon’s headlamp.

•     The electric current may be supplied from batteries or a transformer which reduces the mains voltage to the required level.

•     The transformer may be a separate item of equipment or may be incorporated in the equipment such as in diathermy machines (high-frequency electro-surgical units). To a great extent extra low-voltage illumination is being replaced by fibre optics.

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ELECTRIC EQUIPMENT 2

Care of Electrical Equipments

•     Many modern instruments and pieces of equipment operate from mains voltage 110 or 240 V/AC. All electrical instruments have been tested for safety after manufacture and if not damaged in transport can be assumed to be electrically safe on delivery.

•     With use, cables are damaged, earth connections can get loose or break, internal components can move with vibration/ accidental damage. An incorrect alteration during repairs to the circuit or safety fuses can result in dangerous voltages and currents reaching the patient.

•     Simple checks of plugs, fuses and cables should be made regularly by the OT staff in charge of the electrical equipments and routine maintenance checks performed by a qualified person at fixed intervals as recommended by the manufacturer

•     Earth connections and safety fuses should be regularly checked, making sure that the correct loading fuses are being used

•     Damaged cables should be replaced and any loose components such as switches and sockets repaired

•     All equipments working from mains voltage should have a circuit breaker in the supply lines

•     All mains electrically powered instruments should be kept dry

•     Cardiac defibrillators deliver a high voltage of several thousand volts, together with a relatively high current, making a lethal combination to operator if any serious electrical fault should occur, it is thus even more important that servicing and maintenance of these instruments be entrusted to a qualified electrical engineer

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