Diathermy has been used in surgical procedures for over 100 years (d’Arsonval 1893) for cutting and coagulation of tissues. Harvey Cushing pioneered the use of electrosurgery in neurosurgery, using a generator designed by Bovie in the 1920s, and this name is still synonymous with diathermy to some surgeons.

Although diathermy is still a much-used tool in surgical practice, few surgeons have received formal training in its use. Operating theatres will often have a variety of diathermy units for which ‘standard’ settings are used without reference to the operating conditions. In conventional open surgery, this has only presented a few hazards. The development of laparoscopic and hysteroscopic surgery has greatly increased the number of applications for electrosurgery and has presented new dangers. Only by having an understanding of the principles of this energy source will surgeons avoid the risk of injury to the patient, theatre staff and themselves.

Electrosurgery refers to both types of diathermy, monopolar or bipolar, in which current passes through the patient’s tissue. In monopolar diathermy, the active electrode and return electrode are some distance apart. In bipolar diathermy, the two electrodes are only millimetres apart. Electrocautery refers to the use of a heating element in which no current passes through the patient.

Monopolar diathermy

In monopolar diathermy, one electrode is applied to the patient who becomes part of the circuit. The surface area of the electrode plate is much greater than the contact area of the diathermy instrument to ensure that heating effects are confined to the end of the active electrode (Figure 4.1). The advantage of monopolar diathermy is that it can be used to cut as well as to coagulate tissues.

Figure 4.1 Monopolar and bipolar diathermy systems.

Tissue effects of diathermy

When household electrical current of 50 Hz frequency passes through the body, it causes an irreversible depolarization of cell membranes. If the current is sufficiently large, depolarization of cardiac muscles will occur and death may result. If household current is modified to a higher frequency, above 200 Hz, depolarization does not occur; instead, ions are excited to produce a thermal effect. This is the basis of diathermy. Figure 4.2 illustrates how the frequency of a current influences the effects on the body.

Figure 4.2 Current frequency spectrum.

Factors which influence the effect of diathermy

Cutting and coagulation current

• Type of tissue

Tissue moisture

• Duration of application

• Size and shape of diathermy electrode

Diathermy current

The amount of damage or thermal injury that diathermy produces is determined by the current density and the size of the current.

The current density at the tip of a needle electrode will be very high because the current is concentrated into a small point. The plate used for the return electrode in monopolar diathermy has a large surface area of contact, resulting in a much lower current density. Any thermal effect will therefore be widely dissipated. This highlights the need for the whole surface of the plate to be attached securely to the body. If the plate becomes partially detached, the current density will be greater in the remaining attached part and a burn may result.

The size of the current is influenced by the voltage potential and the resistance to current flow according to the following equation:

Turning up the power output of an electrosurgical unit will increase the size of the diathermy current if the resistance remains constant. Some electrosurgical units can automatically alter the voltage potential to keep the current constant if the resistance changes; however, an alternative design approach allows for control of this voltage (voltage regulation).

The resistance of tissue varies particularly with its water content. Dry tissue has high resistance and moist tissue has lower resistance. Thus, during diathermy of an area of tissue, it is desiccated by the thermal effect and its resistance will increase. To prevent the current flow from falling, some modern electrosurgical units will increase the voltage output. The surgeon should be aware of this because there are additional hazards to working with higher voltages. Insulation failure, capacitance coupling and direct coupling are all more likely with a higher voltage.

Cutting and coagulation

Coagulation and cutting can be achieved by changing the area of contact or the waveform of the current. The cutting waveform is a low-voltage, higher frequency current but the area of contact is the main factor and a cutting effect is achieved when the cutting electrode is not quite in contact with the tissue so that an electrical arc is formed. This causes the water in the cells to vaporize and the cells to explode as they come into contact with the arc. The power and current levels will rise when cutting takes place inside a liquid-filled, relatively non-conductive cavity such as the bladder or uterus. The surgeon must be aware that if the resistance increases when using cutting current (e.g. when cutting through the cervix with a wire loop), some generators will produce a higher voltage to maintain current flow against the increased resistance.

When the electrode is brought into direct contact with tissue and the waveform is modulated, coagulation occurs rather than vaporization. An intermittent waveform is used and thus bursts of thermal energy are interspersed with periods of no energy (Figure 4.3). For the power delivered to the tissue to remain constant, the electrosurgical unit must deliver a higher voltage to compensate for the episodes when no energy is delivered (up to 90% of the time with pure coagulation current). Thus, whilst cutting current at 50 W power will produce a high-frequency current of approximately 200–1000 V, a coagulation current may produce over 3000 V to deliver the same wattage to the tissue. The coagulating effect is produced by slower desiccation and shrinkage of adjacent tissue, producing haemostasis. The higher voltage produced by coagulation current carries a higher risk of inadvertent discharge of energy.

Figure 4.3 Cutting and coagulation waveforms.

If a mixture of the two types of waveform is employed, the advantages of both techniques are exploited. This is normally termed ‘blended’ output and many combinations are possible.

Heat and tissue injury

Diathermy current produces thermal injury to tissues. The temperature generated will dictate the degree of injury (Table 4.1). If carbon is seen on the tip of the diathermy electrode, the surgeon can assume that, at some stage, a temperature of 200°C has been reached.

Table 4.1 The degree of injury caused at different temperatures

Temperature (°C)	Tissue effect
44	Necrosis
70	Coagulation
90	Desiccation
200	Carbonization

Bipolar diathermy

In bipolar diathermy, the current flows between two electrodes positioned a short distance apart because both contacts are on the surgical instrument. Lower power is employed since high power would damage the tips of the instrument. This is safer because the current flow is limited to a small area and lower power is used, but a cutting effect cannot be achieved. These features encourage some surgeons to employ bipolar diathermy exclusively in the laparoscopic environment. However, there is still a small risk of aberrant current flow because the patient, table and diathermy machine are all earthed. In addition, the tissue temperatures are much higher (340°C) and this factor alone can cause unexpected effects.

Bipolar current produces tissue desiccation and has been used commonly in tubal sterilization. More recently, in laparoscopic surgery, its value in coagulating major vascular pedicles has led to its use in laparoscopic hysterectomy and laparoscopic salpingectomy for ectopic pregnancy. The lower power employed also leads to less heat spread to adjacent tissues, which reduces the risk of injury to nearby delicate structures. Engineers are endeavouring to produce reliable bipolar dissectors and scissors to compete with the range of monopolar diathermy instruments available.

Instruments are now available which coagulate a pedicle with bipolar current and utilize a non-electrosurgical blade to cut the pedicle. These instruments are often referred to as tripolar instruments, although this is a misnomer.

Bipolar instrumentation has also been introduced into hysteroscopic surgery. A bipolar electrode may be employed in the outpatient setting for the removal of endometrial polyps. The distension medium used with these devices is saline rather than glycine. Saline is isotonic and therefore reduces the risk of fluid overload associated with a hypotonic solution such as glycine.

Short-wave diathermy

Electrode redesign has led to an interest in the use of short-wave diathermy for its tissue destructive effect (Phipps et al 1990). It has been used in endometrial ablation. In this, the two electrodes form a capacitor in the output circuit with the patient providing the dielectric medium between the two plates. Frequencies of approximately 27 MHz are employed with power levels of approximately 500 W. By altering the shape and size of the electrodes, heating effects may be localized or diffused as required. However, care must be exercised as the effects are not always predictable.

Diathermy safety

Three major safety issues with the use of monopolar diathermy have become apparent with the evolution of electrosurgery in laparoscopic surgery. Each of them involves inadvertent discharge of diathermy current. These issues are:

• insulation failure;

• direct coupling; and

• capacitive coupling.

Insulation failure

Defects in insulation are most likely to cause a discharge of current when higher power is employed. The use of coagulation current carries a greater risk than cutting current. Insulation failure can occur at any point from the electrosurgical unit to the active electrode. The most common site of failure is in the instrument that contains the active electrode. With conventional surgical instruments, the most common site is the joint on diathermy graspers where repeated use wears away the insulation material. Any insulation breakdown, seen as sparks from the joint area, is usually clearly visible because the whole instrument is within the surgeon’s field of view. This contrasts with laparoscopic surgery where the field of view is much smaller and only a small part of the instrument containing the active electrode may be visible. Repeated discharges from a break in the insulation may occur without the surgeon being aware. Damage to insulation most commonly occurs when moving an instrument through the laparoscopic port. Although the port valve may cause damage, the most likely cause is scraping against the sharp edge of the inner end of the port, particularly one constructed of metal.

Concern about insulation failure has fuelled the debate about disposable and reusable instruments. Disposable instruments clearly have an advantage in that the insulation sheath does not have to withstand both repeated use and repeated cleaning cycles. However, disposable instruments are built to much less robust specifications and the insulating material may not withstand harsh treatment in a long case. It is important that surgeons and theatre nurses are constantly vigilant for evidence of trauma to insulation, and reusable instruments must be checked on a regular basis both during and between cases.

Whilst a metal port may cause more trauma to the instruments passing through it, it will allow discharge of diathermy current in the event of insulation failure. The large area of port contact with the skin should enable the current to be dissipated without serious thermal injury. A plastic port would not facilitate such a discharge and the current might therefore flow to adjacent bowel, causing damage that may not be recognized at the time. Sigmoid colon is the most vulnerable piece of bowel because of its proximity to a left lateral port. If a metal port cannula is used, a plastic retaining sleeve must not be used because this prevents any discharged diathermy current passing through the skin back to the ground plate.

Direct coupling

Direct coupling involves the transmission of diathermy current from one instrument to another. Many surgeons use direct coupling to coagulate small vessels which have been grasped with a small forceps, when opening a wound for example. The diathermy instrument is then placed against the small forceps and the pedal pressed. Such a practice carries a real risk of a diathermy burn to the surgeon or assistant. If the surgeon’s glove has a perforation, the diathermy current may flow through the surgeon to ground either through the feet or through contact with the operating table. The surgeon should also be aware that theatre gowns do not provide insulation against high-frequency diathermy current.

The risk of direct coupling will be reduced in laparoscopic surgery if insulated instruments alone are used when diathermy is employed. Since many instruments, such as needle holders, are not commonly produced with insulation, this may restrict instrument choice. The risk of direct coupling to a metal port is increased when the working part of the laparoscopic instrument is large. The surgeon must always try to keep the whole of the metal part visible when using diathermy so that any inadvertent discharge will be seen.

Capacitive coupling

The concept of capacitive coupling is new to most gynaecologists. A capacitor consists of two conductors separated by an insulator. A metal instrument surrounded by an insulated sheath passing through a metal port is a capacitor. When a current passes through the instrument, a capacitive current may develop in the metal port, particularly if it is insulated from the skin. The higher the current passing through the instrument, the greater the capacitive current. If the port is insulated from the skin (by a plastic sleeve), capacitive current may be discharged to adjacent bowel, causing thermal injury. In common with insulation failure, the sigmoid colon is most vulnerable to capacitive current injury due to its proximity to a left lateral port.

A capacitive current can also develop in a gloved hand holding a non-insulated instrument through which diathermy current is passed. This risk is greater if the hand is moist and there is contact between the surgeon and the operating table or the floor.

Other safety issues

Current flow to adjacent organs

The current will follow the path of least resistance, and, if a non-target tissue such as bowel lies in contact with target tissue, the current will flow through the tissue with least impedence. In addition, the impedence will rise as the target vessels desiccate, and the current may then flow to an alternative earth, usually but not necessarily in contact with the pedicle. If the current flows through bowel, damage will result which may not be recognized at the time.

Surgical clothing

Operating theatre gowns do not provide insulation against high-frequency electrosurgical currents. This means that there is always a risk of discharge of electrosurgical current through to the operating table.

Operating theatre footwear used to provide ‘antistatic’ protection. Antistatic theatre shoes were used to prevent build-up of static electricity, which could spark and ignite volatile anaesthetic gases. Since such agents are no longer employed in anaesthesia, there is no need for antistatic footwear. Non-antistatic footwear will generally provide higher resistance between the surgeon and ground, and will therefore reduce the risk of discharge through the surgeon to ground.

Electrosurgical unit

The surgeon should be familiar with the electrosurgical unit in the theatre. Many departments have different units available with different settings and features. The power delivered by a numerical setting may vary greatly in different machines. Many units divide the power output in settings from 1 to 10. Position 5 in one unit may represent a different power output to position 5 in another unit. In addition, there will not always be equal differences between the unit settings, so there may be a different change in output between positions 1 and 2 than between positions 8 and 9. Modern units have overcome this hazard by indicating the power setting on a digital display.

Changes in electrosurgical unit

Prior to 1970, all electrosurgical units had a ‘grounded design’ which provided numerous potential alternative pathways for the discharge of diathermy current to ground, e.g. electrocardiogram leads. In 1970, isolated electrosurgery units were introduced. This meant that the ground electrode discharge returned to the electrosurgical unit. Thus, the whole circuit of electrosurgical current passed through the unit. Whilst this arrangement reduced the risk of inappropriate grounding routes, it did not solve the risk of burns from poor contact of the ground electrode with the patient. Poor contact leads to the development of high current density areas and a subsequent heating effect.

After 1980, some electrosurgical units employed a return electrode monitoring system, which detects failure of contact of the return electrode. Return electrode burns will be significantly reduced with this system.

Since 1990, the growth of minimal access surgery has increased the risk of inadvertent discharge from the active electrode through insulation failure or capacitive coupling. The Active Electrode Monitoring system now marketed by Encision provides an additional protective shield on the active electrode instrument, which picks up discharge of current from any point other than the active part of the electrode and inactivates the unit if such current is detected.

Electrosurgical equipment set-up

It is critically important to be certain that the diathermy ground plate is securely attached in the correct position. Whilst modern machines will give a warning signal when the plate is incorrectly attached, many machines will function if there is partial attachment. Partial attachment may lead to severe burns.

The positioning of the diathermy leads to and from the operating table needs care and attention. Capacitance current can develop alongside the diathermy lead delivering current to the active electrode anywhere along its length. Diathermy leads should not be secured with metal clips to the theatre gowns covering the patients.

Theatre staff must be trained in the use of electrosurgical equipment. Protocols should be in place regarding who attaches the equipment and who switches the machine on. If a patient’s position is changed during the course of an operation, the electrosurgical unit should be switched off prior to the move, and the attachment of the ground electrode should be checked after repositioning.

Risk of fire/explosion

Flammable materials should not be used for skin preparation in gynaecological surgery. Theatre gowns can soak up such solutions which may also pool in the vagina or under the buttocks. Fires have been reported caused by sparks from diathermy current igniting flammable cleansing material.

Pacemakers

Monopolar diathermy should be avoided in patients with internal or external catheter pacemakers. There is a risk of inducing a rhythm disturbance, damage to the device or even electrical burns around the device. If monopolar diathermy is used, short bursts in the cutting mode are advisable. The pacemaker should not lie in the pathway of the diathermy current, but this will not guarantee safety as it is known that radiofrequency current can radiate away from a straight pathway. The electrosurgical unit should be placed as far away from the pacemaker as possible because of the risk of ‘noise’ from the generator. When diathermy is required, a bipolar instrument should be used whenever possible.

Neuromodulators

Implanted neuromodulators are being increasingly employed for the treatment of lower urinary and lower gastrointestinal tract dysfunction. Monopolar or bipolar diathermy should not be employed when these devices have been implanted without consultation with the manufacturer. Similarly, deep brain stimulators may be implanted to treat patients with Parkinson’s disease.

Keloid scarring

Keloid scarring has high tissue resistance so the diathermy ground electrode should not be placed over an area of keloid.

Joint prostheses

The joint prosthesis most commonly encountered by a gynaecologist is in the hip joint. If the prosthesis is unilateral, the diathermy ground plate should be sited on the opposite side. If bilateral prostheses are present, the ground plate should be placed on the flank. If a ground plate is sited over a prosthesis, current may be concentrated through the prosthesis in a preferential pathway and also in the tissue between the plate and the prosthesis, and a thermal injury may occur.

Lasers

A laser is a device capable of producing near-parallel beams of monochromatic light, either visible or invisible, at controlled intensities. This light can be focused, thus concentrating its energy, so that it can be utilized to treat various conditions. The term ‘laser’ is an acronym for ‘Light Amplification by the Stimulated Emission of Radiation’. The process of stimulated emission was foreshadowed by Einstein at the turn of the century, but it was not until 1960 that the first optical device was constructed (Maiman 1960). Since that time, many lasers have been made but comparatively few have found their way into gynaecological practice.

Basic laser physics

A laser consists of three main elements: a power supply, an excitable medium and an optical resonator (Figure 4.4). Atoms or molecules within the medium are raised to high-energy states (Figure 4.5A) by the power supply, and, under normal circumstances, these would decay to the ground state by the emission of energy as photons (Figure 4.5B). By confining the process to an optical cavity and restricting the decay paths, stimulated emission (Figure 4.5C) can take place. This process produces a build-up of photons (light) at a particular wavelength inside the cavity. The laser output is a small fraction of this which is allowed to escape from one end of the cavity.

Figure 4.4 Typical laser systems.

Figure 4.5 Basic atomic processes. (A) Absorption of a photon of energy. (B) Spontaneous emission of a photon. (C) Stimulated emission of an additional photon of energy. , photon; E₀, lower energy state; E₁, higher energy state; , particle.

Many substances have been found to be suitable laser media — solids, liquids, gases or metallic vapours — but the basic principles remain the same. A more detailed explanation of laser physics is provided elsewhere (Carruth and McKenzie 1986).

The radiation emitted is monochromatic (if only one decay path is involved), coherent and collimated. Collimation, or the near-parallel nature of laser light, can be exploited in many ways and is the main feature which makes such devices useful in the medical world. A single convex lens placed in the beam will bring it to a sharp focus, the size of which is dependent upon the width of the collimated beam. The use of different lenses or varying the lens-to-tissue distance alters the diameter of the beam at the point of contact with the tissue (Figure 4.6). This is referred to as changing the spot size.

Figure 4.6 Changing the focal length of the focusing lens while keeping the lens-to-tissue distance constant alters the spot size, the diameter of the beam at the point of contact with the tissue. (A) The focal length of the lens is greater than the lens-to-tissue distance. (B) The focal length of the lens is the same as the lens-to-tissue distance, i.e. the laser is focused on the tissue. (C) The focal length of the lens is less than the lens-to-tissue distance.

The most important determinant of the effects of a laser upon tissue is the power density. This can be calculated approximately as:

where PD is power density, W is power output in watts and D is the effective diameter of the spot in millimetres. D can be measured by firing a short low-power pulse at a suitable target. The power density can be altered by changing either the power or the spot size, but the latter has the greater effect.

Light–tissue interaction

Light impinging on tissue is subject to the normal laws of physics. Some of the light is reflected and some is transmitted through the air–tissue barrier and passes into the tissue where it is scattered or absorbed. Obviously the extent to which each process dominates is dependent upon the physical properties of the light and the tissue. The theory of light–tissue interaction is not as well developed as that of ionizing radiation (Wall et al 1988), but enough is known to explain the macroeffects upon which most laser treatments depend.

At very-low-energy density levels (power density × time), say below 4 J/cm², a stimulating effect on cells has been observed, but above this level, the effect is reversed and suppression occurs (Mester et al 1968). As the energy density rises to 40 J/cm², indirect cell damage can take place if any sensitizing agents present become activated (e.g. haematoporphyrin derivative). Direct tissue damage does not take place until approximately 400 J/cm², when the first thermal effects appear and photocoagulation occurs. Another 10-fold increase in energy density results in complete tissue destruction as it is sufficient to raise the cell temperature rapidly to 100°C, causing tissue vaporization. Obviously these are general observations and other properties of the incident beam will have an influence, but the general 10-fold relationship alluded to above holds although other parameters may be varied. Amongst the most important of these are the wavelength and the pulsatile nature of the radiation involved.

The wavelength absorption characteristics of various body tissues are reasonably well understood, qualitatively if not quantitatively. Figure 4.7 shows the absorption curves for water, melanin and haemoglobin which, to a large extent, will determine the curves for tissue as a whole. In the ultraviolet and the middle-to-far infrared spectrum, absorption by water predominates whereas melanin and haemoglobin effects take over in the visible range. From this graph, it is easy to see that a particular laser, operating at a fixed wavelength, will be preferentially absorbed by one tissue constituent and its effects will be different from those of another laser with a different wavelength.

Figure 4.7 Absorption characteristics of (A) water, (B) melanin and (C) haemoglobin at different wavelengths.

Source: With kind permission from Springer Science+Business Media: Lasers in Medical Science, Photophysical proceses in recent medical laser developments: a review, 1:47–66, 1986, Boulnois J.

So far, it is implied that the laser is operated continuously for long enough for thermal effects to appear [continuous wave (CW) mode]. However, it is relatively simple, by means of a shutter or a controllable power supply, to switch the energy on and off rapidly (pulse mode). In general, the medical definition of a pulse is a burst of energy lasting 0.25 s or less. This does not correspond to the physics definition of a pulse, and care must be taken to avoid confusion. Methods of generating these pulses differ between lasers and the tissue effects can also vary. The reason for this phenomenon is shown in Figure 4.8.

Figure 4.8 The effects of pulse irradiation.

Figure 4.8A shows the output from a CW laser which is modulated by a perfect shutter. The average power delivered to the tissue can be calculated from a knowledge of the CW power, the pulse repetition rate and width. In the case of an electronically controlled high-pulse power system where the time–power curve is not so closely defined (Figure 4.8B), it is much more difficult to determine the average power delivered. It is necessary to measure the energy of the pulse and the pulse repetition rate. The peak power, although impressive, is almost irrelevant.

The effects on tissue of this pulsatile radiation are to reduce the pure thermal effects (lower average power input) whilst maintaining and sometimes enhancing the vaporization potential. Provided the pulse repetition rate is sufficiently low to allow heat dissipation to take place between pulses, the tissue temperature will stabilize at a lower value. These effects are analogous to those induced by modulation in diathermy output which leads to the differences between cutting and coagulation diathermy referred to earlier.

Very short pulses, such as those produced by Q-switched lasers, can cause electromechanical breakdown in tissues because of the extremely high energy densities obtainable. In the early days, these lasers were tested in gynaecology but untoward side-effects were noted (Minton et al 1965).

Common laser systems

Two laser systems established themselves in gynaecological practice during the 1980s:

• the carbon dioxide (CO₂) laser; and

• the neodymium:yttrium aluminium garnet (Nd:YAG) laser.

These will be described in detail, with a further section devoted to other types of laser which are now entering general usage after extensive research.

Carbon dioxide laser

This is the system which has been most used in gynaecology since it was used for the first time in 1973 for the treatment of cervical erosions. This has been because of its clinical stability, ease of use, reliability and easy serviceability. It is a precise laser, especially in ultrapulse mode, making it useful for division of adhesions and accurate and safe vaporization of deposits of endometriosis (Sutton 1993). Although a major drawback is that its output cannot be transmitted by fibres, it has so far not been totally displaced by other lasers but is rivalled by modern diathermy equipment.

As the name implies, the active lasing medium is CO₂ gas. Efficiencies of 15% energy conversion to light output have been achieved. In fact, an analyser has used this ability to detect CO₂ in the breath! The first generation of CO₂ lasers used a flowing gas system with high-voltage direct current excitation. A gas mixture of CO₂, nitrogen and helium has been used to help achieve and maintain lasing conditions. Sealed tube lasers are now available with radiofrequency low-voltage discharges being used for excitation. This has made the machines smaller and removed the need for gas bottles.

The output radiation of 10.6 µm wavelength is well into the infrared region of the spectrum. This radiation is absorbed rapidly by tissue water, and therefore cuts and vaporizes more easily than it coagulates. Most of the incident radiation is absorbed within approximately 0.03 mm of the surface and intense heating occurs. Coagulation will only take place in small blood vessels less than 0.5 mm in diameter, but haemostasis can be facilitated by reducing the power density so that the zone of thermal damage around the central crater is wider.

As the 10.6 µm laser is invisible, an aiming beam must be used so that the operator can see where the therapeutic beam is going to have its effect. A helium–neon (HeNe) laser emitting at 628 nm (red) is incorporated into the system and optically aligned so that it coincides with the therapeutic beam. This alignment can degenerate and should be checked regularly.

As yet, there is no commercially available fibre which can transmit 10.6 µm light efficiently, so most commercial systems use some form of articulated arm. At each joint, there is a mirror which is adjusted so that the beam stays central despite movement between the two adjacent limbs of the arm. The choice of the mirror material is limited because of the need to reflect both the infrared CO₂ beam and the red HeNe aiming beam. It is possible to use waveguide delivery systems to avoid the use of mirrors, but this limits the manoeuvrability of the complete system.

The final delivery to the operation site can be carried out in two ways, both incorporating a focusing lens. For hand-held surgery, the lens at the end of a straight delivery tube focuses the beam on the operative field approximately 1 cm from the end of the tube. The lens-to-tissue distance can thus be varied at will so that the spot size will be changed within a narrow range (Figure 4.9A). Colposcopic delivery involves a mirror after the focusing lens which brings the beam into line with the viewing axis of the colposcope. This mirror is at the end of a joystick so that the beam may be moved around within the field of view (Figure 4.9B). Originally the spot size was changed using lenses of different focal lengths and so was limited to three or four predetermined sizes. Nowadays, the use of zoom optics allows infinite adjustment over a limited range (0.5–4 mm).

Figure 4.9 Laser delivery systems. (A) Hand-held. (B) Colposcopically controlled.

Power outputs of these lasers can be from a few watts up to 100 W continuous. Most commercial systems in gynaecology produce up to 25–35 W as this, coupled with a variable spot size, provides power densities of up to 6000 W/cm², sufficient for tissue cutting and vaporization at a controllable rate. The extra power provided by instruments producing 40–60 W is useful for dealing with patients who bleed during the procedure. Higher peak powers are available with modulation being employed to keep tissue temperatures within acceptable limits but with ‘cleaner’ cuts.

Neodymium:yttrium aluminium garnet laser

This device is a solid-state laser with the active neodymium ions being incorporated in an artificial crystal YAG. Pumping is achieved by energy input from a parallel gas discharge lamp, usually a water-cooled krypton tube, with the output radiation being refocused into the laser crystal. Output power levels up to 100 W continuous can be achieved, but, with a conversion efficiency of 1% or so, nearly 10 kW of input power is needed.

The energy produced is at a wavelength of 1.06 µm and is thus in the near-infrared. As such, it can be transmitted easily down a flexible fibreoptic delivery system and delivered to many more anatomical sites than the CO₂ laser. The emergent radiation has lost its collimation and will diverge quite rapidly. Most fibres have a coaxial flow of gas, usually CO₂, to keep debris away from the end of the fibre. This is particularly necessary where contamination with blood or blood products may make continuous operation difficult.

As with the CO₂ laser, 1.06 µm Nd:YAG radiation is invisible. An HeNe laser (or other light source) needs to be incorporated into the device as an aiming beam. This is also a very useful safety feature as near-infrared radiation can cause irreparable damage to the retina. The Nd:YAG laser is easy to operate as a Q-switched laser. An optoelectronic switch is incorporated inside the laser cavity and the lasing action is prevented for a large percentage of the time. The photon energy therefore builds up to an even higher level than normal, and when the switch is eventually opened, a massive pulse of energy is delivered. The switch can then be closed and the process repeated. This type of action has found a use in ophthalmology where, by focusing the pulse to a very small spot, electromechanical breakdown of tissue can be induced with minimal surrounding damage.

The Nd:YAG laser has a greater depth of penetration and is more suited to hysteroscopic surgery (Sutton 1993). Hysteroscopic procedures include removal of fibroids and polyps, transsection of uterine septae, lysis of adhesions and endometrial ablation.

Other laser systems

Many other laser systems are used in medicine and the time period from research to common usage seems to be getting shorter. It is neither possible nor desirable to give a complete list, but some of the following examples have potential benefits for gynaecological surgery.

Metal vapour lasers

As their name implies, metal vapour lasers consist of a container filled with a heated and vaporized metal in an inert gas atmosphere at low pressure. The electrical discharge used must be pulsed because the necessary conditions cannot be sustained long enough for true CW operation to take place. Two types of metal vapour laser have found a use in medicine — copper and gold. The copper vapour laser produces two beams at 510 and 578 nm at up to 25 W power output. These by themselves are not particularly useful, although the green can be used as a substitute for the argon laser in dermatology. The output is ideally suited to act as an optical pumping source for a dye laser, which can be tuned to provide radiation for photodynamic therapy.

Photodynamic therapy

Photodynamic therapy is a treatment for certain tumours (Spikes and Jori 1987). It relies upon selective retention in tumour tissues of a drug (photosensitizer), such as haematoporphyrin derivative, which only becomes active on exposure to light of a particular wavelength. This provides highly selective tissue necrosis. Each photosensitizer has a particular spectrum of action requiring light of the appropriate wavelength for maximum absorption and effect. Clinically used sensitizers work between 420 nm (blue) and 780 nm (deep red). Longer wavelengths penetrate deeper (blue 1–2 mm and red >5 mm). As there are many decay pathways available, the output is multi-wavelength, but a narrow wavelength range can be selected with suitable optical devices. The copper vapour and dye laser combination can produce over 5 W of red light at 630 mm, which is an absorption peak of haematoporphyrin derivative.

The other metal vapour device is the gold laser. The output of this is at 627.8 nm, a close match to the dye laser, without the added complication of two devices in series.

Argon laser

The argon laser, producing light at 488 nm (blue) and 514.5 nm (blue/green), is particularly favoured by ophthalmologists. The green output of the KTP laser (potassium titanyl-phosphate, 532 nm) has been more useful in gynaecology. The output is derived by taking the Nd:YAG beam and frequency and doubling it in a KTP crystal, thus providing the surgeon with a choice of wavelengths (or even a mixture of the two). The advantages of the light lasers, argon and KTP lasers, over the CO₂ laser is their selective absorption by haemoglobin, less smoke plume production and an easy delivery system that uses lower power settings. They have been considered to be more suitable for treatment of ovarian endometriomas and ectopic pregnancies, as the CO₂ laser energy is strongly absorbed by the water molecule and is rendered ineffective in the presence of blood (Sutton 1993). The main disadvantage of the light lasers is the need to wear special protective glasses which can distort the view of the pelvis.

Ultraviolet lasers

Research into ultraviolet lasers has produced systems which seem to rely on non-thermal mechanisms for tissue destruction. These are the excimer lasers, a term derived from ‘excited dimmer’, where the active medium is made from a combination of two substances which do not normally combine, such as a rare gas and a halide. These lasers have found a place in ophthalmology, and their potential for precise tissue removal offers the microsurgeon a very powerful tool.

The early use of lasers in gynaecology was in the treatment of cervical intraepithelial neoplasia, but subsequently spread to most other areas of the lower reproductive tract. The use of the laser in treatment of intraepithelial neoplasia of the genital tract is described in Chapter 38. Similar diathermy techniques are described in the same chapter.

We are under pressure to decrease health costs, so alternative, less-expensive technology has reduced the use of laser technology in recent years. However, lasers are still used in various clinical settings in obstetric and gynaecological surgery. Some examples include intrauterine laser ablation of placental vessels for the treatment of twin–twin transfusion syndrome (Robyr et al 2005), and ovarian drilling for ovulation induction in patients with anovulatory polycystic ovary syndrome (Farquhar et al 2007). Other uses are being investigated, but the evidence on safety and efficacy outcomes thus far is insufficient to support use in a non-research environment. Examples of these include laparoscopic laser myomectomy and percutaneous laser therapy for fetal tumours. There are also controversial areas regarding the use of lasers which have entered commercial gynaecology without much regulation or scientific evaluation, such as laser vaginal rejuvenation.

Laser safety

All laser systems in current use have no way of distinguishing between patient and operator. The desired effect on a patient can be a serious accident to the surgeon. The subject of the safe construction and operation of lasers in medicine and surgery is thus very important and must be understood by all involved. This section is biased in favour of UK regulations, but the situation is similar in most European countries and the USA, although, of course, regulatory bodies and documents will have different guises.

All lasers sold in the UK must conform to three basic standards. Electrical safety requirements are detailed in BS EN 60601-1-1 (British Standards Institution 2001) and non-ionizing radiation hazards are covered by BS EN 60825-1 and BS EN 60601-2-22 (British Standards Institution 1996, 2007). A further publication by the Medicines and Healthcare Products Regulatory Agency (2008) outlines good laser practice together with some additional equipment safety features. All these publications should be considered by a laser protection adviser (a health authority or trust appointee) who will assist each user in specifying and installing lasers in clinical surroundings. Although the requirements will vary from laser to laser and from site to site, the following sections outline the major considerations involved.