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View all the figures for this chapter.

Endoscopy Practice and Safety

Peter B. Cotton ed.

6. Principles of electrosurgery, laser, and argon plasma coagulation with particular regard to colonoscopy

G. Farin and K.E. Grund

Top of page Editor's note  Next section

This contribution is reproduced by kind permission of the authors and editors from the textbook Colonoscopy: Principles and practice, by Waye JD, Rex DK and Williams CB, Blackwell Publishing 2003. Although targetted at colonoscopy, it is a very valuable review of a complex topic that deserves wider readership.

Top of page Introduction  Previous section Next section

Hemostasis and the ablation of pathologic tissues are the most important indications for thermal techniques in colonoscopy. However, because the colon wall is thin, it is not the ideal organ for the application of thermal techniques. The thickness of the three layers of the colon wall, comprising the mucosa, submucosa, and muscularis propria, varies from 1.5 to 3 mm (Fig. 1) throughout the length of the large intestine. Following insufflation, the wall can be even thinner. Since damage to the muscularis propria of the colon should be avoided during endoscopic interventions, thermal injury must not extend beyond the submucosa in order to avoid complications. As a consequence, only about half of the 1.5–3.0 mm constituting the thin wall of the colon is accessible to the endoscopist for thermal interventions. The necessity that endoscopically applied thermal techniques do not damage the muscularis propria of the colon makes their application within the colon difficult, especially when the lesion to be treated is large.

The application of thermal techniques in the colon requires knowledge of thermal effects in biologic tissues. In addition, the endoscopist must have sufficient training and master the available endoscopes, instruments, and peripheral equipment. This article deals with the theoretical principles concerning the application of thermal techniques, especially in the colon.

Top of page Relevant thermal effects in biological tissues  Previous section Next section

All thermal effects in and on biological tissues—whether intentional or unintentional—depend on the intensity and duration of temperature in the tissue (Fig. 2) almost regardless of the way in which this temperature is reached.

Thermal treatment is among the oldest of therapeutic techniques. Although high-frequency (HF) surgery was introduced about 100 years ago and laser surgery about 30 years ago, the terminology uses words that are centuries old and described various types of cautery. As an example, coagulation is the only term in current use to describe thermal hemostasis, even though different thermal techniques can be used for this purpose. The term 'coagulation' actually encompasses many different tissue effects such as devitalization, coagulation and desiccation.

Thermal devitalization  Previous section Next section

Thermal devitalization is defined as irreversible death of tissue. More precisely, devitalization of a target tissue means irreversible as well as complete death of tissue. Biologic tissue becomes devitalized if its temperature reaches 41.5°C. The higher the temperature, the faster the devitalization. Unfortunately devitalization is not a visible phenomenon and hence can occur in an uncontrolled fashion, and thus it is not used for destruction of pathologic tissue. Even if thermal devitalization is not employed intentionally, some degree of tissue death occurs outside the border of the coagulation zone. The depth of the invisible thermal devitalization zone depends on many different parameters, and it should be assumed for the sake of safety that it occurs in direct proportion to the visible coagulation effect.

Thermal coagulation  Previous section Next section

Thermal coagulation is defined as conversion of colloidal systems from sol to gel state. Biologic tissue becomes coagulated thermally if its temperature increases to approximately 60°C. When this temperature is exceeded, the structure of the cell changes causing the following effects:

  • change of the color of the tissue;
  • formation of derivatives of collagen, e.g. glucose;
  • contraction of collagen.

The change in color of the tissue is the only way to visually control intended as well as unintended coagulation. Unfortunately, color changes can only be seen on the surface but not within the tissue.

Even if thermal devitalization could be used for destruction of pathologic tissue, it is not used for this purpose because it is not controllable. Therefore the coagulation effect is used as a means of controlled devitalization. It should be noted that an invisible thermal devitalization zone of variable depth is unavoidable outside the border of the coagulation zone.

The formation of derivatives of collagen, e.g. glucose, can become adherent after desiccation.

The contraction of collagen can result in narrowing of the lumen of blood vessels and hence cause hemostasis. Even though the term 'coagulation' is used as a synonym for thermal hemostasis, thermal coagulation alone is only efficient for hemostasis of small vessels. Larger vessels (> 0.5 mm) must be compressed mechanically during thermal coagulation to achieve hemostasis.

Thermal desiccation  Previous section Next section

Thermal desiccation is defined as heat-induced dehydration of tissue. If the temperature of tissue is equal to the boiling temperature of intra or extracellular water (c. 100°C), the desiccation effect can dehydrate the tissue quickly, depending on the density of power applied to the target tissue. Thermal desiccation can cause:

  • contraction and shrinkage of tissue, by dehydration;
  • an adhesive effect of glucose;
  • a dry layer that acts to insulate tissue electrically.

Thermal desiccation causes significant contraction by drying and shrinkage of vessels, resulting in hemostasis of small vessels. Larger vessels (> 0.5 mm) must be mechanically compressed during thermal hemostasis.

Desiccation of glucose as a derivative of collagen results in a glue effect, which in turn causes sticking of desiccated tissue to coagulation electrodes, heater probes, the distal end of laser fibers, and also to polypectomy snares.

Desiccated tissue has a relatively high specific electric resistance. A layer of desiccated tissue functions like an electric isolating layer. This can cause a problem during polypectomy if the tissue adjacent to the snare becomes desiccated. When this occurs, there is no cutting effect and the snare can get stuck within the desiccated tissue of the polyp and cannot be moved forward or backward. During use of the argon plasma coagulator (APC) the desiccated electrically isolating layer automatically limits the maximum penetration depth of the thermal effect, described in more detail below.

Thermal carbonization  Previous section Next section

Thermal carbonization is defined as partial oxidation of tissue hydrocarbon compounds if the temperature exceeds 200°C. Because the temperature of tissue containing water does not exceed approx. 100°C, only desiccated and relatively dry tissue can become heated above 200°C and carbonized. Dry tissue will achieve temperatures above 100°C only by an electric spark or laser.

If the temperature of desiccated tissue increases above 200°C in the presence of oxygen (room air), it becomes carbonized after desiccation. However if the target tissue is bathed by a noble gas such as argon, the tissue does not become carbonized.

Even though carbonization of tissue is not a goal in therapeutic colonoscopy, it is relevant during tissue vaporization by laser, because the absorption of light increases when the tissue becomes carbonized to a black color.

Thermal vaporization  Previous section Next section

Thermal vaporization is defined as combustion of desiccated and carbonized tissue. Tissue becomes vaporized during or after desiccation and carbonization when the temperature increases to approximately 500°C and it is bathed in oxygen-containing gas, e.g. air. If the target tissue is within inert gas (e.g. CO2) or noble gas (e.g. argon), the tissue does not become vaporized.

Thermal vaporization can be used directly for the ablation of pathologic tissues as well as indirectly for tissue cutting. In colonoscopy only laser, especially Nd:YAG laser, is used for tissue ablation by vaporization, and only high-frequency surgery is used for thermal cutting of tissue.

Top of page Generation of temperature in thermal tissue  Previous section Next section

Various energy forms, and their respective sources, applicators and application techniques are available for thermal intervention in the colon (Fig. 3). A description of these properties and their relevance for endoscopic applications in the colon follow.

The temperature of tissue can be increased either exogenously, e.g. by means of a heater probe, or endogenously, e.g. by means of electric current or laser; it can also be increased by a combination of both, as in high-frequency surgical cutting, where endogenous heat is caused by electric current and exogenous heat is caused by electric arcs between the active electrode and tissue. For thermal interventions in the colon it is important that the temperature required for an intended purpose is only delivered at the target tissue.

Unintentional thermal damage to adjacent tissues must be avoided. This stipulation is difficult to achieve since it is not possible to heat part of a tissue to a desired temperature without at the same time heating adjacent tissue. Although it is not possible to avoid heat transfer, it may be possible to keep thermal damage of adjacent tissues to a minimum. Where possible, the distance between the target tissue and deeper surrounding tissue can be increased for the purpose of limiting thermal damage by submucosal injection with physiological NaCl solution (Fig. 4).

Some coagulation effect to adjacent (deeper or surrounding) tissue can also be desired in some cases, especially during cutting of vascularized biologic tissue, such as during polypectomy. During polypectomy, the tissue becomes vaporized in front of a cutting electrode and heat spreads to the adjacent tissue (the cut edges) to promote hemostasis.

These aspects should be taken into account when choosing the primary energy form, its source, applicators, and application techniques.

As mentioned previously, in the colon the distances between the tissues which are the desired subject of thermal heating and those tissues which are not intended to be thermally damaged are very small; as a consequence, the diffusion of heat within the surrounding tissue also has to be taken into account. Heat flows from tissues with a higher temperature into tissues with a lower temperature (Fig. 5). This diffusion effect is not used for therapeutic purposes in colonoscopy, and is limited by heating the target tissue to the temperature required only for the short amount of time necessary for the intended purpose.

In order to avoid unintentional damage to the tissue adjacent to the target tissue, it is necessary to know the maximum depth of the tissue injury and how to control the effect produced by the various thermal techniques.

Heater probe  Previous section Next section

Heater probes belong to the family of cautery instruments, which have a very long history. In principle, cautery instruments consist of a handle with a distal tip, which can be heated to a temperature appropriate to cause one of the specific thermal effects in biologic tissue. The heater probe consists of a catheter with a special heat-generating device built into the tip, which converts electric energy to heat energy [1,2]. The heat generated outside the tissue (exogenously) can be applied to a target tissue by touching it with the hot tip.

The temperature of modern heat probes for flexible endoscopy is adjustable and automatically controlled. Modern heat probes are provided with irrigation from a nozzle on the tip, which can be used to clear blood from the site to facilitate a clear view and accurate positioning. A special coating on the tip prevents it from sticking to desiccated tissue.

Because heat probes can be pressed against the target tissue during heat application, even bleeding from medium size vessels can be treated by simultaneously compressing and coagulating the vessel (Fig. 6 a). However, this should be done very carefully to avoid thermal damage to the muscularis propria (Fig. 6 b).

High-frequency surgery  Previous section Next section

General principles of high-frequency electric devices  Previous section Next section

High-frequency surgery (HF surgery) is a thermal technique where the required temperature is reached by conversion of electric energy into heat energy within the target tissue, i.e. endogenously.

High-frequency alternating current (HF current) with frequencies greater than 300 kHz (ICE 6001-2-2) is well suited for the heating of biologic tissues because it does not stimulate either nerves or muscles. The electric energy (E) in tissue caused by the HF current becomes converted (®) endogenously into heat energy (Q). The amount of heat energy (Q) measured in watt-seconds (Ws) which is produced in the tissue is a function (f) of the electric resistance (R) and the square of the averaged value (I2) and the effective duration (Δt) of the HF current (Iav).

E®Q=f(R, Iav2, Δt) (Ws)

The temperature of a biologic material rises proportionally to the amount of heat and inversely proportionally to the specific heat capacity of the tissue in question.

As mentioned above, a requisite for the application of thermal techniques in the colon is that the temperature required for an intentioned purpose is reached and becomes effective only at the target tissue, and unintentional thermal damage to adjacent or lateral tissues must be avoided. In HF surgery, this objective is achieved via the current density (j) and the current flow duration (Δt) in the target tissue. The current density (j) is a function (f) of the amount of current (i) measured in amperes (Amp) which flows through a defined area (A) measured in square centimeters (cm2) at a certain point in time (t) or averaged over a defined time interval (Δt).

j = f(i/A) (A/cm2)

The partial amount of heat (q) generated endogenously through electric current either partially or at an arbitrary point within the tissue is proportional to the specific electric resistance (ρ), the square of the current density (j2), and the effective current flow duration (Δt) at this point of the tissue.

q = f(ρ, j2, Δt) (Ws)

Conduction of an electric current through any material requires that both poles of the electric source be connected to the tissue (through the patient) in an electrically conductive manner. Two electrodes are necessary for this purpose. The electrodes at the target tissue are called active electrodes. The electrodes through which the electric current is conducted away from the tissue (the patient), back to the energy source, without any thermal damage at this electrode, are called neutral electrodes. Applications which use an active and a neutral electrode are called monopolar applications, and the instruments used for these applications are called monopolar instruments (Fig. 7 a). Applications which use both electrodes simultaneously as active electrodes are called bipolar applications, and the instruments used for these applications are called bipolar instruments. As a rule, both active electrodes of bipolar instruments are located close by on the same instrument (Fig. 7 b).

The density of current within the target tissue can be varied in proportion to the size and shape of the contact surfaces of the active electrodes of HF instruments. Most active electrodes used in flexible endoscopy are in the shape of a needle, loop, or ball electrode (Fig. 7 c).

Apart from the shape, the size of the contact surface plays an important role as regards the current density and its distribution both in the target tissue and in adjacent tissue. A smaller contact surface results in a steep reduction in the current density and in the temperature profiles in the tissue independent of the distance from the contact surface (Fig. 8).

HF current can flow through biological tissue only when the tissue contains water and electrolytes. As a consequence, the temperature of tissue containing water cannot rise above the boiling point of water (approx. 100°C). Tissues that contain less water and are drier, have a lower electric conductivity and less HF current can flow through this tissue. Completely dry biologic tissue is an electric insulator, hence no electric current can flow through it, and the temperature cannot rise (Fig. 2a). This fact is of importance during use of argon plasma coagulation.

Electric arcs  Previous section Next section

Electric arcs are ignited between an active electrode and tissues when the peak value of the HF voltage is equal to or greater than 200 V, which is typical if the active electrode consists of metal and the tissue contains water (Fig. 2b). Since these electric arcs reach temperatures far above 300°C, they generate exogenous heat, which raises the temperature of tissue above 100°C, thus causing carbonization and vaporization of dry tissue as described above.

In colonoscopy, carbonization and vaporization of tissue caused by an electric arc is not only unnecessary, but also annoying, since it generates a certain amount of smoke which impedes visibility. Because the depth of heat penetration cannot be controlled during electric arcing, it is not used as a therapeutic tool in endoscopy.

Even if the vaporization effect caused by electric arcs is not directly used in colonoscopy, it is useful indirectly for HF surgical tissue resection.

Top of page Principles of high-frequency surgical coagulation  Previous section Next section

In general, the term 'coagulation' includes the effects of devitalization, coagulation, and desiccation. In colonoscopy HF surgical coagulation can be used for thermal devitalization of pathologic tissue and for hemostasis. Thermal devitalization of pathologic tissue is performed by argon plasma coagulation (APC) or laser and is described in more detail below. Thermal hemostasis can be used to stop spontaneous bleeding as well as to prevent iatrogenic bleeding, for example during resection of polyps.

The spectrum of indications for thermal hemostasis is very wide. Equally wide is the spectrum of the techniques and instruments available for hemostasis, some of which have been developed or designed especially for application in flexible endoscopy. Because the wall of the colon is relatively thin, thermal hemostasis applied directly on the colon wall is a compromise between efficiency and thermal wall damage.

The method and instrument of thermal hemostasis is dependent on the size of the vessels causing bleeding. In small vessels, hemostasis can be achieved by thermal coagulation or desiccation alone. Control of bleeding from larger vessels requires mechanical compression during heat application. This principle is also applicable for hemostasis during polypectomy.

Monopolar coagulation instruments  Previous section Next section

In their most simple form, monopolar coagulation instruments for flexible endoscopy consist of a catheter at the distal end of which is an electrode, often ball-shaped. Because this electrode can be pushed against the target tissue, this instrument is useful for hemostasis not only of small but also of larger vessels. In the colon the risk of deep thermal wall damage has to be taken into consideration. During hemostasis, coagulated or desiccated tissue can stick to the electrode, so that the source of bleeding can be reopened when the electrode is pulled off the site. This problem was addressed by the development of the electro-hydro-thermo probe and by addition of an antisticking coating.

Electro-hydro-thermo probes  Previous section Next section

Electro-hydro-thermo (EHT) probes for flexible endoscopy (Fig. 9) consist of a catheter with an electrode at the distal end (usually ball-shaped). On this electrode is a hole through which water or physiological NaCl solution can be instilled between the electrode and target tissue. When the electric current is applied the contact surface between electrode and tissue does not become dry and the electrode does not stick to the coagulated tissue [3,4]. The instillation of fluid can also be applied for the irrigation of bleeding sources. When applying EHT, the depth of the thermal effect cannot be well controlled. This problem has been addressed with the development of bipolar coagulation probes for flexible endoscopy.

Bipolar coagulation instruments  Previous section Next section

In their most simple form bipolar coagulation instruments for flexible endoscopy consist of a catheter, at the distal end of which are at least two closely placed electrodes (Fig. 10). The HF current flows through the tissue only between these two electrodes. They can be applied either axially or laterally. The depth of the thermal effects which can be reached is relatively small, decreasing the risk of penetration; however, the efficacy is also limited, i.e. the instruments are useful only for small lesions. Bipolar instruments often have irrigation capacity and some have integrated injection needles [5,6].

Top of page Principles of high-frequency surgical cutting with particular regard to polypectomy  Previous section Next section

Biologic tissue can be incised electrosurgically when the HF voltage between an electrode and tissue is sufficiently high to produce electric arcs between the cutting electrode and the tissue; this concentrates the HF current at specific points of the tissue (Fig. 11a). The temperature produced at the interface where the electric arcs contact the tissue (like microscopic flashes of lightning) is so high that the tissue is immediately evaporated or burned away. As the active cutting electrode passes through the tissue, electric arcs are produced wherever the distance between the cutting electrode and the tissue is sufficiently small, producing an incision (Fig. 11b). As mentioned previously, a minimum peak voltage (Up) of 200 Vp is required in order to produce electric arcs between a metal electrode and biological tissue containing water. The intensity of the electric arcs increase in proportion to the peak voltage. Experience has shown that the depth of thermal coagulation along the cut edges increases with increasing peak voltage (Fig. 12).

In the system of HF surgical cutting, an increase of the voltage increases the electric power (P) by the square of the voltage (P = f(U2)), so it is necessary to modulate the amplitude of the voltage (turn it down) to compensate for the strong influence provided by the mathematical power of the square multiplier.

The higher the peak voltage (Up) and the degree of amplitude modulation, the deeper the thermal coagulation of the cut edges. If the voltage is not modulated and its peak value is low, the coagulation depth at the cut edges is minor or nil, it is called 'cut mode', and the HF current caused by this voltage is called 'cutting current.' If the voltage is strongly modulated and its peak value is high resulting in deep coagulation of the cut edges, it is called 'coagulation mode', and the HF current caused by this voltage is called 'coagulation current.' One reason for this confusing terminology is the fact that conventional HF surgical generators do not have the capacity for setting the output voltage, only the output power. Setting of the output power of HF generators is not the best option for polypectomy, but it is the standard at the present time.

In colonoscopy the depth of thermal coagulation and also the possibility of thermal devitalization outside the coagulation zone must be considered. It can be dangerous if the coagulation and/or devitalization occurs outside the desired zone of thermal devitalization. If deep thermal damage occurs, tissue histology may be interfered with. A useful aspect is that coagulation of the cut edge of the colon wall can cause hemostasis, which can be used advantageously. Hence, coagulation of the cut edges always is a compromise between these three aspects in colonoscopy.

Another problem with regard to the adjustability, reproducibility and constancy of the depth of coagulation common to all conventional HF surgical generators is the greater or lesser generator impedance Ri, making the HF output voltage Ua dependent on the HF output current Ia. The greater the generator impedance Ri, the more the HF output voltage Ua depends on the HF output current Ia. Conventional HF surgical generators have a generator impedance of between 200 and 1000 ohms.


The output voltage Ua, and hence also the intensity of the electric arcs and ultimately the depth of coagulation, vary considerably, since the load resistance Ra and current Ia vary from one cut to the next and also during each cutting process. During polypectomy for example the load resistance Ra, which is the electric resistance between a polypectomy snare and a polyp, depends among other things on the size of the polyp and increases during closing the snare because the contact between the snare and tissue becomes smaller and smaller.

Another special problem of HF surgical resection of polyps is that HF surgical cutting can be done with minor mechanical force, as long as the HF voltage between the polypectomy snare and the tissue to be cut is above 200 Vp. Because the speed of the snare while cutting through the polyp has a major influence on the degree of hemostasis of the cut edges, the speed should be appropriate to the size of the polyp's attachment as well as controlled. Control of closure speed can be very difficult or really impossible if there is mechanical friction between the polypectomy snare and catheter or between the slider and the slider bar of the handle of the instrument (Fig. 13).

Mechanical friction can cause uncontrolled speed of the snare and hence uncontrolled or insufficient hemostasis, especially if the snare zips through the polyp. Most of the mechanical force on the polypectomy snare is caused by closing the snare intentionally.

Top of page Technical aspects of polypectomy  Previous section Next section

Polypectomy is one of the most important applications of HF surgery in the colon [7–11] and hemostasis is one of the main problems with polyp resection. If the problem of bleeding caused by resection did not exist, it would be possible to resect polyps or adenoma in a purely mechanical fashion with a thin wire snare in the absence of heat. This would have the advantage that neither the resected specimen (with regard to the histology) nor the wall of the colon (with regard to the risk of perforation) would be thermally damaged. This is possible for tiny polyps, but the endoscopist must tread the path between application of sufficient heat for hemostasis and yet avoid deep thermal damage. For safe polypectomy, the endoscopy team should be familiar with the equipment available for polypectomy [13–15].

Polypectomy snares  Previous section Next section

The ideal polypectomy snares should cut perfectly, and should not coagulate the cut edge of the polyp to permit adequate histologic examination. In addition, the ideal snare should coagulate the cut edge on the colon wall to guarantee safe hemostasis, should not coagulate through the muscularis propria, and can be applied easily and safely. Unfortunately this ideal polypectomy snare is not available, as a number of problems must be addressed. For a perfect cut and minor thermal coagulation of the cut edge on the polyp margin the snare wire should be as thin as possible. For effective coagulation of the cut edge on the wall of the colon the snare wire should be as thick as possible. For easy and safe application on all different polyps the snare should be both flexible as well as stiff and should assume the optimal size for small as well as big polyps. In reality, the available polypectomy snares offer only a compromise of all these features.

A special problem can be caused by the nose at the distal end of polypectomy snares. If this nose is too long, because it is out of endoscopic view, it can touch the mucosa behind the polyp without the operator's knowledge and cause inadvertent damage when electrically activated.

The polypectomy snare handle  Previous section Next section

Polypectomy snare handles should be designed ergonomically for both male and female hands, and should have minor friction between the slider bar and the slider. This is important to provide even loop closure allowing a consistent cut quality and even coagulation.

Polypectomy snare catheters  Previous section Next section

Polypectomy snare catheters should be flexible enough for passing through working channels of twisted and looped endoscopes and have sufficient stiffness to prevent shortening when removing large polyps.

Top of page Safety aspects of high-frequency surgery  Previous section Next section

HF surgery can cause unintended thermal effects outside the target tissue during monopolar applications [12]. This can happen in tissue directly adjacent to the target tissue or remote from the target tissue when the HF current density is higher outside the target tissue.

To prevent thermal damage to the patient's skin, the neutral electrode must be firmly in contact with the skin as recommended in the instruction manual of the specific HF surgery generator.

HF surgery can cause interference in other electronic devices, such as a pacemaker where it can cause reversion of synchronous to asynchronous pacing or possibly pacemaker inhibition.

During polypectomy, the head of a big or stalked polyp must not touch the colon wall because HF current can flow through this contact resulting in uncontrolled thermal effects (Fig. 14 a).

If an endoloop is used for preventing bleeding and is placed on the stalk of a polyp between the colon wall and where the polypectomy snare is placed, the HF current density in the smaller diameter compressed by the endoloop can be much higher compared with the HF current density at the polypectomy snare; this will cause the narrowest part to become heated (within the endoloop) instead of the tissue within the polypectomy snare (Fig. 14 b,c).

If metallic hemoclips are used for hemostasis, the snare must not touch the clips as HF current will be conducted through it.

Top of page Argon plasma coagulation  Previous section Next section

The principle of argon plasma coagulation  Previous section Next section

The principle of argon plasma coagulation (APC) is relatively simple [16]. When an electrode (E) is placed at a distance (d) from the surface of a tissue (G) and a HF voltage (UHF) is applied between the electrode and the tissue, the gas between the electrode and the tissue becomes ionized and hence electrically conductive when the electric field strength (UHF/d) exceeds a critical level. If the gas between the electrode and the tissue is a noble gas (argon, helium, etc.), an electric field strength of about 500 V/mm is needed for ionization. Argon is preferred because of its relatively low cost. The ionized argon forms argon plasma beams between the electrode and the tissue, which can be visualized as small sparks that conduct the HF current to the tissue. An important advantage of argon in comparison to air is its inert character, which neither carbonizes nor vaporizes biologic tissue so that the thermal effects of APC are limited to the devitalization (zone 1), coagulation (zone 2), desiccation (zone 3), and shrinking of tissue (zone 4) as a result of coagulation and desiccation (Fig. 15).

A special aspect of APC is that the direction of the argon plasma beams follows the direction of the electric field between the electrode and the tissue. The electrically active beams are directed from the electrode to electrically conductive tissue closest to the electrode, regardless of whether the tissue is in front of or lateral to the electrode. As soon as the target tissue becomes desiccated and hence loses its electric conductivity, the beams automatically move from desiccated to non-desiccated tissue until a large area of the target tissue is desiccated. As a result of the loss of electric conductivity at a treated site, the depth of desiccation, coagulation, and devitalization is limited.

Equipment for argon plasma coagulation  Previous section Next section

The argon source is an argon cylinder with a pressure-reducing valve (Fig. 16). For safety reasons, the argon source must have automatically controlled flow rates and limitation of the pressure. The HF current source must provide both sufficiently high HF voltage for the ionization of argon as well as sufficiently high HF current to generate adequate heat within the target tissue.

APC probes for flexible endoscopy basically consist of a non-conductive flexible tube (Fig. 17) through which argon flows. An electrode within the distal end is connected to the HF generator by a wire through the lumen of this tube. For safety reasons, the electrode is recessed from the distal end of the tube so that it cannot come into contact with tissue.

As shown in Fig. 18, the depth of coagulation depends on power setting and on application time. In addition, the application technique has a significant influence on the depth. Movement of the activated probe tip will result in a shallower depth of thermal effect than is produced by directing the tip at one point.

When the probe is held at one site for between about 3 and 10 s, the depth of thermal coagulation is up to about 2 mm. Above 10 s the depth increases slowly to its maximum of about 3–4 mm.

Touching the foot pedal activates the flow of argon gas and simultaneously starts the flow of electric current. The time that the foot pedal is depressed may not be the same as the activation time, which refers to the interval when the argon plasma sparks actually touch the target tissue. There may be no or intermittent sparks if the distance between the probe and the tissue is too great.

Figure 19 shows that the shape of an argon gas beam consists of a zone of laminar argon flow, a zone of divergent argon flow and a zone where the flow becomes turbulent. Argon plasma beams can only reach the target tissue when there is argon gas between the distal end of the APC probe and the target tissue. This is the case when the argon gas beam is directed to the target tissue as shown in Fig. 20 (a) (axial APC probe) and Fig. 20 (b) (lateral APC probe). APC probes can be used laterally as well, but the lumen must be filled with argon. The ignited spark will direct itself to the nearest grounded tissue (Figs 20 c,d). If the target tissue is not within the argon gas beam or within an argon-filled lumen the argon plasma beams will not ignite, or plasma beams of air will ignite instead. Air plasma beams do not look very different from argon plasma beams; however, air plasma beams can cause carbonization as well as vaporization of tissue and hence can cause deep damage and perforation of organs. Endoscopists typically use air plasma beams when using the tip of the snare wire to 'spark' a polypectomy site to stop bleeding or destroy residual polyp fragments. Air plasma beams, consisting of ionized air, only travel over extremely short distances, and are uncontrollable.

Safety aspects of argon plasma coagulation  Previous section Next section

As in any monopolar electrosurgical procedure, the neutral electrode must be applied to the skin surface.

Because argon gas is insufflated into the colon during APC, extensive distension of the colon can occur. The distal end of the APC probe must never be pressed against the mucosa or perforation can occur. If the superficial mucosal layer is destroyed by the probe pressure against the colon wall, the flow of argon gas will create instantaneous submucosal emphysema.

Top of page Laser  Previous section Next section

Principle of Nd:YAG laser  Previous section Next section

'Light Amplification by Stimulated Emission of Radiation (LASER)', first described theoretically by Albert Einstein in 1917, and put into practice by T.H. Maiman 5 years after Einstein's death, made possible the generation of electromagnetic radiation in the range of optical wavelengths (light) with an extremely high power density. For about 50 years, the high energy of the laser has been used in medicine. The endoscopic application of laser began in 1975 [54], and following the successful development of a flexible light conductor. Of all the different laser sources, only the argon laser (a = 488/515 nm, Pmax= 20 W), and the Nd:YAG laser (a = 1064 nm, Pmax= 100 W) can be used endoscopically because their wavelength can be conducted through thin flexible light guides without significant loss of energy.

Specific characteristics of Nd:YAG lasers in flexible endoscopy  Previous section Next section

With an adjustable power of up to approx. 100 W, Nd: YAG laser sources are able to generate light with a wavelength of 1064 nm, which is located in the infrared range and is thus invisible to the human eye. With a light guide of 0.6 mm, this light can be guided through an instrumentation channel of a flexible endoscope. The laser light emanates from the light guide in an axial direction with a divergence of approx. 10 degrees.

The invisible Nd:YAG laser is combined with a 'pilot light' in the visible range in order to see where the beam is directed.

The thermal effects within the radiated tissue are primarily dependent on the density of absorption (W/mm2) in the tissue and the duration of effect (Δt). The density of absorption refers to the power of light (W) which is absorbed by the tissue per mm3. The density of absorption is dependent on several variables: the distance (x) of the distal end of the light guide from tissue (Fig. 21), the angle with which the light radiates onto the surface, and the absorption and reflection characteristics of the tissue. The parameters may change rapidly due to coagulation, desiccation, or even carbonization. The latter can cause a dramatic increase in absorption or a decrease in reflection, leading to intentional or unintentional vaporization of tissue or even a perforation of the colon.

For intentional vaporization of larger tumor masses, the distal end of the light guide has to be placed close to the target tissue and the power of the laser has to be set sufficiently high.

When using lasers for thermal hemostasis, the experience of the operator is most important; if the light guide is too far away the density of power could be too low for hemostasis, and if too close, the source of bleeding could be started by vaporization rather than stopped by coagulation (Fig. 22).

The introduction of APC into flexible endoscopy has reduced the need for lasers in endoscopy [57,60].

Top of page Safety aspects of Nd:YAG laser in flexible endoscopy  Previous section Next section

The laser can cause unintended thermal effects outside the target tissue during applications.

During Nd:YAG laser applications all persons including the patient must protect their eyes, even when the distal end of the laser fiber is within the colon, because the light guide can break outside the endoscope. Since Nd:YAG laser is invisible, a break of the laser fiber can damage the retina of unprotected eyes.

Top of page Summary  Previous section Next section

All the different thermal modalities described in this chapter have their special advantages and disadvantages. None of the methods or equipment can yet be regarded as ideal for all cases. A modern endoscopy facility should have adequate equipment to provide optimum treatment for each case as listed in Fig. 23. But endoscopists should not only have the equipment available, they should also be familiar with the physical background as well as with the advantages and disadvantages of all modalities which are available in the endoscopy suite. This, combined with practical skill and experience, and last but not least competent assistance, is the prerequisite for obtaining successful results.

Top of page References  Previous section

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 3 Matek, W & Frühmorgen, P. Electrocoagulation—animal experiments. Endoscopy, 1986; 18 (Suppl. 2); 58–60.

 4 Frühmorgen, P & Matek, W. Electro-hydro-thermo and bipolar probes. Endoscopy 1986; 18 (Suppl. 2): 62–4. PubMed

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Copyright © Blackwell Publishing, 2005

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  A (very) brief history of endoscopy
  Professionalism and quality
Unit design
  Space planning
   Daily room volumes
   Procedure room size
   Preparation and recovery ratios
   Separate entrances
   Common space problems
  Physical infrastructure
  Intake and recovery areas
   Intake areas
   Managing clothes and valuables
   Recovery facilities
  Procedure room reprocessing and storage
   Standard procedure rooms
   Scope reprocessing and storage
   Patient flow issues
   Complex procedure rooms
   Storage of supplies and medications
   Travel carts for emergencies
Unit management
  Major areas of responsibility
  Staffing design
   Staffing emergencies
  Procedure schedules
   Relative time requirements
   Barriers to efficiency
   How many endoscopes?
   Endoscope repair costs
  Endoscope reprocessing
  Coding and billing
Outstanding issues and future trends
  Capsule endoscopy
  Colon screening technologies
  Endoscopy by non-specialists
  Growth of advanced endoscopy
  Moderate sedation
  Deep sedation/analgesia
Advances in monitoring during sedation
  Standard pulse oximetry
  CO2 monitoring
   Transcutaneous CO2 monitoring
  BIS monitoring
Topical anesthetics: are they worth the effort?
Titration vs. bolus administration of sedation and analgesia
  Problems with propofol
  Specific training for use of propofol
  Contraindications of propofol
  Clinical trials of propofol
   Propofol or midazolam?
   Upper endoscopy
   Upper endoscopy and colonoscopy
   Propofol with or without midazolam
   Patient-controlled administration of propofol
   Nurse-administered propofol
   Gastroenterologist-administered propofol
Outstanding issues and future trends
Gastrointestinal endoscopes
  Endoscope design
   Control section
   Insertion tube
   Connector section
   Light source/processors
  Endoscope equipment compatibility
  Endoscope categories
   Esophagogastroduodenoscope (gastroscope)
   Wireless capsule endoscopy
Gastrointestinal endoscopic accessories
  Tissue sampling
   Biopsy forceps
   Single-bite cold-biopsy forceps
   Biopsy cup jaws
   Multi-bite forceps
   Other specialty forceps
   Monopolar hot biopsy forceps
   Reusable vs. disposable biopsy
   Cytology brushes
   Needle aspiration
  Polypectomy snares
  Retrieval devices
  Injection devices
   Injection needles
   Spray catheters
   ERCP catheters
  Hemostatic and ablation devices
   Contact and non-contact thermal devices
   Heater probe
   Laser fibers
   Argon plasma beam coagulator
   Mechanical hemostatic devices
   Band ligation
   Metallic clip application via flexible endoscopes
   Marking with clips
   Detachable loops
  Transparent cap
  Dilation devices
   Push-type fixed-diameter dilators
   Hurst and Maloney dilators
   Savary-type dilators
   American Dilation System dilators
   TTS fixed diameter dilators
   Threaded-tip stent retrievers
   Radial expanding balloon dilators
   TTS dilators
  Achalasia balloon dilators
Outstanding issues and future trends
  Fiberoptic imaging
   Teaching attachments and photography
   Image capture
   Standardized image terminology
   Structured reporting
   The opportunities and challenges of the digital revolution
Digital imaging
  Imaging the gastrointestinal tract using a videoendoscope requires several steps
  Color models
Digitization of color
Color depth
Pixel density
File size
  What detail is needed?
  File compression
  Compression techniques
   Lossless compression
   Lossy compression
  Image file formats
  Color and black and white compression
  JPEG 2000 and beyond
DICOM standard
  Information Objects
   Patient name attributes
  DICOM conformance
  DICOM in endoscopy
  Expanding the scope of DICOM
How much compression is clinically acceptable?
  Studies of compression acceptability
   Vakil and Bourgeois
   Kim (personal communication)
  Developments in compression
Still pictures or live video?
  Video storage developments
What images should be recorded in practice?
  Lesion documentation
  Recording negative examinations
  Structured image documentation
  Costs of image documentation
Image enhancement
  Color manipulation
  Narrow band imaging and spectroscopy
Terminology standardization
  OMED standardized terminology
  Minimal standard terminology—MST
   Problems with MST
Outstanding issues and future trends
Editor's note
Relevant thermal effects in biological tissues
  Thermal devitalization
  Thermal coagulation
  Thermal desiccation
  Thermal carbonization
  Thermal vaporization
Generation of temperature in thermal tissue
  Heater probe
  High-frequency surgery
   General principles of high-frequency electric devices
   Electric arcs
Principles of high-frequency surgical coagulation
  Monopolar coagulation instruments
  Electro-hydro-thermo probes
  Bipolar coagulation instruments
Principles of high-frequency surgical cutting with particular regard to polypectomy
Technical aspects of polypectomy
  Polypectomy snares
  The polypectomy snare handle
  Polypectomy snare catheters
Safety aspects of high-frequency surgery
Argon plasma coagulation
  The principle of argon plasma coagulation
  Equipment for argon plasma coagulation
  Safety aspects of argon plasma coagulation
  Principle of Nd:YAG laser
  Specific characteristics of Nd:YAG lasers in flexible endoscopy
Safety aspects of Nd:YAG laser in flexible endoscopy
Sterilization and disinfection
  High-level disinfection
  What level of disinfection is required?
   Critical items
   Semi-critical items
  The practical problem
  The organisms
  The critical points in reprocessing
Risks of infections associated with endoscopic procedures
  Mechanisms of infection
  Clinical infections
   Infecting organisms
   Vegetative bacteria
   Clostridium difficile
   Mycobacterium tuberculosis
   Atypical mycobacteria
   Serratia marcescens
   Helicobacter pylori
   Human immunodeficiency virus (HIV)
   Hepatitis B
   Hepatitis C (HCV)
   What to do in practice about CJD?
   New variant CJD (vCJD)
   Other infections
  The endoscopic procedures
   Upper gastrointestinal endoscopy
   Lower gastrointestinal endoscopy
   Endoscopic retrograde cholangiopancreatography
   Percutaneous endoscopic gastrostomy
   Endoscopic ultrasound
  Host factors
   Immune competence
   The degree of tissue damage
   Intrinsic sources of infection
   Damaged valves and implants
Antibiotic prophylaxis for endoscopic procedures
  Principles of prevention of bacterial endocarditis
  High risk cardiovascular conditions [43]
  Moderate risk cardiovascular conditions [43]
  Recommendations for antibiotic prophylaxis
   Who should receive antibiotics?
   Clinical problems where opinions diverge
   What antibiotic regimen?
Antibiotic prophylaxis for ERCP
  Prophylactic antibiotic regimens for ERCP
Principles of effective decontamination protocols
  Cleaning is essential
  Effectiveness of recommended protocols
  Endoscope structure
   Common features
   External features
   Common internal features
   Special internal features
   Cleaning equipment
   Cleaning fluids
   Soaking time
   General maintenance
   Work areas
Reprocessing regimens
  Disinfect before and after procedures
  Manual cleaning
  Manual disinfection
  At the end of the list
  Endoscopic accessory equipment
   Cleaning accessories
   Special accessory items
   Sclerotherapy needles
   Water bottles and connectors
Problem areas in endoscope reprocessing
  Rinsing water
   Poor quality water
   Infections from rinsing water
   Bacteria free water
   Water testing
   Recommendations for rinsing water
Variation in cleaning and disinfection regimens depending upon the supposed infective status of the patient
Compliance with cleaning and disinfection protocols
The investigation of possible endoscopy infection transmission incidents
  Common causes
  Golden rules for investigating potential infection incidents
  The investigation process
  Transmission of viral disease
Automatic flexible endoscope reprocessors (AFERs)
  Machine design and principles
   Water supply
   Alarm function
   Fume containment
   Disinfectant supply
   Reprocessing time
   AFERs cannot guarantee to sterilize endoscopes
   Plumbing pathway
   Rinse and dry cycle
   Regular bacteriological surveillance
Quality control in endoscope reprocessing
  Quality control measures
Microbiological surveillance in endoscopy
  Testing procedures
  Interpretation of cultures
  Microbiological surveillance of AFERs
Outstanding issues and future trends
The contract with the patient; informed consent
  Educational materials
What are 'risks' and 'complications'?
  Threshold for 'a complication'
  Timing of unplanned events
  Direct and indirect events
  Data set for unplanned events
General issues of causation and management
  Technical and cognitive performance
  Fitness for procedures
   ASA score
   Other risk indices
  Prompt recognition and management
   Act promptly
  Specific unplanned events
   Failure to diagnose
   Risk factors
   Risk factors
   Cardiopulmonary and sedation complications
   Allergic reactions
   IV site issues
   Miscellaneous and rare events
Preventing unplanned events
Outstanding issues and future trends
Gastroenterologist–pathologist communication
  Endoscopist communication responsibility
  Pathologist communication responsibility
  Question-orientated approach
  Common terminology
Endoscopic biopsy specimens
  Specimen handling and interpretation issues
   Number of biopsies per container
   Tissue processing
   Prep-induced artifact
   Endoscopy-induced artifacts
   Biopsy-induced artifacts
   Crush artifact
   Burn/cautery artifact
   Endoscopic mucosal resection
   Core biopsy
  Regular stains
Exfoliative and fine-needle cytology
  Specimen handling; staining and fixation
   Cytological diagnosis
  Fine-needle aspiration
Organ system overview
   Where and when to biopsy
   Gastroesophageal reflux disease
   Barrett's esophagus
   Infective esophagitis
   Herpes simplex virus
   Adenocarcinoma and squamous cell carcinoma
   Where and when to biopsy
   Inflammatory conditions; gastritis
   H.pylori gastritis
   Hypertrophic folds
   Mass lesions
  Small bowel
   Celiac sprue
   Infective enteropathies
   Whipple's disease
   Mycobacterium avium–intracellulare
   Giardia lamblia
   Mass lesions
   Defining 'normal'
   Inflammatory colitides
   Normal colonoscopy
   Abnormal colonoscopy
   Inflammatory bowel disease
   Pseudomembranous colitis
   Ischemic colitis
   Mass lesions
Special stains
  Histochemical stains
  Immunohistochemical stains
  In situ hybridization
  Flow cytometry
  Electron microscopy
  Molecular pathology
Outstanding issues and future trends
The endoscopy facility and personnel
  Endoscopy facility
   Endoscopy instruments
   Ancillary equipment
   The endoscopist
   Nursing and ancillary personnel
The pediatric patient and procedural preparation
  Patient preparation
   Psychological preparation
   Medical preparation
   Recommendations for fasting
   Bowel preparation
   Antibiotic prophylaxis
  Informed consent
Endoscopic procedures currently performed in pediatric patients
  Indications and limitations
  Patient sedation
  Endoscopic technique
   Therapeutic endoscopy
   Other endoscopic modalities
   Small bowel enteroscopy
   Wireless capsule endoscopy
   Endoscopic ultrasonography
   Endoscopic retrograde cholangiopancreatography (ERCP)
Selected gastrointestinal pathologies in pediatric patients
  Eosinophilic esophagitis
  Food allergic enteropathy and colitis
  Foreign body ingestion
  Helicobacter pylori gastritis
  Polyps in the pediatric patient
  Lymphonodular hyperplasia
Outstanding issues and future directions
General principles of endoscopy training
  Traditional standard means of instruction
   Is self-teaching still acceptable?
  What to teach and how to teach it
  Defining competency and how to access it
   Linking diagnosis and therapy
   How competent?
   Varying rates of learning
   Learning beyond the training period
Training and competency in specific endoscopic procedures
  Esophagogastroduodenoscopy (EGD)
   Published guidelines for training in EGD
   Defining competence for EGD
   Data on acquisition of competency in diagnostic EGD
   Competency and EGD outcome
  Therapeutic EGD techniques
   Standard upper GI endoscopy techniques
   Hemostasis techniques
   Bleeding team
   Retaining competence
   Other specialized therapeutic upper GI endoscopy techniques
  Flexible sigmoidoscopy
   Published guidelines for training in flexible sigmoidoscopy
   Published guidelines for training in colonoscopy
   Defining competence for colonoscopy
   Technical components
   Cognitive objectives
   Minimum training requirements to achieve competency for colonoscopy
   The Cass study
   Competency and colonoscopy outcome
   Acceptable outcomes
   Rate of skills acquisition for colonoscopy
   Cases per week
   Too many cases?
  Therapeutic colonoscopy (biopsy, polypectomy, hemostasis techniques, stricture dilation, stent deployment)
   Standard therapeutic techniques (integral to performance of diagnostic colonoscopy)
   Advanced therapeutic colonoscopy techniques
  Diagnostic and therapeutic ERCP
   Published guidelines for training in ERCP
   Non-technical training
   Defining competence for ERCP
   Technical success
   Varying case difficulty
   Minimum training requirements to achieve competency for ERCP
   Case numbers
   What is a case?
   Competency and ERCP outcome
   Improving after training
   Annual volume
   Competence affects complication rates
   Rate of acquisition of ERCP skills
   Therapeutic ERCP
   Rate of acquisition of therapeutic skills
  Diagnostic and therapeutic EUS
   Defining competency in EUS
   Learning curve for EUS
   Therapeutic EUS
   EUS training opportunities
Complementary methods for instructions in GI endoscopy
  Advances in didactic methods
   Group instruction
   Laboratory demonstrations
  Endoscopy simulators
   Static models
   Courses with static models
   Ex vivo artificial tissue models: the 'phantom' Tübingen models
   Ex vivo animal tissue simulators: EASIE and Erlangen models
   Live animals
   Computer simulation
   GI Mentor™
   Current status of simulators
   Costs of simulators
   EUS models and simulators
  Use of training resources: summary
Endoscopy training 2010—a glimpse into the future
Credentialing and granting of privileges
   ASGE guidelines
Renewal of privileges and privileging in new procedures
  New procedures
Privileging for non-gastroenterologists and non-physician providers
The future of credentialing and privileging
  The use of new technology for credentialing
The role of endoscopic societies in training and credentialing
  Society courses
  Hands-on courses
  Research in training
  Influencing credentialing
Outstanding issues and future trends
Achieving competence—the goal of training
What experience is necessary in training? The fallacy of numbers
Beyond numbers: tools to measure competence
What level of competence is good enough? How is it recognized?
Endoscopic performance beyond training
Issues in measuring endoscopic performance
The report card agenda
The quality of endoscopy units
Outstanding issues and future trends
Most endoscopists are not interested
Is the problem declining?
Newly recognized infections
Compliance with guidelines
What can be done to remedy this sorry state of affairs?
  Infection control staff
  Microbiological surveillance
   British practice
The role of industry
Manual cleaning is key

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