Minimal access surgery (MAS) is performed through small incisions in order to minimise the trauma of the surgical wound. This module of the course is about laparoscopy and, in particular, therapeutic laparoscopy - a form of MAS particularly challenging to the theatre team. The main purpose of this module is to help course participants acquire the skills they need to perform laparoscopy efficiently and, above all, safely.
What happens in theatre is only a relatively brief part of the patient's overall care. For the patient, MAS begins with preoperative assessment and counselling and ends only when there has been a full recovery and return to normal activities. Before turning to skills and safety, we begin with an overview of minimal access surgery and some of the ergonomics relating to its use.
View the introduction to minimal access surgery video clip
Introduction to MAS
The laparoscopic stack
Safe induction and maintenance of the pneumoperitoneum
MAS instrumentation
Grasping and manipulation skills
Advanced dexterity skills
Diathermy
Operations carried out using the minimal access approach should be of the same quality as their conventional open counterpart. It should be emphasised that the difference between minimal access surgery and open surgery is the extent of the access as indicated by the name of the technique. Minimal access surgery must not compromise patient safety. There are several factors which influence the use of minimal access surgery:
With previous abdominal surgery, there is a risk of bowel injury owing to adhesions. The technique and the site of induction of pneumoperitoneum needs to be modified in patients with previous surgery. Laparoscopy is contraindicated in patients with a history of previous extensive abdominal surgery.
Optimum assessment using the minimal access approach requires adequate space to expose and handle different organs. With gross obesity, the laparoscopic approach is more difficult and technically demanding. In the presence of bowel obstruction or organomegaly, the intra- abdominal space is reduced and, therefore, experience and caution are required. In certain cases, laparoscopy may not be practical.
The mechanical and imaging constraints in minimal access surgery make laparoscopic task performance more difficult than its open counterpart. The individual surgeon has to balance his or her own laparoscopic experience against the operative task. While a surgeon may be competent in carrying out bowel anastomosis using an open approach, he or she may not be able to perform laparoscopic bowel suturing.
Some patients require effective and quick intervention as in the cases of uncontrolled shock or faecal peritonitis. These patients are not suitable for lengthy laparoscopic procedures. The surgeon must be prepared to convert to an open approach should he or she encounter technical complications or experience a lack of progress with the procedure. This should not be regarded as a sign of failure. All patients undergoing laparoscopic surgery should be warned of the risks of converting to an open procedure. For example, the 'standard' conversion rate for elective cholecystectomy is about 5% and all patients should be warned of this possibility.
These are the restrictions encountered on handling the tissues by endoscopic instruments:
- Limited degrees of freedom of instrument movement.
- Diminished tactile feedback.
- Small and long instruments.
- Problems of organ retrieval.
The use of an image display system as the visual interface between the surgeon and the operative field has several visual limitations compared to conventional open surgery:
- Two-dimensional imaging
- Reduced field of endoscopic vision
- De-coupling of motor and visual spaces (monitor location)
- Endoscope-instrument-tissue spatial relation (port location)
- Quality of video-endoscopic system (resolution, illumination and chroma)
The limitations of current image display systems are responsible for the degraded task performance in minimal access surgery compared to direct normal vision.
For a particular operation, the surgeon has to select the appropriate endoscope and place the ports and the monitor in optimum locations. The principles of the set-up of endoscopic equipment are summarised below and illustrated in Figures 54 and 55.
Direction of view of the endoscope describes the angle between the centre of the visual field (optical axis) and the physical axis of the endoscope. Endoscopes can be of forward viewing (0°) or forward oblique direction of view (30°, 45°). The angle between the optical axis of the endoscope and the plane of the target is referred to as the optical axis-to-target view angle (Figure 54).
Figure 54
The best task performance during endoscopic work is obtained when the optical axis-to-target view angle approaches 90° and the decrease in this viewing angle causes a significant degradation of task performance. In practice, however, only oblique viewing endoscopes or ones with flexible tips can achieve an adequate optical axis-to-target view angle approximating to 90°. For this reason, forward oblique endoscopes are preferable, despite the easier deployment of forward viewing types.
For bimanual tasks, manipulation, azimuth and elevation angles govern optimal port sites (Figure 55). The manipulation angle is the angle between the active and assisting instruments, while the azimuth angle describes the angle between either instrument and the optical axis of the endoscope. The elevation angle of the instrument is defined as the angle between the instrument and the horizontal plane. These angles determine optimal port location.
Figure 55. Angles govern port location
The maximal efficiency and quality performance of intracorporeal knotting are obtained with a manipulation angle ranging between 45° and 75° with the ideal angle being 60°. A better task efficiency is achieved with an equal azimuth angle on either side of the optical port. In practice, equal azimuth angles may be difficult to achieve but wide azimuth inequality should be avoided since this degrades task efficiency. When a 30° manipulation angle is imposed by the anatomy or build of the patient, the elevation angle should also be 30° as this combination enables the shortest execution time and allows an acceptable level of performance. Likewise with a 60° manipulation angle, the corresponding optimal elevation angle, which yields the shortest execution time and an optimal quality of performance, is 60°. Thus within the range of angles that ensure adequate task efficiency, a good rule of thumb is that the elevation angle should be equal to the manipulation angle.
On planning port location, an adequate intracorporeal instrument length should be obtained. This depends on the size of the patient and the site of the operation. The intra:extra corporeal shaft ratio for optimal task performance is 2:1.
The ports for instruments (active and assisting) and the endoscope should be inserted so that the instrument and endoscope should be aligned in the same direction. The surgeon must avoid operating against the endoscope/camera as this produces a mirror image and makes manipulations extremely difficult.
The best task performance is obtained with the monitor located in front of the operator at the level of the manipulation workspace (hands), permitting 'gaze-down viewing' and alignment of the visual and motor axis. Gaze-down viewing by the endoscopic operator allows both sensory signals and motor control to have a close spatial location and thus brings the visual signals in correspondence with instrument manipulations, similar to the situation encountered during conventional open surgery. In practice, the location of the monitor is determined by the site of the operation. For upper abdominal procedures, such as cholecystectomy and fundoplication, the monitor is placed near the patient's head. During appendicectomy, the monitor is located over the right iliac fossa and the surgeon stands on the left side near the patient's hypochondrium. Members of the operative team should look at the monitor placed in front and must avoid following the procedure on the side monitor.
The operation of the camera is crucial to surgical manipulations. Operating the endoscope and camera is a dynamic process throughout the surgical procedure. The camera operator actively takes part in the operation, and at times it can be quite hard work.
The centre of the endoscopic field has the best illumination and least image distortion. This provides the surgeon with the optimum image quality. The best performance therefore, is obtained with the task maintained in the centre of the endoscopic field. In addition, if the surgeon works at the periphery of the field, instrument movement may accidentally occur outside the displayed image, potentially damaging adjacent structures.
The distance between the endoscope and the target determines the size of the visual field and the resolution at the target area. The smaller the endoscope-to-target distance, the smaller the size of the visual field and the higher the resolution at the target. Withdrawal of the endoscope increases the area of the operative field viewed by the surgeon. The surgeon needs this view to insert endoscopic instruments or to perform a task which requires a large area for manipulation such as knot tying. On the other hand, advancing the endoscope towards the target increases the detail of the image viewed by the surgeon at the expense of a smaller operative field. The surgeon prefers this view to perform detailed tasks, such as dissection and picking up a thread.
As a member of the laparoscopic theatre team you need to know what equipment is needed and how to set it up and use it safely.
Important basic items of equipment for laparoscopic surgery include:
The insufflator supplies carbon dioxide (CO2) to create and maintain the pneumoperitoneum. It is recommended that the intra-abdominal pressure should not rise above 12-14mmHg, to avoid compression of the IVC, with resultant decreased cardiac return (see section on pathophysiology of carbon dioxide pneumoperitoneum below).
A powerful high-intensity light source is necessary to give a clear view of the abdominal cavity. A light source with 150-300W xenon or halogen lamp and automatic intensity control will give continuous optimal illumination. The appropriate liquid light or fibre optic light cable is also essential.
The camera may be single chip or three-chip. Single-chip cameras process the three primary colours, red, blue and green, while three-chip cameras have a chip for each of the three primary colours and therefore give a better definition, especially with red.
The camera head is an optical/electronic interface which is attached to the laparoscope. A standard eye-piece laparoscope requires a coupler to connect to the camera head. A video laparoscope has a camera attached directly to the lens system.
A standard laparoscope uses a rigid rod lens system to transmit the image from within the abdominal cavity. The operating field is illuminated by light conducted through a fibre-optic illumination bundle, alongside the lens system.
A high-resolution colour television monitor is necessary with at least an equal-line resolution to that of the camera. The monitor should be at least 13" in size, ideally 20", depending on the distance from the screen the surgeon is working. The ideal distance between the surgeon and the monitor should be four to five times the diagonal measurement of the screen.
A second monitor is preferable to give both surgeon and assistants a clear and comfortable view of the procedure.
Controls on the monitor allow adjustment of the image if necessary. However, fiddling with the controls should be discouraged.
A video cassette recorder and/or video printer may also be required for teaching purposes and documentation of procedures.
Suction and irrigation is usually necessary. This can be carried out by a suction unit and a pressure bag for the irrigation fluid. Alternatively, the surgeon may prefer to use a suction/irrigation pump. Some surgeons add heparin to the irrigation fluid to discourage blood clotting (e.g. 1,000 units of heparin to 500ml of Hartmann's solution).
The positioning of all equipment must be carefully planned. Exact placement will vary depending on the procedure to be performed, the surgeon's preference and the size of the theatre. However, some generalisations can be made.
The monitors should be positioned on either side of the patient to provide a clear unobstructed view for surgeon and assistant. Ideally, the screen should be positioned directly in the surgeon's line of sight (Figure 56).
Figure 56
The insufflator should be within view of the surgeon so that he or she can always monitor the abdominal pressure.
Instrument trolleys, diathermy, suction/irrigation, etc, should be positioned to allow the surgeon mobility and to give theatre staff access to equipment.
Leads and cables should be positioned so that when connected, they do not become tangled or restrict the surgeon's movements. Take care not to damage an expensive cable with a carelessly applied sharp towel clip!
Picture interference will also be minimised if the diathermy machine is positioned away from the camera/monitors and if the diathermy instrument is not close to the camera head when in use. The diathermy and video leads should also be kept apart.
Specialised storage trolleys with a single power cable leave fewer trailing wires as hazards for theatre staff. The diathermy power cable should be connected into a different socket and preferably a different electrical circuit from the imaging equipment, to reduce picture interference. Do not fix more than one diathermy cable. Remember that all attached electrodes become active when the foot switch is pressed.
Positioning of the patient is dependent on the procedure and the access needed to perform the operation. The patient may need to be in a modified Lloyd-Davis position, e.g. for laparoscopic Nissen's fundoplication, laparoscopic colectomy and laparoscopic gynaecological procedures.
During laparoscopic cholecystectomy a cholangiogram may be needed. Check to ensure the patient is on an x-ray lucent table.
For some procedures, e.g. laparoscopic hernia repair, the surgeon may not want the patient's arms on the chest (for venous access for the anaesthetist) as this may restrict the camera position.
Always make sure that the patient is properly secured to the table. A steep tilt may be needed in some advanced procedures.
For surgery in the pelvis it is sensible to drain the bladder with a urinary catheter. For upper abdominal surgery a nasogastric tube may be inserted to empty the stomach to make space and prevent accidental visceral perforation. Both can usually be removed at the end of the procedure.
The patient is placed supine or in a modified lithotomy position. A diathermy pad is attached to the thigh and the diathermy machine settings checked. The patient is then draped widely to expose the entire abdominal wall, which has been prepared with antiseptic solution.
At this point the surgeon should check the following:
Penetrating the intact abdominal wall to induce the pneumoperitoneum and insert the first port is probably the most hazardous part of a routine laparoscopic operation. If this is not done with care and skill there is a danger of injury to underlying viscera such as bowel and bladder. Even deeper structures like the aorta, iliac vessels and vena cava have been speared by the inept and unwary. Once the first port is in place and the pneumoperitoneum has been induced, the surgeon can insert a laparoscope and work with the abdominal contents safely in view.
There are two main methods, the open and the closed methods. Each has its fervent advocates who say they only use one method. The open method is safest and is increasingly being accepted as best practice. Many surgeons prefer to have both methods available for use when appropriate.
(See Figure 57) Open laparoscopy is favoured for all cases by many surgeons who prefer not to insert a sharp instrument where they cannot see. Open access is recommended to all surgeons where there are scars in the abdominal wall close to the site of insertion of the laparoscope.
A 1-2cm intraumbilical incision is deepened down to the linea alba which is incised between stay sutures. The peritoneum is exposed and an incision made into it under vision. A finger may then be inserted to sweep away adhesions. A blunt-tipped trocar is then inserted which will not penetrate structures attached to nearby scars. A supraumbilical incision may be preferable for the obese patient.
Alternatively, the laparoscope and port can be introduced together so that insertion can be controlled endoscopically. A disposable port and cutter instrument for insertion under visual control is available.
Insufflation through the port begins once it is safely in the peritoneal cavity. A purse string suture around the port may help minimise gas leakage.
The open insertion method is very safe but there is a possibility of increased gas leakage around instruments passed through the incision. Proprietary trocars with occlusive balloons to make a seal round the instrument may help.
Figure 57
This technique is not as safe as the open method and therefore is not encouraged. However, many laparoscopic surgeons still use this technique and the safety issues regarding its use are covered in this course.
Usually an intraumbilical incision is used but for the very obese, for some advanced upper abdominal procedures and where there are pre-existing abdominal wall scars, other access points may be used, such as the left hypochondrium. For simplicity, only the umbilical approach will be detailed here.
The Verres needle is a hollow needle with a spring loaded blunt central core. At the proximal end is a Luer port closed by a tap.
The tap and spring mechanism of the Verres needle should be checked and its patency tested by attaching it to the insufflator and running gas through at 1 litre per minute.
Prior to making an incision an orogastric tube is usually placed to 'decompress' the stomach and a urinary catheter passed (or ensure that the patient has voided urine immediately prior to theatre), so that neither the stomach nor the bladder can be damaged by the Verres needle.
Usually a vertical or transverse incision is made deep inside the inferior aspect of the umbilicus. It overlies the area where skin, deep fascia and parietal peritoneum meet at the thinnest point in the abdominal wall. In this position, the needle has the least chance of tenting the peritoneum and leaving its tip in the space between the posterior rectus sheath and the peritoneum. Gas accidentally insufflated more superficially will cause surgical emphysema of the anterior abdominal wall.
This is a common error for the novice, but merely a nuisance, as opposed to the more dangerous error of too forceful an insertion.
The patient is placed in a Trendelenberg position of 20-30°. The anterior abdominal wall is lifted up by the surgeon and assistant on either side of the umbilicus to create negative pressure within the abdominal cavity.
A Verres needle is then inserted, initially perpendicular to the abdominal wall, and advanced until it penetrates the linea alba and peritoneum. When it does this, there is usually a distinct 'give' as the point enters the cavity. It is now that damage to underlying structures can occur. The needle is advanced under careful control, held in the sensitive pinch grip between forefinger and thumb, like a pen or a dart, to feel the way through the layers.
The sacral promontory with its overlying great vessels rises remarkably closely beneath the umbilicus, especially in a thin patient. As soon as the needle is through the abdominal wall, it is then aimed towards the pelvic cavity. The central spring-loaded core of the Verres needle should advance when the sharp tip of the needle is lying free within the peritoneal cavity (but do not rely on it). The needle is inserted with the tap open so that the negative intra-abdominal pressure caused by lifting the abdominal wall allows some air to enter so that the abdominal contents fall away from the point of puncture.
Once through the peritoneum the needle should move freely from side to side. There are a number of tests to confirm that the tip of the needle is free in the peritoneal cavity.
A drop of saline dropped into the open Luer fitting of the Verres needle should fall from sight.
A small amount of normal saline is injected into the needle. It should flow in without difficulty. Drawing back should draw air or clear fluid into the syringe and not bile, blood or bowel contents.
Slow insufflation at 1 litre per minute produces little rise in the pressure reading if the needle is in the right place.
Occasionally the Verres needle is blocked by a plug of fat. This can sometimes be freed by gently rotating and moving the tip from side to side.
Insufflation can begin once it is certain that the needle is correctly placed. The controls of the insufflator are turned to automatic to deliver a faster flow of gas. The pressure reading is constantly monitored.
The abdominal wall should be percussed at intervals to check for the characteristic uniform tympanic sound as the abdominal cavity fills with gas. If insufflation of the rectus sheath occurs this can be detected by a rise in inflation pressure, asymmetrical distension of the abdominal wall and unevenness of the sound when percussed.
Once liver dullness is lost, the head down angle of the operating table is levelled. As long as there is no appreciable rise in pressure (certainly not above about 14cm of water), insufflation continues until 3.5 to 4 litres of gas have entered and there is visible distension of the abdomen.
If the abdominal cavity is well distended, the peritoneal contents should fall away from the abdominal wall. However, insertion of the first port in the closed method remains one of the most dangerous procedures in laparoscopy.
Pressure on the upper abdomen will move gas into the space below the umbilicus. Lifting the abdominal wall is not usually necessary at this stage and may cause unpleasant bruising.
The port is inserted with great circumspection. The body of the device is held in the palm while an index finger extended along the insertion tube will act as a guard to prevent more than a centimetre or so of the sharp end entering the peritoneal cavity.
Disposable trocars are equipped with ingenious guarding devices which slide forward to cover the point when it penetrates the peritoneum. Unfortunately, time lapse photography has confirmed that damage to intra-abdominal structures can occur before the shield has had time to advance and such devices should not induce a false sense of security.
Once in place the trocar is angled almost horizontally and pushed towards the pelvic cavity with due regard to the great vessels coursing over the sacral promontory. This is particularly crucial if the patient has a significant lumbar lordosis. The laparoscope can then be inserted.
Watch the video screen as the laparoscope is inserted. Sometimes there is a film of peritoneum or an omental adhesion which has to be carefully negotiated by moving the end of the instrument in order to enter the peritoneal cavity.
All other ports are introduced under direct vision.
View the video clip on port siting
The insufflator should be set to a pre-set pressure of 12-14mmHg. The machine detects a fall in pressure and responds by insufflating more gas. If pressure exceeds a pre-set limit an alarm sounds.
The attraction of carbon dioxide as a gas for insufflation is its solubility. This speeds its elimination but increases its physiological effects. When CO2 production exceeds its elimination, acid base and respiratory homeostasis is disturbed.
CO2 absorbed as the result of insufflation is stored until eliminated by the lungs. The total CO2 storage capacity of the human body is approximately 120 litres. Bone is the largest potential long-term reservoir. When CO2 retention occurs for less than an hour or so skeletal muscle and visceral stores are more important.
CO2 pneumoperitoneum can cause adverse cardiovascular, respiratory and metabolic changes. In all patients, there is a 25-30% drop in the cardiac return in the first 20 minutes of a laparoscopic procedure, but most healthy patients demonstrate no ill effects.
There is, however, a risk to patients with reduced cardiopulmonary reserve. CO2, accumulation in these patients results in decreased stroke volume and accelerated heart rate which stresses the myocardium. Ventilation-perfusion shunts occur so that increases in arterial PaCO2 may not be matched by changes in the CO2 measured in the expired gases. Patients with significant respiratory or cardiovascular disease must therefore have their arterial gases monitored.
Insufflation of gas into the peritoneum has a number of effects related to the volume of gas used. Partial obstruction of the inferior vena cava and splinting of the diaphragm become important when the procedure lasts longer than 20 to 30 minutes. Venous pooling in the legs may predispose to deep venous thrombosis. Diaphragmatic splinting may compromise ventilation, especially when there is pre-existing lung disease.
Cardiac dysrhythmias may occur during insufflation. Sinus bradycardia is most common and can be corrected by temporarily releasing the pneumoperitoneum and administering intravenous atropine. Other dysrhythmias are usually secondary to reduced venous return and cardiac output with underperfusion of the myocardium.
The anaesthetist must have adequate intravenous access throughout a laparoscopic procedure and effective monitoring, including central venous pressure measurement if necessary, is mandatory.
Gas insufflated at room temperature does not cause significant hypothermia. However, gas leakage allows water vapour to escape and there may be heat loss as latent heat of vaporisation. (It is as if a wind were blowing over the exposed abdominal contents.) If the procedure is prolonged, the core temperature should be monitored and hypothermia corrected.
Long needles and trocars are available for use in the very obese but they should never be used by mistake in patients of normal stature because of the increased risk to deep structures.
Inserting the Verres needle in thin people may also be problematic. Not only are the great vessels close to the surface, but tactile recognition of the layers of the abdominal wall may be impaired.
The first port must be large enough to allow the laparoscope to pass and a 10mm port is usually selected.
The first and vital step is to identify any structure that could be harmed during the procedure. No two abdominal cavities are identical and significant variations are quite common.
The number and sites of additional instrumentation ports depend upon the operation to be performed. Their diameter depends on the size of the instruments to be passed through. The port trocars are inserted through skin incisions which may be prepared with an injection of bupivacaine.
The course of the epigastric vessels should be avoided. When the ports are in place they are secured by a threaded securing collar or by a suture. When instruments are removed the ports are closed by a gas-tight trumpet or flap valve. The entry of the point is viewed with the laparoscope so that damage to intra-abdominal structures cannot occur.
If a large vessel in the abdominal wall (for example an inferior epigastric vessel) is punctured by a trocar, the bleeding can sometimes be very dramatic. Do not panic. Wait a while because the bleeding sometimes stops spontaneously. If it does not, DO NOT REMOVE THE TROCAR because it marks the track of insertion along which the bleeding vessel is located. A strong suture on a straight needle should be passed directly alongside the trocar and retrieved in the abdomen with a needle holder. It is then passed out through the abdominal wall on the other side of the trocar. The procedure is repeated forming a Z-stitch embracing the track of the trocar. The trocar is removed and the knot tied to achieve haemostasis. Unfortunately, an untidy scar results.
Alternatively, a Foley catheter can sometimes be inserted through the port and the inflated balloon used to tamponade the bleeding. If in doubt, convert to an open procedure.
All ports should be removed under direct laparoscopic vision to be sure that there is no bleeding from port holes. The last port should be removed slowly with the laparoscope inside the port to be sure that there is no bleeding.
The 10mm port holes must be closed with care to avoid later hernias. Most surgeons advocate formal closure of deep layers with interrupted synthetic absorbable or non-absorbable suture (usually using a J-needle) with separate skin closure. Take care not to pick up small bowel in the closing stitch. The 5mm port holes do not require closure of the abdominal wall and simply need skin closure.
The expanding range of laparoscopic procedures creates a demand for novel instruments. However, a number of basic instruments are common to all therapeutic laparoscopic procedures.
A basic instrument set might consist of:
1 x 10mm 0° laparoscope.
2 x Verres needles (120mm and 150mm).
2 x 10mm trocar and cannula with trumpet valve and gas inlet.
2 x 5mm trocar and cannula with trumpet valve and gas inlet.
1 x 5mm insulated grasping forceps.
1 x 5mm insulated grasping forceps with ratchet.
1 x 5mm insulated dissecting forceps.
1 x 5mm insulated scissors.
1 x 5mm reducing sleeve.
1 x 10mm clip applicator.
1 x 5mm right angled diathermy hook.
1 x 5mm suction/irrigator.
1 x 10mm retrieval forceps.
1 x light cable.
1 x diathermy lead.
1 x gas lead.
1 x cholangiography catheter.
Note: Try to ensure that all diathermy instruments are compatible with a single diathermy electrode fitting. Have bipolar forceps available.
Grasping/dissecting forceps and scissors may or may not be insulated and/or rotating. Insulated instruments have the advantage that they do not reflect light.
These instruments are also needed for the open method of inducing pneumoperitoneum.
Always have available, if not ready, the instruments necessary if the case proceeds to open surgery.
10mm 30° laparoscope - for hernias and advanced procedures.
5mm 0° laparoscope - for use with a 5mm port.
2 x 5mm needleholders.
1 x 10mm retractor.
5mm and 10mm Babcocks. (Beware! Some of these are very traumatic.)
5mm and 10mm bowel clamps.
Biopsy forceps.
Bipolar forceps.
Endoscopic stapling instruments.
Endoscopic retrieval bags.
Endoloops.
Desjardins stone grasping forceps.
The number of instruments and sets you will have depends on the level of service, the type of procedures being performed and financial constraints.
It is important for theatre staff to have a good knowledge of the instruments available within their unit. They are then able to offer assistance or guidance, especially if the unexpected occurs or the surgeon is inexperienced. For example, if the cystic duct is too wide to clip safely, an endoscopic stapling gun or endoloop might be a suitable alternative, thus avoiding conversion to an open procedure.
Selecting and purchasing instruments for minimal access surgery is complex as more than one department/specialty is involved. There are a number of manufacturers supplying instruments, each of which may have different preparation, sterilisation, assembly and disassembly, cleaning, and maintenance requirements. It is therefore obviously easier for theatre staff and a better use of resources if some standardisation can be agreed and maintained.
Selection of instruments will also depend on unit policy with regard to disposable equipment and the surgeon's preference.
It is tempting to reuse a disposable instrument but it is impossible to guarantee adequate cleaning and instrument function after re-sterilisation. Reuse must be avoided. Manufacturers will not accept product liability if a disposable product is reused.
The actual cost of disposable instruments, with their saving in time and safety benefits to patients and staff, should be compared with the actual costs of maintaining reusable instruments in optimum working condition.
There are many such exercises that you may be required to perform, such as passing matchsticks through loops or stacking sweets one on top of another.
Surgeons have employed electrical current to cut and coagulate tissue for over 70 years although few have had any formal training in its use. Many of the accidents that occurred in therapeutic laparoscopy arose when surgical diathermy was used. This has drawn attention to the need for better understanding of this useful, but potentially hazardous, surgical tool. Most accidents are caused by unintended burns which are avoidable if diathermy is used with care.
When an electrical current passes through a conductor some of its energy appears as heat. For any given conductor, the heat generated depends upon its resistance and the density of current flow. This is the principle of the light bulb and the electric fire. When a lot of current passes through, a lot of heat is produced. The same applies to human tissue. When a large amount of electrical current passes through a piece of tissue, the temperature rise can be enough to give a useful surgical effect.
In monopolar diathermy, the surgeon uses an active electrode with a small surface area tip to concentrate a powerful current producing heat at the operative site (the power density is high). The large return electrode plate which completes the circuit spreads the current over a wide area so that it is less concentrated and it produces little heat (the power density is low).
In bipolar diathermy, the heating occurs in tissue held between two small active electrodes.
Figure 58
An alternating current of low frequency stimulates nerves and muscles and it is this stimulation which kills someone connected to the mains current. This effect, which is named after Michael Faraday (Faradism), does not occur when the frequency is very high. A low frequency current as small as 1 mA can stimulate the heart fatally, but the radio frequency (RF) currents as high as 2A used in surgical diathermy pass through the body without dangerous neuromuscular effects. These currents have a frequency which is up to a million times that of the mains current which alternates at 50Hz (50 oscillations/sec).
High frequency alternating currents have some surprising properties which have safety implications in laparoscopic diathermy.
View the video clip 'diathermy 1'
Surgical diathermy is used for cutting and coagulation.
Cutting occurs when sufficient heat is applied to tissue to cause cell water to explode into steam. As we have seen, to get a high temperature we need to pack a high current into the tissue.
For coagulation, a less violent heating effect leads to cell death by dehydration and protein denaturation. The dead tissue is shrunken and dried - distortion of walls of blood vessels, coagulation of plasma proteins and stimulation of the clotting mechanism all act to check bleeding. Ideally, intracellular temperatures do not reach boiling point so there should be no unwanted cutting.
You will find that monopolar diathermy is most effective when you hold the active electrode a small distance from the tissue. The electrical discharge arcs across the tiny air gap creating a series of sparks which produce the high temperatures needed for cutting. The CUT current is a continuous wave form. If you set the machine to CUT and gradually reduce the power setting, you will come to a level when the effective voltage is no longer enough to drive sparks across the gap and no current will flow. If you now touch the electrode onto the tissue, current will flow again because it does not have to jump across a gap. There will be no sparks and the current will flow away into the adjacent tissue. The heating effect is relatively gentle with loss of intracellular water and coagulation with tissue necrosis in depth. This effect is called desiccation and gives reasonable coagulation. Desiccation is more commonly achieved by using COAG current in contact mode.
In contact diathermy, the main impedance (resistance) to current flow is at the interface between the electrode and tissue, where it is influenced by the type of tissue and its state of hydration. The impedance of fat is high compared to muscle and contact diathermy works badly on adipose tissue. As diathermy proceeds, the tissue in contact with the electrode dries and impedance rises. Eventually, the current flow is insufficient to produce further heating and the surgical effect ceases. This limits the depth of penetration of diathermy applied to one spot. The effect of contact diathermy also depends upon the size and shape of the active electrode. A ball electrode with a large surface area held in contact with tissue will tend to apply current at a relatively low density, coagulating to a depth of tissue which is proportional to the square of the diameter of the ball. Contact cutting by point diathermy is mainly by physical disruption of tissue softened by coagulation and is usually less effective than non-contact cutting.
If you set the diathermy machine to COAG or press the COAG pedal you can fulgurate tissue. In fulguration, you use a higher effective voltage to make longer, fatter sparks jump an air gap - the word means 'to flash like lightning'. The COAG current has an interrupted (modulated) wave form with the current chopped into bursts.
Because the current is turned off most of the time, COAG current can have large peak voltages and currents and yet apply less electrical energy over a given time than a CUT current of equivalent amplitude. A less explosive, more sustained heating effect leads to coagulation and haemostasis. The high peak voltage can drive current through the high resistance (impedance) of desiccated tissue. Thus fulguration can continue until carbonisation or charring occur.
View the video clip 'diathermy 2'
The CUT current is typically a continuous wave, producing sparks whose heat explodes intracellular water to steam. The COAG current is a sine wave current supplied in bursts to fulgurate tissue. This allows the sustained heating in depth needed for coagulation. Peak voltage and mean power output can be varied by adjusting the duration of bursts of current and their intensity to give a combination of cutting and coagulation. This is known as 'blended' current.
Be wary. Surgical diathermy generators differ widely and there is often little relationship between the output settings of one machine and another. In particular, there may be a significant difference between the power displayed and the power in watts which is actually delivered to the patient. The setting recommended by the manufacturer for a particular application is frequently on a scale which is meaningless to the surgeon.
One of the peculiar properties of alternating currents is that they can apparently pass through insulating material. This effect occurs in an electrical device called a capacitor in which an insulator is sandwiched between two electrode plates. When the alternating current is switched on, it seems to flow from one electrode plate to another.
In laparoscopic surgery, it is potentially possible to construct a capacitor without knowing it. The insulated electrode passes through a metal tube, say a laparoscopic port - the core of the electrode acts as one plate, the metal tube as the other with an insulator between - which results in a capacitor (Figure 59). In these circumstances, even though the instrument is well insulated, a part of the current can flow to the patient. This capacitative coupling is an interesting and remarkable result of the high frequency alternating current which induces an alternating magnetic field, which itself induces electrical currents in nearby conducting objects. This is how diathermy flowing through an active electrode (hook, graspers) can induce a current in its metal cannula despite insulation. This is termed electro-magnetic induction.
Figure 59
The current flow is relatively small, but if there is a small point of contact then dangerous overheating can be produced which could damage adjacent tissues (Figure 59). The current flows from the metal sheath directly to the bowel. It is greater in open circuit activation and in 5mm cannulae compared to 10mm cannulae. There remains some doubt about the frequency with which injury has occurred as a result of capacitative coupling during laparoscopic surgery. Most accidents probably happen through causes which are easier to understand such as inept handling or poor maintenance of diathermy equipment.
Diathermy machines are manufactured to national and international safety standards which minimise the risk of any part of the machine becoming 'live' with mains current. As with any electrical device, servicing must be regular and expert.
Alcohol-based skin preparations can catch fire if they are allowed to pool on or under the patient. This is less likely in endoscopic work but you must still take care that all excess spirit is removed before using diathermy. Better still, avoid flammable chemicals if you can. Do not use diathermy with explosive gases, including those which may occur naturally in the colon.
Although the high frequency current used for surgical diathermy does not cause neuromuscular stimulation, the sparks which it induces may invoke secondary currents which can do so. The sparks make random electrical 'noise' in the midst of which are alternating frequencies able to induce a Faradic effect. Such currents can be electronically suppressed by capacitors in the circuit. However, they may be sufficient to cause trouble in the special conditions of diathermy in the region of nerves or large masses of skeletal muscle which can be induced to contract strongly and unexpectedly. The problem is especially seen in urological surgery where diathermy near the ureteric orifice can induce an 'obturator kick' by stimulation of the obturator nerve and the psoas muscle. The problem is seen with both CUT and COAG current and can usually be abolished by full chemical neuromuscular blockade.
Diathermy currents can interfere with the working of pacemakers with possible danger to the patient. Modem pacemakers are designed to be inhibited by high frequency interference so that the patient may receive no pacing stimulation at all while the diathermy is in use. Some demand pacemakers revert to a fixed rate of pacing and the anaesthetist must have a magnet available so that they can be reset if necessary.
A number of additional precautions should be taken for these patients. First, if monopolar diathermy is to be used, the patient plate should be sited so that the current path does not pass through the heart or the pacemaker. Secondly, the heartbeat should be monitored throughout the operation. Lastly, a defibrillator should be on hand in case a dangerous dysrhythmia develops through malfunction of the pacemaker.
Bums are the most common type of diathermy accident in endoscopic and open surgery. They occur when current flows in some way other than that intended by the surgeon. Burns are much more common in monopolar than bipolar diathermy.
When monopolar diathermy works properly, heating occurs only at the tip of the active electrode. The current passes through the patient's body and escapes safely via the return electrode. Unfortunately this long current path offers opportunities for alternative unwanted passage of current to earth.
Most devices monitor the attachment of the patient plate and sound an alarm when contact is inadequate. A simple method is to attach the plate by two wires through which a small current flows. If a wire breaks, the current is interrupted and the diathermy can be automatically inactivated. This checks the integrity of the connection of the plate to the diathermy machine. It does not guarantee that the plate itself is properly attached to the patient. Another safety device uses a small direct current which in passing through the active electrode, the patient and the patient electrode, monitors the integrity of the whole diathermy circuit. Other machines have even more sophisticated safety measures. Remember that the safety of the return electrode depends upon its proper attachment. Both the surgeon and the theatre nurse have a duty to see that it is checked.
If the patient electrode is incorrectly attached, there is a particular danger that the circuit might be completed by a small earthed contact point such as a drip stand, a metal component of the operating table, electrodes used for patient monitoring or even the surgeon! If the current density at this point is sufficient, the patient (and/or the surgeon) will be burned. All patient monitoring equipment should be isolated from earth wherever this is possible. Electro-cardiograph electrodes should be well-gelled and of a large enough area to disperse the current. Needle electrodes should not be used. As a general rule, the return pad should be sited as near to the operation area as possible so that the main current path will be distant from other potential routes that the current might take to ground.
Safety Rule: always check that the return pad is properly connected, that safety monitors are active and that there are no small earthed contacts attached to the patient.
View the video clip 'diathermy 3'
View the video clip 'diathermy 4'
Inadvertent bums to the patient are a special hazard of laparoscopic surgery. There are several mechanisms:
Probably the most common cause is misidentification of the structure to which the diathermy is applied.
Pressure on the footswitch leads to activation of all the active electrodes which are connected. In open surgery, any devices which are not in use must not be in contact with the patient and an unused electrode should be safely stored in an insulated quiver where it will be safe if the footswitch is inadvertently activated. In laparoscopic surgery, devices connected to the diathermy generator often remain within the operating field while not in immediate use. If they are in contact with tissue when the footswitch is activated, a bum will occur. There is particular danger if the electrode is out of view at the time.
It is possible for burns to occur when conducting parts of instruments other than the operating electrode come into contact with the patient. In practice, this arises when there is a defect or crack in the insulation of a laparoscopic diathermy instrument which allows current to travel to tissue as well as by the intended path from the electrode.
Abrasives used to clean laparoscopic instruments may wear away the thin insulation near the tip increasing the length of the exposed active electrode.
Raising the temperature of the bowel to 60°C for even a short time leads to denaturation of intracellular enzymes and tissue death in situ. Subsequent autodigestion of the necrotic tissue leads to late perforation.
Instruments are more likely to become damaged with age but you must not assume that single-use instruments are immune to this problem. The higher the effective voltage of the current being used, the more likely it is to leak.
Leakage is also more likely if the diathermy is activated when the electrode tip is distant from target tissue (open circuit activation).
Contact or close approximation of the active electrode and another conducting instrument can establish an unwanted and unnoticed current path. This is known as direct coupling of the current. In an open operation such contacts are easily noticed and appropriate action taken. In laparoscopy, arcing between instruments may occur outside (behind) the field of view and you may not notice anything other than that the diathermy does not work as expected at the site where you think you are applying it. Turning up the power in these circumstances can have disastrous consequences. Remember that COAG and BLEND currents have a larger effective voltage and can jump bigger gaps. Open circuit activation is particularly dangerous.
Instrument to instrument coupling is more likely with open circuit activation.
When you have been using the diathermy for some time the tip of the active electrode becomes hot and remains so for some time. The electrode may be hot enough to damage tissue although no current is flowing.
The heating effect of diathermy depends upon the current density and the resistance of the tissue. The sight of penile necrosis on a small boy is so disturbing that most surgeons are aware of the danger of using monopolar diathermy to perform a circumcision. The current path through the base of the infant penis is small in cross-section, the current density is high and the heating effect disastrous. The same effect can also occur when applying diathermy to a pedicled structure such as the appendix or a gall bladder freed from the liver and attached to the common bile duct by the cystic duct. The heating effect may be sufficient to cause destruction of tissue and the effects may be just as awful as penile necrosis.
Safety rule: monopolar diathermy should not be used on organs attached by small pedicles to important structures.
Finally, there is the more difficult concept of capacitative coupling. This is probably very rare and only occurs in special circumstances.
There are two ways to avoid capacitative coupling.
When using a diathermy instrument through a trocar, either:
Also, avoid open circuit activation and avoid using high voltage diathermy currents in non-contact mode (e.g. fulguration).
Bipolar diathermy is intrinsically safer than monopolar diathermy because current passes between two small electrodes on the same hand-piece. Secondary currents induced by the main radio frequency may leak to ground but they are too small to cause trouble. Bipolar diathermy devices are being developed for laparoscopic surgery but their use is not yet widespread because they tend to be less effective at cutting.
View the video clip 'diathermy 5'