Endoscopic surgery

JULIAN BRITTON AND HUGH BARR

Introduction

Surgeons have always wanted to look inside the human body but rigid and primitive instruments, poor illumination, and inadequate anaesthesia originally confined such procedures to the natural orifices. General anaesthesia and, at the end of the nineteenth century, the introduction of electric light and glass telescopes first made cystoscopy feasible and later bronchoscopy and laparoscopy. An angled telescope allowed the surgeon to see around a corner but the continuous curves of the bowel remained a barrier to further progress in gastrointestinal endoscopy until the development of flexible glass fibres. Gynaecologists were the first to appreciate the advantages of laparoscopy. Parallel developments in instrumentation and illumination soon meant that some therapeutic procedures could be performed although there were limitations because the operator was the only one who could see what he was doing and one of his hands was occupied holding the endoscope itself. Nevertheless laparoscopic sterilization and transurethral resection of the prostate have been standard operations for many years.

 

Minimally invasive or endoscopic surgery for a much wider range of operations has become possible as a result of the development of miniature television cameras which can be attached to any suitable telescope. The cameras are unobtrusive, light in weight, and provide a perfect and magnified colour image of the operative field on a television monitor. The surgeon has both hands free to manipulate instruments and any number of assistants can watch what is being done on separate monitors and operate as well. New instruments have been developed to overcome the limitations on access and movement within the body cavities and new ways of performing old and well established operations have also been devised. In that respect this chapter will be out of date by the time it is published but even so the basic principles of endoscopic surgery are already well established.

 

THE BASIC TECHNIQUE

Creating a space in which to work

Some endoscopic operations, such as those on the nasal sinuses, take place within a natural cavity so that no special methods are needed to obtain a space in which to work. But for operations within the chest or the abdomen it is first necessary to create a pneumothorax or a pneumoperitoneum. The most convenient way to introduce gas is to use the spring loaded Veress needle inserted through a small stab incision in the skin (Fig. 1) 844. The needle has a sharp but flat bevelled point within which there is a blunt, hollow stylet through which gas flows from a distal side hole. As soon as the point of the needle penetrates the peritoneum or the pleura the stylet springs forward and pushes away the lung or the bowel thus lessening the risk of penetrating either structure.

 

The Veress needle can be introduced anywhere through the chest wall although the umbilicus is the most popular site in the abdomen. It is best to keep well away from any previous incisions as there are likely to be local adhesions. When creating a pneumoperitoneum it is wise, first, to be sure the bladder is empty and, after insertion, to test that the point of the needle is in the correct place. A hanging drop of saline in the hub of the Veress needle should fall easily into the peritoneum when the abdominal wall is lifted and once gas flow commences the intra-abdominal pressure should initially remain low whilst the gas flow rate should be high. Some surgeons prefer to introduce the first cannula under direct vision through a small skin incision and then to inflate the cavity. A gas-tight seal is obtained with a purse-string suture tied around the port. This is certainly a safe method if local adhesions are to be expected.

 

Carbon dioxide is the best gas to use; it is rapidly soluble should an embolism occur and it does not support combustion. The lung collapses spontaneously once gas is introduced into the pleural space and it is then only necessary to maintain a slight positive intrathoracic pressure. By contrast, maintenance of a pneumoperitoneum requires a constant intra-abdominal pressure of about 15 mmHg. Pressures in excess of this may lead to difficulties with ventilation whilst a fall in pressure will lead to a collapse of the pneumoperitoneum and the operative field will disappear from view. Modern high flow, electronically controlled, insufflators will maintain a preset intra-abdominal pressure and automatically correct minor leaks as well as the more substantial loss of gas that occurs every time an instrument is taken in or out of a port.

 

Artificial cavities can be created almost anywhere in the body by the forced insufflation of carbon dioxide into a natural tissue plane. The fibrous bands that cross these artificial spaces can be a nuisance and an alternative, in some circumstances, is to create the cavity by insufflating a balloon at an appropriate site within the tissues. The balloon is then removed but the cavity is maintained by the continued insufflation of carbon dioxide gas under pressure.

 

Obtaining a view of the operative field

The surgeon must be able to see what he is doing. Modern endoscopes are designed to carry light to illuminate the operative field and to pass the image back to the external television camera all within a single cylindrical metal tube (Fig. 2) 845. The endoscope and the necessary instruments gain access to the operation site through cylindrical cannulae, or ports, placed through the body wall (Fig. 3) 846. Where the cavity is only maintained by positive pressure, as in the abdomen, these ports must be provided with valves to retain the gas within the cavity.

 

The telescope, the light source, and the television camera are essential for endoscopic surgery and are just as sophisticated as the operations for which they are used. Modern equipment is reliable and reusable but breakdowns do occur and will require expert repair so that spare equipment should be available in any large theatre suite. Most of the instruments are made either as reusable items that can be repeatedly sterilized or as single use disposable items. A few instruments, particularly those used to staple tissue together, are only available as disposable items. From the practical point of view either type of instrument is perfectly satisfactory and the choice is dictated purely by preference and cost.

 

Siting the ports

The proposed operation and the shape and size of the individual patient dictate the precise placement of the cannulae. The basic layout is two working ports and one port for the telescope. In general it is best if these three ports are placed at the apices of an equilateral triangle with the operative field midway along one side of the triangle (Fig. 4) 847. Sometimes two sides have to be longer than the third but they should be equal and the endoscope should lie at the apex of the two long sides with the operative field midway along the short side. If this arrangement is followed then the tips of the working instruments will always lie at right angles across the field of view when they are being used. Additional ports, which are mostly used for retraction, should be placed outside the basic triangle.

 

The most common problem is for the operative field to lie further away from the endoscope than the midpoint between the two operating ports. If this happens the telescope and the instruments may touch each other which can make it impossible to work and to see what you are doing at the same time. Even if the endoscope and the instruments do not touch it may still be impossible to see the tips of the instruments as they are being used. This is inherently dangerous because the two-dimensional image makes the perception of depth very difficult. If scissors are being used it is a good rule that the manoeuvre should be abandoned unless the tips of the scissors can be clearly seen and it is absolutely certain that nothing unintended will be cut. An oblique viewing endoscope and instruments with curved blades can sometimes overcome both these difficulties.

 

Inserting the cannulae

Laparoscopic cannulae come in two standard sizes with an outside diameter of 5.5 mm and 11 mm (Fig. 3) 846. They are designed to take 5 mm and 10 mm instruments respectively. Larger and smaller sizes are made for special purposes and reducing sleeves allow the use of small instruments through the larger ports. Most cannulae incorporate a gas-tight valve. Disposable cannulae and the smaller reusable ports use ball or flap valves whilst sliding trumpet valves are fitted to the larger reusable cannulae. Each cannula is fitted with a trocar which should have a sharp hollow-ground pyramidal point. When the trocar is rotated the sharp edges and the pyramidal shape of the point force the tissues apart and also cut some of the fibres so that less force is required to gain entry into a cavity.

 

To insert a cannula the whole assembly is held in the palm of the hand with the index finger lying along the shaft to prevent excessive penetration (Fig. 5) 848. Each trocar and cannula is introduced through a small skin incision and then wound through the body wall with minimal pressure, thereby reducing the risk of a sudden uncontrolled entry into the cavity. Unless an open technique is used the first cannula is inserted blind and therefore carries the greatest risk of damage to underlying structures. Thereafter the entry of each subsequent cannula can be observed directly (Fig. 6) 849 although it is still wise to angle the trocar away from any important structures.

 

Obtaining illumination

An external cold light source with an output of at least 250 W is essential for endoscopic surgery (Fig. 7) 850. Light is conducted to the endoscope through a flexible fibreoptic cable and is automatically controlled by a feedback from the video camera so that more light is available as the field of view enlarges. Even so there are physical limits on the amount of light that can be delivered and losses should be reduced to a minimum. This means taking care not to break the glass fibres within the fibreoptic cable and removing blood, which absorbs light, from the operative field.

 

Acquiring an image

Endoscopes

The standard rigid endoscope is 10 mm in external diameter and contains the light cable and a glass rod-lens telescope (see Fig. 9 852). The illumination and the field of view, which is directly ahead from the tip of the telescope (0° forward viewing), are exactly matched. A wide-angle lens at the tip of the telescope is the most useful for general purposes.

 

There are many variations in this basic design and forward-oblique viewing angles (30 and 45°) are certainly helpful in certain circumstances (Fig. 8) 851. Endoscopes as fine as 0.7 mm in outside diameter are available for intravascular work and for some operations the inclusion of an operating channel alongside the endoscope is an advantage. Endoscopes must be kept clean and undamaged. The camera and the endoscope should be carefully dried before they are put together to eliminate condensation and warming the endoscope and antifog solutions applied to the distal lens will reduce misting.

 

Endoscopes with a flexible end are already made and in the future the video camera may be placed at the tip of the larger instruments. Even stereoscopic endoscopes are under development.

 

The television camera

The colour television camera is externally mounted directly on to the end of the endoscope without the use of a beam splitter (Fig. 9) 852. Any of the modern microchip cameras designed for endoscopic work are suitable although there are minor differences in colour reproduction and ease of use. All of them have a marker to indicate the orientation of the image and correct alignment of the camera and the endoscope is essential when a forward-oblique instrument is used. The cable from the camera leads back to a control box at the side of the operating table (Fig. 7) 850. The electronic image is then fed to two or more monitors but it can also be recorded or transmitted over any distance, even to the other side of the world. Immersion in glutaraldehyde is the usual method of sterilization although the camera and the cable end must be protected from water. An alternative is to place the unsterile camera inside a sterile plastic sheath. This avoids the use of glutaraldehyde and the risk of water damaging the camera or its cable.

 

Performing an operation