Lasers in the theatre

OVER the past four decades, the laser has evolved to become a precise and powerful weapon in the modern surgeon's armamentarium.

Let us look at the past. As early as 1917, Albert Einstein predicted that ordinary Light could be Amplified by the Stimulated Emission of Radiation, and hence the acronym LASER. However, Einstein died five years short of seeing his prediction come true. But he did witness the construction of the first MASER (Microwave Amplification by the Stimulated Emission of Radiation) in 1954, in the (erstwhile) USSR. It was in 1960 that Theodore Maiman successfully worked the first laser. This opened the doors for a series of lasers to be discovered.

There are several types of lasers, depending on the medium and the chemical constituents. Essentially, a laser beam is a monochromatic (single colour wavelength), parallel and coherent packet (or quantum) of rays, made up of a variety of molecules. The CO2 (carbon dioxide) laser is one such laser; it has very low penetration, and is useful for the removal of superficial lesions of the skin, like warts.

The ND:YAG laser (Neodymium, Ytrium - Aluminium Garnet) is probably the most useful and versatile laser in the fields of general surgery and gastroenterology because of its ability to coagulate (clot) bleeding points. Today, its applications have extended to dermatology, neurosurgery, gynaecology, ophtalmology, urology and vascular surgery.

The Argon laser is another, albeit less useful, tool in surgical procedures.

Effects of lasers: The main uses are related to their bio- physical properties.

Low energy lasers (power output less than 100mw and an energy density less than 50mw/sq cm) have biological effects which include activation of bio-chemical reactions and the stimulation of biological tissues. This stimulation is helpful in healing wounds and welding tissues, (including the joining of small vessels and nerves) in dentistry.

The biological effects of high energy lasers are even more dramatic. The ability to concentrate a very high intensity of rays at that focal point is of fundamental importance for therapeutic purposes. Most tissues have a high water content, and this leads to a very marked absorption of infrared radiation. This causes heating of tissues. For example, to study the ND:YAG laser's effect on tissues, its wavelength of 1,064 nm has an affinity for the red part of the colour spectrum. Hence, areas that bleed, attract and concentrate this laser, which then stanches the bleeding by a coagulation process that involves the denaturation of proteins.

Slow heating of a large volume of tissue around the point of impingement of radiation occurs, followed by deep, slowly progressive coagulation. The tissue volume covered by the laser light is heated, which results in delayed destruction of the tissue, with no noticeable structural damage. At the tissue surface, vaporisation occurs, leading to marked shrinking, although the surface itself is hardly damaged. This is the basis of the action of the laser on haemorrhoids (piles). Blood vessels are sealed by the combined effect of shrinkage and uniform coagulation of tissue.

Uses of lasers: These beams can be used directly on tissues or through endoscopes. For example, CO2 lasers are excellent for superficial warts as there is direct action. Haemorrhoids can be very efficiently dealt with by direct application. For application inside the gastro-intestinal tract, laser beams are delivered through the endoscopic channel, to attack, for example, bleeding lesions three or four feet away from the body surface, within the colon (large gut) or stomach.

Clinical applications of lasers: There are two areas of gastroenterology where lasers are extremely useful:

(a) Gastrointestinal (GI) bleeding: Bleeding from the GI tract is classified into upper GI bleeding, i.e. from the oesophagus, stomach and duodenum, or lower GI bleeding, i.e. from the colon, or the rectum. Upper GI bleeding, in turn, can be due to varices which are dilated veins in the gullet, found in portal hypertension, or due to ulcers that erode the lining of the stomach and penetrate into underlying blood vessels. "Non- variceal" or "ulcer" bleeders are in this group.

A frightening emergency of devastating proportions, GI bleeding causes death in minutes to hours if left unattended. Endoscopy is done as soon as possible, in order to differentiate between the variceal and non-variceal types. If bleeding is due to a spurting ulcer, then laser photo-coagulation, through an endoscope, can arrest it immediately. Other causes of bleeding could be due to an abnormal bunch of blood vessels in the stomach or the small intestine called Angiodysplasia which can also bleed profusely. These are imminently and best treated by laser photocoagulation through the working channel of the endoscope. Stomach tumours can also bleed, but can be controlled by laser treatment.

Bleeding from the rectum, (often seen in piles), can sometimes be profuse. There is good news for millions of sedentary Indians who are (literally) sitting on their piles. Piles (or haemorrhoids) are dilated veins on the walls of the terminal part of the gut, close to the anal verge, which are the most common causes of rectal bleeding. There are as many treatments for piles as there are physicians smiting the eyes, from pamphlets to cable TV. Probably, the best method of curing piles, especially early ones, is the application of the ND:YAG laser on to the pile mass, which is done as an out-patient procedure. It is painless and inexpensive. The treatment has revolutionised the management of this common and troublesome problem.

Another cause for lower GI bleeding, especially in the elderly, is angiodysplasia (described earlier) in the large intestine. These are first identified by doing an endoscopy (colonoscopy). Using a bare laser fibre (which can be passed through a working channel in the colonoscope) these bleeding lesions can be photocoagulated. This way, one can avoid undergoing major surgery, which not so long ago, would have been unavoidable.

(b): GI cancers: Another area where lasers have shown good results are in GI tract cancers - both in the upper and lower GI tract. Some cancers block the gastrointestinal lumen (passage) leading to dysphagia (the inability to swallow) when it is in the oesophagus, or constipation or obstruction to the passage of stools, when it is in the lower GI tract. These cancers grow within the lumen of the GI tract and gradually block the passage. Using the laser fibre through the endoscope, these extra growths of the tumour are burnt out thus creating a clear pathway for the food (if the cancer is in the food pipes or oesophagus) or stool (if the tumour had obstructed the lower most part of the gut or rectum). This permits us to palliate these often terminally ill patients and gives them the dignity of swallowing normally and pass stools through the natural passage. This is especially useful in patients who are not fit enough or are too old for surgery or in whom the cancer is too advanced and widespread to be considered for any other kind of radical or major surgery or treatment. In the upper GI tract, obstructing tumours of the stomach and oesophagus are the most common problems to be dealt with in this way, and in the lower GI tract, in obstructing tumours of the rectum and colon. Most patients have lasting relief, with one or two such sessions of laser treatment.

From the fertile imagination of an inspired mind rose an idea which has fructified into reality in the hands of the modern surgeon, allowing him to extend this range of complex procedures on the body, with a minimal amount of tissue damage.

Dr. J. S. RAJKUMAR

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