600 Volts: The Electric Eel at Artis Zoo
SURGEONS WORK WITH electricity on a daily basis. Depending on the voltage, conductivity and frequency, electricity can be harmless, useful, obstructive, dangerous or lethal. On 1 March 2013, an extraordinary operation was performed in Amsterdam that clearly showed the dangers of electricity. But, the operation was not performed by a surgeon and the operating room was not in a hospital. The location was Artis Zoo and the procedure was performed by Marno Wolters, a vet who operates on a wide variety of animals.
Surgeons, of course, restrict themselves to mammals, more specifically to one species of primate, but most operations performed on Homo sapiens can also be carried out on other animals and developments in surgery help advance veterinary medicine. Neutering and spaying operations are part of a vet’s daily work, but they also perform caesarean sections on dogs, stomach operations on cows and tummy tucks on pot-bellied pigs. They repair abdominal hernias on horses, fix fractured bones on cheetahs and perform dental corrections on hippopotami.
There are surgeons who operate on the tiny stomachs and bowels in mice in the context of their scientific research, but it would be especially interesting to perform, say, an oesophageal operation on a flamingo, angioplasty on the carotid arteries in a giraffe’s neck, a pulmonary operation on a turtle, an appendectomy on a koala bear (whose appendix is two metres long), or operate on a tiger’s thyroid gland, if that were possible. How about open-heart surgery on a whale (whose heart is big enough to stand in) or a nose correction on an elephant?
The operation at Artis Zoo was no less remarkable and, with this animal, it was dangerous too. Wolters performed his operation on an Electrophorus electricus, an electric eel. The animal, which had been swimming in the aquarium at the zoo for many years, had developed a swelling in its abdomen. Electric eels are fish around one and a half metres long that have the ability to generate electric shocks, making them more dangerous than a live electric socket under water.
There is nothing extraordinary about an animal that can generate electricity. Every cell in the body continually creates an electrical field between its interior and the outside world. The voltages generated in our own bodies are very weak, but are strong enough to be easily measured. We can measure the electrical impulse of the brain, for example, with electroencephalography (EEG) or of the heart with electrocardiography (ECG). Nerve cells use their electrical charge to transfer signals. Our brains are an enormous regulatory centre that runs on electricity. A lot of energy is required to generate and maintain all that electricity. About a fifth of all the oxygen we need goes to our brains to supply the necessary electrical power.
The organs that an electric eel uses to generate electricity are unique. Rather than producing their electrical charges individually, they generate it in series, so that the power of the charge is cumulative. This enables the eels to produce very high voltages. As they need large quantities of oxygen to generate all this electricity, much more than a fish can extract from the water through its gills, electric eels have to come to the surface regularly to inhale extra oxygen from the air.
An electric eel has three organs that generate electricity. All three are in its tail, which accounts for almost the whole length of the fish. The Sachs’ organ emits weak electrical impulses that the fish uses as a sort of radar to feel its way through its surroundings (its eyes are very small). It is used to locate prey, which can then be paralysed by an electrical charge from the Hunter’s organ. The third, ‘main’ organ is used when the fish is in danger. It can generate a charge of 600 volts, which can immobilise any animal in the vicinity, including humans.
The abdomen of the electric eel at Artis had been swollen for several weeks and was pushing its head upwards. An electric eel’s abdomen is normally small and hardly noticeable between the head and the enormous electrical tail. Initially, the vets at the zoo thought the fish was overeating or was constipated, but reducing its food intake and administering laxatives did not help. Antibiotics also had no effect, so it was probably not an infection. It looked as though the fish had cancer. Its suffering was clearly increasing rapidly and the vets decided to examine it and see if anything could be done. That meant removing the fish from its tank, taking an X-ray and conducting a biopsy – surgically removing a small piece of the swelling and examining it under a microscope. The electric eel would obviously see all this as a threat and would use its 600-volt charges against the keepers. That would exhaust it and it would need extra oxygen. All in all, it was a risky undertaking not only for the humans, but also for the fish itself. The operation therefore had to be carefully prepared.
It was not the first operation on an electric eel. Artis contacted vets in Chicago who had performed the same procedure in 2010. Preparations were made and summarised in a log. It was important to know that an electric eel only emits an electrical charge when it wants to, so never unconsciously. That meant that it would not emit charges if it was asleep – and that had two advantages. Once the fish was under anaesthesia, the operation could be performed without fear of electric shocks. Secondly, the depth of the sleep could be measured simply with a voltmeter in the water. The weaker the charge, the better the anaesthetic was working.
The operation was performed in the gallery behind the large hall of the zoo’s historical aquarium. Everyone wore special electrician’s gloves, the two keepers responsible for catching and moving the fish even wore rubber diving suits, and the operating table was made from a piece of PVC guttering, in which the fish could be laid for the X-ray and the biopsy. Using a net, the fish was transferred to a plastic tank full of water, through which extra air was pumped. The electric shocks were measured with a simple voltmeter, while the anaesthetic (Tricaine) was added to the water. Over the course of an hour, the intensity of the shocks diminished and the fish’s movements decreased.
Once it was fully asleep, it was lifted out of the water and placed in the gully-shaped operating table. The voltmeter showed no more electric charges. The fish’s mouth was continually rinsed with the Tricaine solution. The size of the swelling was now clearly visible and hard lumps could be felt in the swollen belly. An X-ray was taken and, wearing his rubber gloves, Wolters made a small incision in the skin above the tumour. An electric eel does not have scales, but skin similar to that of a real eel, which made Wolters’s job easier. He removed a small piece of tissue from the abdomen and stitched the wound up with absorbable thread. With fish, it is important to use a suture that does not dissolve too quickly. A wound will heal within two weeks in a warm-blooded animal but fish, which are cold-blooded, have a much slower metabolism. So a suture has to remain in place for six to eight weeks to ensure that the wound heals properly. After the small operation, the fish was placed in a tank of fresh water to come around. It soon started to move again and the first shocks immediately registered high voltages.
Around an hour later, however, there was clearly something wrong with the electric eel. The shocks were no longer regular and it became less active. Then, suddenly, it emitted a single high-voltage electrical discharge and stopped moving completely. The fish was dead. It was as though it had exhaled its final breath in the form of electricity. Had the anaesthesia and the operation been too stressful, or had the cancerous tumour proved too great a burden for it to endure?
Sutures
Sutures are performed using a special tool called a needle holder, in which the needle is tightly clamped. A right-handed surgeon holds the needle holder with the thumb and ring finger of his right hand. In his left hand, he holds tweezer-like forceps to lift the tissue and take the needle over from the needle holder. Suture needles are curved, so that the tissue is manipulated as little as possible during stitching. They are disposable needles to which the suture thread is already attached. The needle and thread come in double-layered sterilised packaging. The outer layer can be opened without touching the inner layer. The operating surgeon or his assistant can then take hold of the inner packaging without touching the outer layer. This ensures that no bacteria are passed on when the surgeon is handed the needle. There are sharp needles, blunt needles, cutting needles, and large and small needles. There are absorbable and non- absorbable suture threads, threads made of one piece and others that consist of several threads woven together. All of these combinations of different threads and needles are packaged separately and with threads of different thickness and strength. The strength of the thread is expressed with a number. Number 1 is quite thick, 2 is very thick, and so on up to 5. A 0 thread is finer, but most threads are even thinner. They are indicated by a series of zeros. Two-zero thread (00) is thinner than 0. Three zeros (000) is a normal thickness for a skin suture. Blood vessels are stitched using very thin six-zero thread while threads with 12 zeros – thinner than a human hair – are used in microsurgery.
Wolters conducted an autopsy on the cadaver. The tumour was gigantic and had spread to the liver and the spleen. Microscopic tests later showed that it was metastatic pancreatic cancer. That explained the rapid growth of the tumour. The fish’s prospects would have been very bleak, in any case. Perhaps, by dying after the anaesthesia, it had been spared a lot of suffering.
The electricity that Wolters and his team had to take into account was unpredictable. Surgeons (who operate on people) also have to be aware of the dangers of electricity in their daily work, but fortunately the amount of electricity in an operating room can be regulated and controlled. Electricity is present everywhere during an operation. The anaesthetist’s respiratory machine and the instruments that monitor the heartbeat, oxygen level and blood pressure run on electricity. The operating table needs electricity to move, the lights are of course electric, the equipment used for keyhole surgery depends on electricity, the mobile X-ray machines produce kilovolts of electrical charge, and there are computers in the operating room to record and retrieve medical data and video monitors to watch procedures and look at X-ray photographs – all of which are electrically driven. And there are also some operative methods that require electricity, much closer to the patient and the operating staff than you might expect in such a safe situation. For example, almost no operation can be performed in modern surgery without electrocoagulation. This is applied using a kind of electrical knife evolved from a combination of a scalpel and a branding iron. During electrocoagulation, the patient is literally ‘live’. And yet it is safe.
In the Stone Age, surgeons used stones. Abraham of Ur used a stone knife to perform circumcisions. The Greeks used scalpels of bronze, the Romans used iron and we use steel. In the past hundred years, thanks to technological developments, new types of knife have been devised. Piezoelectricity (well known from the sonar systems in submarines) is applied during operations in a special instrument that uses vibration to dissect and to stem bleeding. Not long after the power of radiation (nuclear power) had been harnessed, gamma rays were used in surgery with a tool known as a gamma knife. Shortly after the development of usable microwaves (e.g. for cooking), the technique was also introduced in surgery, and the same applies to lasers. But the most successful instrument of all remains the simple electric scalpel, which was introduced into surgery shortly after the widespread introduction of electricity into daily life (the electric light bulb).
Experiments with using electric filaments to stem surgical bleeding by cauterisation (known as electrocauterisation, from the Latin word cauterium, branding iron) were conducted as early as 1875. The filament was, however, much too hot and cauterised the surrounding tissues in a much wider area than was intended. It was slow and imprecise, not to mention dangerous.
French physicist Jacques-Arsène d’Arsonval went a step further. He knew that electricity mainly generated heat at the point of greatest resistance. The human body is large enough to conduct electricity without much resistance and it could also flow freely through the metal of the scalpel. The point of greatest resistance was therefore where the scalpel and the body came into contact, more specifically in the small zone of tissues around the tip of the electric knife, exactly where the heat was required for the surgical effect. Moreover, the heat was only generated when there was contact between the scalpel and the tissues.
D’Arsonval came up with the idea that the power of the electric current, which is harmful to the body, could be kept at a low level if the energy were transferred in the form of alternating rather than direct current. Alternating current (AC) is the kind of electricity that comes out of our wall sockets. It is in principle lethal, having a paralysing effect on the nerves, the heart and the muscles. But the French physicist discovered that the undesirable effects of the alternating current disappears if the frequency is sufficiently increased, to above 10,000 hertz.
An electric knife is connected to a generator with a wire. The generator then has to be connected to the patient with a second wire, to complete the electric circuit. The patient thus becomes part of the circuit. Today, that second wire is connected to the patient by means of a conductive disposable adhesive pad attached to the thigh, generally called the ‘patient plate’. A surgeon will therefore never start an operation until he has asked the operation team if ‘the plate has been attached’.
Heat stems the flow of blood by converting the proteins in the blood and in the surrounding tissues from liquid to solid, just as the white of an egg solidifies when it is boiled. This specific property of protein is known as coagulation. When you do this with electricity, it is called electrocoagulation. If the temperature is increased by applying even more heat to a small area of tissues, all the water in the cells will evaporate suddenly, causing them to explode before the proteins have had the chance to coagulate. The effect is not to stem the bleeding but to cut the tissues.
In the 1920s, American engineer William Bovie further elaborated on the principle of electrocoagulation. He developed a generator in which the level of energy in the tissues could be much better regulated. He achieved that by increasing the frequency of the alternating current to as high as 300,000 hertz. His generator supplied this current in pulses, in what is known as modulated alternating current. Moreover, he could regulate the voltage. A higher voltage was compensated for by reducing the number of pulses per minute, so that the total energy level did not rise too high. This enabled the effect of the heat applied to vary from coagulation to cutting, while the current remained within safe limits. This principle continues to be applied unchanged in surgery today and, in many countries, the electrosurgical device is still called ‘the Bovie’ after its inventor.
Bovie’s instrument was introduced into surgery by Harvey Cushing – the pioneer of neurosurgery – in Boston on 1 October 1926. Cushing focused on the one organ in the human body in which bleeding cannot be stemmed simply by applying pressure, stitching or tying off: the brain.
The brain and most tumours in the head are amply supplied with blood by small blood vessels. Consequently, removing brain tumours proved to be an extremely bloody operation. Cushing developed a number of precautionary measures to deal with that. He used small silver clips that he could attach to small blood vessels to stop them bleeding and which could be left behind in the tissues. Cushing also made a habit of removing brain tumours in sections. If he was forced to stop operating because of excessive loss of blood, he would continue the procedure some days or weeks later when the patient’s blood levels had recovered. This was known as the piecemeal method. With major operations, he would ask a volunteer to be present in the operating theatre to donate blood for the patient on the spot if necessary. Mostly, they would be medical students who would take the opportunity to observe the pioneering brain operations close up.
Cushing described the operation in which he used electrocoagulation for the first time in a medical journal, to publicise the importance of this new method of stemming bleeding. He was, however, by no means the first to apply the new technique. Several surgeons had preceded him, but Cushing’s application of electrocoagulation in neurosurgery was so successful and Cushing himself was so famous that the publication of the astounding results of that one operation in 1926 proved decisive in advancing the use of the method.
But first a serious problem had to be solved before electrocoagulation could be used more widely. Although the city of Boston was already using alternating current to light streets and houses, the Brigham Hospital, where Cushing worked, still ran on direct current. The operating room therefore had to be connected to alternating current especially for Cushing’s groundbreaking operation by running a wire up from the street.
On that day, Cushing used William Bovie’s generator to operate on a man with a malignant tumour of the skull, an extracranial sarcoma. He had been forced to suspend his operation on the man three days earlier because of excessive loss of blood. Cushing had not made any great effort to understand the physics behind the coagulation device, saying, ‘One may learn to pilot a motor driven vehicle without necessarily knowing the principles of the internal combustion engine.’ He had therefore asked Bovie to be present in the operating room in person. If Cushing needed to regulate the amount of current applied to stem the bleeding, Bovie could fiddle with the knobs to give him more or less voltage and more or fewer pulses. Cushing reopened the wound from the first operation and continued removing the tumour piece by piece. This time, rather than using scalpel and scissors, he used electrocoagulation. The smell of the smoke as he cauterised the tumour was so bad that spectators in the gallery became nauseous. The medical student waiting to give blood fainted and fell off his chair, but Cushing was immediately convinced: the method was astounding.
During the next operation, to remove a similar tumour from the skull of a twelve-year-old girl, Cushing was able, with Bovie’s assistance, to remove the tumour completely in one session. Both patients recovered well without complications and Cushing continued to use the Bovie device in all of his subsequent operations. It even enabled him to perform operations that he had previously never dared to undertake. ‘I am succeeding in doing things inside the head that I never thought it would be possible to do,’ he wrote to a colleague. Surgeons from a wide variety of disciplines all over the world started to follow his example.
At first, things would still sometimes go wrong. During one operation on the skull, a blue flame shot out of the patient’s opened frontal sinus. A spark from the electrocoagulation had ignited the flammable ether that the patient was inhaling as an anaesthetic and that had escaped through the surgical opening. After that, Cushing ensured that the anaesthetic was administered rectally rather than through inhalation. On another occasion, Cushing received a shock from a metal wound retractor that he inadvertently leaned on with his arm. That inspired him to use wooden instruments and a wooden operating table for a while, until Bovie found a better solution by adjusting the settings on his generator.
Today, a wide variety of measures are taken to protect patient and operating team from electric shocks. The team wear surgical rubber gloves and the patient, operating table and all electrical equipment are earthed. The whole operating room is a Faraday cage: there is a network of copper wires in the walls and doors to ensure that electrical charges from outside, such as a lightning strike or an overload on the power grid, cannot enter the room and disrupt the operation. Moreover, modern operation complexes are isolated from the outside world. In other words, not a single electrically conductive wire may lead to them directly: the electrical circuits used in the operating room are all supplied through transformers and the data in the computer network is transmitted through fibre-optic cables.
Bovie’s electrocoagulation device has hardly changed in almost a century. It has been refined and made safer, and the circumstances in which it is used have to comply with much stricter requirements than in the pioneering age of Cushing. However, although the whole concept of electrocoagulation can now be considered completely safe, the charge administered to patients is still not much different from that generated by an electric eel – several hundred volts.