Use of Gases in Anesthesia

During the past 150 years, a number of gases have been adopted in anaesthesia practice.

There are three natural anaesthetics, sleeping, fainting, and death: Oliver Wendell Holmes (1809-94) US writer and physician.

"The role of anaesthesia will broaden as newer surgical techniques develop in the area of organ transplants" - Dr Dipankar das gupta Head of Department Anaesthesiology Jaslok Hospital

Anaesthesia is the loss of feeling or sensation. It may be accomplished without the loss of consciousness, or with partial or total loss of consciousness. While the search for pain control during surgery dates back to the ancient world, it was not until 1846 that it went on record that a patient was successfully rendered unconscious during a surgical procedure. Performed in a Boston hospital, the operation used a gas called ether to anaesthetise the patient while a neck tumor was removed. Developments in anaesthesia has made possible complex operations like open heart surgery and organ transplants. Medical tests that would otherwise be impossible to perform are routinely carried out with the use of anaesthesia. Before the landmark discovery of ether as an anaesthetic, patients who needed surgery for either illness or injury had to face the surgeon's knife with only the help of alcohol opium, or other narcotics. Often a group of men held the patient down during the operation in case the narcotic or alcohol wore off before it was over. Under these conditions, many patients died just from the pain of the operation. In one of the closing paragraphs of his great monograph describing his research, published in the summer of 1800, Davy left us this tantalising observation: As nitrous oxide in its extensive operation appears capable of destroying physical pain, it may probably be used with advantage during surgical operations in which no great effusion of blood takes place. Thus, the concept of surgical pain relief via gas inhalation appeared at the very beginning of the 19th Century.

The gases useful in practice are oxygen, carbon dioxide, nitrous oxide cycloproprane, helium, and compressed medical air. During the past 150 years, a number of gases have been adopted into anaesthesia practice, some of which have now disappeared from the clinical armamentarium as better agents appeared. Yet the oldest gas used for surgical pain relief, nitrous oxide, remains a frequently used agent in certain types of surgeries and dental procedures. Though discovery of nitrous oxide marked the advent of gas anaesthesia, it was use of oxygen, which helped us use this technique safely.

Eureka! Nitrous oxide

In 1776, Joseph Priestley, a British chemist, discovered the gas nitrous oxide. Another British chemist, Humphry Davy, proposed nitrous oxide as a means for pain-free surgery, but his views were dismissed by other physicians of the day. In the next century, Horace Wells, a Connecticut dentist, began to experiment with nitrous oxide, and in 1845, attempted to demonstrate its anaesthetic qualities to a public audience. However, the patient woke before the operation was over and began to scream in pain. Because of this spectacle, it took another 20 years before nitrous oxide again gained attention. By 1870, nitrous oxide was a commonplace dental anaesthetic as a gas which can be compressed into liquid, non-explosive, and non-inflammable form. It has low toxicity and a weak anaesthetic agent. It was used as the sole anaesthetic agent for dental or outpatient procedures. It can be used to maintain anaesthesia during major surgery in combination with other anaesthetic agents; but it is not used on its own to produce a deep level of anaesthesia. Usually, it is administered to the patient in the proportion of two-thirds nitrous oxide to one-third oxygen.

Nitrous oxide mixed in equal proportions with oxygen is used as an analgesic agent for dental surgery or maternity work. 'Entonox' is the British oxygen company name for this premixed combination.

Oxygen

In 1674, John Mayow of Oxford demonstrated the existence of oxygen when he showed that both fire and respiration could continue until one-fifth part of the air in an enclosed chamber has been used up. Joseph priestly in 1775 called it 'dephlogisticated air' and Frenchmen Antoine Lavoisier and Pierre Laplace gave the name oxygene. Present in the air at a concentration of approximately 21 per cent, oxygen cannot be ignited, but its presence will aid combustion. It is explosive whilst under pressure and when brought into contact with oil or grease. It should not be administered to patients in concentrations above 40 per cent.

Carbon dioxide

Another gas, carbon dioxide stimulates the respiration making it deeper, but not increasing the rate. Sometimes it is used when spontaneous respiration does not occur after an operation. It can also be used in low proportions to the total gas mixture being administered, as an aid to the smooth induction of anaesthetic agents (i.e. used with nitrous oxide and oxygen for a short period before using the anaesthetic agent, reduces the patients resistance to breathing in the agent). However, these techniques have been made obsolete by modern day drugs and monitoring.

Cyclopropane

Cyclopropane, a gaseous anaesthetic agent, was synthesised by August Von, Freund of Poland. In 1929, the anaesthetic properties of the gas were described by GWH Lucas and VE Henderson of Toranto in 1929. Waters, Sir Harold Griffith, Stanely Rowbotham popularised the use of the gas. The virtue of the gas was that its use from the cylinder did not require a pressure reducing valve. The major gain in using cyclopropane was that oxygen could be used simultaneously in a high percentage (90 per cent). The gas was on decline in 1960 and was abandoned for its explosive nature.

Xenon

Xenon is an interesting anaesthetic which gives great advantages to both patients with limited cardiovascular reserve and those who require hemodynamic stability. It has low toxicity and is not teratogenic. Xenon gives rapid induction and recovery. Its low blood solubility can take to diffusion hypoxia if xenon is not substituted by 100 per cent oxygen at the end of anaesthesia. It has been shown that, compared to other anaesthetic regimens, xenon anaesthesia produces the highest regional blood flow in the brain, liver, kidney and intestine. In conclusion, the most important positive effects of xenon are cardiovascular stability, cerebral protection and favorable pharmacokinetics. Negative points are high cost and the limited number of ventilators supplying xenon.

The Future

Since World War II, many changes have taken place in anaesthesiology. Important discoveries have been made with such volatile liquids as halothane and synthetic opiates. The technology of delivery systems has been greatly improved. But with all these changes, the basic goal of anaesthesia has been the same-the control of a motionless surgical field in the patient. In the next 50 years, it is possible that the goals of anaesthesia will be widened. The role of anaesthesia will broaden as newer surgical techniques develop in the area of organ transplants. Anaesthesia may also be used in the future to treat acute infectious illness, mental disorders, and different types of heart conditions. There may be a wide range of new therapeutic applications for anaesthesia.

Anaesthesiologists compete strongly for research funds. Better trained anaesthesiologists need to do research to gain further knowledge on the effects and mechanisms of anaesthesia. Since understanding and controlling pain is the central problem of anaesthesiology, it will be necessary to gain more knowledge about the mechanism of pain and pain control. New anaesthetics, delivery, and monitoring systems will need to be developed to keep up with the pace of medical development as it moves closer to noninvasive surgical techniques.

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