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History Of Anesthesia, Nitrous Oxide, Chloroform, Emergence Of Anesthesiology, Types Of Anesthesia, Theory Of The Mechanism Of AnesthesiaEther

Anesthesia is the loss of feeling or sensation. It may be accomplished without the loss of consciousness, or with partial or total loss of consciousness.

Anesthesiology is a branch of medical science that relates to anesthesia and anesthetics. The anesthetist is a specialized physician in charge of supervising and administering anesthesia in the course of a surgical operation. Depending on the type of operation and procedures used, there are two types of anesthesia: general anesthesia, which causes a loss of consciousness, and local anesthesia, where the anesthetic "freezes" the nerves in the area covered by the operation. In local anesthesia, the patient may be conscious during the course of the operation or given a sedative, a drug that induces sleep.

The gas ether was discovered in 1540 and given its name in 1730. The gas was first successfully used by an American physician, Crawford W. Long, in an operation in 1842. The operation, however, was unrecorded, so official credit went instead to William Morton for his 1846 demonstration of an operation with the use of ether.

General anesthesia

There are three phases to general anesthesia. The anesthetist must first induce the state of unconsciousness (induction), keep the patient unconscious while the procedure is performed (maintenance), then allow the patient to emerge back into consciousness (emergence).

A drug commonly used to induce unconsciousness is thiopentone sodium. It is a barbiturate that produces unconsciousness within 30 seconds after being injected intravenously. Thiopentone does not reduce pain; it actually lowers the threshold of pain. It is used in the induction stage to bring about a quick state of unconsciousness before using other drugs to maintain the anesthetic condition during surgery.

Other agents used for the induction and maintenance of anesthesia are gases or volatile liquids such as nitrous oxide, halothane, enflurane, methoxyflurane and cyclopropane.

Nitrous oxide is still commonly used in dentistry, minor surgery, and major surgery when it is accompanied by other anesthetics. Though the gas has been used for many years, it is still uncertain how nitrous oxide accomplishes its anesthetic effect. Mixtures of oxygen and nitrous oxide appear to enhance its effect. Unlike other agents used today, it appears to have no toxic side effects on the body.

Halothane is a colorless liquid with a very low boiling point. Its use, though, may be connected to liver toxicity. Enflurane and methoxyflurane are also liquids that are useful as analgesics (pain relievers) and muscle relaxants, but they also may have undesirable side effects. Cyclopropane, which is an expensive and explosive gas used for rapid induction and quick recovery, has over the years been replaced with the use of halothane.

The anesthesiologist interviews the patient before the operation and examines his or her medical records to determine which of the many anesthetic agents available will be used. Cyclopropane or atropine may be given before the operation to relieve pain and anxiety. When a muscle relaxant is given for the surgical procedure, the anesthesiologist monitors the respiratory equipment to ensure the patient is breathing properly.

Administration of the anesthetic is usually accomplished by the insertion of a cannula (small tube) into a vein. Sometimes a gas anesthetic may be introduced through a mask. If a muscle relaxant is used, the patient may not be able to breathe on his own, and a breathing tube is passed into the windpipe (trachea). The tube then serves either to deliver the anesthetic gases or to ventilate (oxygenate) the lungs.

During the course of the surgery, the anesthesiologist maintains the level of anesthetic needed to keep up the patient's level of anesthesia to the necessary state of unawareness while monitoring vital functions, such as heart beat, breathing, and blood/gas exchange.

COMPLICATIONS OF GENERAL ANESTHESIA. There are a number of possible complications that can occur under general anesthesia. They include loss of blood pressure, irregular heart beat, heart attack, vomiting and then inhaling the vomit into the lungs, coma, and death. Although mishaps do occur, the chance of a serious complication is extremely low. Avoidance of complications depends on a recognition of the condition of the patient before the operation, the choice of the appropriate anesthetic procedure, and the nature of the surgery itself.

Local anesthesia

Local anesthetics block pain in regions of the body without affecting other functions of the body or overall consciousness. They are used for medical examinations, diagnoses, minor surgical and dental procedures, and for relieving symptoms of minor distress, such as itching, toothaches, and hemorrhoids. They can be taken as creams, ointments, sprays, gels, or liquid; or they can be given by injection and in eye drops.

Some local anesthetics are benzocaine, bupivacaine, cocaine, lidocaine, procaine, and tetracaine. Some act rapidly and have a short duration of effect, while others may have a slow action and a short duration. They act by blocking nerve impulses from the immediate area to the higher pain centers. Regional anesthetics allow for pain control along a wider area of the body by blocking the action of a large nerve (nerve block). Sprays can be used on the throat and related areas for a bronchoscopy, and gels can be used for the urethra to numb the area for a catherization or cystoscopy.

Spinal anesthesia is used for surgery of the abdomen, lower back and legs. Spinal or epidural anesthesia is also used for surgery on the prostate gland and hip. A fine needle is inserted between two vertebrae in the lumbar (lower part) of the spine and the anesthetic flows into the fluid surrounding the spinal cord. The nerves absorb the anesthetic as they emerge from the spinal fluid. The area anesthetized is controlled by the location of the injection and the amount of absorption of the anesthetic by the spinal fluid.

COMPLICATIONS OF LOCAL ANESTHESIA. It is possible to have adverse reactions to local anesthetics, such as dizziness, hypotension (low blood pressure), convulsions, and even death. These effects are rare but can occur if the dose is too high or if the drug has been absorbed too rapidly. A small percentage of patients (1-5%) may develop headaches with spinal anesthesia.

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