WHAT IS GENERAL ANESTHESIA?
The American Society of Anesthesiologists has specific criteria for the definition of general anesthesia. General anesthesia is the induction of a loss of unconsciousness by pharmacological means. In this state, the patient will be unarousable to verbal, tactile, and painful stimuli. Because of upper airway obstruction, some form of intervention, usually insertion of a laryngeal mask airway or endotracheal tube, is typically required to maintain airway patency. Spontaneous ventilation is frequently inadequate, necessitating the use of partial or full mechanical support with positive pressure ventilation. Cardiovascular function may be impaired, often leading to hypotension and dysrhythmias.
The primary goals of general anesthesia are to achieve:
In 1846, Dr. William Morton gave the first public demonstration of general anesthesia by ether. At the time, physical examination of the patient provided the only clues to the depth of anesthesia. Inexperienced anesthetists could easily overdose the patient. It was not until World War I that the anesthesia community had the first true systematic approach for monitoring. Dr. Arthur Guedel, better known for his widely used oropharyngeal airway, was responsible for this system. As the medical officer responsible for supervising anesthesia services for the U.S. Army, he was concerned about the safe administration of ether by the nonmedical personnel. Guedel created one of the first safety systems in anesthesiology with his chart that explained the signs of ether anesthesia with increasing depth. He published this classification system as an article in 1920 and later in a textbook in 1937.
The Guedel classification for the stages of general anesthesia is based on the administration of a sole volatile anesthetic: diethyl ether. Although patients were commonly premedicated with atropine and morphine, ether was the only induction agent available at the time. It provided amnesia, analgesia, and muscle relaxation. Ether has not been used in the United States since the early 1980s. Today, “balanced anesthesia” uses multiple classes of drugs (intravenous anesthetics, opioids, neuromuscular blocking agents, and benzodiazepines) for induction that can easily mask the classical clinical signs of each Guedel stage of anesthesia. These drugs also have a greater safety profile compared to diethyl ether. In addition, modern monitors of respiration, circulation, and consciousness add to the clinical information provided by physical examination of the patient. Some anesthesiologists, therefore, may consider Guedel’s work to be obsolete. Others still use his classification when it comes to describing emergence from anesthesia and inhalation inductions in children.
STAGES AND SIGNS OF GENERAL ANESTHESIA
The first stage of anesthesia, sometimes known as the induction stage, begins with the initial administration of anesthesia and ends with loss of consciousness. The patient experiences sedation, analgesia (but can still feel pain), and eventually amnesia. ...