On Oct. 16, 1846, Boston dentist Dr. William T.G. Morton demonstrated the use of ether during surgery. Using a specially designed glass inhaler containing an ether-soaked sponge, he administered the anesthetic to Gilbert Abbott, a printer who needed treatment for a vascular tumor on his jaw. After several minutes, Abbott was rendered unconscious and the surgeon was able to surgically remove the tumor.
Upon wakening, Abbott informed the physicians and medical students in the theater that he had experienced no pain. The surgeon reportedly remarked, "Gentlemen, this is no humbug."
News of the discovery spread quickly and, within months, it was hailed as the "greatest gift ever made to suffering humanity."
The goal of general anesthesia is to rid the patient of pain and to awaken with a clear head and no side effects, such as nausea. That is now possible by inducing sedation with a wide variety of drugs in a controlled manner.
Brown and his co-authors -- Ralph Lydic, a sleep expert from the University of Michigan, and Dr. Nicholas Schiff, a coma expert from Weill Cornell Medical College in New York -- compared the physical signs and electroencephalogram (EEG) patterns of general anesthesia to those of sleep.
While it is common to describe general anesthesia as going to sleep, there actually are significant differences between the states, with only the deepest stages of sleep being similar to the lightest phases of anesthesia induced by some kinds of agents.
While natural sleep normally cycles through a predictable series of phases, general anesthesia involves the patient being taken to and maintained at the phase most appropriate for the procedure, and the phases of general anesthesia at which surgery is performed are most similar to states of coma.
"People have hesitated to compare general anesthesia to coma because the term sounds so harsh, but it really has to be that profound or how could you operate on someone?" Brown said.
"The key difference is this is a coma that is controlled by the anesthesiologist and from which patients will quickly and safely recover."
One of the most widely used drugs, Propofol -- the drug abused as a sleeping aid by pop singer Michael Jackson -- has been around since 1990. "It is extremely potent and very powerful," he said.
The drug "goes everywhere," Brown said, to the arousal centers in the brain stem, decreasing the levels of excitatory neurons; in the thalamus, the neural control center; in the cortex, the part of the brain that controls memory and consciousness; and then down the body to suppress action in the muscles and respiratory center.
"There are six areas of the brain where one drug is working," Brown said.
Only about 0.1 to 0.2 percent of all patients -- about 20,000 to 40,000 a year out of 21 million surgeries in the United States -- are aware of what's happening during the procedure, according to the Joint Commission, a regulatory committee that monitors safety at hospitals.
"Basically, there are three cases [where awareness happens]," Brown said. "A woman comes in for an emergency Caesarian section and you try not to give as much anesthesia to the mother so it doesn't go to the baby, because it crosses the placenta.
"And in a major trauma gunshot wound. You give as little of the drug as possible because the drug suppresses blood flow."