NEW YORK, Mar 18 (Reuters Health) -- A team of researchers from the University of California-Irvine have come one step closer to understanding the precise effect that anesthesia has on the brain -- a discovery that could lead to the development of more effective forms of anesthesia with fewer side effects, the authors suggest.
Dr. Michael Alkire, an assistant clinical professor of anesthesiology, and his research team discovered that the anesthetic gas halothane targets the area of the brain that appears necessary for a person to remain conscious.
In conjunction with his previous research into the mechanism of anesthesia, the study "can help us fine-tune the anesthetics we use now and may help create new ones that work on targeted areas of the nervous system," Alkire said in a statement. "Just as important, the studies also help us begin to understand how wakefulness and memory are maintained by different parts of the brain."
Researchers examined the brains of five male volunteers with an imaging technique called positron emission tomography (PET) scanning while they were awake and after the anesthetic had taken effect. Subjects were given intravenous glucose that was tagged with a low-level radioactive tracer, during the scan. The absorption of the radioactive glucose in the brain was then measured.
The PET scan data showed that halothane reduced activity in the specific areas of the brain, including the thalmus and the mid-brain. The structures contained in the thalmus control sensory information such as hearing, touch, and vision by coordinating nervous system impulses from the rest of the body. The mid-brain is responsible for automatic functions such as breathing and heartbeat.
In their report, published in the journal Anesthesiology, the researchers suggest that halothane gas induces unconsciousness by reducing activity in the parts of the mid-brain that are responsible for sending wake-up signals to the thalmus -- an area of the brain that passes the signals along to the thinking centers in the cerebral cortex. When both the mid-brain and thalamus are unable to process sensory information from the body, a person becomes unconscious.
"Most all anesthetics depress cardiovascular and respiratory function to some extent," Alkire explained in an interview with Reuters Health. "A primary reason you have an anesthesiologist with you during surgery is to make sure you continue to breathe and have sufficient blood pressure during the anesthetic. This physiologic depression occurs because the anesthetics are not specific and they depress neuronal function throughout the central nervous system, including those parts of the brain responsible for breathing and blood pressure control. Thus, a targeted anesthetic (that) turned off consciousness without affecting the brain's breathing or blood pressure centers could be much safer."
"By knowing exactly how (anesthetics) work, we can begin to see what it takes for the brain to keep us awake," Alkire said. "We will be able to select an anesthetic based on the target brain structures we want to hit, reducing side effects and affecting brain functions in the best way for each kind of medical procedure."
SOURCE: Anesthesiology 1999;90.
