Awake?
EEG can be used to ensure that you are really in.
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the prospect of surgery while not fully "in" may seem like the stuff of horror movies. But a thousand patient remembers moments of awareness under general anesthesia, the doctor evaluate. Memories are sometimes neutral images or sounds of the operating room, but sometimes patients report being fully aware of the pain, terror and immobility. Although surgeons carefully monitor vital signs such as pulse and blood pressure, anesthesiologists have no clear signal as to whether the patient is conscious. But a new study finds that the brain can produce an early warning signal that consciousness returns-that is detectable by an electroencephalography (EEG), the recording of neuronal activity via electrodes on the skull.
"We have known since the 1930s that brain activity changes significantly with increasing doses of anesthetic," says corresponding author of the study, Patrick Purdon anesthesiologist at Massachusetts General Hospital in Boston. "But the monitoring of a patient's brain with EEG has never become common practice."
in the early 190s, some anesthesiologists began using an approach called (BIS) bispectral index, where the readings from a single electrode connected to a device that calculates and displays a unique number indicating where the patient's brain activity falls on a scale of 100 (fully conscious) to zero (a "flatline" GET ). While between 40 and 60 is considered the target range for unconsciousness. But this index and similar are only indirect measures, Purdon says. in 2011, a team led by Michael Avidan anesthesiologist at Washington University School of Medicine in St. Louis, Missouri, found that monitoring the BIS index was slightly less successful in preventing awareness during surgery of the measurement method exhaled anesthetic base nonbrain- in the patient's breath. Among the 2861 patients treated with BIS index, seven had memories of the surgery, while only two of 2852 patients were analyzed everything souvenir breath.
Despite this, Purdon and colleagues expressed hope that "unconsciousness signature" in the brain could be found. Last year, the team worked with three epilepsy patients who had electrodes implanted in their brains to surgery to reduce their seizures. Recording from single neurons in the cortex, where consciousness is thought to reside, the researchers gave patients an injection of propofol, an anesthetic. They asked volunteers to press a button every time they heard a voice, recording the activity of neurons. Loss of consciousness, defined as the time when patients stopped pressing, immediate was 40 seconds after injection. As immediately, neurons groups began to issue a slow oscillation characteristic, a kind of undulation in the electric field of the cells. Neurons are not completely inactive, but bursts of activity took place only at specific points in this oscillation, resulting in activity incompatible brain cells.
The next step was to see if the same signature can be detected on the outside, with an EEG. Purdon and his team recruited 10 healthy volunteers "go under" very slowly with propofol: Anesthesia was delivered gradually as the drop-off process was not 40 seconds, but nearly an hour. Every 4 seconds, the volunteers pressed a button in response to clicks or words, including their names, until they reached unconsciousness.
At that time, the researchers report today in Proceedings of the National Academy of Sciences , EEG readings showed a similar activity to that seen in study of patients with epilepsy. Alpha waves, associated with relaxation and drowsiness, increased loss of consciousness, as did the even slower, "low frequency waves." Both business models began to decline with the return of consciousness.
The researchers also found a unique pattern of the transition period. During the transition in and out of unconsciousness, waves almost canceling: The highest point or "peak" of alpha waves are produced at "trough" of low frequency waves. This combination, called the model "trough-max" can be read on an EEG and can be the early warning signal that the patient returns to consciousness. When the patient is deeply unconscious, motive "peak-max" in which the strengths of the two types of waves occur together, can prove to be a reliable sign that the patient is out.
" There is a rigorous, elegant study, "says Avidan." the trough max model may well prove to be an early warning signal. "he cautions, however, that the volunteers were healthy and did not undergo actual surgery, so further research in surgical patients are needed to confirm the results.
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