those intended or act at targeted sites for
too long a time.
That may be reassuring to the more
than 20 million patients who are put
under general anesthesia each year in
the United States. Though new drugs
and procedures have made anesthesia
safer and more comfortable, patients still
may experience nausea, abnormal heart
rhythms or fogginess after surgery. In
extremely rare cases more serious effects
such as brain injury or death can result.
“We’ve made a lot of progress in
anesthesiology as far as taking care of
patients,” Brown says. “But it’ll be much
more reassuring when we can say to
them, ‘We have a good idea what’s hap-
pening inside your brain.’ ”
Beyond all that, mapping the path-
ways of neural activity taking the brain
to this particular type of unconscious-
ness may help scientists understand
how it compares with sleep and coma,
which may ultimately lead to new sleep
medicines or new ways to help patients
recover after a severe brain injury.
BOTH: PRIMAL PICTURES/PHOTO RESEARCHERS, ADAPTED BY JANEL KILEY
Before general anesthesia’s discovery in
the 1840s, patients simply had to endure
the trauma of surgery, although alcohol
or opiates sometimes numbed the pain.
After observing in 1844 that nitrous
oxide — or laughing gas — could stifle
pain, dentist Horace Wells had a tooth
pulled while on the gas. Taking several
deep inhalations, he nodded off, giving his
colleague ample time to yank the tooth.
Feeling no pain during the procedure,
Wells took his discovery to the medical
community: At Massachusetts General
Hospital, he gave a patient a whiff of
nitrous oxide before extracting a tooth.
The demonstration didn’t go as
planned, as the patient moaned during the procedure. But another dentist,
William Morton, began experimenting with ether. In 1846 Morton used
ether to knock out a patient while a
surgeon removed a neck tumor. By
1847 either ether or chloroform was
routinely administered during surgery
to put patients into a dreamless, pain-free state. In the early 20th century, as
surgical procedures advanced, these
gases were replaced by mixtures of
nitrous oxide and oxygen or intravenous narcotics, ultimately giving doctors
more control over zonked-out patients.
Today, anesthesiologists administer about a dozen drugs to produce the
desired effects. Sedatives help with
relaxation, opiates take away the pain
and a muscle relaxant paralyzes the
body. Other drugs added to the mix render patients unconscious and make sure
they don’t remember the experience.
During surgery, anesthesiologists
know when to intervene. They use a
mechanical ventilator to control breathing, ensuring that a patient is inhaling
and exhaling slowly, deeply and rhythmically, and they continually check for
signs of perspiration. Beeping monitors
signal trouble if it should arise.
Though not standard practice, brain
activity is recorded during some sur-geries. Electroencephalograph, or EEG,
signals track brain cell firings by measuring surface electrical activity through
sensors usually placed on a patient’s forehead. Some EEG monitors do additional
number crunching — translating readings
into ballpark assessments of a patient’s
level of consciousness and spitting out a
number ranging from 0 to 100. A value of
100 means that the patient is fully awake,
while a score of 0 — a flatline — indicates
no brain activity at all. Anesthesiologists
generally want to keep a patient’s score
within a range of 40 to 60.
While such measurements give anesthesiologists a rough way to gauge how
much anesthetic is needed — preventing
too much or too little — the devices can’t
always tell whether or not a patient retains
any sensory awareness. Anesthesiologist George Mashour of the University of
Michigan in Ann Arbor says that doctors
still don’t have a monitor that can reliably
detect consciousness in a paralyzed and
otherwise unresponsive patient.
“The reality is, there is no standard
device or monitor for the brain during
surgery,” Mashour says. “Which is pretty
interesting if you consider the fact that
the brain is one of the main target organs
of general anesthesia.”
One of the difficulties in learning how
the brain suspends consciousness is
the way in which general anesthesia
is induced, Brown says. Drug mixtures
are administered first intravenously
and then by inhalation, sending multiple drugs throughout every part of the
brain and nervous system within seconds. Because the drugs go everywhere,
it has been difficult to discern which circuits need to be hit for a person to reach
a surgery-ready state.
But a picture is beginning to emerge.
Using PET (positron emission tomography) and functional MRI scanners,
scientists can actually image brain activity when people go under. Though such
techniques can’t be used during surgery,
Turning off By imaging people’s brains as they ease into a state of general anesthesia,
researchers are getting a better sense of which brain regions shut down (some key players
labeled) and in what order. Such information may help doctors better target anesthetic drugs.
Anterior cingulate cortex Posterior cingulate cortex Frontal lobe Parietal lobe