Posts tagged anaesthesia

Anesthesia makes otherwise painful procedures possible by derailing a conscious brain, rendering it incapable of sensing or responding to a surgeon’s knife. But little research exists on what happens when the drugs wear off.

(Image caption: Unconscious states. New findings suggest the anesthetized brain must pass through certain ‘way stations’ on the path back to consciousness. Above, the prevalence of particular clusters of brain activity states as recorded in rats that had been administered an anesthetic. The longest appear in red and the shortest in yellow and green.)

“I always found it remarkable that someone can recover from anesthesia, not only that you blink your eyes and can walk around, but you return to being yourself. So if you learned how to do something on Sunday and on Monday, you have surgery, and you wake up and you still know how to do it,” says Alexander Proekt, a visiting fellow in Don Pfaff’s Laboratory of Neurobiology and Behavior at Rockefeller University and an anesthesiologist at Weill Cornell Medical College. “It seemed like there ought to be some kind of guide or path for the system to follow.”

The obvious explanation is that as the anesthetic washes out of the body, electrical activity in the brain gradually returns to its conscious patterns. However, new research by Proekt and colleagues suggests the trip back is not so simple.

“Using statistical analysis, our research shows that the recovery from deep anesthesia is not a smooth, linear process. Instead, there are dynamic ‘way stations’ or states of activity the brain must temporarily occupy on the way to full recovery,” Pfaff says. “These results have implications for understanding how someone’s ability to recover consciousness can be disrupted by, for example, brain injury.”

Proekt, along with former postdoc Andrew Hudson, now an assistant professor in anesthesiology at the University of California, Los Angeles, and Diany Paola Calderon, a research associate in the lab, put rats “under” using the common medical and veterinary anesthetic isoflurane. As the rats recovered, the team monitored the electrical potential outside neurons, known as  local field potentials (LFPs), in particular parts of the brain known, from previous elecrophysiological and pharmacological studies, to be associated with wakefulness and anesthesia. These recordings gave them a sensitive handle on the activities of whole groups of neurons in particular parts of the thalamus and cortex.

In the awake brain, of both humans and rats, neurons generate electrical voltage that oscillates. Many of these oscillations together form a signal that appears as a squiggly line on a recording of brain activity, such as an LFP. When someone is asleep, under anesthesia, or in a coma, these oscillations occur more slowly, or at a low frequency. When he or she is awake, they speed up. The researchers examined the recordings from the rats’ brains to figure out how the electrical activity in these regions changed as they moved from anesthetized to awake.

“Recordings from each animal wound up having particular features that spontaneously appeared, suggesting their brain activity was abruptly transitioning through particular states,” Hudson says. “We analyzed the probability of a brain jumping from one state to another, and we found that certain states act as hubs through which the brain must pass to continue on its way to consciousness.” While the electrical activity in all the rats’ brains passed through these hubs, the precise path back to consciousness was not the same each time, the team reports today in the Proceedings of the National Academy of Sciences.

“These results suggest there is indeed an intrinsic way in which the unconscious brain finds its way back to consciousness. The anesthetic is just a tool for severely reducing brain activity  in a way in which we can control,” Hudson says.

In other scenarios, including coma caused by brain injury or neurological disease, the disruption to brain activity cannot be controlled, making these states much more difficult to study. However, the team’s results may help explain what is going on in these cases. “Maybe a pathway has shut down, or a brain structure that was key for full consciousness is no longer working. We don’t know yet, but our results suggest the possibility that under certain circumstances, someone may be theoretically capable of returning to consciousness but, due to the inability to transition through the hubs we have identified, his or her brain is unable to navigate the way back,” Calderon says.

(Source: newswire.rockefeller.edu)

Exposure to general anaesthesia increases the risk of dementia in the elderly by 35%, says new research presented at Euroanaesthesia, the annual congress of the European Society of Anaesthesiology (ESA). The research is by Dr Francois Sztark, INSERM and University of Bordeaux, France, and colleagues.

Postoperative cognitive dysfunction, or POCD, could be associated with dementia several years later. POCD is a common complication in elderly patients after major surgery. It has been proposed that there is an association between POCD and the development of dementia due to a common pathological mechanism through the amyloid β peptide. Several experimental studies suggest that some anaesthetics could promote inflammation of neural tissues leading to POCD and/or Alzheimer’s disease (AD) precursors including β-amyloid plaques and neurofibrillary tangles. But it remains uncertain whether POCD can be a precursor of dementia.

In this new study, the researchers analysed the risk of dementia associated with anaesthesia within a prospective population-based cohort of elderly patients (aged 65 years and over). The team used data from the Three-City study, designed to assess the risk of dementia and cognitive decline due to vascular risk factors. Between 1999 and 2001, the 3C study included 9294 community-dwelling French people aged 65 years and over in three French cities (Bordeaux, Dijon and Montpellier).

Participants aged 65 years and over were interviewed at baseline and subsequently 2, 4, 7 and 10 years after. Each examination included a complete cognitive evaluation with systematic screening of dementia. From the 2-year follow-up, 7008 non-demented participants were asked at each follow-up whether they have had a history of anaesthesia (general anaesthesia (GA) or local/locoregional anaesthesia (LRA)) since the last follow-up. The data were adjusted to take account of potential confounders such as socioeconomic status and comorbidities.

The mean age of participants was 75 years and 62% were women. At the 2-year follow-up, 33% of the participants (n=2309) reported an anaesthesia over the 2 previous years, with 19% (n=1333) reporting a GA and 14% (n=948) a LRA. A total of 632 (9%) participants developed dementia over the 8 subsequent years of follow-up, among them 284 probable AD and 228 possible AD, and the remaining 120 non-Alzheimer’s dementia. The researchers found that demented patients were more likely to have received anaesthesia (37%) than non-demented patients (32%). This difference in anaesthesia was due to difference in numbers receiving general anaesthetics, with 22% of demented patients reporting a GA compared with 19% of non-demented patients. After adjustment, participants with at least one GA over the follow-up had a 35% increased risk of developing a dementia compared with participants without anaesthesia.

Dr Sztark concludes: “These results are in favour of an increased risk for dementia several years after general anaesthesia. Recognition of POCD is essential in the perioperative management of elderly patients. A long-term follow-up of these patients should be planned.”

(Source: eurekalert.org)