Tag: anaesthesia

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Brain Structures Predict Risk of Awareness under Anaesthesia

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Awareness during anaesthesia is an extremely rare but horrific risk for patients. Now, for the first time, neuroscientists have identified brain structures which could predict an individual’s predisposition this phenomenon. The findings, just published in the journal Human Brain Mapping, could help identify patients who need larger anaesthetic doses.

Although anaesthesia has been used in clinical medicine for over 150 years, scientists do not fully understand why its effect on people is so varied. One in four patients presumed to be unconscious during general anaesthesia may in fact have subjective experiences, such as dreaming. Estimated to occur in 1:1000 to 1:20 000 cases, some patients may have awareness under general anaesthetic. These experiences may range from hearing sounds to the pain of surgery combined with the sensation of suffocation and paralysis in the setting of neuromuscular blockade.

The researchers from Trinity College Dublin found that one in three participants were unaffected by moderate propofol sedation in their response times, thus thwarting a key aim of anaesthesia – the suppression of behavioural responsiveness.

The research also showed, for the first time, that the participants who were resistant to anaesthesia had fundamental differences in the function and structures of the fronto-parietal regions of the brain to those who remained fully unconscious. Crucially, these brain differences could be predicted prior to sedation.

Lorina Naci, Associate Professor of Psychology, Trinity who lead the research said:

“The detection of a person’s responsiveness to anaesthesia prior to sedation has important implications for patient safety and wellbeing. Our results highlight new markers for improving the monitoring of awareness during clinical anaesthesia. Although rare, accidental awareness during an operation can be very traumatic and lead to negative long-term health outcomes, such as post-traumatic stress disorder, as well as clinical depression or phobias.”

“Our results suggest that individuals with larger grey matter volume in the frontal regions and stronger functional connectivity within fronto-parietal brain networks, may require higher doses of propofol to become nonresponsive compared to individuals with weaker connectivity and smaller grey matter volume in these regions.”

The research, conducted in Ireland and Canada, investigated 17 healthy individuals who were sedated with propofol, the most common clinical anaesthetic agent. The participants’ response time to detect a simple sound was measured when they were awake and as they became sedated. Brain activity of 25 participants as they listened to a simple story in both states was also measured.

Source: Trinity College Dublin

Categories : Obstetrics & Gynaecology Pain ManagementTags : Leave a comment

Study Finds No Adverse Effects Denying Nitrous Oxide in Labour

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Birthing women denied nitrous oxide(N20) to relieve labour pain as a result of the COVID pandemic received opioids instead, without any adverse outcomes for mother or child, according to a new study published in the Australian and New Zealand Journal of Obstetrics and Gynaecology. Some anaesthetists have also argued for reducing N20 use as it is a greenhouse gas.

The study, conducted at Lyell McEwin Hospital in Australia, looked at the impact of withholding nitrous oxide (N20), a decision adopted by many hospitals worldwide over fears of virus transmission from the aerosol-generating procedure.

Anaesthetist Professor Bernd Froessler and colleagues compared patient notes for all 243 women birthing at Lyell McEwin over a seven week period in March/April 2020, half of whom did not have access to N20.

They found that although opioid use “significantly increased” when N20 was withheld, there was no increase in epidural use and no change in labour duration, Caesarean section rates, birthing complications or newborn alertness.

Nitrous oxide is used by more than 50% of Australian women to relieve pain in labour, followed by epidurals (40%) and opioids (12%), according to the Australian Institute of Health and Welfare.

However, N20 represents 6% of global greenhouse gas emissions, with 1% due to medical use (ie, around 0.06% of total global warming is due to medical N20). This has led to a debate in medical circles whether it should be replaced with other methods of pain relief.

Many obstetricians argue that effective pain relief in childbirth should be the priority, particularly given the low percentage of emissions, but the Australian and New Zealand College of Anaesthetists has advocated for a reduction in N20 use in a bid to improve environmental sustainability in anaesthesia.

“Obviously no-one wants to deprive labouring women of adequate and easy pain relief but given there are other analgesic options, including epidurals and opioids, perhaps these could be considered,” said Prof Froessler.

UniSA statistician and researcher Dr Lan Kelly said that the findings should reassure women that pain relief besides N20 does not compromise their health or their baby’s.

However, in a recent Sydney Morning Herald article, principal midwifery officer at the Australian College of Midwives, Kellie Wilton, said mothers should not be made to feel guilty about their pain relief choices and suggested hospitals could introduce nitrous oxide destruction systems to allow for its ongoing use.

When nitrous oxide destruction systems were introduced in Swedish hospitals, the carbon footprint from the gas was halved.

Source: University of South Australia

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MRI Unveils Secrets of Brains under Anaesthesia

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Depiction of a human brain
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A study published in eLife reveals how the brains of humans and other primates under anaesthesia differ from mammals such as mice, with the visual cortex in primates being isolated from certain effects.

Anaesthesia still holds mysteries for modern science. Electroencephalography (EEG) studies show that, during anaesthesia, the brain is put into a deep sleep-like state in which periods of rhythmic electrical activity alternate with periods of complete inactivity. This state is called burst-suppression. Until now, it was unclear where exactly this state happens in the brain and which brain areas are involved.

Shedding light on the phenomenon would help better understand how the brain functions under anaesthesia. To this end, researchers used functional magnetic resonance imaging (fMRI) to study the precise spatial distribution of synchronously working brain regions in anaesthetised humans, long-tailed macaques, common marmosets and rats. They were able to show for the first time that the areas where burst-suppression is evident differ significantly in primates and rodents. While in rats large parts of the cerebral cortex synchronously show the burst-suppression pattern, in primates individual sensory regions, such as the visual cortex, are excluded from it.

“Our brain can be thought of as a full soccer stadium when we are awake,” explained Nikoloz Sirmpilatze, lead author of the study. “Our active neurons are like tens of thousands of spectators all talking at once. Under anaesthesia, however, neuronal activity is synchronised. You can measure this activity using EEG as uniform waves, as if all the spectators in the stadium were singing the same song. In deep anaesthesia, this song is repeatedly interrupted by periods of silence. This is called burst-suppression. The deeper the anaesthesia, the shorter the phases of uniform activity, the bursts, and the longer the periodically recurring inactive phases, the so-called suppressions.”

The phenomenon is caused by many different anaesthetics, some of which vary in their mechanisms of action. And burst-suppression is also detectable in coma patients. However, it is not known whether this condition is a protective reaction of the brain or a sign of impaired functioning. It has also been unclear where in the brain burst-suppression occurs and which brain areas are involved, as localisation by EEG alone is not possible.

To answer this question, the researchers fMRI. In the first part of the study, the researchers established a system to evaluate fMRI data in humans, monkeys and rodents in a standardised manner using the same method. To do this, they used simultaneously-measured EEG and fMRI data from anaesthetised patients that had been generated in a previous study. “We first looked to see whether the burst-suppression detected in the EEG was also visible in the fMRI data and whether it showed a certain pattern,” says Nikoloz Sirmpilatze. “Based on that, we developed a new algorithm that allowed detecting burst-suppression events in the experimental animals using fMRI, without additional EEG measurement.”

The researchers then performed fMRI measurements in anaesthetised long-tailed macaques, common marmosets and rats. In all animals, they were able to detect and precisely localise burst-suppression as a function of anesthetic concentration. The spatial distribution of burst-suppression showed that in both humans and monkey species, certain sensory areas, such as the visual cortex, were excluded from it. In contrast, in the rats, the entire cerebral cortex was affected by burst-suppression.

“At the moment, we can only speculate about the reasons,” said Nikoloz Sirmpilatze, who was awarded the German Primate Center’s 2021 PhD Thesis Award for his work. “Primates orient themselves mainly through their sense of sight. Therefore, the visual cortex is a highly specialised region that differs from other brain areas by special cell types and structures. In rats, this is not the case. In future studies, we will investigate what exactly happens in these regions during anaesthesia to ultimately understand why burst-suppression is not detectable there with fMRI.”

Susann Boretius, senior author of the study adds: “The study not only raises the question of the extent to which rodents are suitable models for many areas of human brain research, especially when it comes to anaesthesia, but the results also have many implications for neuroscience and the evolution of neural networks in general.”

Source: Deutsches Primatenzentrum (DPZ)/German Primate Center

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Equivalent Hip Surgery Outcomes for Spinal vs General Anaesthesia

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Research comparing general versus spinal anaesthesia for hip fracture surgery shows similar outcomes for patients, challenging the common thinking that patients receiving spinal anaesthesia fare better. 

Led by researchers from the Perelman School of Medicine at the University of Pennsylvania, the study was published in the New England Journal of Medicine and presented at Anesthesiology 2021, the annual meeting of the American Society of Anesthesiologists (ASA).

“Available evidence has not definitively addressed the question of whether spinal anaesthesia is safer than general anaesthesia for hip fracture surgery, an important question to clinicians, patients, and families. Our study argues that, in many cases, either form of anaesthesia appears to be safe,” said lead investigator Mark D. Neuman, MD, MSc, an associate professor of Anesthesiology and Critical Care. “This is important because it suggests that choices can be guided by patient preference rather than anticipated differences in outcomes in many cases.”

While most of the 250 000 annual hip fracture patients in the US undergo general anaesthesia, spinal anaesthesia increased by 50% between 2007 and 2017, while in the United Kingdom and other countries, spinal anaesthesia is used in over 50% of hip fracture cases. [PDF]

Most recent comparisons of general anaesthesia versus spinal anaesthesia come from non-randomised studies, some indicating fewer cognitive and medical complications with spinal. Some patients may choose spinal anaesthesia for lower complications, while those choosing general may have a fear of spinal injection or insufficient anaesthesia. 

The study enrolled 1600 patients, all at least 50 years old, who had broken a hip. Among older populations, hip fractures are particularly worrisome as they can lead to a loss of mobility, linked to a doubling or even tripling the risk of near-term death. The patients were randomised into two groups, a major advantage for the study.

The researchers combined subsequent patient death rates and whether they regained the ability to walk, even with a walker. By 60 days post-surgery, 18.5% of patients assigned to spinal anaesthesia had either died or become newly unable to walk versus 18% of patients who received general anaesthesia. Mortality at this point was 3.9% of patients who received spinal anaesthesia died versus 4.1% who got general anaesthesia.

Additionally, to examine how the different forms of anaesthesia factored into potential cognitive complications, the researchers also examined post-operative delirium. Delirium was experienced in 21% of spinal anaesthesia patients versus 20% for general anaesthesia.

“What our study offers is reassurance that general anaesthesia can represent a safe option for hip fracture surgery for many patients,” said Prof Neuman. “This is information that patients, families, and clinicians can use together to make the right choice for each patient’s personalised care.”

Source: Perelman School of Medicine at the University of Pennsylvania