Miya Pearson
Sleep and anesthesia may seem similar, but they are two entirely different conditions. While sleep is an active process with neurons clocking in to work, anesthesia involves the use of drugs called anesthetics to keep you comfortable and prevent you from feeling pain during medical procedures. Anesthesia can be administered in different ways, including local anesthesia, which numbs a small section of your body, and sedation, also known as twilight sleep, which relaxes you enough to nap but allows you to wake up if needed. General anesthesia, on the other hand, induces a deep sleep-like state by hijacking the neural circuitry responsible for sleep regulation, resulting in profound unconsciousness and amnesia. Despite its discovery 170 years ago, scientists are still working to fully understand how anesthesia works to develop better strategies and reduce side effects.
| Characteristics | Values |
|---|---|
| How it feels | Sleep and anesthesia feel similar, but they are different |
| Neural pathways | Sleep and anesthesia may use common neuronal and genetic substrates |
| Brain waves | Anesthesia changes the character of brain waves, transforming them from very high frequency, small amplitude waves to very low frequency, large amplitude waves |
| Brain regions communication | Anesthesia results in brain regions being unable to communicate with each other |
| Amnesia | Anesthesia can cause amnesia |
| Maintenance of stable state | Anesthesia keeps the body in a stable state by maintaining a consistent blood pressure, heart rate, and body temperature |
| Pain blocking | Regional anesthesia blocks pain perception in a specific area without making the patient unconscious |
| Hormones | Hormones play a role in maintaining the state of general anesthesia |
| Anesthesia-activated cells | Most anesthesia-activated cells are a kind of hybrid cell that connects the nervous system and the endocrine system |
| Anesthesia types | Local, regional, and general anesthesia |
| Anesthesia side effects | Back pain or muscle pain, chills caused by low body temperature (hypothermia), difficulty urinating, nausea and vomiting, pain, tenderness, redness or bruising at the injection site |
| Anesthesia risks | Anesthetic awareness, collapsed lung (atelectasis), malignant hyperthermia |
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What You'll Learn
- Sleep anaesthesia is induced by drugs that inhibit brain activity
- Anaesthetics activate neurons in the brain
- Anaesthetics alter neurotransmission in the cerebral cortex, brain stem, and thalamus
- Anaesthetics maintain a stable state in the body
- Anaesthetics can cause side effects like delirium and cognitive impairment
Sleep anaesthesia is induced by drugs that inhibit brain activity
Anaesthetics act through sleep neural circuits, but not necessarily in the same way as natural sleep. They target the neural circuits regulating sleep and wakefulness, particularly the thalamic relay neurons responsible for transmitting information to the cortex. The deactivation of the thalamus leads to cortical inhibition, which is a key mechanism in inducing unconsciousness.
Additionally, anaesthetics may inhibit N-methyl-D-aspartate (NMDA) receptors, which are excitatory cation channels activated by glutamate. By reducing excitatory signals in critical neuronal circuits, anaesthetics induce unconsciousness. This is particularly evident in the effects of ketamine anaesthesia, where ketamine promotes glutamate release in specific brain regions, contributing to a dissociative state.
Recent research has also suggested that anaesthetics may activate certain neurons in the brain, rather than simply inhibiting them. This discovery highlights the complex nature of anaesthesia and the need for further investigations to improve our understanding of its mechanisms. By studying the neural pathways and the role of hormones, scientists aim to develop newer drugs with fewer side effects, enhancing the safety and effectiveness of anaesthesia in medical procedures.
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Anaesthetics activate neurons in the brain
Despite the fact that general anaesthesia has been used in surgical procedures since 1846, the exact mechanisms of how it works are still not fully understood. The traditional view was that anaesthetics simply inhibit brain activity, but recent research has revealed a more complex picture.
It is now known that certain brain circuits are very active during sleep, and that sleep is not just a passive process. This has led scientists to question whether anaesthetics might do more than just suppress brain activity.
A 2019 study by Fan Wang, a professor of neurobiology at Duke University, found that several general anaesthetic drugs knock patients out by hijacking the neural circuitry that makes people fall asleep. The researchers traced this neural circuitry to a tiny cluster of cells at the base of the brain, in the hypothalamus, which is responsible for regulating bodily functions, mood, and sleep. These cells, called neuroendocrine cells, are activated by multiple classes of anaesthetic drugs.
Neuroendocrine cells are similar to neurons in that they receive signals from the nervous system, but they respond by producing and releasing hormones. The discovery of their role in anaesthesia is significant because it highlights how hormones may play a vital role in controlling states that affect the whole brain. Furthermore, the study found that pre-activating these neuroendocrine cells made mice stay under general anaesthesia for longer. This suggests that these cells play a key role in maintaining the state of general anaesthesia.
While the exact mechanisms of how anaesthesia works are still being investigated, these findings have important implications for the development of new drugs that can induce sleep with fewer adverse reactions.
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Anaesthetics alter neurotransmission in the cerebral cortex, brain stem, and thalamus
Despite being a medical miracle that has enabled millions of patients to undergo life-saving surgeries without pain, the exact mechanism of how general anaesthesia works has eluded scientists since its discovery 170 years ago. However, recent research has shed light on the role of anaesthetics in altering neurotransmission in the cerebral cortex, brain stem, and thalamus.
Anaesthetics have been shown to substantially reduce the global cerebral metabolic rate and blood flow, with the thalamus being a common site of modulation. This reduction in blood flow to the thalamus may be pivotal in inducing loss of consciousness and hypnosis. The thalamus is part of a presumptive consciousness circuit that also includes the medial parietal cortex, precuneus, and posterior cingulate cortex, as well as lateral frontoparietal association areas. Observations from epilepsy, stroke, vegetative state, and anesthesia suggest that this common cortical area is critical for consciousness.
Furthermore, anaesthetics have been found to depress glutamate transmission via presynaptic actions. They also alter the intracellular free calcium concentration and glutamate release, depressing presynaptic transmitter release. Calcium channels, particularly the P/Q-type, are important targets for the action of general anaesthesia. Anaesthetics such as ketamine, etomidate, and thiopental inhibit calcium channel currents, reducing the probability of calcium channel opening and increasing the rate of channel inactivation.
Additionally, anaesthetics bind to GABA receptors, activating interneurons that inhibit the rest of the brain. This changes the character of brain waves, transforming them from very high-frequency, small-amplitude waves to very low-frequency, large-amplitude waves. As a result, brain regions can no longer communicate with each other, leading to profound unconsciousness and amnesia.
In summary, anaesthetics alter neurotransmission in the cerebral cortex, brain stem, and thalamus by modulating calcium and glutamate activity, targeting GABA receptors, and reducing cerebral metabolic rate and blood flow. These combined effects disrupt brain connectivity and consciousness, rendering patients unconscious during surgery.
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Anaesthetics maintain a stable state in the body
Despite being a common medical procedure, the exact mechanisms of how anaesthesia works are not fully understood. Anaesthetics are drugs that keep patients comfortable and prevent them from feeling pain during medical procedures. They work by acting on the neural circuits that regulate sleep and wakefulness, inducing unconsciousness.
General anaesthesia keeps the body in a stable state by maintaining a consistent blood pressure, heart rate, and body temperature. This is achieved by inhibiting the brain's normal activities, which results in the inability to move or feel pain. The brain waves transform from very high-frequency, small-amplitude waves to very low-frequency, large-amplitude waves. This change in brain wave patterns prevents brain regions from communicating with each other, resulting in profound unconsciousness and amnesia.
Regional anaesthesia, on the other hand, blocks pain perception in a specific area without rendering the patient unconscious. Local anaesthesia is another type of anaesthesia that numbs a small section of the body, allowing patients to remain awake during the procedure.
Recent research has provided valuable insights into the role of hormones in maintaining the state of general anaesthesia. A study by a Duke University team found that several anaesthesia drugs knock patients out by hijacking the neural circuitry responsible for sleep. This circuitry involves a cluster of cells at the base of the brain that regulates hormones controlling bodily functions, mood, and sleep.
The discovery of the involvement of these neuroendocrine cells has opened up new possibilities for understanding anaesthesia's neural pathways and developing better medications for sleep disorders.
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Anaesthetics can cause side effects like delirium and cognitive impairment
While the discovery of general anaesthesia has been a medical miracle, enabling millions of patients to undergo invasive, life-saving surgeries without pain, anaesthetics can cause side effects like delirium and cognitive impairment.
Anaesthetics can induce the release of dopamine, which gives people a sense of feeling good. However, this can also lead to hallucinations, agitation, and aggression, which are symptoms of delirium. Post-operative delirium is the most common complication of surgery for older adults, affecting up to 50% of seniors. It is characterized by marked changes in mental function, including confusion, disorientation, persistent sleepiness, hallucinations, agitation, or aggression. Delirium can be mistaken for dementia, and if not identified early and treated, can lead to long-term health issues, including cognitive decline and functional decline.
The risk of post-operative delirium and cognitive dysfunction is higher when unnecessarily deep anaesthesia is used. This is due to the long-lasting neurotoxicity of general anaesthetics. Pre-existing cognitive impairment may also increase the risk of post-operative cognitive dysfunction (POCD). POCD can manifest as delirium, the development of dementia, or a decline in cognitive function in patients with pre-existing dementia.
To reduce the risk of post-operative delirium and cognitive dysfunction, it is important to identify patients who are at risk before surgery. The UT Southwestern Perioperative Optimization of Senior Health (POSH) program evaluates patients before surgery for their potential risk of developing complications, including post-operative delirium. During surgery, brain function monitoring can help facilitate anaesthetic titration to reduce anaesthetic exposure and patient risk. After surgery, brain-stimulating activities, such as reading or solving crossword puzzles, can help patients avoid delirium and maintain their cognitive function.
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Frequently asked questions
Sleep anesthesia, or sedation, is a type of anesthesia that relaxes you to the point where you'll nap but can wake up if needed to communicate.
Sleep anesthesia uses drugs called anesthetics to keep you comfortable and prevent you from feeling pain during medical procedures. Sleep anesthesia works by altering neurotransmission at multiple sites in the cerebral cortex, brain stem, and thalamus.
Most anesthesia side effects are temporary and go away within 24 hours. Depending on the anesthesia type and how it is administered, you may experience back pain or muscle pain, chills, difficulty urinating, nausea, and vomiting.
