The Millstone Times June 2021
What’s the Difference Between Sleep and Anesthesia? By Pam Teel The anesthetic state and natural sleep share many neurobiological features and yet are two distinct states. There are two main sleep states: rapid eye move-
ment (REM) sleep and non-REM sleep. The brain and body slow down during non-REM sleep, while REM sleep is very much like an awake state. Through the night, you go between the two states in cycles of about 90 minutes, four to six times total. It’s a natural physiologic process that needs to take place for your mental and physical health. During sleep, the brain moves between the slow waves of non-REM sleep and the fast waves of REM sleep. Anesthesia is nothing like that. Under general anesthesia, brain waves are held hostage in the same state and remain there for the length of the operation until they turn the anesthetics off and allow you to slowly come out of it. General anesthesia is a drug-induced, reversible coma that has a few com- ponents: Analgesia- you don't perceive pain, unconsciousness- you're not aware of what's happening, Amnesia- you’re not forming memories, Akinesia- you can’t move. Sleep is actively generated in the brain and is dependent on homeostatic drive and circadian rhythms. The ease of onset and maintenance of sleep is subject to environmental factors such as temperature, noise, light and chemical stimulants.
Once NREM is established, there is regular cycling between this state and REM sleep at approximately 90-min intervals. The onset of sleep is known to be regulated by a variety of neurotransmitter systems. In recent years, the prevailing supposition is that sleep–wake regulation is contingent on fast neu- rotransmitters such as GABA and glutamate. The ventrolateral preoptic area (VLPO) is known to be important in sleep onset. GABAergic neurons project from the VLPO to arousal areas such as the histaminergic tuberomammillary nucleus in the posterior hypothalamus, the serotonergic dorsal raphe and the noradrenergic locus coeruleus. Adenosine is one of the brain's chief somnogens and accumulates as a degradation product of adenosine triphosphate during prolonged intervals of waking. Adenosine binding in the VLPO is associated with increased activity in this region, promoting non-REM sleep General anesthesia keeps the body in a stable state by maintaining a consistent blood pressure, heart rate, and body temperature. Regional anesthesia blocks pain perception in a specific area without making the patient unconscious. It’s a common technique for orthopedic surgeries in the lower part of the body, like knee surgery. Sedative drugs block memory formation and make the patient less aware of what’s going on, which is helpful for uncomfortable procedures like colonoscopies. Anesthetic drugs block the brain’s ability to send information between regions. Many of the commonly used anesthetics bind to GABA receptors, a type of receptor found in inhibitory interneuron’s all over the nervous system. These interneuron’s act like routers in a computer network: they connect and modulate all the excitatory neurons in the brain. If you control the interneuron’s, you can control the rest of the circuits in the brain. Binding to GABA receptors activates interneuron’s to inhibit the rest of the brain. The enhanced inhibitory activity changes the character of brain waves, the synchronized electrical activity of groups of neurons. They transform from very high frequency, small amplitude waves to very low frequency, large amplitude waves. As long as the patient receives the anesthesia, the brain stays in this state. The brain waves become so structured and regimented that they can't transmit information anymore. As a consequence, brain regions can no longer communicate with each other, resulting in profound unconsciousness and amnesia. The anesthesiologist may administer an opioid and muscle relaxants to ensure adequate analgesia and akinesia, respectively. When the drug wears off, the brain rhythms slowly return to normal, and the patient comes to. You can’t dream if you're under full general anesthesia and unconscious, but if you're in a lighter state of sedation, then you certainly can dream. Sometimes, after sedation, people wake up with a good feeling and interpret it as being well-rested. That's because sedative drugs can induce the release of dopamine, which gives you a sense of feeling good. It is not the same feeling as waking up from a good night’s sleep. If a neuroscientist used electroenceph- alography (EEG) to record your brain’s electrical activity while you were under anesthesia, the results would look different from how they appear when you are sleeping. In fact, your brain waves under anesthesia would more closely resemble those seen were you to have the terrible misfortune of falling into a coma after brain illness or injury. Doctors often tell surgery patients that they will be ‘put to sleep’ during the operation, but in terms of the neurological effects of the anesthesia, it would be more accurate (and more unsettling) to tell them that they will be put into a reversible coma. Some people do experience side effects after coming out of the anesthesia which include: temporary confusion and memory loss, although this is more common in the elderly, dizziness, difficulty passing urine, bruising or soreness from the IV drip, nausea and vomiting, shivering and feeling cold, and sore throat from the breathing tube.
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