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Twilight anesthesia is a type of anesthetic technique where a mild dose of general anesthesia is applied that affects the brain as well as the entire body. The patient is not unconscious, but sedated. During surgery or other medical procedures, the patient is under what is known as a "twilight state", where the patient is relaxed and "sleepy", able to follow simple directions by the doctor, and is responsive. Generally, twilight anesthesia causes the patient to forget the surgery and the time right after. It is used for a variety of surgical procedures and for various reasons. Just like regular anesthesia, "twilight anesthesia is designed to help a patient feel more comfortable and to minimize pain associated with the procedure being performed."
Twilight anesthesia is commonly known as I.V. sedation and calls for an easy awakening and speedy recovery time by the patient. Anesthesia is used to control pain by using medicines that reversibly block nerve conduction near the site of administration, therefore, generating a loss of sensation at the area administered. Close monitoring by the anesthesiologist will sometimes be provided, to help keep the patient comfortable during a medical procedure, along with other drugs to help relax the body. It can also help control breathing, blood pressure, blood flow, and heart rate and rhythm, when needed.
There are four levels of sedation by anesthesia.
Level One 
This level called Minimal sedation causes anxiolysis, a drug induced state in which the patient responds normally to verbal commands. Although the cognition and coordination of the patient are impaired, cardiovascular and ventilatory functions remain unaffected.
Level Two 
In this level called Moderate sedation/analgesia or conscious sedation', a drug induced depression of consciousness during which the patient responds purposefully to verbal commands, either alone or accompanied with light physical stimulation. Breathing tubes are not required for this type of anesthesia. This is Twilight Anesthesia.
Level Three 
In this level called Deep sedation/analgesia, a drug-induced depression of consciousness during which the patient cannot be easily aroused, but responds purposefully following repeated or painful stimulation. Ventilatory functions may be impaired, breathing tubes are required. Cardiovascular functions are usually sustained.
Level Four 
In this level called Anesthesia, a combination of general anesthesia and spinal or major regional anesthesia. It does not include local anesthesia. Ventilatory function is often impaired and cardiovascular functions may be impaired.
Several factors are taken into consideration when determining which level of anesthesia is used under which type of medical procedures. Along with the factors determined, different types of anesthesia medications are used depending on the medical procedure being done. While the patient is under level two of sedation by anesthesia, depending on the type and dose administered, they are in a state that is known as a “twilight” state, thus attaining the name "twilight anesthesia."
Drugs and technology used 
The same drugs used in general anesthesia are also used for twilight anesthesia, except in smaller doses and in a bolus interval (A concentrated mass of a substance administered intravenously for diagnostic or therapeutic purposes). These drugs can be administered via gases, such as nitrous oxide (laughing gas), or intravenously, with drugs such as Ketamine (Pediatrics primarily, and infrequently in adults), propofol, and midazolam. They provide a light sleep, anxiety relief, and amnesia (loss of any memories of surgery). It's important to remember that twilight anesthesia alone is not used to provide relief from surgical pain, therefore, it is always given in conjunction with a local or regional anesthetic. Additionally, IV sedation is frequently administered as a cocktail of several agents including those previously mentioned for induction and maintenance of anesthesia, as well as a Benzodiazepine (usually midazolam, but temazepam or flunitrazepam are also used via the oral route) and a narcotic/systemic analgesic such as demerol or fentanyl. As discussed in the levels of sedation by anesthesia, assistance with breathing tubes (ETT or LMA) are not generally used for this type of anesthesia.
A few studies have been geared towards studying the effects of post operative analgesic regimes that measure the quality of recovery period and health-related quality of life. Factors other than degree of analgesia and presence of analgesic agent-related side effects (e.g., fatigue, physical functioning, and mental health) may potentially influence these outcomes. Twilight anesthesia offers a limited recovery period after procedures, and is usually associated with less nausea and vomiting than general anesthesia which makes it a popular choice among doctors who are performing procedures such as minor plastic surgeries.
Twilight anesthesia is applied to various types of medical procedures and surgeries. It is a popular choice among surgeons and doctors who are performing anything from minor plastic surgeries to dental work, and procedures that do not require extensive operations or long durations in favor of less nausea and a limited recovery period after surgery. Twilight anesthesia is used:
- Ambulatory Surgical Centers
- Cosmetic Surgeons
- ENT Surgeons
- General Surgeons
- MRI Centers
- Oral Surgeons
- Orthopedic Surgeons
- Pediatric Dentists
- Plastic Surgeons
- Podiatrists/Foot Surgeons
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