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General anaesthetics are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced coma that causes lack of awareness to painful stimuli, sufficient to facilitate surgical applications in clinical and veterinary practice. General anaesthetics do not act as analgesics and should also not be confused with sedatives. General anaesthetics are a structurally diverse group of compounds whose mechanisms encompass multiple biological targets involved in the control of neuronal pathways. The precise workings are the subject of some debate and ongoing research.
Inhalants are a broad range of household and industrial chemicals whose volatile vapors or pressurized gases can be concentrated and breathed in via the nose or mouth to produce intoxication, in a manner not intended by the manufacturer. They are inhaled at room temperature through volatilization or from a pressurized container, and do not include drugs that are sniffed after burning or heating. For example, amyl nitrite (poppers), nitrous oxide and toluene – a solvent widely used in contact cement, permanent markers, and certain types of glue – are considered inhalants, but smoking tobacco, cannabis, and crack cocaine are not, even though these drugs are inhaled as smoke or vapor.
Nitrous oxide, commonly known as laughing gas, nitrous, nitro, or nos, is a chemical compound, an oxide of nitrogen with the formula N
2O. At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen.
Anesthesia or anaesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia, paralysis, amnesia, and unconsciousness. An individual under the effects of anesthetic drugs is referred to as being anesthetized.
General anaesthesia (UK) or general anesthesia (US) is a method of medically inducing loss of consciousness that renders a patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general anaesthetic medications, which often act in combination with an analgesic and neuromuscular blocking agent. Spontaneous ventilation is often inadequate during the procedure and intervention is often necessary to protect the airway. General anaesthesia is generally performed in an operating theater to allow surgical procedures that would otherwise be intolerably painful for a patient, or in an intensive care unit or emergency department to facilitate endotracheal intubation and mechanical ventilation in critically ill patients. Depending on the procedure, general anaesthesia may be optional or required. Regardless of whether a patient may prefer to be unconscious or not, certain pain stimuli could result in involuntary responses from the patient that may make an operation extremely difficult. Thus, for many procedures, general anaesthesia is required from a practical perspective.
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving.
An anaesthetic machine or anesthesia machine is a medical device used to generate and mix a fresh gas flow of medical gases and inhalational anaesthetic agents for the purpose of inducing and maintaining anaesthesia.
An anesthetic or anaesthetic is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness.
Awareness under anesthesia, also referred to as intraoperative awareness or accidental awareness during general anesthesia (AAGA), is a rare complication of general anesthesia where patients regain varying levels of consciousness during their surgical procedures. While anesthesia awareness is possible without resulting in any long-term memory of the experience, it is also possible for victims to have awareness with explicit recall, where they can remember the events related to their surgery.
Desflurane (1,2,2,2-tetrafluoroethyl difluoromethyl ether) is a highly fluorinated methyl ethyl ether used for maintenance of general anesthesia. Like halothane, enflurane, and isoflurane, it is a racemic mixture of (R) and (S) optical isomers (enantiomers). Together with sevoflurane, it is gradually replacing isoflurane for human use, except in economically undeveloped areas, where its high cost precludes its use. It has the most rapid onset and offset of the volatile anesthetic drugs used for general anesthesia due to its low solubility in blood.
Nitrous oxide is an inhaled gas used as a pain medication and together with other medications for anesthesia. Common uses include during childbirth, following trauma, and as part of end-of-life care. Onset of effect is typically within half a minute, and the effect lasts for about a minute.
A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.
An inhalational anesthetic is a chemical compound possessing general anesthetic properties that is delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vaporiser and an anesthetic delivery system. Agents of significant contemporary clinical interest include volatile anesthetic agents such as isoflurane, sevoflurane and desflurane, as well as certain anesthetic gases such as nitrous oxide and xenon.
A halogenated ether is a subcategory of a larger group of chemicals known as ethers. An ether is an organic chemical that contains an ether group—an oxygen atom connected to two (substituted) alkyl groups. A good example of an ether is the solvent diethyl ether. What differentiates a halogenated ether from other types of ethers is the substitution (halogenation) of one or more hydrogen atoms with a halogen atom. Halogen atoms include fluorine, chlorine, bromine, and iodine.
Medical gas supply systems in hospitals and other healthcare facilities are utilized to supply specialized gases and gas mixtures to various parts of the facility. Products handled by such systems typically include:
Following is a list of instruments used in the practice of anesthesia
Throughout recorded history, attempts at producing a state of general anesthesia can be traced back to the writings of ancient Sumerians, Babylonians, Assyrians, Egyptians, Indians, and Chinese. Despite significant advances in anatomy and surgical technique during the Renaissance, surgery remained a last-resort treatment largely due to the pain associated with it. However, scientific discoveries in the late 18th and early 19th centuries paved the way for the development of modern anesthetic techniques.
A breathing circuit is those parts of a breathing apparatus, which direct the flow of supplied breathing gas to, and sometimes from, the user. The breathing circuit may be open, closed, or semi-closed, depending on whether breathing gas is recycled. A closed or semi-closed circuit will include components which remove carbon dioxide from the exhaled gas and add oxygen before it is delivered for inhalation, so that the mixture remains stable and suitable for supporting life. Terminology may vary slightly between fields of application. In diving and industrial rebreathers, the closed or semi-closed breathing circuit may also be called the loop, or breathing loop. In medical equipment the closed or semi-closed circuit may be called the circle system.
Nitrous oxide, desflurane, and isoflurane are the most commonly used anesthetic gases. They may cause some complications due to their leakage and storage failure.
Inhalation sedation is a form of conscious sedation where an inhaled drug should:
- Depress the central nervous system (CNS) to an extent that surgeons can operate with minimal physiological and psychological stress to the patient
- Modify the patient's state of mind such that communication is maintained and the patient can respond to verbal command
- Carry a margin of safety wide enough to render the unintended loss of consciousness and loss of protective reflexes unlikely.
References
- 1 2 Magee, P; Tooley, M (2011). "28 Environmental Safety". The Physics, Clinical Measurement and Equipment of Anaesthetic Practice for the FRCA (Online ed.). Oxford Academic Books. pp. 369–374. ISBN 9780191918032 . Retrieved 20 February 2024.
- ↑ Dorsch, JA; Dorsch, SE (2012). Understanding anesthesia equipment (5th ed.). Wolters Kluwer Health. p. 378. ISBN 9781451178678 . Retrieved 20 February 2024.
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