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General anaesthesia | |
---|---|
Equipment used for anaesthesia in the operating room | |
Specialty | Anaesthetics |
Uses | Facilitating surgery, terminal sedation [1] |
Complications | Anaesthesia awareness, [2] overdose, [3] death [4] |
MeSH | D000768 |
MedlinePlus | 007410 |
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. [5] 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. [5] 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 (such as movement or muscle contractions) that may make an operation extremely difficult. Thus, for many procedures, general anaesthesia is required from a practical perspective.
A variety of drugs may be administered, with the overall goal of achieving unconsciousness, amnesia, analgesia, loss of reflexes of the autonomic nervous system, and in some cases paralysis of skeletal muscles. The optimal combination of anesthetics for any given patient and procedure is typically selected by an anaesthetist, or another provider such as a nurse anaesthetist (depending on local practice and law), in consultation with the patient and the surgeon, dentist, or other practitioner performing the operative procedure. [6]
Attempts at producing a state of general anaesthesia can be traced throughout recorded history in the writings of the ancient Sumerians, Babylonians, Assyrians, Egyptians, Greeks, Romans, Indians, and Chinese. During the Middle Ages, scientists and other scholars made significant advances in the Eastern world, while their European counterparts also made important advances.
The Renaissance saw significant advances in anatomy and surgical technique. However, despite all this progress, surgery remained a treatment of last resort. Largely because of the associated pain, many patients chose certain death rather than undergo surgery. Although there has been a great deal of debate as to who deserves the most credit for the discovery of general anaesthesia, several scientific discoveries in the late 18th and early 19th centuries were critical to the eventual introduction and development of modern anaesthetic techniques. [7]
Two enormous leaps occurred in the late 19th century, which together allowed the transition to modern surgery. An appreciation of the germ theory of disease led rapidly to the development and application of antiseptic techniques in surgery. Antisepsis, which soon gave way to asepsis, reduced the overall morbidity and mortality of surgery to a far more acceptable rate than in previous eras. [8] Concurrent with these developments were the significant advances in pharmacology and physiology which led to the development of general anaesthesia and the control of pain. On 14 November 1804, Hanaoka Seishū, a Japanese surgeon, became the first person on record to successfully perform surgery using general anaesthesia. [9]
In the 20th century, the safety and efficacy of general anaesthesia was improved by the routine use of tracheal intubation and other advanced airway management techniques. Significant advances in monitoring and new anaesthetic agents with improved pharmacokinetic and pharmacodynamic characteristics also contributed to this trend. Finally, standardized training programs for anaesthesiologists and nurse anaesthetists emerged during this period.
General anaesthesia has many purposes and is routinely used in almost all surgical procedures. An appropriate surgical anesthesia should include the following goals:
Instead of receiving continuous deep sedation, such as via benzodiazepines, dying patients may choose to be completely unconscious as they die. [1]
The biochemical mechanism of action of general anaesthetics is still controversial. [10] Theories need to explain the function of anaesthesia in animals and plants. [11] To induce unconsciousness, anaesthetics have myriad sites of action and affect the central nervous system (CNS) at multiple levels. General anaesthesia commonly interrupts or changes the functions of CNS components including the cerebral cortex, thalamus, reticular activating system, and spinal cord. Current theories on the anaesthetized state identify not only target sites in the CNS but also neural networks and arousal circuits linked with unconsciousness, and some anaesthetics potentially able to activate specific sleep-active regions. [12]
Two non-exclusionary mechanisms include membrane-mediated and direct protein-mediated anesthesia. Potential protein-mediated molecular targets are GABAA,and NMDA glutamate receptors. General anesthesia was hypothesized to either enhance the inhibitory transmission or reduce the excitatory transmission of neuro signaling. [13] Most volatile anesthetics have been found to be a GABAA agonist, although the site of action on the receptor remains unknown. [14] Ketamine is a non-competitive NMDA receptor antagonist. [15]
The chemical structure and properties of anesthetics, as first noted by Meyer and Overton, suggest they could target the plasma membrane. A membrane-mediated mechanism that could account for the activation of an ion channel remained elusive until recently. A study from 2020 demonstrated that inhaled anesthetics (chloroform and isoflurane) could displace phospholipase D2 from ordered lipid domains in the plasma membrane, which led to the production of the signaling molecule phosphatidic acid (PA). The signaling molecule activated TWIK-related K+ channels (TREK-1), a channel involved in anesthesia. PLDnull fruit flies were shown to resist anesthesia, the results established a membrane mediated target for inhaled anesthetics. [16]
Prior to a planned procedure, the anesthesiologist reviews medical records, interviews the patient, and conducts a physical examination to obtain information regarding their medical history and current physical state, and to determine an appropriate anesthetic plan, including what combination of drugs and dosages will likely be needed for the patient's comfort and safety during the procedure. A variety of non-invasive and invasive monitoring devices may be necessary to ensure a safe and effective procedure. Key factors in this evaluation are the patient's age, gender, body mass index, medical and surgical history, current medications, exercise capacity, and fasting time. [17] [18] Thorough and accurate preoperative evaluation is crucial for the effective safety of the anesthetic plan. For example, a patient who consumes significant quantities of alcohol or illicit drugs could be undermedicated during the procedure if they fail to disclose this fact, and this could lead to anaesthesia awareness or intraoperative hypertension. [2] [19] Commonly used medications can also interact with anaesthetics, and failure to disclose such usage can increase the risk during the operation. Inaccurate timing of last meal can also increase the risk for aspiration of food, and lead to serious complications. [6]
An important aspect of pre-anaesthetic evaluation is an assessment of the patient's airway, involving inspection of the mouth opening and visualisation of the soft tissues of the pharynx. [20] The condition of teeth and location of dental crowns are checked, and neck flexibility and head extension are observed. [21] [22] The most commonly performed airway assessment is the Mallampati classification, which evaluates the airway base on the ability to view airway structures with the mouth open and the tongue protruding. Mallampati tests alone have limited accuracy, and other evaluations are routinely performed addition to the Mallampati test including mouth opening, thyromental distance, neck range of motion, and mandibular protrusion. In a patient with suspected distorted airway anatomy, endoscopy or ultrasound is sometimes used to evaluate the airway before planning for the airway management. [23]
Prior to administration of a general anaesthetic, the anaesthetist may administer one or more drugs that complement or improve the quality or safety of the anaesthetic or simply provide anxiolysis. Premedication also often has mild sedative effects and may reduce the amount of anaesthetic agent required during the case. [6]
One commonly used premedication is clonidine, an alpha-2 adrenergic agonist. [24] [25] It reduces postoperative shivering, postoperative nausea and vomiting, and emergence delirium. [6] However, a randomized controlled trial from 2021 demonstrated that clonidine is less effective at providing anxiolysis and more sedative in children of preschool age. Oral clonidine can take up to 45 minutes to take full effect, [26] The drawbacks of clonidine include hypotension and bradycardia, but these can be advantageous in patients with hypertension and tachycardia. [27] Another commonly used alpha-2 adrenergic agonist is dexmedetomidine, which is commonly used to provide a short term sedative effect (<24 hours). Dexmedetomidine and certain atypical antipsychotic agents may be also used in uncooperative children. [28]
Benzodiazepines are the most commonly used class of drugs for premedication. The most commonly utilized benzodiazepine is Midazolam, which is characterized by a rapid onset and short duration. Midazolam is effective in reducing preoperative anxiety, including separation anxiety in children. [29] It also provides mild sedation, sympathicolysis, and anterograde amnesia. [6]
Melatonin has been found to be effective as an anaesthetic premedication in both adults and children because of its hypnotic, anxiolytic, sedative, analgesic, and anticonvulsant properties. Recovery is more rapid after premedication with melatonin than with midazolam, and there is also a reduced incidence of post-operative agitation and delirium. [30] Melatonin has been shown to have a similar effect in reducing perioperative anxiety in adult patients compared to benzodiazepine. [31]
Another example of anaesthetic premedication is the preoperative administration of beta adrenergic antagonists, which reduce the burden of arrhythmias after cardiac surgery. However, evidence also has shown an association of increased adverse events with beta-blockers in non-cardiac surgery. [32] Anaesthesiologists may administer one or more antiemetic agents such as ondansetron, droperidol, or dexamethasone to prevent postoperative nausea and vomiting. [6] NSAIDs are commonly used analgesic premedication agent, and often reduce need for opioids such as fentanyl or sufentanil. Also gastrokinetic agents such as metoclopramide, and histamine antagonists such as famotidine. [6]
Non-pharmacologic preanaesthetic interventions include playing cognitive behavioral therapy, music therapy, aromatherapy, hypnosis massage, pre-operative preparation video, and guided imagery relaxation therapy, etc. [33] These techniques are particularly useful for children and patients with intellectual disabilities. Minimizing sensory stimulation or distraction by video games may help to reduce anxiety prior to or during induction of general anaesthesia. Larger high-quality studies are needed to confirm the most effective non-pharmacological approaches for reducing this type of anxiety. [34] Parental presence during premedication and induction of anaesthesia has not been shown to reduce anxiety in children. [34] It is suggested that parents who wish to attend should not be actively discouraged, and parents who prefer not to be present should not be actively encouraged to attend. [34]
Anesthesia has little to no effect on brain function, unless there is an existing brain disruption. Barbiturates, or the drugs used to administer anesthesia do not affect auditory brain stem response. [35] An example of a brain disruption would be a concussion. [36] It can be risky and lead to further brain injury if anesthesia is used on a concussed person. Concussions create ionic shifts in the brain that adjust the neuronal transmembrane potential. In order to restore this potential more glucose has to be made to equal the potential that is lost. This can be very dangerous and lead to cell death. This makes the brain very vulnerable in surgery. There are also changes to cerebral blood flow. The injury complicates the oxygen blood flow and supply to the brain.
Guedel's classification, described by Arthur Ernest Guedel in 1937, [3] describes four stages of anaesthesia. Despite newer anaesthetic agents and delivery techniques, which have led to more rapid onset of—and recovery from—anaesthesia (in some cases bypassing some of the stages entirely), the principles remain.
General anaesthesia is usually induced in an operating theatre or in a dedicated anaesthetic room adjacent to the theatre. General anaesthesia may also be conducted in other locations, such as an endoscopy suite, intensive care unit, radiology or cardiology department, emergency department, ambulance, or at the site of a disaster where extrication of the patient may be impossible or impractical.
Anaesthetic agents may be administered by various routes, including inhalation, injection (intravenous, intramuscular, or subcutaneous), oral, and rectal. Once they enter the circulatory system, the agents are transported to their biochemical sites of action in the central and autonomic nervous systems.
Most general anaesthetics are induced either intravenously or by inhalation. Commonly used intravenous induction agents include propofol, sodium thiopental, etomidate, methohexital, and ketamine. Inhalational anaesthesia may be chosen when intravenous access is difficult to obtain (e.g., children), when difficulty maintaining the airway is anticipated, or when the patient prefers it. Sevoflurane is the most commonly used agent for inhalational induction, because it is less irritating to the tracheobronchial tree than other agents. [38]
As an example sequence of induction drugs:
Laryngoscopy and intubation are both very stimulating. The process of induction blunts the response to these maneuvers while simultaneously inducing a near-coma state to prevent awareness.
Several monitoring technologies allow for a controlled induction of, maintenance of, and emergence from general anaesthesia. Standard for basic anesthetic monitoring is a guideline published by the ASA, which describes that the patient's oxygenation, ventilation, circulation and temperature should be continually evaluated during anesthetic. [39]
Anaesthetized patients lose protective airway reflexes (such as coughing), airway patency, and sometimes a regular breathing pattern due to the effects of anaesthetics, opioids, or muscle relaxants. To maintain an open airway and regulate breathing, some form of breathing tube is inserted after the patient is unconscious. To enable mechanical ventilation, an endotracheal tube is often used, although there are alternative devices that can assist respiration, such as face masks or laryngeal mask airways. Generally, full mechanical ventilation is only used if a very deep state of general anaesthesia is to be induced for a major procedure, and/or with a profoundly ill or injured patient. That said, induction of general anaesthesia usually results in apnea and requires ventilation until the drugs wear off and spontaneous breathing starts. In other words, ventilation may be required for both induction and maintenance of general anaesthesia or just during the induction. However, mechanical ventilation can provide ventilatory support during spontaneous breathing to ensure adequate gas exchange.
General anaesthesia can also be induced with the patient spontaneously breathing and therefore maintaining their own oxygenation which can be beneficial in certain scenarios (e.g. difficult airway or tubeless surgery). Spontaneous ventilation has been traditionally maintained with inhalational agents (i.e. halothane or sevoflurane) which is called a gas or inhalational induction. Spontaneous ventilation can also be maintained using intravenous anaesthesia (e.g. propofol). Intravenous anaesthesia to maintain spontaneous respiration has certain advantages over inhalational agents (i.e. suppressed laryngeal reflexes) however it requires careful titration. Spontaneous Respiration using Intravenous anaesthesia and High-flow nasal oxygen (STRIVE Hi) is a technique that has been used in difficult and obstructed airways. [40]
General anaesthesia reduces the tonic contraction of the orbicularis oculi muscle, causing lagophthalmos (incomplete eye closure) in 59% of people. [41] In addition, tear production and tear-film stability are reduced, resulting in corneal epithelial drying and reduced lysosomal protection. The protection afforded by Bell's phenomenon (in which the eyeball turns upward during sleep, protecting the cornea) is also lost. Careful management is required to reduce the likelihood of eye injuries during general anaesthesia. [42] Some of the methods to prevent eye injury during general anesthesia includes taping the eyelids shut, use of eye ointments, and specially designed eye protective goggles.
Paralysis, or temporary muscle relaxation with a neuromuscular blocker, is an integral part of modern anaesthesia. The first drug used for this purpose was curare, introduced in the 1940s, which has now been superseded by drugs with fewer side effects and, generally, shorter duration of action. [43] Muscle relaxation allows surgery within major body cavities, such as the abdomen and thorax, without the need for very deep anaesthesia, and also facilitates endotracheal intubation.
Acetylcholine, a natural neurotransmitter found at the neuromuscular junction, causes muscles to contract when it is released from nerve endings. Muscle paralytic drugs work by preventing acetylcholine from attaching to its receptor. Paralysis of the muscles of respiration—the diaphragm and intercostal muscles of the chest—requires that some form of artificial respiration be implemented. Because the muscles of the larynx are also paralysed, the airway usually needs to be protected by means of an endotracheal tube. [6]
Paralysis is most easily monitored by means of a peripheral nerve stimulator. This device intermittently sends short electrical pulses through the skin over a peripheral nerve while the contraction of a muscle supplied by that nerve is observed. The effects of muscle relaxants are commonly reversed at the end of surgery by anticholinesterase drugs, which are administered in combination with muscarinic anticholinergic drugs to minimize side effects. Examples of skeletal muscle relaxants in use today are pancuronium, rocuronium, vecuronium, cisatracurium, atracurium, mivacurium, and succinylcholine. Novel neuromuscular blockade reversal agents such as sugammadex may also be used; it works by directly binding muscle relaxants and removing it from the neuromuscular junction. Sugammadex was approved for use in the United States in 2015, and rapidly gained popularity. A study from 2022 has shown that Sugammadex and neostigmine are likely similarly safe in the reversal of neuromuscular blockade. [44]
The duration of action of intravenous induction agents is generally 5 to 10 minutes, after which spontaneous recovery of consciousness will occur. [45] In order to prolong unconsciousness for the duration of surgery, anaesthesia must be maintained. This is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen and a volatile anaesthetic agent, or by administering intravenous medication (usually propofol). Inhaled anaesthetic agents are also frequently supplemented by intravenous analgesic agents, such as opioids (usually fentanyl or a fentanyl derivative) and sedatives (usually propofol or midazolam). Propofol can be used for total intravenous anaesthetia (TIVA), therefore supplementation by inhalation agents is not required. [46] General anesthesia is usually considered safe; however, there are reported cases of patients with distortion of taste and/or smell due to local anesthetics, stroke, nerve damage, or as a side effect of general anesthesia. [47] [48]
At the end of surgery, administration of anaesthetic agents is discontinued. Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (this occurs usually within 1 to 30 minutes, mostly depending on the duration of surgery). [6]
In the 1990s, a novel method of maintaining anaesthesia was developed in Glasgow, Scotland. Called target controlled infusion (TCI), it involves using a computer-controlled syringe driver (pump) to infuse propofol throughout the duration of surgery, removing the need for a volatile anaesthetic and allowing pharmacologic principles to more precisely guide the amount of the drug used by setting the desired drug concentration. Advantages include faster recovery from anaesthesia, reduced incidence of postoperative nausea and vomiting, and absence of a trigger for malignant hyperthermia. At present, TCI is not permitted in the United States, but a syringe pump delivering a specific rate of medication is commonly used instead. [49]
Other medications are occasionally used to treat side effects or prevent complications. They include antihypertensives to treat high blood pressure; ephedrine or phenylephrine to treat low blood pressure; salbutamol to treat asthma, laryngospasm, or bronchospasm; and epinephrine or diphenhydramine to treat allergic reactions. Glucocorticoids or antibiotics are sometimes given to prevent inflammation and infection, respectively. [6]
Emergence is the return to baseline physiologic function of all organ systems after the cessation of general anaesthetics. This stage may be accompanied by temporary neurologic phenomena, such as agitated emergence (acute mental confusion), aphasia (impaired production or comprehension of speech), or focal impairment in sensory or motor function. Shivering is also fairly common and can be clinically significant because it causes an increase in oxygen consumption, carbon dioxide production, cardiac output, heart rate, and systemic blood pressure. The proposed mechanism is based on the observation that the spinal cord recovers at a faster rate than the brain. This results in uninhibited spinal reflexes manifested as clonic activity (shivering). This theory is supported by the fact that doxapram, a CNS stimulant, is somewhat effective in abolishing postoperative shivering. [50] Cardiovascular events such as increased or decreased blood pressure, rapid heart rate, or other cardiac dysrhythmias are also common during emergence from general anaesthesia, as are respiratory symptoms such as dyspnoea. Responding and following verbal command, is a criterion commonly utilized to assess the patient's readiness for tracheal extubation. [6]
Postoperative pain is managed in the anaesthesia recovery unit (PACU) with regional analgesia or oral, transdermal, or parenteral medication. Patients may be given opioids, as well as other medications like non steroidal anti-inflammatory drugs and acetaminophen. [51] Sometimes, opioid medication is administered by the patient themselves using a system called a patient controlled analgesic. [52] The patient presses a button to activate a syringe device and receive a preset dose or "bolus" of the drug, usually a strong opioid such as morphine, fentanyl, or oxycodone (e.g., one milligram of morphine). The PCA device then "locks out" for a preset period to allow the drug to take effect, and also prevent the patient from overdosing. If the patient becomes too sleepy or sedated, they make no more requests. This confers a fail-safe aspect that is lacking in continuous-infusion techniques. If these medications cannot effectively manage the pain, local anesthetic may be directly injected to the nerve in a procedure called a nerve block. [53] [54]
In the recovery unit, many vital signs are monitored, including oxygen saturation, [55] [56] heart rhythm and respiration, [55] [57] blood pressure, [55] and core body temperature.
Postanesthetic shivering is common. Apart from causing discomfort and exacerbating pain, shivering has been shown to increase oxygen consumption, catecholamine release, risk for hypothermia, and induce lactic acidosis. [58] A number of techniques are used to reduce shivering, such as warm blankets, [59] [60] or wrapping the patient in a sheet that circulates warmed air, called a bair hugger. [61] [62] If the shivering cannot be managed with external warming devices, drugs such as dexmedetomidine, [63] [64] or other α2-agonists, anticholinergics, central nervous system stimulants, or corticosteroids may be used. [51] [65]
In many cases, opioids used in general anaesthesia can cause postoperative ileus, even after non-abdominal surgery. Administration of a μ-opioid antagonist such as alvimopan immediately after surgery can help accelerate the timing of hospital discharge, but does not reduce the development of paralytic ileus. [66]
Enhanced Recovery After Surgery (ERAS) is a society that provides up-to-date guidelines and consensus to ensure continuity of care and improve recovery and peri-operative care. Adherence to the pathway and guidelines has been shown to associate with improved post-operative outcomes and lower costs to the health care system. [67]
Most perioperative mortality is attributable to complications from the operation, such as haemorrhage, sepsis, and failure of vital organs. Over the last several decades, the overall anesthesia related mortality rate improved significantly for anesthetics administered. Advancements in monitoring equipment, anesthetic agents, and increased focus on perioperative safety are some reasons for the decrease in perioperative mortality. In the United States, the current estimated anesthesia-related mortality is about 1.1 per million population per year. The highest death rates were found in the geriatric population, especially those 85 and older. [68] A review from 2018 examined perioperative anesthesia interventions and their impact on anesthesia-related mortality. Interventions found to reduce mortality include pharmacotherapy, ventilation, transfusion, nutrition, glucose control, dialysis and medical device. [69] Interestingly, a randomized controlled trial from 2022 demonstrated that there is no significant difference in mortality between patient receiving handover from one clinician to another compared to the control group. [70]
Mortality directly related to anaesthetic management is very uncommon but may be caused by pulmonary aspiration of gastric contents, [71] asphyxiation, [72] or anaphylaxis. [4] These in turn may result from malfunction of anaesthesia-related equipment or, more commonly, human error. In 1984, after a television programme highlighting anaesthesia mishaps aired in the United States, American anaesthesiologist Ellison C. Pierce appointed the Anesthesia Patient Safety and Risk Management Committee within the American Society of Anesthesiologists. [73] This committee was tasked with determining and reducing the causes of anaesthesia-related morbidity and mortality. [73] An outgrowth of this committee, the Anesthesia Patient Safety Foundation, was created in 1985 as an independent, nonprofit corporation with the goal "that no patient shall be harmed by anesthesia". [74]
The rare but major complication of general anaesthesia is malignant hyperthermia. [75] [76] All major hospitals should have a protocol in place with an emergence drug cart near the OR for this potential complication. [77]
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.
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.
Isoflurane, sold under the brand name Forane among others, is a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritation with isoflurane. Isoflurane is given via inhalation.
Sevoflurane, sold under the brand name Sevorane, among others, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used as an inhalational anaesthetic for induction and maintenance of general anesthesia. After desflurane, it is the volatile anesthetic with the fastest onset. While its offset may be faster than agents other than desflurane in a few circumstances, its offset is more often similar to that of the much older agent isoflurane. While sevoflurane is only half as soluble as isoflurane in blood, the tissue blood partition coefficients of isoflurane and sevoflurane are quite similar. For example, in the muscle group: isoflurane 2.62 vs. sevoflurane 2.57. In the fat group: isoflurane 52 vs. sevoflurane 50. As a result, the longer the case, the more similar will be the emergence times for sevoflurane and isoflurane.
Propofol is the active component of an intravenous anesthetic formulation used for induction and maintenance of general anesthesia. It is chemically termed 2,6-diisopropylphenol. The formulation was approved under the brand name Diprivan. Numerous generic versions have since been released. Intravenous administration is used to induce unconsciousness after which anesthesia may be maintained using a combination of medications. It is manufactured as part of a sterile injectable emulsion formulation using soybean oil and lecithin, giving it a white milky coloration.
Spinal anaesthesia, also called spinal block, subarachnoid block, intradural block and intrathecal block, is a form of neuraxial regional anaesthesia involving the injection of a local anaesthetic or opioid into the subarachnoid space, generally through a fine needle, usually 9 cm (3.5 in) long. It is a safe and effective form of anesthesia usually performed by anesthesiologists that can be used as an alternative to general anesthesia commonly in surgeries involving the lower extremities and surgeries below the umbilicus. The local anesthetic with or without an opioid injected into the cerebrospinal fluid provides locoregional anaesthesia: true anaesthesia, motor, sensory and autonomic (sympathetic) blockade. Administering analgesics in the cerebrospinal fluid without a local anaesthetic produces locoregional analgesia: markedly reduced pain sensation, some autonomic blockade, but no sensory or motor block. Locoregional analgesia, due to mainly the absence of motor and sympathetic block may be preferred over locoregional anaesthesia in some postoperative care settings. The tip of the spinal needle has a point or small bevel. Recently, pencil point needles have been made available.
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.
Postoperative nausea and vomiting (PONV) is the phenomenon of nausea, vomiting, or retching experienced by a patient in the post-anesthesia care unit (PACU) or within 24 hours following a surgical procedure. PONV affects about 10% of the population undergoing general anaesthesia each year. PONV can be unpleasant and lead to a delay in mobilization and food, fluid, and medication intake following surgery.
Bispectral index (BIS) is one of several technologies used to monitor depth of anesthesia. BIS monitors are used to supplement Guedel's classification system for determining depth of anesthesia. Titrating anesthetic agents to a specific bispectral index during general anesthesia in adults allows the anesthetist to adjust the amount of anesthetic agent to the needs of the patient, possibly resulting in a more rapid emergence from anesthesia. Use of the BIS monitor could reduce the incidence of intraoperative awareness during anaesthesia. The exact details of the algorithm used to create the BIS index have not been disclosed by the company that developed it.
A post-anesthesia care unit (PACU) and sometimes referred to as post-anesthesia recovery or PAR, or simply recovery, is a part of hospitals, ambulatory care centers, and other medical facilities. Patients who received general anesthesia, regional anesthesia, or local anesthesia are transferred from the operating room suites to the recovery area. The patients are monitored typically by anesthesiologists, nurse anesthetists, and other medical staff. Providers follow a standardized handoff to the medical PACU staff that includes, which medications were given in the operating room suites, how hemodynamics were during the procedures, and what is expected for their recovery. After initial assessment and stabilization, patients are monitored for any potential complications, until the patient is transferred back to their hospital rooms.
Veterinary anesthesia is a specialization in the veterinary medicine field dedicated to the proper administration of anesthetic agents to non-human animals to control their consciousness during procedures. A veterinarian or a Registered Veterinary Technician administers these drugs to minimize stress, destructive behavior, and the threat of injury to both the patient and the doctor. The duration of the anesthesia process goes from the time before an animal leaves for the visit to the time after the animal reaches home after the visit, meaning it includes care from both the owner and the veterinary staff. Generally, anesthesia is used for a wider range of circumstances in animals than in people not only due to their inability to cooperate with certain diagnostic or therapeutic procedures, but also due to their species, breed, size, and corresponding anatomy. Veterinary anesthesia includes anesthesia of the major species: dogs, cats, horses, cattle, sheep, goats, and pigs, as well as all other animals requiring veterinary care such as birds, pocket pets, and wildlife.
Alfaxalone, also known as alphaxalone or alphaxolone and sold under the brand name Alfaxan, is a neuroactive steroid and general anesthetic which is used currently in veterinary practice as an induction agent for anesthesia and as an injectable anesthetic. Though it is more expensive than other induction agents, it often preferred due to the lack of depressive effects on the cardiovascular system. The most common side effect seen in current veterinary practice is respiratory depression when Alfaxan is administered concurrently with other sedative and anesthetic drugs; when premedications aren't given, veterinary patients also become agitated and hypersensitive when waking up.
Guedel's classification is a means of assessing the depth of general anesthesia introduced by Arthur Ernest Guedel (1883–1956) in 1920.
Flurothyl (Indoklon) is a volatile liquid drug from the halogenated ether family, related to inhaled anaesthetic agents such as diethyl ether, but having the opposite effects, acting as a stimulant and convulsant. A clear and stable liquid, it has a mild ethereal odor whose vapors are non-flammable. It is excreted from the body by the lungs in an unchanged state.
Postanesthetic shivering (PAS) is shivering after anesthesia.
Emergence delirium is a condition in which emergence from general anesthesia is accompanied by psychomotor agitation. Some see a relation to pavor nocturnus while others see a relation to the excitement stage of anesthesia.
Postoperative residual curarization (PORC) or residual neuromuscular blockade (RNMB) is a residual paresis after emergence from general anesthesia that may occur with the use of neuromuscular-blocking drugs. Today residual neuromuscular blockade is defined as a train of four ratio of less than 0.9 when measuring the response to ulnar nerve stimulation at the adductor pollicis muscle using mechanomyography or electromyography. A meta-analysis reported that the incidence of residual neuromuscular paralysis was 41% in patients receiving intermediate neuromuscular blocking agents during anaesthesia. It is possible that > 100,000 patients annually in the USA alone, are at risk of adverse events associated with undetected residual neuromuscular blockade. Neuromuscular function monitoring and the use of the appropriate dosage of sugammadex to reverse blockade produced by rocuronium can reduce the incidence of postoperative residual curarization. In this study, with usual care group receiving reversal with neostigmine resulted in a residual blockade rate of 43%.
The following outline is provided as an overview of and topical guide to anesthesia:
Total intravenous anesthesia (TIVA) refers to the intravenous administration of anesthetic agents to induce a temporary loss of sensation or awareness. The first study of TIVA was done in 1872 using chloral hydrate, and the common anesthetic agent propofol was licensed in 1986. TIVA is currently employed in various procedures as an alternative technique of general anesthesia in order to improve post-operative recovery.
Approved by the House of Delegates on October 25, 2005, and last amended on October 17, 2018
Approved by the ASA House of Delegates on October 21, 1986, last amended on October 20, 2010, and reaffirmed on December 13, 2020