General anaesthesia facts for kids

Quick facts for kids General anaesthesia
Equipment used for anaesthesia in the operating room
Specialty	Anaesthetics
Uses	Facilitating surgery, terminal sedation
Complications	Anaesthesia awareness, overdose, death
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. 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 (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.

History

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.

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. 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.

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.

Purpose

General anaesthesia has many purposes and is routinely used in almost all surgical procedures. An appropriate surgical anesthesia should include the following goals:

1. Hypnosis/Unconsciousness (loss of awareness)
2. Analgesia (loss of response to pain)
3. Amnesia (loss of memory)
4. Immobility (loss of motor reflexes)
5. Paralysis (skeletal muscle relaxation and normal muscle relaxation)

Instead of receiving continuous deep sedation, such as via benzodiazepines, dying patients may choose to be completely unconscious as they die.

Anesthesia and the brain

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. An example of a brain disruption would be a concussion. 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.

Induction

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.

Maintenance

The duration of action of intravenous induction agents is generally 5 to 10 minutes, after which spontaneous recovery of consciousness will occur. 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 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. 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.

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).

Emergence

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. 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.

See also

• Local anaesthesia