Anesthesiology and Reanimation · Year 6 · Medical University of Sofia

Anesthesia - definition, history notes. General and local anesthesia. General anesthesia - definition, types: volatile, intravenous, rectal.

Free notes for topic 01 of the Anesthesiology and Reanimation syllabus, open without an account. Written by a senior student against the syllabus question and checked line by line by a second student before publishing. How content is made

Updated 8 November 2026

Summary

note

Anaesthesia is the abolition of sensation, and analgesia is the abolition of pain. General anaesthesia is a pharmacologically induced, reversible state of unconsciousness that combines unconsciousness, amnesia, analgesia, depression of reflexes and muscle relaxation. It is produced by inhaled (volatile) agents, by intravenous agents, or by drugs given rectally. Local and regional anaesthesia remove sensation from one part of the body and leave the patient conscious. The modern practice of anaesthesia began with the public demonstration of ether in Boston on 16 October 1846.

1. Definition of anaesthesia

note

The word anaesthesia comes from the Greek an- (without) and aisthēsis (sensation). Anaesthesia is defined as the abolition of sensation. When the effect of ether was discovered, "anaesthesia" was adopted as the name for the new phenomenon.

Analgesia

note

Analgesia is defined as the abolition of pain. Analgesia is one component of a general anaesthetic.

2. History of anaesthesia

note

The milestones below are listed in date order.

Year	Event
1772	Nitrous oxide is isolated.
1799	The anaesthetic properties of nitrous oxide are described.
1842	Dr Crawford Long, an American physician, is recognised as the first to give ether vapour by inhalation to induce surgical anaesthesia. His work was not publicised at the time.
1844	Dr Wells demonstrates the use of nitrous oxide for tooth extraction.
1846	Dr William Morton, a dentist, gives ether to Edward Gilbert Abbott for a tumour removal performed by Dr John Collins Warren at Massachusetts General Hospital, on 16 October 1846.
1847	Dr James Simpson, in England, gives ether to a woman in labour to relieve the pain of labour.
1853	Dr John Snow gives chloroform to Queen Victoria during the birth of Prince Leopold.
1878	The endotracheal tube is developed. It allows controlled ventilation and the direct administration of anaesthetic gases into the lungs, improving the precision of anaesthesia delivery.
1885	Dr William Halsted introduces local anaesthesia with cocaine.
1934	Thiopental is first used.
1942	Curare is used as a muscle relaxant, which marks the beginning of the "Age of Anaesthesia" and makes more complex surgery possible.
1970s	Monitoring technologies, including pulse oximetry and capnography, are developed and improve patient safety.

The first public demonstration

note

The operation of 16 October 1846 at Massachusetts General Hospital is widely considered the first public demonstration of anaesthesia. It introduced the practice to the medical community. For this reason 16 October is often celebrated as the birthday of anaesthesiology.

Studio portrait of Dr John Collins Warren, a man in a dark coat seated beside a skull, the surgeon named for the 1846 operation

John Snow and the first anaesthesiologist

note

Dr John Snow is regarded as the first anaesthesiologist, because he was the first to devote his medical practice to the administration of anaesthetics.

3. General anaesthesia: definition and components

note

General anaesthesia is defined here by its components, followed by the practical phases of an anaesthetic.

General anaesthesia defined

note

General anaesthesia is a pharmacologically induced, reversible state of unconsciousness. It is characterised by several key components, which are described below. Each component can be produced by a different drug, so a general anaesthetic is usually a combination of agents rather than a single one.

The triad of general anaesthesia

note

The classic triad of general anaesthesia has three elements:

Unconsciousness: the patient is fully unaware of the surroundings and has no memory of the procedure. This includes the suppression or absence of reflexes.
Analgesia: the patient is free from pain, which ensures comfort and prevents the physiological stress response to surgical stimuli.
Muscle relaxation: the muscles are relaxed to make surgical access and manipulation possible and to prevent movement during the procedure.

Components of general anaesthesia

note

Five components are described in full. The examples are the agents named in the lectures.

Component	What it means	Examples
Unconsciousness	The patient is fully unaware of the surroundings and does not remember the operation.	Inhalational and intravenous agents.
Amnesia	A state similar to deep sleep or hypnosis, so that perioperative events cannot be recalled.	Benzodiazepines such as midazolam, or inhalational agents such as sevoflurane.
Analgesia	The patient is free from pain.	Opioids such as fentanyl and morphine, non-opioid analgesics, and adjuncts such as ketamine.
Depression of reflexes	Significant suppression of autonomic and somatic reflexes. This helps to keep the circulation stable and prevents involuntary movement.	Agents that depress the reflexes during the anaesthetic.
Muscle relaxation	A profound reduction in muscle tone. It gives the surgeon exposure and prevents movement. It is particularly important in abdominal and thoracic operations, and in surgeries requiring a precise and immobile field.	Neuromuscular blocking drugs (muscle relaxants).

The practical phases of an anaesthetic

note

Induction is the period that begins with the administration of an anaesthetic agent and ends when a stable surgical stage of anaesthesia is established.
Maintenance is sustaining the state of anaesthesia throughout the surgical procedure.
Recovery (emergence) is the period from the discontinuation of the anaesthetic agents to the full return of consciousness and the restoration of physiological function.

4. Types of general anaesthesia

note

General anaesthesia is given by inhalational (volatile) agents, by intravenous agents, or by rectal administration of certain drugs.

Volatile (inhalational) general anaesthesia

note

Inhalation anaesthesia is the delivery of gases or volatile liquids through the respiratory system for the induction and maintenance of general anaesthesia. The gases are nitrous oxide and xenon. The volatile liquids are halothane, enflurane, isoflurane, sevoflurane and desflurane. Inhalational anaesthetics act on the central nervous system to produce loss of consciousness and loss of response to noxious stimuli.

Five inhalational agents are currently used to induce or maintain general anaesthesia: nitrous oxide, isoflurane, sevoflurane, desflurane and xenon. The agents themselves, their pharmacokinetics and the equipment used to give them are described in the next topic.

Intravenous general anaesthesia

note

Intravenous anaesthetics are agents that induce loss of consciousness in one arm-brain circulation time. Compared with inhalational agents, intravenous induction gives a smoother and more rapid induction of anaesthesia.

Intravenous anaesthetics are used for:

induction of anaesthesia;
maintenance, either alone or together with an inhalational agent;
sedation during regional anaesthesia;
sedation in the intensive care unit;
treatment of status epilepticus.

The intravenous agents named in the lectures are propofol, etomidate, ketamine and thiopental. Benzodiazepines (midazolam, diazepam and lorazepam) are often given with them as sedatives.

Choosing intravenous or inhalational induction

note

Induction flow chart: intravenous induction gives faster onset and avoids the excitatory phase of anaesthesia, while inhalational induction is used when IV access is difficult, when difficult intubation is anticipated, and for patient preference such as children

Intravenous induction is chosen for its faster onset, and because it avoids the excitatory phase of anaesthesia. Inhalational induction is chosen when intravenous access is difficult, when difficult intubation is anticipated, and when the patient prefers it, as with children. A handwritten note on the lecture slide adds that a small child without intravenous access is an example.

Rectal general anaesthesia

note

Some drugs have been given per rectum. The lectures mention the rectal route for two agents. Thiopental has previously been used rectally, although its onset by this route is slow. Ketamine can be given orally or rectally for sedation, and by the epidural route for analgesia.

5. Local and regional anaesthesia

note

Local and regional techniques remove sensation from part of the body, and the patient stays conscious.

Local anaesthesia

note

Local anaesthetics produce a transient and reversible loss of sensation (analgesia) and muscle relaxation in a circumscribed region of the body. The patient stays conscious, and the process is normally reversible.

Regional anaesthesia

note

Regional anaesthesia is any technique that induces the absence of sensation in part of the body. In the figure below, the needle is placed in the epidural space of the spinal column, and the region supplied by that level of the spinal cord is desensitised.

Regional anaesthesia by epidural needle placement: spinal column, epidural space, the needle, and a body diagram with the desensitised region

Regional anaesthesia is used to:

provide anaesthesia for a surgical procedure;
provide analgesia after an operation or during labour and delivery;
treat patients with chronic pain syndromes and cancer.

Types of local and regional anaesthesia

note

surface (topical) anaesthesia;
peripheral nerve blocks;
intravenous regional anaesthesia (IVRA);
epidural anaesthesia;
spinal (intrathecal) anaesthesia.

6. General and local anaesthesia compared

note

The choice between a general and a local technique depends on the site, the extent of the surgery and the patient.

Features of general and local anaesthesia

note

Feature	General anaesthesia	Local anaesthesia
Site of action	CNS	Peripheral nerves
Area of body involved	Whole body	Restricted area
Consciousness	Lost	Unaltered
Care of vital functions	Essential	Usually not needed
Poor health patients	Risky	Safer
Non-cooperative patients	Possible	Not possible
Major surgery	Preferred	Cannot be preferred
Minor surgery	Not preferred	Preferred

Two panels: general anaesthesia, with a patient breathing through a face mask, and regional anaesthesia (epidural, spinal-subarachnoid, peripheral nerve block), with a patient awake

Why regional anaesthesia is not always chosen

note

Regional anaesthesia is not always the right choice, for several reasons:

hypotension;
risk of toxicity from the local anaesthetic;
many patients prefer to be asleep;
the technique requires specific skills;
the patient can talk and may be anxious during the operation;
it is not reliable for surgery longer than two hours.

All 34 Anesthesiology and Reanimation topics · exam study support, not clinical guidance. SuperMed is not affiliated with the Medical University of Sofia.

Start free. No card needed.

Every account starts free, with Medical Ethics, Urology and Computer Science open in full and free topics in Cytology, Latin Language, Medical Chemistry, Medical Physics, Medical Biology, Anatomy, Biophysics, Medical Psychology, MCS (Disaster Medicine), Physiology, Biochemistry, Social Medicine, Medical Genetics, General Pathology, Pharmacology, Pathophysiology, Microbiology, Internal Medicine, Nephrology, Cardiology, Pulmonology, Gastroenterology, Internal Medicine (Clinical), Obstetrics and Gynecology, Pediatrics, Forensic Medicine and Deontology, Physiotherapy and Rehabilitation, Anesthesiology and Reanimation, Dental Materials, Preclinics of Prosthetic Dental Medicine, Medical Psychology (Dental Medicine), SMME (Social Medicine & Medical Ethics), Preclinics of Pediatric Dental Medicine, Hygiene and Epidemiology, General Surgery, Preclinics of Conservative Dental Medicine, Preclinics of Oral and Maxillofacial Medicine, Dental Public Health, Dental Prophylaxis, Diagnostic Imaging, Dental Allergology, Dental Implantology, Physiotherapy, Cytology & Histology, Medical Chemistry, Medical Physics, Anatomy I, Biophysics and Medical Biology. Super opens the rest. Super is €14.99 a month.

Create a free account