Introduction to Anesthesiology

Anaesthesia, derived from the Greek words "an-" meaning "without" and "aisthēsis" meaning "sensation," traditionally referred to the state of having sensation, including pain, temporarily blocked or removed. It is a pharmacologically induced and reversible condition characterized by amnesia, analgesia (lack of pain perception), loss of responsiveness, loss of skeletal muscle reflexes, and decreased flight or fight response, which can occur simultaneously. This state allows patients to undergo surgical procedures and other medical interventions without experiencing distress and pain.

Anaesthesia can also be defined as a "reversible lack of awareness," encompassing total lack of awareness (as seen in general anaesthesia) or lack of awareness of a specific part of the body, such as during a spinal anaesthetic.

The term "anesthesia" was suggested by Oliver Wendell Holmes Sr. in 1846 to describe the sleep-like state induced by the administration of ether.

• First successful public demonstration of anesthesia was on 16th October 1846 at Massachusetts Gen Hosp, Boston, USA by W.T.G. Morton
• Colton popularized the use of nitrous oxide in anesthesia in 1863.
• Chloroform was introduced into clinical anesthesia in 1847 by James Young Simpson, a professor of midwifery in Edinburgh University.
• Dr. John Snow popularized the use of chloroform in 1853 by administering it for analgesia in labor on Queen Victoria for the birth of her 8th child, Prince Leopold.
• The oral airway was introduced by Hewitt in 1913
• Edmund Boyle introduced the Boyle’s anesthetic machine in 1917
• Endotracheal anesthesia with wide-bore tube was popularized in 1920 by Magill.
• IV anesthesia was popularized by Lundy of Mayo Clinic in 1934 with thiopentone
• Griffith and Johnson of Montreal, Canada introduced d-tubocurarine into clinical anesthesia for muscle relaxation in 1942.
• Koller of Vienna introduced the use of topical cocaine as a topical anesthesia in 1884

The practice of anaesthesia has expanded well beyond rendering patients insensible to pain during surgery or obstetric delivery.

The specialty is unique in that it requires a working familiarity with most other specialties including surgery and its subspecialties, internal medicine, pediatrics, and obstetrics as well as clinical pharmacology, applied physiology, and biomedical technology.

Scope of Anaesthesia Practice

• Assessment of, preparation for, and preparation of patients for anaesthesia.
• Relief and prevention of pain during and following surgical, obstetric, therapeutic, and diagnostic procedures.
• Monitoring and maintenance of normal physiology during the perioperative period.
• Management of critically ill patients.
• Diagnosis and treatment of acute, chronic, and cancer-related pain.
• Clinical management and teaching of cardiac and pulmonary resuscitation.
• Evaluation of respiratory function and application of respiratory therapy.
• Conduct of clinical, translational, and basic science research.
• Supervision, teaching, and evaluation of the performance of both medical residents and paramedical personnel involved in perioperative care.
• Administrative involvement in healthcare facilities, organizations, and medical schools necessary to implement these responsibilities.

Types of anesthesia include:

1. Local anaesthesia
2. Regional anaesthesia
3. General anaesthesia
4. Dissociative anaesthesia

Types of Anaesthesia

Local anaesthesia: Inhibits sensory perception within a specific location on the body, such as a tooth or the urinary bladder.

Regional anaesthesia: Renders a larger area of the body insensate by blocking transmission of nerve impulses between a part of the body and the spinal cord. Two frequently used types of regional anaesthesia are spinal anaesthesia and epidural anesthesia.

General anaesthesia: Refers to inhibition of sensory, motor, and sympathetic nerve transmission at the level of the brain, resulting in unconsciousness and lack of sensation.

Dissociative anaesthesia: Uses agents that inhibit transmission of nerve impulses between higher centers of the brain (such as the cerebral cortex) and the lower centers, such as those found within the limbic system.

The practice of modern anaesthesia evolved from the first public demonstration of ether anaesthesia at Massachusetts General Hospital, Boston, on October 16th, 1846. Before this period, several methods were tried to alleviate pain.

Methods Used to Alleviate Pain Before Ether:

• Opium poppy (benzylisoquinoline alkaloids containing morphine and codeine)
• Coca leaves placed in wounds to relieve pain
• Mandrake roots, alcohol, and phlebotomy (to the point of unconsciousness) were used to allow surgeons to operate
• Refrigeration anaesthesia (cold) and carotid compression (inducing unconsciousness)
• Mesmerism
• Regional anaesthesia consisting of compression of nerve trunks (nerve ischemia)
• In South America, surgeons chewed coca leaves and spat saliva into operative wounds.

• Curare was introduced in 1942 by Harold Griffith and Enid Johnson in Canada.
• It facilitated tracheal intubation and provided muscle relaxation.
• Before the introduction of curare, muscle relaxation was achieved with large doses of inhalational anesthetic, resulting in respiratory and circulatory depression and prolonged emergence.
• Later additions to neuromuscular blocking drugs included gallamine, decamethonium, metocurine, alcuronium, and pancuronium, but many of these had side effects.
• In the search for drugs with fewer side effects, vecuronium, atracurium, pipecuronium, doxacurium, rocuronium, and cis-atracurium have been introduced.
• Succinylcholine (suxamethonium) was released in 1951 and is a standard agent for facilitating tracheal intubation due to its rapid onset and offset.
• Side effects of succinylcholine led to the introduction of mivacurium, which has minimal side effects but a slower onset of action and prolonged duration compared to succinylcholine.
• Rocuronium is now the alternative agent of choice for facilitating tracheal intubation.

Neuromuscular Blocking Drugs

Depolarizers (Cause vagolysis)

• Succinylcholine (suxamethonium)

Non-Depolarizers (Aminosteroids)

• Pancuronium
• Vecuronium
• Pipecuronium
• Rocuronium
• Doxacurium
• Metocurine
• Gallamine (crosses placenta, contraindicated in obstetrics)

Non-Depolarizers (Benzylisoquinolinium, Associated with histamine release)

• D-tubocurarine
• Atracurium
• Cis-atracurium
• Mivacurium

• Local anaesthesia owes its origin to Carl Koller, an ophthalmologist, who used topical cocaine for surgical anaesthesia of the eye.
• August Bier administered the first spinal anaesthesia in 1898 using 0.3ml of cocaine.
• He described intravenous regional anaesthesia (IVRA, Bier’s technique) in 1908.
• Lumbar epidural anaesthesia was described in 1921 by Fidel Pages.
• Local anaesthetics later introduced between 1930 and 1972:
• Dibucaine
• Tetracaine
• Lidocaine
• Chloroprocaine
• Mepivacaine
• Prilocaine
• Bupivacaine
• Etidocaine
• Ropivacaine and levobupivacaine are new agents similar to bupivacaine but less cardiotoxic.

Classification of Local Anaesthetic Agents

The state of general anaesthesia can be described in terms of 3 basic components:

1. Unconsciousness (Hypnosis): With the development of unconsciousness, the patient is oblivious to all sensation, but somatic and autonomic reflexes to pain and noxious stimuli can still occur. Unconsciousness is achieved with IV and inhalational anaesthetics.
2. Analgesia (Areflexia): Withdrawal of a limb or flight (somatic reflexes) and hypertension, tachycardia, and sweating (autonomic reflexes) are part of the subconscious reaction to pain. These potent reflexes must be subdued during anaesthesia with analgesics such as opioids, NSAIDs, and paracetamol.
3. Muscle Relaxation: The degree of muscle relaxation required varies according to the operation. In general, only a mild degree of muscle relaxation is necessary for superficial operations on the body wall or extremities, but moderate to profound muscle relaxation is required for operations within body cavities. Muscle relaxation is achieved with neuromuscular blocking drugs.