Anesthesiology: History and Basic Concepts

Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. General anesthesia is induced via the administration of gaseous or injectable agents before surgical procedures or other medical interventions. On the other end of the spectrum is local anesthesia, which is achieved via the use of topical agents or the local administration of injectable anesthetics to the area of concern. The use of anesthetics has been well documented in history, but the practice of modern anesthesiology only began by the end of the 18th century.

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Anesthesiology is the field of medicine focusing on interventions that bring about a state of anesthesia, which is characterized by a reversible loss of consciousness, as well as analgesia, amnesia, and muscle relaxation.

State of anesthesia

  • Induced via the administration of gaseous or injectable agents before surgical procedures or other medical interventions
  • Effects:
    • Analgesia: relief from pain or the prevention of pain
    • Amnesia: loss of awareness and/or memory of pain/experience
    • Hypnosis: temporary unconsciousness or the absence of anxiety
    • Paralysis: adequate muscle relaxation

Certified personnel who perform and manage anesthesia

  • Anesthesiologists
  • Certified registered nurse anesthetists
  • Anesthesia assistants

Settings where anesthesia is performed

  • ORs
  • EDs
  • Endoscopy suites
  • Interventional radiology suites
  • Interventional cardiology laboratories
  • Ambulatory surgical centers (centers for “day surgery”)
  • Post-anesthesia care units (PACUs)
  • ICUs


  • The practice of medicine was transformed in the middle of the 19th century with the discovery of general anesthesia.
  • In previous centuries, surgery was performed as a last resort and desperate measure due to the unbearable pain it caused.
  • The use of chemical compounds to induce a state of anesthesia in modern medicine dates back to the 18th century with the introduction of inhaled anesthetics.
Historical landmarks in the development of anesthesia
4000 BCE–0 CEThe use of opium poppy; herbal remedies using Hyoscyamus niger, Mandragora, and aconitum; and acupuncture performed with bones, cannabis vapors, and carotid compression is documented in records from ancient China, Greece, and Egypt.
1799–1850 CE
  • 1799: Humphry Davy observes that nitrous oxide (N2O) relieves physical pain.
  • 1805: Friedrich Sertürner isolates morphine from opium.
  • 1845: Horace Wells inhales N2O as anesthesia for his own dental extraction at Massachusetts General Hospital.
  • 1845: William Morton is the 1st to publicly and successfully demonstrate the use of ether anesthesia for surgery.
  • 1847: James Simpson administers chloroform to relieve pain during childbirth.
1850–1900 CE
  • 1853: Charles Pravaz and Alexander Wood invent the hollow hypodermic needle and create the syringe.
  • 1853 & 1857: John Snow popularizes obstetric anesthesia by using chloroform during Queen Victoria’s births.
  • 1863: Quincy Colton reintroduces N2O as an inhalation anesthetic.
  • 1884: Karl Koller introduces cocaine as an ophthalmic anesthetic.
  • 1898: August Bier conducts the 1st spinal block using cocaine.
1900–1925 CE
  • 1901: Caudal epidural analgesia is described.
  • 1902: The words “anesthesiology” and “anesthesiologist” are coined.
  • 1923: Isabella Herb administers the ethylene-oxygen surgical anesthetic.
1925–1950 CE
  • 1929: John S. Lundy popularizes the use of the IV anesthetic thiopental (Pentothal).
  • 1942: The 1st successful use of a muscle relaxant as an anesthetic is recorded.
  • 1944: Lidocaine is introduced as a local anesthetic.
1950–1975 CE
  • 1954: Perioperative mortality related to anesthesia begins to be recorded.
  • 1956: Michael Johnstone clinically introduces halothane, the 1st modern-day brominated general anesthetic.
  • 1960: Joseph Artusio begins human trials of the inhalational anesthetic methoxyflurane.
  • 1964: Günter Corssen begins human trials of the dissociative IV anesthetic ketamine.
  • 1966: Robert Virtue begins human trials of the inhalational anesthetic enflurane.
  • 1972: The inhalational anesthetic isoflurane is introduced into clinical practice.
1975–2000 CE
  • 1992: The inhalational anesthetic desflurane is introduced into clinical practice.
  • 1993: A safe and systematic approach to ventilation during general anesthesia is established.
  • 1994: The inhalational anesthetic sevoflurane is introduced into clinical practice.
2000 CE–presentThe American Society of Anesthesiologists establishes a Simulation Education Network (SEN) to continue educating and certifying anesthesiologists.

Preoperative Evaluation

Focused evaluation and planning for anesthesia should be completed in advance for all surgeries, interventions, and procedures.

  • Risk stratification is an important part of preoperative planning.
  • Low-risk individuals can be evaluated immediately before anesthesia on the day of the procedure. 
    • Low-risk individuals are those who are:
      • < 65 years of age
      • Having stable and adequately controlled medical conditions
      • Undergoing low-risk procedures
    • Risk increase with:
      • Age
      • Complexity of comorbid medical conditions
      • Complexity of planned anesthesia and/or medical/surgical procedures
      • Duration of planned anesthesia and/or medical/surgical procedures
  • Intermediate-to-high risk may need stabilization and/or optimization of comorbid medical conditions prior to anesthesia and/or planned procedures.
  • Emergency anesthesia and/or planned procedure necessitate the initiation of measures with minimal preparation time and are, by their very nature, high risk.


  • Assessing medical status and readiness for the planned procedure
  • Reducing the risks of anesthesia and surgery
  • Creating an anesthetic plan and preparing the individual

Components of preoperative evaluation

  • Clinical evaluation:
    • Medical history
    • Current medications
    • History of prior anesthesia and surgeries
    • Physical examination
  • Risk assessment:
    • Evaluation of factors that increase the likelihood of perioperative morbidity and mortality
    • An objective observation commonly used by the anesthesiology team to create ventilation and intubation plans
    • Assessment of the anatomy of the head and neck to determine the difficulty of intubation:
      • Mallampati classification is used to assess ease of airway access for intubation.
      • Graded I–IV based on the difficulty associated with oropharyngeal characteristics
    • Inclusion of the individual’s underlying health problems
    • Identification of medication allergies
    • Response to prior anesthesia methods
    • Other aids in risk assessment include:
      • Prognostic biomarkers (e.g., B-type natriuretic peptide)
      • CBC (to rule out anemia, infection, thrombocytopenia)
      • Electrolyte panel (to evaluate electrolyte imbalance and metabolic disturbance)
      • Coagulation studies (to evaluate for coagulopathy)
      • Creatinine, GFR
      • CRP
      • Functional status/ability to engage in daily activities as reported subjectively by the individual
  • Optimization of diseases and comorbidities:
    • Optimally managing and treating comorbidities before surgery and anesthesia to decrease morbidity and mortality
    • Common examples include:
      • Hypertension
      • Ischemic heart disease
      • Heart failure
      • Obstructive sleep apnea
      • Diabetes mellitus
      • Thyroid disease
      • Anemia
    • Smoking cessation at least 2 weeks before surgery
  • Preoperative testing:
    • Diagnostic testing for preexisting conditions and comorbidities should be obtained preoperatively to monitor conditions postoperatively.
    • Patient-specific testing, for example:
      • If blood transfusion is anticipated, blood typing and crossmatching are imperative before surgery and anesthesia.
      • If a woman of childbearing age is to undergo surgery and anesthesia, a pregnancy test is indicated to avoid fetal loss.
Summary of high-risk conditions that warrant preoperative assessment and perioperative planning
Preexisting disease/conditionDiagnostic testing
Age > 65 yearsAlbumin, creatinine, hemoglobin
Alcohol abuseECG, electrolytes, hemoglobin, liver function test, platelet count, PT/INR
AnemiaCBC, creatinine, ferritin, iron, transferrin saturation, TSH, T3, T4, vitamin B12, blood typing, screening
Cardiac diseaseBNP, ECG, +/- stress testing
DiabetesCreatinine, HbA1c, glucose
Liver diseaseAlbumin, BUN, creatinine, electrolytes, hemoglobin, liver function test, platelet count, PT/INR
Pulmonary diseaseChest X-ray
Thyroid diseaseT3, T4, TSH
T3: triiodothyronine
T4: thyroxine
TSH: thyroid-stimulating hormone
Table: Risk-stratification categories used to classify perioperative risk based on subject characteristics (preoperative risk classification by the American Society of Anesthesiologists)
American Society of Anesthesiologists physical status classificationDefinitionExamples
IA normal, healthy individual without known diseasesHealthy, nonsmoker, minimal alcohol use
IIAn individual with mild systemic diseaseCurrent smoker, mild hypertension, mild lung disease
IIIAn individual with severe systemic diseasePoorly controlled hypertension or diabetes mellitus, chronic obstructive pulmonary disease
IVAn individual with severe systemic disease that is a constant threat to lifeRecent MI, severely reduced ejection fraction, sepsis, ARDS
VAn individual who is not expected to survive without the intended operationBrain bleed, ruptured aneurysm, massive trauma
VIAn individual declared brain dead or whose organs are being harvested
Modified Mallampati classification

Mallampati classification to assess ease of airway access for intubation:
I: The soft palate, fauces, uvular, and pillars are visible.
II: The soft palate, fauces, and part of the uvula are visible.
III: The soft palate and base of the uvula are visible.
IV: Only the hard palate is visible.

Image: “Modified Mallampati classification” by Department of Anaesthesiology, Copenhagen University Hospital, Nordsjælland Hospital, 3400, Hillerød, Denmark. License: CC BY 2.0

Patient education

  • Essential for the affected individual’s satisfaction and safety
  • Provides information on how to reduce the risks of surgery and anesthesia:
    • Stop smoking before and after surgery.
    • Medications that are to be taken or avoided before surgery
    • Cessation of eating and drinking by midnight prior to the procedure to prevent aspiration of gastric contents
    • Sanitary measures prior to the procedure (e.g., antibacterial soap prep)
  • Involve the individual in the decision-making and planning steps.
  • Answer all questions.
  • Address all concerns.

Informed consent

  • Based on the premise that individuals have the right to receive information and ask questions about recommended treatments so that they can make well-informed decisions about their care
  • Treating physicians should discuss all risks and complications associated with the procedure and associated anesthesia before asking for informed consent.
  • Results in the individual’s agreement or refusal to undergo a specific medical intervention
  • Usually obtained in a written format

Anesthesia plan

The creation of a plan for anesthesia involves the consideration of:

  • Surgery requirements
  • Duration of surgery
  • Comorbidities
  • Postoperative considerations
  • The individual’s preference
  • Preferences of the surgeon and the anesthesiologist

Postoperative care

Considerations include:

  • Pain management
  • Hemodynamics
  • Pulmonary hygiene
  • Early interventions
  • Requirement of ICU vs appropriate hospital wing vs outpatient care for recovery

Types of Anesthesia

Several types of anesthesia are used for surgery or other medical procedures. Choosing the appropriate type depends on:

  • Procedure to be performed
  • Procedure requirements
  • Area that needs to be anesthetized
  • Duration of surgery
  • Patient-specific comorbidities
  • Postoperative anesthesia plans and considerations
  • Individual’s preference
  • Preferences of the provider and the anesthesiologist

Types of anesthesia:

  • General
  • Neuraxial
  • Peripheral nerve block
  • IV regional anesthesia
  • Monitored anesthesia care (MAC)

General anesthesia

  • Drug-induced loss of consciousness
  • Affects the whole body
  • Appropriate for most major surgical procedures
  • The goal of general anesthesia is to attain:
    • Unconsciousness
    • Analgesia
    • Muscle relaxation with immobility
    • Blockage of noxious stimuli during surgery

The 3 stages of general anesthesia are:

  1. Induction:
    • Accomplished via inhalation or IV
    • Airway management is integral and is initially via a face mask followed by the transition to endotracheal intubation.
  2. Maintenance:
    • Typically achieved via a primary inhalation technique using IV drugs
    • Goal is to reduce the total dosage of any 1 agent; thus, anesthetic combinations are commonly used.
  3. Emergence:
    • Involves removing anesthetic agents and reversing their residual effects for the return of consciousness and movement
    • Extubation can be performed when the individual can protect their airway, follow simple commands, and ventilate without assistance.
Table: Induction agents
ClassCommonly used drugs
IV sedative-hypnoticsPropofol, etomidate, ketamine
IV adjuvantsOpioids, lidocaine, midazolam
Inhalation agentsNitrous oxide, halothane, isoflurane
Neuromuscular blockersVecuronium, rocuronium, succinylcholine

Neuraxial anesthesia

  • A type of anesthesia that involves anesthetizing the nerves of the CNS
  • Neuraxial anesthesia is commonly used for lower abdominal and lower extremity surgeries or for pain relief.
  • 2 main types:
    • Spinal anesthesia: A needle is inserted between the vertebrae and the anesthetic is injected directly into the subarachnoid space.
    • Epidural anesthesia: A catheter is inserted between the vertebrae and the anesthetic is injected directly into the epidural space.
Localization of epidural

Epidural anesthesia is commonly used during childbirth:
Anesthesiologists place a catheter between the L3 and L4 vertebrae into the epidural space for the continuous delivery of local anesthetics. Common epidural agents include lidocaine, bupivacaine, and ropivacaine.

Image: “Localization of epidural” by Gurch. License: Public Domain

Peripheral nerve blocks

  • A type of regional anesthesia
  • The anesthetic is injected near a specific nerve or a bundle of nerves to block sensations of pain from a specific area of the body.
  • Commonly used for procedures involving the upper and lower extremities
  • Fluoroscopy or ultrasound guidance is often used for needle or catheter insertion and placement.
  • Long-acting local anesthetics provide prolonged postoperative analgesia.
Ultrasound-guided nerve block

Ultrasound-guided nerve block:
Ultrasound demonstrating a needle (row of white arrowheads) and an anesthetic solution (dark area surrounding the ulnar nerve) injected around the ulnar nerve for successful peripheral nerve block. Anesthetic blockade of a nerve bundle blocks all nerves downstream, providing adequate analgesia for a procedure. Notice how the anesthesiologist identified the ulnar artery to avoid puncturing it.

Image: “Ultrasound-guided nerve block” by Richard Amini et al. License: CC BY 4.0

Intravenous regional anesthesia (IVRA)

  • Also known as a “Bier block”
  • Less invasive alternative to peripheral nerve blocks
  • Suitable for shorter procedures of the hand, forearm, and foot
  • Estimated blockage time: approximately 1.5 hours
  • Appropriate for surgeries lasting 1 hour or less
  • Procedure:
    1. Compression and exsanguination of the extremity using an Esmarch bandage
    2. A tourniquet is used to keep the blood out of the extremity and retain anesthesia.
    3. An infusion of 0.5% lidocaine via a peripheral vein establishes anesthesia.
    4. The surgeon can work in a completely anesthetized and bloodless surgical field for a limited time.
Bier block

Basic setup for a Bier block

Image by Lecturio.

Monitored anesthesia care

  • Involves monitoring an individual’s vitals and administering sedatives, anxiolytics, or analgesics accordingly
  • Commonly used during outpatient procedures
  • If needed, anesthesiologists are ready to convert to general anesthesia at any time.
  • A common example is administering propofol whenever an anesthesiologist deems it necessary during an endoscopy based on the individual’s vitals and mobility.

Perioperative Monitoring

Standard monitors

  • Used by the anesthesiology team during a procedure
  • Includes:
    • Pulse oximetry
    • ECG
    • Noninvasive blood pressure monitoring device
    • Thermometers
    • Integrated monitors with alarms

Monitoring of ventilation

  • Serialized visual inspection, auscultation, palpation, and O2 saturation
  • Ventilation monitoring is essential during anesthesia due to the risk of respiratory depression and hypoxia.
  • Ventilation is monitored in several ways:
    • Clinical monitoring:
      • Visualization of chest excursion
      • Auscultation of breath sounds
      • Movement of the reservoir bag
      • O2 saturation monitor
    • Capnography: a graph showing the respiratory rate and CO2 concentration over time
    • Other measures:
      • End-tidal CO2 concentration
      • Inspired O2 concentration
      • Quantitative volume of expired gas
Normal capnogram

Normal capnogram reflecting appropriate CO2 levels in an individual receiving general anesthesia:
Capnography reflects adequate ventilation during surgery.

Image by Lecturio.

Monitoring of hemodynamics

  • Serialized recording of automated blood pressure, ECG, and HR
  • More accurate hemodynamic monitoring can be achieved via invasive approaches such as:
    • Intra-arterial pressure monitor
    • Central venous pressure monitor
    • Pulmonary artery catheter
    • Transesophageal echocardiography (TEE) probes
  • Hemodynamics are monitored based on:
    • Vitals signs
    • Fluids (IV input and urine output)
  • Vasoactive drugs can be administered to maintain optimal intravascular volume status throughout anesthesia.

Monitoring of neurologic status

  • Neurologic status may be difficult to assess in individuals who are sedated and/or paralyzed.
  • EEG may be used for the neuromonitoring of cortical function.
  • IM paraspinal and/or limb electrodes may be used to monitor nerve stimulation during neurosurgical, orthopedic, or interventional spinal procedures.
  • Intracranial pressure may be monitored during neurosurgical procedures.

Depth of anesthesia

  • Monitored based on end-tidal concentrations of inhalation anesthetics
  • The goal of anesthesia is stage II or III, depending on the type of anesthesia chosen.
  • Stage III requires endotracheal intubation for airway protection.
  • If the desired stage III enters stage IV, prompt reversal is necessary.
Table: Stages of anesthesia depth
Stage IConscious and rational with decreased pain perception
Stage IIUnconscious and reflexive with an irregular breathing pattern
Stage IIIInability to protect the airway due to increased muscle relaxation
Stage IVCardiovascular and respiratory depression (medullary)

Postoperative Care

All individuals are monitored postoperatively in a PACU, where standard procedures are followed:

  • Antiemetics for postoperative nausea and/or vomiting
  • Fluid administration and monitoring for the inability to void via strict inputs and outputs
  • Respiratory, cardiovascular, and neurological monitoring
  • Monitoring and control of hypothermia and hyperthermia
  • Pain control
  • Reassurance, reorientation, and potential drug reversal for delayed emergence (failure to return to a conscious state within 60 minutes of anesthesia cessation)
  • Recovery assessment
  • Reduction of postoperative adverse events
  • Streamline discharge
  • Transferring to an ICU vs appropriate hospital wing vs outpatient care for recovery


  1. Falk, S. (2020) Overview of anesthesia. Retrieved October 15, 2021, from
  2. Robinson, D., Toledo, A.H. (2012). Historical development of modern anesthesia. Journal of Investigative Surgery: The Official Journal of the Academy of Surgical Research, 25, 141–149.
  3. Harrah, S. (2015). Medical Milestones: Discovery of Anesthesia & Timeline. University of Medicine and Health Sciences. 
  4. Nizamuddin, J. (2019). Anesthesia for surgical patients. Schwartz’s Principles of Surgery, 11e. McGraw-Hill. 
  5. Romero-Ávila, P. (2021). Historical development of the anesthetic machine: From Morton to the integration of the mechanical ventilator. Brazilian Journal of Anesthesiology (English Edition), 71, 148–161.
  6. Wood Library-Museum of Anesthesiology. History of Anesthesia. Retrieved June 21, 2021, from

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