History

• 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 Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of 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 Inhaled anesthetics Inhaled anesthetics are chemical compounds that can induce and maintain general anesthesia when delivered by inhalation. Inhaled anesthetics can be divided into 2 groups: volatile anesthetics and gases. Volatile anesthetics include halothane, isoflurane, desflurane, and sevoflurane. Inhaled Anesthetics.

Historical landmarks in the development of anesthesia

Years	Events
4000 BCE–0 CE	The 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 Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of 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 Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of 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–present	The 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.

Goals

• 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 Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview, infection, thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia)
    • Electrolyte panel (to evaluate electrolyte imbalance and metabolic disturbance)
    • Coagulation studies Coagulation studies Coagulation studies are a group of hematologic laboratory studies that reflect the function of blood vessels, platelets, and coagulation factors, which all interact with one another to achieve hemostasis. Coagulation studies are usually ordered to evaluate patients with bleeding or hypercoagulation disorders. 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 Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
    • Ischemic heart disease Ischemic heart disease Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. Coronary Heart Disease
    • Heart failure
    • Obstructive sleep apnea Obstructive sleep apnea Obstructive sleep apnea (OSA) is a disorder characterized by recurrent obstruction of the upper airway during sleep, causing hypoxia and fragmented sleep. Obstructive sleep apnea is due to a partial or complete collapse of the upper airway and is associated with snoring, restlessness, sleep interruption, and daytime somnolence. Obstructive Sleep Apnea
    • Diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. 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 Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care test is indicated to avoid fetal loss.

Summary of high-risk conditions that warrant preoperative assessment and perioperative planning

Preexisting disease/condition	Diagnostic testing
Age > 65 years	Albumin, creatinine, hemoglobin
Alcohol abuse	ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG), electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes, hemoglobin, liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver function test, platelet count, PT/INR
Anemia	CBC, creatinine, ferritin, iron, transferrin saturation, TSH, T3, T4, vitamin B12 Vitamin B12 Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12, blood typing, screening
Cardiac disease	BNP, ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG), +/- stress testing
Diabetes	Creatinine, HbA1c, glucose
Liver disease	Albumin, BUN, creatinine, electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes, hemoglobin, liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver function test, platelet count, PT/INR
Pulmonary disease	Chest X-ray
Thyroid disease	T3, T4, TSH

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 classification	Definition	Examples
I	A normal, healthy individual without known diseases	Healthy, nonsmoker, minimal alcohol use
II	An individual with mild systemic disease	Current smoker, mild hypertension, mild lung disease
III	An individual with severe systemic disease	Poorly controlled hypertension or diabetes mellitus, chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)
IV	An individual with severe systemic disease that is a constant threat to life	Recent MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction, severely reduced ejection fraction, sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock, ARDS ARDS Acute respiratory distress syndrome is characterized by the sudden onset of hypoxemia and bilateral pulmonary edema without cardiac failure. Sepsis is the most common cause of ARDS. The underlying mechanism and histologic correlate is diffuse alveolar damage (DAD). Acute Respiratory Distress Syndrome
V	An individual who is not expected to survive without the intended operation	Brain bleed, ruptured aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms, massive trauma
VI	An individual declared brain dead or whose organs are being harvested

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 Postoperative care After any procedure performed in the operating room, all patients must undergo close observation at least in the recovery room. After larger procedures and for patients who require hospitalization, observation must continue on the surgical ward. The primary intent of this practice is the early detection of postoperative complications. Postoperative Care

Considerations include:

• Pain management Pain Management Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is a subjective experience. Acute pain lasts < 3 months and typically has a specific, identifiable cause. 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

Class	Commonly used drugs
IV sedative-hypnotics	Propofol, etomidate, ketamine
IV adjuvants	Opioids Opioids Opiates are drugs that are derived from the sap of the opium poppy. Opiates have been used since antiquity for the relief of acute severe pain. Opioids are synthetic opiates with properties that are substantially similar to those of opiates. Opioid Analgesics, lidocaine, midazolam
Inhalation agents	Nitrous oxide, halothane, isoflurane
Neuromuscular blockers Neuromuscular blockers Neuromuscular blockers are skeletal muscle relaxant medications that block muscle contraction through a couple of mechanisms. Depolarizing neuromuscular blockers bind to nicotinic cholinergic receptors (nAChRs), locking the ion channel open. This results in muscle relaxation and paralysis. Neuromuscular Blockers	Vecuronium, 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 Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of 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.

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 Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology 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 Local anesthetics Local anesthetics are a group of pharmacological agents that reversibly block the conduction of impulses in electrically excitable tissues. Local anesthetics are used in clinical practice to induce a state of local or regional anesthesia by blocking sodium channels and inhibiting the conduction of painful stimuli via afferent nerves. Local Anesthetics provide prolonged postoperative analgesia.

Intravenous regional anesthesia (IVRA)

• Also known as a “Bier block”
• Less invasive alternative to peripheral nerve blocks
• Suitable for shorter procedures of the hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand, forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term "forearm" is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. 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.

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.