In the name of Allah

Introduction to Anesthesia

Dr. M.MasjediAss. Prof. of anesthesia,Fellowship of critical care medicineSUMS - 2015

Definition of Anesthesia

Anesthesia literally means “no no sensationsensation” Derived from the Greek verb for “to perceive” Oliver Wendell Holmes suggested the name "Anesthesia"

History of AnesthesiaHistory of Anesthesia 1818thth Century Surgery Century Surgery

Original in the Royal College of Surgeons of England, London.

Historical ReviewHistorical Review

1771-Joseph Priestly1771-Joseph Priestly - discovery of 02- discovery of 02 1772-Joseph Priestly - discovery 1772-Joseph Priestly - discovery

of N20of N20

Late 1700's-Pneumatic MedicineLate 1700's-Pneumatic Medicine

Historical ReviewHistorical Review

1798- 1798- Sir Humphrey Davies Sir Humphrey Davies first mention of first mention of inhalational properties of inhalational properties of N20N20 ( relief of pain ( relief of pain caused by an erupting wisdom tooth) but caused by an erupting wisdom tooth) but clinicians clinicians overlookedoverlooked his suggestion his suggestion

1846- 1846- Horace Wells Horace Wells :observed significant leg :observed significant leg injury without pain , next day received N2O injury without pain , next day received N2O for for extraction of one his teethextraction of one his teeth

Early 1800's - Early 1800's - recreational use ether frolics recreational use ether frolics

History of History of AnesthesiaAnesthesia

1540 : A1540 : A flammable ,volatile liquid synthesized by flammable ,volatile liquid synthesized by Cordus (Cordus (sweet vitriolsweet vitriol))

1740 : Frobenius named it 1740 : Frobenius named it Ether Ether (from the greek word (from the greek word for ignate or blaze)for ignate or blaze)

1842 Used 1842 Used as anesthetic as anesthetic , publicized , publicized as anesthetic in as anesthetic in

1846 by Dr. William Morton1846 by Dr. William Morton

ChloroformChloroform used as anesthetic in 1853 by Dr. John Snow used as anesthetic in 1853 by Dr. John Snow

One of the most significant events in the history of medicine

Oct. 16, 1846 - Ether Day : First demonstration of the use of ether in anesthesia at Mass. Gen. Hosp.( Ether dome ) -Dr. William T.G. Morton ( First anesthesia specialist)

Historical ReviewHistorical Review1850’s - 1850’s - Chloroform/EtherChloroform/Ether - multiple deaths - multiple deaths

1863 - 1863 - N20N20 reintroduced by Colton reintroduced by Colton

1887 - The first 1887 - The first anesthesia machine anesthesia machine - N20/02- N20/02

1953- 1953- Fluorinated anestheticsFluorinated anesthetics

1954- 1954- Halogenated drugs; Halothane Halogenated drugs; Halothane (more pleasant (more pleasant odor, higher potency, favorable pharmacokinetic, odor, higher potency, favorable pharmacokinetic, nonflammability& low toxicitynonflammability& low toxicity))

1960:Enflurane,Isoflurane,desflurane,Sevoflurane1960:Enflurane,Isoflurane,desflurane,Sevoflurane

XenonXenon : inert gas ,under investigation : inert gas ,under investigation

History of AnesthesiaHistory of Anesthesia Operation Under Ether -1852Operation Under Ether -1852

“The effect of the gaseous inhalation in neutralizing the sentient faculty was made perfectly distinct to my mind..”Massachusetts General Hospital, Boston

AnesthesiaNow covers :1. OR2. PACU3. PREOP. CLINIC4. RESP. CARE5. ICU (gen.surg.,cardiac surg.,Tx.)6. PAIN CLINIC (acute & chronic pain services)7. OPIOD DETOXIFICATION8. TRAUMA team9. EMERGENCY DEPT.10. CPCR

Types of Anesthesia Local Anesthesia: loss of sensory perception over a

small area of the body

Regional Anesthesia: loss of sensation over a specific region of the body (e.g. lower trunk)

Monitored Anesthesia Care (MAC) :conscious sedation + observation & management of complications

General Anesthesia: loss of sensory perception of the entire body

General Anesthesia (defenition) loss of response to & perception of all external stimuli

Components of General Anesthesia:1. Unconsciousness

2. Analgesia (most GA’s are poor analgesics)

3. Amnesia

4. Anexiolysis

5. Areflexia

6. Attenuation of autonomic responses to painful stimuli

Gas Volatile liquids* BarbituratesBarbiturates

Misc.

OpioidsOpioids

BenzodiazepinesBenzodiazepines

(nitrous oxide) (halothaneisoflurane,desflurane,

sevoflurane)

(thiopental)

(midazolam)

(fentanyl)

(etomidate, propofol)

General Anesthetics

Inhalational Parenteral

Inhalation anesthesia Total intravenous anesthesia Inhalation plus intravenous (“Balanced

Anesthesia”)Most common

Anesthetic Techniques

Induction- initial entry to surgical anesthesia

Maintenance- continuous monitoring and medication Maintain depth of anesthesia, ventilation, fluid balance,

hemodynamic control, hoemostasis

Emergence- resumption of normal CNS function Extubation, resumption of normal respiration

Phases of General Anesthesia

Inhalation Anesthetics

Gas enters the blood plasma but rapidly leaves it in preference for a lipid environment such as cell membranes/ the brain

Inhaled and exhaled gases

Aveoli Blood Tissues, including Brain

The “Old Theory” of General Anesthesia

Induction

Anesthetic molecules partition into lipid bilayers

A non-specific miracle occurs….

Unconsciousness

Remove anesthetic

The exact opposite of the non-specific miracle occurs….

Patient wakes up

( cell lipid bilayer physical properties?)

(some GA’s produce stereospecific effects!?)

Potentiation of inhibitory ‘receptors’ GABAA

Glycine Potassium channels

Inhibition of excitatory ‘receptors’ NMDA (glutamate) AMPA (glutamate) Nicotinic

acetylcholine Sodium channels

Receptors Possibly Mediating CNS Effects Of Inhaled Anesthetics

Inhalation Anesthetics

Applying a gas rather than a solid or a liquid

special set of terms: Concentration –µg/litre or µM is possible but difficult because of the volatility of the drug

MAC – minimum alveolar concentration (as a percentage) to induce pain insensate anesthesia

Minimum alveolar concentration Alveolar concentration required to

prevent movement in 50% of subjects in response to skin incision

standard stimulus represents brain concentration consistent within and between

species additive

Agent MAC Nitrous oxide 104 Desflurane 6.6 Sevoflurane 1.8 Enflurane 1.63 Isoflurane 1.17 Halothane 0.75

Factors increasing MAC

Hyperthermia Chronic ETOH abuse Hypernatremia Increased CNS transmitters

MAOI Amphetamine Cocaine Ephedrine L-DOPA

Factors decreasing MAC Increasing age Hypothermia Hyponatremia Hypotension (MAP<50mmHg) Pregnancy Hypoxemia (<38 mmHg) O2 content (<4.3 ml O2/dl) Metabolic acidosis

Narcotics Ketamine Benzodiazepines 2 agonists LiCO3

Local anesthetics ETOH (acute) And many more

Factors with no influence on MAC Duration of anesthesia Sex Alkalosis PCO2

Hypertension Anemia Potassium Magnseium

Intravenous anesthesia

Intravenous Anesthetic Agents

1656 : First attempt at intravenous anesthesia by Wren -- opium into his dog

1934 : Use in anesthesia with thiopental

Many ways to meet requirements-- muscle relaxants, opoids, nonopoids

Appealing, pleasant experience

Narcotic agonists (opioids)

Used for years for analgesic action-- civil war for wounded soldiers

Predominant effects are analgesia, depression of sensorium and respirations

Mechanism of action is receptor mediated

Muscle Relaxants Neuromuscular Junction

Local Anesthetics Mechanism of action is by reversibly blocking

sodium channels to prevent depolarization Anesthetic enters on axioplasmic side and

attaches to receptor in middle of channel

Anesthesia subspecialities Intensive care medicine Anesth. For thoracic surg. Anesth. For cardiac & vascular surg. Neurosurgical anesth. Organ transplant Anesth. For hepatobil. & genitourinary sys. Anesth. For OB & laparoscopic surg. Ped. & geriatric anesth. Anesth. For robotic & LASER surg. Anesth.for trauma Anesth. For Ophth. & ENT operations CPCR

Thank you!