Anesthesia - Anesthesia - Lecture Slides, Slides of Biomedical Engineering

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Anesthesia

History of Anesthesia

Ether synthesized in 1540 by Cordus Ether used as anesthetic in 1842 by Dr. Crawford W. Long Ether publicized as anesthetic in 1846 by Dr. William Morton Chloroform used as anesthetic in 1853 by Dr. John Snow

History of Anesthesia

Endotracheal tube discovered in 1878 Local anesthesia with cocaine in 1885 Thiopental first used in 1934 Curare first used in 1942 - opened the “Age of Anesthesia”

Basic Principles of

Anesthesia

Anesthesia defined as the abolition of sensation

Analgesia defined as the abolition of pain

“Triad of General Anesthesia” need for unconsciousness need for analgesia need for muscle relaxation

Nitrous Oxide

Prepared by Priestly in 1776 Anesthetic properties described by Davy in 1799 Characterized by inert nature with minimal metabolism Colorless, odorless, tasteless, and does not burn

Nitrous Oxide

Simple linear compound Not metabolized Only anesthetic agent that is inorganic

Nitrous Oxide Systemic Effects

Minimal effects on heart rate and blood pressure May cause myocardial depression in sick patients Little effect on respiration Safe, efficacious agent

Nitrous Oxide Side Effects

Manufacturing impurities toxic Hypoxic mixtures can be used Large volumes of gases can be used Beginning of case: second gas effect End of case: diffusion hypoxia

Nitrous Oxide Side Effects

Inhibits methionine synthetase (precursor to DNA synthesis) Inhibits vitamin B-12 metabolism Dentists, OR personnel, abusers at risk

Halothane

Synthesized in 1956 by Suckling Halogen substituted ethane Volatile liquid easily vaporized, stable, and nonflammable

Halothane Systemic Effects

Inhibits sympathetic response to painful stimuli Inhibits sympathetic driven baroreflex response (hypovolemia) Sensitizes myocardium to effects of exogenous catecholamines-- ventricular arrhythmias Johnson found median effective dose 2.1 ug/kg Limit of 100 ug or 10 mL over 10 minutes Limit dose to 300 ug over one hour Other medications

Halothane Systemic Effects

Decreases respiratory drive-- central response to CO 2 and peripheral to O 2 Respirations shallow-- atelectasis Depresses protective airway reflexes Depresses myocardium-- lowers BP and slows conduction Mild peripheral vasodilation

Halothane Side Effects

Malignant Hyperthermia-- 1/60,000 with succinylcholine to 1/260,000 without halothane in 60%, succinylcholine in 77% Classic-- rapid rise in body temperature, muscle rigidity, tachycardia, rhabdomyolysis, acidosis, hyperkalemia, DIC most common masseter rigidity family history

Halothane Side Effects

Malignant Hyperthermia (continued) high association with muscle disorders autosomal dominant inheritance diagnosis--previous symptoms, increase CO2, rise in CPK levels, myoglobinuria, muscle biopsy physiology--hypermetabolic state by inhibition of calcium reuptake in sarcoplasmic reticulum