Chapter 6 -introduction to inhalationa anesthesia
- 1. Inhalational Anesthetic Agent s By Eyayalem Melese ,MSC Anesthetist 1 By Eyayalem M,MSc,Aesthetist
- 2. Inhalational Anesthetic Agents (IAA) IAA: refers to the delivery of gases or vapors from the respiratory system to produce anesthesia Potency is measured by their MAC value MAC or Potency. MAC (minimum alveolar concentration) is the lowest concentration of the anesthetic in pulmonary alveoli needed to produce immobility in response to a painful stimulus (surgical incision in 50% individuals. the most commonly used IAA are: Nitrous oxide - Halothane Isoflurane - Enflurane Desflurane - Sevoflurane 2 By Eyayalem M,MSc,Aesthetist
- 3. 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 3 By Eyayalem M,MSc,Aesthetist
- 4. Nitrous Oxide Simple linear compound Not metabolized Only anesthetic agent that is inorganic 4 By Eyayalem M,MSc,Aesthetist
- 5. Nitrous Oxide Major difference is low potency MAC value is 105% Weak anesthetic, powerful analgesic Needs other agents for surgical anesthesia Low blood solubility (quick recovery) 5 By Eyayalem M,MSc,Aesthetist
- 6. 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 6 By Eyayalem M,MSc,Aesthetist
- 7. Nitrous Oxide Side Effects Manufacturing impurities toxic Hypoxic mixtures can be used Large volumes of gases can be used Inhibits precursor to DNA synthesis Inhibits vitamin B-12 metabolism Dentists, OR personnel, abusers at risk 7 By Eyayalem M,MSc,Aesthetist
- 8. Halothane Synthesized in 1956 by Suckling Halogen substituted ethane Volatile liquid easily vaporized, stable, and nonflammable 8 By Eyayalem M,MSc,Aesthetist
- 9. Halothane Most potent inhalational anesthetic MAC of 0.75% Efficacious in depressing consciousness Very soluble in blood and adipose Prolonged emergence 9 By Eyayalem M,MSc,Aesthetist
- 10. Halothane Systemic Effects Inhibits sympathetic response to painful stimuli Inhibits sympathetic driven baroreflex response (hypovolemia) Sensitizes myocardium to effects of both endogenous (light anesthesia)& exogenous catecholamine's-- ventricular arrhythmias 10 By Eyayalem M,MSc,Aesthetist
- 11. Halothane Systemic Effects Decreases respiratory drive-- central response to CO2 and peripheral to O2 ◦Respirations shallow-- atelectasis ◦Depresses protective airway reflexes Depresses myocardium-- lowers BP and slows conduction Mild peripheral vasodilation 11 By Eyayalem M,MSc,Aesthetist
- 12. Halothane Side Effects “Halothane Hepatitis” -- 1/10,000 cases ◦fever, jaundice, hepatic necrosis, death ◦metabolic breakdown products are hapten-protein conjugates ◦immunologically mediated assault ◦exposure dependent 12 By Eyayalem M,MSc,Aesthetist
- 13. 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 13 By Eyayalem M,MSc,Aesthetist
- 14. Enflurane Developed in 1963 by Terrell, released for use in 1972 Stable, nonflammable liquid Pungent odor MAC 1.68% 14 By Eyayalem M,MSc,Aesthetist
- 15. Enflurane Systemic Effects Potent inotropic and chronotropic depressant and decreases systemic vascular resistance-- lowers blood pressure and conduction dramatically Inhibits sympathetic baroreflex response Sensitizes myocardium to effects of exogenous catecholamine-- arrhythmias 15 By Eyayalem M,MSc,Aesthetist
- 16. Enflurane Systemic Effects Respiratory drive is greatly depressed- - central and peripheral responses ◦increases dead space ◦widens A-a(Alveolar arterial) gradient ◦produces hypercarbia in spontaneously breathing patient 16 By Eyayalem M,MSc,Aesthetist
- 17. Enflurane Side Effects Metabolism one-tenth that of halothane-- does not release quantity of hepatotoxic metabolites Metabolism releases fluoride ion-- renal toxicity Epileptiform EEG patterns 17 By Eyayalem M,MSc,Aesthetist
- 18. Isoflurane Synthesized in 1965 by Terrell, introduced into practice in 1984 Not carcinogenic Non flammable,pungent Less soluble than halothane or enflurane MAC of 1.30 % 18 By Eyayalem M,MSc,Aesthetist
- 19. Isoflurane Systemic Effects Depresses respiratory drive and ventilatory responses-- less than enflurane Myocardial depressant-- less than enflurane Inhibits sympathetic baroreflex response-- less than enflurane Sensitizes myocardium to catecholamines -- less than halothane or enflurane 19 By Eyayalem M,MSc,Aesthetist
- 20. Isoflurane Systemic Effects Produces most significant reduction in systemic vascular resistance-- coronary steal syndrome, increased ICP Excellent muscle relaxant-- potentiates effects of neuromuscular blockers 20 By Eyayalem M,MSc,Aesthetist
- 21. Isoflurane Side Effects Little metabolism (0.2%) -- low potential of organotoxic metabolites No EEG activity like enflurane Bronchoirritating, laryngospasm 21 By Eyayalem M,MSc,Aesthetist
- 22. SEVOFLURANE Physical and chemical properties This is a newer inhalational agent. It is non-flammable with a pleasant smell. It has a very low blood/gas solubility and provides the most rapid induction and recovery of all currently available inhalational agents. It has a MAC of 1.7%. 5% is metabolized in the liver. 22 By Eyayalem M,MSc,Aesthetist
- 23. Systemic effects • Central nervous system − No significant effect on ICP or CBF at clinical levels • Cardiovascular system − Does not sensitise the myocardium to catecholamines • Respiratory system − Decrease in minute volume − Increase in respiratory rate − No airway irritation 23 By Eyayalem M,MSc,Aesthetist
- 24. sevoflurane Uses It is becoming the agent of choice for inhalational induction especially in children but also in adults. 24 By Eyayalem M,MSc,Aesthetist
- 25. sevoflurane Advantages • Rapid induction • Rapid recovery • Minimum cardiovascular effects Disadvantages • High cost • If being used as sole inhalational agent in a draw-over system it would require two OMVs in series to give an adequate concentration. 25 By Eyayalem M,MSc,Aesthetist
- 26. Comparative Characteristics Of Inhaled Anesthetics By Eyayalem M,MSc,Aesthetist 26
- 28. Local Anesthetics Followed general anesthesia by 40 years Koller used cocaine for the eye in 1884 Halsted used cocaine as nerve block First synthetic local-- procaine in 1905 Lidocaine synthesized in 1943 28 By Eyayalem M,MSc,Aesthetist
- 29. 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 29 By Eyayalem M,MSc,Aesthetist
- 30. Block of neural impulses Local anesthetics produce a conduction block of neural impulses, preventing the passage of Na+ through Na+ channels. 30 By Eyayalem M,MSc,Aesthetist
- 31. Local Anesthetics Linear molecules that have a lipophilic and hydrophilic end (ionizable) ◦low pH-- more in ionized state and unable to cross membrane ◦adding sodium bicarb-- more in non-ionized state 31 By Eyayalem M,MSc,Aesthetist
- 32. Local Anesthetics Two groups: esters and amides ◦esters metabolized by plasma cholinesterase ◦amides metabolized by cytochrome p-450 32 By Eyayalem M,MSc,Aesthetist
- 33. Common Local Anesthetics 33 By Eyayalem M,MSc,Aesthetist
- 34. Local Anesthetic Toxicity Central nervous system ◦initially-- lightheadedness, circumoral numbness, dizziness, tinnitus, visual change ◦later-- drowsiness, disorientation, slurred speech, loss of consciousness, convulsions ◦finally-- respiratory depression 34 By Eyayalem M,MSc,Aesthetist
- 35. Local Anesthetic Toxicity By Eyayalem M,MSc,Aesthetist 35
- 37. Local Anesthetic Toxicity Cardiovascular ◦myocardial depression and vasodilation-- hypotension and circulatory collapse Allergic reactions-- rare (less than 1%) ◦preservatives or metabolites of esters ◦rash, bronchospasm 37 By Eyayalem M,MSc,Aesthetist
- 38. Prevention and Treatment of Toxicity Primarily from intravascular injection or excessive dose -- anticipation ◦aspirate often with slow injection ◦ask about CNS toxicity ◦have monitoring available ◦prepare with resuscitative equipment, CNS-depressant drugs, cardiovascular drugs ◦ABC’s 38 By Eyayalem M,MSc,Aesthetist
- 39. Treatment of Toxicity 39 By Eyayalem M,MSc,Aesthetist
- 40. Cocaine South American Indians used to induce euphoria, reduce hunger, and increase work tolerance in sixth century Many uses in head and neck-- strong vasoconstrictor, no need for epinephrine Mechanism is similar-- blocks sodium channel, also prevents uptake of epinephrine and norepinephrine 40 By Eyayalem M,MSc,Aesthetist
- 41. Cocaine May lead to increased levels of circulating catecholamines-- tachycardia, peripheral vasoconstriction Safe limits (200-400 mg)-- use with epinephrine clinically 41 By Eyayalem M,MSc,Aesthetist