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Lecture Presentation
N STHETICS
Prof. S.V. Tembhurne
Department of Pharmacology
S.N.I.O.P, Pusad. India
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Categories of Anesthetics
General anesthetics
Central nervous system (CNS) depressants used to
produce loss of pain sensation and consciousness Local anesthetics
Used to cause loss of pain sensation and feeling in a
designated area of the body
Does not produce the systemic effects associatedwith severe CNS depression
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Important difference between general
and local anesthetic are as fallows
Local anesthetics General anesthetics
Site of action CNS Peripheral nerve
Area of body involved Whole body Restricted area
Consciousness Lost Unaltered
Care of vital function Essential Usually not need
Physiological trespass High Low
Poor health patient Risky Safer
Use in non cooperative
patient
Possible Not possible
Major surgery Preferred Cannot be use
Minor surgery Not preferred preferred
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Agents Involved in Balanced
Anesthesia
Preoperative medications
Sedative–hypnotics
Antiemetics
Antihistamines
Narcotics
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Local Anesthetics
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Local Anesthetics L As )
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
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Local Anesthetics LAs)
Local anesthetic can be produced bycooling. Clinically used LAs have no/minimal local irritant
action and block sensory nerve endings, nervetrunks, neuromuscular junction, ganglionic synapse
and receptor (non selective) i.e. structures whichfunction through increased sodium permeability.
They also reduced release of acetylcholine frommotor nerve endings. Injected around a mixednerve they cause anesthesia of skin and paralysis
of voluntary muscle supplied b that nerve.
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Classification
Injectable:
1) Low potency, short duration:-Procaine, Chloroprocaine2) Intermediate potency and duration: - Lignocaine, prilocaine
3) High potency, long duration: - Tetracaine (Amethocaine),Bupivacaine.Ropivacaine Dibucaine (Cinchocaine)
Surface anesthetics
A) Soluble: Cocaine
Lignocaine
Tetracaine
Benoxinate
B) Insoluble: Benzocaine
Butylaminobenzoate (Butamben)
Oxethazaine.
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Occasionally use local anesthetics in other
countries:-
Mepivacaine, Etidocaine, cyclomethycaine, Dyclonine,Proparacaine.
Anesthetics which having local irritancy and
other prominent systemic activity:-
Propranolol, Chlorpromazine, H1 antihistamine, Quinine.
Estered linked local anesthetics: Cocaine,
procaine, Chloroprocaine, Tetracaine, and Benzocaine.
Amide linked Local anesthetics: Lignocaine, Bupivacaine, Dibucaine, Prilocaine, and Ropivacaine.
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Mechanism of action
Mechanism of action is by reversibly blocking
sodium channels to prevent depolarization
Anesthetic enters on axioplasmic side andattaches to receptor in middle of channel
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Mechanism
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Characteristics
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
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Characteristics
Two groups: esters and amides
esters metabolized by plasma cholinesterase
amides metabolized by Liver microsomes by
dealkylation and hydrolysis.
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Features of Amide LAs
compared to ester LAs)
Produced more intense and longer lasting anesthesia
Bind to α1 acid glycoprotein in plasma.
Not hydrolyzed by plasma esterase. Rarely cause hypersensitivity reaction; no cross
sensitivity with ester LAs.
Because of their short duration, less intense analgesiaand higher risk of hypersensitivity, the ester linked LAs
are rarely used for infiltration or nerve block, but are stillused on mucous membrane.
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Structure
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Pharmacokinetic of Local
Anesthetics:
Soluble surface anesthetics are rapidly
absorbed from mucous membranes and
abraded areas; but absorption from intact
skin is poor. Procaine is negligible bound toplasma protein, but amide LAs are bound to
plasma protein.
After oral ingestion both procaine and
Lignocaine have high first pass metabolism
in the liver. Thus they are not effective orally
for antiarrhythmic purpose.
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Toxicity Profile
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Local Anesthetic Action/Toxicity
Central nervous system initially-- lightheadedness, circumoral numbness,
dizziness, tinnitus, visual change
later-- drowsiness, disorientation, slurred speech,loss of consciousness, convulsions
finally-- respiratory depression.Cocaine having more potent action on CNS.
Blood vessels:Fall in blood pressure due to sympathetic
blockage, relaxation of arteriolar smooth muscle.Toxic doses of Las produce cardiovascular
collapse.
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Cardiovascular myocardial depression and vasodilation-- hypotension
and circulatory collapse
They have quinidine like antiarrhythmic action.
Procaine cannot used as a antiarrhythmic agentbecause of short duration of action and propensity tocause CNS effect, but its amide derivative
procainamide is a classical anti-arrhythmic action. At high dose they induce arrhythmias.
Bupivacaine is more cardiotoxic
Lignocaine is used as an antiarrhythmic
Allergic reactions-- rare (less than 1%) preservatives or metabolites of esters
rash, bronchospasm
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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
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Treatment of Toxicity
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Individual compounds
Cocaine- Obtained from Erythroxylem coca) South American Indians used to induce
euphoria, reduce hunger, and increase worktolerance 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 andnorepinephrine
May lead to increased levels of circulatingcatecholamine-- tachycardia, peripheralvasoconstriction
Safe limits (200-400 mg)-- use with epinephrineclinically
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Procaine
It is the first synthetic local anestheticsintroduced in 1905.
It is not surface anesthetics.
PABA is released on hydrolysis ofprocaine which can antagonized theantibacterial action of sulfonamide given totreat the infection.
Procaine penicillin injected i.m. acts for 24hours.
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Lignocaine
Introduced in 1948
Lignocaine hydrochloride is used both topically and byinjection.
It block the conduction within 3 min. where as procainemay take15 min.
Cross sensitivity with ester LAs is not seen. Central effect of Lignocaine are drowsiness, mental
clouding, altered taste and tinnitus.
Overdose may cause muscle twitching, convulsion,cardiac arrhythmias, fall in BP,coma and respiratoryarrest
It is rapidly metabolized in liver by dealkylation to formmonoethylglycinexylidide and glycine xylidide.
Lignocaine is a popular antiarrhythmic
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Prilocaine
It is similar to Lignocaine but does notcause vasodilation at the site of infiltration
and has lower CNS toxicity due to larger
volume of distribution. It is readily metabolized in liver and
kidneys. The principal metabolite excreted
in the urine is o-toluidine. This is believed
to cause methaemoglobinaemia.
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Eutectic Lignocaine/Prilocaine
It can anesthetize the intact skin after
surface application.
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Tetracaine (Amethocaine)
A PABA ester, more potent and more toxic
due to slow metabolism. It is used for surface anesthesia and spinal
anesthesia.
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Bupivacaine
It is a potent and long acting (180-360 min.)
amide linked LA: used chiefly for infiltration and
regional nerve block, epidural and spinal
anesthesia.
It has high lipid solubility; distributed in tissue orethan in blood after spinal and epidural injection.
It is more prone to prolong QT interval and also
cause cardiac depression.
Should not used for intravenous regional
analgesia.
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Ropivacaine
It is a congener of Bupivacaine, equally
long acting but less cardiotoxic.
It block the fiber involved in pain
transmission
Used for postoperative and labour pain, it
can also be employ for nerve block.
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Dibucaine (Cinchocaine)
It is a most potent, most toxic and longest
acting LA (180-600 min.).
Used as a surface anesthetics on lessdelicate mucous membrane (anal canal)
and occasionally for spinal anesthesia of
long duration.
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Benoxinate
It is a good surface anesthetics for the
eye; has little irritancy.
0.4 percent solution rapidly producecorneal anesthetics
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Benzocaine and
Butylaminobenzoate Butamben)
Both are PABA derivative –can antagonisesulphonamide locally.
It is hydrolysed by esterases in the plasma to 4-aminobenzoic acid.
It has very low aqueous solubility, these are notsignificantly absorbed from mucous membraneor abraded skin.
Produce long lasting effect without systemic
toxicity. Is often used in combination with other drugs for
temporary local relief of pain associated withdental procedures, sore throat, hemorrhoids andpruritis.
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Oxethazaine
Topical anasthetics,unique in ionizing to avery small extent even at low PH values.
Effective in anaesthetising gastric mucosa
despite acidity of the medium. swallowedalong with antacid it afford symptomatic
relief in gastric, drug induced gastric
irritation,gastroesophageal reflex andheartburn of pregnancy
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Methods of Administering Local Anesthetics
Topical/Surface anesthesia
Infiltration anesthesia (infiltered under the skin in the area ofoperation)
Conduction block (injected around nerve trunk)
Field block
Nerve block
Spinal anesthesia (injected in subarachnoid space)
Drug used in spinal anesthesia are: Lignocaine, Tetracaine,Bupivacaine, Dibucaine
complication of spinal anesthesia:
Respiratory paralysis -Pulmonary complication
Hypotension due to sympathetic blocker.
HeadacheNeurological complication
septic meningitis
Nausea and vomiting
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Intravenous regional anesthesia -mainly used forupper limb and orthopedic procedure.
Epidural anesthesia: Lignocaine and Bupivacaine aremost popular epidural Anastasia. It divided into 3category depending on the site of injection.
Thoracic-used generally for pain relief from thoracic/upper abdominal surgery.
Lumber: produce anesthesia of lower abdomen,pelvis and hind limb.
Caudal :given in sacral can produce anesthesia ofpelvic and peripheral region-used mostly for vaginaldelivery,anorectal,and genitourinary operation.
Duration of action of both anesthesia is prolong by
adrenaline. Cardiovascular complication are similar tospinal anesthesia but neurological and headache areless.
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Goals of General
Anesthetics
Analgesia
Loss of pain perception
UnconsciousnessLoss of awareness of one’ s surroundings
Amnesia
Inability to recall what took place
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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 byDr. John Snow
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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”
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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
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Potent CNS depressantsGeneral anesthesia = most severe state of
intentional drug-induced CNS depression
= opioid narcotic + volatile anesthetic (no pain +unconsciousness)
Depression of all CNS functions
- sedation, sleep, depressed reflexes,amnesia, unconsciousness
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Risk Factors Associated With
General Anesthetics
CNS factors
Cardiovascular factors
Respiratory factors
Renal and hepatic function
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Mechanism
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Mechanism
The research finding that the anesthetics act on ligandgated ion channels (but not voltage sensitive ionchannels) are the major target of anesthetics action. TheGABA A receptor gated chloride channel is the mostimportant of these. Many inhalation anesthetics,
barbiturates, benzodiazepines and propofol potentiatethe action of inhibitory transmitter GABA to open chloridechannels.
Action of glycine (activate chloride channels) in thespinal cord and medulla is augmented by barbiturates,
propofol and many inhalation anesthetics. This actionmay block responsiveness to painful stimuli resulting influorinated anesthetics and barbiturates, in addition,inhibit neuronal cation channel gated by nicotiniccholinergic receptor.
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Stages of Anesthesia
Stage 1: The analgesia stage
Stage 2: The excitement stage
Stage 3: Surgical anesthesia
Stage 4: Medullary paralysis
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Stage 1: The analgesia stageStart from beginning of anesthetic inhalation and lastsupto the loss of consciousness. Pain is progressively
abolished during these stage patient remains abolishedduring this stage. Patient remains conscious, can hearand see, and fees a dream like state. Reflexes andrespiration remain normal. Though some minor and evenmajor operation can be carried out during this stage, it israther difficult to maintain-use is limited to shortprocedure.
Stage 2: The excitement stage/ Stageof Delirium:From loss of consciousness to beginning of regular respiration.Excitement is seen-patient may shout, struggle and hold his breath;muscle tone increases, jaw are tightly closed, breathing is jerkey;vomiting, involuntary micturition or defecation may occur. Heart rateand BP may rise and pupils dilate due to sympathetic stimulation.
No stimulus should be applied or operative procedure carried out
during this stage.
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Elimination
When anesthetic administration is
discontinued, gradient are reversed and
the channel of absorption (pulmonary
epithelium) becomes the channel of
ellimination.
Most of general anesthetics are eliminated
unchanged. metabolism is significant only
for halothane. Other are practically notmetabolized
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Inhalational Anesthetic Agents
Inhalational anesthesia refers to thedelivery of gases or vapors from the
respiratory system to produce anesthesia
Pharmacokinetics--uptake, distribution,and elimination from the body
Pharmacodyamics- MAC value
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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.
Simple linear compound
Not metabolized Only anesthetic agent that is inorganic
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Major difference is low potency
MAC value is 105%
Weak anesthetic, powerful analgesic
Needs other agents for surgical
anesthesia
Low blood solubility (quick recovery)
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Nitrous Oxide Systemic Effects
Minimal effects on heart rate and blood
pressure
May cause myocardial depression in sickpatients
Little effect on respiration
Safe, efficacious agent
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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
Inhibits methionine synthetase (precursor toDNA synthesis)
Inhibits vitamin B-12 metabolism
Dentists, OR personnel, abusers at risk
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Ether
It is highly volatile liquid, produces irritating vapors which
are inflammable and explosive. Ether is a potent anesthetics, produce good analgesia
and marked muscle relaxation by reducing Ach outputfrom motor nerve ending
It is highly soluble in blood-induction is prolonged and
unpleasant with struggling, breath holding, salivation andmarked respiratory secreations(atropine must be givenas premedication to prevent the patient from drowsing inhis own secretion.
Post anesthetics nausea, vomiting and retching aremarked.
It does not sensitize the heart to adrenaline and is nothepatotoxic.
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Halothane Systemic Effects
Inhibits sympathetic response to painfulstimuli
Inhibits sympathetic driven baroreflex
response (hypovolemia) Sensitizes myocardium to effects of
exogenous catecholamines- ventricular
arrhythmias
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Halothane Systemic Effects
Decreases respiratory drive-- centralresponse to CO2 and peripheral to O2
• Respirations shallow-- atelectasis
• Depresses protective airway reflexes
Depresses myocardium by reducingintracellular calcium concentration-- lowersBP and slows conduction
Mild peripheral vasodilation
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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.
Malignant Hyperthermia due to intracellular release ofcalcium from sarcoplasmic reticulum causingpersistent muscle contraction and heat production--1/60,000 with succinylcholine to 1/260,000 without halothane in 60%, succinylcholine in 77%
Classic-- rapid rise in body temperature, musclerigidity, tachycardia, rhabdomyolysis, acidosis,hyperkalemia, DIC
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Malignant Hyperthermia (continued)
• treatment--early detection, d/c agents,
hyperventilate, bicarb, IV dantrolene (2.5
mg/kg), ice packs/cooling blankets,
lasix/mannitol/fluids. ICU monitoring
• Susceptible patients-- preop with IV
dantrolene, keep away inhalational agents
and succinylcholine
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Enflurane
Developed in 1963 by
Terrell, released for
use in 1972
Stable, nonflammable
liquid
Pungent odor
MAC 1.68%
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Enflurane Systemic Effects
Potent inotropic and chronotropic depressant
and decreases systemic vascular resistance--lowers blood pressure and conductiondramatically
Inhibits sympathetic baroreflex response
Sensitizes myocardium to effects of exogenouscatecholamines – arrhythmias.
Respiratory drive is greatly depressed-- centraland peripheral responses
increases dead space widens A-a gradient
produces hypercarbia in spontaneously breathingpatient
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Enflurane Side Effects
Metabolism one-tenth that of halothane-- doesnot release quantity of hepatotoxic metabolites
Metabolism releases fluoride ion-- renal toxicity
Epileptiform EEG patterns
Stimulates salivary and respiratory secretion.
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Isoflurane
Synthesized in 1965 byTerrell, introduced intopractice in 1984
Isomer of enflurane Not carcinogenic
Nonflammable, pungent
Less soluble than
halothane or Enflurane MAC of 1.30 %
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Isoflurane Systemic Effects
Depresses respiratory drive and ventilatory responses--less than enflurane
Myocardial depressant-- less than enflurane
Inhibits sympathetic baroreflex response-- less thanenflurane
Sensitizes myocardium to catecholamines -- less thanhalothane or enflurane.
Produces most significant reduction in systemic vascularresistance-- coronary steal syndrome, increased ICP
Excellent muscle relaxant-- potentiates effects ofneuromuscular blockers
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Desflurane has distinct property in their highvolatility, lower oil: gas partition coefficient and
very low solubility in blood and tissue because of
which induction and recovery are very fast.
Patient can discharge few hours after surgery. Sevoflurane is polyfluronated anesthetic which
is intermediate between isoflurane and
desflurane,no problem in induction.
Sevoflurane does not cause sympathetic
stimulation and airway irritation even during
rapid induction.
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Intravenous Anesthetic
Agents
First attempt at intravenous anesthesia by
Wren in 1656-- opium into his dog
Use in anesthesia in 1934 with thiopental Many ways to meet requirements-- muscle
relaxants, opoids, nonopoids
Appealing, pleasant experience
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Inducing agent:
Thiopental
Barbiturate
Water soluble
Alkaline
Dose-dependentsuppression ofCNS activity--decreased
cerebralmetabolic rate(EEG flat)
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Thiopental Systemic Effects
Rapid onset of action; ultrashort recovery period Varied effects on cardiovascular system in
people-- mild direct cardiac depression-- lowers
blood pressure-- compensatory tachycardia
(baroreflex) Dose-dependent depression of respiration
through medullary and pontine respiratory centers
IV route: Onset 1 min; duration 20–
30 min T½: 3–8 hours; metabolized in the liver, excreted
in the urine
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Thiopental Side Effects
Noncompatibility
Tissue necrosis--gangrene
Tissue stores
Post-anesthetic course Laryngospasm occur generally when respiratory
secretion or other irritant are present it can preventedby atropine premedication and administration ofsuccinylcholine immediately after thiopentone.
Succinylcholine and thiopentone react chemically-should not mixed in same syringe.
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Other uses
Occasionally used for rapid control of
convulsion.
I.V infusion of subanasthetic doses can be
used to facilated psychiatric verbal
communication with psychiatric pateint.
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Etomidate
Structure similar to
ketoconozole
Direct CNS depressant(thiopental) and GABA
agonist
Redistribution
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Etomidate Systemic Effects
Little change in cardiac function in healthy and
cardiac patients
Mild dose-related respiratory depression Decreased cerebral metabolism.
it suppress the production of steroid from
adrenal and is not suited for continuous i.v. use.
It is poor analgesic
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Etomidate Side Effects
Pain on injection (propylene glycol)
Myoclonic activity
Nausea and vomiting (50%)
Cortisol suppression
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Propofol
Rapid onset and short duration of action
Myocardial depression and peripheral
vasodilation may occur-- baroreflex notsuppressed
Not water soluble-- painful (50%)
Minimal nausea and vomiting
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Slower acting drugs
Benzodiazepine
Produce sedation and amnesia
Potentiate GABA receptors
Slower onset and emergence
BZDs are poor analgesic: an opoids pr nitric oxide is usually added if theprocedure is painful
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BZDs decrease muscle tone by central action,
but require neuromuscular blocking drugs for
muscle relaxation of surgical grade.
They donot provoke postoperative nausea or
vomiting.
Involuntary movement are not stimulated.
The anesthetic action of BZDs can be reversedby flumazenil
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Diazepam
Often used as premedication or seizureactivity, rarely for induction
Minimal systemic effects-- respirations
decreased with narcotic usage Not water soluble-- venous irritation
Metabolized by liver-- not redistributed
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Lorazepam
Slower onset of action (10-20
minutes)-- not used for induction
Used as adjunct for anxiolytic
and sedative properties
Amnesia are more profound
Not water soluble-- venous
irritation
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Midazolam
More potent than diazepam or
lorazepam
Induction slow, recoveryprolonged
May depress respirations when
used with narcotics
Minimal cardiac effects
Water soluble: non irritating
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Dissociative anesthesia:
Ketamine
Pharmacologically related to the hallucinogen phencyclidine
Interrupts cerebral association pathways -- “Dissociativeanesthesia”
Stimulates central sympathetic pathways
Primary site of action is the cortex and subcortical area; not inreticular activating system.
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Ketamine has been recommended for
operation on the head and neck, in patient
who have bled, in asthamatic(relieves
bronchospasm).
It is good for repeated use; particularly
suitable for burn dressing.
It may dangerous for hypertensive and in
ischemic heart but is good for hypovolemic
patient.
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Ketamine Systemic and Side Effects
Characteristic of sympathetic nervous
system stimulation-- increase HR, BP, CO
Maintains laryngeal reflexes and skeletalmuscle tone
Emergence can produce hallucinations
and unpleasant dreams (15%)
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Clonidine
It is selective α2 adrenergic agonist used as a
antihypertensive.
Stimulation of central α2
adrenoceptors producessedation and analgesia.
Administered before surgery, clonidine reduce
the dose of anesthetic/analgesic drug, resulting
in less overall depression of cardiovascularfunction for the same level of anesthesia.
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Narcotic agonists opiods)
Used for years for analgesic action-- civil war forwounded soldiers
Predominant effects are analgesia, depressionof sensorium and respirations
Mechanism of action is receptor mediated
Minimal cardiac effects-- no myocardial
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Minimal cardiac effects no myocardial
depression
Bradycardia in large doses Some peripheral vasodilation and histamine
release -- hypotension
Side effects nausea, chest wall rigidity,
seizures, constipation, urinary retention
Meperidine, morphine, alfentanil, fentanyl,
sufentanil are commonly used
Naloxone is pure antagonist that reversesanalgesia and respiratory depression
nonselectively- acts 30 minutes, effects may
recur when metabolized
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Muscle Relaxants
Current use of inhalational and previous
intravenous agents do not fully providecontrol of muscle tone
First used in 1942-- many new agents
developed to reduce side effects andlengthen duration of action
Mechanism of action occurs at theneuromuscular junction
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Muscle Relaxants
Neuromuscular Junction
Non-depolarizing Muscle
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Relaxants
Competitively inhibit end plate nicotinic
cholinergic receptor
Intermediate acting (15-60 minutes):atracurium, vecuronium, mivacurium
Long acting (over 60 minutes):
pancuronium, tubocurarine, metocurine Difference-- renal function
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Non-depolarizing Muscle
Relaxants
Tubocurare-- suppress sympathetics, mast
cell degranulation
Pancuronium-- blocks muscarinics Reversal by anticholinesterase-- inhibit
acetylcholinesterase
neostigmine, pyridostigmine, edrophoniumside effects muscarinics stimulation
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Depolarizing Muscle Relaxants
Depolarize the end-plate nicotinic receptor
Succinylcholine used clinically
short duration due to plasma cholinesteraseside effects-- fasiculations, myocyte rupture,
potassium extravasation, myalgias
sinus bradycardia-- muscarinic receptormalignant hyperthermia
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Techniques
History and physical examination
Induction
Maintenance Emergence
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Agents Involved in Balanced
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Anesthesia
Preoperative medications
Sedative–hypnotics
Opiods
Antiemetics Anticholinergics
Antihistamines
Neuroleptics
Narcotics
Why there is need to give
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preoperative medication
For relief of anxiety and facilated smooth induction.
Amnesia for pre- and postoperative events.
Supplement analgesic action of anesthetics andpotentiate them so that less anesthetics is needed.
Decrease the secretion and vagal stimulation caused byanesthetics.
Antiemetics effect extending to the postoperative period.
Decrease acidity and volume of gastric juice so that it is
less damaging if aspired.
Sedative-antianxiety drugs: BZDs have become popular drug forth ti b th d t ilit d th
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preanesthetics because they produce tranquility and smootheninduction, there is loss of recall of preoperative events. Theycounteract CNS toxicity of anesthetics. Barbiturate is absolute.
Promethazine: is an antihistaminic with sedative, antiemetic and Anticholinergics properties. It is particularly use in children.
Anticholinergics: Atropine or hyoscine have been used, primarilyto reduce salivary and bronchial secretions. The main aim of theiruse now is to prevent vagal bradycardia and hypotension, andprophylaxis of laryngospasm which is precipitated by respiratorysecretion. they dilate pupils, abolish the pupilary sign and increasesigns and increase chances of gastric reflex by decreasing tone oflower esophageal sphincter.
Glycopyrrolate: Is a longer acting quaternary atropine substitute. it isa potent antisecretory and antibradycardiac drug; acts rapidly andless likely to produce central effect.
Neuroleptics: chlorpromazine,triflupromazine or haloperidol arefrequently used in premedication. They allay anxiety, smootheninduction and have antiemetic action. however they potentiaterespiratory depression and hypotension caused by the anestheticsand delay recovery.
Involuntary movement and muscle dystonias can occur, specially inchildren.
Antihistamines: H2 blockers patient undergoing prolonged
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Antihistamines: H2 blockers, patient undergoing prolongedoperations, obese patients are at increased risk of gastricregurgitation and aspiration pneumonia.Ranitidine or Famotidinegiven night before and in the morning benefit by raising PH of gastric
juice; may also reduce its volume and thus chances of regurgitation.prevention of stress ulcer is another advantage.
Antiemetics:metaclopramide preoperatively is effective in reducingpost operative vomiting. By enhancing gastric emptying and tone ofLES, it reduces the chance of reflux and its aspiration.Extrapyramidal effect and motor restlessness can occur.
Domperidol is nearly as effective and does not produceExtrapyramidal side effect.
Opiods: Morphine or pethidine ally anxiety and apprehension of theoperation, produce pre- and post operative analgesia, smootheninduction, reduce the dose of anesthesia required and supplementpoor analgesic(thiopentone, halothane) or weak nitrous oxide
anesthetics. Use of opiods is now mostly restricted to those having preoperative
pain. When indicated fentanyl is mostly injected just beforeinduction.
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