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ANESTHESIA
Claro M. Isidro md
Anesthesia
• Loss of consciousness• Analgesia• Adequate muscle relaxation
Analgesia
•Loss of sensation to pain
Types of Anesthetics:
•General Anesthetics• Reversible loss of consciousness• Loss of CNS activity
•Local Anesthetics• No loss of consciousness• Reversible loss of pain sensation
GENERAL ANESTHETICS:
INHALATIONAL ANESTHETICS
INTRAVENOUS ANESTHETICS
STAGES OF GENERAL ANESTHESIA(Guedel)
• Stage I: Analgesia• Stage II:Excitement/ Delirium• Stage III: Surgical Anesthesia
– Plane I: reg. breathing loss of eye movement
– Plane II initiation of IC muscle paralysis
– Plane III: completion ICM paralysis– Plane IV: diaphragmatic paralysis
• Stage IV: Medullary Paralysis
Pharmacokinetics:• tension (partial pressure) in the brain
depth• tension in this tissues rate of
induction and recovery
• Flow of anesthetic during induction:Anesthesia Lungs Arterial Brain &
machine blood tissues
GENERAL ANESTHETICS:
Pharmacokinetics: • absorption (uptake)• distribution• metabolism• elimination lungs
Principal objective:To achieve a constant and optimal brain partial pressure of the inhaled anesthetic
GENERAL ANESTHETICS:
• 2 PHASES:2 PHASES:
– Pulmonary PhasePulmonary Phase
– Circulatory PhaseCirculatory Phase
GENERAL ANESTHETICS: UPTAKEGENERAL ANESTHETICS: UPTAKE
• Pulmonary Phase Concentration of the anesthetic
agent in the inspired gas
Pulmonary ventilation
Transfer of anesthetic gases from alveoli to blood• solubility of the agent• rate of pulmonary blood flow• partial pressure in the alveoli
and mixed venous blood
GENERAL ANESTHETICS: UPTAKEGENERAL ANESTHETICS: UPTAKE
GENERAL ANESTHETICS: SOLUBILITYPartition Partition
CoefficientCoefficientBlood:GasBlood:Gas Brain:BloodBrain:Blood
SolubleSoluble
MethoxyfluraneMethoxyflurane 1212 22
IntermediateIntermediate
HalothaneHalothane 2.42.4 1.91.9
EnfluraneEnflurane 1.91.9 1.51.5
IsofluraneIsoflurane 1.41.4 1.61.6
Poorly solublePoorly soluble
Nitrous OxideNitrous Oxide 0.460.46 1.11.1
DesfluraneDesflurane 0.420.42 1.31.3
SevofluraneSevoflurane 0.590.59 1.71.7
As a rule, the more soluble an anesthetic in the blood the more of it must be dissolved to raise the partial pressure.
• Pulmonary Phase Concentration of the anesthetic
agent in the inspired gas
Pulmonary ventilation
Transfer of anesthetic gases from alveoli to blood• solubility of the agent• rate of pulmonary blood flow• partial pressure in the alveoli
and mixed venous blood
GENERAL ANESTHETICS: UPTAKEGENERAL ANESTHETICS: UPTAKE
GENERAL ANESTHETICS: UPTAKEGENERAL ANESTHETICS: UPTAKE
• Circulatory or Distribution Phase SolubilitySolubility
tissue:blood solubility coefficienttissue:blood solubility coefficient
Tissue Blood FlowTissue Blood Flow Vessel-Rich group – 75% of COVessel-Rich group – 75% of CO Muscle Group – 3%Muscle Group – 3% Fatty Group – 2%Fatty Group – 2% Vessel-Poor group - <1%Vessel-Poor group - <1%
Partial Pressure of Gas in Arterial Partial Pressure of Gas in Arterial Blood and TissuesBlood and Tissues
• RECOVERY and EMERGENCEFactors affecting rate of Elimination
• SOLUBILITY IN BLOOD & TISSUE• BLOOD FLOW
• Flow of anesthetic during elimination:
Tissue/ Blood Lungs AnesthesiaBrain Machine
GENERAL ANESTHETICS:GENERAL ANESTHETICS:
Ideal Characteristics of Inhalational Anesthetics:
• Rapid & pleasant induction & recovery• Rapid changes in depth of anesthesia• Adequate relaxation of smooth muscle• Wide margin of safety• Absence of toxic effect
INHALATIONAL ANESTHETICS
• GASEOUS ANESTHETIC:• NITROUS OXIDE• CYCLOPROPANE
• VOLATILE ANESTHETIC:
A. HalogenatedA. Halogenated B. Non B. Non HalogenatedHalogenated
1. 1. HalothaneHalothane 1. Ether1. Ether
2. Enflurane2. Enflurane 2.2. Chloroform Chloroform
3.3. Isoflurane Isoflurane
4. Methoxyflurane4. Methoxyflurane
5. Sevoflurane5. Sevoflurane
6.6. Desflurane Desflurane
Halothane• 2 bromo-111 triflouroethane • is a non ether derivative ( an ethane)• vapor is pleasant to smell and non-irritating• can cause a dose dependent reduction of arterial
blood pressure due to: 1. Direct depression of the myocardium 2. The normal baroreceptor mediated tachycardia
in response to hypotension is obtunded • sensitizes the myocardium to catecholamines
leading to cardiac arrhythmia’s • causes a dose related reduction in the ventilatory
response to carbon dioxide • produce adequate muscle relaxation• has no toxic effect on the kidneys
• Repeatedadministration over a short period of time has been implicated to produce halothane hepatitis
• another dreaded complication is malignant hyperthermia, which is characterized by the following:
1. Rapid rise in body temperature 2. massive increase in oxygen consumption 3. increase production of carbon dioxide• Cardiotoxic, Hepatotoxic but not Nephrotoxic
Enflurane• 2 chloro-112 trifluroethyl difluromethyl ether• an halogenated ether derivative • produce mild stimulation of salivation and bronchial• cause dose dependent myocardial depression
similar to that of halothane• sensitizes the myocardium to the effect of
catcholamines , no unusual effect on the GIT • muscle relaxation is greater than that of halothane• contraindicated in patient with seizure disorder
because it cause CNS irritability in high doses• the free fluoride radical a metabolite of enflurane
has been implicated to its renal toxicity so it is contraindicated in patient with renal disorder
• Cadiotoxic, Nephrotoxic but not Hepatotoxic
Isoflurane• 1 chloro-222 trifluroethyl difluromethyl ether • an halogenated ether derivative• the chemical and physical properties are similar to
those of its isomer enflurane• does not sensitize the myocardium to the effect of
cathecholamines • cerebral blood flow is increased while the cerebral
metabolism is reduced• produce adequate muscle relaxation • less nephrotoxic than enflurane • less hepatotoxic than halothane• agent of choice for cardiac surgery• non Cardiotoxic, non Hepatotoxic, non
Nephrotoxic• Least vicerotoxic
Methoxyflurane• 2,2dichloro- 1,1 difluroethyl methyl ether • it is clear, colorless liquid with sweet fruity odor • non flammable and non explosive in air • most potent of the inhalational anesthetic• induction of anesthesia is slow due to its high
solubility coefficient• respiratory and cardiovascular depression is
generally similar to that of halothane • sensitize the myocardium to the effects of
catecholamines • nephrotoxicity and hepatotoxicity are the major
disadvantage • most toxic of the inhalational anesthetic• Cardiotoxic, Hepatotoxic, and Nephrotoxic
Desflurane• a fluorinated methyl ethyl ether that differ from
isoflurane only by substitution of a fluoride atom from chlorine
• can produce a dose related decrease in blood pressure and cardiac output
• non Cardiotoxic, non Hepatotoxic, non Nephrotoxic
Sevoflurane• also a fluorinated methyl ethyl ether• not irritating to the airways• cardivascular effect is similar to isoflurane
Non Hologenated
Ether • first anesthetic discovered • seldom use today because of its flammability and
explosive property
Chloroform• no longer use today because of liver toxicity • non explosive and non flammable • has rapid induction and recovery
Gaseous Anesthetics
Nitrous Oxide
• sweet smelling, non irritating, colorless gas• the only inorganic gas in common use
possessing anesthetic properties• potent analgesic but a weak anesthetic in
the sense that it does not produce adequate muscular relaxation
• ventilatory drive is not affected• little or no cardiovascular effect
Cyclopropane• explosive and flammable property
INHALATIONAL ANESTHETICS
• GASEOUS ANESTHETIC:• NITROUS OXIDE• CYCLOPROPANE
• VOLATILE ANESTHETIC:
A. HalogenatedA. Halogenated B. Non B. Non HalogenatedHalogenated
1. 1. HalothaneHalothane 1. Ether1. Ether
2. Enflurane2. Enflurane 2.2. Chloroform Chloroform
3.3. Isoflurane Isoflurane
4. Methoxyflurane4. Methoxyflurane
5. Sevoflurane5. Sevoflurane
6.6. Desflurane Desflurane
BARBITURATES• the most commonly use barbiturates is the ultra short acting
thiopental• following a single IV anesthetic dose of thiopental
unconsciousness occur after 10-20 seconds and returns in 20-30 minutes
• poor analgesic and may even increase the sensitivity to pain (hyperalgesia) when administered in inadequate amounts.
• Not irritating to the respiratory tract• Cerebral blood flow and cerebral metabolic rate are reduced• Produce a dose related depression of respiration and circulation• Agent of choice for induction of anesthesia in patient with
increased intracranial pressure and hypertension• Contraindicated in patient with acute intermittent porphyria and
hypotension
INTRAVENOUS ANESTHETICSINTRAVENOUS ANESTHETICS
Benzodiazepines (Diazepam) • first introduced for the treatment of anxiety• rapidly absorbed from the GIT after oral
administration• hypnosis and unconsciousness may be produced
with large doses• cause amnesia in 50% of patients
characteristically Anterograde type• may cause moderate depression of circulation
and respiration• they are not analgesic and it is necessary to
combine several drugs to achieve surgical levels of anesthesia
Ketamine HCl • used for induction of dissociative anesthesia• a sensation of dissociation is noticed within 15
seconds and unconsciousness becomes apparent within another 30 seconds and lasts for some 40 minutes
• intense analgesia and amnesia are established rapidly
• muscular relaxation is poor• cardiovascular and respiratory system are stable• drug of choice for induction of anesthesia in
children and hypotensive patients• contraindicated in patients with hypertension
because it increase sympathetic activity • can cause increase intraocular pressure• contraindicated in patient with glaucoma
Propofol
• 2,6 Diisoprophylpenol• produces anesthesia at a rate similar to
that of barbiturates• cause marked decrease in systemic blood
pressure during induction• post operative vomiting is less common
and may have anti-emetic property • hypersensitivity is less common
Properties of a Desirable Local Anesthetic
• should not be irritating to tissues• should not cause permanent damage
to nerves• have low systemic toxicity• must be effective • should have rapid onset but long
duration of action
• MOA: block nerve conduction
• Structure:– aromatic group (Hydrophobic lipophilic)– amide group (hydrophilic)
• tertiary amine or secondary amine– intermediate chain
•Ester or Amide
LOCAL ANESTHETICSLOCAL ANESTHETICS
Structure
CH2-
CH3
NH2 O-O-CH2-CH2-N
O CH2-CH3
Aromatic grp Alkyl Amide grpLipophilic chain Hydrophilic
• METABOLISM:
Ester plasma and liver esterases metabolite: PABA
Amide liver
• EXCRETION:
kidneys
LOCAL ANESTHETICSLOCAL ANESTHETICS
• ROUTES OF ADMINISTRATION:
1. Topical2. Local Infiltration3. Nerve Block4. Spinal or Intrathecal injection5. Epidural 6. Caudal
LOCAL ANESTHETICSLOCAL ANESTHETICS
LOCAL ANESTHETICSLOCAL ANESTHETICS
ESTERS:ESTERS:
1.1. CocaineCocaine
2.2. ProcaineProcaine
3.3. ChloroprocaineChloroprocaine
4.4. TetracaineTetracaine
AMIDES:AMIDES:
1.1. LidocaineLidocaine
2.2. BupivacaineBupivacaine
3.3. MepivacaineMepivacaine
4.4. DibucaineDibucaine
5.5. PrilocainePrilocaine
6.6. EtidocaineEtidocaine
May also be classified into
a. Short acting – cocaine, procaineb. Intermediate acting – lidocaine,
mepivacaine, dibucaine, prilocainec. Long acting – tetracaine,
bupivacaine, etidocaine
1. Hepatotoxic agent a. Isoflurane
2. Nephrotoxic agent b. Barbiturate3. Cardiotoxic agent c. Enflurane4. Thiopental d. Halothane5. Flammable agent e. Ether
a.Amide LA b. Esther LA6. Lidocaine7. Tetracaine8. Cocaine9. Bupivacaine10. Etidocaine