General anesthesia Ma Ling Department of Anesthesiology

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General anesthesia

• Ma Ling
• Department of Anesthesiology
• Shengjing Hospital, China Medical University
• Tel [phone]

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What is general anesthesia?

• A. pain relief (analgesia)
• B. blocking memory of the procedure (amnesia)
• C. producing unconsciousness
• D. inhibiting normal body reflexes to make
  surgery safe and easier to perform
• E. relaxing the muscles of the body

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Definition

• General anesthesia is anesthetics-induced
  reversible suppression on CNS, and has the
  following manifestations
• producing unconsciousness
• pain relief (analgesia)
• blocking memory of the procedure (amnesia)
• inhibiting normal body reflexes to make surgery
  safe and easier to perform
• relaxing the muscles of the body

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Course of General Anesthesia
Maintenance period
IVInhale
Lost consciousness
Induction period
quickly
Recovery period
Exhale
IV
awake
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Route of Action
Intravenous anesthetics
Inhalation anesthetics
Alveolar
blood
Central nervous system
Anesthesia
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Inhalation anesthetics

• Through airway
• Maintenance (most) induction (some)
• Most are halogenated hydrocarbons
• Mechanism interact with the brain cell membrane,
  details are not clear

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How to compare anesthetic potency?

• MAC (minimum alveolar concentration)
• ????????
• The concentration (at 1atm) required to
  prevent movement in 50 of subjects following a
  surgical stimulus
• Oil-gas partition coefficient
• Anesthetic potency
• MAC
• MAC is also an index for depth of anesthesia

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Inhalational anesthesia

• Lower MAC higher potency

Elder hypotension hypothermia
hypothyroidism concurrent use of opioids
Infant pyrexia drug abuser
MAC
MAC
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How to determine its controllability?

• Blood-gas partition coefficient (solubility)
• The lower the blood-gas partition coefficient
  
• the easier for the partial pressure in alveolar,
  blood and brain to get equilibrium
• the easier to control its concentration
  in brain

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Physicochemical property

• (1) oil-gas partition coefficient
• anesthetic potency
  MAC
• (2) blood-gas partition coefficient
• controllability

reverse
reverse
reverse
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Which has the best anesthetic potency?Which
takes effect fastest?
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FA alveolar concentration of anestheticFI
inspired concentration of anesthetic

• FA /FI shows the increasing rate of anesthetic
  in alveolar

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Factors determine FA FA /FI

• Effect of ventilation
• Effect of concentration
• Cardiac output
• Blood-gas partition coefficient (solubility)
• Alveolar-to-venous anesthetic gradient

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Metabolism of inhalation anesthetics

• Major eliminated by lung
• Minor metabolized in liver
• metabolic rate, media product and the final
  product

decide toxicity
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Nitrous Oxide (N2O), ??

• MAC 105, low anesthetic potency, inhalation
  conc.50-70 (FiO2gt0.3) , in combination with
  other agent
• B/G 0.47, fast
• Respiratory system non-irritant, no injury
• Cardiovascular system almost no-depression
• Diffuse hypoxia inhale 100 O2 5-10min
• Increase cavity pressure forbidden in colon
  obstruction

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Enflurane, ???

• Propertiesclear colourless volatile anesthesia,
  pleasant smell
• MAC 1.7, B/G 1.9, Metabolism 2
• Cardiovascular Myocardial contractility reduced
  
• Systemic vascular
  resistanceBP
• Sensitivity of
  myocardium to catecholamine
• Respiratory non-irritant dose dependent
  inhibition
• Muscle relaxation
• Induction and maintenance, unavailable in USA
• Patient with epilepsy history should be avoided
  (seizure activity on EEG)

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Isoflurane, ???

• Properties clear colourless volatile
  anesthesia, pungent odor
• MAC 1.15 B/G 1.4 Metabolism 0.2
• Cardiovascular mild depression of myocardial
  contractility
• systemic
  vascular resistanceBP
• coronary steal
• little
  sensitization of myocardium to Catecholamine
• Respiratory dose dependent inhibition
• Muscle relaxation
• Maintanence

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Sevoflurane, ???

• Properties clear colourless volatile
  anesthetic pleasant smell
• MAC 2 B/G 0.65 (rapid induction in
  children) Metabolism 2
• Cardiovascular similar to isoflurane
• Respiratory dosedependent inhibition, no
  irritate to airway
• Muscle relaxation similar to isoflurane
• Both Induction and maintenance
• Decomposition in soda lime and when temperature
  rises

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Desflurane, ???

• Properties clear colorless volatile anesthesia
• MAC 6.0-7.25 B/G 0.42 (very rapid onset)
  Metabolism 0.02
• Cardiovascular similar to isoflurane but no
  coronary steal
• Respiratory no pungent odor but irritant
• Muscle relaxation stronger than isoflurane
• Induction and maintenance
• Nausea and vomiting
• Special vaporizer, expensive

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Halothane, ??

• Properties clear colorless volatile anesthesia
  pleasant smell
• MAC 0.75 B/G 2.4 Metabolism 20
• Cardiovascular Myocardial contractility reduced
  
• Systemic vascular
  resistanceBP
• Increase
  sensitization of myocardium to catecholamine
• Respiratory non-irritant pleasant smell
  dilate bronchial inhibition
• Muscle relaxation
• Induction and maintenance
• Halothane associated hepatitis seldom in use
  now, unavailable in China

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Questions

• What are the MACs of different anesthetics?
• What determines the anesthetic potency?
• Which anesthetics is the best choice in induction
  of anesthesia in children?
• Which halogenated anesthetic takes effect
  fastest?

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• Intravenous anesthetics

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Ideal Intravenous anesthetic

• Water-soluble, no pain on injection
• Rapid onset, rapid recovery, little accumulation,
  little depression on respiratory-cardiovascular
  system. No nausea and vomiting, no interact with
  muscle relaxant, no release of histamine.

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Intravenous anesthetics
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Thiopentone

• Sedationhypnosis lost consciousness
• 2.5 4-6mg/kg
• Onset 30s
• Analgesic effect poor
• CNS cerebral metabolic
  rate
• 
  anticonvulsant
• Cardiovascular myocardial
  contractility
• 
  vasodiltation, BP
• Respiratory VT RR
• bronchial
  muscle tone
• Indications induction/anticonvul
  sant/anesthesia.

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Propofol, ???

• Out-patient anesthesia
• Induction 2mg/kg maintenance TCI/TIVA
• Supplement to local anesthesia
• Sedation in ICU
• Side effect cardiovascular respiratory
  suppression, excitatory phenomenon, pain on
  injection

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Sodium hydroxybutyrate, ????

• Site Cortex(??)?hippocampus(??)?limbic
  system(????)
• Normal physical sleeping
• CirculationBP slightly increase?HR reduce
• Respiration TV increase?frequency slow
• IndicationInduction and maintenance
• basal anesthesiaketamine
  (poor analgesia effect)
• Dosage 50-100mg/kg
• Onset 5-10min, duration45-60min

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Questions

• Which drug has dissociated anesthesia?
• Which drug can depress steroid synthesis?
• Which intravenous anesthetic can increase
  intracranial pressure?
• What is the induction dosage of propofol?

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Muscle relaxants(?????)

• Skeletal muscle relaxants
• No anesthetic effect
• Cannot make patient lost consciousness
• Cannot produce amnesia
• Suitable condition for surgery
• Avoid hazardous of deep anesthesia
• No analgesia

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Mechanism interfere with the normal action of
acetylcholine (ACH) at the motor end plate, block
the receptors on the postsynaptic muscle membrane
Presynaptic membrane
ACH
Postsynaptic membrane
Depolarization Muscle contraction
ACH
synaptic gap ACH
ACH
ACH
ACH
Impulse
repolarization
??????ACH
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Classification

• Depolarizing muscle relaxants
• suxamethonium (Succinylcholine,
  scoline)
• Nondepolarizing muscle relaxants
• Pancuronium
• Vecuronium
• Atracurium
• Tubocurarine

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Depolarizing muscle relaxantSuxamethonium (????)

• similar to acetylcholine (ACH),binding to
  receptor, depolarizing contraction
  (fasciculation)
• cant be hydrolyzed by cholinesterase,NO
  responses to further action,flaccid-muscle
  relaxant
• Indication tracheal intubate 1-2mg/kg
• peak at 1min, 4-5min,
  recover at 10min
• Side effects muscle pains
• intraocular,
  intragastric, intracranial pressure
• hyperkalaemia
• Malignant hyperthermia

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Nondepolarizing muscle relaxant

• tubocurarine(????)
• binding to receptor , but non-depolarizing
  compete for the receptors
• antagonist by inhibitor of cholinesterase
  (neostigmine????) ?

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Muscle relaxants

• agents intubating dose onset
  action duration
• (mg/kg)
  (min) (min)
• Scoline 1-2
  0.5 3-8
• ????
• Tubocurarine 0.6 4-6
  30-40
• ????
• Pancuronium 0.1 3-6
  30-6
• ????
• Atracurium 0.6
  3-5 15-35
• ????
• Vecuronium 0.1
  2-3 25-30
• ????

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Muscle relaxants

• ??? advantage side effect
  metabolisam histamine release
• Scoline rapid fasciculation,K
  cholinesterase (-)
• pressure
• 
  
• Tubocurarine asthma
  kidney ?bile ()
• Pancuronium HR
  liver kidney bile ()
• Atracurium Hoffmann
  Hoffmann?????? ()
• Vecuronium
  liver kidney bile (-)
• Cis-atracurium Hoffmann
  Hoffmann??????

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Atracurium and cisatracurium

• Dose intubation 0.5-0.6mg/kg
• maintenance 0.15-0.2mg/kg
• Time intubation 90-120s
• duration 20-25min
• Release histamine, hypotension
• Spontaneous degradation in plasma, unaffected by
  liver or renal function
• Cisatracurium more potent

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Rocuronium

• Dose intubation 0.6-0.7mg/kg
• maintenance 0.15-0.2mg/kg
• Time intubation 90-100s
• duration 20-30min
• Can be used for rapid sequence intubation

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Vecuronium

• Dose intubation 0.1mg/kg
• maintenance 0.02-0.03mg/kg
• Time intubation 90-120s
• duration 15-20min
• No histamine release, can be used in patients
  with asthma

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Pancuronium

• Dose intubation 0.15-0.2mg/kg
• maintenance 0.1mg/kg
• Time intubation 100-120s
• duration 10-15min
• Hypertension and tachycardia may occur
• Long-acting

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Questions

• What is the mechanism of the action of muscle
  relaxants? And the classification of them?
• Which drug can induce malignant hyperthermia?

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Thank you!