general anaesthesia
TRANSCRIPT
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General anaesthesia
Henning Andreas Haga
Associate professor
Norwegian School of Veterinary Science
Anaesthesia
• A reversible drug induced condition of unconsciousness.
• Goals:– Unconsciousness
– Muscle relaxation
– Analgesia
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Anaesthetics
• Injections
• Gas
Side effects
• Respiratory depression
• Cardiovascular depression
• Risk of reduced oxygen tension (hypoxia)
• Balance between moving animals and respiratory arrest.
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Injection
• Subcutaneously (under skin)
• Intramuscullary (into muscle)
• Intraperitoneally (into abdominal cavity)
• Intravenously (into vein)
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• Subcutaneous, intramuscular or intraperitoneal injection.
• Simple, but less control
Injection
Injection
• Subcutaneous, intramuscular or intraperitoneal injection
• Simple but less control
Time
Eff
ect
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Intravenous anaesthesia
• Rapid effect
• Easy to administer more
• Intravenous access
TidPla
smak
onse
ntra
sjon
Intravenous induction
• Rapid
• Good control
• Can be given to effect
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Intravenous anaesthesia
0
0
Tid
Pla
smak
ons
entras
jon
(ng/m
l)
Infusjonskons
0
0
Tid Plasm
akonse
ntras
jon (ng/m
l)
Boluskons
Plasmakons
Infusjonskons
Intravenous anaesthesia
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Species difference
• 10 mg xylazine is a suitable dose to sedate a cow (500 kg) and a cat (5 kg)
• Diclofenac, NSAID kills vulture through residues in carcasses.
• Ketamine doses: – Horse 2.5 mg/kg– Pig 15 mg/kg– Rat 70 mg/kg
• Diazepam (Valium©), excitation in some animals
Anaesthetic gas
Anaesthetic gas
Gas anaesthesia
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Why gas?
Anaesthetic machine
• You need to convert fluid into gas
• You need to remove CO2
• You need to administer oxygen
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Gas induction
• Possible to use only one anaesthetic
• Rapid recovery• No drug need to be
matbolised• Stressful• Sevoflurane better for
induction than isoflurane
Maintainance of gas anaesthesia
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Maintainance of gas anaesthesia• Transition from
injection to gas, need to consider for how long the injection has effect
Tid
Gass
Injeksjon
MAC
• Minimum alveolar concentration
• The alveolar gas concentration inhibiting movement as a response to a standardised nociceptive stimulus in 50 % of animals.
• MAC differs between species, but the order between the gases within a species is similiar.
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MAC
MAC
1,89 %Mean
1,65 %11
1,85 %10
1,85 %9
2,35 %8
1,75 %7
2,05 %6
2,25 %5
1,85 %4
1,65 %2
1,65 %1
Individual isoflurane MACPig number
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Perception →←Modulation
Transduction →
Transmission →
General anaesthesia
↓↓↓↓
Analgesia
Blodtrykk, mmHg
55
60
65
70
75
0 5 10 15 20
Tid, minutter
Gje
nnom
snitt
stry
kk, m
mH
g
Bedøvelse Kastrasjon
Kontroll
Testikkel
Streng
Theta power
59
60
61
62
63
0 5 10 15 20
Tid (minutter)
The
ta p
ower
(dB
)
Streng
Kontroll
Testikkel
Injeksjon Kastrasjon
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Aims of anaesthesia
• Unconsciousness
• Muscle relaxation
• Analgesia
With one drug?
Balanced anaesthesia
• In contrast to one single anaesthetics doing all
• Combination of drugs to minimise side effects and taylor drugs to the need of the patient
• Drug combination depends upon:– Species
– Nociception to be expected
– Duration of procedure
– Equipment and expertise avaiable
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Maintainance
• Gas for unconsciousness.
• Analgesics should optimally take care of nociception.
Monitoring of anaesthesia
• Manuel:– Respiratory
movements
– Pulse rate and quality
– Mucous membrane colour
• Electronic equipment– Pulsoximetry
– Multi gas analyser
– Elektrocardiography
– Blood pressure
– etc....
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Temperature
Recovery from anaesthesia
• Take care of the needs of the animal– Oxygen
– Temperature
– Fluids
• Analgesia!– Do not let an animal
wake up to pain.
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Take home message
• Pain and nociception induces malign physiological changes
• Combination of analgesics may be wise• Anaesthetised does not feel pain, but they respons
to nociceptive input• Anaesthesia is a balance between respiratory and
cardiovascular compromise and moving animal.• Perioperative pain management important for
postoperative pain.