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Pharmacology I > 14. General anaesthetics: Injectable anaesthetics > Flashcards

14. General anaesthetics: Injectable anaesthetics Flashcards

1
Q

Analgesia

A

Lack of pain sensation

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2
Q

Anaesthesia

A

Lack of sensation, total loss of motoric activity (+pain?)

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3
Q

Give the stages of general anaesthesia

A

Stage:

  1. Disordered consciousness - Induction
  2. Excitement
  3. Surgical anaesthesia
  4. Overdose
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4
Q

Induction is by…

A

Injectable anaesthetics

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5
Q

Maintenance is by…

A

Inhalational anaesthetics

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6
Q

List the injectable anaesthetics

A
  • Barbiturates
  • Propofol
  • Imidazole anaesthetics
  • Steroid anaesthetics
  • NMDAr antagonists (dissociative anaesthetics)
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7
Q

List the barbiturate anaesthetics

A
  • Pentobarbital
  • Methohexital
  • Hexobarbital
  • Thiopental
  • Thiamylal
  • Phenobarbital
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8
Q

List the steroid anaesthetics

A
  • Alfadolone
  • Alfaxolone (in fix combination)
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9
Q

Imidazole anaesthetics

A
  • Etomidate
  • Medomidate
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10
Q

NMDAr/Dissociative anaesthetics

A
  • Ketamine
  • Tiletamine
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11
Q

Other injectable anaesthetics

A
  • Propofol
  • Propanidid
  • MgSO4
  • Chloral hydrate
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12
Q

Properties of ideal injectable anaesthetics

A
  • Water + Lipid soluble
  • Sufficiently potent (volume)
  • Good analgesic activity
  • Should produce muscle relaxation
  • Non-irritant to tissue
  • Rapid + safe induction
  • High TI
  • It should have a pharmacological antagonist
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13
Q

Barbiturates: Mechanism of effects combined

A
  • GABA-BDZ-Barbiturate-receptor complex (GABAA) allosteric action.
  • Further supposed effects: Decrease in Ca2+ accumulation → inhibition in the release of transmitters
  • Stabilisation of membranes
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14
Q

Barbiturates: paradox phenomenon

A

General inhibition

  • But the sensitivity of certain structures differs
  • Some are suitable for general anaesthesia
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15
Q

Barbiturates: Pharmacological effects

A
  • CNS
  • Circulation
  • Respiration
  • Unconsciousness
  • Muscle relaxation
  • Analgesia (but not appropriate)
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16
Q

Barbiturates: Kinetics

A
  • pKa
  • Lipophilicity
  • Lipoid/water partition
  • Redistribution
  • Metabolism
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17
Q

Barbiturates are classified according to…

A

The duration of action:

  • Short-acting
  • Ultra-short acting
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18
Q

Administration of barbiturates

A

Only IV

  • Effective & harmless
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19
Q

Barbiturates: Pharmacokinetics

A
  • Duration (IV) :
    • = 15-60min (short)
    • = 5-8min (ultra-short)
  • Distribution: Fast - Complete, BBB
  • Placenta → Foetus (pronounced side effect)
  • Redistribution → Fat, muscle → Leave CNS → Wake up
  • Accumulation (fat) → Readministration Ø
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20
Q

Barbiturates: Indication

A
  • Induction, general anaesthesia (combination)
  • Convulsive state, epilepsy (pentobarbital I.v)
  • Euthanasia
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21
Q

Barbiturates: Contra-indications

A
  • Younger age (under 2 months)
  • Diminished cardia output
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22
Q

Barbiturates: Side effect

A

Small therapeutic index (Life-threatening)

  • Respiratory depression
  • Cardiovascular depression
  • Tissue irritation
  • Prenarcotic excitation (Cats)
    • Postnarcotic excitation (Horse, dog)
  • Greyhounds are oversensitive
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23
Q

List the ultra-short acting barbiturates

A
  • Thiopental
  • Methohexital
  • Hexobarbital
  • Pentobarbital
  • Thiamylal
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24
Q

Dosage: Methohexital

A

BRIETAL®

IV:

  • Large animal = 5-10mg/kg
  • Small animal = 25-30 mg/kg
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25
Q

Dosage: Thiopental

A

INTRAVAL®

IV:

  • Large animal = 5-10mg/kg
  • Small animal = 25-30 mg/kg
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26
Q

Dosage: Hexobarbital

A

NOVOPAN®

IV

  • Horse = 10-20mg/kg
  • Cat = 30-40mg/kg
  • Lab. animals = 100mg/kg (IP)
27
Q

Dosage: Pentobarbital

A

NEMBUTAL®

IV

  • Cat & Dog = 25-35mg/kg
  • Lab animals = 50-80mg/kg (IP)
28
Q

Dosage: Thiamylal

A

SURITAL®

IV

  • Horse = 4-6mg/kg
  • Cattle = 8-12mg/kg
  • Dog & Cat = 10-20mg/kg
29
Q

Pentobarbital (short-acting) effect

A
  • IV: 15-60min duration
  • Anaesthesia
  • Euthanasia
30
Q

Thiopental (ultra-short) effect

A
  • IV 5-8min duration
  • Accumulation, slow/long wake-up
  • Ø Readministration
  • Prior to inhalational anaesthesia (rare) (side-effect)
31
Q

Propofol: Pharmacological effect

A

GABAA

  • Unconsciousness
  • Muscle relaxation (good)
  • Analgesia (not pronounced) → Combination (opioids)
32
Q

Propofol: Pharmacokinetics

A
  • Duration
    • IV = 30-45sec → 5-15min
      • Quick recovery (minutes)
  • Distribution: fast - Complete, BBB, placenta
  • Quick hepatic + extrahepatic metabolism
    • Can be administered during liver failure
  • Elimination in the form of metabolites
    • Glucuronide conjugate
33
Q

Propofol: Indications

A
  • Induction and maintain general anaesthesia
  • TIVA (Total IV anaesthesia) with opioids and sedatohypnotics
  • Convulsions, epileptic seizure (rare)
34
Q

Propofol: Contraindications

A
  • Cardiac impairment
  • Respiratory impairment
  • Renal impairment
  • Hepatic impairment
35
Q

Propofol: Side effects

A
  • Transient apnoea during induction
  • Cardiovascular depression
  • Vomiting, excitation during recovery (rare)
  • Allergy, septicaemias
  • Increased ICP & occular pressure
36
Q

Propofol: Proprietary products

A
  • Narcofol inj.
  • Vetofol 1.0%
  • Fresofol® 1.0%
  • Diprican inj./inf. (human)
37
Q

Propofol: Dosage

A

IV

  • Induction
    • Mammals = 5-6mg/kg
    • Reptiles & birds = 10mg/kg
  • Maintenance
    • 2.5-5mg/kg (double-bolus)
    • or continuous infusion = 0.1/mg/kg/min
38
Q

List the Imidazole anaesthetics

A
  • Etomidate
  • Metomidate
39
Q

Etomidate: Pharmacological effect

A

GABAA receptor

  • Unconsciousness
  • Muscle Relaxation - Good
  • Analgesia (not pronounced) → Combination (opioids)
40
Q

Etomidate: Pharmacokinetics

A
  • Duration: IV = up to 10-20min
  • Distribution: Fast - Complete, BBB, placenta
  • Quick wake-up & excitation
41
Q

Etomidate: Indications

A
  • Induction, before inhalational anaesthesia
  • Combination (opioids)
    • Short procedures
42
Q

Etomidate: Side effects

A

Broad therapeutic index

  • Severe tissue irritation - only IV
  • Respiratory depression (mild)
  • Cardiovascular depression Ø
  • Adrenocortical suppression (2-3 hours)
  • Pre-/postnarcortic excitation
43
Q

Etomidate: Dosage

A

Mouse = 23-33mg/kg (IP)

44
Q

Metomidate

A

Methyl analogue of etomidate used mainly in pigs

  • Moderate analgesic effect
  • Highly acidic
  • Cardio-respiratory depression is moderate
  • Resps. ↓ but volume ↑
  • Horses: Tremors, convulsions
45
Q

Metomidate: Dosage

A
  • Dog = 10-15mg/kg IV
  • Cat = 3-5mg/kg IV
  • Pig 4-10mg/kg IV (with Azaperone)
  • Reptiles = 10mg/kg IM
  • Fish = 1-20mg/L water
46
Q

Give a steroid anaesthetic

A

Alfaxalone/Alfadolone = Althesin®

47
Q

Alphaxalone/alfadolone: Pharmacological effect

A
  • Unconsciousness
  • Muscle relaxation - Good
  • Analgesia (not pronounced) → Combination (opioids)
48
Q

Alphaxalone/alfadolone: Pharmacokinetics

A
  • Onset:
    • IV 30sec;
    • IM 5-10min
  • Duration = up to 10-30min
  • Quick metabolism; Ø Accumulation
    • Readministration
  • Quick recovery
49
Q

Alphaxalone/alfadolone: Side effect

A

Broad therapeutic index

  • Cardiovascular depression
    • Hypotension, negative ionotropic
  • Histamine release → Allergy → Necrosis (rare)
  • Postnarcotic excitation (rare)
    • Stimulation during recovery (vocalisation)
50
Q

Alphaxalone/alfadolone: Licensed product

A
  • Cremofor → Cat
51
Q

NMDA-r antagonists

A
  • Ketamine
  • Tiletamine
52
Q

Ketamine: Proprietary names

A
  • Bioketan® inj.
  • CP-Ketamin® inj
  • Narketan® inj.
  • Calypsol® inj. (human)
53
Q

Tiletamine: Proprietary name

A

Zoletil® inj. 50/100

54
Q

Ketamine: Pharmacological effect

A

An antagonist of the NMDA receptors in the CNS

  • Unconsciousness (species-dependent) → Catalepsy
  • Analgesia - Pronounced (modulation of opioid receptors)
  • Ø Muscle relaxation → Muscle rigidity
55
Q

Ketamine: Pharmacokinetics

A
  • Onset:
    • IV: 1min
    • IM: 5-10min
  • A relatively long duration of action - Delayed recovery (hours)
  • Distribution: Crosses placenta barrier
  • Metabolised in the liver (80%) into norketamine
    • Norketamine → Hydroxylised → Urine and bile
56
Q

Ketamine: Indications

A
  • Anaesthesia
    • Induction
    • Maintenance
57
Q

Ketamine: Contra-indications

A
  • Sole use in horses & dogs
  • Hepatic & liver impairment
  • Late-pregnancy
58
Q

Ketamine: Side effects

A
  • Catalepsy-like condition
  • ↑ Sympathetic tone
  • ↑ CO, HR, BP, arrhythmias
  • Mild respiratory depression, ↑ tidal volume
  • Salivation
  • Pre-/postaesthetic excitations, convulsion
  • ↑ ICP/eye pressure
59
Q

Ketamine: Dosage

A

IM (SC, IV) 10% injection

  • Dogs & horses → Used in combination ONLY
  • α2-agonists
60
Q

Ketamine: TI

A

Broad TI

61
Q

Ketmaine: Metabolisation in cats and dogs

A
  • Dog: Primary metabolized in liver
  • Cat: Primarily excreted by kidneys
62
Q

Neuroleptanalgesia

A

A state of sedation combined with analgesia

(neuroleptic + analgesic)

63
Q

Give an example of a combination used for neuroleptanalgesia

A

Etorphine & Acepromazine

Pharmacology I (19 decks)

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