Lecture 16-17 - anaesthetics

Question 1

Definition of anaesthesia

Answer 1

• lack of sensation, total loss of motoric activity
  
  • local: without loss of consciousness
  • general: total loss of consciousness

Question 2

The stages and signs of general anaesthesia?

Answer 2

Stage 1: disordered consciousness - induction
Stage 2: excitement
Stage 3: surgical anesthesia (ie. unconsciousness, amnesia, immobility, unresponsive to surgical stimulation)
Stage 4: overdose

Question 3

Injectable anaesthetics (+ examples)

Answer 3

• barbiturates (pentobarbitlal, hexobarbital)
• propofol
• imidazole anaesthetics (etomidate, medomidate)
• steroid anaesthetics (alfadolone, alfaxolone)
• NMDAr antagonists
• dissociative anaesthetics (ketamine, tiletamine)

Question 4

Properties of ideal injectable anaesthetics

Answer 4

• water + lipid soluble
• sufficiently potent (volume)
• possess good analgesic activity
• produce muscle relaxation
• non-irritant to tissue
• rapid and safe induction and recovery
• limited effect on vital functions
• have high TI
• not have direct reno- and hepatotoxicity
• rapid metabolism
• neither chemical nor pharmacological incompatibility should occur
• have pharmacological antagonist

Question 5

Barbiturates

• pharmacological effets
• kinetics
• classification
• application

Answer 5

• effects: CNS, circulation, respiration
• kinetics: pKa, lipophylicity, lipoid/water partition, redistribution, metabolism
• classification: short acting, ultra-short acting
• application: IV, effective and harmless

Question 6

Long, middle-long acting barbiturates?

Answer 6

• allobarbital
• amobarbital
• barbital
• phenobarbital

Question 7

Short, ultra-short acting barbiturates?

Answer 7

• pentobarbital
• methohexital
• hexobarbital
• thiopental
• thiamylal
• venobarbital

Question 8

Barbiturates (ultra-short acting)

• pharmacological effect
• pharmacokinetics
• indication

Answer 8

• effect: unconsciousness, muscle relaxation
• pharma: duration iv short: 15-60 min, ultra-short: 5-8 min. Fast distribution, able to cross blood-brain barrier. Redistribution in fat and muscle
• indication: induction, general anaesthesia (combination), convulsive state, epilepsy, euthanasia

Question 9

Barbiturates (ultra-short acting)

• side effects
• dose

Answer 9

• side effects: small TI, respiratory depression (neonates), cardiovascular depression, tissue irritation, prae/postnarcotic excitations
• dose: mg/kg bw (depends on specie and drug)
  Thiopental, metohexital:
  
  • large animal: 5-10
  • small pets: 25-30 IV
    Hexobarbital
  • horse: 10-20
  • cat: 30-40 IV
  • lab animals: 100 IP

Question 10

Pentobarbital (short)

Answer 10

• IV, 15-60 min duration

- anaesthesia, euthanasia

Question 11

Thiopental (ultra-short)

Answer 11

• IV, 5-8 min duration
• accumulation, slow/long wake up
• Ø re-administration
• prior to inhalation anaesthesia (rarely), side effects

Question 12

Propofol

• pharmacological effect GABAa
• pharmacokinetics
• elimination

Answer 12

• effects: unconsciousness, muscle relaxation, analgesia in combination with opioids
• pharma: duration IV 30-45 min (up to 5-15 min). Fast - complete distribution, blood brain barrier, placenta. Quick hepatic + extrahepatic metabolism
• elimination: in urine in form of metabolites, mainly as glucuronide conjugate or other inactive forms

Question 13

Propofol

• indications
• side effects
• dose

Answer 13

• indications: induction and maintain general anaesthesia, TIVA with opioids and sedatohypnotics, convulsions, epileptic seizure (rarely)
  
  • contra indications: cardiac. respiratory,
    renal, hepatic impairment
• side effects: transient apnoea during induction, cardiovascular depression, vomiting, excitation during recovery, allergy, septicaemias, increased ICP and ocular pressure
• dose: mg/kg IV
  
  • induction: 5-6 (mammalians), 10 (reptile
    and bird)
  • maintenance: 2.5-5 (second bolus) or
    continuous infusion 0.1/min

Question 14

Etomidate (imidazole)

• pharmacological effects
• pharmacokinetics

Answer 14

• effects: unconsciousness, muscle relaxation, analgesia in combination with opioids
• pharma: duration IV up to 10-20 min. Fast - complete distribution, blood brain barrier, placenta. Quick wake up + excitation

Question 15

Etomidate (imidazole)

• indication
• side effets
• dose

Answer 15

• indication: induction (before inhalational anaesthesia), combination (opioids)
• side effects: broad TI, respiratory depression (mild), cardiovascular insufficiency, tissue irritation (acidic pH, only IV), prae/postnarcotic excitations, adrenocortical suppression
• dose: mouse 23-33 mg/kg bw IP

Question 16

Metomidate (imidazole)

Answer 16

• commonly used in pigs
• moderate analgesic effect
• highly acidic, IV only into large veins
• frequent prae/post anaesthetic excitation
• moderate cardio-respiratory depression
• dose: mg/kg
  
  • pig: 4-10 IV (with azaperone)
  • dog: 10-15 IV
  • cat: 20-25 IV

Question 17

Steroid anaesthetics

• pharmacological effects
• pharmacokinetics
• side effects
• licenced product

Answer 17

• effects: unconsciousness, muscle relaxation, analgesia in combination with opioids
• pharma: IV 30 min, IM 5-10, duration up to 10-30 min. Quick metabolism, quick recovery
• side effects: broad TI, cardiovascular depression, histamine release, postnarcotic excitation
• product: cremofor (cat), cyclodextrine (dog, cat)

Question 18

Ketamine (NMDA receptor antagonist)

• pharmacological effects
• pharmacokinetics

Answer 18

• effects: unconsciousness (specie dependent), analgesia, muscle rigidity
• pharma: onset IV 1 min, IM 5-10 min, relative long duration of action, distribution- crosses placenta barrier, metabolised in liver (80%) into norketamine which is excreted in urine and bile

Question 19

Ketamine (NMDA receptor antagonist)

• indications
• side effects
• administration

Answer 19

• indications: anaesthesia (in comb), induction and maintenance
  
  • contra indications: sole use in horses and
    dogs, hepatic and/or liver impairment,
    late pregnancy
• catalepsy, increased symp. nervous system tone, increased cardiac output, heart rate and blood pressure, mild respiratory depression, salivation, prae/post anaesthetic excitation, hallucinations
• admin: IM (SC, IV) (5) - 10 % injection
  
  • dogs, horses only in combinations

Question 20

Zoletil

Answer 20

• very fast onset unconsciousness (2-5 min)
• side effects: increased sympathetic tone, dose dependent respiratory depression, pain response when the drug is given by the IM or SC
• dose: cats 10-15 mg/kg, dogs 5-10 mg/kg

Question 21

Combined anaesthesia

• balanced anaesthesia
• TIVA

Answer 21

Balanced anaesthesia

• combination of antimuscarinics, sedatives, opioids, anaesthetics and muscle relaxants
• goal: “good sleep”, safe and deep anaesthesia, pain control, less side effects, relaxed body, smooth recovery

TIVA (total intravenous anaesthesia)

• combination of agents given exclusively by the intravenous route without the use of inhalation agents
• eg: propofol + fentanyl + lidocaine + ketamine

Question 22

Neuroleptanalgesia

Answer 22

• a sate sedation combines with analgesia
• similar, but not equal to a light plane anaesthesia
• animal does not respond to pain or surroundings, but is not totally unconscious
• advantages: less amount of sedatives (safer), prior anaesthesia (safer induction, analgesia more pronounced)

Question 23

Inhalational anaesthetics

Answer 23

• halothane
• isoflurane
• sevoflurane
• dinitrogen mooxide
• desflurane
• methoxyflurane
  —-> all organic halogenated (liquid, more stable, increased
  efficacy)

Question 24

Criteria for the efficacy

Answer 24

Inhaled air -> alveolar air -> blood -> brain

Question 25

Halothane

Answer 25

- most efficacious - induction/arousal phases are long - excitements are frequent - obese animal --> delayed awake - dose: induction 4 - 5%, maintenance 1.5 - 2.5%

Question 26

Isoflurane

Answer 26

- indications: induction and maintain general anaesthesia - contra indications: younger age, pregnant, lactating animals, susceptibility to malignant hyperthermia - side effects: cardiovascular and respiratory depression, cardiac arrhytmias, malignant hyperthermia - dose: induction 2-5 %, maintenance 0.25-3 %

Question 27

Sevoflurane

Answer 27

- indications: induction and maintain general anaesthesia - contra indications: younger age, pregnant, lactating animals, susceptibility to malignant hyperthermia - side effects: cardiovascular and respiratory depression, cardiac arrhytmias - dose: induction 5 - 7 %, maintenance 3.3 - 3.8 %

Question 28

Desflurane

Answer 28

- side effects are more common that of formerly mentioned drugs: respiratory tract irritation, tachycardia

Question 29

Methoxyflurane

Answer 29

- because of low gas-tension and excitements more preferred to use for maintenance - respiratory inhibition is more pronounced - contraindicated in reptiles, strong nephrotoxicity