Anaesthesia - Gas

Front 1

What are the main groups of INJECTABLE anaesthetics? (5)

Back 1

Carboxylated imidazole
Barbiturates
Phenols
Cyclohexamines
Steroid anaesthetics

Front 2

What is the main difference between GAs and LAs?

Back 2

GAs exert their main effects on the CNS while LA’s work by blocking conduction of impulses in peripheral sensory nerves.

Front 3

What are the three effects that GA’s have? Which can vary?

Back 3

Produce unconsciousness, analgesia and muscle relaxation; of which, analgesia and muscle relaxation can vary.

Front 4

What are main goals of MOA of GA’s?

Back 4

Either reduced transmitter release or reduced postsynaptic response

Front 5

What is MAC and what is it inversely proportional to?

Back 5

Minimum Alveolar Concentration, proportional to POTENCY.

Front 6

What are the most sensitive regions of the brain to anaesthetics?

Back 6

The thalamic sensory relay nuclei and the deep layer of the cortex

Front 7

What are some benefits of INJECTABLE anaesthetics? (4)

Back 7

Minimal equipment required
Easy to administer
No pollution
Can use TIVA

Front 8

How are most INJECTABLE anaesthetics given and how long until the effect is seen?

Back 8

Mostly IV, and cause loss of consciousness in one ‘arm-brain’ circulation time.

Note: Ketamine given IM.

Front 9

What are BARBITURATES a derivative of?

Back 9

Barbituric acid

Front 10

Name 4 BARBITURATES

Back 10

Thiopental
Pentobarbital
Phenobarbital
Methohexital

Front 11

Barbiturate pharmacokinetics
-lipid solubility
-pKa
-PPB
-Vd
-Metab

Back 11

-highly lipid soluble
-ex. thio 7.6 (61% unionised at pH 7.4) and metho 7.9 (75% unionised)
-around 85%
-LARGE >1L/kg
-liver, oxidation and desulfation

Front 12

How is THIOPENTAL made up?

Back 12

Made up as a sodium salt because free acid is insoluble in water. Is presented as a dry powder and dissolved in water for IV injection.

Front 13

Side effects of THIOPENTAL?

Back 13

Possible apnoea
Cardivascular depression and hypotension
Respiratory depression
Irritant if given extravascularly

Front 14

Which animals indicate THIOPENTAL use?

Back 14

Cats and dogs mostly, but also used in ruminants and horses

Front 15

Discuss muscle relaxation and analgesia for THIOPENTAL.

Back 15

Poor muscle relaxation
No analgesia

Front 16

Pharmacokinetics of PENTOBARBITAL?
-Solubility?
-Admin
-DOA

Back 16

-Water soluble, but instable so presented in propylene glycol
-IV or IP
-Long duration

Front 17

Side efx of PENTOBARBITAL? (3)

Back 17

Hypotension
Respiratory depression
Excitement in recovery

Front 18

Analgesia in pentobarbital?

Back 18

None!

Front 19

What is PENTOBARBITAL used for?

Back 19

Mostly for euthanasia, not recommended for anaesthesia

Front 20

Name the phenol INJECTABLE anaesthesia

Back 20

Propofol!

Front 21

How is PROPOFOL supplied?

Back 21

As a WHITE aqueous/oil emulsion in soy bean oil, egg lecithin and glycerol (the only white IV substance!)

Front 22

PROPOFOL pharmacokinetics?
-spectrum
-admin
-ionisation
-PPB
-Vd

Back 22

-cats and dogs
-IV ONLY
-virtually unionised, extremely lipid soluble
-98%
-HUGE 3L/kg

BASICALLY, excellent pharmacokinetic properties!!

Front 23

Metabolism of PROPOFOL

Back 23

Metab rapidly in liver to quinol sulfate and glucuronide conjugates and has extrahepatic sites in lungs, kidneys and blood. This is useful if dealing with a serious hepatopathy.

Front 24

How does PROPOFOL affect analgesia and muscle relaxation?

Back 24

GOOD muscle relaxant
OKAY at analgesia

Front 25

Problems with Propofol? (4)

Back 25

Dose-dependent cardiovascular depression
Post-induction cyanosis
Apnoea
Respiratory depression

Front 26

What would indicate use of PROPOFOL?

Back 26

-Sight hounds
-Same day short operations
-TIVA in dogs
-Asthmatic cats

Front 27

What is the Cyclohexamine injectable anaesthetic drug?

Back 27

KETAMINE

Front 28

What is ketamine originally derived from?

Back 28

LSD

Front 29

What species is KETAMINE licensed in?

Back 29

Horses, dogs, cats

Front 30

How is KETAMINE administered?

Back 30

IV, IM (painful!), SC, IP and MM

Front 31

KETAMINE pharmacokinetics
-PPB
-Metab
-Excretion

Back 31

-low, 25-30%
-By liver
-Excreted by kidneys

Front 32

Describe ketamine's "dissociative anaesthetic" effect.

Back 32

This is marked sensory loss with analgesia, amnesia and paralysis of movement without actual loss of consciousness.

Front 33

Ketamine MOA

Back 33

NMDA receptor (excitatory) antagonist (blocks it!)

Front 34

Effects of KETAMINE?
-CNS
-CVS
-Resp

Back 34

CNS: unconciousness, maintained cranial nerve reflexes, increased ICP
CVS: increased sympathetic tone (higher HR, CO, BP)
Resp: depression, bronchodilation

Front 35

Pregnancy contraindication for KETAMINE?

Back 35

No drug exists for pregnant animals, ALL are contraindicated because of marked placental transfer. Just monitor.

Front 36

How is KETAMINE used?

Back 36

-Horses for 'triple drip'
-Cats, combo with ACP, a-2, opiods
Cattle, sheep and pigs...but not licensed

Front 37

Problems with Ketamine (4)?

Back 37

High sym tone
Increased ICP
Glaucoma
Epilepsy

Front 38

What are the two STEROID injectable anaesthetics?

Back 38

-Saffan (alphaxalone/alphadalone)
-Alfaxan

Front 39

What species is SAFFAN licensed in?

Back 39

Cats

Front 40

Steroid anaesthetic MOA?

Back 40

Act on GABAa receptors to keep channels open. This hyperpolarises them and therefore decreases excitability

Front 41

Why not use SAFFAN in dogs?

Back 41

It is a viscous solution made with Cremophor EL (polyethoxylated caster oil), which dogs are potentially anaphylactic to.

Front 42

SAFFAN pharmacokinetics
-admin
-PPB
-Metab

Back 42

-IV, IM
- <50%
-Liver

Front 43

Problems with SAFFAN (2)?

Back 43

-rare pulmonary or cerebral oedema
-oedema and flushing of pawa, pinnae

Front 44

ALFAXAN
-SOA
-Admin

Back 44

Made of the most important part of Saffan, Alfaxalone.
-Dogs and cats
-IV only

Front 45

What is the injectable carboxylated imidazole anaesthetic?

Back 45

ETOMIDATE

Front 46

Etomidate MOA

Back 46

Same as SAFFAN, act on GABAa receptors

Front 47

ETOMIDATE pharmacokinetics
-PPB
-TI
-Metab

Back 47

-75%
-Low
-FAST...hepatic and plasmatic esterases

Front 48

Which drug is good for animals with CVS problems?

Back 48

Etomidate

(Ketamine is NOT)

Front 49

Which injectable anaesthetic is BEST for TIVA (and which are bad?!)

Back 49

PROPOFOL best

Etomidate bad becuase suppresses stress reponse
Ketamine good for horses

Front 50

What is in a TRIPLE DRIP combo?

Back 50

a2-agonist
ketamine
gge (glyceryl guiacolate ether)

Front 51

What does a combo of sedatives and opiods do?

Back 51

Used to produce sedation/light anaesthesia - called neuroleptanalgesics

Front 52

What are (5) neuroleptanalgesic combos?

Back 52

ACP + etorphine (LA IMMOBILON)
Methotrimeprazine + etorphine (SA IMMOBILON)
Fentanyl + fluanisone (HYPNORM)
ACP + opiods
a2 agonists + opiods

Front 53

LA IMMOBILON
-SOA
-Why caution?
-Problems?

Back 53

-Horses and wild animals
-Self-injection = death. Have NALOXONE with you.
-Enterohepatic recycling, hypoxia, hypertension and tachycardia

Front 54

SA IMMOBILON
-SOA
-Admin
-Produces?
-Problems?

Back 54

-Dogs
-IV, IM, SC
-Deep sedation, hypnosis and analgesia
-Resp depression, bradycardia, renal failure

Front 55

HYPNORM
-SOA
-Admin
-Produces?
-What drug improves sedation

Back 55

-Small mammals
-IV, IM, SC, IP
-Deep sedation and good analgesia
-Diazepam

Front 56

What is the difference between a vapour vs a gas?

Back 56

Vapour is a substance that at room temperature and at sea level pressure is a liquid (ex. volatile anaesthetics)

Gas is a substance that at room temperature and at sea level pressure is gas (oxygen and N2O)

Front 57

What is a 'critical temperature'?

Back 57

The room temp above which a gas cannot be liquefied however much pressure is applied

Ex. O is -118C and N2O is 36C

Front 58

What is vapour pressure?

Back 58

The pressure exerted by molecules escaping from the liquid surface to enter in the gaseous state. It indicates the ability of a liquid to evaporate and depends on temperature.

Front 59

Do you have to use different vaporisers for different volatile anaesthetics?

Back 59

Yes becuase they are set for different vapour pressure "curves" (pressure and temp).

Exception - can use the same for isoflourane and halothane because have the same curve!

Front 60

What is saturated vapour pressure?

Back 60

Pressure when there is a dynamic equilibrium and this determines the max conc of an anaesthetic.

Front 61

Describe the range of saturated vapour pressures that one can see.

Back 61

Anywhere from 3 kPa for methoxyflurane to 31.5 kPa for isoflurane (this is 31% of atm!) to 88.5 kPa for desflurane.

Front 62

State Henry's Law.

Back 62

The V of gas dissolved in a solvent, at given temp, depends on its partial P and its solubility.

V = PP x S

Front 63

What are the two main theories that state how inhalational anaesthetics work?

Back 63

Lipid theory postulates that it interacts with the lipid bilayer.

Protein theory postulates that it binds with hydrophobic binding sites on protein molecules.

Front 64

What is a partition coefficient?

Back 64

The ratio of conc of agents in 2 phases at equilibrium (ex. blood:gas or oil:gas)

Front 65

What does the blood:gas coefficient determine?

Back 65

The speed of induction and recovery.

Basically "the solubility in blood"

Front 66

The lower the solubility of a gas in blood means what?

Back 66

The faster the process of equilibrium!

Front 67

Which is the most soluble and least soluble inhalational anaesthetic in blood?

Back 67

Methoxyflurane is the MOST soluble (coefficient 15) and Desflurane and N2O are the least (0.42). IE, use N2O!

Front 68

The oil:gas coefficient determines what?

Back 68

The potency.

Front 69

The higher an inhalational agents solubility in lipid (oil) means what?

Back 69

The more potent the gas is and the lower the MAC is.

Front 70

Describe the varying degrees of oil:gas coefficients out there for inhalational agents?

Back 70

Methoxyflurane is 940 (ie, highly lipid soluble, potent and low MAC)

N2O is 1.4 (ie not as lipid soluble, not as potent and high MAC)

Front 71

Recovery can be delayed by what (re: blood and fat)?

Back 71

The more soluble it is in blood and the more soluble it is in fat!

Front 72

Due to lipid solubility, which gas should be used?

Back 72

One in the middle of oil:gas coefficient - sevoflurane, halothane or isoflurane

Front 73

Describe species differences in amounts of inhalational agents with desflurane as an example.

Back 73

Not always same for different species (iso and sevo very similar in cats and dogs). Example is desflurane, which is 7% in dogs but almost 10% in cats! Would need to up or down vaporiser depending on species.

Front 74

Do you start high or low with inhalational agents on the vaporiser?

Back 74

Start high and work down (ie start at 3 for cats to start, even tho halo, iso and sevo MACs are 1.1, 1.6 and 2.6 respect)

Front 75

How can you measure conc of an inhalational anaesthetic in the brain?

Back 75

Measure the end-expiration because it goes brain-arterial blood-alveolus-end expiration!

Front 76

Describe the potential toxicity issue with HALOTHANE.

Back 76

20% metab in liver (like methoxyflurane) produces toxic Br and Cl.

Front 77

What type of gas is HALOTHANE?

Back 77

Halogenated hydrocarbon

Front 78

Describe adverse affects of HALOTHANE due to potency.

Back 78

Very potent (oil:gas is 234) so this can produce respiratory and heart failure, meaning a low BP due to hypotension, dilation and myo depression

Front 79

HALOTHANE analgesia?

Back 79

NONE

Front 80

What is malignant hyperthermia in pigs and what inhalational guy can cause it?

Back 80

HALOTHANE! Its increase heat production in pigs in skeletal muscle due to an increase Ca release from the sarcoplasmic reticulum. This means higher temp and an acidosis.

Front 81

What type of inhalational agent is ISOFLURANE and discuss:
-metab
-solubility
-use

Back 81

Halogenated ether

-not in liver!
-less soluble in blood and lipid than halothane (low potency)
-most widely used!

Front 82

Main effects of ISOFLURANE?

Back 82

Causes hypotension and powerful coronary vasodilation affect, maintains liver bloodflow (dif from halothane) and doesnt increase ICP as much as halothane.

Front 83

SEVOFLURANE
-type
-solubility
-liver metab

Back 83

-halogenated ether
-barely soluble in blood, medium potency (more than desflurane but less than iso!)
-3% but makes nephrotoxic inorganic Fl-

Front 84

Affects of SEVOFLURANE

Back 84

Same, low BP, respiratory depressant (between iso and halo), hepatic flow maintained, ICP lowered!

Front 85

Problem with SEVOFLURANE?

Back 85

Reacts with SODA LIME producing 'compound A' which is nephrotoxic

Front 86

DESFLURANE
-type
-solubility
-liver metab

Back 86

-halogenated ether
-low solubility in blood and fat; low potency and high MAC (7-9%!)
-barely

Front 87

Problems with DESFLURANE
-soda lime
-vaporiser

Back 87

-LOTS of CO when reacting with soda lime produced
-difficult to have precise vaporisation bc has a wierd vaporiser unlike the rest

Front 88

Affects of DESFLURANE

Back 88

The usual, except irritant to respiratory system. Hepatic blood flow maintained and ICP lowered.

Front 89

N2O
-type
-solubility
-MAC help
-metab

Back 89

-NOT A VAPOUR, an inert organic gas
-LOWEST blood and fat solubility, but highest MAC so cannot use as anaesthetic
-lowers MAC of volatile agents, reducing amount needed and lowering CVS effects
-none in liver

Front 90

What is N2O's 2nd gas effect?

Back 90

During induction, N2O moves from alveolus to caps fast so that conc of remaining gas (anaesthetic!) in alveolus is HIGH - results in faster induction.

Use 60% N2O/30% O2 for smallies.

Front 91

What is diffusion hypoxia WRT N2O?

Back 91

This is the opp of the 2nd gas effect. N2O diffuses out of caps into alveolus fast and the end of anaesthesia, which can dilute O2 in alveoli and cause hypoxia.

Front 92

What is the tx for diffusion hypoxia?

Back 92

Give 100% O2 for 5-10 min at the end of anaesthesia

Front 93

Negative effects of N2O?

Back 93

Reduces FiO2, causes hypoxia, increases ICP and pollutes (bone marrow depletion!)