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Anaesthesia > Injectable and Inhalational Anaesthetic Agents > Flashcards

Injectable and Inhalational Anaesthetic Agents Flashcards

1
Q

Injectable agent use

A

Injectable agents are commonly used to induce and sometimes maintain general anaesthesia.

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2
Q

Indications for use of injectables

A

Induction agent for inhalational anaesthetics

To supplement inhalational agents

Sole agent for short surgical procedures, clinical examination, radiography etc.

To suppress CNS stimulation in certain conditions eg. some poisonings, tetanus, seizures etc.

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3
Q

Injectable routes of administration

A

Intravenous

Intramuscular

Subcutaneous

Intraperitoneal

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4
Q

What is induction?

A

Induction is the process where the animal leaves the normal conscious state and enters into the anaesthetised state.

I/v route is the most common route used for induction of anaesthesia

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5
Q

The route of drug administration affects…

A

a) The speed of onset of anaesthesia
b) Duration of the anaesthetic
c) Timing of the peak effect of the drug

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6
Q

How are injectable anaesthetics metabolised

A

Metabolised by the liver where they are converted from lipid to water soluble forms.

This allows them to be excreted in bile and urine via the kidneys.

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7
Q

Induction agents

A

Propofol

Alfaxalone

Barbiturates

Ketamine

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8
Q

Propofol - Route and characteristics

A

Propofol is a water soluble PHENOL anaesthetic

Route - IV only

Characteristics -

  • Rapid loss of consciousness
  • Rapid recovery – metabolised by liver
  • Useful in total intravenous anaesthesia (TIVA)
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9
Q

Propofol - Advantages and disadvantages

A

ADV-
• rapid metabolism and recovery
• Free from hangover if single dose given
• Non-cumulative therefore can be used as part of TIVA protocol
• Non-irritant peri-vascularly

DIS
• May cause APNOEA if injected too fast
• May cause hypotension and occasional bradycardia
• May cause twitching, spontaneous muscle activity and excitable recoveries

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10
Q

Alfaxalone - Route and characteristics

A

This is a STEROID anaesthetic

Route- IV (dogs, cats and rabbits)

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11
Q

Alfaxalone - Advantages and disadvantages

A 
ADV-
•	Rapid smooth induction
•	Minimal cardiorespiratory depression 
•	No pain on injection/ no perivascular tissue irritation
•	Rapidly eliminated from the body

DIS-
• Adequate premed required for smooth induction
• Must be kept quiet during the recovery period to avoid over excitement (drug is rapidly eliminated from system)

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12
Q

Barbiturates - Advantages and disadvantages

A

Barbiturates as anaesthetic agents in modern practice has now been superceded by agents such as propofol and alfaxalone.

ADV-
rapid induction of unconsciousness combined with good muscle relaxation

DIS-
no analgesia is provided , drugs generally have myocardial and respiratory depressant effects

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13
Q

Ketamine - Advantages and disadvantages

A

Ketamine is a ‘dissociative anaesthetic’.

Route- IV, IM, SC, MMs

ADV-
Analgesic properties (may be used with lignocaine & morphine via MLK infusion)

can be used alone in cats

DIS-

Hard to monitor

The onset of anaesthesia tends to be SLOW

Poor muscle relaxation

injection can be painful

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14
Q

TIVA

A

Total Intravenous Anaesthesia

Alternative to gaseous anaesthetics

Ideally utilising constant rate infusion & syringe driver

useful where inhalational delivery would compromise access for surgery

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15
Q

Barbiturate anaesthetics

A

Highly lipid soluble, (enter the brain tissue rapidly - onset of anaesthesia is fast 15-30 seconds)

Barbiturate levels in muscle and fat rise more slowly

Gradually blood levels fall as drug enters muscle/fat

When blood level falls drug leaves brain tissue into plasma and is redistributed

Animal shows signs of recovery but drug is still present in muscle/fat and is slowly released and metabolised by the liver and excreted in urine over time

Not suitable choice for animals with renal hepatic or cardiovascular disease

Increased potency and prolonged recovery in thin animals due to lack of body fat to redistribute drug

Not suitable for shocked patients due to reduced blood flow to fat and increased cardiac and cerebral blood flow

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16
Q

Signs of dissociative anaesthesia

A

Eyes remain open

Pupils dilated

Protective airway reflexes maintained

Cranial nerve reflexes less depressed compared to other agents

Heart rate increases – BP usually maintained

Breathing moderately reduced

Salivation increases

17
Q

Neuroleptanalgesics

A

Tranquilliser combined with analgesic e.g. benzodiazepine and ketamine or alpha2-agonist and ketamine

18
Q

Ketamine mixtures

A

ACP

Diazepam

Xylazine

Medetomidine

19
Q

Opioid mixtures

A

Often combined with neurolepts eg. ACP but beware of hypoventilation and arrhythmmias

20
Q

I/M administration

A

Can only be used for certain drugs

Dose required is usually much greater than the iv dose

Whole calculated dose must be given

Takes longer to onset of effect than if given iv

May be painful

May be associated with prolonged recovery

Hypnorm and ketamine mixtures are commonly given i/m

21
Q

Carrier gases

A

Inhaled anaesthetics are transported in carrier gases

OXYGEN

NITROUS OXIDE –see later

22
Q

Use of O2

A

Uses; 100% pure O2 is given to animals with

Anaemia
Pulmonary pathology
Hypoventilation
Animals recovering from N2O anaesthesia/supplied during recovery if needed

It may be used pre and post operatively routinely *

23
Q

Nitrous Oxide Advantages

A

Odourless

Combined with oxygen as a carrier gas

Analgesic properties (at concentrations of over 20%) and non-irritant

Used in conjunction with other anaesthetic agents

Usually given at 66% delivered

Has an anaesthetic sparing effect

second gas effect – it enhances the uptake of other inhalational agents

24
Q

Nitrous Oxide Disadvantages

A

not use more than 80% N2O as this will lower oxygen below normal levels

diffuses into gas-filled spaces & accumulates – can compromise certain patients.

Should be avoided in cases with pathological abdominal or thoracic distension Eg. pneumothorax or GDV

25
Q

Nitrous oxide- diffusion hypoxia

A

N2O has low solubility in blood

At the end of anaesthesia when administration of N2O ceases, the N2O present in blood diffuses back into the alveoli and ‘dilutes’ the alveolar air so less O2 is available.

If the animal is breathing room air hypoxia may occur.

ALL PATIENTS SHOULD RECEIVE 5-10 MINS OF PURE OXYGEN ONCE THE N2O IS SWITCHED OFF

26
Q

Inhalational anaesthetics advantages

A

Depth of anaesthesia readily altered

Concentration of anaesthetic in blood or brain may be altered rapidly by changing vaporiser setting

Elimination of inhaled agents occurs mainly via the lungs therefore advantage if liver/kidney patient

Allows constant delivery of oxygen alongside agent

Most patients are intubated therefore IPPV may be performed and anaesthetic is ‘safer’

27
Q

Inhalational anaesthetics advantages

A

Need for anaesthetic machine and range of equipment – cost

Hazards, personnel health risk, explosion risk

Knowledge required of circuits and machine

Induction and recovery possibly delayed due to lung pathology

28
Q

MAC

A

Minimum Alveolar Concentration

Measure of anaesthetic potency

Quantity of anaesthetic required to immobilize 50% of patients

Agents with lower MAC value are most potent.

29
Q

High blood gas solubility

A

Agents with a high solubility take longer to work and recovery may be longer as they can build a reservoir in plasma eg. halothane

30
Q

Low blood gas solubility

A

Agents with lower blood gas solubility tend to have more rapid induction and recovery eg. sevoflurane.

31
Q

Inhalational agent examples

A

Halothane
Isoflurane
Sevoflurane
Desflurane

32
Q

Halothane

A

Formerly the most commonly used volatile anaesthetic in practice

Sweet smelling, clear liquid at room temperature

Non flammable and non explosive

Decomposes in UV light

Contains antioxidant

Fast acting anaesthetic

33
Q

Halothane- physiological effects

A

Potent anaesthetic

Modest muscle relaxation

Poor analgesic

Dose-dependent depression of CVS

Predisposes heart to arrhythmias – sensitises the heart to catecholamines

Vasodilatation (brain, uterus, skin)
Decreases respiratory rate

34
Q

Isoflurane

A

CURRENT ‘POPULAR’ VOLATILE AGENT IN VETERINARY PRACTICE

Liquid without additives or preservatives

Pungent smell

Greater margin of safety than halothane

Rapid induction

Rapid recovery

Is less potent therefore higher inspired concentrations needed to maintain anaesthesia

35
Q

Isoflurane properties

A

Good muscle relaxation
Good analgesic

Rapid recovery

Transient excitability esp following painful surgery

Hypotension

Does NOT sensitise the heart to arrhthymias

POTENT RESPIRATORY DEPRESSANT

POORLY TOLERATED FOR MASK INDUCTION – pungent smell and irritant to airways.

36
Q

Sevoflurane

A

INCREASING POPULARITY IN VETERINARY PRACTICE

Rapid induction and rapid recovery
when compared to isoflurane as has lower blood;gas solubility

Pleasant non-irritant odour

Well tolerated for mask induction

UNSTABLE IN PRESENCE OF SODA LIME

37
Q

Sevoflurane physiological effects

A

Similar cardio-pulmonary effects as iso

Hypotension (dose dependent)

Does NOT sensitise the heart to catecholamines

RESPIRATORY DEPRESSION (DOSE DEPENDENT)

Very little liver metabolism – liver friendly

38
Q

Desflurane

A

Relatively ‘new’ agent

Lowest blood;gas solubility allowing rapid alterations in anaesthetic depth and fast recovery

Irritant to respiratory tract in high concentrations (but well tolerated in mask induction)

Rapidly excreted via lungs
Requires a special temperature controlled pressured vapouriser - expensive

Anaesthesia (9 decks)

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