Injectables to produce unconsciousness

Question 1

pharmacological properties of propfol

Answer 1

• a ‘hindered’ phenol: toxic drugs particularly in cats

- high lipid solubility but poor water solubility

Question 2

Original propofol

• shelf life
• dosing
• advantage

Answer 2

must be discarded within 6 hours of opening
-significant waste
-or risk of sepsis
suitable as single dose, repeated boluses or continuous infusion
Advantage: clears rapidly from body

Question 3

Propofol plus

• difference
• shelf life
• limitations (2)

Answer 3

• benzyl alcohol preservative added
• shelf life of 28 days once broached
• limited to infusion duration of 30min in dogs: after which benzylalcohol will become toxic
• do not repeat within 10 days in cats

Question 4

Propofol: adverse effects

Answer 4

cardiovascular depression
		-vasodilation  hypotension
		-myocardial depression at higher doses
respiratory depression
		-post-induction apnoea; occasional cyanosis at 			        induction

excitatory phenomena
-muscle twitching; hypertonus
pain on injection

Question 5

Recovery from propofol

Answer 5

recovery of consciousness from all induction agents is initially due to redistribution of drug

speed of metabolism of drug influences the “hangover effect”

metabolism:
hepatic metabolism
extra-hepatic metabolism
		-lung
		-kidney?
		-blood?
slower in cats than in dogs
	-lack of glucuronide conjugation

Question 6

Alfaxalone dosage

Answer 6

suitable for single induction dose, multiple incremental doses or continuous infusion
-Because it is very rapidly cleared by liver

Question 7

Pros (3) and cons (2) of alfaxalone

Answer 7

Advantages:

• high therapeutic index
• possibly less CV depression cf. propofol
• minimal hangover

Disadvantages

• more expensive than propofol
• recoveries can be ‘rough’ (esp. in absence of premedication)

Question 8

Ketamine

• admin
• effects

Answer 8

-can be given SC, IM or IV (propofol, alfaxalone – IV only)
-produces a state of “dissociative anaesthesia”
-profound analgesia coupled with ‘superficial’ sleep
active reflexes:
-swallowing, movement, open eyes

Question 9

CV effects of ketamine

Answer 9

• direct -ve inotropic (contractility) effect in vitro
• increased sympathetic tone in vivo
• increased HR and contractility
• increased cardiac output and arterial blood pressure

Question 10

Respiratory effects of ketamine

Answer 10

• transient apnoea possible with IV administration
• ventilation usually well maintained when given by SC or IM routes
• laryngeal and pharyngeal reflexes maintained: patients can swallow: safer in aspirating patients?

Question 11

Adverse effects of ketamine (6)

Answer 11

• CNS stimulation: excitement/seizures
• pain on injection (not with IV route)
• emergence delirium
• hypertension and tachycardia
• salivation
• muscle rigidity

Question 12

Ketamine rule

Answer 12

only used in combination with other drugs: BZP/alpha 2 agonist as these will They depress CNS and offset muscle rigidity

Question 13

Ketamine and BZP dosing

Answer 13

0.2mg/kg diazepam + 5mg/kg ketamine IV

1ml / 10kg of a 1:1 vol:vol mixture of “Valium” and ketamine

Question 14

When should ketamine be used?

Answer 14

• aggressive animals
• where IV access can’t be established
• in cases of haemodynamic instability

Question 15

What is the triple combination in cats?
Why is it used?
What is the side effect?

Answer 15

medetomidine (MDT) 80mcg/kg
+ ketamine 2.5-7.5mg/kg
+ butorphanol 0.2mg/kg IM

Essentially provides premedication, induction and maintenance in the one injection

stings

Question 16

Why is triple combination less used in dogs?

What must be done when using it in dogs?

Answer 16

• dogs very sensitive to CNS effects of ketamine (seizures)

- the medetomidine / opioid must be administered first, and ketamine only given once profound sedation has been achieved

Question 17

What are the considerations when reversing the triple combination?

Answer 17

MDT can be antagonised after 40min (cats only): after 40 mins ketamine is starting to wear off in cats

Must not be reversed in dogs as it will leave the ketamine in system causing a seizure

remaining analgesia is only butorphanol (very poor) is give NSAID before reversing

Question 18

Pros (3) and cons (2) of triple combination

Answer 18

Advantages:

• convenience (no need for IV access)
• very useful for aggressive cats
• reasonable duration of surgical anaesthesia

Disadvantages:

• no titrating anaesthetic to effect
• because inhalation maintenance not required, people tend not to protect airway or supply oxygen

Question 19

What is the co-induction agent and when would it be used?

Answer 19

a ‘co-induction’ technique is the use of more than one agent to induce anaesthesia

when critically ill patients can not tolerate the CV depressant effects that most of the induction agents have

Question 20

What properties (2) must a co-induction agent have?

Answer 20

• allow a reduction in the required dose of the hypnotic

- have minimal cardiovascular depressant effects of their own

Question 21

Name 2 induction agents and their dosages

Answer 21

0.2-0.5mg/kg IV diazepam

2-10ug/kg IV fentanyl

Question 22

When would you use TIVA?

Answer 22

• where inhalational anaesthetic agents not available

- where airway cannot shared e.g. bronchoscopy, some airway surgeries

Question 23

What is NOT an appropriate TIVA?

Answer 23

Ketamine: it is broken down to norketamine which is an active metabolite: starts to accumulate and animal will get deeper and deeper

Question 24

What drugs are suitable for TIVA?

What makes them suitable?

Any considerations?

Answer 24

Propofol and alfaxalone

• rapid clearance from the body
• smooth recovery with little hangover

poor reflex suppression, therefore, usually administered with an analgesic agent

Question 25

What drugs are best for TIVA in dogs vs cats?

Are there any considerations about these?

Answer 25

Propofol and alfaxalone are suitable for TIVA in dogs

alfaxalone is suitable for TIVA in cats

• delayed recovery after propofol infusions
• Heinz body anaemia with consecutive day administration