Injectables to produce unconsciousness Flashcards
pharmacological properties of propfol
- a ‘hindered’ phenol: toxic drugs particularly in cats
- high lipid solubility but poor water solubility
Original propofol
- shelf life
- dosing
- advantage
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
Propofol plus
- difference
- shelf life
- limitations (2)
- 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
Propofol: adverse effects
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
Recovery from propofol
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
Alfaxalone dosage
suitable for single induction dose, multiple incremental doses or continuous infusion
-Because it is very rapidly cleared by liver
Pros (3) and cons (2) of alfaxalone
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)
Ketamine
- admin
- effects
-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
CV effects of ketamine
- direct -ve inotropic (contractility) effect in vitro
- increased sympathetic tone in vivo
- increased HR and contractility
- increased cardiac output and arterial blood pressure
Respiratory effects of ketamine
- 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?
Adverse effects of ketamine (6)
- CNS stimulation: excitement/seizures
- pain on injection (not with IV route)
- emergence delirium
- hypertension and tachycardia
- salivation
- muscle rigidity
Ketamine rule
only used in combination with other drugs: BZP/alpha 2 agonist as these will They depress CNS and offset muscle rigidity
Ketamine and BZP dosing
0.2mg/kg diazepam + 5mg/kg ketamine IV
1ml / 10kg of a 1:1 vol:vol mixture of “Valium” and ketamine
When should ketamine be used?
- aggressive animals
- where IV access can’t be established
- in cases of haemodynamic instability
What is the triple combination in cats?
Why is it used?
What is the side effect?
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
Why is triple combination less used in dogs?
What must be done when using it in dogs?
- 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
What are the considerations when reversing the triple combination?
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
Pros (3) and cons (2) of triple combination
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
What is the co-induction agent and when would it be used?
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
What properties (2) must a co-induction agent have?
- allow a reduction in the required dose of the hypnotic
- have minimal cardiovascular depressant effects of their own
Name 2 induction agents and their dosages
0.2-0.5mg/kg IV diazepam
2-10ug/kg IV fentanyl
When would you use TIVA?
- where inhalational anaesthetic agents not available
- where airway cannot shared e.g. bronchoscopy, some airway surgeries
What is NOT an appropriate TIVA?
Ketamine: it is broken down to norketamine which is an active metabolite: starts to accumulate and animal will get deeper and deeper
What drugs are suitable for TIVA?
What makes them suitable?
Any considerations?
Propofol and alfaxalone
- rapid clearance from the body
- smooth recovery with little hangover
poor reflex suppression, therefore, usually administered with an analgesic agent
What drugs are best for TIVA in dogs vs cats?
Are there any considerations about these?
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
