P19: General Intravenous Anaesthetics

Describe the use of etomidate

ultra-short acting hypnotic sedative with GABA-like effects

Describe the use of ketamine

rapid acting general anaesthetic with analgesic activity,
slow onset

Describe the use of propofol

onset of action is rapid,
induction is smooth,
duration of action short (2-10 minutes),
possible to use as a continuous infusion

Describe the use of tiletamine-zolazepam

nonnarcotic, nonbarbiturate injectable anaesthetic

How can myoclonus and excitement during induction or recovery of etomidate be prevented?

adequate pre-induction sedation with a tranquiliser or opioid drug

How does propofol cause direct myocardial depression?

decrease in Ca2+ and myofilament sensitivity to Ca2+

How is etomidate metabolised?

rapid hepatic hydrolysis (does not accumulate)

How is propofol metabolised?

glucuronide synthase in liver

How is thiopental metabolised?

slowly by hepatic microsomal system

In which animals is propofol used and for what?

cats and dogs,
short procedures or prior to inhalant anaesthesia

What are anticholinergic agents used for as pre-anaesthetic medications?

prevent profuse salivation and bradycardia (atropine)

What are central muscle relaxants used for as pre-anaesthetic medications?

induction of anaesthesia in horses, cattle, and swine (Guaifenesin)

What are examples of barbiturates?

thiopental, pentobarbital, hexobarbital

What are examples of dissociative anaesthetics?

ketamine, tiletamine, phencyclidine

What are examples of miscellaneous IV anaesthetics?

metomidate, propanilid

What are examples of nonbarbiturates?

propofol, etomidate, chloral hydrate

What are opioids used for as pre-anaesthetic medications?

provide analgesia (morphine)

What are the advantages of intravenous anaesthesia?

excitation stage not seen;
act more rapidly (unconsciousness in 20 seconds);
simple application;
suitable for bronchial/pulmonary diseases;
normally used for induction of anaesthesia

What are the contraindications of tiletamine-zolazepam?

not used in patients with severe cardiac or pulmonary dysfunction;
not used during any stage of pregnancy (teratogenic potential unknown)

What are the disadvantages of intravenous anaethesia?

large volume of distribution and wake up is associated with redistribution and metabolism of the drug;
depth of anaesthesia is less controlled;
ceases to act only after metabolised and excreted;
many are classified as controlled substances (restrictions on purchase, storage, use)

What are the doses of thiopental?

dogs: 15-30 mg/kg IV
cats: 20 mg/kg IV
cattle, sheep: 15 mg/kg IV

What are the effects of tiletamine-zolazepam?

good muscle relaxation during deep surgical anaesthesia;
normal pharyngeal-laryngeal reflexes;
cataleptic anaesthesia

What are the groups of compounds used as intravenous anaesthetics?

barbiturates, nonbarbiturates, dissociative anaesthetics, miscellaneous agents

What are tranquilisers used for as pre-anaesthetic medications?

provide preoperative sedation and amnesia and help to prevent or counteract CNS stimulation caused by some anaesthetics (acepromazine)

What effect does ketamine have?

lacks cardiopulmonary depressant effects,
psychotomimetic effects following recovery,
postoperative nausea, vomiting and salivation,
raised intracranial pressure

What effect does thiopental have?

profound hypnosis and anaesthesia;
skeletal muscles are light relaxed;
cardiovascular and respiratory depression;
motoric reaction and tonus are not sufficiently inhibited;
decreases tonus and mobility of GIT and urinary tract;
accumulation occurs giving slow recovery

What effects does etomidate have?

minimal depression of cardiovascular and respiratory function,
decreases cerebral blood flow, metabolic rate, and oxygen consumption;
inhibits adrenal steroidogenesis by inhibiting 11β-hydroxylase, reducing the normal increase in plasma cortisol associated with anaesthesia and surgery (up to 3 hours);
myoclonus and excitement can occur either or initiation or recovery

What is ketamine contraindicated for?

patients with prior hypersensitivity;
animals to be used for human consumption;
not to be used alone for major surgery

What is the effect of propofol?

decreases cerebral flow and cerebral oxygen consumption (safe for the use in animals with head trauma or increased intracranial pressure);
myoclonic twitching and limb paddling;
myocardial depression;
peripheral vasodilation and venodilation (blood pressure and cardiac output decrease);
cardiovascular and respiratory depression;

What is the mode of action of ketamine inducing anaesthesia and amnesia?

functionally disrupting the CNS through overstimulating the CNS or inducing a cataleptic state;
inhibits GABA;
blocks serotonin, norepinephrine, and dopamine in CNS

What is the pharmacologic action of tiletamine characterised by?

profound analgesia

What is thiopental contraindicated for?

absence of suitable veins;
history of hypersensitivity reactions to barbiturates;
shortness of breath;
gravidity (readily crosses placental barrier)

What is thiopental soluble in?

fat

What is thiopental used for?

induction of anaesthesia,
sole anaesthetic agent for very short procedures

What negative effects does etomidate have and why?

may cause pain and haemolysis upon IV injection as it is very hypotonic,

What procedures is ketamine used for?

diagnostic, or minor, brief surgical procedures that do not require skeletal muscle relaxation

Which animals is etomidate used in and for what?

dogs and cats,
prior to inhalant anaesthesia,
sole anaesthetic agent for short procedures

Which animals is tiletamine-zolazepam used in, and for what?

dogs: restraint and minor procedures of short duration requiring mild to moderate analgesia
cats: restraint and anaesthesia combines with muscle relaxation

Which intravenous anaesthetics are commonly used for induction of anaestheis?

thiopental, propofol, etomidate

Which species can ketamine be used in?

humans, sub-human primates, cats, other species

Which types of drugs can be used as pre-anaesthetic medications?

opioids, tranquilisers, anticholinergic agents, central muscle relaxants

Why are pre-anaesthetic medications used?

facilitate anaesthesia and surgery by improving rapidity and smoothness of induction, reducing anxiety, providing analgesia and amnesia, and compensating for some side effects of anaesthesia (salivation, bradycardia)

Why is thiopental an excellent induction agent for general anaesthesia?

ultra-short acting, rapidly acting

Why is tiletamine not used on its own?

does not provide adequate muscle relaxation for abdominal surgical procedures