Injectable general anesthetics cont. + Preanesthetic medications

Question 1

What is propofol

Answer 1

• an intravenous anesthetic used for induction and maintenance of anesthesia
Popular in veterinary
medicine due to its smooth induction and recovery.

Question 2

Mechanism of action of propofol

Answer 2

• effect on the inhibitory GABA receptor - ↓the rate of GABA dissociation from
its receptors - ↑ opening of chloride channels - hyperpolarization of postsynaptic cell membranes and inhibition of the postsynaptic neurons - hypnosis and amnesia.

Question 3

Propofol indications

Answer 3

• induction of general anesthesia (followed with inhal. anesthesia)
• maintenance of anesthesia (via CRI)
• short-term sedation, long-term sedation (e.g., ventilator patients),
• treatment of status epilepticus
• used almost exclusively in small animals for economic reasons

Question 4

Effect of propofol on the muscles

Answer 4

Excellent muscle relaxation

Question 5

Proposal and analgesia

Answer 5

Does not provide analgesia

Question 6

Name the 2 dissociative anesthetics

Answer 6

Ketamine and Tiletamine

Question 7

What are dissociative anesthetics

Answer 7

• have been extensively used in vet. medicine and may still be the most common class of anesthetics in use.
• Newer phencyclidine derivatives
– ketamine HCl - drug of abuse in humans
– tiletamine HCl - only in combination with zolazepam
• When anesthetized with ketamine, patients appeared to feel dissociated from or unaware of their environment, but did not always appear asleep (cataleptic).
– Later it was determined that these drugs did indeed dissociate the thalamocortical and limbic systems causing the change in awareness.

Question 8

Mechanism of action of dissociative anesthetics

Answer 8

-noncompetitive antagonists at N-methyl-D-aspartate (NMDA) receptors - prevent the binding of glutamate at the NMDA receptor- depressed activity at the thalamocortical and limbic systems and depression of nuclei in the reticular activating system
• Anesthesia with dissociatives produces an altered consciousness or catalepsy - drugs make them “not care” about what is going on around them.
• produce analgesia!!! which partially mediated through activation of mu and kappa opioid receptors. The NMDA receptor is also involved in pain processing

Question 9

Effect of dissociative anesthetics on the muscles

Answer 9

little muscle relaxation and may cause muscle rigidity

Question 10

Dissociative anesthetics and analgesia

Answer 10

provide a significant amount of analgesia

Question 11

Dissociative anesthetics and the eyes

Answer 11

Many patients do not close their eyes, can have muscle tone and muscle movement, and often do not look “asleep”. It is important to protect the corneas

Question 12

Dissociative anesthetics indications

Answer 12

• chemical restraint, rapid induction of anesthesia, and to provide analgesia;
  • can safely be used in most species

Question 13

What species can dissociative anesthetics be used in?

Answer 13

All except for New Zealand White rabbits

Question 14

Describe neurosteroids

Answer 14

Include alphaxalone and alphadolone
• Neuroactive steroids are agonists at the γ-aminobutyric acid (GABA) receptor. This results in inhibition of pathway activation controlling arousal and awareness.
• great for very short surgical anesthesia in dogs and cats ( about 5-10 minutes)
– ~ 25% of cats will have edema of feet, ears, and muzzle, which resolves usually within 2 hours

Question 15

What are preanesthetics agents?

Answer 15

A preanesthetic agent is a drug that is given before the administration of an anesthetic agent to decrease anxiety and to obtain a smoother induction of, maintenance of and recovery from anesthesia.
• usually administered to animals 15-45 min. before induction of general anesthesia.
- Basically, they are any drugs except for general anesthetics that are used before general anesthesia

Question 16

What are the primary and secondary aims of using preanesthetic anesthesia

Answer 16

• The primary aims of preanesthetic medication are to calm the animal, to facilitate handling, and to relieve preoperative pain.
• Secondary goals are:
– to minimize undesirable reflex autonomic nervous system activity
• parasympathetic: vagal nerve, salivary and bronchial secretions;
• sympathetic: arrhythmic and arterial blood pressure alterations,
– to supplement general anesthesia (to add to level of analgesia, sedation and to reduce
anesthetic requirement),
– to minimize undesirable postanesthetic recovery complications,
– to prevent infection and to continue treatment of intercurrent disease.

Question 17

Advantages of preanesthetic agents

Answer 17

-reduced stress of animal, 
• smoother induction and recovery,
• decreased amount of induction and possibly maintenance agent 
• analgesia intra and postoperatively, 
• reduced secretions,
• reduced autonomic reflexes,
• handler safety!!!!!!!!!!

Question 18

Name the groups of preanesthetic medications

Answer 18

• anticholinergics - parasympatholytics
• tranquilizers
• alpha-2 agonists
• opioids
• phencyclidines
• neuroleptanalgesics