Induction

Question 1

What are the priorities during induction of anesthesia?

Answer 1

• Establish patent airways, give oxygen
• Maintain cardiovascular function
• Maintain anesthesia

Question 2

What is induction? When does it happen?

Answer 2

• Transition from a (semi-) conscious state to unconsciousness
• Dangerous and stressful event
• Happens almost invariably via administration of a short-acting anesthetic IV

Question 3

What are the different injectable anesthetics?

Answer 3

• Dissociative anesthetics
  
  • Ketamine, tiletamine, phencyclidine
• Propofol
• Barbiturates
  
  • Thiopental, phentobarbital
• Imidazole derivatives
  
  • Etomidate, metomidate
• Neurosteroids
  
  • Alphaxalone, alphadolone

Question 4

Ketamine

Answer 4

• Old but relatively safe anesthetic
• Onset is slower than that of thiopental
  
  • Only differs by a few seconds–more important in equine
• Has active metabolite
• Eliminated slower from cats than dogs
• Dysphoria may be present during recovery

Question 5

Ketamine–CV effects

Answer 5

• Direct negative inotropic effect
• Causes catecholamine release (sympathomimetic effect) therefore indirectly increases HR and contractility
• Danger–if the catecholamine stores are depleted (very sick patient) or under anesthesia (catecholamine release inhibited) negative inotropic effect may dominate
  
  • Can lead to death (instant)

Question 6

Ketamine–respiratory effects

Answer 6

• Minimal respiratory depression
• Apneustic breathing (breath hold at full inspiration)
• FRC of the lungs is higher than with other agents
• Bronchodilation (useful in asthma)
• Upper airway reflexes may work (gagging) but do not function well

Question 7

Intracerebral pressure (ICP)

Answer 7

• The body compensates by squeezing out CSF and blood volumes from the skull
• If the critical volume is reached pressure goes up and the brain herniates
• There is hardly any perfusion in that state and the prognosis is grave
• The anesthetist can manipulate IC blood volume and therefore can control ICP

Question 8

What are some factors that increase cerebral blood volume?

Answer 8

• Hypercapnia, hypoxia
• Hypertension
• Effects of drugs

Question 9

Ketamine–CNS effects

Answer 9

• Cerebral vasodilation–intracerebral volume and pressure increase (ICP)
• May worsen cerebral perfusion and cause brain herniation in patients with elevated ICP
• Cerebral metabolic O₂ consumption increases
• May be seizurogenic but may also be used to treat epileptic seizures

Question 10

Other effects of ketamine?

Answer 10

• Increased salivation
• Open eyes (corneal drying or damage)
• Some muscle tone may remain
• Intraocular pressure increases
  
  • Harmful with corneal damage (e.g. descemetocele)

Question 11

Indications of ketamine?

Answer 11

• Hypovolemic shock
• Asthma
• Most risk patients may tolerate it in small doses
• Useful for chemical immobilization of aggressive animals

Question 12

Contraindications of ketamine?

Answer 12

• Brain trauma or tumor
• Perforating eye injury
• HCM and most other heart diseases
• Epilepsy

Question 13

Telazol–general

Answer 13

• Contains tiletamine (similar to ketamine) and zolazepam (benzodiazepine)
• Effect is similar to diazepam-ketamine, but Telazol is longer lasting
• Formulated as powder to be diluted as needed
• Useful for aggressive small animals or wild animals

Question 14

Propofol–general

Answer 14

• Fast onset short duration
• Fast metabolism in the liver
• No accumulation (slight in cats)
• Smooth induction and recovery
• Ideal for TIVA
• The basic formulation does not contain preservative
• Give only IV

Question 15

Propofol–CV effects

Answer 15

• Vasodilation (hypotension)
  
  • Not really an issue in healthy animal
• Negative inotropy (mild effect)
  
  • High doses
• No reflex tachycardia

Question 16

Propofol–respiratory effects

Answer 16

• Respiratory rate decreases
• Apnea possible (depending on dose and speed of administration)
  
  • Can be life-threatening in the field
• Tidal volume decreases
• Does not inhibit laryngeal movement (intubation may be difficult)

Question 17

Propofol–CNS effects

Answer 17

• Cerebral vasoconstriction
• Intracerebral blood volume and ICP decreases
  
  • ​Very good choice for brain trauma/complications
• Cerebral metabolic O₂ consumption decreases
• Has antiepileptic effect and may be used to terminate status epilepticus
• May cause muscle twitches

Question 18

Barbiturates–general

Answer 18

• Short acting: thiopental (induction of anesthesia)
• Middle duration: pentobarbital (euthanasia)
• Long acting: phenobarbital (anti-epileptic medicament)

Question 19

Thiopental–general

Answer 19

• Fast onset and short duration
• Fast resdistribution
• Slow metabolism
• May cumulate after repeated doses
• Strong alkaline pH
• May cause tissue damage if given paravenously
• Removed from USA

Question 20

Thiopental–CV effects

Answer 20

• Negative inotropy (more than that of propofol)
• Vasodilation (less than that of propofol)
• Respiratory and CNS effects are similar to those of propofol

Question 21

Etomidate–general

Answer 21

• Formulated in propylene glycol or lipid emulsion
• Fast onset, short duration
• No cummulation
• Minimal CV effects

Question 22

Etomidate–CV effects

Answer 22

• Almost none
• Not arrhythmogenic
• Does not affect HR or BP in appropriate small doses
• Number 1 choice for induction of hemodynamically unstable patients

Question 23

Etomidate–other effects

Answer 23

• Respiratory depression weaker than with propofol
• Effect on ICP similar to propofol
• May produce or terminate seizures
• Inhibits cortisol secretion (6 hrs after an induction dose)
• May cause vomiting even while unconscious
• Excitement and twitching is common
• Recommended to give soon after fentanyl injection (decrease the etomidate dose and inhibit vomiting)
• Not an easy-to-use drug–needs experience

Question 24

Alfaxalone–all ze thingzz

Answer 24

• Steroid anesthetic (neurosteroid)
• Minimal CV effects
• Onset slower than with propofol
• Duration ~20 min
• Recovery can be rough after high doses
• No allergic reaction (unlike Saffan)
• New and promising drug