Injectable anesthetics

Question 1

What are the principles (goals) of general anesthesia?

Answer 1

• Unconsciousness (hypnosis)
• Analgesia
• Muscle relaxation
• Lack of movement in response to surgical stimulus

Question 2

TIVA

Answer 2

Total intravenous anesthesia–induction and maintenance of anesthesia using only intravenous agents

Question 3

PIVA

Answer 3

Partial intravenous anesthesia–induction and maintenance of anesthesia using both intravenous and inhalant agents

Question 4

What is ‘balanced anesthesia?’

Answer 4

A combination of techniques to achieve induction and maintenance anesthesia (always used now)

Question 5

Comparison of inhalation and TIVA

Answer 5

• Inhalation
  
  • Equipment demanding
  • No cummulation
  • Easier to monitor and control anesthetic depth
  • Safe airways, 100% O2 mechanical ventilation
• TIVA
  
  • Easier technique
  • Drugs may cummulate
  • More difficult to monitor and control anesthetic depth
  • Airways??

Question 6

T/F: TIVA does not mean that you don’t give O₂

Answer 6

TRUE–Intubation and administration of 100% O₂ is beneficial for every anesthetized patient regardless of anesthetic technique and agent of choice!

Question 7

What are the 2 drug administration strategies for induction of anesthesia?

Answer 7

• Classical–give half the calculated dose slowly IV then top it up with small boluses to effect
• Bolus dosing–give only small boluses up to effect as needed; a single bolus is not expected to be ‘harmful’

Question 8

What types of systems are the classical and bolus administration techniques?

Answer 8

• Classical = analogue system
• Bolus = digital system

Question 9

What are the advantages/disadvantages of the digital system?

Answer 9

• Advantages
  
  • Only need to know 1 dose
  • May induce anesthesia with smaller doses
• Disadvantages
  
  • First bolus may be too little
  • May give double dose initially if indicated

Question 10

Context-sensitive half-life

Answer 10

• Elimination half-life of an agent after long CRI
• Depends on the duration of the CRI

Question 11

What are the characteristics of an ideal agent for TIVA?

Answer 11

• Short acting
• Short context sensitive 1/2 life (not cummulating)
• Does not have active metabolite
• Has wide therapeutic window
• Provides smooth recovery, etc.

Question 12

Propofol-fentanyl TIVA (general)

Answer 12

• Most common in small animal anesthesia
• Give loading dose before
• Start CRI higher, reduce rate later on

Question 13

Alphaxalone TIVA (general)

Answer 13

• Does not cummulate if CRI is not too long
• Excessive doses may lead to prolonged recovery and dysphoria, especially in cats
• Should combine with opioid analgesics!

Question 14

Etomidate TIVA

Answer 14

• Quick metabolism, no cummulation
• Almost ideal agent except for one thing:
  
  • Inhibition of cortisol secretion
  • Patients died in human ICR after 2-3 days of etomidate CRI
• NOT AN OPTION FOR TIVA

Question 15

Ketamine based TIVA

Answer 15

• Cumulates after large or repeated doses causing delayed and rough recovery
• Triple dip: anesthetic mixture for horses
  
  • Guaifenesin
  • Xylazine (may substitute other alpha₂)
  • Ketamine
• Suitable for field procedures