Induction Agents

Question 1

Barbiturates (Thiopental)

Answer 1

• thiopental, methohexital, pentobarbital and phenobarbital
• ultrashort acting (10-15mins) IV
• rapid, smooth and excitement free induction
• excitment and hypertonus can occur if an inadequate dose is administered to an unsedated or poorly sedated animal.
• Thiopental
• dose dependent decrease in cerebral metabolic oxygen requirements, cerebral blood flow and intra-cranial pressure
• good for head trauma, brain tumors, hydrocephalus and possible seizures

Question 2

What are the precautions in barbituate use?

Answer 2

• Can cause peripheral vasodilation which can lead to hypotension
• Usually a compensatory increase in heart rate to offset vasodilation
• Hypotension usually not an issue in normal healthy patients
• Avoid drug in CHF, hypovolemic and pre-existing hypotension patients
• Bigeminy (normal ECG followed by a VPC)
• common at induction and no Tx needed
• Must use IV
• strong alkalinity can cause sloughing and necrosis if injected perivascular
• infuse with 0.5-2mL of lidocaine
• dilute drug with saline if perivascular
• highly protein bound
• hence will enhance effect if given concurrently with NSAIDs and benzodiazepines
• hypoproteinemia will greatly prolong the duration and effect
• Sight hounds or any skinny patient lack the body fat and muscle for redistribution of drug and hence prolonged effects seen
• cummulative in the body, therefore don’t use CRI or repeated doses