Barbiturates Flashcards
Name the four classes of barbiturates with an example and the duration of each.
- Ultrashort –> Methohexital - ~30 sec
- Short –> Thiopental - 10-20 min
- Intermediate –> Pentobarbital - ~1-2 hr
- Long –> Phenobarbital - ~12 hr
Which class is used as an anticonvulsant but not an anesthetic?
- Long
Induction time of barbiturates depends on ______.
Lipid solubility
What drug is highly lipid soluble and which is less lipid soluble?
- Thiopental
- Pentobarbital
Explain redistribution.
- Drugs are in the blood stream
- Vessel rich tissue (brain) receives the most blood flow and the most drug
- Less vessel rich (Muscle and fat) receive less blood flow so the levels rise slowly in these tissues
- As the drug enters these tissues the level falls in the blood stream in the brain
Why can these drugs not be redosed?
- Muscle and fat will act as a sponge and the levels will remain high in the brain which will prolong the drugs effect
What two effects does this drug have on vital systems?
- Respiratory depression
- Cardiac toxicity
When using these drugs _____ is common after induction and cardiac toxicity occurs in the ______.
- Apnea
- First 10 minutes
What is cardiac toxicity?
- Bradycardia and hypotension
- Increased catecholamine induced arrhythmias
How do you prevent cardiac toxicity?
- Give slowly over 10 - 15 seconds
- Use dilute concentrations
What is the role of protein in this class?
- The drug circulates in two fractions
- The free drug exerts its effect and bound drugs do not
- With low protein levels there is more free drug which causes a greater effect
These drugs have greater effects with ______ pH.
Low
What do you do and what may occur if these drugs are given perivascularly?
- Infiltrate with isotonic saline
- Patient will be stuck in stage 2
Why is this drug never administered to sight hounds?
- Sight hounds have a low fat content which inhibits redistribution
Which barbiturate is safe to use in sight hounds?
- Methohexital
