test 5 IV anesthetics Flashcards
Stages of General Anesthesia
- Induction
- Maintenance
- Recovery
Induction anesthesia
- Time from administration to development of effective anesthesia
• Propofol
• IV
• Produces unconsciousness in 30-40 seconds
• Additional IV or inhaled agents
• To produce desired depth of anesthesia
• Inhaled agents used for children without IV access
• Neuromuscular blocker
• Facilitate tracheal intubation and muscle relaxation
Maintenance anesthesia
- Provides sustained anesthesia
• Monitoring
• Vital signs
• Response to stimuli
• Volatile anesthetics
• Commonly used for maintenance
• Opioids
• Inhalation agents not good analgesicsRecovery from anesthesia
- Time from discontinuation of anesthetic until consciousness and reflexes return
• Redistribution from site of action
• Reversal agents for neuromuscular blockers
• Patient closely monitored
Depth of Anesthesia
• Four sequential stages characterized by increasing CNS depression as anesthetic accumulates in the brain
Stage I
- Analgesia
- Loss of pain sensation
• Results from interference with sensory transmission in the spinothalamic tract
• Progression from conscious and conversational to drowsy
• Amnesia occurs as stage II is approached - epi usually released so increase in HR
- pupil size normal
Stage II
- Excitement
- combative behavior
-try to skip this stage
• Delirium and possibly combative behavior
• Increase in BP and respiration
• Irregular BP and respiration
• Risk of laryngospasm
• This stage is shortened or eliminated when rapid-acting IV agents are given before inhalation anesthetics - pupil size may be dilated
Stage III
- Surgical Anesthesia
• Gradual loss of muscle tone and reflexes
• Further CNS depression
• Regular respiration
• Relaxation of skeletal muscles and loss of spontaneous movement
• 4 planes of Stage III
• Ideal stage for surgery!
4 Planes of Stage III
• Plane I
• Light anesthesia
• Most reflexes still present
- Pupil size normal
• Plane II (most surgeries performed at this level)
• Medium anesthesia
• Muscles relaxed, reflexes absent
- Pupil size slightly dilated
• Plane III
• Deep anesthesia
• Intercostal muscles relaxed, respiration endangered
- Pupil size moderately dilated
• Plane IV
• Too deep
• All muscles, including diaphragm and intercostals are paralyzed
- Pupil size widely dilatedStage IV
- Medullary Paralysis • Respiratory arrest • Circulatory collapse • Ventilation and circulation must be supported to prevent death • Death within 1-5 minutes - Pupil size widely dilated
Intravenous Anesthetics
Uses
- Rapid induction
- Used alone for short procedures
- Continuous infusion for longer cases
- Low doses used for sedation
Induction with IV Anesthetics
- Once unbound, lipid-soluble (to get into the brain), non-ionized molecules cross into the brain it exerts its effects
- Exact mode of action of IV anesthetics- UNKNOWN
Recovery from IV Anesthetics
• Due to REDISTRIBUTION from sites in the CNS
- out of the brain into the blood stream
• Rapid recovery after single IV dose
• Metabolism and plasma clearance only important for infusions and repeat doses
IV Anesthetic Considerations
• When CO is reduced, the body compensates by sending more CO to the brain
• The dose of the drug must be reduced
• Induction time takes longer
- SLOW TITRATION of a REDUCED DOSE is key for safe induction when cardiac output is low
IV Anesthetics- Propofol (Diprivan)
• Used for induction and/or maintenance
• First choice for induction
• 30-40 seconds
• Widely used
• Poorly water soluble
• Supplied as emulsion containing soybean oil and egg phospholipid
• Redistribution half life: 2-4 minutes
• Elimination half life: 2-4 hours
• Depresses CNS
• Some excitatory phenomena: muscle twitching, spontaneous movement, yawning, hiccupping
• Decreases blood pressure
• No myocardial depression
• Does not provide analgesia
• Narcotic supplementation required
• Sedation at low doses
• Antiemetic effects (helps for post-op nausea and vomiting)
- might help protect the heart
