Week 8 - CNS Anaesthetics Flashcards
What are the 3 main effects of Anaesthesia?
Unconsciousness
Loss of response to painful stimuli
Loss of reflexes
What are the 3 main targets of Anaesthesia?
Thalamus
Cortex
Hippocampus
What are the 4 stages of anaesthesia?
1 - Analgesia
2 - Delerium
3 - Surgical anaesthesia (4 planes)
4 - Medullary paralysis (multi-systems failure)
What are the characteristics of Stage 1: Analgesia?
- conscious
- all reflexes
- inability to feel pain
What are the characteristics of Stage 2: Delerium?
- Vomiting, Salivation, Coughing
- Increased tone, BP, HR
- loss of awareness
What are the characteristics of Stage 3: Surgical anaesthesia; Phase 1 & 2?
- regular breathing rhythm
- progressive reduction in tidal vol
- pupils larger
- depressed vomoting, withdrawal, corneal reflex
What are the characteristics of Stage 3: Surgical anaesthesia; Phase 3?
- Used for surgery
- Regular breathing rhythm
- Small tidal vol
- pupils 3/4 dilated
- depression of laryngeal (gag) reflex
What are the characteristics of Stage 3: Surgical anaesthesia; Phase 4?
- irregular, diaphragmatic shallow breathing
- pupils fully dilated
- depression of cranial and anal sphincter reflex
What are the characteristics of Stage 4: Medullary paralysis?
- Respiratory failure
- Cardiovascular failure
- Lack of pupillary reflex
What is the aim of surgical anaesthesia regarding the 4 Stages?
To move from Stage 1 to 3 quickly, avoiding stage 2.
How is moving from Stage 1 to 3 quickly and avoiding stage 2 acheived?
- By a combination of inhalation and IV
- a rapid IV induction, maintained by inhalation
What are the type of anaesthetics?
- opiates and alcohol (used for centuries)
- inhalation (maintenance)
- Parentally/IV (induction)
What are the main types of Inhalation anaesthetics??
-Nitours Oxide (gas)
-Halogenated hydrocarbons (liquid)
Eg Halothane
What are the main types of Intravenous anaesthetics?
- Barbiturates
- Propofol
- Ketamine
What are the characteristics of Inhalation Anaesthetics?
-most common
-takes minutes to act
-depth of anaesthesia realted to amount in CNS
–hard to predict with gas
- clearance via lungs
Eg. Halothane, Nitrous Oxide, Xenon
What are the characteristics of Nitrous Oxide?
- poor anaesthetic
- good analgesic
- low toxicity for acute usage
What are the characteristics of Halothane?
-used with nitrous oxide
-deep anaesthesia at low [] (2%)
Can cause
-dysrhythmias
-liver damage
What are the characteristics of IV anaesthetics?
- used for induction
- act rapidly (20s)
eg. thiopental, propofol
What are the characterisitics of Thiopental?
- Barbituate CNS depressant
- highly lipid soluble = pass BBB
- Blood [] decrease rapidly (80% in 2mins)
- Long duration effect due to leeching from adipose tissue.
What are the characteristics of Propofol?
- similar to Thiopental
- fast acting w/ rapid metabolism
- rapid recovery, less hangover
What are the characteristics of Ketamine?
- not a barbituate
- Blocks glutamate receptors
- blocks ion channels opened by ACh
- muscle tone and respiration remain normal.
What are 3 types pre-anaesthetic adjuvants?
- Benzodiazapines
- Analgesics
- Antimuscurinics
What is the aim of using Benzodiazapines as a pre-anaesthetic adjuvant?
- Relieve anxiety
- Produces some amnesia
What is the aim of using Analgesics as a pre-anaesthetic adjuvant?
Relieves anxiety
Provides post op. analgesia