Anaesthetics Flashcards
What are the types of anaesthetics?
General and local
What are the subdivisions of general anaesthesia?
Onhalation or volatile
IV
WHat is the other less common category of anaesthesia?
Conscious sedation- small amounts of anaesthetic or benzodiazepine to produce a sleepy state
WHart are the stages of anaesthesia in surgery?
Predication Induction Intraoperative analgesia Muscle paralysis- intubation Maintencance Reversal of muscle paralysis and recovery which includes [pstoperative analgesia Provision for PNV
What are some examples of IV general anaesthetics?
Popofol
Barbiturates
Etomidate
Ketamine
What are some examples of volatile general anaesthetics?
N2O Chloroform Cycloporpane Diethyl-ether Fluroxene Xenon
WHat are the stages in Guedel’s sign?
Stage 1- analgesia and consciousness
Stage 2- unconscious, breathing erratic with delirium–> excitement phase
Stage 3- Surgical anaesthesia with 4 subdivisions
Stage 4- respiratory paralysis and death
WHat is weird about the stages of Guedel’s sign?
Stage 2, instead of further relaxing, leads to an excitement phase with stecatic breathing
For volatile general anaesthetics, what is used to describe potency?
MAC- Minimum alveolar concentration
What is the definition of MAC?
[Alveolar] at 1 atm at which 50% of subjects fail to move to a surgical stimulus (premeditated breathing O2/air)
What factors affect induction and recovery?
Partition coefficients
What are partition coefficients also known as?
Solubility
What are the subdivisions of partial coefficients?
Blood: Gas partition (in the blood)
- low value fast induction and recovery e.g. deslurane
Oil:Gas partition (in fat)
Determines potency and slow accumulation due to partition into fat
What affects MAC
Age (High in infants, lower in elderly)
Hyperthermia (increased); Hypothermia (decreased)
Pregnancy (Increased)
Alcoholism (Increased)
Central stimulants (Increased)
Other anaesthetics and sedatives (decreased)
Opioids (decreased)- have a MAC sparing efefct
What is the result of the combination of MAC and NO?
MAC sparing, so to get same surgical plane and alagesia, need to use a lot less analgesia if NO is used as well
Describe the relationship between potency and GABA interaction?
Anaesthetic agents partition into fat and interact with GABA receptors
Why are GABA receptors critical targets for anaesthetics?
It is a major inhibitory transmitter in the CNS that allows Cl- condictance
WHat are the results of potentiating GABA activity?
ANxiolysis
Sedation
Anaesthesia
What are exceptions to the use of GABA receptors as a target? What receptors do they target instead?
Xe
N2O
Ketamine
They use NMDA receptors
What balance do anaesthetics modulate?
In the CNS, the balance between excitation (Glutamate) and inhibition (GABA)
WHat are the brain circuitry targets in general anaesthetics?
Reticular formation is depressed (conscious control)
Thalamus (sensory)
Hippocampus is depressed (Memory)
Brainstem depressed (resp and some CVS)
Dorsal horn in spinal cord ( analgesia) and moror neuronal activity (MAC)
WHat are the target sites for IV anaesthetics?
Same as inhalation- so GABA receptors and NMDA by the exceptions
How do we describe IV anaesthetic potency?
TIVA (Total IV Anaesthesia) is sued to define pk based on algorithm to infuse as a rate to maintain the set point
What are IV anaesthetics used in conjunction with and when does the switch occur?
Bolus iV to end pt and then switch to volatile
What are examples of uses of local and regional anaesthesia?
Dentistry Obstretrics Regional surgery Post io Chronic pain management
What are some examples of local anaesthetics?
Lidocaine
Bupivacaine
Ropivacaine
Procaine
Describe the structure of a basically local anesthetic
Aromatic ring - Link- Amine
What are the 2 types of links in the structure of local anaesthetics
Ester link
Amide Link
Which of the 2 types of links leafs to showered duration of action?
Ester link because plasma is full of esterases
What is the relationship of lipid solubility with potency?
Higher solubility leads to higher potency
Describe the mechanism of action of local anaesthetics
Bind to voltage gated Na channels and blocks the Na influx therefore AP is blocked
They block small myelinated afferent nerves preferentially and hence lead to nociceptive and symptoms block
What does use dependant block mean?
The more active the channel, the greater the local anaesthetic effect
Where are upper extremity regional anaesthetics administered?
Interscalene, supraclavicular, infraclavicular, axillary
Where are lower extremity regional anaesthetics administered?
Femoral, sciatic, popliteal and sphenous
What are the main anaesthetic side effects of general anaesthetics?
PONV (opioids) CVS- hypotension POCD (cognitive dysfunction) Chest infection BEWARE ALLERGIES
