Lecture 25 - Anaesthetics Flashcards
What are the 2 main methods that anaesthetics act?
General
Local
What are the 2 ways by which general anaesthesia can be administered?
Inhaled or volatile
Intravenous
What are the ways by which local anaesthesia is given?
Regionally so injection
What is conscious sedation?
When a small amount of anaesthetic or benzodiazepines to produce a sleepy-like state
What type of drug is give as a premedication (to help calm a patient down before surgery) for anaesthesia?
Hypnotic-benzodiazepine
How can you induce anaesthesia?
IV
Inhalational
What type of drug is often given as an Intra operative analgesic?
Opioid like fentanyl
What type of drug needs to be given to allow for intubation?
Muscle relaxant
What drugs need to be given to a patient after surgery?
Reverse muscle relaxants so can breathe again
Post op analgesia
Anti-emetic
How does inhaational volatile general anaesthesia work?
Liquid containing anaesthetic gets vaporised into a gas and so gets delivered to lungs via an agent specific vaporiser
What is the most common anaesthetic delivered intravenously to induce anaesthesia?
Propofol
Barbiturates
Etomidate
Ketamine
What are some gases/volatiles that can be delivered to induce anaesthetics?
Xenon
Fluorxene
Halothane
Nitrous oxide (N2O)
Chloroform
Desflurane
What are the 3 main features that are observed as a patient goes under anaesthesia?
Muscle tone
Breathing
Eye movement
Guedels signs
What are the 4 stages of anaesthesia? (Guedels signs)
1 = analgesia and consciousness (muscle normal and slight eye movement)
2 = uncosncosius, erratic breathing, delirium (moderate eye movment and increased muscle tone)
3 = surgical anaesthesia muscles become increasingly relaxed and eye movment. Becomes zero
4 = flaccid muscles, respiratory paralysis
What is achieved in anaesthesia?
Analgesia
Hypnosis (loss of consciousness)
Depression of spinal reflexes
Muscle relaxes
As anaesthetic concentration increases, what repsonse are lost first to last?
First:
Memory
Consciousness
Movement
Cardiovascualr response
Last
How do you measure potentcy of a volatile aneasthetic?
MAC
Minimum Alveolar Concentration
What is Minimum Alveolar Concentration (MAC)?
The alveolar concentration of a volatile anaesthetic at which 50% of patients fail to move to a surgical stimulus
How is the concentration of volatile anaesthetic in the alveoli at equilibrium related to the conc at the spinal cord?
They are equal
What is the anatomical site/substrate for MAC (Minimum ALveolar Concentrtation)?
Spinal cord
What values determine how fast induction and recovery will be?
BLood:Gas partition coefficient (measure of solubility/how it partitions into the blood)
What partition coefficient determines the potentcy of an anaesthetic?
Oil:Gas partition
(How it partitions into fat)
What are some factors affecting Minimum Alveolar Concentration of a volatile anaesthetic?
Age (high in infants, low in elderly)
Hyperthermia (inc)
Hypothermia (dec)
Pregancy (inc)
Alcoholism (inc)
Central stimulants (inc)
Other anaesthetics and sedatives (dec)
Opioids (dec)
Why is Nitrous Oxide often added to other volatile anaesthetics?
To reduce the required dosing/ MAC
What determines the potency of an anaesthetic?
Lipid solubility
How are potency and lipid solubility related?
Higher lipid solubility = higher potency
What receptor do most anaesthetics interact with to provide effects?
GABA(a)
What is the major method of action of most anaesthetics causing anaesthesia?
Anaesthetics bind to and potentiate GABA(a) receptors leading to enhanced Cl- influx leading to hyperpolarisation. Of neurones
What is the effect of most anaesthetics potentiating GABA activity?
Anxiolytics
Sedation
Anaesthesia
Which anaesthetics dont potentiate GABA activity?
Xenon
Argon
N2O
Ketamine
What receptor do Xe, Argon, N2O and ketamine act on?
What neurotransmitter is involved?
NMDA receptors
Glutamate
The balance of activity of what 2 receptors determines the aneasthetic status?
NMDA glutamate receptor excitation
GABA(a) receptor inhibition
What is the function of the reticular system?
What is the affect of depressing its connectivity to the cortex in anaesthesia?
The activating system which increases arousal keeping a person awake
Person loses consciousness
What is the purpose of suppressing the connections from the thalamus to the cortex in anaesthesia?
Thalamus transmits and modifies sensory information so if depressed loss of sensation
What is the purpose of suppressing the connections from the hippocampus to the cortex in anaesthesia?
Loss of memory
What part of the body is depressed leading to analgesia?
Spinal cord-depression in dorsal horn
(Maybe periaqueductal grey too)
What are the main IV anaesthetics?
Propofol (rapid)
Barbiturates (rapid)
Ketamine (slower)
What is it called when IV anaesthetic is the sole method of anaesthesias?
TIVA
Total IntraVenous Anaesthesia
How do we describe IV anaesthesia potency?
Plasma conc to a acheive a specific end point like loss of eyelash reflex or a certain BIS value (Bispectral index) 0= brain inactivity 100 = full brain function
What is the process of induction in mixed anaesthesia?
IV bolus to end point then switch to the volatile
What are some scenarios where local and regional aneasthetic issued?
Dentistry
Obstetrics
Regional surgery (patient awake)
Post-op (wound pain)
Chronic pain management
What are some local anaesthetics?
Lidocaine
Bupivacaine
Ropivacaine
Procaine
How is pKa (dissociation constant) related to the time of onset of local anaesthetic?
Lower pKa the faster the onset since theres more unionised drug which is present to access the site
What leads to a local anaesthetic having a longer duration?
Higher protein binding
What are the 2 types of chemical link which change how long anaesthetics last?
Ester link
Amide link
Which chemical link takes longer to break down leading to the aneasthetic lasting longer, ester link or amide link?
Amide link
Most cells have esterases so ester links are gonna get broken down so dont last as long
Are anaesthetics going to prefer blocking highly active neurones or inactive neurones?
Highly active
What do local anaesthetics block to causes anaesthetic affect?
Voltage gated sodium channels
What are the 2 pathways by which voltage gated sodium channels become blocked by local anaesthetics?
Hydrophobic pathway
Hydrophilic pathway
What is the hydrophilic pathway of local anaesthesia?
Charged local aneasthetic directly goes in and blocks the channel of a open sodium voltage gated ion channel
What is the hydrophobic pathway of local anaesthesia?
Uncharged local anaesthetic passes through plasma membrane into the cell
Becomes charged within the cell
Then goes into and blocks the open voltage gated Na+ channel
What is the benefit of administering both local anaesthetic like lidocaine with adrenaline?
The adrenaline helps prolong the duration which the local anaesthetic is able to act at its intended site
Since adrenaline causes vasoconstriction
What does a high value of pKa indicate?
Slow speed of onset of action
How does bupivacaine differ in terms of potency and duration of action compared to procaine?
Bupivacaine is more potent and longer duration of action
What is regional aneasthesia?
Selectively anaesthetising a part of the body causing a block of a nerve
What types of drugs are used for regional anaesthesia?
Local anaesthetic
Opioid
What is the point in the neck you can inject local anaesthetic to cause nerve block in. The upper limb?
Interscalene triangle (Erbs point)
Where can local anaesthetic be injected to cause nerve block in the lower limb?
Femoral nerve
Sciatic nerve
Popliteal nerve
Spahenous nerve
What side effects do opioids typically cause in anaesthesia?
Nausea and vomiting
What are some side effects of general anaesthesia?
Post op nausea and vomiting (opioids)
CVS (HYPOTENSION)
Post op Congnitive dysfunction
Chest infection
What are some side effects of local and regional anaesthetic?
Depends on agent use and usually occurs due to systemic spread
Locals that block Na+ VGC are cardiovascular toxic
What type of hyeprsensitivty can occur due to anaesthesia?
Type I allergic reactions (Anaphylaxis)
