L31 - general anaesthetics Flashcards
triad of balanced general anaesthesia
amnesia
analgesia
akinesis
amnesia
lack of response and recall to noxious stimuli - unconsciousness
analgesia
pain relief
akinesis
muscle relaxation / paralysis
general anaesthesia
total loss of sensation
brain arm circulation time
time it takes for drug to travel from site of injection to brain
10-20s
how many brain arm circulation times induce loss of consciousness
2
IV agents for amnesia drugs
- quick onset
- short duration (terminates due to redistribution from muscle to fat)
Cp50
the concentration of the agent in the blood that prevents movement after a skin incision in 50% of patients
timeline of events
- monitoring
- IV access to give anaesthetic agents
- start the process
- maintain the process
- reverse the process
what do IV GAs do
- hyperpolarise nerve cells, preventing conduction of action potentials alone neurones
action of GAs on inhibitory and excitatory neurones
- excite inhibitory neurones
- inhibit excitatory neurones
ideal properties of IV induction agents
- Simple preparation
- Compatible with other agents and IV fluids
- Painless on administration
- High potency and efficacy
- Predictable action within one circulation time
- Minimal cardiovascular effects or other toxicity
- Depression of airway reflexes for intubation
- Rapid and predictable offset of effect
- Rapid metabolism for minimal hangover
most common IV induction agent
propofol
propofol
- lipid based
- excellent suppression of airway reflexes (prevents gag reflex or vomiting when equipment inserted into mouth)
- decreases incidence of post-op nausea and vomiting (PONV)
unwanted effects of propofol
- marked drop in HR and BO
- pain on injection
- involuntary movements
thiopentone
- barbiturate (anti-epileptic properties)
- faster than propofol
- used for rapid sequence induction
- protects brain
unwanted effects of thiopentone
- drops BP and increases HR
- rash / bronchospasm
- intra-arterial injection (thrombosis and gangrene as travels up arteries and blocks blood flow)
best drug for minor procedures
ketamine
muscle relaxation not required
ketamine
- dissociative anaesthesia
- slow onset (90s)
- rise in HR/BP
- bronchodilation
unwanted effects of ketamine
- nausea and vomiting
- emergence phenomenon
dose of propofol used
1.5-2.5mg/kg
dose of thiopentone used
4-5mg/kg
dose of ketamine used
1-1.5mg/kg
drug with the quickest onset
etomidate
dose of etomidate
0.3mg/kg
lowest incidence of hypersensitivity reaction
etomidate since it is steroid based
unwanted effects of etomidate
- pain on injection
- spontaneous movements
- adrenal-cortical suppression
- high incidence of PONV
how to maintain amnesia
- propofol induction (total IV anaesthesia)
- inhalation agents (inhalation anaesthesia)
how long do amnesia induction agents last without maintaining them
4-10mins
when to give amnesia agents (Vapours)
immediately after induction
how are amnesia agents administered
vaporisers
breathing circuits
physical properties of the ideal inhalation agent for amnesia
- non-flammable
- stable
- long shelf life
- environmentally friendly
- cheap and easy to manufacture
biological properties for the idea inhalation agent for amnesia
- pleasant to inhale
- non-irritant
- fast onset
- high potency
- minimal effect on other systems
- no biotransformation
- non-toxic to theatre personnel
neurological effects of anaesthetics
amnesia
hypnosis
immobility
agents of amnesia
isoflurane
sevoflurane
desflurane
MAC
concentration of the vapour which prevents the reaction to the standard surgical stimulus in 50% of patients
what does a low solubility of a GA mean
fast equilibrium = fast recovery
what does a highly fat soluble GA mean
GA given for a long time accumulates in far = hangover effect for hours
sevoflurane
- sweet smelling
- inhalation induction
desflurane
- low lipid solubility
- rapid onset and offset
- long operations
isoflurane
- least effect on organ blood flow
adverse effects on amnesic agents
- vasodilation
- decrease cardiac contractility
- can affect organ perfusion
- malignant hyperthermia
- hepatotoxicity
preferred inhalation amnesic agent for a long surgery
desflurane
preferred inhalation amnesic agent for a chubby child with no IV access
sevoflurane
preferred inhalation amnesic agent for an organ retrieval from a donor
isoflurane
what is analgesia required for
- insertion of airway
- laryngeal mask airway
- intubaiton
- intra-op pain relief
- post-op pain relief
akinesis
muscle relaxant required for intubation and surgery
depolarising akinesia agent
suxamethonium
non-depolarising akinesia agent
short acting: mivacurium
intermediate acting: vecoronium
long acting: pancoronium
assessing unconsciousness
- lineal signs
- measure MAC
- BIS monitor
- isolated forearm
- Evoked potentials
BIS monitor
A bispectral index (BIS) monitor is commonly utilized to assess depth of sedation when administering sedative, hypnotic, or anesthetic agents during surgical and medical procedures. The depth of sedation is calculated by measuring cerebral electric activity via an electroencephalogram (EEG).
most commonly used opioid induction agent
Fentanyl
Best Induction agent for a patient with a history of heart failure requires a general anaesthetic
Etomidate
as causes least harm-dynamic changes
best induction agent for a burn change
ketamine
Best Induction agent for a patient undergoing arm operation under GA with an laryngeal mask airway (LMA).
propofol
as it causes suppression of airway reflexes
what does MAC stand for
Minimum alveolar concentration
Most commonly used non-opiod analgesic agent in anaesthesia is
paracetamol
