Anaesthesia Flashcards
Sleep =
Period of rest of body and mind. Rapidly reversible with external stimuli
Sedation =
Allows patients to tolerate unpleasant diagnostic/surgical procedures.
What is maintained in sedation?
Verbal contact
Coma =
State of extreme unresponsiveness in which an individual exhibits no voluntary movement or behaviour
Anaesthesia is classified into:
General
Local
Triad of balanced anaesthesia =
Hypnosis
Areflexia
Analgesia
Areflexia =
no response to surgical stimuli
Undesirable effects of anasthesia =
Decreased cardiac contractility
Sympathetic inhibition
Respiratory depression
At too high concentrations, anasthesia can cause =
All brain functions to be depressed
Respiratory failure - death
Classes of general anasthetics
Inhalation
Intravenous
Inhalational anasthetics:
Gas
Liquids
Ex of gas GA
N2O
Cyclopropane
Ex of liquid GA
Halothanes: halothane, isoflurane
Intravenous GA:
Inducing
Dissociative
Neurolept
Inducing GA ex:
Propofol
Thipentane
Etomidate
Dissociative DA ex;
Ketamine
MoA of inducing GA
GABA agonist, increase GABA sensitivity
MoA of ketamine:
NMDA antagonist
Thiopentane is a
Barbituate
Side effects of thiopentane
- CVS depression
- Resp depression
- Bronchoconstrictions
What shouldn’t be given to asthmatics?
Thiopentane
MoA of inhalational GA
NMDA antagonist
Onset of IV vs inhalational
Inhalation: slow, alveolar gas exchange
IV: rapid
Offset of IV vs inhalational:
Inhalational: alveolar gas exchange
IV: redistribution, metabolism
Metabolism of inhalational vs IV
Inhalational: almost none
IV: liver
Types of local anaesthetics:
Esters
Amides
MoA of LA:
Voltage gated Na+ antagonists
Effect of LA depends on:
Diffusion graident
Fiber size
Myelination
Which fibers do LAs work on?
Alpha delta
C fibers
Alpha delta fibers nociceptors:
Mechanical
Thermal
C fiber nociceptors:
Polymodal
1st pain vs 2nd pain
1st pain = alpha delta, sharp, localised
2nd pain = c fibers, dull, diffuse
LA are less effective in what type of tissue?
Acidic
Due to LAs being weak bases, what do they not work on
Abscesses
LA toxicity occurs when
Sodium channels in ALL excitable tissue potentially blocked
What organ shows the first sign of LA toxicity?
Brain
First signs of LA toxicity =
Perioral tingling
Feeling of doom
LA toxicity is initially
Excitory =
agitation
confusion
perioral tingling
After excitatory LA toxicity becomes
Depressive:
CNS = LOC, respiratory arrest
Heart = cardiac arrest
General management of LA toxicity -
- Recognise
- Stop injecting
- ABC, oxygen, crash call
- Intralipid
Intralipid =
20% lipid solution provides lipid load to vascular space. LA absorbed into lipid solution.
2 types of neuromuscular blocking agents =
- Depolarising
2. Non-depolarising
Neostigmine =
AChE
Tubcurarine =
Non-depolarising blocking agent
Suxamethonium =
Depolarising blocking agents
Succinylcholine =
Depolarising blocking agents
Depolarising NMB agent =
- Binds to nicotinic cholinergic receptor and causes depolarisiation
What patient should you not give depolarising NMB agent to?
Hyperkalaemic
Effects of depolarising NMB on parasympathetic NS:
Muscle fasiculations
Bradycardia
Hyperkalaemia
Moa of non-depolarising NMB agent =
Competes with Ach for binding site. Doesn’t stimulate receptor
Non-depolarising NMB agent has no=
K+ efflux
No fasiculations
Novochock is =
AchEi
Side effects of nerve agents:
Bradycardia Increase secretions (saliva, bronchial, GI - foaming at mouth)
Treatment for nerve agents =
Atropine
Risks of GA
- CNS, CVS, RS depression
- Aspiration of gastric contents
- Awareness
- Postop nausea and vomiting, respiratory complications
- death
Why are patients of GA nil by mouth?
Apiration of gastric contents
Benefits of GA
Unconscious
Optimal access
Total control of RS< CVS, CNS
Complications easy to treat
Risks of LA
Not suitable for operation
Fails
Nerve injury
Toxicity
Benefits of LA
Avoid GA complications
Less GI disturbance
Less risk of DVT
4 stages of anasthesia:
- Induction
- Excitement
- Surgical
- Danger
Induction stage:
Analgestia –> LOC
Pupils in induction stage:
Reflex present
Excitement phase:
FOllows LOC.
Irregular respiration, HR, uncontrolled movement, vomiting, breath holding, pupil dilation
Pupils in excitement phase:
Dilated, reflex present
Surgical phase:
Resp depression, skeletal muscles relax
Pupils in surgical phase:
dilate , no reflex
Overdose phase:
Severe brainstem and medullary depression
Pupils in overdose phase:
Dilated
MAC:
Measures exhaled concentration
BIS =
Bispectral index monitor
What does BIS do?
Interprets EEG into wakefulness scale
BIS when fully awake =
100
BIS when no EEG activity
0
BIS scale for surgical anaesthesia =
45-60