Anaesthetic Flashcards
What are the anaesthetic techniques?
General
- Inhalational or volatile
- Intravenous
Local
-Regional
What is conscious sedation?
Use of small amounts of anaesthetic or benzodiazepines to produce a sleepy like state.
What are the practical aspects of anaesthesia?
- Premedication (Hypnotic-benzodiazepine).
- Induction (usually intravenous but may be inhalational).
- Intraoperative analgesia (usually an opioid).
- Muscle paralysis by facilitating intubation/ventilation/stillness.
- Maintenance (intravenous and/or inhalational).
- Reversal of muscle paralysis and recovery which includes postoperative analgesia (opioid/NSAID/paracetamol).
- Provision for PONV.
How are anaesthetics administered?
- Gases: Volatiles are delivered via the lungs
- Intravenous with Propofol, barbiturates, Etomidate, Ketamine
Describe Stage 1 of Guedel’s signs.
Analgesia and consciousness
- Muscle tone is normal
- Breathing is normal
- Eye movement is slight
Describe Stage 2 of Guedel’s signs.
Unconscious, breathing erratic but delirium could occur, leading to an excitement phase.
- Muscle tone is normal to markedly increased
- Breathing is reduced
- Eye movement is moderate
Describe Stage 3 of Guedel’s signs
Surgical anaesthesia, with four levels describing increasing depth until breathing weak.
- Muscle tone gets increasingly relaxed
- Breathing is increasingly reduced
- Eye movement goes from slight to none
Describe Stage 4 of Guedel’s signs
Respiratory paralysis and death.
- Muscle tone is flaccid
- Breathing is markedly reduced
- Eye movement is not existent
What is the MAC?
- Minimum Alveolar Concentration at which 50% of subjects fail to move to surgical stimulus
- At equilibrium the alveolar concentration = spinal cord
- Anatomical substrate for MAC is spinal cord
What are the factors affecting induction and recovery?
- Low value for Blood:Gas partition results in fast induction and recovery
- Oil:Gas partition determine potent and slow accumulation due to partition in fat
Why do obese people sometimes take longer to wake up form anaesthetic?
-Anaesthetic accumulates in fat and can move into blood
When is MAC increased?
- Age (High in infants lower in elderly)
- Hyperthermia (increased);
- Pregnancy (increased)
- Alcoholism (increased)
- Central stimulants (increased)
When is MAC decreased?
- Hypothermia (decreased)
- Other anaesthetics and sedatives (decreased)
- Opioids (decreased)
How does nitrous oxide affect the MAC?
- Nitrous oxide is very often added to other volatile agents (reduced dosing)
- Decrease the MAC so greater potency of the anaesthetic
What is the relationship between anaesthetic, Lipid and GABA?
-Anaesthetic potency correlates lipid solubility and GABA activity
Why is GABA important?
- GABA receptors are a critical target.
- They are a major inhibitory transmitter
How is GABA activity potentiated?
- LGIC potentiates GABA activity
- This leads to Anxiolysis, Sedation and Anaesthesia
How do anaesthetic work?
- Anaesthetic potentate GABA mediated Cl- conductance to depress CNS activity
- NMDA is probably another side
Except XeN2O and Ketamine
How is brain consciousness varied?
- Consciousness is a balance between excitation (glutamate) and inhibition (GABA)
- Anaesthetics modulate this balance
How does anaesthetic affect the brain circuitry?
- Reticular formation depressed resulting in lost of connectivity
- Thalamus transmits and modifies sensory information
- Hippocampus depressed
- Brainstem s depressed
- Spinal cord depressed by affecting the dorsal horn and motor neuronal activity
What are the main intravenous anaesthetics?
- Propofol (rapid)
- Barbiturates (rapid)
- Ketamine (slower).
How do intravenous anaesthetics work?
- Can be uses as sole anaesthetic in TIVA
- All potentiate GABA with exception of ketamine
How Do We Describe Intravenous Anaesthetic Potency?
-Plasma concentration to achieve a specific end point (loss of eyelash reflex or a BIS value)
Describe the methods of administering Intravenous Anaesthetic Potency?
- For induction in mixed anaesthesia : Bolus to end point then switch to volatile.
- TIVA uses a defined PK based algorithm to infuse at a rate to maintain set point. Preceded by a bolus.
What are the characteristics of local anaesthetics?
- Increased lipid solubility so greater potency
- Faster onset due to lower pKa
- Increased metabolism
- Increased duration of protein binding
How does Bupivacaine stimulate wound analgesia?
- Cocaine archetypal
- Amide so longer duration
- Block is use dependant
- Blocks small myelinated nerves in preference hence nociceptive and sympathetic blocked
- Increases duration of adrenaline
Describe the features of regional anaesthesia.
- As the name suggests selectively anaesthetising a part of the body.
- Often described as a ‘block’ of a nerve and hence the patient remains awake.
- Uses local anaesthetic and or an opioid.
What are common uses of regional anaesthetics?
- Upper extremity (e.g.,); interscalene, supraclavicular, infraclavicular, axillary.
- Lower extremity (e.g.,) ; femoral, sciatic, popliteal, saphenous.
- Extradural / Intrathecal / Combined (labour).
What are the main side effects of general anaesthesia?
- Opoids in particular can cause post operative nausea and vomiting
- Hypotension
- Post operative cognitive decline
- Chest infection
- Allergic reaction/Anaphylaxis
What are the main side effects with local and regional anaesthesia?
-Depends on the agent used and usually result from systemic spread for example Locals are Na+ channel blockers so cardiovascular toxicity.
What are exmaples of local anaethetics?
- Lidocaine
- Bupivacaine
- Ropivacaine
- Procaine.
