Anaesthetics Flashcards
Describe the hierarchy of anaesthesia types
Anaesthesia;
- General: IV or Inhalation/ Volatile
- Local: Can be used as Regional
What is conscious sedation
Use of small amounts of anaesthetic/ benzodiazepine to induce a ‘sleepy state’
IV anaesthetic agents can be used for ‘Induction’ or as the sole anaesthetic in TIVA (Total IV Anaesthesia)
List 4 IV Anaesthetic agents
- Propofol (rapid)
- Barbiturates (rapid)
- Etomidate
- Ketamine (slower)
Describe the 4 stages of Guedel’s Signs
Stage 1, Analagesia;
- Conscious
- Slight eye movement, normal muscle tone
Stage 2, Unconscious;
- Erratic breathing
- Excitement phase
- Moderate eye movement
- Normal to increased muscle tone
Stage 3, Surgical Anaesthesia;
- Slight eye movement-> No eye movement
- Slightly relaxed-> Markedly relaxed muscle tone
Stage 4, Respiratory Paralysis;
- No eye movement
- Flaccid muscle tone
- No breathing-> Death
How is the potency of Volatile Anaesthetics described/ measured?
Minimum Alveolar Concentration, MAC;
- [Alveolar] at which 50% of subjects fail to move to surgical stimulus
- At EQM, [Alveolar]=[Spinal cord]
List 8 things that affect the MAC
- Age (Higher in infants)
- Hyperthermia/ Hypothermia (higher/ lower)
- Pregnancy (increased)
- Alcoholism (increased)
- Central stimulants (increased)
- Other anaesthetics + sedatives (decreased)
- Opioids (decreased)
- Partition Coefficients
List and describe how 2 Partition Coefficients affect the MAC
Blood: Gas Partition;
- Blood solubility
- Low value/ solubility= Fast induction and recovery
Oil: Gas Partition;
- Fat solubility
- Determines Potency and rate of accumulation into fat
Suggest a chemical that is often added to volatile anaesthetic agents to lower the MAC
Nitrous Oxide, N2O
How do we describe potency of IV Anaesthetic agents?
- [Plasma] needed to achieve a specific end point (e.g loss of eyelash reflex)
Describe the role of inhibitory GABAa receptors in Anaesthesia
(Main targets of anaesthetic agents)
- GABAa receptors exist in membrane bilipid layer
- Anaesthetic agent’s potency correlates with ability to bind to and activate GABAa receptor
- GABAa receptor activation-> Cl- influx-> Hyperpolarisation of cells
All anaesthetics except for which THREE potential GABAa mediated Cl- conductance to depress CNS activity?
- N2O
- Xenon
- Ketamine
(These probably inhibit excitatory NMDA receptors)
List 5 systems of the Brain/ CNS circuitry targeted by Anaesthesia
- Reticular formation
- Thalamus
- Hippocampus (Memory affected)
- Brainstem (Respiratory and CVS effects)
- Spinal Cord (Dorsal horn and motor activity)
List 5 indications for Local Anaesthesia (thus Regional too)
- Dentistry
- Obstetrics
- Regional surgery (patient awake)
- Post-op (wound pain)
- Chronic Pain management
List 3 Local Anaesthetics
- Bupivacaine
- Ropivacaine
- Procaine
List 3 characteristics of Local Anaesthetics
- High lipid solubility + potency
- Dissociation constant, pKa gives some clue about time of onset (Low pKa= Faster onset)
- Protein binding determines duration of action (Higher binding= Longer duration)