CPTP 3.23 Neuropharmacology 8 General anaesthetics Flashcards Preview

CPTP 3 > CPTP 3.23 Neuropharmacology 8 General anaesthetics > Flashcards

Flashcards in CPTP 3.23 Neuropharmacology 8 General anaesthetics Deck (42)
Loading flashcards...

Do local anaesthetics have a hydrophobic or a hydrophilic group?

Both. They are amphiphilic


One drug has a pKa of 7.9. Another has a pKa of 8.9. Which has more of its neutral form?

The drug with a pKa of 7.9 (which happens to be lidocaine)

pKa is dissociation constant, so higher number means more ionised form


How are general anaesthetics administered?

Systemically via:
• Inhalation (volatile anaesthetics)
• Injections (liquid anaesthetics)


What is the triad of anaesthesia?

The three things that is required of a general anaesthetic:
• Unconsciousness
• Analgesia
• Muscle relaxation


How is the triad of anaesthesia usually achieved?

No agent provides all three so is achieved by using combinations of drugs and adjunct medicines. Depends on the surgery needed (i.e. intubation needs lots of relaxation)


What are the three kinds of adjunct medications in surgery?

• Medication given before surgery

• Medication given during surgery

• Medication given after surgery


What are benzodiazepines used for in surgery?

• Presurgery anxiolysis for extremely stressed patients
• Presurgery amnesia to make them not remember 'going under'


What are H2 blockers used for in surgery?

Give an example drug

To prevent gastric acid secretion in high-risk GORD (or pregnant) patients and prevent them breathing in gastric acid



What are antimuscarinic drugs used for in surgery?

Give an example drug

Decrease salivary secretions and bradycardia during surgery



Name the formulary neuromuscular blocking drugs and what they are used for

Suxamethonium and Atracurium
• Intubation
• Suppress muscle tone for fine surgery


What is the mechanism of action of suxamethonium?

Depolarising neuromuscular blocking drug
• Activates the acetylcholine receptor so much that it enters a state whereby it can no longer generate an EPSP


Describe the solubility of general anaesthetics

Lipid soluble


In general, how do general anaesthetics work?

Reducing neuronal activity in the CNS by decreasing excitatory activity and increasing inhibitory activity (in particular the reticular activating system)


What adverse effects can result from general anaesthetics?

There is a very fine line of a therapeutic window between sedation and:
• Cardiovascular depression
• Respiratory depression


What are the theories of the mechanisms of action of general anaesthetics?

Physicochemical theory
• Lipid solubility theory - anaesthetic effect is exerter through some perturbation of the lipid bilayer

Structural theory
• Anaesthetic effect is exerted through interactions with proteins


Describe the lipid solubility theory of general anaesthetic mechanism of action

What observation supports this?

Anaesthesia results when a sufficient amount of anaesthetic dissolves in the lipid bilayer to perturb the physical properties of that layer, altering the excitability of proteins within it.

The Meyer-Overton Rule:
• General anaesthetics which are more soluble in lipids are more potent


What evidence overturns the lipid solubility theory of general anaesthetics?

• Not all small lipid-soluble molecules are general anaesthetics
• Not all general anaesthetics are small lipid-soluble molecules
• Stereoisomers of existing anaesthetics do not work as general anaesthetics


Which proteins are interacted with in the structural theory of general anaesthetics?

Which of these is the 'most important' protein, which all anaesthetics are thought to work on?

• 5-HT3
• Nicotinic

• Glycine

GABA-A is the most important receptor


How do general anaesthetics work on GABA-A receptors?

When anaesthetic is present, GABA is enhanced, and stays on the receptor for longer, thus allowing in more Cl- and hyper-polarising the cell


Which formulary general anaesthetics are inhaled?

• Nitrous Oxide
• Isoflurane


What causes loss of consciousness when inhaling nitrous oxide recreationally?

Oxygen starvation


What is nitrous oxide used for (with reference to the triad of anaesthesia)?

Good at pain relief

Poor at unconsciousness

Poor at neuromuscular suppression


Which formulary general anaesthetics are intravenously administered?

• Propofol
• Thiopental sodium


What are the stages of anaesthesia, as it anaesthesia is deepened?

Stage 1: Analgesia
• Amnesia
• Analgesia
• Euphoria
Stage 2: Excitement
• Excitement
• Delirium
• Combative
Stage 3: Surgical anaesthesia
• Unconsciousness
• Regular respiration
Stage 4: Medullary depression (side effects)
• Too far
• Respiratory arrest
• Cardiac arrest
• No eye movement


How is stage 2 moved through as quickly as possible?

Induction of anaesthesia is done with an intravenous anaesthesia


How is anaesthesia administered during surgery? Explain why it is administered in this way.

At the start of surgery: intravenous
• Ensures stages I and II are passed as quickly as possible

During surgery: inhalation
• Maintains the patient steadily in stage III
• This is achieved through a self-regulating negative feedback, whereby too much anaesthesia will depress breathing, reducing the anaesthetic administered


What is level of anaesthesia correlated with when using inhaled anaesthetics?

The partial pressure of the volatile anaesthetic in brain tissue


What is the movement of an inhalation agent driven by?

The partial pressure gradients:
• The pressure generated by a compartment is affected by the partition coefficient of the volatile anaesthetic in blood and body tissue


What is a partition coefficient

A coefficient that represents the solubility of volatiles in different media, and thus the AMOUNT of anaesthetic in each compartment in equilibrium (the only thing that is evened out is the pressure)

e.g. the blood/gas coefficient is the ratio of the amount of anaesthetic dissolved in blood to the amount of the same volume of gas in contact with that blood
• '2' would imply twice the anaesthetic dissolved in blood compared to the amount in alveoli


What do partition coefficients affect?

• How rapidly the drug is absorbed
• Onset time
• Offset time
• Potency