Pharmacology of Anaesthesia

Question 1

What is the aim of general anaesthetics?

Answer 1

To produce insensibility in the whole body + unconsciousness

they are centrally acting drugs: hypnotics, analgesics

Question 2

What are the aims of regional and local anaesthetics?

Answer 2

Regional= produce insensibility in an area of the body - applied to nerves supplying relevant area

Local= produce insensibility in only relevant part of the body
applied directly to the tissues

Question 3

What techniques and equipment is used?

Answer 3

Tracheal intubation
Ventilation
Fluid therapy
Regional anesthesia
Monitoring

Question 4

What is the triad of anaesthesia?

Answer 4

Analgesia- pain relief
Hypnosis- unconsciousness
Muscle relaxation

Allows anaesthetic to be split into separate components as an individual may not require all three

Question 5

What are the features of balanced anaesthesia?

Answer 5

Allows flexibility - allows different drugs and techniques to be used to tailor to each patient

Requires to titrate doses separately = more accurate and allows more control over components of the triad

Avoid overdosage

Question 6

What are the problems of anaesthesia?

Answer 6

Polypharmacy: chance of drug reactions/allergies
Muscle relaxation: requires artificial ventilation
Separation of relaxation and hypnosis: awareness can occur

Question 7

What are the mechanisms of general anaesthetics?

What are the 2 types of general anaesthetics?

Answer 7

Interfere with neuronal ion channels:
hyperpolarises neurones and suppresses neuronal activity

Inhalation agents dissolve in membranes (direct effect)
IV agents cause allosteric binding

Question 8

In what order does general anaesthesia affect the body’s functions?

Answer 8

Interrupt cerebral function first (complex processes first)

LOC early, then hearing, then primitive functions (reflexes) later

Question 9

What are the features of intravenous anaesthesia?

Answer 9

Rapid onset of unconsciousness

Rapid recovery (due to disappearance of drug from circulation)

Question 10

What are inhalation anaesthetics?

Where is the uptake?

Answer 10

They are halogenated hydrocarbons

Both uptake + excretion is via lungs

Concentration gradients= lungs > blood > brain

Question 11

What is MAC (minimum alveolar concentration)?

What is it used for

Answer 11

Concentration of drug in the alveoli required to produce anaesthesia

Can measure potency:
low number = high potency

Question 12

What are the features of induction and awakening by inhalation anaesthetics?

Answer 12

Induction = slow
But good for maintenance of anaesthesia (prolongs duration, flexible)

Awakening= by stopping inhalation administration
+ washout to reverse concentration agent

Question 13

What is the common sequence of administration of general anaesthesia?

Answer 13

IV induction the inhalation maintenance

Question 14

What effects does CENTRAL general anaesthetic have on the cardiovascular system?

Answer 14

Depresses CVS centre:

• reduce sympathetic outflow
• negative inotropic effect on heart
• reduced vasoconstrictor tone leads to vasodilation

Question 15

What effects does DIRECT general anaesthetic have on the cardiovascular system?

Answer 15

• negative inotropic effect
• vasodilation by decreased peripheral resistance
• venodilation: decreases velour return and cardiac output

Question 16

What effects does general anaesthetic have on respiratory function?

Answer 16

Anaesthetic agents are respiratory depressants

• reduce hypoxic and hypercarbic drive
• decreases tidal volume
• increases resp rate
• paralyse cili
• decrease functional residual capacity

Question 17

What are the effects of muscle relaxants?

Answer 17

Paralyse skeletal muscle

Respiratory and airway muscles are affected as much as any other

Question 18

What are the indications for muscle relaxants?

Answer 18

Ventilation and intubation
When immobility is essential
Body cavity surgery access

Question 19

What problems are there with muscle relaxants?

Answer 19

Awareness: when there is insufficient dosage so patient is awake but paralysed

Incomplete reversal: airway obstruction, ventilatory insufficiency

Question 20

What is the purpose of analgesia?

What is the purpose of intraoperative analgesia?

Answer 20

Prevents feeling of unpleasant stimulus

Intraoperative analgesia:
Prevents arousal of patient due to pain
Contributes sedative effect
Suppresses reflex responses to painful stimuli

Question 21

What is the purpose of local and regional analgesia?

Answer 21

Retain awareness/consciousness
Produces analgesia but no direct hypnosis

Does not have global effects of general anaesthesia
Spares respiratory function

Question 22

What is the limiting factor of local anaesthetics?

Answer 22

Toxicity

When absorption > rate of metabolism = the anaesthetic agents cause high plasma level and vasoconstrictors reduce blood flow and reduce absorption

Question 23

What are some signs and symptoms of local anaesthetic toxicity?

Answer 23

Numbness and tingling around mouth
Tinnitus
Visual disturbances
Muscular twitching
Drowsiness
CVS depression
Convulsions
Coma
Cardiorespiratory arrest

Question 24

What does local anaesthetic toxicity depend on?

Answer 24

Dose used
Rate of absorption
Patient weight
Drug (some more toxic than others)