Anaesthetics: Principles and Pharmacology

Question 1

what does anaesthesia mean?

Answer 1

without feeling/ perception

Question 2

what is general anaesthesia?

Answer 2

produces insensibility in the whole body usually causing unconsciousness

caused by centrally acting drugs: hypnotics, analgesics

Question 3

what is regional anaesthesia?

Answer 3

produces insensibility in an area or region of the body

local anaesthetics applied to nerves supplying the relevant area

Question 4

what is local anaesthesia?

Answer 4

produces insensibility in only the relevant part of the body

local anaesthetic applied directly to the tissues

Question 5

what types of drugs have been developed to be used in anaesthesia?

Answer 5

anaesthetics: inhalational, intravenous, local

muscle relaxants

analgesics

Question 6

what advancements have been made in anaesthetic techniques and equipment?

Answer 6

• tracheal intubation
• ventilation
• fluid therapy
• regional anaesthesia
• monitoring

Question 7

what is the triad of anaesthesia?

Answer 7

• analgesia
• hypnosis
• relaxation

Question 8

what agents assist in relaxation during anaesthesia?

Answer 8

• muscle relaxants
• local anaesthetics
• general anaesthetic agents

Question 9

what agents assist in analgesia during anaesthesia?

Answer 9

• local anaesthetics
• opiates
• (general anaesthetic agents)

Question 10

what agents assist in hypnosis during anaesthesia?

Answer 10

• general anaesthetic agents

- (opiates)

Question 11

what is meant by balanced anaesthesia?

Answer 11

using multiple agents to do different jobs

• doses titrated separately = more accurate to requirements
• prevents overdose, allows flexibility

Question 12

what problems does polypharmacy present?

Answer 12

increased chance of drug reactions/ allergies

Question 13

what problems does muscle relaxation present?

Answer 13

• artificial ventilation

- airway control

Question 14

what problems does separation of relaxation and hypnosis present?

Answer 14

risk of awareness

Question 15

how do general anaesthetic agents work?

Answer 15

hyperpolarise neurones making them less likely to fire

inhalational agents
- dissolve in membranes -> direct physical effect

IV agent
- allosteric binding to GABA receptors -> open chloride channels

Question 16

what care is required when a patient is under general?

Answer 16

ABC - long drawn out resus

• airway management
• respiratory function (breathing)
• cardiovascular monitoring
• care of an unconscious patient

Question 17

what are the features of IV anaesthesia?

Answer 17

rapid onset of unconciousness

rapid recovery

Question 18

how does the concentration of IV agent differ in tissue over time?

Answer 18

• blood and vessel rich organs: decreases
• viscera: rapid increase then slower decrease
• muscle: slow increase and decrease in muscle
• fat: slow increase

Question 19

what are inhalational agents composed of?

Answer 19

halogenated hydrocarbons

Question 20

how are inhalational anaesthetics administered?

Answer 20

uptake and excretion via lungs

• partial pressure gradient: lungs > blood > brain
• cross the alveolar BM easily
• arterial partial pressure equates closely to alveolar partial pressure

Question 21

what is MAC?

Answer 21

minimum alveolar concentration

• drug concentration required in alveoli to produce anaesthesia
• low number= high potency

Question 22

what are the features of inhalational anaesthetics?

Answer 22

induction: slow
maintenance: prolong duration and therefore very flexible

awakening: stop inhalational administration
washout using gas agent minus the anaesthetic to reverse concentration gradient

Question 23

what sequences of anaesthesia can be used?

Answer 23

IV induction and inhalational maintenance

Question 24

what IV agents are used?

Answer 24

• propofol

- opiate (remifentanil)

Question 25

what effect does GA have on the CVS centrally?

Answer 25

depresses cardiovascular centre

• reduces sympathetic outflow
• negative inotropic/chronotropic effect on heart
• reduced vasoconstrictor tone -> vasodilation

Question 26

what effect does GA have on the CVS directly?

Answer 26

• negatively inotrophic
• vasodilation –> decreased peripheral resistance
• venodilation –> decreased venous return and cardiac output

Question 27

what effect do all anaesthetic agents have on the respiratory system?

Answer 27

respiratory depressants:

• reduce hypoxic and hypercarbic drive
• decrease tidal volume and increase rate

paralyse cilia

decrease FRC

• lower lung volumes
• VQ mismatch

Question 28

what are the indications for muscle relaxants?

Answer 28

• ventilation and intubation
• when immobility is essential
• body cavity surgery

Question 29

what problems can arise when using muscle relaxants?

Answer 29

• awareness
• incomplete reversal: airway obstruction, ventilator insufficiency
• apnoea: dependence on airway and ventilator support

Question 30

why is intraoperative analgesia used?

Answer 30

• prevention of arousal
• opiates contribute to hypnotic effect of GA
• suppression of reflex responses to painful stimuli e.g. tachycardia , hypertension

Question 31

why may regional anaesthetic be used intraoperatively?

Answer 31

• intense/complete analgesia

- no direct hypnotic effects but eliminates painful surgical stimuli

Question 32

What physiological effects do local and regional analgesia have?

Answer 32

• retention of awareness / consciousness
• lack of global effects of GA
• derangement of CVS physiology proportional to size of anaesthetised area
• relative sparing of respiratory function