General anesthesia

Question 1

function of general anesthesia

Answer 1

medically induce a coma
aim is to ensure :
1. analgesia
2. amnesia
3. unconsciousness
4. relaxation of skeletal muscles
5. loss of control of reflexes of autonomic nervous system

Question 2

stages of GA

Answer 2

1. analgesia
2. excitement
3. surgical anaesthesia
4. medullary depression

Question 3

types of GA

Answer 3

inhaled and intravenous

Question 4

what affects conc. of inhaled anaesthetic effect

Answer 4

1. solubility of gas
   - lower solubility in blood = faster / higher onset of action
2. concentration of anaesthetic in gas
   - increased conc = faster transfer from blood to brain
3. rate and depth of pul. ventilation
   - increase rate of ventilation = increase absorption
4. pulmonary blood flow
   - increase blood flow = lesser time to diffuse from air to blood
5. arteriovenous concentration grdient
   - high conc gradient = longer time to achieve equilibrium in brain

Question 5

how does gaseous anaesthetic enter brain?

Answer 5

air -> lungs -> blood -> brain

Question 6

how are gaseous GA excreted

Answer 6

mainly via Lungs
- hepatic metab also contributes to clearance
- bacteria in GIT breaks down nitrous oxide !!

Question 7

long duration of exposure of gaseous GA can lead to…

Answer 7

more soluble anaesthetics accumulating in skin, muscle , fat -> slower rate of elimination

Question 8

CVS effects

Answer 8

1. variable effect on HR
2. decrease mean arterial pressure
3. decrease CO
4. depress myocardial function

Question 9

respiratory effects

Answer 9

1. decrease minute ventilation
2. reduced hypercapnia response
3. increase apnoic threshold
4. depression of mucociliary function

Question 10

brain effects

Answer 10

increase cerebral blood flow by decreasing cerebral vascular resistance

Question 11

renal effects

Answer 11

impairs renal autoregulatory function due to reducing renal bloodflow

Question 12

liver effects

Answer 12

1. decrease hepatic blood flow
2. repeat exposure of halothane -> liver damage

Question 13

uterus effects

Answer 13

halogenated anaesthetics are potent uterine muscle relaxants !

Question 14

Types of intravenous GA

Answer 14

1. barbiturates
2. benzodiazapine
3. propofol
4. ketamines

Question 15

Name a barbiturate

Answer 15

Thiopental

Question 16

What do barbiturates bind to

Answer 16

GABA receptors + AMPA receptors (to depress glutamate mediated excitation)

Question 17

Funfacts of barbiturates ig

Answer 17

• commonly used for induction of anaesthesia as it rapidly crosses BBB after intravenous bolus and sufficient doses given
• quick loss of consciousness
• high lipid solubility → hence thiopental distributes out of blood and brain to muscle and fat
• potent respi depressant + decreases arterial BP, SV and CO + decrease cerebral metab , O2 consumption and blood flow

Question 18

Who are barbiturates recommended for

Answer 18

recommended for patients with raised intracranial pressure as it can decrease cerebral blood flow

Question 19

Name 3 benzodiazepines

Answer 19

Diazepam, Lorazepam, Midazolam

Question 20

what is a benzodiazepine antagonist administered for recovery

Answer 20

flumazenil

Question 21

Why is Propofol favoured

Answer 21

faster rate of onset than barbiturates but also faster recovery rate

Question 22

how is propofol metabolised

Answer 22

metab rapidly by liver and excreted by kidney

Question 23

what is propofol used for

Answer 23

induction and maintenance of anaesthesia

Question 24

special qualities of ketamine

Answer 24

1. only intravenous GA with both analgesic and anaesthetic properties
2. stimulates cardiovascular system via stimulation of Central sympathetic NS and inhibiting reuptakes of noradrenaline -> useful in poor risk elderly patients / those in cardiogenic / septic shock

Question 25

neurological effects of ketamine

Answer 25

post op illusions, dreams, disorientation

Question 26

Alternatives to general anaesthesia

Answer 26

1. balanced anaesthesia
2. monitored anaesthetic care
3. conscious anaesthetic care

Question 27

balanced vs monitored anaesthetic care

Answer 27

• both involve sedation
  balanced = patient is reliant on ventilation to breath
  monitored = patient NOT reliant on ventilation to breath

Question 28

monitored vs conscious sedation

Answer 28

monitored sedation = deeply sedated + anasthesiologist needed
conscious sedation = not as deeply sedated, conscious ! anasthesiologist not needed

Question 29

if patient wakes up distressed :

Answer 29

1. administer supplementary oxygen
2. ensure patient’s airway not obstructed + adequate ventilation
3. examine patient for signs of volume overload and treat haemodynamic derangements with appropriate drugs to lower bP !!