Principles of Anaesthetics and Pharmacology Flashcards
1
Q
What are the different kinds of anaesthesia?
A
- General
- Produces insensbility in the whole body, usually causing unconsciousness
- Centrally acting drugs – hypnotics/analgesics
- Regional
- Producing insensibility in an area or region of the body
- Local anaesthetics applied to nerves supplying relevant area
- Local
- Producing insensibility to only the relevant part of the body
- Local anaesthetics applied directly to the tissue
2
Q
What is anaesthesia?
A
Anaesthesia = insensibility
3
Q
What is general anaesthesia?
A
- Produces insensbility in the whole body, usually causing unconsciousness
- Centrally acting drugs – hypnotics/analgesics
4
Q
What is regional anaesthesia?
A
- Producing insensibility in an area or region of the body
- Local anaesthetics applied to nerves supplying relevant area
5
Q
What is local anaesthesia?
A
- Producing insensibility to only the relevant part of the body
- Local anaesthetics applied directly to the tissue
6
Q
What are different types of drugs used in anaesthesia?
A
- Inhalation anaesthetics
- Intravenous anaesthetics
- Muscle relaxants
- Local anaesthetics
- Analgesics
7
Q
What are some different techniques and equipment used in anaesthesia?
A
- Tracheal intubation
- Ventilation
- Fluid therapy
- Regional anaesthesia
- Monitoring
8
Q
What are some of the functions of the modern anaesthetic machine?
A
- Regulation of fresh gases and mixing to deliver precise concentrations of gaseous agents
- Addition of precise concentrations of inhaled anaesthetics gases
- CO2 removal to allow recirculation of inhaled gases
- Mechanical ventilation, now microprocessor controlled contained within machine
- Most monitoring now normally integrated into anaesthetic machine
9
Q
What is the operative and anaesthetic mortality rate?
A
- Operative mortality 1:25 (4%)
- Anaesthetic mortality 1:400,000 (0.00024%)
10
Q
What system is used to assess anaesthesia patients?
A
ASA system
11
Q
What are the biggest drivers for improved safety in anaesthesia?
A
- Training of specialist anaesthetists
- Modern anaesthetic drugs and techniques
- Modern monitoring standards and equipment
12
Q
What are the 3 components of anaesthesia (triad of anaesthesia?
A
- Hyponosis
- Unconsciousness
- Analgesia
- Pain relief
- Relaxation
- Skeletal muscle relaxation to provide immobility and permit artificial ventilation
13
Q
Balanced anaesthesia uses different drugs for different jobs, what are advantages and problems with this?
A
- Advantages:
- Avoid over-dosage
- Great flexibility
- Since titrated doses separately is more accurate to requirements
- Problems
- Polypharmacy – chance of drug reactions/allergies
- Muscle relaxation – problems controlling airway
- Separation of relaxation and hypnosis – “awareness”, possibility of patient being awake yet paralysed and unable to communicate
14
Q
What are the effects of general anaesthesia?
A
- Hypnosis (mainly)
- Cerebral functions lost from most complex functions to primitive functions being lost later (such as reflexes) – higher doses required to affect these primitive functions
- Relaxation
- Analgesia (barely any)
15
Q
What is the mode of action of general anaesthesia?
A
- Open chlorine channels to hyperpolarise neurons making them less likely to fire
16
Q
What is the adminstration of general anaesthesia?
A
- IV
- Allosteric binding to GABA receptors, opening chloride channels
- Rapid onset, rapid recovery due to redistributing to other areas of the body such as muscle and fat
- Concentration builds up slower in fat and muscle due to them having less blood supple than viscera
- Inhalation
- Dissolve in membranes having direct physical effect – uptake and excretion via lungs using partial pressures lungs > blood > brain
- MAC = minimum alveolar concentration, measure of potency with low number being a high potency
- Onset of action is slow, effect lasts longer, awakening requires stopping inhalation agent or wash out (reversal of concentration gradient)
- Can be monitored better than IV by using inhalation and exhalation
- Most anaesthesia is IV induction then inhalation maintenance
17
Q
What is the mode of action of IV GA?
A
- Allosteric binding to GABA receptors, opening chloride channels
18
Q
What are 2 examples of IV anaesthetic?
A
Thiopentone and propofol
19
Q
Describe the duration of IV GA?
A
- Rapid onset, rapid recovery due to redistributing to other areas of the body such as muscle and fat
- Concentration builds up slower in fat and muscle due to them having less blood supple than viscera
20
Q
How is IV anaesthetic administered?
A
- Target Controlled Infusion (TCI) pump system
- Allows very accurate infusion to achieve specific blood or brain concentrations of agents using complex pharmacokinetic algorithms
Big problem with Total Intravenous anaesthesia (TIVA) is that we currently can’t measure the drug concentration in real time
Therefore, we use computers to calculate what is in essence, a real time guess
Uses lots of calculations and assumptions about patients physiology based on age, sex and size
21
Q
What is the mode of action of inhalation GA?
A
- Dissolve in membranes having direct physical effect – uptake and excretion via lungs using partial pressures lungs > blood > brain
22
Q
What are inhaled general anaesthetics?
A
Halogenated hydrocarbons
23
Q
What is MAC?
A
- MAC = minimum alveolar concentration, measure of potency with low number being a high potency
24
Q
What does a low MAC mean?
A
- MAC = minimum alveolar concentration, measure of potency with low number being a high potency
25
Describe the duration of inhalation GA?
* Onset of action is slow, effect lasts longer, awakening requires stopping inhalation agent or wash out (reversal of concentration gradient)
26
How is most GA administered?
* Most anaesthesia is IV induction then inhalation maintenance
27
What are the risks of GA?
* Cardiovascular impact
* Care of unconscious patient
* Impairment of respiratory function and control of breathing
28
What effects does GA have on the CVS?
* Central
* Depress cardiovascular centre
* Reduce sympathetic outflow
* Negative inotropic/chronotrophic effect on heart
* Reduced vasoconstrictor tone -\> vasodilation
* Direct
* Negatively inotopic
* Vasodilation -\> decreased peripheral resistance
* Venodilation -\> decreased venous return, decrease cardiac output
29
What are consequences of GA depressing CV centre?
* Reduce sympathetic outflow
* Negative inotropic/chronotrophic effect on heart
* Reduced vasoconstrictor tone -\> vasodilation
30
Does GA cause veso/venodilation to increase or decrease?
* Negatively inotopic
* Vasodilation -\> decreased peripheral resistance
* Venodilation -\> decreased venous return, decrease cardiac output
31
What effect does GA have on the respiratory system?
* All aesthetic agents are respiratory depressants
* Reduce hypoxic and hypercarbic drive
* Decreased tidal volume and increased rate
* Paralyse cilia
* Decreased functional residual capacity
* Lower lung volumes
* VQ mismatch
32
What are consequences of GA depressing respiratory system?
* Reduce hypoxic and hypercarbic drive
* Decreased tidal volume and increased rate
33
Regional anaesthesia has what effects?
Muscle relaxants
34
Why must muscle relaxants be used with drug for unconsciousness?
If uses systemically must also be used with a drug for unconsciousness as being paralysed and awake is very unpleasant
35
What are indications for muscle relaxants?
* Ventilation and intubation
* When immobility is essential
* Microscopic surgery, neurosurgery
* Body cavity surgery (access)
36
What are potential problems of muscle relaxants?
* Awareness
* Incomplete reversal
* Airway obstruction, ventilatory insufficiency in immediate post-op period
37
What is the most important aspect of anaesthesia triad?
Anaesthesia is the most important aspect of the triad, often sufficient on its own with no other drugs for procedure
38
Why is analgesia needed even when patient is unconscious?
* Prevention of arousal (being woken up)
* Opiates contribute to hypnotic effect of GA
* Suppression of reflex responses to painful stimuli
* Such as tachycardia, hypertension
39
Why is regional anaesthesia often used with GA?
Regional anaesthesia is often used with GA to remove painful stimuli to allow lower levels of GA to be used
40
What drugs does general analgesia use?
* Opiods, includes
* Fentanyl
* Short acting and potent
* Morphine
* Oxycodone
* Remifentianil
* Very short acting and very potent
* Effect – analgesia and hyponosis
41
What are the effects of GA drugs?
* Effect – analgesia and hyponosis
42
What drugs does local analgesia use?
Lignocaine, bupivacaine and ropivacaine produce analgesia with no hypnosis
43
What is the mode of action of local analgesia?
* Mode of action – blocking Na channels and preventing action potential from propagating
44
What is the effect of local analgesia?
* Effect – analgesia and relaxation
45
What are advantages and risks of local analgesia?
* Advantages – retain awareness, lack of global effect of GA, relative sparing of respiratory function
* Risks – derangement of CVS physiology
46
What are advantages of using US guided regional anaethesia?
* Safer more effective delivery of LA
* Less likelihood of LA going intravenously or direct nerve or vascular injury
