Anaesthetics Flashcards
What are the three principles of general anaesthesia?
Amnesia - lack of response and recall to noxious stimuli (unconsciousness)
Analgesia - pain relief
Akinesis - immobilisation/paralysis
Why is akinesia important?
People can still move in their sleep, therefore important to stop this
What are the three main types of anaesthesia?
general - total loss of sensation
regional - loss of sensation to a region or part of body
local - topical, infiltration (to site of intervention)
What are induction agents?
Medications which induce a loss of conscious
How long do induction agents take to work?
‘one arm-brain circulation’ (how long it takes for blood to get from arm to brain)
10-20 seconds
What is routinely monitored in pts. undergoing anaesthetic?
ECG SpO2 NIBP Airway gas monitoring Airway pressure Nerve stimulator and temp. (if indicated)
When might you use a nerve stimulator to monitor a patient on anaesthetic?
If pt. is undergoing muscle relaxant
to check whether the effects are wearing off, esp. at the end of the operation
What are the 4 key induction agents?
Propofol
Thiopentone
Ketamine
Etomidate
Which is the most commonly used induction agent?
Propofol
What does propofol look like?
White emulsion
lipid based
What are the benefits of propofol?
Excellent suppression of airways
Decreases incidence of PONV
What dose of propofol should be used?
1.5-2.5 mg/Kg
What are the unwanted effects of propofol?
Marked drop in HR and BP
Pain on injection
Involuntary movements
How commonly used is thiopentone?
1-2% of pts.
What type of drug is thiopentone?
barbiturate
When is thiopentone mainly used? why?
Used mainly in rapid sequence induction
acts faster than propofol
What are the benefits of ketamine?
Dissociative anaesthesia
What is the most appropriate anaesthetic for a pt. requiring a burn dressing?
Ketamine
What is the most appropriate anaesthetic for a pt. undergoing an arm operation under GA with an LMA?
Propofol
What is the most appropriate anaesthetic for a pt. with Hx of heart failure requiring a general anaesthetic?
Etomidate
What is the most appropriate anaesthetic for a pt. with intestinal obstruction requiring an emergency laparotomy?
Thiopentone
What is the most appropriate anaesthetic for a pt. with porphyria coming for an inguinal hernia repair?
Propofol (NOT thiopentone)
How long is does the action of an induction agent last?
4-10 minutes
What is usually used to maintain amnesia after the 4-10 mins?
Inhalation/volatile agents
What are the benefits of thiopentone?
Anti-epileptic and cerebra-protective
What are the unwanted effects of thiopentone?
Drop in BP, but rise in HR
Rash/bronchospasm (due to histamine release)
Intra-arterial injection: thrombosis and gangrene
When is thiopentone contra-indicated?
Porphyria
What is the dose of thiopentone?
4-5 mg/Kg
What is the dose of ketamine usually given?
1 - 1.5 mg/Kg
What is the onset of ketamine?
90 seconds (slow onset)
What does ketamine do to HR and BP?
Increases both
What is the effect of ketamine on the airways?
Bronchodilation
What are the unwanted effects of ketamine?
Nausea and vomiting
Emergence phenomenon: vivid dreams, hallucinations
What are the benefits of etomidate?
Rapid onset
haemodynamic stability
low incidence of hypersensitivity reaction
What is the dose of etomidate?
0.3 mg/Kg
What are the unwanted effects of etomidate?
pain on injection
spontaneous movements
adreno-cortical suppression
high incidence PONV
How are inhalation anaesthetic agents administered to patients?
via vaporisers (turns liquid drugs in to inhalable gas)
What are four main amnesic inhalation agents?
isofulrane
sevoflurane
desflurane
enflurane
What are the benefits of the sevoflurane?
sweet smelling
can also be used in inhalation induction (eg. if pt. scared of needles/paeds/IVDU
What are the benefits of desflurane?
Low lipid solubility
Rapid onset and offset
Why is desflurane used in long operations?
Because low lipid solubility, leaves body more easily, therefore recovery is quicker
What are the benefits of isoflurane?
least effect on organ blood flow
What does MAC stand for?
Minimum alveolar concentration
What is the definition of minimum alveolar concentration?
The concentration of vapour that prevents the reaction to a standard surgical stimulus (traditionally a set depth and width of skin incision)
in 50% of subjects.
What constitutes 1 MAC is different in different inhalants
What is the MAC of nitrous oxide?
104%
What is the MAC of sevoflurane?
2%
What is the MAC of isofulrane?
1.15%
Is ketamine a good analgesic?
yes, causes profound analgesia
What does ketamine (in particular) do to the memory of a patient?
Causes anterograde amnesia
What is the MAC of desflurane?
6%
What is the MAC of enflurane?
1.6%
How does one change the MAC of vapour being given?
Adjust dial on vaporiser
What is the best inhalation agent for a long, 8 hour, finger re-implantation? Why?
Desflurane
Low lipid solubility - quick recovery from anaesthetic (pt. will be under for a long time due to length of op)
What is the best inhalation agent for a paediatric patient, with no IV access? Why?
Sevoflurane
Sweet smelling and no needle needed for induction (therefore less distressing for child when placing cannula)
What is the best inhalation agent for organ retrieval from a donor? Why?
Isoflurane
Doesn’t impact organ blood flow
Do analgesics take more or less time to work than induction agents? How much time? What impact does this have on when it is given to the patient?
More time
about 1-5 minutes
generally given before the induction agents (make ventilation interventions less uncomfortable for pts.)
What class of analgesia is generally given to pts. in surgery?
opioids
When are short-acting opiates used in anaesthetics?
Intra-op analgesia: to suppress response to laryngoscopy, surgical pain
What are key features of the short-acting, intra-op. opiates given in theatre?
rapid onset
high potency
Give three examples of the short-acting opioids used in theatre? Which one is most commonly used?
Fentanyl (most commonly used)
Remifentanil
Alfentanil
Give three examples of the long acting intra-op/post-op analgesia given to pts.
Morphine
Oxycodone
Which analgesic is given in almost all surgical patients?
paracetamol
When are long-acting opioids generally used in theatre?
intra-op
post-op
given just before end of surgery so pt. wakes up pain free
What other analgesics can be given to patients recovery from surgery?
Paracetamol (most commonly used)
NSAIDS: diclofenac, parecoxib (IV), Ketorolac (IV)
Weak opioids: tramadol, dihydrocodeine (most common one given)
What is the most commonly used oral opioid in adults?
codeine
Give 2 examples of IV NSAIDS
Ketorolac
Parecoxib
How is akinesia achieved in anaesthetics?
Muscle relaxants
Briefly explain what happens at a neuromuscular junction to cause muscle contraction
Action potential arrives at NM junction, by travelling along axon
Causes calcium channels to open (calcium floods in to end of exon)
Causes vesicles to merge with membrane at NM, release ACh
Ach binds to nicotinic receptors
This causes depolarisation of the nicotinic receptors
This causes muscle contraction
What are the two groups of muscle relaxants?
Depolarising
Non-depolarising
How do depolarising muscle relaxants work?
Act similar to ACh on nicotinic receptors
BUT V. SLOWLY HYDROLYSED BY AChesterase
Cause muscle contraction (fasciculations all over body)
Muscles fatigue and then relax
What are the draw-backs/things to be mindful of when using depolarising muscle relaxants?
Fasciculations can cause cell breakdown in muscle, which can cause hyperkalaemia
Its often wake up feeling achey
How do non-depolarising muscle relaxants work?
Block nicotine receptors (competitive inhibitor)
Causes muscles to relax
Give an example of a depolarising muscle relaxant
Suxamethonium
What does of suxamethonium would you give?
1-1.5 mg/Kg
What are the adverse effects of suxamethonium?
Muscle pains Fasciculations Hyperkalaemia Malignant hyperthermia Rise in ICP, IOP (wouldn't be ideal in opthalmic surgery) and gastric pressure
When is suxemethonium most commonly used?
In rapid sequence induction
has rapid onset and rapid offset
Do non-depolarising muscle relaxants have more or less side effects than depolarising?
Less
Do non-depolarising muscle relaxants have a faster or slower onset of effect than depolarising?
slower onset (take more time)
What is the duration of a depolarising muscle relaxant? long, short or variable?
Short
What is the duration of a depolarising muscle relaxant? long, short or variable?
variable (depending on drug given)
Give some examples of short-acting non-depolarising muscle relaxants
Atracurium
Mivacurium
Give some examples of intermediate-acting non-depolarising muscle relaxants
vecuronium
rocuronium
Give some examples of long-acting non-depolarising muscle relaxants
pancuronium
How does one reverse the effects of a muscle relaxant?
Neostigmine (+glycopyrrolate to prevent cardiac muscle being effected (otherwise, bradycardia is caused))
What happens if neostigmine given without glycopyrrolate? What class of drug is glycopyrrolate? How does this impact heart rate?
Bradycardia
Anti-muscarinic agent
Blocks muscarinic effects of ACh, which are increased due to administration of neostigmine
What is neostigmine?
Anti-cholinesterase (binds to acetylcholinesterase)
Increases amount of ACh by preventing it being broken down at NM junction
Increases ability for muscular contraction
What are side effects of neostigmine?
Nausea and vomiting
What would one do at the end of surgery?
Stop anaesthetic vapours
Give oxygen
Perform throat suction
Reverse muscle relaxation
What other key drugs would you consider giving a pt. post-operatively? (excluding analgesia) Why?
Anti-emetics
Nausea and vomiting v. common after general anaesthesia
Vomiting can cause increased hospital stay, increased bleeding, incisional hernias and aspiration pneumonia
Why might you prescribe a patient vaso-active drugs intra-operatively?
To treat hypotension (v. dangerous if left untreated)
What are the classes of anti-emetic agents? Give examples each class.
5HT3 blockers: ondensetron Anti-histamines: cyclizine Steroids: dexamethasone Phenothiazine: prochlorperazine Anti-dopaminergic: metaclopramide
What are the three most-commonly used anti-emetics in anaesthetics (in order of commonness)
1) Ondansetron (used in about 95% of pts.)
2) Dexamethasone
3) Cyclizine
Which are the most commonly used vaso-active drugs given in intra-operative hypotension?
Ephedrine
Phenylephrine
Metaraminol
Which vaso-active drugs are given in severe hypotension whilst under anaesthetic (eg. in ICU)?
Noradrenaline
Adrenaline
Dobutamine
How does ephedrine effect BP and HR? What receptors do they work on?
Rise in HR (and contractility) = RISE IN BP
alpha and beta receptors
How does phenylephrine and meteraminol effect BP and HR? What receptors do they work on?
RISE IN BP
DROP in HR
alpha and beta receptors
If you wanted to increase a patients’ BP and HR, which vaso-active drug(s) would you use?
Ephedrine
If you wanted to increase a patients’ BP, but reduce HR, which vaso-active drug(s) would you use?
Phenylephrine
Metaraminol
Which vast-active agent would you use in intensive care or severe sepsis?
Noradrenaline
Adrenaline
Put the following elements of general anaesthesia using and LMA in order:
Opioid (fentanyl/afentanyl)
Oxygenation
Bag valve mask ventilation
Induction agent (propofol)
Turn on volatile agent (sevoflurane/isoflurane)
Insert LMA
1) Oxygenation
2) Opioid
3) Induction agent
4) Turn on volatile agent
5) Bag valve mask ventilation
6) LMA insertion
Put the following elements of general anaesthesia using intubation in order: Opioid (fentanyl/afentanyl) Oxygenation Bag valve mask ventilation Induction agent (propofol) Turn on volatile agent (sevoflurane/isoflurane) Endotracheal intubation Muscle relaxant
1) oxygenation
2) opioid
3) induction agent
4) muscle relaxant
5) turn on volatile agent
6) bag valve mask ventilation
7) endotracheal intubation
What is the ASA (american Society of Anaesthesiologists) grading?
Physical status classification system for assessing fitness for surgery
What is ASA grade 1?
Healthy pt.
No systemic disease
What is ASA grade 2? Give some examples of pts. who might fall in to this category.
Mild-moderate systemic disease with no functional limitation
eg. asthma
life-style/medication controlled diabetes
What is ASA grade 3? Give some examples of pts. who might fall in to this category.
Severe systemic disease
Imposing functional limitation on pt.
eg. stable angina, insulin-dependent diabetes
What is ASA grade 4? Give some examples of pts. who might fall in to this category.
Severe systemic disease which is a constant threat to life
eg. unstable angina, heart failure, end-stage COPD
What is ASA grade 5? Give some examples of pts. who might fall in to this category.
Moribund pt.
Not expected to survive with or without operation
eg. isachaemic bowel, severe head injury, palliative care op.
What is ASA grade 6? Give some examples of pts. who might fall in to this category.
Brainstem-dead pt. whose organs are being removed for donor purposes
What is added to the ASA grading to show that the cases are an emergency?
‘E’ suffix
What is the ASA grade of a normal fit healthy patient
1
What is the ASA grade of a 70 yr old pt., on ICU with non-survivable brain injury for insertion of an ICP monitor?
5
What is the ASA grade of a pt. with well-controlled asthma or hypertension?
2
What is the ASA grade of a moderately obese diabetic patient on insulin?
3
What is the ASA grade of a 20 yr old pt. with severe head injury from a road traffic accident?
At least 4
What are the different surgical grades?
Grade 1 (minor): eg. removal of moles, lipomas, nails etc.
Grade 2 (intermediate): eg. IND of abscesses, tonsillectomy, hernia repair
Grade 3 (major): eg. fracture repair, appendectomy
Grade 4 (major +): joint replacement, bypasses, lung surgery, GI surgery, emergency laparotomy
What grade of surgery is an emergency laparotomy?
4
what grade of surgery is an in-growing toe nail surgery?
1
What grade of surgery is a knee arthroscopy?
2
What grade of surgery is a fracture NOF fixation?
3
What pre-operative investigations are required in a normal pt under the age of 60?
FBC (if SG > 3)
U&Es (if SG > 4)
ECG not needed
What pre-operative investigations are required in a normal pt aged 60-80?
FBC (if SG > 2)
U&Es (if SG >3)
ECG (if SG >3)
What pre-operative investigations are required in a normal pt over the age of 80?
FBC
U&E
ECG
NO MATTER WHAT SURGICAL GRADE
What comorbidity would make you want to do an FBC before surgery (no matter what SG)?
Severe renal disease
What comorbidity would make you want to a U&Es before surgery (no matter what SG)?
renal or CVS disease
What comorbidity would make you want to do an ECG before surgery (no matter what SG)?
renal or CVS disease
Which routine investigations are usually not indicated in surgery (except for in specific patients)?
INR APTT CXR urine analysis serum glucose
What special investigation would you do for a patient with afro-carribean or +ve family Hx?
test for sickle cell - sickling test (or ask GP if they’ve been tested - if born in UK)
What special investigation would you do for a female patient of child-bearing age (14-45)?
urine pregnancy test
What special investigation would you do for a patient requiring ICU admission or respiratory disease with ASA 3 or 4?
CXR
If a patient is not fit for surgery, what would you do?
Try and optimise health eg. prescribe ABX, refer back to GP for treatment/stabilisation
May need to reschedule surgery
How long do patients have to be fasted from solid food prior to surgery?
6hrs
A 20 year old man is scheduled for elective tonsillectomy. He had a slice of toast with tea 4 hours ago. Is he fit for surgery?
NO
Fasted from solids <4 hours prior to surgery
Why do we try and minimise period of time pts. need to fast?
Discomfort for pt
Hypoglycaemia risk
Risk of dehydration
Reduced rate of recovery
What is the purpose of fasting patients?
To prevent aspiration of gastric contents
What is the gastric emptying time of water?
10-20 mins
How long must a patient NOT have water/clear fluids for, before surgery?
2 hours
How long must a patient NOT have breast milk for, before surgery?
4 hours
How long must a patient NOT have animal milk for, before surgery? why?
6 hours
Because it curdles with acid, therefore forms a solid in stomach
How long must a patient NOT have boiled sweets/chewing gum for, before surgery?
2 hours
How long must a patient NOT have alcohol for, before surgery?
24 hours
30 yr old M, had tea at 6pm yesterday and had 50 mL of water 30 mins before surgery. Is he fit for surgery? Why/why not?
NO
water consumed <2hrs prior to surgery
50mL - too large a quantity
30 yr old M, had dinner at 6pm yesterday and is down for the afternoon list (starting at 1:30pm). You see him at 7am on the morning. Is he fit for surgery and what could you do to avoid adverse effects of prolonged fasting?
tea and toast within the next half an hour
set up some fluids (to prevent dehydration)