Anaesthetics Flashcards
How long must a patient fast after eating a light meal or milk?
6 hours
How long must a patient fast after drinking alcohol?
24 hours
How long must a patient fast after drinking breast milk?
Breast milk has less fat than regular milk. Less fat means less to thicken in the stomach, so requires less time to empty from the stomach. So 4 hours!
How long must a patient fast after drinking clear juice, tea, or water?
2 hours
What amount of water is acceptable for patients to swallow their tablets with before surgery?
30mls
Is a patient chewing gum or sucking on boiled sweets before their operation?
Yes, but this should be avoided as it can increase stomach acid which contributes to gastric volume
What is involved in preoxygenation in rapid sequence induction?
Preoxygenate with a tight fitting mask with high flow oxygen for three to five minutes, or ask the patient to take five vital capacity breaths. The mask is not removed until laryngoscopy.
This replaces the two litres of functional residual capacity in the lungs with oxygen, allowing eight minutes without ventilation before hypoxemia
After preoxygenation, what is the next step of rapid sequence induction
Application of cricoid pressure (10N) to occlude the oesophagus- this is not removed until the tube is in the right place
After cricoid pressure is applied, what is the next step of RSI?
Thiopentone (4-5mg/kg) is administered and lasts for 4-8mins, immediately followed by suxamethonium (1.5-2.5 mg/kg) which lasts for six minutes. Cricoid force increased at loss of consciousness.
What occurs after induction and the administration of suxamethonium in RSI?
Fasciculations occur 45-60 seconds after suxamethonium
After this, intubate
What five factors indicate the tube is correctly placed?
Misting of the tube Breathing sounds heard on auscultation Expired CO2 detected on the monitor See tube pass vocal cords Chest expansion
What are the standard induction doses of propofol, Thiopentone, etomidate, and ketamine?
Propofol- 1.5-2.5 mg/kg
Thiopentone- 4-5
Etomidate- 0.3
Ketamine- 1-1.5
How long does each induction drug take to work?
Thiopentone- 20-30s
Propofol- 45-60s
Etomidate- 30-40s
Ketamine- 90s
How long does each induction drug last?
Etomidate- 3-6 mins
Propofol- 4-7 mins
Thiopentone- 9-10 mins
Ketamine- 10-12 mins
What are the physiological and unwanted effects of propofol?
Decrease in HR and BP Apnoea for 60s Pain on injection Involuntary movements Reduced post op nausea and vom
What are the unwanted and physiological effects of Thiopentone?
Antiepileptic properties and cerebroprotective
Decreases BP but increases HR!
Causes rash and bronchospasm
Causes thrombosis if injected into arteries
Contraindicated in porphyria
What are the physiological and unwanted effects of etomidate?
Haemodynamically stable
Least likely to cause hypersensitivity
Pain on injection
Involuntary movements
Most likely to cause post op N+V
Suppresses cortisol levels- do not use in sepsis
What are the physiological and unwanted effects of ketamine?
Increases HR and BP!
Dissociative effects may be distressing for patients
Causes bronchodilation!
What is the minimum alveolar concentration?
Concentration of vapour that prevents reaction to a standard surgical stimulus in 50% of subjects
What are the minimum alveolar concentrations of the inhaled anaesthetics?
Nitrous oxide- 104% Sevoflurane- 2% Isoflurane- 1.15% Desflurane- 6% Enflurane- 1.6%
What factors increase the MAC?
Infants, children Hyperthermia Hyperthyroidism Hypernatraemia Chronic alcohol or opioid use Increased catecholamines
What factors decrease MAC?
Neonates The elderly Hypothyroidism Hyponatraemia Acute alcohol intake Acute opioid, benzo intake Lithium Magnesium Pregnancy Anaemia
When is sevoflurane used?
For inhalational induction, due to its sweet smell
When is desflurane used?
For long operations, as it has low lipid solubility and therefore does not get absorbed into fat, reducing the time needed to wear off
When is isoflurane used?
Isoflurane does not effect organ blood flow
Therefore it is useful for organ transplantation operations
What is the purpose of short acting opioid analgesics? And give examples
To reduce autonomic responses to surgery and laryngoscopy
Fentanyl, remifentanil, alfentanil
What is the purpose of long acting opioid analgesics in anaesthetic?
For intraoperative and postoperative analgesia
Morphine, oxycodone
What NSAIDs are typically used for analgesia in anesthestics?
Diclofenac
Parecoxib- usually given IV
Ketorolac- usually IV
When are NSAIDS contraindicated in anaesthesia?
High risk of bleeding eg vascular surgery
Bleeding disorders
Asthma
Renal dysfunction
History of GI bleeds
Concurrent use if ace inhibitors, nephrotoxic drugs
Which weak opioids are commonly used in anaesthesia?
Tramadol
Dihydrocodeine
Which neuromuscular blockers are depolarising and how do they work?
Bind to acetylcholine receptors at neuromuscular junctions and are very slowly hydrolysed by acetylcholinesterase.
Therefore short period of muscle fasciculations lasting 40-60s.
Suxamethonium
What are the uses and side effects of suxamethonium? And it’s dose
1-1.5mg/kg
Used in rapid sequence induction due to its rapid onset
Adverse effects: Muscle pains Fasciculations Hyperkalaemia Malignant hyperthermia Rise in icp, iop, gastric pressure
How do the non-depolarising neuromuscular blockers function?
Block nicotinic receptors on neuromuscular junctions without activating the muscle, competing with acetylcholine
What are the short, intermediate, and long acting non-depolarising neuromuscular blockers?
Short- mivacurium
Intermediate- vecuronium, rocuroniun
Long- pancuronium
All have relatively slow onset and less side effects than depolarising drugs
What drugs reverse neuromuscular blockade?
Neostigmine
This is an acetylcholinesterase inhibitor
Often given with glycopyrrolate, an antimuscarinic, to counter the unwanted increase in acetylcholine in parasympathetic synapses causing bradycardia, N+V
It doesn’t work on suxamethonium
What proportion of patients experience post operative nausea and vomiting?
25%
May result in aspiration pneumonia, bleeding, and incisional hernias
Whig patients are more at risk of PONV
Female patients
Non smokers
Patients who experience motion sickness or previous PONV
Patients on opioids as part of anaesthesia
Patients with two or more of these should receive two anti emetics
Which drugs are used to increase BP and how do they work?
Ephedrine- increase heart rate and contractility
Phenylepherine- increase vasoconstriction, reduce HR
Metaraminol- increase vasoconstriction
So use ephedrine if low HR, phenylephrine and metaraminol if high HR
Where do each of the three neurons travel?
First order neuron: sensory nerve with free nerve endings, cell body in dorsal root ganglion
2nd neuron: crosses midsection to join lateral spinothamic tract
3rd neuron: thalamus to primary sensory cortex on post central gyrus
What post operative analgesia would you recommend for a operation with a pain intensity score of 1?
Paracetamol 1g QDS (4g max 24 hr dose)
Ibuprofen 200-400mg TDS prn
Avoid in asthma, kidney disease, IHD, peptic ulcer
What post operative analgesia would you recommend for a operation with a pain intensity score of 2?
Reg paracetamol and ibuprofen as per PIS 1
And
Codeine 30-60mg QDS max 240mg in 24 hours
What post operative analgesia would you recommend for a operation with a pain intensity score of 3?
Reg paracetamol and NSAID as per PIS 2
And
PCAS morphine
Epidural/single shot
Spinal
What is a typical PCAS regimen?
1mg morphine bolus
5 minutes lockout period
12 mg max in an hour
How so local anaesthetics work?
Prevent Na+ influx to depolarise first order neuron
This prevents transmission of signal further in the pathway
Local anaesthetics block only the anatomical area being infiltrated and areas distal from this point
Which local anaesthetics are esters?
Procaine
Cocaine
Amethocaine
Which local anaesthetics are amides?
Mepivacaine Bupivacaine Lidocaine Lignocaine Prilocaine
What is the maximum dose of lignocaine, with and without adrenaline?
Lignocaine
With adrenaline: 3mg/kg
Without adrenaline: 7mg/kg
Comes in 1% and 2% concentration
1% = 10mg in 1ml
What is the maximum dose of bupivacaine with and without adrenaline?
Bubivacaine
With adrenaline: 2 mg/kg
Without adrenaline: 2mg/kg
What is the max dose of prilocaine with and without adrenaline?
6mg/kg without adrenaline
9mg/kg with adrenaline
Why is the max dose of a local anaesthetic increased when used with adrenaline?
Adrenaline is a vasoconstrictor so it decreases the amount of local anaesthetic which is removed by the blood
Therefore more LA can be used because the LA stays where you want it to
How would your use of LA change when treating a large area?
If larger lesions, more LA is required to cover the area, so give with adrenaline
Use more dilute solutions to cover more area
Where does he subarachnoid space end?
S2
Where can you do a spinal block?
Below L1
But usually between L3/4
Where does the epidural space end?
S4/5
At the sacricoccygeal hiatus
Where can you do am epidural block?
Any level, but the higher up you go the more risk there is of spreading to brain, causing apnoea, hypotension etc
What LA is used with spinal analgesia?
Heavy bupivacaine as it is more dense than CSF and sinks in the subarachnoid space
What are the characteristics of spinal anaesthesia?
Lasts 2-3 hours- longer with opioids
Intense motor block
Quick onset
What are the characteristics of epidural anaesthesia
Slower onset
Less motor blocking
Can put in catheter- patient control
What is the CEPOD definition of an immediate/emergency operation?
An operation to treat a medical condition risking life and/or limb
Resuscitation simultaneous with intervention
Occurs within minutes of decision to operate
Eg fasciotomy, AAA
What is the CEPOD definition of an urgent operation?
An intervention for acute onset or clinical deterioration of potentially life/limb threatening conditions.
Occurs within hours of decision to operate
What is the CEPOD definition of a scheduled/expedited operation?
Patient requiring early treatment whee the condition is not an immediate threat to life/limb/organ survival
Occurs within days of decision to operate
Eg hip replacement, cholecystectomy, repair of tendon
What is the CEPOD definition of an elective operation?
Intervention planned or booked in advance of routine admission to hospital
Timing to suit patient, hospital and staff
What is ASA grade 1?
A healthy patient with no systemic disease
What is ASA grade 2?
Mild to moderate systemic disease with no functional limitation
What is an ASA grade 3 patient?
Severe systemic disease imposing functional limitation on patient
What is an ASA grade 4 patient?
Severe systemic disease which is a constant threat to life
What is an ASA grade 5 patient?
Moribund patient who is not expected to survive with or without the operation
What is an ASA grade 6 patient?
A brainstem dead patient whose organs are being removed for donor purposes
What are examples of grade 1 (minor) surgery?
Cystoscopy
Drainage of abscess
Excision of skin lesions
What is an example of a grade 2 (intermediate) surgery?
Elective appendicectomy
Inguinal hernia
What is an example of a grade 3 (major) surgery?
Hysterectomy
Thyroidectomy
What is an example of a grade 4 (major+) surgery?
Joint replacement
Thoracic operations
THR
Radical neck dissections
What are contraindications to epidural or spinal anaesthesia?
Hypovolaemia- patient likely to experience fall in CO as compensatory vasoconstriction is lost
Low cardiac output
Local skin sepsis - infection risk
Coagulopathy - risk of epidural haematoma
Raised ICP- risk of precipitating coning
What are complications of central neural blockade via spinal/epidural
Hypotension and bradycardia- due to sympathetic blockade causing vasodilation. If blockade extends above T5, cardio accelerator nerves are blocked and unnopposed vagal tone causes bradycardia
Nausea and vomiting
Post dural puncture headache - persistent leak of CSF
What are the early and late signs of local anaesthetic toxicity?
Early - circumpolar paraesthesia, numbness of tongue, visual disturbances, lightheadedness, slurred speech
Late - grand mal convulsions with coma, respiratory depression, cv collapse, hypotension, bradycardia
Why do all patients require oxygen after anaesthesia?
To counter the effects of diffusion hypoxia if nitrous oxide has been given
To compensate for any hypo ventilation
To compensate for vq mismatch
To meet the increased oxygen demand when shivering
What temperature is a unit of packed RBCs kept at?
2-6 degrees
How long may a unit of packed RBCs kept for? (Shelf life)
42 days
How quickly must a unit of packed RBCs be transfused after removal from the fridge?
Within 30 mins
The unit can be transfused over a maximum of an hour
At what haemoglobin conc is blood transfusion indicated?
Always if hb is <8g/dl in patients with cardio or resp disease, over 65 etc
What are the risks of RBC transfusion?
Acute haemolytic transfusion reaction - usually ABO incompatibility because if clerical error - Haemolysus, shock, Renal failure
Bacterial contamination - rare
Transfusion related acute lung injury
Allergy
Viral infections - although every donation tested for hep B, hep c, HIV
What causes prolonged apnoea when using suxamethonium?
Pseudocholinesterase deficiency resulting in insufficient enzyme to metabolise suxamethonium
Period of apnoea is dependent on whether patient is heterozygotic or homozygotic for the faulty allele
What is the dose of dexamethasone and when is it given during anaesthesia?
4-8 mg IV
Given at induction, as causes perineal flushing in awake patients
What is the dose of ondansetron, and when is it given?
4-8mg IV
Given at end of surgery
What is the dose and side effects of cyclizine?
50mg IV given at end of surgery
As prn drug: 25mg TDS
May cause tachycardia due to anti vagal properties
When and how is Amethocaine used?
Given topically at site of IV cannulation
4% ametop cream
Effective in 45 minutes
What is the dosage of paracetamol? Oral and IV, children and adults
20mg/kg oral
15mg/kg IV
Up to 50 kg, when the adult dose is given which is 1g paracetamol IV (perfalgan)
What is the dose of morphine?
0.1mg/kg IV
Often 10mg IV morphine prescribed in post op recovery in the ‘once only’ section
What is the dose of codeine?
0.5mg/kg
How are lmwh used in venous thrombolaxis?
Started on admission or evening before surgery
Dalteparin- 2500u
Enoxaparin- 2000u
Tinzaparin- 3500u
What agent reverses rocuronium?
Suggamadex
