Anaesthetics Flashcards
In most operations in which 3 drugs are administered to induces general anaesthesia, why are 3 separate drugs (for amnesia, analgesia and akinesis) given?
To minimises side effects
What are the four main induction agents (induce loss of consciousness)?
Propofol, thiopentone, ketamine and etomidate
What is the most commonly used (95%) induction agent?
Propofol
What is the safe dose of propofol to use?
1.5-2.5 mg/kg
Key side effects to be aware of for propofol?
Greatly reduces heart rate and blood pressure, pain on injection, involuntary movements.
What benefit is there of using thiopentone over propofol?
It is faster acting and, as such, is mainly used for rapid sequence induction. Additionally, thiopentone has anti-epileptic properties and is brain-protective.
What is the safe dose of thiopentone to use?
4-5 mg/kg
Thiopentone is a barbiturate and, therefore, has several side effects. What are they?
Reduced BP, increased HR, rash, bronchospasm, potential thrombosis and gangrene if injected intra-arterially.
What condition is a contra-indication to using thiopentone?
Porphyria
What is the safe dose of ketamine?
1-1.5 mg/kg
What type of procedures is ketamine most appropriate for?
Short procedures - it produces anterograde amnesia and profound analgesia
What effect does ketamine have on heart rate and blood pressure?
Increases both
What are some unwanted side effects of ketamine?
Nausea and vomiting, emergence phenomenon (vivid dreams and hallucinations)
Is the onset of etomidate fast or slow?
Rapid onset
What is the safe dose of etomidate?
0.3 mg/kg
What are the four maintenance inhalational drugs commonly used?
Isoflurane, sevoflurane, desflurane, enflurane
What are the benefits of using etomidate?
Haemodynamically stable drug. Also, has the lowest incidence of hypersensitivity reaction.
What are the unwanted side effects of etomidate?
Pain on injection, spontaneous movements, high incidence of post-operative nausea and vomiting.
Also, as it is a steroid-based drug it can cause adreno-cortical suppression.
What is Minimum Alveolar Concentration (MAC)?
One MAC is the concentration of vapour that prevents reaction to a standard surgical stimulus in 50% of patients
How much is one MAC of sevoflurane?
2%
How much is one MAC of isoflurane?
1.15%
How much is one MAC of desflurane?
6%
How much is one MAC of enflurane?
1.6%
Which inhalational agent is best for paediatric patients without iv access and why?
Sevoflurane - it is sweet smelling
Which inhalational agent is best for long operations due to its rapid onset and offset and why?
Desflurane - has low lipid solubility
Which inhalational agent is best for organ retrieval operations and why?
Isoflurane - has least effect on organ blood flow
What is the most commonly used analgesic in anaesthetics?
Fentanyl - rapid onset and high potency
Why are muscle relaxants required for ~50% of operations?
To enable easier intubation and smoother surgery
Give an example of a depolarising muscle relaxant
Suxamethonium
How do depolarising muscle relaxants work?
Act similarly to Acetylcholine at the neuromuscular junction but are very slowly hydrolysed by acetylcholinesterase therefore cause continual muscle contraction leading to fatigue and, ultimately, relaxation
What is the safe dose of suxamethonium?
1-1.5 mg/kg
When is suxamethonium used?
Rapid sequence induction. It has rapid onset and offset.
What are the side effects of suxamethonium?
Muscle pains, fasciculations, hyperkalaemia, bradycardia, malignant hyperthermia, raised ICP, raised intra-ocular pressure, raised gastric pressure
How do non-depolarising muscle relaxants work?
Compete with ACh and block nicotinic receptors at the NMJ thereby preventing depolarisation.
How do non-depolarising agents differ from depolaring agents in terms of properties?
Non-depolarising muscle relaxants are slower onset, have more variable duration of action (short, intermediate, long), and have fewer side effects.
What drugs are used to reverse muscle relaxants?
Neostigmine and glycopyrrolate
How does neostigmine work?
It is an anticholinesterase so prevents ACh from being broken down
For a patient who is having an LMA inserted, what is the order of steps to follow?
- Oxygenation
- Opioid (fentanyl)
- Induction agent (propofol)
- Turn on volatile agent (sevo/isoflurane)
- Bag-valve mask ventilation
- Insert LMA
For a patient who is having endotracheal intubation, what is the order of steps to follow?
- Oxygenation
- Opioid (fentanyl)
- Induction agent (propofol)
- Muscle-relaxant (rocuronium)
- Turn on volatile agent (sevo/isoflurane)
- Bag-valve mask ventilation
- Endotracheal intubation
How do local anaesthetics work?
Block the transmission of nerve impulses transiently by inhibiting sodium channels in the nerve axon so the sensory information is blocked at the site of application and does not reach the brain.
What are the 2 types of local anaesthetic?
Amides - have a NH- link
Esters - have a COO- link
Give examples of amides
Amides have 2 ‘i’s in the name so:
Lignocaine, prilocaine, levobupivacaine, bupivacaine
Give examples of esters
Esters only have one ‘i’ in the name so:
Procaine, benzocaine, cocaine, tetracaine (=Ametop)
Why is adrenaline given with some local anaesthetics?
Adrenaline is a vasoconstrictor so it will reduce the systemic absorption of local anaesthetic thus can give higher doses of the Local anaesthetic –> preferable!
What is the safe maximum dose of lignocaine without adrenaline?
3 mg/kg
What is the safe maximum dose of lignocaine with adrenaline?
7 mg/kg
What is the safe maximum dose of bupivacaine/levobupivacaine with or without adrenaline?
2 mg/kg
What is the safe maximum dose of prilocaine without adrenaline?
6 mg/kg
What is the safe maximum dose of prilocaine with adrenaline?
9 mg/kg
What is the range of ASA grades?
Grade 1 (a healthy patient with no systemic disease) to Grade 6 (a brainsteam dead patient whose organs are being removed for donor purposes). Also for emergency cases, the suffix ‘E’ is used.
What pre-operative investigation should be carried out in African/Afro-caribbean origin patients?
Sickle cell test
What is the risk associated with inadequate fasting before an operation?
Pulmonary aspiration - as little as 30ml can be associated with significant morbidity and mortality
What is the recommended minimum fasting time for solids/milk-containing foods?
6 hours
What is the recommended minimum fasting time for breast-fed infants?
4 hours
What is the recommended minimum fasting time for clear fluids?
2 hours
What is the recommended minimum fasting time for alcohol?
At least 24 hours before surgery as it delays gastric emptying
What are some signs of local anaesthetic toxicity?
Tingling sensation around mouth, ringing in ears, seizures, eventually no pulse and poor resp effort.
What drug can be given to reduce and reverse local anaesthetic toxicity?
Intralipid - absorbs free local anaesthetic from blood.
What level should spinals and epidurals be given to reduce risk of damage to the spinal cord?
Below L2 down to S2
What layers are punctured when giving a spinal?
Skin, subcut fat, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, and dura
Give 2 examples of short acting non-depolarising muscle relaxants
Atracurium
Mivacurium
Give 2 examples of intermediate acting non-depolarising muscle relaxants
Vecuronium
Rocuronium
Give an example of a long acting non-depolarising muscle relaxant
Pancuronium
