Anaesthetics Flashcards
T/F glass shows up on xray
T. It’s radio-opaque
Best anaesthetic for short procedure?
Lidocaine & bupivicaine are both commonly used local anaesthetics, but lidocaine has a faster onset and shorter duration of action, making it more suitable for short procedures.
Initial pain relief for suturing
Lidocaine and paracetemol
What can cold spray be used for
Cold spray is a volatile compound which evaporates to cool the skin and relieve pain. Cold spray can be useful in closed injuries, but should not be used on an open wound.
Which nerve fibres are affected by local anaesthetics
They act on small unmyelinated C fibres, which transmit pain and temperature sensation, before the larger A fibres, which transmit touch and power.
What channels do local anaesthetics act on
Local anaesthetics inhibit the influx of sodium into the cell.
What is the time of onset of lidocaine
What is the duration of action
4 minutes onset
2hrs duration of action
How can lidocaine be made more effective, and less painful on injection
More effective: The addition of adrenaline causes local vasoconstriction and delays anaesthetic washout into the circulation, so that its effect can last longer. There is also less bleeding.
Less painful on injection: Subcutaneous injection is made less painful by using anaesthetic warmed to room temperature, and injecting slowly through a small needle.
When must you not add adrenaline to local anaesthetic
When injecting into digits, you should not add adrenaline to your local anaesthetic as it can cause ischaemia.
What are the potential side effects of local anaesthetics
Can affect neural processes in the cardiovascular and central nervous systems, causing cardiac arrhythmias, neurotoxicity and central respiratory depression.
They can also cause allergic reactions, resulting in minor urticaria or in the worse scenario, anaphylaxis.
Lidocaine overdose affects which system at lower and higher concentration
What about bupivocaine
Primarily affects CNS:
- light-headedness,
- dizziness,
- drowsiness
Secondarily, and at higher plasma levels, the cardiovascular system:
- myocardial depression,
- peripheral vasodilatation -> hypotension and bradycardia)
Bupivocaine is actually cardiotoxic so is worse for the cardiovascular effects
Symptoms of lidocaine overdose
Light headiness
Convulsions
Perioral Paraesthesia
Hypotension
What type of molecule is lidocaine
Lidocaine is an amide-based local anaesthetic
What is the mechanism of action of lidocaine
It penetrates the interior of an axon and then reversibly blocks the sodium channels by binding to a receptor in those channels.
This prevents the generation of action potentials when a critical number of the channels are blocked.
Where is lidocaine metabolised
In the liver, and is excreted in the urine
Order the nerve fibres in terms of which are first affected by lidocaine, through to last
Pain fibres
Autonomic fibres
Coarse touch
Motor
Related to fibre diameter i.e. smaller the most sensitive, as few channels need to be blocked to reach the analgesic threshold. Thus, light touch may still be preserved even when the patient cannot feel pain. Motor nerves are the last to be blocked.
What is regional anaesthetic?
Using local anaesthetic to anaesthetise a specific body region
What is spinal anaesthetic
A regional anaesthetic:
Spinal where local anaesthetic is injected into the intrathecal space at the lower lumbar region – usually L3/4
What is epidural anaesthetic
A regional anaesthetic:
Epidural where local anaesthetic is injected into the epidural space, usually via a catheter inserted into and left in the space for at least the duration of surgery
What is a field block
A regional anaesthetic:
Field block where local anaesthetic is infiltrated into the inguinal region before and during surgery.
What is a Bier’s block and brachial plexus block
Regional anaesthetic techniques
A Bier’s block is a regional technique for anaesthetising the forearm and Brachial plexus blocks are for shoulder and upper limb surgery.
T/F regional anaesthetic agents have no effect on the CNS
True, unless:
1) Overdose
2) Spinal anaesthesia (other than this, it affects the peripheral nerves)
T/F patients undergoing surgery with regional anaesthesia are always awake
F.
Patients undergoing surgery under regional anaesthesia are often given sedative drugs or the technique is combined with a general anaesthetic.
What is the most frequently used regional anaesthesia and why
Bupivacaine (often known by it’s trade name Marcaine) is the most frequently used local anaesthetic agent in regional anaesthesia because of its long duration of action
(compare this to lidocaine (=lignocaine) which is used in short suturing procedures due to its shorter duration of action)