Local and Regional Anaesthesia Flashcards
What is ‘analgesia’?
The state when only pain relied is provided - enough for minor surgeries e.g. suturing.
What is ‘anaesthesia’?
The state when analgesia is accompanied with muscle relaxation - used for major surgeries.
Regional +/- general anaesthesia can be used.
Where can local anaesthetics be used?
- Topically to mucous membrane - e.g. eye!
- Subcutaneous infiltration
- IV after tourniquet = IVRA
- Directly around nerves - e.g. brachial plexus
- In the extradural space (‘epidural’)
- In the subarachnoid space (‘spinal’)
Name 2 methods of central neural blockade?
- Epidural - LA in the extradural space
2. Spinal - LA in the subarachnoid space
What infiltration analgesic is usually used for short procedures?
Lidocaine 0.5%
What infiltration analgesic is usually used for pain relief from surgery?
Bupivacaine 0.5% or Chirocaine
What can be added to infiltration analgesia if a large dose or prolonged effect is required?
Adrenaline
- When giving infiltration analgesia, what structures are you trying to avoid?
- How do you know if you have done this correctly?
- Blood vessels - should be subcut.
- Aspirate the needle once it is in subcutaneously - if any blood is seen on aspiration, discard the syringe and start again.
- Where should LA be injected when performing a brachial plexus block?
- What can be used to locate the nerves?
- How long does the block last?
- Either supra-clavicular OR through the axilla.
- A nerve stimulator / ultrasound is also being used.
- Several hours - important to warn the surgeon and px.
- What is a TAP block?
2. What is it used for?
- Transversus abdominis plane block - LA between the transversus abdominis and internal oblique muscles.
- To anaesthetise the nerves supplying the skin + muscles of anterior abdominal wall (parietal peritoneum).
E.g. appendicectomy, hernia repair, laproscopic surgery.
- Where is epidural anaesthesia inserted?
2. Where can the site of the epidural be?
- Into the potential space OUTSIDE the dura.
2. Anywhere between the craniocervical junction (C1) to the sacrococcygeal membrane.
The extent of anaesthesia in an epidural is determined by what 3 factors?
- Which spinal level it was inserted - spread is greater in thoracic > lumbar region.
- The volume of anaesthetic injected.
- Gravity - tipping the px head-down encourages spread cranially. If the px is upright, this limits the spread.
What anatomical layers are pierced during an epidural?
Skin - SC fat - supraspinous ligament - interspinous ligament - ligamentum flavum = epidural space.
Below what level can spinal anaesthesia be inserted?
L2 (and above S1)
What can be added to LA during a spinal and what is the advantage of adding this?
0.10 - 0.25 mg of morphine / diamorphine = extends the duration of analgesia for up to 12 hours postoperatively.
What are the contraindications to performing epidural / spinal anaesthesia?
- Hypovolaemia = e.g. due to blood loss or dehydration. Falls in cardiac output as compensatory vasoconstriction is lost.
- Low, fixed cardiac output = e.g. aortic / mitral stenosis. Reduces venous return and further reduces cardiac output - lack of perfusion to vital organs.
- Local skin infection
- Coagulopathy = risk of epidural haematoma.
- Increased ICP = risk of coning.
- Allergy to LA
- Uncooperative px
What are the side effects of epidurals?
Hypotension / bradycardia, N+V, post-dural puncture headache
Why do epidurals cause:
- Hypotension?
- Bradycardia?
- Anaesthesia of thoracic + lumbar nerves = sympathetic block. This causes VASODILATION and REDUCED VENOUS RETURN = cardiac output falls.
- If block extends above T5 = cardioaccelerator nerves are also blocked. The unopposed vagal tone = bradycardia.
Why does N+V occur as a side effect of epidurals and what can be given to help this?
Hypotension (first sign), cerebral hypoxia, vagal stimulation during upper-abdo surgery.
Atropine 0.3 - 0.6mg - particularly if there is bradycardia OR Odansetron 4mg IV.
- What causes post-dural puncture headache?
2. How can this be resolved?
- Persistent leak of CSF from the needle hole in the dura. Usually frontal or occipital, exacerbated by straining - majority will resolve spontaneously.
- By injecting 20-30 ml of px’s own blood into epidural space = epidural blood patch.
What causes local anaesthetic toxicity?
- Rapid absorption of a dose.
- Inadvertent IV injection - if failure to aspirate.
- Overdose - calculation error or not taking into account pre-existing hepatic / cardiac disease.
What are the mild / early signs of LA toxicity?
Circumoral paraesthesia ( = numbness or tingling about the mouth), numbness of the tongue, visual disturbances, light headedness, slurred speech, twitching, mild hypotension, bradycardia.
What are the severe / late signs of LA toxicity?
General tonic-clonic seizure - followed by coma, respiratory depression - leads to apnoea, CV collapse - profound hypotension + bradycardia and ultimately cardiac arrest.
(Seizure - resp depression - CV collapse - cardiac arrest)
How do you manage LA toxicity?
Airway = maintain. Tracheostomy may be needed if protective reflexes are absent - to prevent aspiration.
Breathing = give 100% oxygen + ventilate if required.
Circulation = raise px legs to aid venous return + give IV crystalloid / colloid. Treat bradycardia with IV atropine.
Disability = treat convulsions with diazepam 5-10mg IV (can cause resp. depression). Seek assistance if recurrence or no change.
What can be given when local anaesthetic toxicity causes profound cardiovascular collapse?
Initially = 1.5 ml/kg 20% lipid emulsion / 1 min Then = infusion of 20% lipid emulsion at a rate of 15ml/kg/h
If no change after 5 mins of this = repeat 2 boluses 5 mins apart, double the rate of infusion.
MAX DOSE = 12 ML / KG
What are the advantages of performing blocks in px who are awake?
- Block can be checked before surgery commences.
- Lower risk of nerve injury - px will complain if needle touches nerve.
- Px can cooperate with positioning.
What are the advantages of performing blocks under general anaesthesia?
- More pleasant for the px
- No risk of px suddenly moving
- Allows easier positing of px if they are in pain.
- If needle hits the nerve then the damage is already done…
What are the potential benefits of regional anaesthesia?
- Avoids systemic effects of GA.
- Avoid drugs that cause resp. depression.
- Less disturbance of control of co-existing systemic disease.
- Airway reflexes are preserved.
- May improve surgical access - e.g. during laparotomy.
- Reduced blood loss.
- Can be continued post-op for pain relief.
- Reduces complications after major surgery.
- Cheaper.
(T/F) Regional anaesthesia:
- Offers no advantage to px with COPD.
- May increase blood loss during surgery.
- Causes less disturbance of concurrent disease requiring medical therapy.
- May hinder access for the surgeon during laparotomy.
- F = spontaneous ventilation is preserved + respiratory depressant drugs avoided.
- F = decreases blood loss.
- T = less disturbance partly due to modified stress response.
- F = muscle relaxation and contraction of bowel will improve access.
(T/F) Local anaesthetic drugs can be used:
- intra-arterially after the application of a tourniquet.
- by direct injection into the nerves.
- SC
- Intrathecally (into the spinal theca)
- F = dangerous! Bier’s block = IV after application of tourniquet.
- F = this would cause nerve damage - should only be injected adjacent to nerves.
- T
- T = spinal anaesthesia!
(T/F) Contraindications of spinal anaesthesia =
- Coagulopathy
- Severe aortic stenosis
- Local skin sepsis
- Major trauma
- T = risk of epidural haematoma.
- T = low fixed cardiac output will be further reduced by vasodilation + reduced venous return.
- T = risk of introducing infection e.g. meningitis.
- T = these px are likely to be hypovolaemic + very vasoconstricted. Sudden vasodilation = massive fall in BP and cardiac output.
(T/F) Local anaesthetic toxicity:
- May be caused despite using a safe dose of the drug.
- May initially present with grand mal convulsions.
- Should initially be managed by raising px legs to treat hypotension.
- Is a common complication of epidural anaesthesia.
- T = if injected into a vascular area or inadvertently directly IV.
- T = in severe cases.
- F = Inital Rx would be to stop if still injecting and use ABCDE approach.
- F = Rare (1:10,000)
