Systemic complications Flashcards
What are 5 common issues that LA can cause?
- Vaso-vagal syncope
- Systemic effects of a vasoconstrictor
- Methemoglobinemia
- Overdose
- Allergies
What is vaso-vagal syncope?
- The vagus nerve is associated with parasympathetic control
- When the vagus nerve is overstimulated, the heart temporarily slows down. The brain is deprived of oxygen, causing the patient to lose consciousness
- People are more likely to faint if sitting upright
- People are more likely to faint if they have not eaten recently
- Most commonly: 20-30 year old males
- Elderly people (orthostatic hypotension)
How do you manage a syncope?
- Follow DRSABCD
- Restore blood flow / oxygenation to the brain
- Elevate legs, lower head
- Apply monitors (pulse oximeter, sphygmomanometer)
- Supplemental oxygen if needed
When do vasoconstrictive effects occur? What are the effects of a vasoconstrictor?
- Occurs when LA solution is injected into vessels or absorbed rapidly
- It causes increased BP, HR and Respiratory
How do you manage systemic effects of a vasoconstrictor?
How do you avoid such effects?
Management
• Reassure patient that their symptoms will go away
Avoidance:
• Aspirate, multiple times to ensure you aren’t in a blood vessel
• Inject very slowly
• Infiltrate instead of block
• If a patient requests different LA then use a different LA (eg citanest with felypressin, or plain lignocaine)
What is methemoglobinemia? What are signs and symptoms?
Description:
· Methaemoglobin is a form of haemoglobin that has a high affinity for oxygen, meaning it cannot release it effectively to body tissues.
· Occurs when red blood cells contain methaemoglobin at levels higher than 1%
· Low levels: skin and blood colour changes
· High levels: neurologic and cardiac symptoms (hypoxia)
· Extremely high levels: usually fatal
Signs and symptoms:
• Blueness around the mouth, hands and feet
• Breathing difficulties
• Vomiting and diarrhoea
• In severe cases, lethargy or losing consciousness
Which LA cause methemoglobinemia
Causes:
• Local anaesthetics (esp. prilocaine)
• Build-up of metabolite ortho-toluidine
• Benzocaine (in some topical anaesthetics)
How you manage methemoglobinemia?
Management:
• Call for help
• Oxygen!
• Methylene blue injection which reduces MeHb back to OxyHb
• Other drugs such as ascorbic acid like vitamin C
What are signs and symptoms of overdosing? Which effects occur first?
Recognise early signs of overdose: · Inhibitory interneurons are blocked, causing initial excitatory phenomena including: · Circumoral tingling (around mouth) · Visual and aural disturbances · Tremors · Dizziness · Convulsions/seizures
Finally, central neurones are depressed, leading to:
· Coma
· Respiratory arrest
Later, cardiac effects: · Reduced myocardial contractility: decreased heart rate, decreased blood pressure · Arrhythmias · Death · Bupivacaine is the most cardiotoxic
What increases the likelihood of overdosing?
· Site of injection · Type of LA (a vasodilator increases likelihood of overdose) · Dose injected · Weight of patient · Rate of administration · Degree of protein binding · Metabolism of drug: hepatic function. Choose a drug that isn't metabolised by the liver · Rate of elimination: Renal function
What causes an overdose?
· LA works by blocking impulses, thus it antagonises sodium channels
· Sodium channels are found on all excitable cell membranes
· In overdose, CNS effects occur before CVS effects
· The LA can bind to the heart and cause relaxation
· There is an initial excitatory response then depression
· Unexpected overdoses can occur due to things heart and haptic failure
How do you manage an overdose?
· DRSABCD
· Support the patient O2, airway, CPR
· Administration of a fat emulsion such as ‘Intralipid’ because LA is fat soluble
How do you avoid an overdose?
Describe advantages, disadvantages and application techniques
Infiltrate instead of block!
Advantages:
• Injects away from major blood vessels
• Minimise systemic absorption by using a different type of LA or by using a vasoconstrictor
• Superficial injection with less wait time
Disadvantages
• May not provide profound LA effect
Technique
- Inject using articaine infiltration at apex of tooth (even mandibular teeth)
- Inject at papilla using lignocaine. Start buccally and advance lingually,
- Inject enough so lingual papilla blanches
- Wait 2-3 minutes
How do you avoid an overdose if you’re performing a block?
· Aspirate!!!!
· Be aware of maximum dose and inject slowly
Are most people allergic to LA?
No. Most patients who report an allergy to local anaesthetics describe adrenergic-reaction symptoms (reaction to vasoconstrictor).
