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22 Cards in this Set
- Front
- Back
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What are local anaesthetics used for?
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They can be used to provide local and regional blockade of sensory nerves. It is the only technique that completely inhibits sensation of pain and other stimuli at the blocked site.
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What are the 2 main indications for use of local anaesthetic agents?
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Simple surgery without general anaesthesia
Stitch up horse under sedation Delivery calf Caesarean section in ruminant 2. Adjunct to general anaesthesia Provide peri-operative analgesia Reduce requirement for other anaesthetic agents |
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Describe how Local anaesthetics work on the nerve?
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1. When the nervet terminal is stimulated, Na channels open resulting in an influx of sodium from the ECF into the nerve. This increases membrane potential > influx of sodium in neighbouring areas > action potential.
LA binds to Na channels reversible> prevents formation of action potential. |
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What are the 5 factors that affect activity of LA?
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1. characteristics of the nerve fibre.
2. nerve activity 3. pH 4. protein binding 5. pheripheral vasodilation. |
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How does the nerve type affect the activity of LA?
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Unmyelinated nerves:
greater surface area available for local anaesthetics to work Myelinated nerves: susceptible to blockade at nodes 2-3 nodes must be blocked larger nerves: > distance between nodes → < susceptible to blockade |
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How does the size of the nerves affect activity of LA?
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The small nerves (a -beta and gamma= touch and pressure) are blocked more readily than larger nerves (A-delta= motor nerves) Thus pain sensation will be blocked at a lower concentration than motor nerves.
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How does the nerve activity affect activity of LA?
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Na channels must be open for LA to reach the site of action thus, for the local anaesthetic to be effective the nerve have to be stimulated.
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How does ph affect the onset of action of LA?
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Ionised drug is not lipid soluble; the more ionised drug present the slower the onset.
Non- ionised form is lipid soluble and able to diffuse across the membrane. |
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How does vasodilation affect the durationof LA?
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↑ removal → ↓duration of activity
Many local anaesthetics cause vasodilation Use of vasoconstrictors increases duration |
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How does LA affect the cardiovascular system?
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La > vasodilation > Decreased HR and contractility > hypotension / bradycardia/ bradyarrythmia and cardiac arrest
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What are the effects of LA on the CNS? At higher and lower doses?
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Low doses: depression > sedative
Higher doses> CNS excitation which include muscle tremors |
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How is La used in muscles?
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Blockade of motor nerves causes paralysis
Epidural: Hindlimb weakness Brachial plexus Forelimb weakness |
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What are the 3 topical routes of administerin LA?
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Topical
Mucous membranes Larynx Skin |
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define infiltration and give 2 examples?
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Injection of LA into the skin that come into contact with the local aanesthetic at/ near the site of injection.
Eg Incision site and dentals |
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Define regional block. Give examples./
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Regional block
= block several nerves at one location e.g. Brachial plexus e.g. Paravertebral |
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Wha are the 2 techniques for spinal injections? Where are the locations?
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Spinal injection
Subarachnoid Epidural space Dogs/cats/small ruminant: lumbo-sacral space Horses/cattle: sacro- coccygeal; c1-c2 |
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What are the 5 factors that affect epidural spread?
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1. The site of injection
2. The volume of solution injected 3. Position of the animal 4. The speed of injection 5. Pregnancy 6. Obesity. |
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What are the 5 complications associated with epidurals?
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1, Infection
2. Respiratory muscle weakness/ apnoea 3. Urinary retention 4. Systemic administration > Cardiotoxicity |
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What are the 3 contraindications for epidurals?
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1. Sepsis
2. Coagulapathy 3. Skin infections. |
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Describe the onset and duration and uses for lignocaine.
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> Rapid onset
> Short duration Common uses: Topical (spray) local infiltration Nerve blocks IVRA Regional Epidurals |
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Describe the onset and duration and uses for bupivacaine.
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Delayed onset
Long duration Common uses Infiltration Intra-pleural/peritoneal Intra-articular Epidural Can be combined with lignociane |
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What are the uses of mepivacaine ?
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Most commonly used in horses for lameness exam
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