Book
Veterinary Anesthesia
- Local Anaesthesia by surface application (Topical)
1- Intended line infiltration
2- Field block
Onset Duration
Lidocaine 10-15 min 1-2 h
Mepivacaine 5-10 min 2-2.5 h
Bupivacaine 15-20 min 2.5-6 h
Ropivacaine 5-15 min 2.5-4 h
Local anesthetic – how do they work?
- Diffusion into the nerve
- Sodium channel blockers
- Lipid solubility – potency
- Concentration – onset time and block intensity
- Protein Binding – duration of action
Adverse effects
- Local site reaction
- Central nervous system
- Cardiovascular system
- Nerve injury
– Needle induced
– Drug induced
- Allergic reaction – methylparaben
- Methemoglobinemia
The principal advantages of field block are:
a- Absence of distortion of the anatomical features in the line of incision.
b- Ischemia of the tissues within the blocked area if a vasoconstrictor is incorporated in the solution of local analgesic.
c- Muscle relaxation.
d- Absence of interference with the healing of the wound which often claimed to be the chief objection to direct local infiltration analgesia.
Topical application
- Ophthalmic – proparacaine
- Laryngeal – lidocaine
- Topical – prilocaine + lidocaine
CNS Toxicity
- Large blood vessels (epidural)
- CNS toxicity symptoms usually occur before cardiovascular toxicity
- Seizure activity - diazepam + oxygen
Toxic dosage
- Lidocaine 10 to 20 mg/kg
- Bupivacaine 2 to 3 mg/kg
- USE ½ OR LESS THAN TOXIC DOSAGE -
- Cats are more sensitive than dogs
- Birds are more sensitive than cats
