Due to their size and anatomy, cattle are not very good candidates for general anaesthesia meaning that many procedures performed use local techniques. Most surgeries performed on these patients can be done standing with a small amount of sedation and regional and local nerve blocks. Local techniques are also used in cattle for procedures such as castration and dehorning.
General anaesthesia is rarely carried out in these species. As previously mentioned, cattle are not ideal candidates for general anaesthesia for a number of different reasons. Aspiration of ruminal contents can frequently occur due to regurgitation. Eructation prevents the development of bloat in cattle when they are fully concious. However, when in lateral or dorsal recumbancy the ability to eructate is reduced or completely absent depending on the amount of ingesta present. If bloat does develop, combined with the weight of the abdominal viscera, breathing may be impeded further due to compression against the diaphragm. These risks can be minimised by:-
- Starving the patient for 24-48 hours before the procedure.
- Remove water 8-12hours before the procedure.
- In lateral recumbancy, make sure that the head is elevated such that it is sloping down so that any regurgitant and saliva can flow out of the mouth.
- Upon recovery, leave the ET tube cuff inflated until the patient is in sternal recumbancy, swallowing and can pull its tongue back into its mouth.
Local techniques are most commonly used in these species in combination with sedation.
Local Nerve Blocks
Auriculopalpebral Nerve Block
This block can be used to prevent the eyelids moving during clinical examination or surgery. It blocks the orbicularis oculi muscle. The nerve course runs from the base of the ear past the eye ventrally along the facial crest.
Cornual Nerve Block
This block is used for dehorning. The nerve can be found at the orbit running behind the lateral ridge of the frontal bone. The nerve supplies the horn coruim and the skin around the base of the horn.
Peribulbar and Retrobulbar Block
This block involves the use of a curved needle inserted laterally to the lateral canthus such that it curves around the back of the eye. As with any nerve block, care should be taken to make sure that the local is not injected into a blood vessel at this point. this block can be used to provide local anaesthesia for surgeries such as enucleation.
Inverted L Block
This block involves infiltration of the skin, subcutaneous and deeper tissues with local anaesthetic in an inverted L shape. It is commonly used for standing surgeries such as caesarean sections and displaced abomasum corrections where a flank incision is needed.
Paravertebral Nerve Block
Paravertebral blocks involve perineural injection of the spinal nerves at the point if the intervertebral foramen. It is also used to provide analgesia for procedures involving flank incisions but its advantage over the inverted L block is that is also acts upon the peritoneum and the abdominal wall muscles are relaxed.
Caudal epidural blocks involve injecting between the first and second coccygeal vertebrae. Epidural blocks can also be performed in the lumbosacral region.
Intravenous Regional Blocks
This technique can be used for procedures such as digit amputation. A tourniquet is placed around the limb, and local is injected into a vein such that it can flow around the region but not systemically as blood flow of the foot is occluded. Once the procedure has finished, the tourniquet should be removed slowly to prevent systemic effects of the agent.