Lidocaine and bupivacaine are the drugs most commonly used in veterinary medicine.
Lidocaine patches: effective for pain management of wounds or incisions. Ethyl chloride spray: skin cooling may cause frostbite; used for skin biopsies. Eutectic mixture: lidocaine and prilocaine cream (EMLA cream); applied to shaved skin and covered for 10 minutes; used for minor procedures such as catheterization. Splash block: anesthetic sprays of lidocaine or direct application of bupivacaine in soaked sponges to wounds or open surgical sites. Bupivacaine is instilled through a chest tube during thoracic surgery. Mucous membrane application: conjunctiva, nose, mouth, larynx, or lining of urethra via topical sprays, drops, or ointments.
Epinephrine causes local vasoconstriction. Use lidocaine without epinephrine on incisions, ears, tails, or digits; in animals with cardiac disease; and for intravenous techniques. Local anesthetic injections may be painful in an awake patient so sodium bicarbonate can be added to decrease the pain.
Animals at risk for developing these problems are those under general anesthesia for >90 minutes, obese animals, those who received neuromuscular blocking agents, those with a preexisting lung disease, those with recent head trauma, those undergoing surgical procedures that involve the chest or diaphragm, horses, and adult ruminants.
A mask cannot be used for manual or mechanical ventilation because air being delivered will not meet the patient’s oxygen requirements and some of the air may enter the stomach, which increases the risk of vomiting.
The anesthetist must be careful not to overinflate the lungs.
When weaning a patient off a ventilator, the anesthetic is turned off and the patient breathes pure oxygen; the number of bmp provided by the ventilator gradually decreases until spontaneous breathing takes over again. Sometimes the patient must be coaxed into spontaneous breathing by pinching the toe pads, gently rubbing the thorax or abdomen (small animals), or twisting an ear (large animals).
Neuromuscular blocking agents inhibit normal reflexes. Animals cannot blink so ophthalmic lubricant must be used to prevent corneas from drying. Hypothermia can also be a problem because it slows metabolism and delays anesthesia recovery. Order of appearance of paralysis: first facial and neck paralysis, then tail, limb, and abdominal muscle paralysis, and finally intercostal muscles and diaphragm paralysis.
Adverse effects include bradycardia and increased bronchial and salivary secretions.
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