Answering Your Questions: Practical analgesia in cats - Veterinary Medicine
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Answering Your Questions: Practical analgesia in cats
Cats will suffer in silence, so it's our job to either predict when they will face pain or recognize when they are feeling pain. Then we must choose suitable drugs from our armamentarium to prevent or relieve their discomfort.


VETERINARY MEDICINE


Q What do we need to know about the use of epidurals in cats (e.g. morphine, lidocaine, and morphine with xylazine hydrochloride)?

Epidurals can be safely performed in cats and offer an extremely effective analgesic alternative to systemic drugs. Cats differ anatomically from dogs in that the feline spinal cord does not end until the first or second sacral vertebral body. So when performing a lumbosacral epidural, you have a greater chance of advancing the needle into the subarachnoid space. If this occurs and cerebrospinal fluid wells up into the hub of the epidural needle, administer half the calculated dose of morphine (i.e. 0.05 mg/kg vs. 0.1 mg/kg).

In my practice, preservative-free morphine is the drug we most commonly use as an epidural analgesic in cats. The recommended epidural dose is 0.1 mg/kg at a total administered volume of 0.2 ml/kg injected over 60 seconds. The expected time to onset of effect is 45 to 60 minutes, with an expected duration of about 12 hours. Morphine injected into the lumbosacral epidural space provides good analgesia for hindlimb, perineal, and abdominal surgeries and may provide some analgesic benefit for thoracotomies.

Venous absorption of lidocaine from the epidural space occurs quickly in people (i.e. within two minutes after injection), and epidurally administered lidocaine may be associated with toxic venous concentrations in cats.9 Although epidural lidocaine administration in cats has been recommended in the literature,10 exercise caution when deciding on the dose and total number of injections to administer.

The use of epidural xylazine in cats has not been reported, although the use of epidural medetomidine (also an alpha2 agonist) in cats caused marked systemic cardiorespiratory depression and sedation.11,12 Xylazine would probably have similar effects if given epidurally to cats.

Q Is concomitant use of epidurals and inhalant anesthesia safe in cats?

Yes. In fact, epidural morphine has an inhalant-sparing effect because of the marked regional analgesia it provides. Therefore, epidural morphine not only provides long and effective caudal analgesia, it reduces the amount of inhalant required to maintain a surgical plane of anesthesia by about 30% to 50%. So the cardiorespiratory depressant effects of the inhalants are reduced, resulting in safer anesthesia overall. Of course, no anesthetic is truly safe without close and expert monitoring.

Q Can you provide a few tips for relief practitioners who may be working in practices that use few or no analgesics in cats?

Opioids are the safest and most effective analgesic agents available in modern medicine. Unfortunately, many practitioners fear the manageable side effects of opioids (e.g. bradycardia, mild respiratory depression). So first I would try to persuade these practitioners that increasing the availability of different opioid options is in their patients' best interest. With a little enlightenment, the practice owner might take your advice and start providing more opioid options.

If you just don't have access to opioids or some of the newer nonsteroidal anti-inflammatory drugs (NSAIDs), consider using local anesthetic blocks, alpha2 agonists, and ketamine hydrochloride. If appropriate for the surgical procedure, a local anesthetic block with bupivacaine (infiltrated subcutaneously at a total dose of less than 2 mg/kg) can block pain for up to 12 hours. Keep in mind, however, that local anesthetics applied to a vascular area (e.g. the peritoneal cavity or pleural space as a splash block) will be systemically absorbed almost as quickly as an intravenous injection.13 Examples of when a local anesthetic block might be appropriate for a cat include a ring block for wound management or a declaw procedure or a line block for abdominal surgery.


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Source: VETERINARY MEDICINE,
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