Anesthetic and pain related mortality would appear to be an easily quantifiable statistic that could be used to measure the
outcome of the profession's current anesthetic practices. However, to rely solely on death rate as the measure of the quality
of anesthetic care provided is inadequate. The anesthetist's goal should be to minimize the risks to the patient's health
while reducing pain and stress.
Pain management in critical feline patients
All therapies have potential adverse effects. The key to clinical management of pain is to balance the potential risks to
the potential benefits of proposed treatments. Generally adverse effects of analgesic drugs can be categorized as minor and
major. Minor complications would include behavior changes (euphoria, dysphoria), vomiting and nausea, and other non-life threatening
reactions. Major complications are potentially life-threatening and must have more weight when considering the risk-benefit
of treatment. Major adverse effects would include severe cardiopulmonary depression, renal toxicity, and other severe physiological
changes. Most young healthy patients undergoing elective procedures will have the ability to compensate for major adverse
effects such as mild renal impairment of cardiopulmonary depression. However, critically ill animals and older patients may
lack the ability to compensate and would be more likely to have catastrophic adverse events associated with some of the commonly
recommended analgesic drugs.
Opioids are a diverse group of natural and synthetic drugs used extensively in the management of post-operative pain in man
and animals. Use in the surgical patient is becoming more widespread with the development of novel delivery systems such as
the transdermal patch. The traditional view that a given drug always behaves as either an agonist or an antagonist at a particular
receptor is a gross over-simplification, and recent studies have demonstrated that a number of variables appear to contribute
to the effectiveness of various opioids in the clinical setting. Dosage, species, and stimulus intensity, character and duration
can all alter the overall analgesic effect of an opioid. Opioids dampen peripheral and central afferent nociceptive transmission
and thus, are extremely effective in treating acute inflammatory pain associated with recent surgical trauma. They are not,
however, equally efficacious in managing all types of pain. Neuropathic pain syndromes are often characterized by a poor or
short-lived response to opioid therapy.
Local anesthetics act either by blocking sodium channels that prevent nerve impulse transmission and nociceptor excitation,
or by inhibiting modulatory nociceptive processing when administered centrally. In addition to their well-known topical, local
and regional effects, recent studies have documented the efficacy of low dose intravenous lidocaine infusions in the management
of hyperalgesia and neuropathic pain states induced by trauma or surgical procedure.
Non-steroidal anti-inflammatory drugs continue to be the mainstay of chronic pain management in both human and veterinary
patients. Recent development of more selective agents has generated considerable interest in their use for intra- and postoperative
pain as well. Traditionally, it has been believed that the analgesic effects of NSAIDs are related to their ability to inhibit
cyclooxygenase activity and prevent prostaglandin synthesis and peripheral nociceptor sensitization. However, there is considerable
evidence that at least some NSAIDs have a central spinal site of action, and may act synergistically with other analgesic
Alpha 2 adrenergic agonists bind to alpha 2 receptors located in the dorsal horn of the spinal cord, modulating the release
of substance P, calcitonin gene-related peptide and various other neurotransmitters involved in rostral transmission of nociceptive
information. Opioids likely exert their analgesic action through similar modulatory pathways and co-administration may result
in additive or synergistic drug interactions. In humans alpha 2 agonists are often used as "rescue therapy" when opioid tolerance
has developed. Use in surgical patients should be reserved for patients that have been stabilized with normal cardiopulmonary
A label indication for use in cats is a new feature of Dexdomitor when compared to Domitor. Although Domitor was used in cats
however this was off-label. The dose of dexmedetomidine is approximately 20-40 mcg/kg. The IM route of administration is convenient
when handling stressed patients, but intravenous administration will usually result in a faster onset of action. Dexmedetomidine
is suitable for various short-term feline procedures, specifically for procedures requiring sedation and/or analgesia but
not requiring intubation. The reversal agent atipamezole (Antisedan) is not approved for use in cats, however previous experience
with atipamezole reversal of Domitor in cats suggests it is effective.
Table 1. Sedative analgesic combinations for MINOR surgical and diagnostic procedures
§ Medetomidine doses are µg/kg (note in table).
‡ Induction of general anesthesia can be accomplished with minimal doses of Propofol, Thiopental, or Ketamine following initial
exam or diagnostic procedure.
* Anticholinergics are routinely co-administered with these regimens when continuing to general anesthesia (glycopyrrolate
0.01 mg/kg IM).
Note – alpha 2 agonists and acepromazine should be used with careful consideration of the cardiovascular effects commonly
associated with these drugs in critical patients.
Table 2. Regional anesthesia techniques
§ Inhalant anesthetic dose requirements are usually significantly reduced. Appropriate monitoring including end-tidal CO2,
pulse oximetry, and arterial blood pressure should be used to monitor respiratory and cardiovascular depression.