Opioid-Free Perioperative Analgesia
World Small Animal Veterinary Association Congress Proceedings, 2019
B. Wright

CEO, Mistral Vet, Fort Collins, CO, USA

Managing anesthesia without opioids provides a challenge, as opioids have long been the cornerstone of acute pain management. When use of opioids is not limited by supply issues, legal issues, or individual intolerance, they should still be considered for treating acute pain. Narcotics are highly effective at treating acute pain, have a high margin of safety, and they cause minimal cardiovascular changes. Despite being very effective at treating acute pain, narcotics also stimulate glial activation, and contribute to neuro-inflammation, tolerance and dependence. They amplify pain in the long run, while suppressing pain in the short term. Thus, even when used clinically, they should be used with other tools to decrease the neuro-amplification and immune modulation they cause (such as NSAIDs, local anesthetics, and other classes of pain medications).

Once accustomed to using multi-modal approaches to treat pain, including both pharmacologic and non-pharmacologic approaches, opioids become an option rather than a requirement in the perioperative period. A description of a typical pattern of case management, either without the use of opioid, or with limited use of opioids (including partial agonists or mixed agonist/antagonist drugs) follows.

Opioid-reducing pre-anesthetic handling and premedication: keep the patient as calm as possible. Opioids provide a reliable adjunct to sedating patients preoperatively, and without them some of the preanesthetic period requires increased consideration of hospital environment, such as separating cats and dogs, leaving pets with their sources of comfort until ready for procedures, use of calming sounds, smells, lighting and use of items such as thunder-shirts.

Oral sedation options for use prior to coming to the clinic in fearful patients:

  • Gabapentin: 10–20 mg/kg (or 100 mg/cat) can be very sedating until a patient becomes tolerant of this dose. Generally a very safe drug even at high doses, where PK is limited by absorption.
  • Melatonin: usually combined with gabapentin or a different oral medication. Dose is extrapolated to be ∼1 mg for creatures <10 lb, 3 mg from 10–40 lb, and 5 mg above 40 lb. Also a very safe supplement, even at high doses. There is a sustained release version available for dogs that are up at night with dementia.
  • Trazodone: usually about 10 mg/kg. This drug is a partial antagonist of serotonin in the brain, and also has some SSNRI effects. High doses, or combinations with other SSRIs or tramadol create the risk of serotonin syndrome, which can be severe.
  • Benzodiazepines: as listed above—oral versions include alprazolam and diazepam. This is not an option for cats, as repeated dosing of benzodiazepines in cats has been associated with hepatic injury. Unreliable behavioral effects also limit the usefulness of this class, although when paired with other drugs they may be efficacious.

Transmucosal drug options (stand-alone or in combination with oral medications):

  • Acepromazine, dexmedetomidine, ketamine and buprenorphine have shown some fair absorption characteristics in dogs.
  • Dexmedetomidine, ketamine, buprenorphine, methadone, and to a lesser degree, hydromorphone have shown some reasonable absorption characteristics in cats.

Parenteral drug options: Without opioids in the mix, the usual medications remain: acepromazine, alpha-2 agonists, benzodiazepines, and low doses of most of the induction drugs. Premedicate between 15 minutes and two hours prior to anticipated surgery time (short for dexmedetomidine, long for acepromazine/trazadone).

  • Gentlest (and also least effective): midazolam (0.1–0.4 mg/kg)
  • Moderate (both non-reversible): acepromazine (injection 0.01–0.05 mg/kg) or trazadone (2–6 mg/kg oral)
  • Most sedating (also analgesic and reversible): dexmedetomidine

Reserve anticholinergics for as-needed use except as noted under special conditions

Note: Very anxious animals should be given oral sedation before coming to the clinic. This can be drugs such as: gabapentin, trazadone, or acepromazine, and supplement melatonin

Catheters can be placed in non-premedicated dogs, but if you choose this route, you should use topical lidocaine to desensitize the skin, and reduce the likelihood of patients becoming fearful on this and future visits. Practice low-stress restraint techniques!

Adjust drug dosages as necessary for your patient—so much of this is experiential… wisdom of practice experience!

All drugs should be dosed to the patient’s ideal body weight (with a nod to body surface area—larger animals require relatively less drug per body weight than smaller animals). Likewise, older animals require relatively less drug than younger animals.

Disease and concurrent drug therapy may reduce drug requirements (or increase them!)

A smooth anesthetic period involves lack of awareness, analgesia, smooth induction, rapid recovery, maintenance of balanced autonomic reflexes, lack of movement. A smooth anesthetic period helps to beget a smooth recovery.

Without the use of opioids, an appropriate non-steroidal anti-inflammatory should be used early in the procedure, once a trend of adequate blood pressure has been established. Addition of local anesthetic should be used throughout the procedure. Wherever possible, a long-acting local anesthetic block should be performed before recovery. A diverse knowledge of local blocks and constant rate infusion techniques is important:

Local anesthetic educations videos are available at the WSAVA-GPC website: https://wsava.org/wp-content/uploads/2020/01/Local-anesthetic-educational-videos.pdf. (VIN editor: The original link was modified on 9-3-20.)

Infusions and local blocks to master:

  • All dental blocks
  • Testicular blocks (and line blocks) for neuters
  • Line blocks/pedicle blocks for spays
  • Coccygeal blocks for urethral obstruction/anal sacs
  • Epidurals or femoral/sciatic blocks for orthopedics (knees)
  • Declaw blocks
  • Ear canal blocks for TICA
  • CRIs or PIVA

Recovery: As mentioned pre-induction, a quiet, controlled recovery situation improves recoveries when less parenteral medication is on board to modify this period.

Pain should be well controlled with NSAIDs, locoregional techniques and application of analgesic micro-doses as needed (such as dexmedetomidine, ketamine).

All surgical wounds for which it is not contraindicated (skin flaps) should have ice placed for 15 minutes during the recovery period.

Other nonpharmacologic techniques for providing analgesia in the postoperative period include laser therapy (done before ice, or at least 2 hours after), acupuncture, pulsed electrical fields (PEMF loops, beds, jackets), and compression wraps where appropriate. A knowledge of these techniques becomes more important when perioperative opioid medications are limited or unavailable.


Speaker Information
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B. Wright
CEO, Mistral Vet
Fort Collins, CO, USA

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