May 29, 2019
Pre-surgical pain management begins not in the operating room, but in the home.
Providing appropriate pain medications and keeping animals warm and comfortable during and after surgery are important, but ensuring they come into the clinic relaxed is a new and critical component of pre-surgical prep. Even for minor procedures, it’s vital to survival and normal healing and recovery.
“That’s actually a new concept, and I think that’s why maybe not everyone has adopted it yet,” says Tamara Grubb, DVM, PhD, DACVAA, at Washington State University College of Veterinary Medicine. “We just didn’t realize the impact of animals coming in stressed or in pain.”
Uncontrolled pain in animals results in a number of physiological effects, including increased myocardial work, hypoventilation, decreased gastrointestinal motility, release of cortisol and catecholamines, hyperglycemia, muscle protein catabolism, effects on water and electrolyte balance, and delayed wound healing.
Those are among the reasons veterinarians should identify and manage pre-existing pain from osteoarthritis or other conditions before pets undergo surgery or dentistry, Dr. Grubb says. Taking them into surgery without appropriate pain management can exacerbate the condition, especially if animals are manipulated during the procedure.
Among the elements of comfort, stress reduction, and pain relief are emotional support, control of nausea and vomiting, low-stress handling by veterinarians and nurses, and a soothing physical environment.
Introducing Fear Free or American Association of Feline Practitioners (AAFP) Feline Friendly practices into hospital management and design adds to pet comfort pre- and post-operatively, according to Michael C. Petty, DVM, in the proceedings for his 2018 VMX lecture, “Care of the surgical patient: At home, in hospital and home again.” Those measures can include rubber flooring for better footing, especially for older animals or those with degenerative joint disease or neurologic conditions; playing calming music in reception areas and wards; placing cats in cages with separate litterbox and sleeping areas; and warm, padded exam and surgical tables.
Getting pets into the clinic in a less stressful way can save lives, especially when it comes to cats.
“Every study that has been published has shown cats have a higher risk of death related to anesthesia than dogs, and I think a lot of that stems from the stress level they come in at,” says Sheilah Robertson, MRCVS, DACVA, senior medical director for Lap of Love Veterinary Hospice.
Having owners administer gabapentin to cats the night before or the morning of the procedure can help them remain calm and ensure more accurate physiological data, such as heart rate and blood glucose levels before administering anesthesia. A study of 20 healthy cats published in the Nov. 15, 2017, issue of Journal of the American Veterinary Medical Association found that orally administering a 100-mg gabapentin capsule to cats 90 minutes before transport to the veterinary clinic resulted in a significant decrease of stress-related behaviours during transport and examination. The cats also were less aggressive and more compliant.
For dogs, administering trazodone prior to arrival can have a similar effect. Animals who experience carsickness arrive stressed from salivating, vomiting, or defecating during the car ride. Prescribing maropitant to be given before they travel can help ensure they arrive in better physical and emotional condition.
“We want owners to understand that if their pet has high anxiety or stress, the sensation of pain can be exacerbated, and if we have those drugs on board before there are any pain impulses, they’re much more effective,” Grubb says.
And individual animals have specific needs. Some respond very differently to pain than others do. Breeds such as beagles and Shetland sheepdogs, as well as Nordic dogs, can have a reputation as ‘crybabies,’ reacting excessively or vocally to what seem like minor procedures.
“That vocalization may mean nothing, and it may mean pain,” Grubb says. “I really do think at some point we will recognize certain breeds do have a genetic predisposition for a heightened pain response, like redheads in human medicine. We know there’s a genetic reason they may be more sensitive to pain or that the pain drugs may not work as well. I think it’s in our future to know which breeds experience pain in a more intense way.”
New drugs, animal reactions to drugs, the opioid shortage, and controlling nausea and vomiting all affect how pets are anesthetized. New takes on old protocols make a difference, too.
Cats, of course, are poster children for special-needs patients. They respond to opioids and NSAIDs differently than dogs and need lower dosages. In the case of sedatives, just the opposite is true. Cats are more resistant to sedatives, Grubb says, and require a higher dose for those drugs to be effective.
Cats have some new options coming up. A bupivacaine liposome injectable solution, currently available only for dogs, offers three days of analgesia from a single injection. A favourable report on the drug from the U.S. Food and Drug Administration (FDA) means it is likely it will be approved for use in cats soon south of the border, says Dr. Robertson, who describes it as “a huge breakthrough in local anesthesia.”
Some dogs also may respond differently to certain drugs or doses of drugs. In particular, Nordic breeds such as Siberian huskies or Alaskan malamutes may experience these effects, becoming dysphoric under higher doses of opioids.
“This does not mean opioids should be withheld,” says Jordyn Marie Boesch, DVM, DACVAA, who lectures on anesthesiology and pain medicine at Cornell University’s College of Veterinary Medicine. “The lowest effective dose should be used instead or the need for opioids reduced with another technique, such as locoregional anesthesia. If I’m concerned about dysphoria upon an animal’s recovery, I will often lightly sedate or tranquilize the pet prior to recovery from anesthesia.”
Local anesthetic blocks aren’t new, but their importance and utility are being newly scrutinized, in part due to limitations on and shortages of opioids that can be used in animals. Local blocks can help to fill that void, especially immediately after surgery, Grubb says. An old drug, ketamine, traditionally has been used as an anesthetic, but is now used in pain management. A constant rate infusion of ketamine decreases the overall sensation of pain and allows analgesic drugs to work better.
“We use it all the time for acute pain, surgery, and trauma, and are starting to use it in chronic pain to break the pain cycle in patients that are really painful,” Grubb says. “That allows the true analgesic drugs to work better.”
Pre-emptive analgesia depends on the patient and procedure, as well as other factors. Options include opioids and/or dexmedetomidine in the pre-medication protocol; a locoregional anesthetic technique such as infiltration, an epidural, or a peripheral nerve block; or a ketamine CRI, Dr. Boesch says.
“The use of multiple drugs in combination, what is called multi-modal analgesia, should be used whenever possible, as it typically results in better analgesia,” she said. “It can also reduce side effects because lower doses of each drug can be used.”
Preventing or reducing post-operative nausea and vomiting (PONV) is also an important part of limiting post-surgical pain and discomfort. Medicating animals with maropitant pre-operatively may help to prevent PONV, limiting adverse effects, such as dehydration, electrolyte imbalances, and aspiration pneumonia; decreasing agitation during the recovery phase; and improving post-surgical appetite.
“There’s a good study in dogs that showed they were quicker to return to normal feeding post-operatively if they had maropitant preoperatively,” Grubb says. “As normal return to feeding is part of the healing process, that’s important to any patient’s care.”
Use of maropitant, an antiemetic, has another beneficial side effect: the ability to use less gas anesthetic. Maropitant may have an analgesic effect, as well. The evidence for that is not yet definitive, but clinical experience suggests the drug reduces visceral pain in cats and dogs.
“I encourage clinicians here to routinely administer maropitant to both dogs and cats orally the night before anesthesia,” Boesch says. “Alternatively, clinicians can send maropitant home with owners for administration with the pet’s dinner the night before if they are being dropped off for anesthesia in the morning. A single dose prevents vomiting for 24 hours.”
Another good option is ondansetron. This drug can be used post-operatively for pets that still appear to be nauseous. Anesthetic drugs, such as acepromazine and propofol, also have antiemetic effects.
Use of ‘balanced anesthesia’—a combination of drugs to provide discrete elements of anesthesia, such as analgesia and muscle relaxation—allows for lower dosages of the primary general anesthetic and limits the potential for harmful side effects, including depressed respiration and low blood pressure. With new drugs and computerized infusion pumps, techniques now can involve a single drug or combination of drugs administered by injectable infusion. Both partial and total intravenous anesthesia permit stable, consistent anesthesia; better hemodynamic support; smoother recovery; and analgesia as well as sedation.
Nonetheless, some pets are still ‘masked under’ to induce unconsciousness, despite scientific data showing that restraining and masking a dog down increases the animal’s risk of anesthetic death and is likely distressing for it. Similar, mortality data does not exist for cats, but it is still strongly advised against.
“When cats struggle to get away, it’s not safe for personnel and it’s very stressful for the animal,” Robertson says. “It’s bad for the heart. It can cause arrhythmias. It’s a massive dose they have to give them to get them asleep, so it’s not surprising to me they end up with low blood pressure, difficulty breathing, and other complications.”
Humans are at risk, too, with this procedure. They are not only dealing with a struggling frightened animal with teeth and claws, but also are exposed to inhalant gas. Long-term chronic exposure to inhalant gas may cause health problems.
“The safest way to induce sleep is to give a pre-medication so they are calmer; then give an injectable drug followed by the inhalant,” Grubb said.
A number of non-pharmaceutical options can help decrease pet pain after surgery. The simplest is icing incisions to reduce inflammation and provide analgesia. It can be done while waiting for pets to regain consciousness as long as they are otherwise kept warm. Icing is easy for owners to continue at home as well. Suggest using a cold pack wrapped with a washcloth to provide insulation between the incision and the pack.
Physical rehab techniques are an important component of analgesic plans. Acupuncture, light massage, stretching, and joint mobility techniques can be good additions to post-operative care. Pets in recovery or at home can benefit from deep, soft bedding if they have fractures or contusions, or soft food if they have had teeth extracted.
“The bottom line is many options are available, and veterinarians are strongly encouraged to utilize as many of them as possible,” Boesch says
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