Case based acute/perioperative pain management (Proceedings)

There are many factors affecting patient outcome after a surgical procedure. This list includes postoperative pain which is, perhaps, the best example of predicable acute pain. Inadequate attention to pain management generally increases both patient morbidity and mortality. Inadequate pain management also increases the requirements for induction and maintenance anesthetics, predictably increases the hypotensive and respiratory depressant effects of these potent drugs. In addition, health care professionals have a moral and ethical obligation to provide the most compassionate patient care possible. Effective pain management is undeniably a basic patient right.

Studies have shown that the intensity of the perioperative pain directly affects the patient risk of developing chronic postoperative pain. To provide the best control over pain we need to address it from the earliest possible point in time which should be preemptively whenever possible. Delivering effective analgesics prior to the painful event is the first step in patient pain control. Presurgical medications should be strategically selected to target multiple points along the pain pathways providing multimodal analgesic benefit. Continuing pain management into the postop period maximizes patient comfort and patient return to normal function.

Preanesthetic Medication: Mu opioids remain the most attractive preanesthetic foundation. This author favors the inclusion of midazolam in preanesthetic combinations to enhance both sedative and analgesic effects. Mu opioids and midazolam, in combination, form a particularly attractive pre preanesthetic pairing for geriatric and less healthy patients. Healthy patients will benefit from the addition of a third pre preanesthetic element; either acepromazine or (dex)medetomidine. Including this third element gains additional stress relief, a key component in pain and morbidity reduction. As a side note, this author does not use butorphanol for any procedures of a painful nature. In addition, the calcium channel blocker, gabapentin 5 mg/kg PO, may be administered 2 hours preoperatively for additional patient analgesic benefit.

Presurgical Analgesia: There few procedures that do not lend themselves to the use of local anesthetics either as local/regional blocks or intravenous infusions. The most common local block locations in practice include dental/facial, declaw ring blocks, incisional line blocks, intra-articular, and intratesticular blocks. Constant rate IV Infusions of pure mu agonist opioids, lidocaine, and ketamine are excellent titratable analgesic combinations targeting the opioid receptors, sodium ion channels, and the NMDA/glutamate receptors respectively. Analgesic CRIs are well suited to procedures of any type supporting both the balanced multimodal analgesic principle and the balanced anesthesia principle. Epidural applications of analgesics and local anesthetics are often thought to be beyond the reach of general veterinary practice but that does not need to be so. The author knows general practitioners in rural private settings routinely performing epidurals on spay and neuter surgery patients. NSAID administration preoperatively can be beneficial and is recommended by the author if the newer generation COX-2 selective drugs are used and if the practice understands how to appropriately monitor blood pressures and is fully capable of effectively supporting blood pressures.

Intraoperative Analgesia: While the continuation of an analgesic CRI is an ideal method to manage intraop analgesia for any surgical patient there are other worthy considerations. During a more painful surgical element, IV bolus mu agonist opioids are excellent tools to enhance analgesia and minimize anesthetic needs. Fentanyl, methadone, oxymorphone, and hydromorphone are all well suited to this end. Soaker catheters can be placed intraoperatively to facilitate continued infusions of local anesthetic at particularly painful regions.

Immediate Postoperative Analgesia: CRIs are often extended into the postoperative period and may be maintained for days in certain situations. Dose rates must generally be reduced as CRI duration is extended over lengthier periods. Soaker catheter local anesthetic infusions may be in place and may be continued for days if soaker catheter integrity is maintained. Cryo Cuff chiller systems are outstanding devices for managing pain and edema at sites located on extremities.

NSAIDs should be considered for all NSAID tolerant non-GI surgery patients if NSAIDs were not already included in the preoperative medications.

Buprenorphine is an attractive transitional opioid helping to diminish the sedative and dysphoric aspects of the pure mu agonists fentanyl, methadone, oxymorphone, and hydromorphone. Dosed at 0.020 to 0.060 mg/kg, the analgesia provided by buprenorphine appears substantial and long lived, possibly lasting up to 12 hours at higher doses. Buprenorphine is particularly attractive for postoperative pain of a mild to moderate nature.

The fentanyl patch is attractive as a fire-and-forget analgesic but it has two main drawbacks. Most importantly, studies have shown that a significant percentage of patients may fail to achieve any significant plasma levels of the drug. Secondly, there is a significant delay between application and significant analgesic influence, especially for dogs (up to 24 hours).

To Go Home Analgesics: Oral medications can be initiated postoperative once the patient is tolerant of PO drug administration.

NSAIDs are very attractive in the postoperative phase with few exceptions: NSAID intolerant patients and GI surgical patients. NSAIDs use should be moderately short term for postop fracture patients. Extended NSAID use in cats is subject to much debate, appearing somewhat perilous at this time.

Tramadol is an excellent postoperative analgesic best suited to dogs. It possesses weak mu agonist properties as well as some monoamine reuptake inhibitory analgesic qualities. Its profile suggests the 5 mg/kg QID dosing is the preferred schedule for use in dogs. Buprenorphine derlivered transmucosally is a very attractive home administered opioid. The TM route has been shown to be as effective as IV delivery in cats (there is developing support for an attractive TM bioavailability in dogs). Buprenorphine has little taste making pets reasonably tolerant of TM administration.

Amantadine is an oral NMDA antagonist. It should be included in the postoperative period for dogs sustaining moderate to severe pain related injuries. Amantadine is typically dosed at 3 to 5 mg/kg PO once daily. Unfortunately, its bitter taste makes it poorly suited to cat use.

Gabapentin 5 mg/kg PO BID to TID is very attractive when managing perioperative pain for both dogs and cats. Unlike tramadol and amantadine, gabapentin is generally well accepted and well tolerated by cats. Gabapentin and be teamed with TM buprenorphine and short term NSAID use to cover many postoperative pain scenarios.

The author does not recommend the PO use of buprenorphine or butorphanol in flavored liquids or any other oral vehicle. While butorphanol's weak analgesic properties make it questionable for any significantly painful event, the enterohepatic first pass effect effectively renders either opioid useless, eliminating the vast majority of drug before reaching systemic circulation.

While the buprenorphine patch is not yet a proven analgesic method for pet pain management the lidocaine patch has many useful applications. They can be used over an area of injury or used adjacent to the incision after a surgical procedure. Unlike the fentanyl patch, the lidocaine patch can, and should, be cut to fit the patient's need. Caution must be exercised to prevent patient ingestion of any portion of the patch as lidocaine toxicity would be a likely consequence.

Our patients are naturally inclined to hide their signs of pain. This is especially true in an unfamiliar setting surrounded by unfamiliar people and animals. Often an animal in pain appears reasonably comfortable to the hospital staff. As a result, pain medications may be withheld. The author suggests a blanket pain strategy be adopted proportional to the expected level of pain for that given injury or surgery. Staff training should include guidelines to help detect those patients that have unmet analgesic needs. The AAHA/AAFP pain management guidelines are an excellent reference for staff pain awareness training.

The pet's family needs to be included in the pain management team. The practice should provide coaching advice and handout material detailing the signs that they should be monitoring for at home; signs that would indicate inadequate patient analgesia.

In addition, postoperative physical rehabilitation therapy (PRT) is an extremely important aspect of patient management. This discipline focuses on maximizing patient return to function, especially after spinal and orthopedic injury or surgery. PRT helps to minimize functional decline including muscle atrophy, joint restrictions, loss of positional awareness, and decreased muscle flexibility. PRT is capable of contributing significant pain relieving benefits though a variety of modalities.

This session will review analgesic management options for routine surgeries as well as analgesic options for common advanced surgeries as time allows.