Pain Case of the Month: A Routine Procedure Turns Out to Be Painful to Manage

In overall healthy dogs and cats, acute pain management, especially for a routine elective procedure such as an ovariohysterectomy (OHE), should closely follow the rules of the acronym MPM: (1) mechanism base (that is, pain pathways) of pain management, (2) preemptive analgesia, and (3) multimodal analgesia approach. At the onset, this case had the presentation of a routine OHE in a healthy dog, but the dog had a unique reaction that required an adjustment in pain management.

The patient was a seven-month-old, intact female Siberian husky, presented for OHE with recent estrus.

by Jeff Ko, DVM, DACVAA

Introduction

In overall healthy dogs and cats, acute pain management, especially for a routine elective procedure such as an ovariohysterectomy (OHE), should closely follow the rules of the acronym MPM: (1) mechanism base (that is, pain pathways) of pain management, (2) pre-emptive analgesia, and (3) multimodal analgesia approach. At the onset, this case had the presentation of a routine OHE in a healthy dog, but the dog had a unique reaction that required an adjustment in pain management.

Signalment and History

The patient was a seven-month-old, intact female Siberian husky, presented for OHE with recent estrus. Bodyweight was 20 kg. Physical exam showed the dog was agitated and very nervous but otherwise healthy. Packed cell volume, total protein, and blood urine nitrogen and blood glucose were all within normal ranges.

Premedication consisted of maropitant 1 mg/kg, subcutaneously (SC), acepromazine 0.02 mg/kg, intramuscularly (IM), and buprenorphine 20 mcg/kg, IM. The sedation was poor after premedication and the dog remained nervous and agitated.

Anesthesia was induced 15 minutes after premedication using propofol at 5 mg/kg, IV, to effect for endotracheal intubation and then maintained using isoflurane in 100% oxygen in a semiclosed circuit. The isoflurane concentration was adjusted to effect to maintain a surgical plane of anesthesia.

Balanced electrolyte solution was administered at 5 mL per kg per hour, IV, during the surgery.

The surgery was a three-clamp technique for the OHE. Because the patient was a relatively large dog, the surgical incision to the abdominal wall was a bit longer than usual, and because of the recent estrus, the tissue handling to the reproductive tract was a bit rougher and the bleeding was a little more than usual. The dog required a relatively high concentration of isoflurane (2.5%–3%) during the surgery, especially when removing ovarian pedicles and during ligation of the uterine stump.

Upon extubation, the dog woke up screaming and struggled vigorously. A microdose of dexmedetomidine at 1 mcg/kg was administered IV as well as carprofen at 2.2 mg/kg, SC. The dog gradually settled and became quiet for approximately five minutes before starting to vocalize again.

Diagnosis and Treatment

The pain was assessed by using a modification of CMPS (modified short-version Glasgow Composite Measure Pain Scale, which includes observing the dog’s behavior from a distance, interacting with the dog, and palpitating the wound). The CMPS revealed that the dog needed a rescue, especially when the palpation of the incisional site and abdomen showed that the dog was in pain. A rescue dose of buprenorphine at 40 mcg/kg, IV, was given. The dog was then reassessed for any further discomfort. As the abdominal incisional site was relatively tense and painful upon palpation, a lidocaine patch was placed on the incisional site for pain relief. The owner agreed to pick up the dog later in the day so that the dog could be observed and assessed for pain in her home environment.

The owner was called daily, and they reported that the dog appeared to be comfortable and had started eating and drinking that night.

Before the dog was sent home, she received an additional dose of buprenorphine at 40 mcg/kg, SC. Carprofen at 4.4 mg/kg, PO, was prescribed every 24 hours for three days. The owner was instructed to leave the lidocaine patch in place for the next three days. The owner was called daily, and they reported that the dog appeared to be comfortable and had started eating and drinking that night. These additional measures and pain management adjustments alleviated the dog’s pain from the OHE procedure.

Discussion and Conclusions

This “routine” OHE case turned out to be not so routine in terms of pain management because of several factors: The dog was anxious and had a higher sensitivity to the pain. This was revealed when the dog did not sedate well and required a higher-than-usual concentration of isoflurane for maintenance. This information escaped the practitioner’s awareness and did not prompt the practitioner to more aggressively manage the pain of this dog perioperatively. Retrospectively, a previsit hospital oral gabapentin (10 mg/kg), trazodone (10 mg/kg), or a combination of these two drugs might have benefited this dog.
When it comes down to pain management for a surgical procedure, in addition to the aforementioned acronym of MPM, the mechanism base of pain management, pre-emptive analgesia, and multimodal analgesia approach, an acronym of “triple As” also should be considered (Gurney 2012; Clark 2014). The “triple As” are (1) anticipate the degree of surgical pain before the painful stimulation, (2) assess the efficacy of the analgesic drug given and the degree of pain perioperatively, and (3) alleviate any further pain through a different approach (Gurney 2012).

In this case, the initial pain management was to use a “regular” dose of buprenorphine and a postoperative nonsteroidal anti-inflammatory drug (NSAID; carprofen) to handle the dog’s pain and inflammation related to the OHE. With the pain pathways of the pain management approach, we know that buprenorphine worked on the central nervous system and the NSAID worked on the surgical site. However, the carprofen was administered after the surgery. Therefore, only two (opioid and NSAID) out of five pharmacologic classes of drugs (the remaining three being local anesthetics, dissociatives, and alpha-2 agonists) were given to this dog, which played a role in the rough, painful recovery.

It is important to realize that typical features of pain can be quite different between patients and also can fluctuate in the same patient at different times.

In addition, the so-called regular dose of buprenorphine also presented a problem in this case. Buprenorphine is suitable for treating mild to moderate pain. Buprenorphine is also unique because at low doses (such as the 20 mcg/kg used in this case), it has a slow onset (30–45 minutes) of action after administration (Gurney 2012). In addition, there is a high variation in analgesia and analgesic duration due to low doses of buprenorphine in dogs (Abbo, et al. 2008; Ko, et al. 2011), and likely so in cats. In order for analgesia to be pre-emptive, adequate analgesics must be given (Gurney 2012). The inadequate dose of buprenorphine, together with a slow onset of its analgesic action, might not establish the pre-emptive part of the analgesia before surgical stimulation, which in this case led to the dog’s painful response intraoperatively. The dog’s high isoflurane maintenance requirement might be an indicator for such failure. Our clinical experience and studies (Abbo, et al. 2008; Ko, et al. 2011) have shown that initial high doses of buprenorphine are more likely to overcome the slow onset of action and generate a more uniform response among all individuals with a long duration of action. A dose of 80–120 mcg/kg (of any route—SC, IM, IV, or OTM) of buprenorphine is likely to minimize the dog’s pain and individual variations in response to this drug. This “high” dose of buprenorphine is likely to provide an analgesia for up to 24 hours (Abbo, et al. 2008; Ko, et al. 2011).

It is important to realize that typical features of pain can be quite different between patients and also can fluctuate in the same patient at different times. Therefore, it is risky to rely on a single analgesic-class drug to effectively and reliably treat all pain. To follow the “triple As” principles of pain management, this dog fell outside the expected degree of pain. When the dog had a rough recovery, the practitioner did not know whether it was dysphoria or pain that induced this dog’s vocalization and struggling. A small dose of dexmedetomidine was given IV to alleviate the dog’s rough recovery and ruled out dysphoria as the cause because the dog resumed vocalization within a short time, indicating pain as the cause of vocalization. Three classes of analgesics had been used to alleviate this dog’s pain by this time: a rescue dose of buprenorphine, an NSAID, and a local anesthetic (lidocaine patch) (Ko, et al. 2007). These three drugs are longer lasting and in this case were suitable for sending the dog home without continued therapy in the hospital.

As an alternative to these three drugs, the practitioner could have used dexmedetomidine to sedate the dog and performed abdominal line blocks with liposomal bupivacaine and injectable NSAIDs, as well as oral NSAIDs for take-home medication. Certainly, the dog could have been rescued with a more potent opioid such as hydromorphone. However, hydromorphone is relatively short lived, and any patient would be required to stay in the hospital for additional dosing. Another way to provide a longer duration of analgesia would be to perform an epidural and administer preservative-free morphine, which may last approximately eight hours.

In short, this is a case in which a routine elective procedure was performed on a patient whose level of pain was higher than anticipated. The same scenario could happen during other, more painful procedures, such as amputation or any other abdominal surgeries. The key points that I like to emphasize here are the flexibility of using adequate dosing and enough variations in multimodal pain pathway analgesics for pain management. Pre-emptive action should be taken early enough to allow analgesic drugs to take action. We should not always assume that animals will have a routine response to pain. Anticipating and reassessing the dog’s pain is always necessary so that modifications to the pain management protocol can be made. 

Discussion by Mike Petty, DVM, CCRT, CVPP, DAAPM

Buprenorphine is a common opioid that we use in our canine patients, yet there is no dog-approved product out on the market. Most of our dosing is extrapolated from humans and other animals or based on our clinical experience. In this pain case, higher doses of buprenorphine are explored: As an agonist/antagonist opioid, buprenorphine has a ceiling effect, which should give it a better safety margin than other opioids.

Mike Petty, DVM, CCRT, CVPP, DAAPM, is in private practice in Canton, Michigan. He is a frequent national and international lecturer on topics related to pain management. Petty offers commentary on each Pain Case of the Month.

Sources

Abbo, L. A., J. C. Ko, L. K. Maxwell, R. E. Galinsky, D. E. Moody, B. M. Johnson, and W. B. Fang. 2008. “Pharmacokinetics of Buprenorphine Following Intravenous and Oral Transmucosal Administration in Dogs.” Veterinary Therapeutics 9, no. 2 (Summer): 83–93.

Clark, L. 2014. “Pre-Emptive or Preventive Analgesia—Lessons from the Human Literature?” Veterinary Anaesthesia and Analgesia 41, no. 2 (March): 109–12.

Gurney, M. A. 2012. “Pharmacological Options for Intraoperative and Early Postoperative Analgesia: An Update.” Journal of Small Animal Practice 53, no. 7 (July): 377–86.

Ko, J. C., L. J. Freeman, M. Barletta, A. B. Weil, M. E. Payton, B. M. Johnson, and T. Inoue. 2011. “Efficacy of Oral Transmucosal and Intravenous Administration of Buprenorphine Before Surgery for Postoperative Analgesia in Dogs Undergoing Ovariohysterectomy.” Journal of the American Veterinary Medical Association 238, no. 3 (February): 318–28.

Ko, J., A. Weil, L. Maxwell, T. Kitao, and T. Haydon. 2007. “Plasma Concentrations of Lidocaine in Dogs Following Lidocaine Patch Application.” Journal of the American Animal Hospital Association 43, no. 5 (September–October): 280–83.

Jeff Ko, DVM, DACVAA, is a professor of anesthesiology at the Department of Veterinary Clinical Sciences at Purdue University. He has published more than 100 refereed articles. Recently, he published the second edition of A Color Handbook of Small Animal Anesthesia and Pain Management.

 

Photo credit: ©iStock.com/Fil_Studio

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