Letters: Was butorphanol adequate?

We read with interest the "Clinical Exposures" case report "A peritoneopericardial diaphragmatic hernia in a cat" in the April 2004 issue. While the diagnostic and surgical management of this case was excellent, the analgesic support was inadequate.

According to the authors, the only analgesic this cat received was butorphanol. It is not specified how far in advance of surgery the cat received the butorphanol, but we are concerned that it might have been wearing off by the time of the procedure. Current analgesic references suggest that butorphanol's analgesic duration of effect is, at most, one to three hours. The cat in this report received only one postoperative injection of butorphanol, which allowed a total of two to six hours of perioperative analgesia. The cat was discharged with instructions to receive oral butorphanol twice a day. The first-pass effect and duration of action render this an inappropriate and ineffective analgesic in this case.1

Certainly, butorphanol is good for mild to moderate visceral pain in cats and has low cardiac and respiratory depressive effects, but adding a pure mu agonist such as hydromorphone, oxymorphone, morphine, or fentanyl, or even a partial mu agonist such as buprenorphine, would have been much more appropriate and effective. Additional considerations could have included adding an NMDA antagonist, such as a continuous-rate infusion of ketamine, during the perioperative period and an NSAID such as meloxicam for postoperative pain relief. The multimodal approach to pain control is important for us to consider.

Our feline patients are good at hiding pain, having evolved to do so in order to avoid predation. It behooves us as our patients' advocates to use appropriate analgesia based on current knowledge of drugs and the pain process rather than the habits of what has been done in the past. Mere survival is no longer an adequate measure of anesthetic success. Rather, minimizing morbidity needs to be considered.

We were also taken aback by the lack of mention of supportive care or monitoring of this cat. We assume these were done, but it would be useful to include these details.

REFERENCE

1. Lascelles, B.D.X.; Robertson, S.A.: Use of thermal threshold response to evaluate the antinociceptive effects of butorphanol in cats. AJVR 65 (8):1085-1089; 2004.

SUGGESTED READING

1. Gaynor, J.S.; Muir, W.: Handbook of Veterinary Pain Management. Mosby, St. Louis, Mo., 2002.

2. Tranquilli, W.J. et al.: Pain Management for the Small Animal Practitioner. Teton NewMedia, Jackson, Wyo., 2000.

3. Mathews, K.A.: Pain assessment and general approach to management. Vet. Clin. North Am. (Small Anim. Pract.) 30(4):729-755; 2000.

4. Lamont, L.A.: Feline perioperative pain management. Vet. Clin. North Am. (Small Anim. Pract.) 32 (4):747-763; 2002.

5. Paddleford, R.R.: Preanesthetic agents. Manual of Small Animal Anesthesia. W.B. Saunders, Philadelphia, Pa., 1999; pp 12-30.

6. Wagner, A.E. et al.: Myths and misconceptions in small animal anesthesia. JAVMA 223 (10):1426-1432; 2003.

Angela Dyer, DVMPenasquitos Pet Clinic9728 Carmel Mountain Road, Suite ESan Diego, CA 92024

Robert Stein, DVMAmherst Small Animal Hospital2177 Kensington Ave.Snyder, NY 14226

Kerrin Hobin, DVMHarbor Veterinary Hospital2202 Soquel Ave.Santa Cruz, CA 95062

Twelve additional veterinarians signed this letter.

The authors respond: Thank you for your concern about the perioperative management of this cat. Pain management is of the utmost importance in our patients, especially when they undergo surgical procedures. In this case, butorphanol was given 30 minutes before induction. The total prep and surgery time lasted about 90 minutes, and the patient received another butorphanol dose about two hours after the first one. The cat received intravenous fluids (26 ml/hr) throughout induction, surgery, and recovery. Also, patient monitoring during anesthesia was routine and included pulse oximetry, ECG, capnography, blood pressure, and temperature. The cat's temperature was controlled during prep, surgery, and recovery by using water-filled heating pads, warmed rice socks, and intravenous fluid warmers.

As mentioned in the article, the patient was discharged to the referring veterinarian six hours after surgery. All additional analgesic administration was given at the referring veterinarian's discretion. The referring veterinarian was also the cat's owner. Therefore, the postoperative protocol in this case differed from that typically followed in our hospital. The referring veterinarian reported that the cat was apparently comfortable while receiving butorphanol and returned to normal physiologic activity within 24 hours.

Recent information suggests that the duration of analgesic action provided by any opioid, be it a full mu agonist, partial mu agonist, or even an agonist-antagonist such as butorphanol, can be extremely variable depending on the dose, pain syndrome treated, and patient's sex and species.1 The procedure we performed in this cat is considered to produce moderate pain; and as butorphanol is considered adequate for mild to moderate visceral pain, it was deemed appropriate in this case.2

We use current anesthesia and analgesia protocols on a case-by-case basis with the welfare of the patient being of the highest concern. We agree that a more potent and specific mu agonist could have been used, and in hindsight, perhaps, we should have considered using an alternative medication. However, given our present knowledge concerning the tremendous variability in individual pain tolerance and drug efficacy, the use of butorphanol would not necessarily be considered inappropriate as long as it is coupled with aggressive pain assessment and patient monitoring.

REFERENCES

1. Lascelles, B.D.; Robertson, S.A.: Antinociceptive effects of hydromorphone, butorphanol, or the combination in cats. J. Vet. Intern. Med. 18 (2):190-195; 2004.

2. Mathews, K.A.: Pain assessment and general approach to management. Vet. Clin. North Am. (Small Anim. Pract.) 30 (4):729-755; 2000.

Joshua F. Rexing, DVMVeterinary Teaching HospitalCollege of Veterinary MedicineUniversity of Illinois1008 W. Hazelwood DriveUrbana, IL 61802

Bradley R. Coolman, DVM, MS, DACVS Veterinary Surgical Services5818 Maplecrest RoadFort Wayne, IN 46835