Use of a pulsed electromagnetic field for treatment of post-operative pain in dogs: a pilot study

Objective: To determine if pulsed electromagnetic field (PEMF) therapy reduces post-operative pain in dogs following ovariohysterectomy, and to evaluate PEMF interaction with post-operative morphine analgesia.

Study design: Randomized controlled clinical trail.

Animals: Sixteen healthy dogs weighing 18 (10-32) kg [median (range)] and aged 13 (3-36) months.

Materials and methods: Anesthesia consisted of atropine (0.04 mg kg^-1, SC), acepromazine (0.02 mg kg^-1, SC), fentanyl (0.01 mg kg^-1, SC), thiopental (10-15 mg kg^-1, IV) and halothane in oxygen. Ovariohysterectomies were performed by senior veterinary students. Pain score (numeric rating scale, 0-28), pulse rate, respiratory rate, indirect mean arterial pressure (MAP), and body temperature were evaluated prior to anesthetic premedication, at extubation, 30 minutes after extubation, and then hourly for 6 hours. Following extubation, dogs were randomly divided into four groups: a control group that received 0.9% NaCl, IV, and no PEMF; a magnet group that received 0.9% NaCl, IV, and PEMF; a morphine group that received morphine 0.25 mg kg^-1, IV, and no PEMF; and, a magnet/morphine group that received morphine 0.25 mg kg^-1, IV, and PEMF. A single observer, blinded to treatment, obtained all behavioral observations and physiologic data. Data were analyzed using the Kruskal-Wallis statistical test with a significance of p < 0.05.

Results: Significant differences in MAP (mm Hg) [median (range)] occurred at 300 minutes [morphine 108 (83-114) and magnet/morphine 90 (83-97) < magnet 135 (113-117)], and at 360 minutes [magnet/morphine 93 (81-100) < control 127 (111-129) and magnet 126 (111-129)]. At 30 minutes the total pain score for the magnet/morphine group [1.5 (0-5)] was significantly less than control [8 (6-13)], but not different from magnet [5.5 (4-7)] or morphine [4.5 (2-9)].

Conclusions and clinical relevance: Although no clear benefit was seen in this study, the results suggest that PEMF may augment morphine analgesia following ovariohysterectomy in dogs, and that further study of the analgesic effects of PEMF is warranted.