Studio sul dolore post-operatorio dopo ovariectomia

Heidi L Sha¡ord DVM, Peter W Hellyer DVM, MS, Dipl ACVA, Kenneth T Crump CVT, Ann E Wagner DVM, MS, Dipl ACVA, Khursheed R Mama DVM, MS, Dipl ACVA & James S Gaynor DVM, MS, Dipl ACVA Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State Uni-versity, Fort Collins, USA

Uso della magnetoterapia per il trattamento post-operatorio nei cani: uno studio pilota.

Abstract

L’obiettivo era determinare se la magnetoterapia riduceva il dolore post operatorio in cani dopo l’ovariectomia e determinare l’interazione della magnetoterapia con l’analgesia da morfina post-operatoria.

Introduzione

L’interesse nell’uso terapeutico della magnetoterapia è cresciuto negli ultimi anni da quando la magnetoterapia ha guadagnato in USA l’approvazione da parte dell’ente “Food and Drug Administration” per la terapia di pazienti umani con fratture scom-poste e pseudoartrosi congenite (Basset 1993).

L’uso della magnetoterapia è stato incorporato nel trattamento delle tendiniti sia negli umani (Binder et al. 1984) che nei cavalli (Auer et al.1983). Inoltre, è stato dimostrato che la magnetoterapia migliora la guarigione delle ferite nel cane. Il sollievo dal dolore cronico è stato un problema comune associato al trattamento con magnetoterapia nei pazienti umani (Binder et al.1984; Ellis 1993,Trock et al.1994) Nessuno studio ha studiato il sollievo dal dolore mediato dalla magnetoterapia negli animali. L'obiettivo di questo studio pilota era di ottenere informazioni preliminari per valutare gli effetti analgesici della magnetoterapia nei cani. In particolare, abbiamo analizzato la capacità di una magnetoterapia terapeutica di controllare il dolore post-operatorio e valutato la sua interazione con l'analgesia della morfina post-operatoria nei cani sottoposti a ovarioisterectomia di routine.

Sedici cagne intatte non gravide ,di peso corporeo di 18 Kg (10 -32 di media) e 13 mesi (3 - 36 mesi di media) sono stati i soggetti di questo studio pilota.

Sono stati presentati all'Ospedale Veterinario della Colorado State University dalla Larimer County Humane Society per ovarioisterectomia elettiva. Il Comitato per la cura degli animali della Colorado State University ha approvato l'uso dei cani per gli studi.

Tutti i cani sono stati verificati in buona salute sulla base di esami fisici e concentra-zione totale delle proteine plasmatiche determinata il giorno prima dell'intervento chirurgico.

Trattamento elettromagnetico ad impulsi

L'unità magnetica è stata fissata all'esterno della gabbia e il campo magnetico è stato misurato utilizzando un gaussometro a tre vie e controllato per essere all'interno della gabbia. L'unità magnetica ha emesso un campo elettromagnetico pulsato a 0,5 Hz per periodi alternati di 20 minuti e poi per 20 minuti spento per il periodo di recupero di 6 ore. La configurazione dell’unità elettromagnetica pulsata è stata raccomandata dal produttore per il sollievo dal dolore negli animali (Peppin 1998). Durante il periodo di recupero, i cani in morfina sono stati esposti a un'unità elettromagnetica non funzionale, benché visibilmente identica.

Valutazione del dolore

Sono stati valutati nove criteri differenti di risposta comportamentale e fisiologica al dolore per determinare il punteggio del dolore cumulativo. Il criterio include il comfort, movimento, aspetto, comportamento non provocato, comportamento interattivo, vocalizzazione, frequenza cardiaca, frequenza respiratoria e pressione media arteriosa.
I cani sono stati osservati per circa 10 minuti al giorno in un momento preciso. Qualsiasi cane che esibiva un eccesso di dolore, definito come un punteggio di dolore cumulativo di più di 17, è stato somministrato immediatamente morfina (0,5 mg kg 1, IV) e rimosso dallo studio.

Discussione

In questo studio pilota, abbiamo scoperto che la magnetoterapia ha contribuito all'analgesia post-operatoria nei cani sottoposti a ovarioisterectomia elettiva. La MAP di entrambi i gruppi morfina e morfina / magnete tendeva a ritornare ai valori basali di T 1/4 300, mentre quella dei gruppi di controllo e dei magneti tendeva ad aumentare. Sammarco et al. (1996) hanno riportato una tendenza simile alla MAP postoperatoria che aumenta nel tempo in un gruppo di controllo di cani. Sebbene l'analgesia e la sedazione della morfina fossero diminuite di T 1/4 300, i cani trattati con morfina potrebbero aver sperimentato maggiore analgesia e sedazione e ridotto rilascio di catecolamina endogena nel corso dello studio, il che avrebbe potuto contribuire a ridurre la MAP rispetto ai cani non ricevendo la morfina.

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

Heidi L Sha¡ord DVM, Peter W Hellyer DVM, MS, Dipl ACVA, Kenneth T Crump CVT, Ann E Wagner DVM, MS, Dipl ACVA, Khursheed RM ama DVM, MS, Dipl ACVA & James S Gaynor DVM, MS, Dipl ACVA Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, USA
(Veterinary Anaesthesia and Analgesia, 2002, 29, 43^48)

Correspondence: Peter Hellyer, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.

Abstract

Objective To determine if pulsed electromagnetic ¢eld (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 aged13 (3^36) months.

Materials and methods Anesthesia consisted of atropine (0.04 mg kg
1, SC), acepromazine (0.02 mg kg
1, SC), fentanyl (00.1mg 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, 30m inutes 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 signi¢cance of p < 0.05.

Results Signi¢cant di¡erences in MAP (mm Hg) [median (range)] occurred at 300 minutes [morphine 108 (83^114) and magnet/morphine 90 (83^97)

Conclusions and clinical relevance Although no clear bene¢t 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 e¡ects of PEMF is warranted.

Keywords analgesia, pulsed electromagnetic ¢eld.

Introduction

Interest in the therapeutic use of electromagnetic ¢elds has grown over the past two decades since pulsed electromagnetic ¢eld (PEMF) therapy gained Food and Drug Administration (USA) approval for the treatment of humanpatientswith nonunion fractures and congenital pseudoarthrosis (Bassett1993). Use of PEMF has been incorporated into the treatment of tendinitis in both humans (Binder et al. 1984) and horses (Auer et al.1983). In addition, PEMF has been shown to enhance wound healing in the dog (Scardino et al. 1998). Relief from chronic pain has been a common ¢nding associated with PEMF treatment in human patients (Binder et al.1984; Ellis 1993,Trock et al.1994), however, PEMF therapy does not appear to provide analgesia in acute pain models (Kavaliers&Ossenkopp1985;Reed et al.1987).No studies have investigated PEMF-mediated pain relief in animals. The objective of this pilot study was to obtain preliminary information evaluating the analgesic e¡ects of PEMF in dogs. Speci¢cally, we investigated the ability of a therapeutic PEMF to control post-operative pain, and evaluated its interaction with post-operative morphine analgesia in dogs undergoing routine ovariohysterectomy

Pulsed electromagnetic ¢eld treatment

The magnetic ¢eld unitwas attached to the outside of the cage and the magnetic ¢eld was measured using a tri¢eld gaussmeter and con¢rmed to be within the cage. The magnetic ¢eld unit delivered a pulsed electromagnetic ¢eld at 0.5 Hz for alternating periods of 20m inutes on and 20m inutes o¡ for the 6-hour recovery period. The pulsed electromagnetic ¢eld con¢guration was recommended by the manufacturer for relief of pain in animals (Peppin 1998). Control and morphine dogs were exposed to a nonfunctional, though visibly identical, electromagnetic ¢eld unit during the recovery period.

Evaluation of pain

Nine di¡erent criteria re£ecting behavioral and physiologic responses to pain were evaluated to determine the cumulative pain score (Appendix A). Criteria included comfort, movement, appearance, unprovoked behavior, interactive behavior, vocalization, heart rate, respiratory rate and mean arterial pressure. Dogs were observed for approximately 10m inutes at each data collection point. Any dog exhibiting excessive pain, de¢ned as a cumulative pain score of 17, was administered morphine (0.5 mg kg
1, IV) immediately, and removed from further study.

Discussion

Inthis pilot study, we found that PEMFcontributed to post-operative analgesia in dogs undergoing elective ovariohysterectomy. The MAP of both the morphine and morphine/magnet groups tended to return towards baseline values by T ¼ 300, whereas that of the control and magnet groups tended to increase. Sammarco et al. (1996) reported a similar trend of post-operativeMAP increasing over time in a control group of dogs. Although morphine analgesia and sedation were expected to have diminished by T ¼ 300, dogs receiving morphine may have experienced greater analgesia and sedation, and decreased endogenous catecholamine release throughout the study, all of which could have contributed to lower MAP than dogs not receiving morphine. As found in a previous study,MAP, heart rate and respiratory rate did not appear to correlate with behavioral indications of pain (Conzemius et al.1997). Pain scores for all groups tended to be greatest at the time of extubation. Post-anesthetic delirium may have contributed to high scores at this time. The pain scores of control dogs tended to be greater than all other groups for the ¢rst 180m inutes. Lascelles et al. (1997) reported a similar trend in pain scores of control dogs following ovariohysterectomy. In this study, the magnet group tended to have lower pain scores than the control and morphine groups during the ¢rst 180m inutes following extubation. It is possible that PEMF potentiation of morphine analgesia contributed to the ¢nding that morphine/magnet pain scores were signi¢cantly less than control at T ¼ 30. Our results suggest that exposure to a PEMF does not interfere with morphine analgesia, unlike a previous study which found that exposure to a rotating magnetic ¢eld, not a PEMF, inhibited morphine analgesia in rats (Kavaliers & Ossenkopp1985). Ovariohysterectomy has been used by other investigators as a standardized model of surgical pain (Lascelles et al. 1997, 1998) and for description of post-operative behavioral parameters indogs (Hardie et al. 1997).We used both objective (MAP, HR, RR) and subjective (behavioral observation) measures to help determine the severity of post-operative pain. We tried to minimize observer variability by having a single person obtain all pain score data. The behavioral comments o¡er insight into individual animal responses to treatments and suggest that all dogs in the control group were uncomfortable. Quantitative behavioral measurements may have detected more subtle di¡erences between groups and are recommended for future studies of PEMF-mediated analgesia.
PEMF therapy has proven successful in the treatment of pain associated with chronic tendinitis and osteoarthritis in people (Binder et al. 1984; Trock et al. 1994). Results of this pilot study suggest that PEMF may mediate acute post-surgical pain relief and that further research on clinical application and mechanisms of action is warranted.