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Can Vet J. 2017 February; 58(2): 149–156.
PMCID: PMC5234314

Language: English | French

Perioperative analgesic use by Ontario veterinarians, 2012

Abstract

The objectives of this study were to describe the routine use of analgesics by Ontario veterinarians for common surgeries in dogs and cats, and to compare routine use of analgesics between species and surgeries, using Chi-square analyses. In total, 239 veterinarians responded to the questionnaires; a response rate of 13.1%. Fifty-two percent to 79% of veterinarians used meloxicam for both species and all surgeries. Approximately 9% of veterinarians did not use analgesics for dog ovariohysterectomy and castration, while 16% to 22% did not use analgesics for these surgeries in cats. Veterinarians used and dispensed analgesics to dogs more often than to cats (P < 0.05). Many (60% or more) veterinarians administered analgesics pre-emptively to both dogs and cats for all surgeries. Continuing education for veterinarians needs to focus on understanding of pre-emptive analgesia, preventive analgesia, and the importance of dispensing analgesic drugs after surgery for all surgeries.

Résumé

Utilisation de l’analgésie péri-opératoire par les vétérinaires de l’Ontario, 2012. Les objectifs de cette étude consistaient à décrire l’utilisation routinière de l’analgésie par les vétérinaires de l’Ontario pour les chirurgies courantes chez les chiens et les chats et à comparer l’utilisation routinière de l’analgésie entre les espèces et les chirurgies en utilisant des analyses du chi-carré. Au total, 239 vétérinaires ont répondu aux questionnaires, pour un taux de réponse de 13,1 %. De cinquante-deux à 79 % des vétérinaires avaient recours au méloxicam pour les deux espèces et toutes les chirurgies. Environ 9 % des vétérinaires n’ont pas utilisé d’analgésie pour l’ovario-hystérectomie et la castration canines, tandis que de 16 % à 22 % n’ont pas eu recours à l’analgésie pour ces chirurgies chez les chats. Les vétérinaires utilisaient et distribuaient des analgésiques aux chiens plus souvent qu’aux chats (P < 0,05). Plusieurs vétérinaires (60 % ou plus) ont administré des analgésiques de manière préventive aux chiens et aux chats pour toutes les chirurgies. La formation continue des vétérinaires doit continuer de se concentrer sur la compréhension de l’analgésie préventive et sur l’importance d’administrer des analgésiques après la chirurgie pour toutes les chirurgies.

(Traduit par Isabelle Vallières)

Introduction

Analgesic medications to reduce surgical pain are crucial for the wellbeing and overall health of an animal (1). The College of Veterinarians of Ontario (CVO) states that it is the ethical obligation of veterinary professionals to prevent and relieve pain in animals (2). Veterinary professionals’ interest in and knowledge of evaluating and treating pain in animals has increased (3). A greater understanding of the pathophysiological process of pain transmission has led to more comprehensive guidelines for perioperative pain management (3).

All animals undergoing surgical procedures should receive analgesia (2). Hansen and Hardie in 1993 (4) were the first to question the adequacy of post-surgical analgesia. Their study, conducted in a United States veterinary teaching hospital, characterized the frequency and determinants of post-surgical analgesic intervention in companion animals. In that study, 7% of cats received analgesia after surgery, while 28% of dogs received analgesia after extubation (4). In a subsequent Canadian study (5), veterinarians surveyed about post-operative pain management were classified as analgesic users or non-users. Animals undergoing orthopedic surgery received the highest rates of analgesic medication at 84% and 70% of dogs and cats, respectively (5). Animals undergoing castration received the lowest rate of post-operative analgesics, with only 11% of dogs and 9% of cats receiving analgesics. Similar studies in other countries also investigated analgesic use by veterinarians (69). All reported inadequate analgesic use, especially for the most common surgeries, ovariohysterectomy and castration. Another Canadian study in 2001 asked veterinarians about pre- and post-incisional analgesic use (10). These authors reported that the frequency of post-operative analgesic use had increased in Canada compared with a 1996 study (10). In 2002, studies in Finland and New Zealand reported disparities in analgesic use between dogs and cats (11,12). Although both species had similar pain scores, dogs received analgesia more frequently than did cats. Similarly, a study of veterinarians in Britain concluded that the veterinary profession is increasing analgesic use over time (13). Although use in dogs was comparatively high, use in cats required improvement. More recently, studies in Brazil and Switzerland evaluated the use of multimodal and pre-emptive analgesic techniques, with the latter used by more than 70% of veterinarians (14,15).

Despite the improvements noted, there remains an important gap in knowledge about provision of ideal patient care. The objectives of the current study were to describe the use of analgesics by Ontario veterinarians for routine elective surgeries in dogs and cats, and to compare routine use of analgesics between dogs and cats, and among types of surgery.

Materials and methods

A questionnaire, developed in an iterative manner by the senior authors (CD, CK, RJ), was based on the overall objectives of the study and the expectations of participants completing the study online. Portions of the questionnaire were modeled after surveys by Williams et al (12) and Hewson et al (10). Veterinary graduate students at the Ontario Veterinary College (OVC) and 12 veterinarians in private practice pre-tested the initial draft. The pre-test veterinarians were chosen by geographic location, year of graduation, and type of practice. The questionnaire was reduced in size and complexity, and was limited to require either dog or cat responses per participant based on feedback from the pre-test.

On approval of the project by the University of Guelph Research Ethics Board, participants were recruited through both the Ontario Veterinary Medical Association (OVMA) magazine and the OVMA online newsletter. Study participants were licensed Ontario veterinarians who had an e-mail address, were members of the OVMA, and reported that they regularly treated dogs and/or cats in their practices. Responses to the questionnaire were collected through Limesurvey (LimeSurvey Project Team 2015, Limesurvey Project, Hamburg, Germany), a self-administered online survey tool. The questionnaire was available to participants from September 13, 2012 to January 6, 2013.

Participants who graduated in odd years were asked to complete the questionnaire focused on dog surgery, while even-year graduates were asked to complete the cat questionnaire. Participants had the option of completing the second questionnaire. The questions on the species-based questionnaire were the same, except that respondents were asked about analgesic use for cruciate surgery in dogs and onychectomy in cats. For each completed questionnaire, participants were offered an entry in a draw for free registration to the 2014 OVMA conference.

The questionnaires included demographic questions, and 6 additional sections addressing multiple aspects of veterinarians’ attitudes and practices regarding pain management and analgesic use. Questions pertaining to demographics included gender, year of graduation, and school of graduation. This manuscript reports on the section of the questionnaire pertaining to the routine use of analgesics, specifically, timing and route of administration, and choice of analgesics for each of several routine elective surgeries.

Participants were asked if they routinely or never gave analgesic drugs to dogs or cats for 5 common surgical procedures. The specified surgeries were ovariohysterectomy, castration, dental procedures with major extractions, laparotomy, cruciate repair (dog only), and onychectomy (cat only). The data presented are from a survey of practicing veterinarians who perform these surgeries routinely. From a list of 9 analgesic drugs, consisting of non-steroidal anti-inflammatory drugs (NSAIDs) approved for use in animals, and some opioids, participants were asked to select the analgesic used and its common route of administration, for each surgery. Participants were also asked about timing of analgesic administration, where they could choose from 4 options: before or during surgery, pre-extubation, or post-extubation. Pre-emptive analgesia referred to administration of an analgesic before surgery. Additionally, participating veterinarians were asked which analgesics were routinely dispensed after surgery. For each question, there was an option for the participant to include up to 3 analgesics that were not listed, in a section called “other.”

Statistical analyses

All statistical analyses were performed using STATA version 13.1 (StataCorp LP, College Station, Texas, USA). Descriptive statistics were generated to describe perioperative analgesic use and analgesics dispensed by surgery type in dogs and in cats. Pearson’s Chi-squared tests were used to identify differences in the proportions of veterinarians using specific analgesics for i) specific surgeries between species, and ii) within species and among surgeries, iii) drugs dispensed by surgery between species, and iv) drugs dispensed within species among surgeries. The strengths of the significant associations were described by an odds ratio. Fisher’s exact tests were used when the expected value of any 1 cell represented fewer than 5 veterinarians.

Frequency counts of the number of veterinarians using any analgesic drug during each of the time points were tabulated. The 3 most commonly used analgesics by timing within species and surgery were reported, provided that at least 4% of the respondents used the analgesic. Logistic regression was used to determine the association between gender and year of graduation on the analgesic use within surgery between species and among surgeries within species before, during, and after surgery. Year of graduation by gender was determined for 5-year intervals by graduation year. This distribution of participants was compared to that of OVMA membership using Pearson’s Chi-squared tests. Statistical analysis outcomes were considered significant at a P < 0.05 level.

Results

One hundred participants completed the dog questionnaire and were included in the analysis. Of these participants, 66.0% were female, 30.0% were male, and 4.0% did not disclose their gender. The cat questionnaire was completed by 139 participants. Of these participants 69.1% were female, 30.2% were male, and 0.7% did not disclose their gender. The majority of respondents to either the dog or cat questionnaire had graduated from the OVC (84.0% and 83.5%, respectively). Neither gender nor year of graduation was associated with analgesic use. For most graduation years, respondents were reflective of the demographic distribution of the OVMA. Women who graduated between 2010 and 2012 were more likely to participate (OR = 1.7; 1.07 to 2.63; P = 0.02); however, women who graduated between 1990 and 1994 were less likely to participate (OR = 0.4; 0.23 to 0.83; P = 0.009). Overall, women were more likely to participate than men (OR = 1.8; 1.3 to 2.4; P = 0.0001) and in particular, men who graduated between 1995 and 1999 were less likely to participate (OR = 0.16; 0.06 to 0.38; P < 0.0001). Most respondents to both the dog and cat questionnaires worked in small animal practice (87.0% and 83.4%, respectively), including 1% from feline-only practices. Nine percent of those who completed the dog questionnaire and 11.0% of those who completed the cat questionnaire were in mixed-animal practices, with the remainder being in referral practices or other categories. Of the 1691 OVMA members 15.3% of those working in small animal practice and 5.0% working in mixed-animal practice responded. The overall response rate for the questionnaires was 13.1%.

Analgesics used by veterinarians, in dogs and cats, according to surgery type, are presented in Table 1. Meloxicam was the most commonly used analgesic across the 2 species and all surgeries, followed by hydromorphone. Between 8% and 10% of veterinarians did not report using analgesics for dogs during ovariohysterectomy and castration surgeries. Similarly, 16% and 22% of veterinarians did not report using analgesics for cats for ovariohysterectomy and castration surgeries, respectively. Carprofen was administered to cats (off-label) for ovariohysterectomy and castration surgeries by 1% to 2% of veterinarians. Fentanyl was used in 19% of dogs undergoing cruciate repairs and 14% of cats undergoing onychectomy; significantly greater than fentanyl use for other surgeries (P < 0.05). Local anesthetics were administered to both dogs and cats for all surgery types, and were given by more than half of the veterinarians surveyed to animals undergoing dental procedures with major extractions. Tramadol and ketamine were the most common drugs listed as “other.”

Table 1
Percent of participating Ontario veterinarians routinely using specific analgesics perioperatively in dogs (n = 100) and cats (n = 139), 2012

Reports of timing of analgesic administration are provided in Table 2. Greater than 61% of veterinarians reported administering analgesic drugs pre-emptively to both dogs and cats for all surgeries. The percentage of veterinarians dispensing analgesics after surgery varied both by surgery type and between the 2 species (Table 3).

Table 2
Percent of participating Ontario veterinarians routinely administering analgesics perioperatively at a specific time during surgery in dogs and cats, 2012
Table 3
Analgesics dispensed by Ontario veterinarians (%) to dogs (n = 100) and cats (n = 139) following specific surgical procedures

Deracoxib, meloxicam, and tramadol were more likely to be dispensed for dogs than for cats after ovariohysterectomy and castration. However, buprenorphine was more often dispensed for cats than dogs after ovariohysterectomy, dental procedures, and exploratory laparotomy. Analgesic drugs were more often dispensed for dogs than for cats. For ovariohysterectomy and castration, 17% and 26% of veterinarians, respectively, did not dispense analgesics for dogs. For ovariohysterectomy and castration, 34% and 62% of veterinarians, respectively, did not dispense analgesics for cats.

Table 4 illustrates the timing of treatment for the 3 most commonly used analgesics within species and by surgery type. In both dogs and cats, hydromorphone and butorphanol were most commonly administered before surgery. Meloxicam was administered most frequently during and after surgery.

Table 4
The 3 most frequently used drugs by species, surgery, and time of administration as described by Ontario veterinarians, 2012

Discussion

Meloxicam was the most commonly used analgesic for both dogs and cats and among surgeries (Table 1). This finding differs from earlier studies conducted in New Zealand (12), and in Canada (10), in which carprofen and butorphanol were the 2 most commonly used perioperative analgesics. Meloxicam, an NSAID, was approved for use in veterinary medicine in Canada in 2003 (16). The use of meloxicam has increased since the previous Canadian study (10). When the last survey was conducted in Canada (in 2001), meloxicam was not licensed for use in cats (10). In dogs, Mathews et al (17) reported that meloxicam has a longer and more efficacious analgesic effect than butorphanol.

Carprofen was the second most common NSAID reported in dogs in this study (Table 1). Carprofen was used by 83% of veterinarians in New Zealand for dogs and cats (12). In New Zealand, carprofen is approved for use in both cats and dogs. Carprofen has a shorter duration of action (12 to 18 h) (18) than meloxicam (24 h) (17), but is an acceptable analgesic in veterinary practice (19). Authors have suggested that a single dose of carprofen in the perioperative period is an effective and safe analgesic. However, when repeated doses are required other NSAIDs have safer feline profiles than carprofen, which can cause renal toxicity (20). In Canada, use of carprofen in cats constitutes extra-label drug usage.

Butorphanol was used as a perioperative analgesic by 22% to 45% of veterinarians in this study, depending on species and surgery. Butorphanol has a short duration of action (1 to 2 h) (21,22) and is suggested only when surgery is anticipated to produce mild to moderate pain, such as ovariohysterectomy and castration (1). Although it is an opioid, butorphanol is not licensed in Canada as an analgesic for dogs and cats, but rather as an antitussive for dogs (22). In the current study, butorphanol was most often administered before surgery and appeared among the top 3 drugs administered before surgery across all surgeries and both species (Table 4). This differs from the previous Canadian study, in which butorphanol was the most commonly used drug both before and after incision (10). Previous to that, butorphanol was the opioid most commonly used by Canadian veterinarians for post-operative pain control (5). Ontario veterinarians are now more commonly using NSAIDs during and after surgery, rather than using opioids for post-operative analgesia (Table 4). Butorphanol, a kappa agonist/mu antagonist, can reverse the effects of pure mu agonists such as hydromorphone and fentanyl if they are administered together (23), leaving the animal with only mild analgesic effects. Both hydromorphone and fentanyl are more potent full opioid analgesics, and therefore more effective than butorphanol (22). Hydromorphone has a longer duration of action (2 to 4 h) than that of butorphanol (22), and was the opioid administered most often in the current study. Veterinarians indicated that they routinely administered butorphanol, hydromorphone, and fentanyl for various surgeries. Our survey questions did not allow us to distinguish whether these drugs are being administered to the same or different animals, depending on individual animal characteristics. Nor did the questionnaire provide an opportunity for veterinarians to discuss analgesic drug combinations. The appropriate use of drug combinations is an important area for continuing professional education.

Tramadol is an opiate-like analgesic agent, acting through central nervous system inhibition of the pain pathway. It is not approved for use in animals. Veterinarians reporting they used tramadol in this study indicate extra-label drug use. Although tramadol is viewed as an effective analgesic for management of moderate to severe pain in humans, this is not always the case in animals. Although tramadol appears to be effective in cats (24), it is not expected to have substantial opioid effects in dogs (24). In this study, tramadol was administered in the perioperative period to 3% to 8% of dogs and up to 3% of cats, and dispensed to 8% to 40% of dogs and up to 7% of cats.

Local anesthetics were administered perioperatively to both dogs and cats for all surgeries in this study. For the more common surgeries, ovariohysterectomy and castration, 25% and 33% of veterinarians administered a local anesthetic to dogs, respectively, while 24% and 25% of veterinarians did so for cats, respectively. The highest percentage of veterinarians administered local anesthetics perioperatively for dental surgeries with major extractions in both dogs and cats, and to cats during onychectomy. In comparison, most participants in a recent British study did not commonly use local analgesic techniques perioperatively (13). The previous Canadian study also reported low usage of local anesthetics (10), with the highest use of local anesthetic blocks for tail docking in puppies (11%) and onychectomy in cats (11%).

Most veterinarians provided perioperative analgesia to dogs (92%) and cats (84%) for ovariohysterectomy. This is similar to reports from New Zealand where 76% of dogs and 64% of cats received analgesia for ovariohysterectomy (12). This indicates an increased usage of analgesia by veterinarians over the past decade, although disparity still exists between the 2 species; dogs were routinely treated more often with analgesic drugs than were cats, a consistent finding from other studies (7,12). Within each surgery, 8% to 12% more veterinarians routinely administered analgesics to dogs than to cats. In the United Kingdom, veterinary concerns about the side effects of analgesic drugs in cats were a factor in less frequent use of analgesia (7), indicating another area of focus for continuing education. Although dogs and cats react differently to analgesic drugs, there is no evidence to suggest that they might feel pain differently or have different requirements for effective analgesia.

A basic understanding of the pathophysiology of pain is crucial in order for practicing veterinarians to employ effective pain management (3). Analgesic drugs inhibit sensitization of nerves to pain at the peripheral and central nervous system levels. Initiating treatment before nociceptive input into the nervous system can help prevent the peripheral and central sensitization process (25). This is known as pre-emptive analgesia, in which peripheral and central sensitization are controlled by administering analgesic drugs before surgery (3).

The 1996 survey in Canada asked veterinarians about their use of analgesics after surgery (5). The 2006 Canadian study reported 87% to 97% of dogs received pre-incisional analgesics for the surgeries the survey asked about (10). There was no question on pre-emptive analgesia. Cats received pre-incisional analgesics 87% to 92% of the time (10). Pascoe (26) suggests that it is far better to prevent pain than to treat it, and this should be accomplished through pre-medication. He states that pre-medication should be used to decrease anxiety, as well as providing analgesia before the painful procedure. At least 61% and 71% of veterinarians reported administering analgesics to dogs and cats, respectively, before surgery. Pre-emptive pain relief is especially important for shorter surgeries in which an analgesic may have to be administered early to reach therapeutic effect in order to control post-operative pain (17). While pre-emptive analgesia is an important concept, it is also imperative that we consider an approach that minimizes the long-term negative complications associated with poor management techniques. Preventive analgesia is a broader approach to pain management, focused on the importance of good analgesia practices throughout the perioperative period (27). This pain management practice decreases postoperative pain and lowers analgesic requirements.

Multi-modal analgesia, which promotes the use of 2 or more classes of analgesic drugs as safer and more effective than a single class of drugs alone (3), is recommended as an important tool in pain management (28). However, the current study did not determine how many veterinarians are using multimodal analgesia. Earlier studies rarely reported use of multimodal analgesia (5,8,9,11). A British study suggested that the importance of using multiple classes of drugs had been recognized, yet this approach was not widely used (7). Similarly, in South Africa, multimodal drug use was recommended but not investigated (8). Since then, many recommendations to use both an NSAID and an opioid have surfaced (1,3,15,28). The combination of these 2 classes of drugs generally confers better analgesia for moderate to severe pain through a synergistic effect (1). The use of local anesthetics by veterinarians in the current study speaks to potential multimodal analgesic use in this population. The rationale is that local analgesics are rarely administered as the sole analgesic, and would, therefore, likely be given with another analgesic drug, as was described in a recent study by Hunt et al (13,29).

Overall, 8% to 14% of veterinarians did not report using analgesics in dogs for the surgeries included in the study, while 16% to 23% of veterinarians did not report using analgesics for surgeries for cats. This finding is concerning, given that the licensing body governing quality practice and standards in Ontario issued a position statement in October 2013, while this study was being conducted, directing that veterinarians were obligated to provide analgesia to all patients where the potential for pain exists (2). Clearly, a greater focus on continuing education is needed to meet the professional ethical standard in Ontario. A recent study in Switzerland showed more Swiss veterinarians (92% to 98%) than Ontario veterinarians report using analgesia during surgery (15). However, in Brazil, fewer veterinarians (78%), than those in the current study, reported giving analgesic drugs to cats during ovariohysterectomy (14).

Our questionnaire specifically asked about analgesic use for specific surgeries. However, one of the important limitations of our work is that participants were unable to indicate that they did not perform any of the given surgeries. This is likely most significant for cruciate surgery in dogs and onychectomy in cats, as well as exploratory laparotomy in both species. It is possible that individuals who did not report using analgesics in fact did not perform the surgery in question. They would then have been misclassified as analgesic non-users. We assume that most veterinarians who elected to complete the survey are involved in elective sterilization procedures. The potential lack of use of analgesia in these surgical procedures thus remains an important focus for education and priority for future studies.

In contrast to the previous Canadian study, our questionnaire asked about dispensing analgesic medication after common surgeries (10). For most surgeries, veterinarians reported dispensing analgesics for both dogs and cats, although veterinarians treating dogs (74% to 86%) consistently dispensed analgesics more often than when treating cats (38% to 76%). Meloxicam was most often dispensed across both species and all surgeries. Dispensing an NSAID has many positive implications, as NSAIDs have been proven to be effective for pain control and are available in once per-day oral formulations (30).

Buprenorphine was the opioid most commonly dispensed for cats in this study and was occasionally dispensed for dogs. Buprenorphine has a bioavailability of only 3% to 6% when administered orally to dogs (31). Between 3% and 8% of veterinarians dispensed buprenorphine to dogs for various routine surgeries. The route of administration for buprenorphine when dispensed was not included in this study.

This study summarizes the use of analgesics by 239 veterinarians in Ontario. This is similar to the number of veterinarians surveyed in previous studies across Canada (5,10). However, the previous studies sent questionnaires to a random sample of veterinarians. The current study was available to all veterinarians who were members of the OVMA. In total, 15.3% of OVMA members in small animal practice participated in this study, but only 5.0% of those in mixed animal practice participated. On the basis of demographics, the participants were mostly representative of OVMA members by gender and year of graduation. The low response rate is likely due to the length of the questionnaire, individuals being unaware of the survey, and/or the limitation of using an online format only.

Bias may have been introduced in several ways because of the voluntary nature of the questionnaire. This effect may have also been driven by the incentive provided. Also the demographics of OVMA members may bias the demographics of those who participated in the survey. Since the questionnaire specifically asked about analgesic use, it is also possible that non-responders did not wish to discuss their analgesic use, in contrast to responders. The characteristics of the non-responders are unknown.

This study has identified many positive perioperative analgesic practices. This is the first study in Canada to collect information on analgesics dispensed and their use before, during, and after surgery. The common practice of analgesic use (86% to 92% in dogs and 77% to 84% in cats), and the number of veterinarians reporting use of pre-emptive analgesia (for example, 89% for ovariohysterectomy in dogs) are encouraging. Continuing education for veterinarians needs to focus on routine use of analgesics for all dogs and cats undergoing routine surgery, and the importance of pre-emptive analgesia, and of dispensing analgesic drugs after surgery. Future research is needed to establish whether veterinarians are employing a multimodal approach effectively, if they use a preventive analgesia plan, and also the reasons for not using analgesics for routine surgeries.

Acknowledgments

We are grateful to the OVMA for advertising the survey to their members and for providing demographics of the members. We also thank all participating veterinarians and we acknowledge funding from Pet Trust. CVJ

Footnotes

Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office (gro.vmca-amvc@nothguorbh) for additional copies or permission to use this material elsewhere.

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