A comparison of preoperative tramadol and morphine for the control of early postoperative pain in canine ovariohysterectomy
Introduction
Postoperative pain can result in many undesirable effects such as a decrease in food intake, exacerbated protein catabolism, depression of respiratory function, cardiac dysrrhythmias, central hypersensitivity to noxious stimuli and chronic pain (Morton & Griffiths 1985; Carroll 1996; Lascelles & Waterman 1997; Carroll 1999; Gaynor 1999; Grisneaux et al. 1999). All these changes delay recovery (Lascelles 1999).
In view of the necessity for the recognition and treatment of pain in animals, many strategies are being evaluated to improve our understanding and to devise new methods to better control postoperative pain. Opioids are amongst the best therapeutic tools to control pain because they are highly effective and reasonably safe. Side effects, mainly respiratory depression, can be reversed by the administration of an opioid antagonist or agonist-antagonist agent (Fox et al. 1994). These drugs may be administered preoperatively without the risk of renal problems or bleeding disorders associated with the use of nonsteroidal anti-inflammatory drugs (Mathews et al. 1996).
Morphine is the prototype opioid and is still an agent of choice for the treatment of severe pain in dogs and cats (Lascelles & Waterman 1997; Gaynor 1999). Its main adverse effect is respiratory depression although this is not marked in dogs (Taylor & Houlton 1984; Hendrix et al. 1996). Tramadol (Tramal, Searle, São Paulo, Brazil) is a synthetic analogue of codeine. Because it is a weak μ-opioid agonist, it produces significantly less respiratory depression (Duthie 1998). In people, its clinical action is primarily mediated by inhibition of neuronal norepinephrine reuptake, as well as by the inhibition of 5-hydroxytryptamine (serotonin, 5-HT) reuptake. An alpha-2 adrenergic effect was shown by the inhibition of the antinociceptive effect of tramadol after yohimbine administration in the cat (Desmeules et al. 1996). In people, this agent is used widely because in equipotent doses it has the same analgesic effect as morphine to relieve mild-to-moderate pain, but causes less respiratory depression (Houmes et al. 1992; Viegas et al. 1993; Tarradel et al. 1996; Mildh et al. 1999). Its use in veterinary medicine is still limited, and to our knowledge, there are no published clinical data that may prove its efficacy and safety in dogs and cats.
Opioids and other classes of analgesics may be administered before surgery. This strategy is called preemptive analgesia and is a method that aims at the inhibition of central sensitization (Raffe 1997; Lascelles 1999). The aims of this study were to compare the quality of analgesia, together with the incidence and severity of respiratory depression and other side effects produced by intravenous (IV) tramadol versus IV morphine in dogs, when given prior to surgery. The magnitude of some neuroendocrine changes was also measured.
Section snippets
Animals
A comparative double-blind randomized study design was used. Thirty female dogs of different breeds and ages varying from 2 to 14 years were used. All animals had pyometra diagnosed by abdominal ultrasound. All owners were aware that their animals needed surgical treatment and gave written informed consent. The Ethical Committee of the hospital approved the investigation. Exclusion criteria were: renal or hepatic dysfunction assessed by standard laboratory tests (urea, creatinine, alkaline
Results
There were no differences (p > 0.05) with regard to age, mass and data collected before the induction of anesthesia between groups. Surgical time was similar in both groups (57.1 ± 14.6 and 57.7 ± 11.8 minutes for groups I and II, respectively). Blood pressure and heart rate did not vary significantly after analgesic administration in groups I or II, nor between the groups. Respiratory rate showed significant changes during anesthesia (Fig. 1a). In the two groups, a decrease in respiratory
Discussion
Although many authors (Lascelles & Waterman 1997; Pibarot et al. 1997) encourage and defend the need for control groups, which do not initially receive any analgesic therapy, for humanitarian reasons, we decided not to use an untreated control group. It is well known that this surgical procedure causes moderate pain (Fox et al. 1994) and we thought it unnecessary to subject another group of animals to such stimulation. Secondly, a group receiving the analgesic postoperatively for comparison was
Conclusions and clinical relevance
There were no significant differences between the analgesia provided by morphine and tramadol in this study suggesting that tramadol may be as effective as morphine for postoperative analgesia for ovariohysterectomy in dogs. Further studies are needed to confirm our results.
Acknowledgements
The authors are grateful to FAPESP (project number 98/7654–4) for supporting this experiment, to the INCOR from FM-USP for the cathecolamine analysis, to the Hospital das Clínicas from FM-USP to the cortisol analysis, and to the Service of Obstetrics of the Veterinary Hospital of FMVZ-USP for the surgical procedures.
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2021, Veterinary Anaesthesia and AnalgesiaCitation Excerpt :A total of 642 dogs were included in the studies that reported sex, and 478 (74.4%) were female. The surgeries performed were ovariohysterectomy (Mastrocinque & Fantoni 2003; Mondal et al. 2005; Carareto et al. 2007; Gupta et al. 2009; Fajardo et al. 2012; Kongara et al. 2012; Morgaz et al. 2013; Stănescu et al. 2013; Oliveira et al. 2016; Saberi Afshar et al. 2017; Uscategui et al. 2017; Zhang et al. 2017; Meunier et al. 2019; Ugwu et al. 2020), orchiectomy (Kongara et al. 2013), cruciate ligament repair and other orthopedic surgeries (Schuszler et al. 2010; Rialland et al. 2012; Davila et al. 2013; Cardozo et al. 2014; Benitez et al. 2015; Marques 2015), eye enucleation (Delgado et al. 2014), hemilaminectomy (Giudice et al. 2017), thoracic surgery (Read et al. 2019), maxillectomy and mandibulectomy (Martins et al. 2010) and mastectomy (Uscategui et al. 2017). A total of 10 studies were excluded from this review—three studies because outcome data were not evaluated or reported in detail (Yasbek & Fantoni 2005; Sandoval et al. 2010; Santos & Herrera 2014), two studies because the analgesic effect of tramadol was compared against tramadol combined with another analgesic drug (Teixeira et al. 2013; Kaka et al. 2018) and one study for each of the following reasons: because it was not randomized (Tudor et al. 2018), pain was not assessed during the first 24 hours after surgery (Vullo et al. 2004), the pre-emptive effect of tramadol versus carprofen was compared, but all animals were administered hydromorphone (Karrasch et al. 2015), analgesia was evaluated only during the intraoperative period (Ospina-Argüelles et al. 2017) and because a pain scale was not used (Mondal et al. 2006).