Veterinary surgeons are becoming increasingly aware of postoperative pain, and to meet higher expectations for pain management, improvement in pain control is required for pets undergoing surgery. To date, pain control has focused primarily on the use of opiates and NSAIDs. However, these medications can be associated with substantial adverse effects, such as sedation, dysphoria, respiratory depression, gastrointestinal ulceration, and renal and liver damage, and may not offer adequate pain relief in some patients when used alone.1,2 Therefore, there is a need to investigate alternative analgesics or a means for providing additional pain control in clinical settings.
Local anesthetics have been used as part of both multimodal and preemptive analgesic protocols, in the form of peripheral nerve blocks, epidural injections, intra-articular or intracavitary instillation, systemic infusion, or regional blocks.3 Infiltration of anesthetic at the incision site (incisional blocks) is a popular analgesic modality because of their ease in application and they can be applied prior to the creation of an incision (preemptive use) or with other analgesic modalities (multimodal use).3 However, the efficacy of incisional blocks in preventing or treating acute surgical pain in small animals and humans is debatable. In vivo studies4–15 in humans have demonstrated some degree of additional analgesia when local anesthetics are added to both a preoperative and postoperative analgesic protocol, and several have even shown a preemptive analgesic effect. On the other hand, numerous studies16–21 in humans have failed to demonstrate an added benefit of regional blocks when used either as part of a multimodal protocol or when used preemptively, and from 1 metaanalysis study,4 it was concluded that local anesthetic infiltration offered no improvement in pain relief when used preemptively, compared with postoperative treatment. With regard to small animals, the literature is sparse. Local bupivacaine infiltration in cats undergoing onychectomy has actually been shown to transiently increase pain scores at 2 hours after surgery, compared with local saline (0.9% NaCl) solution infiltration.22 A recently published study23 on preincisional and postincisional bupivacaine infiltration in dogs undergoing celiotomies revealed that preincisional infiltration with bupivacaine decreased pain scores on a numerical rating scale (as assessed by interaction with the investigator and behavioral response to manipulation), compared with postincisional infiltration or placebo treatments.
There is evidence that local anesthetics may affect wound healing through toxic effects on muscles and anti-inflammatory effects, delaying wound healing and promoting infection.24–30 Despite these potentially detrimental effects, studies30,31 have failed to demonstrate a decline in tensile strength when healing wounds have had prior treatment with local anesthetics. While much work has been done regarding the effects of local anesthetics on healing properties in vitro, there are limited in vivo studies investigating wound-healing complications secondary to treatment with incisional blocks in a clinical situation.
The objectives of the study presented here were to determine the analgesic effect of incisional blocks with bupivacaine as part of a multimodal analgesic protocol in dogs undergoing ovariohysterectomy and to determine the effect of incisional blocks with bupivacaine on incisional healing and complications in dogs. With regard to the first objective, it was hypothesized that infiltration with bupivacaine at the incision site would offer additional pain relief and preemptive treatment with bupivacaine would be associated with a greater analgesic benefit than postoperative treatment with bupivacaine. The hypothesis for the second objective was that infiltration of the incision site with bupivacaine would be associated with a lower inflammatory response but would also result in an increased risk for complications, such as infection, hernia formation, and delayed healing.
Materials and Methods
Study protocol—Shelter-owned sexually intact female dogs of various ages and breeds scheduled to undergo routine ovariohysterectomy by fourth-year veterinary students at the veterinary teaching hospital were prospectively entered in the study. The project was approved by the animal care and use committee of the institution prior to implementation of the study. Dogs entered into the study were randomly assigned to 1 of 4 treatment groups. Dogs in group I represented the negative control and underwent routine ovariohysterectomy with no perioperative incisional injections. Dogs in group II represented the placebo group and received an IM and SC injection of saline solution over the planned incision site prior to performing a routine ovariohysterectomy. Dogs in group III and IV represented the test population, in which group III dogs received an IM and SC injection of bupivacainea over the planned incision site prior to performing a routine ovariohysterectomy, for preemptive analgesia, and group IV dogs received an IM and SC injection of bupivacaine at the incision site following routine ovariohysterectomy. For ovariohysterectomy, all dogs were premedicated with acepromazine (0.01 mg/kg [0.005 mg/lb], IM), morphine (1 mg/kg [0.45 mg/lb], IM), and atropine (0.02 mg/kg [0.01 mg/lb], IM), and general anesthesia was induced with thiopental (15 mg/kg [6.8 mg/lb], IV) to effect. General anesthesia was maintained with isoflurane, and depth of anesthesia was monitored by a supervising veterinarian (usually HLW). Incisional injections (groups II through IV) were administered by fourth-year veterinary students to the surgical site following standard aseptic preparation by veterinary technicians. Twenty-two–gauge, 2-inch needlesb were used, and the needle was directed through multiple tissue planes, so as to administer the injection throughout the superficial and deep tissues of the incision site. Solutions for incisional injections were drawn from multidose vials that were changed on at least a weekly basis; injections were given at a volume of 0.8 mL/kg (0.4 mL/lb). For all bupivacaine injections, a 2 mg/kg (0.9 mg/lb) dose was diluted to the proper volume in saline solution prior to administration. Dogs in all groups received 1 dose of hydromorphone (0.1 mg/kg [0.05 mg/lb], SC) at extubation and buprenorphine (0.02 mg/kg, SC) every 6 hours for 24 hours, as required by the institution's animal care and use committee. Carprofen (2.2 mg/kg [1.1 mg/lb], SC or PO) was administered every 12 hours for 3 days.
Pain assessment—Patients were evaluated after surgery for signs of pain at regular intervals throughout their hospital stay by an observer (CLF) who was blinded to treatment groups. The planned time points for assessment were 4, 8, 12, and 24 hours after surgery, and these time points were adhered to as closely as scheduling would allow. Pain assessment was performed by use of the Glasgow composite measures pain score (short form)32 and a mechanical stimulation test with von Frey filaments. The Glasgow score was obtained by answering a series of questions pertaining to observations of the patient's behavior while undisturbed in its environment and its response to human interactions (Appendix). To evaluate incisional pain with von Frey filaments, first, a control filament was applied to within 2 mm of the incision margin to determine the patient's response to the hand and testing device. Then, the smallest test filament was applied to the same location with enough force to cause a slight bend in the filament. If the patient did not respond (look at the incision or attempt to move away), filaments of increasing stiffness were applied to the incision until a response was achieved or the maximum force of 300 g was reached. This was repeated 3 times, and the smallest filament that reliably created a response was recorded. To control for the dog's natural response to the filament and evaluate the possibility of allodynia, an area along the ventrolateral portion of the thorax was also tested in the same fashion and the smallest filament that created a reliable response was recorded. Patients receiving a Glasgow pain score of > 10 that were not scheduled for routine delivery of an analgesic were administered a rescue dose of buprenorphine (0.02 mg/kg, IM).
Wound healing assessment—Incisions of all patients were evaluated by an observer who was blinded to treatment groups (CLF) at regular intervals throughout hospitalization, coinciding with pain assessment. The planned time points for inspection of the incision were 4, 8, 12, and 24 hours after surgery. Additionally, incisions were examined again for long-term healing at the time of recheck evaluation and suture removal (14 to 21 days after surgery). Incisions were evaluated for edema, erythema, discharge, and complications such as incisional infection or dehiscence. Edema was measured in both length and width along the incision by use of calipers, and the surface area was calculated. Erythema and discharge were both semiobjectively scored on a scale of 0 to 3, with zero representing none present and 3 representing a severe degree of erythema or discharge. Any degree of dehiscence was recorded, and the length and treatment for the dehiscence were recorded. Any complication, including injury directly attributable to the application of the incisional block (ie, inadvertent visceral injury or disruption of the suture line), hernia formation, irregular appearances of the incision, or incisional infection, was also recorded.
Statistical analysis—A 1-way ANOVA was used to evaluate differences in age, weight, surgical time, and length of the incision among treatment groups to ensure that all treatment groups consisted of a similar study population. A Fisher exact test was used to compare the number of incisional complications, the requirement for rescue analgesics, and the grade of incisional discharge among treatment groups. A Kruskal-Wallis test was used to evaluate the effect of treatment on Glasgow composite measures pain score and von Frey filament score at various time points. An ANOVA for repeated measures was used to evaluate the effect of treatment, time, and treatment-time interaction on incisional reaction (surface area of edema, erythema score, discharge score, and length of incisional dehiscence). A value of P < 0.05 was considered significant. Data are presented as mean ± SD.
Results
Ninety-two shelter-owned dogs were entered into the study. Group I (no incisional injection) contained 26 dogs, group II (preincisional saline solution infiltration) contained 12 dogs, group III (preincisional bupivacaine infiltration) contained 21 dogs, and group IV (postincisional bupivacaine infiltration) contained 33 dogs. Numbers of dogs in each group were not similar because of scheduling conflicts and the availability of investigators. For all dogs, times for the assessments of pain and incision site were 4.8 ± 0.8 hours, 8.1 ± 0.7 hours, 11.9 ± 0.6 hours, and 19.5 ± 1.3 hours after surgery and the follow-up time for incision healing was 18 ± 8 days. There were no significant differences in age, weight, or surgery time among treatment groups (Table 1). The incision length was significantly greater in group III, compared with the other treatment groups. Since the dogs used in this study were shelter-owned dogs available for adoption, follow-up at suture removal was only obtained for 37 of the 92 (40%) dogs. Follow-up information was available at suture removal for 12 dogs in group I, 6 dogs in group II, 10 dogs in group III, and 9 dogs in group IV. The remainder of dogs were adopted and lost to follow-up. Overall, 6 complications were reported; 3 patients had inflamed but healed incisions at the time of suture removal that required no treatment (2 from group III and 1 from group IV), 1 patient developed a hernia at the level of the linea alba with an intact skin incision (group III), another patient received a splenic laceration while receiving an incisional block (group III), and 1 patient developed a presumed incisional infection that responded to antimicrobial treatment (group II). There were no cases of incisional dehiscence reported. While not necessarily directly related to bupivacaine injection prior to creation of an incision, group III had significantly (P = 0.015) more overall complications than did group I by the time of suture removal. There was no significant difference in the number of complications between the remaining treatment groups.
Mean ± SD age, weight, surgery time, and incision length of 92 dogs that underwent ovariohysterectomy.
Variable | Treatment group | P value* | |||
---|---|---|---|---|---|
I (n = 26) | II (n = 12) | III (n = 21) | IV (n = 33) | ||
Age (y) | 1.8 ± 1.8 | 1.4 ± 0.8 | 1.2 ± 1.2 | 1.3 ± 1.6 | 0.49 |
Weight in kg (lb) | 15.1 ± 12.0 (33.3 ± 26.3) | 16.5 ± 8.3 (36.3 ± 18.2) | 16.6 ± 7.4 (36.6 ± 16.3) | 12.59 ± 8.08 (27.7 ± 7.8) | 0.38 |
Surgery time (min) | 132 ± 111 | 127 ± 36 | 118 ± 32 | 133 ± 134 | 0.96 |
Incision length (mm) | 51 ± 25 | 52 ± 20 | 67 ± 23 | 53 ± 18 | 0.05 |
P ≤ 0.05 indicates significant difference for variable among treatment groups.
Group I = No injection. Group II = Preincisional infiltration with saline (0.9% NaCl) solution. Group III = Preincisional infiltration with bupivacaine. Group IV = Postincisional infiltration with bupivacaine.
Glasgow composite measures pain scores were not significantly different among treatment groups at each time point. From 4 to 24 hours, the Glasgow composite measures pain score significantly decreased for group I, group III, and group IV. For group II, the Glasgow composite measures pain score did not significantly (P = 0.125; power = 0.78) decrease from 4 to 24 hours. There were no dogs with Glasgow composite measures pain scores > 10 at any of the measured time points, and therefore, no doses of rescue analgesics were administered. The responses to von Frey filaments placed near the incision were not significantly different among treatment groups at each time point. From 4 to 24 hours, the score for the von Frey filament test was not significantly different for group I (P = 0.066; power = 0.98), group III (P = 0.074; power = 0.56), and group IV (P = 0.742; power = 0.90). The score for the von Frey filament test was significantly decreased for group II (P = 0.031) between 4 and 24 hours after surgery. There were no differences in responses to the von Frey filaments being placed at a site distant to the incision.
Between 4 hours after surgery and the time of suture removal, the surface area of edema was not significantly (P = 0.70) different among treatment groups (Table 2). Compared with other treatment groups, the degree of erythema was significantly (P = 0.017) higher in group II at 4 hours after surgery and significantly (P = 0.028) lower in group IV at 24 hours after surgery (Table 3). The amount of erythema was significantly (P < 0.001) decreased over time; however, the effect was similar for each treatment group (P = 0.43). Likewise, there was no significant difference among treatment groups in the severity of discharge from the incision at any time point (Table 4).
Mean ± SD surface area of incisional edema for 92 dogs that underwent ovariohysterectomy.
Time after surgery | Edema surface area (mm2) | ||||
---|---|---|---|---|---|
Group I (n = 26) | Group II (n = 14) | Group III (n = 21) | Group IV (n = 33) | ||
4 h | 1,186 ± 782 | 1,454 ± 1,036 | 940 ± 692 | 914 ± 621 | 0.15 |
8 h | 1,456 ± 791 | 1,996 ± 1,435 | 1,325 ± 811 | 1,271 ± 672 | 0.104 |
12 h | 1,915 ± 1,243 | 2,015 ± 1,192 | 2,033 ± 1,260 | 1,634 ± 824 | 0.602 |
24 h | 2,072 ± 1,187 | 1,627 ± 1,022 | 2,332 ± 2,146 | 2,094 ± 1,093 | 0.629 |
Suture removal† | 419 ± 170 | 2,664 ± 3,241 | 715 ± 1,004 | 1,446 ± 1,052 | 0.256 |
Comparison of values among treatment groups at each time point; values of P ≤ 0.05 indicate significant differences among groups.
Only 37 of the 92 dogs were available for follow-up examination: 12 dogs in group 1, 6 dogs in group II, 10 dogs in group III, and 9 dogs in group IV.
See Table 1 for remainder of key.
Mean ± SD incisional erythema score for 92 dogs that underwent ovariohysterectomy.
Time after surgery | Erythema score (possible range, 0–3) | ||||
---|---|---|---|---|---|
Group I (n = 26) | Group II (n = 14) | Group III (n = 21) | Group IV (n = 33) | ||
4 h | 1.5 ± 1.0 | 1.7 ± 0.6 | 1.6 ± 0.9 | 1.0 ± 0.6 | 0.017 |
8 h | 1.4 ± 1.0 | 1.6 ± 0.9 | 1.5 ± 1.1 | 1.0 ± 0.6 | 0.089 |
12 h | 1.3 ± 1.0 | 1.1 ± 0.9 | 1.3 ± 1.0 | 1.00 ± 0.7 | 0.647 |
24 h | 1.4 ± 0.9 | 1.4 ± 0.70 | 1.3 ± 1.0 | 0.8 ± 0.6 | 0.028 |
Suture removal† | 0.1 ± 0.3 | 0.3 ± 0.8 | 0.9 ± 0.8 | 0.4 ± 1.1 | 0.126 |
Mean ± SD incisional discharge score for 92 dogs that underwent ovariohysterectomy.
Time after surgery | Discharge score (possible range, 0–3) | ||||
---|---|---|---|---|---|
Group I (n = 26) | Group II (n = 14) | Group III (n = 21) | Group IV (n = 33) | ||
4 h | 0.0 ± 0.2 | 0.0 ± 0.0 | 0.1 ± 0.3 | 0.1 ± 0.4 | 0.317 |
8 h | 0.1 ± 0.3 | 0.1 ± 0.3 | 0.0 ± 0.2 | 0.1 ± 0.3 | 0.776 |
12 h | 0.1 ± 0.4 | 0.2 ± 0.4 | 0.2 ± 0.5 | 0.1 ± 0.3 | 0.927 |
24 h | 0.0 ± 0.2 | 0.2 ± 0.4 | 0.1 ± 0.5 | 0.0 ± 0.0 | 0.245 |
Suture removal† | 0.0 ± 0.0 | 0.2 ± 0.4 | 0.0 ± 0.0 | 0.0 ± 0.0 | 0.185 |
Discussion
In this study, we were unable to demonstrate supplemental analgesia from a bupivacaine incisional block in dogs receiving a multimodal analgesic protocol and undergoing ovariohysterectomy. Furthermore, preincisional infiltration of bupivacaine may have increased the number of complications of surgery. As expected for typical postoperative pain, the composite pain scores decreased in all treatment groups (except the placebo group [preincisional saline solution infiltration]) from 4 to 24 hours after surgery. However, there was no effect of either preincisional or postincisional bupivacaine infiltration on postoperative analgesia when measured with a composite pain score or by mechanical stimulation of the incision.
In a recent study of dogs undergoing a laparotomy, Savvas et al23 were able to demonstrate a significant increase in pain relief for dogs receiving preincisional infiltration with bupivacaine, compared with dogs receiving postincisional infiltration with bupivacaine or saline solution as a placebo. The dogs that received preincisional infiltration required less rescue analgesics, compared with all other treatment groups.23 In the study from Savvas et al,23 dogs underwent a laparotomy for a variety of surgical procedures. Therefore, the amount of soft tissue trauma and the type of tissue manipulated were not the same for each procedure. This should not have been a complicating variable in our study, as all dogs underwent routine ovariohysterectomy. However, in our study, veterinary students performed ovariohysterectomy and their inexperience in tissue handling and proper surgical technique may have introduced a variable in tissue trauma to all treatment groups that may have affected postoperative pain evaluation. Additionally, the use of perioperative NSAIDs and opioids likely decreased the amount of incisional pain, compared with the dogs in the study from Savvas et al.23 This may have decreased postoperative pain to a low enough degree that we could not detect a biological difference among treatment groups. This is supported by the fact that none of the dogs in our study population required rescue analgesia. The dogs in the study reported by Savvas et al23 did not receive an NSAID and only received 1 dose of a narcotic preoperatively, thus allowing a sufficient degree of pain to allow detection of analgesic benefit among treatment groups and increasing the need for rescue analgesics.
While it is still unclear whether somatic or visceral pain predominates following ovariohysterectomy in patients, it is possible that tearing of the suspensory ligaments of the ovaries in dogs might be a more important source of pain than body wall incision after ovariohysterectomy. Thus, application of bupivacaine at the level of the abdominal wall incision will not have a large impact on postoperative pain because it does not address pain originating from the suspensory ligaments of the ovaries. In our study, the ovariohysterectomy was performed by breaking down the suspensory ligaments of the ovaries manually. This maneuver results in tearing the peritoneum and usually results in a response from the anesthetized patient if the level of analgesia is not sufficient, indicating a substantial component of visceral pain during the procedure. Carpenter et al33 demonstrated an improvement in postoperative pain scores in dogs after delivering the bupivacaine both intraperitoneally at the level of the manipulated viscera and incisionally at the level of the manipulated somatic tissue. On the other hand, Bubalo et al34 examined the effects of local anesthetic applied to the ovarian pedicle prior to manipulation during an ovariohysterectomy and found no difference in autonomic responses between the treated and placebo groups and there was no isoflurane-sparing effect to lidocaine treatment.
Dogs present a difficult challenge when assessing pain. Physiologic variables have been shown to be insensitive and inconsistent indicators of pain in dogs.35 Therefore, investigators have relied on behavioral responses to pain, like the Glasgow composite measures pain score, to objectively evaluate postoperative pain. The Glasgow composite measures pain score is a validated assessment of interactive and noninteractive behaviors typically indicative of pain and has been shown to be effective in identifying and characterizing acute postoperative pain.36,37 In our study, we used the Glasgow composite measures pain score (short form) to assess postoperative pain, so as to identify differences among treatment groups.32 This scoring method, however, does not distinguish between somatic (ie, body wall) pain or visceral (ie, organ) pain. As such, we could not separate the incisional pain, treated with bupivacaine infiltration, from the visceral pain. Furthermore, the natural demeanor of a dog may affect the interpretation of the Glasgow pain score despite the component of the scale that does not require interaction with the dog. All dogs in our study were from the humane society and most were friendly. However, there were individuals that were shy and their natural behaviors may have been misinterpreted as pain. Our indication to administer rescue analgesics was based on a Glasgow composite measures pain score > 10, which is higher than the suggested cutoff of 6. This was to avoid confounding variables of rescue narcotics on serial assessments of pain score and von Frey filament tests. The small number of dogs in each of the treatment groups that exceeded 6 on the Glasgow composite measures pain score did not appear to be overly uncomfortable, but rather, the higher number was more likely attributable to their natural demeanor (ie, timid and attempting to avoid human interaction).
Von Frey filaments were also used in an effort to characterize the degree of somatic pain related to the incision and to identify any somatic analgesia imparted by the local anesthetic. The von Frey filaments provide mechanical stimulation to the incision, and their use has been validated as an objective measurement of incisional pain, useful in a variety of species in both a clinical and laboratory setting.38,39 Both an area near the incision and an area remote to the incision are tested, to allow for differentiation between incisional pain and the natural response of the animal to the filaments. However, individuals may respond negatively toward the von Frey filaments placed away from the incision as a result of mechanical hyperalgesia, which has been shown to occur following ovariohysterectomy in dogs.38 To avoid inciting any visceral pain when testing the natural response of the dog to the von Frey filament, the filament was not placed near the insertion of the suspensory ligaments of the ovaries on the abdominal wall.
The overall incidence of complications in this study was not excessively high, especially for surgery performed by veterinary students.40 However, there was a higher rate of complications by the time of suture removal in dogs that received preincisional infiltration of bupivacaine (group III), compared with dogs that received no injection at the incision site (group I). Four of the 6 dogs that had complications were from group III (preincisional infiltration) and included 2 dogs in which the incision appeared healed but excessively inflamed at suture removal, 1 dog with postoperative hernia formation at the level of the linea alba, and 1 dog in which the spleen was lacerated on preincisional injection of the bupivacaine. This higher number of complications in group III does not necessarily indicate that bupivacaine instillation was the reason for each of the reported complications. For instance, the complications in the 2 dogs with excessively inflamed incisions in group III could have been attributed to the anti-inflammatory effects of bupivacaine predisposing to a low-grade infection or they may have been a result of improper tissue handling by veterinary students or suture reaction. Neither of these patients required treatment for their local inflammation. The laceration of the spleen was not a complication due to the bupivacaine itself but, rather, a technical error that should be considered prior to performing any type of injection. The postoperative hernia could have been attributed to poor healing of the linea alba secondary to bupivacaine administration or, more likely, a result of improper technique used by the veterinary student in suturing this layer. In addition, the higher number of complications in group III may be a consequence of a longer incision, rather than actual treatment with a preincisional injection of bupivacaine. Dogs in group III had significantly longer incisions than dogs in the other treatment groups, and this may have represented a greater inexperience of the veterinary students operating on dogs in this group, which could have led to a greater degree of tissue trauma and improper surgical technique. Lastly, while available follow-up data were similar among treatment groups, the numbers of dogs lost to follow-up may have skewed the number of complications. Nonetheless, it is interesting to note that the group not receiving a perioperative injection (group I) did not have any complications. This may indicate that both saline solution and bupivacaine affect wound healing or, alternatively, that a more global problem exists with the injection process itself.
In our study, the degree of edema and discharge were not different among treatment groups. However, the erythema score was significantly higher in group II (placebo group) than other treatment groups at the 4-hour time point and was significantly lower in group IV at the 24-hour time point, compared with other treatment groups. Since the volume of infused bupivacaine or saline solution were similar among treatment groups and the incision length of group II was similar to that of groups I and IV, the postoperative erythema in group II at the 4-hour time point was likely triggered by the mechanical manipulation of the tissue and not by the treatment itself. It is possible that instillation of saline solution naturally incited an inflammatory response. The lower erythema score in group IV at the 24-hour time point could be attributed to the anti-inflammatory properties of bupivacaine, although this effect was not seen in group III.
Potential adverse effects of local anesthetics on the healing of incisions have been documented.24,27 Both in vitro and in vivo studies27–29 have demonstrated that local anesthetics have inherent anti-inflammatory effects, which may be beneficial to healing by preventing an excessive inflammatory response or may have a negative impact on healing by predisposing the incision to delayed healing and infection. Furthermore, in vitro and in vivo studies24–26 have demonstrated that local anesthetics at therapeutic concentrations can cause local toxic effects on muscles. Clinically, the resulting muscle necrosis could lead to muscle dysfunction, increased pain, and potentially hernia formation when the abdominal body wall is involved.24–26 Despite these potentially damaging properties inherent to local anesthetics, there is not yet evidence that anti-inflammatory effects and toxic effects on muscles are of any clinical importance when regional blocks are applied to the body wall. However, most clinical studies24,27 focus on the effects of regional blocks on analgesia for the patient rather than on toxic effects on muscles or anti-inflammatory effects. Therefore, muscle pain may be written off as standard surgical morbidity associated with postoperative pain and toxic effects on muscles secondary to local anesthetics may not be considered or investigated.24 Furthermore, most clinical studies do not follow patients long enough to detect long-term complications associated with healing.27
In conclusion, this study did not detect any additional analgesic benefit of infiltration with bupivacaine at the incision site, either preemptively or following surgery, when used as part of a multimodal analgesic protocol for dogs undergoing routine ovariohysterectomy. While dogs that received a preincisional infiltration of bupivacaine had a higher number of complications, there is no evidence that it was the bupivacaine itself that led to each of the complications. Rather, it appeared that any incisional injection (saline solution or bupivacaine) in this study was associated with a greater number of complications. While the benefit of incisional blocks may still be questionable when used together with other analgesics, there does not appear to be a direct link between infiltration of the incision site with bupivacaine and complications with wound healing.
Bupivacaine hydrochloride injection, Hospira, Lake Forrest, Ill.
22 G × 2-inch BD local anesthesia security bead needle, BD Medical Systems, Franklin Lakes, NJ.
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Appendix
Glasgow composite measures pain scale (short form) for assessing severity of postoperative pain in dogs undergoing ovariohysterectomy.
Situation | Question | Descriptor | Score* |
---|---|---|---|
Look at dog in kennel | Is the dog…? | Quiet | 0 |
Crying or whimpering | 1 | ||
Groaning | 2 | ||
Screaming | 3 | ||
Is the dog…? | Ignoring any wound or painful area | 0 | |
Looking at wound or painful area | 1 | ||
Licking wound or painful area | 2 | ||
Rubbing wound or painful area | 3 | ||
Chewing wound or painful area | 4 | ||
Put lead on dog and lead out of kennel | When rising and walking, is the dog…? | Normal | 0 |
Lame | 1 | ||
Slow or reluctant | 2 | ||
Stiff | 3 | ||
Refusing to move | 4 | ||
Apply gentle pressure 5 cm (2 in) around incisional site | Does the dog…? | Do nothing | 0 |
Look around | 1 | ||
Flinch | 2 | ||
Growl or guard area | 3 | ||
Snap | 4 | ||
Cry | 5 | ||
Overall | Is the dog…? | Happy and content or happy and bouncy | 0 |
Quiet | 1 | ||
Indifferent or nonresponsive to surroundings | 2 | ||
Nervous or anxious or fearful | 3 | ||
Depressed or nonresponsive to stimulation | 4 | ||
Is the dog…? | Comfortable | 0 | |
Unsettled | 1 | ||
Restless | 2 | ||
Hunched or tense | 3 | ||
Rigid | 4 |
Add scores for each question together to get total score.