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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

Objectives

To evaluate the isoflurane sparing effect of intratesticular lidocaine administration in dogs undergoing castration.

Methods

Thirty dogs received a standardised anaesthetic regimen including systemic analgesia with intramuscular buprenorphine at a dose of 0·02 mg/kg and intravenous carprofen at a dose of 4 mg/kg. Dogs were randomly assigned to a lidocaine group receiving 1 mg/kg lidocaine into each testis or a control group receiving no lidocaine. Baseline physiological parameters were measured after 10 minutes at an end-tidal isoflurane concentration of 1·3%. End-tidal isoflurane concentration was altered throughout surgery to maintain these parameters within 10% of baseline and recorded at five time points. T0 was baseline, T1 was the start of surgery, T2 to T3 were clamping of the testicular pedicles and T4 was skin closure. End-tidal isoflurane concentrations were compared using analysis of variance and Bonferroni tests.

Results

Fifteen healthy dogs were included in each study group. End-tidal isoflurane concentration was significantly lower in the lidocaine group compared to the control group at T2 (P<0·01), T3 (P<0·01) and T4 (P<0·01).

Clinical Significance

Intratesticular lidocaine reduces isoflurane requirements in dogs undergoing castration.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

Castration is one of the most commonly performed surgeries in general practice in the UK and is considered to be a moderately painful procedure (Dohoo and Dohoo 1996, Raekallio and others 2003, Hewson and others 2006). One survey (Capner and others 1999) reported that only 30% of veterinary surgeons administered analgesia to dogs undergoing castration. Almost all the analgesia administered was systemic, with 27% administering only a non-steroidal anti-inflammatory drug (NSAID), 50% administering only an opioid and 23% administering an NSAID and an opioid. The use of local anaesthetic agents has been shown to have benefits over systemic analgesia in human anaesthesia (Bonnet and Marret 2005). Several studies have shown that the administration of lidocaine either into the testes or spermatic cord decreases pain and nocifensive responses associated with castration in horses (Haga and others 2006, Portier and others 2009), piglets (McGlone and Hellman 1988, White and others 1995, Haga and Ranheim 2005, Ranheim and Haga 2006), lambs (Wood and others 1991, Dinniss and others 1997, Molony and others 1997) and calves (Stafford and others 2002). No studies have investigated the effect of intratesticular lidocaine administration in dogs undergoing elective castration.

This study was designed to examine the effect of intratesticular lidocaine on intraoperative nocifensive responses through assessment of an isoflurane sparing effect in dogs undergoing elective castration, receiving an anaesthetic protocol which is commonly used in general practice.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

The study protocol was approved by the local ethics committee. Dogs between six months and eight years of age admitted for elective castration were eligible for inclusion. Animals judged to be healthy upon clinical examination by the lead investigator were included (American Society of Anesthesiologists’ classification I or II). Exclusion criteria included aggressive temperament, extreme anxiety, pre-existing behaviour indicative of pain and previous adverse reaction to NSAIDs. All dogs had their age, bodyweight (BW) and body condition score (out of nine) recorded (Laflamme 1997). All dogs were treated as day-patients, being admitted before 09.00 hours and discharged between 16.00 and 18.00 hours the same day. Owners were asked to fast dogs from midnight the night before surgery but water was not restricted.

Dogs were premedicated with 0·03 mg/kg acepromazine (ACP injection 2 mg/mL, Novartis Animal Health) and 0·02 mg/kg buprenorphine (Vetergesic, Alstoe Animal Health) injected into the cervical epaxial muscles. After 30 to 40 minutes, a 20 to 22 SWG catheter (Optiva, Medex) was placed into a cephalic vein. Anaesthesia was induced with 2 to 4 mg/kg propofol (Propoflo, Abbott Animal Health) given intravenously (iv) to effect over 45 to 60 seconds to allow orotracheal intubation with a cuffed endotracheal tube. Dogs weighing under 10 kg BW were connected to a Bain breathing system with a fresh gas flow of twice the estimated minute volume (200 mL/kg×BW kg). This flow was increased or decreased to a rate just over the point where rebreathing could be observed on the capnograph. Dogs weighing over 10 kg BW were connected to a circle breathing system with a fresh gas flow of 4 L/min. Anaesthesia was maintained with isoflurane (Isoflo, Abbott Animal Health) vapourised in oxygen. Hartmann's solution (Vetivex 11, Dechra Veterinary Products) was given at a rate of 10 mL/kg/hour iv throughout surgery. Carprofen 4 mg/kg iv (Rimadyl Small Animal Solution for Injection 5%, Pfizer) was administered to all dogs after the induction of anaesthesia.

In addition to clinical monitoring, the electrocardiogram (ECG), respired gases [including capnography and end-tidal isoflurane (E'Iso) concentrations], pulse oximetry and oesophageal temperature were monitored continuously via a multi-parameter monitor (S/5, Datex Ohmeda). The monitor was fully calibrated as per the manufacturer's instructions before the start of the trial period. Estimation of systolic blood pressure (SBP) was performed using a Doppler blood flow detector (Ultrasonic Doppler Flow Detector; Model 811-B, Parks Medical Electronics), with an occlusive cuff and sphygmomanometer. The palmar carpal artery was used for all readings and the occlusive cuff, width of approximately 40% limb circumference, was placed immediately proximal to the carpus. Heart rate (HR), respiratory frequency (ƒR), Doppler SBP, end-tidal carbon dioxide (PE'CO2) and E'Iso concentration, arterial blood oxygen saturation (SpO2) and isoflurane vapouriser setting were recorded every 5 minutes and at each of the experimental time points. Body temperature was maintained between 37°C and 38°C using hot air blankets (Bair Hugger Model 505, Augustine Medical) and heat pads (Hot Dog Patient Warming System, Hot Dog International).

Initially, vapouriser settings were adjusted until the E'Iso concentration had remained at 1·3% for 10 minutes. This was considered to be baseline and the initial experimental measurements (HR, SBP, ƒR and PE'CO2) were made at this point. During this period patients were prepared for prescrotal castration in a routine aseptic manner, which included preparation of the scrotum. Dogs were randomly assigned to two treatment groups: a lidocaine group and a control group (block randomised to give two equal group sizes). Dogs in the lidocaine group received a slow injection of 1 mg/kg lidocaine (2% lidocaine hydrochloride, B Braun Melsungen) into the body of each testis using a 1″ 22-SWG hypodermic needle and appropriate sized syringe. This is equivalent to 1 mL/20 kg BW/testis of 2% lidocaine solution. The lidocaine injection was stopped if pressure within the testis was subjectively considered to be excessive by digital palpation (i.e. if testis became firm and swollen). Dogs in the control group received no additional treatment. Throughout anaesthesia, vapouriser settings were adjusted in order to maintain cardiovascular parameters and PE'CO2 within 10% of these baseline values. Where the baseline ƒR was below 10, ƒR rate was maintained at baseline ±1 breath per minute and, where ƒR was between 10 and 20, ƒR rate was maintained between baseline ±2 breaths per minute. A period of 1 minute was given in order for patients to stabilise at the new isoflurane concentration. In those animals connected to a circle breathing system the reservoir bag was emptied into the scavenging system after every vapouriser change. Appropriate anaesthetic depth was ensured throughout anaesthesia by regular assessment of jaw tone, eye position and palpebral reflex. Experimental readings (HR, SBP, ƒR, PE'CO2 and E'Iso concentration) for statistical comparison were taken at five time points throughout anaesthesia as follows; T0 was baseline, T1 was after the first skin incision, T2 and T3 were after the clamping of first and second testicular pedicles, respectively, and T4 was the point at which the first skin suture was placed. Immediately before skin closure, animals in the lidocaine group received a further 1 mg/kg lidocaine applied as an incisional splash block to the surgical wound. If at any point during surgery an E'iso concentration of over 2·1% was required, rescue analgesia was to be provided with 1 µg/kg fentanyl iv.

All surgeries were performed by a final-year veterinary student supervised by a surgery resident or senior surgeon.

Unblinded postoperative pain scores were assessed by the anaesthetist before discharge from the hospital 5 to 6 hours after surgery using the short form of the Glasgow Composite Pain Scale for dogs.

Additional analgesia (0·02 mg/kg buprenorphine im) was administered to all dogs at the time of discharge.

Statistical Analysis

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

A sample size calculation was performed on pilot data (five dogs per group) to determine the number of cases required to give a power of 80% (1−β=0·8), with clinical significance considered to be a reduction in E'Iso by at least 20%. Data sets were tested for normality using the D'Agostino-Pearson normality test. Normally distributed data are presented as mean and standard deviation (mean ±sd). Non-normally distributed data are presented as median and interquartile range (median, IQR). Single measures were compared between groups using a Student's t test for normal data or a Mann–Whitney U test for non-normal data. E'Iso levels were analysed using a repeated-measures two-way analysis of variance (ANOVA). Bonferroni post hoc tests were used to assess differences between groups at individual time points. Significance was set at the 5% level (α=0·05). A standard computer statistics package (Graphpad Prism, Graphpad Software Inc) was used for all data analyses.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

The sample size calculation revealed that 10 dogs per group were required to achieve a power of 80%. Because of the randomisation system used in the study, additional numbers of dogs were required in order to give equal group sizes. The first point where group sizes were even was when 30 dogs had been enrolled into the trial (15 per group). No statistically significant differences were observed between the treatment groups with regard to age (P=0·66), BW (P=0·71), BCS (P=0·39) and baseline measurements of HR (P=0·92), SBP (P=0·24), ƒR (P=0·83) and PE'CO2 (P=0·37) (Table 1).

Table 1. Animal data and baseline (T0) physiological variables for both groups
Patient variableLidocaine groupControl group
  1. IQR Interquartile range, PE'CO2 End-tidal carbon dioxide

Mean (±sd) age (years)2·1 (±1·9)1·8 (±1·7)
Mean (±sd) bodyweight (kg)18·0 (±11·2)15·3 (±13·6)
Mean (±sd) body condition score5·2 (±0·8)5·0 (±0·6)
Mean (±sd) baseline heart rate (beats/minute)90·7 (±18·1)91·2 (±12·0)
Median (IQR) baseline Doppler systolic blood pressure (mmHg)96 (92, 110)102 (96, 115)
Median (IQR) baseline respiratory rate (breaths/minute)8 (6, 12)9 (6, 17)
Mean (±sd) baseline PE'CO2 (mmHg)49·3 (±5·9)47·5 (±5·4)

E'Iso levels were significantly higher than baseline at time points T1, T2, T3 and T4 in both groups. There were no statistically significant differences in E'Iso concentration between the lidocaine group and control group at T0 or T1 (Fig 1). E'Iso concentration was significantly lower in the lidocaine group compared to the control group at T2 (P<0·01), T3 (P<0·01) and T4 (P<0·01) (Fig 1). There were no statistically significant differences in E'Iso concentration between T1 and T4 in the lidocaine group, whereas E'Iso concentration at T2 to T4 was significantly higher than at T1 (P<0·01 for all comparisons) in the control group. No dogs in the trial required rescue analgesia during anaesthesia.

image

Figure 1. Columns define mean E'Iso % and bars define standard deviation. *denotes statistically significant difference between groups (P<0·01)

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A number of adverse effects were observed following intratesticular injection but none were considered of any clinical significance. Although no injection was stopped because of excessive intratesticular pressure and no increase in haemorrhage at the surgical site was noted, a spot of blood on the scrotal skin following injection in all cases and mild haematoma formation and/or haemorrhage within the tunica or testis in 9 of 30 (30%) of injected testes were observed.

Postoperative pain scores before discharge were significantly lower (P=0·01) in the lidocaine group (median 3, IQR 2 to 4) compared to the control group (median 5, IQR 4 to 7). In the control group, 7 of 15 (47%) pain scores were at a level that would warrant the administration of additional analgesia (pain score >6) compared with 1 of 15 (7%) in the lidocaine group.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

The administration of intratesticular lidocaine reduced the inhaled anaesthetic requirements of dogs undergoing castration in this study population. There were increased isoflurane requirements in both groups following initial skin incision which is unsurprising as intratesticular lidocaine is unlikely to desensitise prescrotal skin. Further increases in isoflurane requirements occurred in the control group following retraction of the testicles (T2 and T3), whereas they did not significantly change in the lidocaine group. This suggests that intratesticular lidocaine is highly effective at blocking nocifensive autonomic responses to testicular retraction.

The combination of NSAID and opioid used in the anaesthetic protocol is considered by the authors to be an effective analgesic combination for procedures associated with mild to moderate pain, so it was perhaps surprising that the use of lidocaine made such a difference to isoflurane requirements. Minimal adverse effects were noted following intratesticular injection; haematoma or haemorrhage formation was mild and was not considered to be clinically significant as the testes were destined for removal. These results suggest that this technique can make a clinically and statistically significant contribution to intraoperative analgesia.

This study was designed to include an anaesthetic protocol that is commonly used in general practice. ACP, a phenothiazine derivative, is the most widely used pre-anaesthetic sedative in general practice in the UK (Brodbelt 2006) and is commonly given with an opioid to provide neuroleptanalgesia. Buprenorphine, a relatively long-acting, partial μ-opioid receptor agonist licensed in the UK to provide analgesia in dogs, is typically used. Propofol and isoflurane are the most commonly used induction and maintenance agents, respectively (Brodbelt 2006), but neither have intrinsic analgesic properties. Carprofen was chosen as the NSAID and incorporated into the anaesthetic protocol, since NSAIDs are commonly prescribed for analgesia in dogs undergoing elective castration (Capner and others 1999). It was felt that the protocol used in this study was an appropriate reflection of techniques used in general practice in the UK and therefore met the considered objectives. Time points were chosen to correspond with the beginning and end of surgical stimulus and the points of maximal surgical stimulation and nociceptive response (Taylor and Weary 2000).

To exert its antinociceptive effect, lidocaine must be distributed proximally to the point where the noxious stimulus occurs, in this case clamping of the testicular pedicle. It has been shown that intratesticular lidocaine distributes rapidly into the spermatic cord of the horse (Haga and others 2006) and that a noticeable antinociceptive effect is seen within 10 minutes of administration in piglets (Ranheim and others 2003, Haga and Ranheim 2005). In fact, an auto-radiographic study in pigs, in which 1% lidocaine with 5 µg/mL epinephrine was administered into the body of the testis, demonstrated that lidocaine concentrations in the spermatic cord were greater 3 minutes after injection compared to 10 minutes after injection (Ranheim and others 2005). This implies that the peak of local anaesthetic effect may have been missed in this study. Therefore, we believe that the analgesia seen with this procedure is achievable even in a busy general practice situation because lidocaine can be administered during the clipping and aseptic preparation of the surgical site.

The lower isoflurane requirements observed in the lidocaine group could have been due to systemic absorption of lidocaine. Intravenous lidocaine administration has been shown to decrease the minimum alveolar concentration of isoflurane in dogs (Valverde and others 2004). As a result of the rapid distribution of lidocaine from the testis (Ranheim and others 2005) it is possible that systemic absorption of lidocaine occurred in this study. However, this phenomenon is unlikely to have had a significant effect because systemic uptake ought to have also reduced the isoflurane requirements at the initial skin incision, which was not demonstrated. Also, in horses that received intratesticular lidocaine, a large proportion of the drug has been shown to remain in the removed testes (Haga and others 2006). Therefore, it is likely that the lidocaine was working at a local rather than systemic level.

There are several limitations to this study. A reduced E'Iso concentration was used as a surrogate measure for an improved level of analgesia. The benefits of this measurement are that it is easy to perform, allows simple comparisons to be made and utilises readily available technology. The major disadvantage is that any perceived lowering of end-tidal anaesthetic concentrations does not necessarily correspond with reduced nociception (Quasha and others 1980, Webb and O'Brien 1988). Individual sensitivities to isoflurane or the other sedative and analgesic drugs used may mean that at any given end-tidal anaesthetic concentration, one dog may be in a far deeper plane of anaesthesia than another. Clinically all the animals appeared to be at a similar plane of anaesthesia but this is a qualitative not quantitative assessment. However, the similar E'Iso levels between the groups at the first surgical cut can be considered to imply that the level of anaesthesia in each case was similar, at the level required to inhibit autonomic nocifensive responses to noxious stimuli to within 10% of baseline. We, therefore, feel that there was little difference in depth of anaesthesia between the groups.

Body temperature can also affect an individual's sensitivity to inhaled anaesthetic agents. This may therefore lead to a reduced response to noxious surgical stimuli and a perceived improvement in analgesia in such animals. However, the maintenance of patient body temperature between 37°C and 38°C should have helped to reduce the impact of this phenomenon on the results.

There is likely to be an element of dilution of end-tidal gas with fresh gas in smaller patients on a Bain breathing system and this will affect the accuracy of the measured end-tidal partial pressures. Randomisation ensured distribution of smaller dogs to both groups (three in the lidocaine group and four in the control group) which would spread any effect across the study population. Therefore, we believe that the effect on results is likely to be minimal.

Another criticism of this study is that the lead investigator was not blinded to the treatment groups. To render the anaesthetist unaware of the subject allocation, one option would have been to administer a placebo intratesticular injection of an equivalent volume of saline to mimic the administration of lidocaine. This option was considered by the investigators but would not have benefited the individual animal. In addition, because intratesticular injections can cause nocifensive responses in themselves, it was not considered to be ethically acceptable. It was also felt to be unnecessary during anaesthesia because changes in isoflurane concentration were prescription-based, i.e. they were altered to maintain cardiovascular and respiratory parameters within 10% of baseline. Another option would be for the lead investigator to leave the room whilst any treatment was being administered. This was not possible as all dogs that received the lidocaine injections developed a small haemorrhage (generally a single drop of blood) on the skin surface which could be easily observed on the investigator's return. This was even noticeable when the testes were covered with a sterile swab in an attempt to hide the injection sites.

Despite the lack of blinding, we have reported the postoperative pain scores as the pain scoring system used in this study is considered to be relatively objective, reproducible and robust (Holton and others 2001, Morton and others 2005, Reid and others 2007, Murrell and others 2008). Despite this there remains a considerable potential for observational bias, so in the light of this limitation these results should be viewed with a degree of scepticism. A further study assessing postoperative pain in a more stringent blinded manner is warranted before the method's true effect on postoperative analgesia can be properly evaluated.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

These results suggest that intratesticular lidocaine is a useful analgesic technique in dogs undergoing elective castration and should be considered as an adjunct to standard anaesthetic practice. Further studies are required before any longer-term benefit can be established.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

The primary author is a Petsavers Sponsored Senior Clinical Training Scholar in Anaesthesia and Analgesia. The study has been fully funded by Petsavers. The study passed both the University and Petsavers ethics committees.

Conflict of interest

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References

None of the authors of this article has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Statistical Analysis
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. Conflict of interest
  11. References
  • Bonnet, F. & Marret, E. (2005) Influence of anaesthetic and analgesic techniques on outcome after surgery. British Journal of Anaesthesia 95, 52-58
  • Brodbelt, D. C. (2006) The confidential enquiry into perioperative small animal fatalities. PhD Thesis, Royal Veterinary College, University of London
  • Capner, C. A., Lascelles, B. D. X. & Waterman-Pearson, A. E. (1999) Current British veterinary attitudes to perioperative analgesia for dogs. Veterinary Record 145, 95-99
  • Dinniss, A. S., Mellor, D. J., Stafford, K. J., Bruce, R. A. & Ward, R. N. (1997) Acute cortisol responses of lambs to castration using a rubber ring and/or a castration clamp with or without local anaesthetic. New Zealand Veterinary Journal 45, 114-121
  • Dohoo, S. E. & Dohoo, I. R. (1996) Factors influencing the post operative use of analgesics in dogs and cats by Canadian Veterinarians. Canadian Veterinary Journal 37, 552-556
  • Haga, H. A. & Ranheim, B. (2005) Castration of piglets: the analgesic effects of intratesticular and intrafunicular lidocaine injection. Veterinary Anaesthesia and Analgesia 32, 1-9
  • Haga, H. A., Lykkjen, S., Revold, T. & Ranheim, B. (2006) Effect of intratesticular injection of lidocaine on cardiovascular responses to castration in isoflurane-anesthetized stallions. American Journal of Veterinary Research 67, 403-408
  • Hewson, C. J., Dohoo, I. R. & Lemke, K. A. (2006) Perioperative use of analgesics in dogs and cats by Canadian veterinarians in 2001. Canadian Veterinary Journal 47, 352-359
  • Holton, L., Reid, J., Scott, E. M., Pawson, P. & Nolan, A. (2001) Development of a behaviour based scale to measure acute pain in dogs. Veterinary Record 148, 525-531
  • Laflamme, D. (1997) Development and validation of a body condition score system for dogs: a clinical tool. Canine Practice 22, 10-15
  • Mcglone, J. J. & Hellman, J. M. (1988) Local and general anesthetic effects on behavior and performance of two- and seven-week-old castrated and uncastrated piglets. Animal Science 66, 3049-3058
  • Molony, V., Kent, J. E., Hosie, B. D. & Graham, M. J. (1997) Reduction in pain suffered by lambs at castration. Veterinary Journal 153, 205-213
  • Morton, C. M., Reid, J., Scott, E. M., Holton, L. L. & Nolan, A. M. (2005) Application of a scaling model to establish and validate an interval level pain scale for assessment of acute pain in dogs. American Journal of Veterinary Research 66, 2154-2165
  • Murrell, J. C., Psatha, E. P., Scott, E. M., Reid, J. & Hellebrekers, L. J. (2008) Application of a modified form of the Glasgow pain scale in a veterinary teaching centre in the Netherlands. Veterinary Record 162, 403-408
  • Portier, K. G., Jaillardon, L., Leece, E. A. & Walsh, C. M. (2009) Castration of horses under total intravenous anaesthesia: analgesic effects of lidocaine. Veterinary Anaesthesia and Analgesia 36, 173-179
  • Quasha, A. L., Eger, E. I. & Tinker, J. H. (1980) Determination and applications of MAC. Anesthesiology 53, 315-334
  • Raekallio, M., Heinonen, K. M., Kuussaari, J. & Vainio, O. (2003) Pain alleviation in animals: attitudes and practices of Finnish veterinarians. Veterinary Journal 165, 131-135
  • Ranheim, B. & Haga, H. A. (2006) Local anaesthesia for pigs subject to castration. Acta Veterinaria Scandinavica 48(Suppl 1), S13
  • Ranheim, B., Haga, H. A., Andresen, Ø. & Ingebrigtsen, K. (2003) Distribution of radioactive lidocaine injected into the testes in piglets: preliminary results. Proceedings of the 8th World Congress of Veterinary Anaesthesia. Knoxville, TN, USA. p 59. Veterinary Anaesthesia and Analgesia 31
  • Ranheim, B., Haga, H. A. & Ingebrigsen, K. (2005) Distribution of radioactive lidocaine injected into the testis in piglets. Journal of Veterinary Pharmacology and Therapeutics 28, 481-483
  • Reid, J., Nolan, A. M., Hughes, J. M. L., Lascelles, D., Pawson, P. & Scott, E. M. (2007) Development of the short-form of the Glasgow Composite Measure Pain Score (CMPS-SF) and derivation of an analgesic intervention score. Animal Welfare 16, 97-104
  • Stafford, K. J., Mellor, D. J., Todd, S. E., Gregory, N. G., Bruce, R. A. & Ward, R. N. (2002) Effects of local anaesthesia or local anaesthesia plus a non-steroidal anti-inflammatory drug on the acute cortisol response of calves to five different methods of castration. Research in Veterinary Science 73, 61-70
  • Taylor, A. & Weary, D. (2000) Vocal responses of piglets to castration: identifying procedural sources of pain. Applied Animal Behavioral Science 70, 17-36
  • Valverde, A., Doherty, T. J., Hernandez, J. & Davies, W. (2004) Effect of lidocaine on the minimum alveolar concentration of isoflurane in dogs. Veterinary Anaesthesia and Analgesia 31, 264-271
  • Webb, A. I. & O'brien, J. M. (1988) The effect of acepromazine maleate on the anesthetic potency of halothane and isofurane. Journal of the American Animal Hospital Association 24, 609-613
  • White, R. G., Deshazer, J. A., Tressler, C. J., Borcher, S., Davey, A. & Waninge, A. M. (1995) Vocalization and physiological response of pigs during castration with or without a local anesthetic. Journal of Animal Science 73, 381-386
  • Wood, G. N., Molony, V., Fleetwood-Walker, S. M., Hodgson, J. C. & Mellor, D. J. (1991) Effects of local anesthesia and intravenous naloxone on the changes in behaviour and plasma concentration of cortisol produced by castration and tail docking with tight rubber rings in young lambs. Research in Veterinary Science 51, 193-199