Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse

Comparison of Xylazine and Lidocaine Infusion versus Medetomidine Continuous Rate Infusion during General Anesthesia with Isoflurane in Horses Undergoing Emergency Laparotomy

(1) The main goals of general anesthesia include pain management and a safe anesthetic protocol for smooth recovery. In this retrospective study, we compared two anesthetic protocols for general anesthesia with isoflurane during emergency laparotomy: sedation with xylazine and the intraoperative infusion of lidocaine (X group) versus medetomidine as a preoperative sedation and intraoperative infusion (M group). (2) The medical records of horses who underwent emergency laparotomies between 2016 and 2023 were reviewed. According to the anesthetic protocol, patients were allocated to the X or M groups. Data about the horse, signalment, history, and anesthetic variables were analyzed. (3) Group X had a significantly higher heart rate (HR), lower respiratory rate (RR) and mean and diastolic arterial pressure (MAP/DAP). A progressive increase in HR and RR was observed in both groups. Group X underwent a decrease in RR and an increase in DAP. In Group M, a decrease in MAP and DAP was observed. Group M exhibited a longer recovery time with similar recovery scores. Both protocols provided safe anesthesia for emergency laparotomy, with minor cardiovascular and respiratory depression. Minor respiratory depression was detected when xylazine was used, while recovery was longer with medetomidine.

Pain Mitigation Strategies for Disbudding in Goat Kids

Pain mitigation strategies for disbudding in goat kids have gained significant attention in recent years because of growing concerns for animal welfare. Disbudding, the removal of horn buds in young goats, is a common practice to enhance safety and manage herd dynamics. However, the procedure will cause pain and distress if not managed effectively. This review covers the array of pain mitigation techniques currently available for disbudding, including the efficacy of these strategies in reducing pain and stress during the disbudding process, with specific attention to the potential toxicity associated with local anesthetics. The current best practice for disbudding on the farm suggests sedation/analgesia with an alpha-2 agonist, the placement of a two-point cornual nerve block, and then an NSAID for postoperative pain. In conclusion, this review offers recommendations for future research directions aimed at enhancing the welfare of young goats subjected to the disbudding procedure. These suggestions hold the promise of fostering significant improvements in the overall well-being of these animals.

Lidocaine constant rate infusion in isoflurane anesthetized neonatal foals

Introduction

In horses, lidocaine infusion is administered intraoperatively for analgesia and for a reduction of inhalant anaesthetic requirement. The objective of the study was to describe the anaesthetic effects of lidocaine infusion in isoflurane anaesthetised foals.

Methods

Twelve foals (<3 weeks old) undergoing surgery were included in the study (LIDO group). Foals were premedicated with midazolam and butorphanol IV, anaesthesia was induced with ketamine and propofol IV and maintained with isoflurane. Lidocaine was administered intraoperatively at 0.05 mg/kg/min. Also, the anaesthetic records of 11 foals in which lidocaine was not administered intraoperatively were retrospectively evaluated and they were considered as a historical control group (HC). Heart rate (HR), mean arterial pressure (MAP) and fraction of expired isoflurane were monitored continuously. Time of extubation, time to reach sternal recumbency and standing were recorded. The quality of recovery was assessed.

Results

HR decreased in both groups compared with baseline values and intraoperatively the differences were statistically significant (p = 0.01 and p = 0.03 respectively in the LIDO and HC groups). Intraoperatively the HR was significantly lower in the LIDO group (71.2 ± 13.4 bpm) compared with the HC group (87.1 ± 17.7 bpm) (p = 0.0236). The number of foals requiring inotropic support (LIDO n = 7 and HC n = 9) was not statistically associated with the treatment group (p = 0.371). The extubation time, the time to reach the sternal recumbency and the quality of recovery did not differ significantly between the two groups (p = 0.7 and p = 0.6 respectively).

Discussion

In conclusion, in anaesthetised foals the addition of lidocaine does not provide a sparing effect on isoflurane requirement, and it does not interfere with the quality of recovery, however it decreases significantly the HR, which is pivotal in foals for the maintenance of cardiac output and peripheral perfusion. Therefore, a continuous patient monitoring is essential.

Preliminary Investigation of Side Effects of Polymyxin B Administration in Hospitalized Horses

Neuro- and nephrotoxicity of polymyxins are known but clinical studies in horses are lacking. The aim of this study was to describe neurogenic and nephrogenic side effects of hospitalized horses receiving Polymyxin B (PolyB) as part of their treatment plan. Twenty horses diagnosed with surgical colic (n = 11), peritonitis (n = 5), typhlocolitis (n = 2), pneumonia, and pyometra (each n = 1) were included. Antimicrobial treatment was randomized to GENTA (gentamicin 10 mg/kg bwt q24 h IV, penicillin 30.000 IU/kg q6 h IV) or NO GENTA (marbofloxacin 2 mg/kg bwt q24 h IV, penicillin 30.000 IU/kg q6 h IV). The duration of PolyB treatment ranged from 1 to 4 days. Clinical and neurological examinations were performed, and serum PolyB concentrations were measured daily during and three days following PolyB treatment. Urinary analysis, plasma creatinine, urea and SDMA were assessed every other day. Video recordings of neurological examinations were graded by three blinded observers. All horses showed ataxia during PolyB treatment in both groups (median maximum ataxia score of 3/5, range 1-3/5). Weakness was detected in 15/20 (75%) horses. In 8/14 horses, the urinary γ-glutamyltransferase (GGT)/creatinine ratio was elevated. Plasma creatinine was mildly elevated in 1/16 horses, and SDMA in 2/10 horses. Mixed-model analysis showed a significant effect of time since last PolyB dose (p = 0.0001, proportional odds: 0.94) on the ataxia score. Ataxia and weakness should be considered as reversible adverse effects in hospitalized horses receiving PolyB. Signs of tubular damage occurred in a considerable number of horses; therefore, the nephrotoxic effect of polymyxins should be considered and urinary function monitored.

Safety and accuracy of blind vs. ultrasound‐guided dorsal retrobulbar nerve blocks in horses—A cadaveric study

OBJECTIVE

There is limited knowledge regarding the safety and accuracy of ultrasound-guided retrobulbar nerve blocks in horses. The aim of this study was to compare these parameters between blind and ultrasound-guided injection techniques for the dorsal retrobulbar nerve block in horses.

METHODS

Equine cadaver heads were used to inject the retrobulbar space with contrast medium (CM). Injections were performed either blindly based on anatomic landmarks (blind group, n = 44) or under ultrasonographic guidance (US-group, n = 44), equally divided between an experienced and unexperienced operator. Needle position and distribution of CM were assessed with computed tomography imaging and evaluated by a board-certified veterinary diagnostic imager blinded to the technique. Safety and accuracy of both techniques were compared.

RESULTS

Ocular penetration was observed in two cases (n = 2/44) in the blind group but not in the US group (n = 0/44). No intrathecal, intraneural, or intravascular injections were seen in either group. Safety was significantly improved in the US group (p = .026). There was no statistically significant difference between the groups regarding the accuracy of the injection. Excellent accuracy was achieved more often with the ultrasound-guided technique (n = 11/22) than with the blind technique (n = 7/22) when performed by the unexperienced operator, but this difference was not statistically significant.

CONCLUSION

To prevent globe-threatening complications and improve the safety of the injection, we recommend using the ultrasound-guided injection technique for the dorsal retrobulbar nerve block.

Clinical effects and pharmacokinetics of nebulized lidocaine in healthy horses

Background

Nebulized lidocaine appears promising as a novel corticosteroid-sparing therapeutic for equine asthma, but its safety and pharmacokinetic behavior have yet to be confirmed.

Objective

To describe the effect of nebulized lidocaine on upper airway sensitivity, lung mechanics, and lower respiratory cellular response of healthy horses, as well as delivery of lidocaine to lower airways, and its subsequent absorption, clearance, and duration of detectability.

Animals

Six healthy university- and client-owned horses with normal physical examination and serum amyloid A, and no history of respiratory disease within 6 months.

Methods

Prospective, descriptive study evaluating the immediate effects of 1 mg/kg 4% preservative-free lidocaine following nebulization with the Flexineb^®. Prior to and following nebulization, horses were assessed using upper airway endoscopy, bronchoalveolar lavage, and pulmonary function testing with esophageal balloon/pneumotachography and histamine bronchoprovocation. Additionally, blood and urine were collected at predetermined times following single-dose intravenous and nebulized lidocaine administration for pharmacokinetic analysis.

Results

Upper airway sensitivity was unchanged following lidocaine nebulization, and no laryngospasm or excessive salivation was noted. Lidocaine nebulization (1 mg/kg) resulted in a mean epithelial lining fluid concentration of 9.63 ± 5.05 μg/mL, and a bioavailability of 29.7 ± 7.76%. Lidocaine concentrations were higher in epithelial lining fluid than in systemic circulation (C_max 149.23 ± 78.74 μg/L, C_ELF:C_maxplasma 64.4, range 26.5–136.8). Serum and urine lidocaine levels remained detectable for 24 and 48 h, respectively, following nebulization of a single dose. Baseline spirometry, lung resistance and dynamic compliance, remained normal following lidocaine nebulization, with resistance decreasing post-nebulization. Compared to the pre-nebulization group, two additional horses were hyperresponsive following lidocaine nebulization. There was a significant increase in mean airway responsiveness post-lidocaine nebulization, based on lung resistance, but not dynamic compliance. One horse had BAL cytology consistent with airway inflammation both before and after lidocaine treatment.

Conclusions

Nebulized lidocaine was not associated with adverse effects on upper airway sensitivity or BAL cytology. While baseline lung resistance was unchanged, increased airway reactivity to histamine bronchoprovocation in the absence of clinical signs was seen in some horses following nebulization. Further research is necessary to evaluate drug delivery, adverse events, and efficacy in asthmatic horses.

Retrograde Approach to Maxillary Nerve Block: An Alternative in Orofacial Surgeries in Horses

Simple Summary

Maxillary nerve (MN) desensitization can improve quality and safety of orofacial surgeries in horses, especially when a standing procedure is elected. The purpose of this retrospective study is to report results from 15 horses undergoing orofacial surgery which received an MN block with the retrograde approach within the infraorbital canal. The same technique was used in horses scheduled for orofacial surgeries and grouped as requiring general anesthesia or standing analgo-sedation. From the retrieved anesthetic records, regardless of the group, clinical and physiological parameters continuously monitored during surgery were stable, and none of the horses showed complications during or after the block. These results confirm the feasibility of this loco-regional anesthetic technique as a valid approach to the MN without risk of damaging periorbital structures, which is reported with traditional techniques. Evident landmarks for this approach and limited chances to injure vital structures enclosed within the infraorbital canal make the operator experience less relevant than the ability required to block the MN according to approaches, which currently aim at the pterygopalatine fossa. This substantiates the retrograde approach to block the MN is safe and easy to perform in horses undergoing orofacial surgeries at regions where this nerve provides sensory innervation.

Abstract

The aim of this study was to retrospectively report outcomes resulting from the approach to the maxillary nerve block (MNB) through the infraorbital canal, in terms of needles selection, drawbacks or side effects during or after block execution, and analgesic efficacy leading to clinical and cardiovascular stability during surgery. Anesthetic records of 15 horses undergoing orofacial surgery in standing analgo-sedation (STA, n = 6) and in general anesthesia (GEN, n = 9) were retrieved and analyzed. Horses in group STA required surgery for dental extraction, nasal polyp resection and maxillary/frontal sinusitis. Horses in group GEN underwent surgery for fronto-maxillary, nasal and dental diseases. Size 19 and 20 G Tuohy needles were used in adult horses weighing 350–600 kg, while size 21 and 22 G were used in younger horses or ponies. None of the horses in both groups showed complications related to the block and physiological parameters were stable and within normal ranges during surgery; overall, an adequate anesthetic/sedation depth was achieved. Our results confirm the in vivo applicability of the MNB approached within the infraorbital canal, which had been described only on cadaveric specimens. The retrograde technique resulted in a valid and easy approach to the maxillary nerve that avoids damage to periorbital structures and side effects reported with traditional techniques.

Ventricular arrhythmias in horses: Diagnosis, prognosis and treatment

Ventricular arrhythmias (VAs) are often incidental or coincidental with systemic disease. Ventricular arrhythmias are also the most likely cause of many sudden cardiac deaths in horses. This dichotomy creates challenges in the management of horses with VAs. This review presents current knowledge of diagnosis, prognosis and treatment of VAs in horses.

Systemic and local effects of lidocaine or mepivacaine when used for intravenous regional anaesthesia of the distal limb in standing sedated horses

BACKGROUND

Local anaesthetics are being combined clinically with amikacin in intravenous regional limb perfusion (IVRLP), with limited knowledge on the analgesia provided and its onset and duration of action after tourniquet application and release.

OBJECTIVE

To evaluate the systemic clinical effect, limb withdrawal to nociceptive stimulation, and plasma and synovial fluid concentrations after IVRLP with lidocaine or mepivacaine in standing sedated horses.

STUDY DESIGN

Prospective, controlled, randomised, cross-over study.

METHODS

Six healthy adult horses were sedated and received IVRLP with lidocaine, mepivacaine or saline (negative control), or perineural anaesthesia of the medial and lateral palmar and palmar metacarpal nerves (positive control) in one forelimb with a 3-week washout period between trials. Electrical and mechanical stimuli were used to test nociceptive threshold of the limb before and after IVRLP/perineural anaesthesia. For lidocaine and mepivacaine trials, blood was collected from the jugular vein and synovial fluid from the radiocarpal joint before, during and out to 24 hours after IVRLP. Drug concentrations were measured using high-performance liquid chromatography.

RESULTS

Nociceptive thresholds for lidocaine, mepivacaine and perineural anaesthesia trials were significantly increased compared with saline and baseline values at 10, 20 and 30 minutes, with no differences between anaesthetic trials. During this time, horses had lower heart rates than IVRLP with saline. After tourniquet release at 30 minutes, nociceptive thresholds for lidocaine and mepivacaine trials gradually returned to baselines, whereas perineural anaesthesia trial remained unchanged out to an hour. Plasma lidocaine and mepivacaine concentrations were ≤50 ng/mL while the tourniquet was in place, significantly increasing 10 minutes after tourniquet release. Maximal lidocaine and mepivacaine concentrations in synovial fluid were reached 25 minutes after IVRLP injection.

MAIN LIMITATIONS

Amikacin was not included in the perfusate.

CONCLUSION

Similar to perineural anaesthesia, IVRLP with lidocaine or mepivacaine provides anti-nociception to the distal limb in standing sedated horses while a tourniquet is applied with concentrations remaining below toxic levels in plasma and synovial fluid.

Is There Still a Place for Lidocaine in the (Postoperative) Management of Colics?

Intravenous lidocaine is widely used to prevent or treat postoperative ileus in horses. Clinical studies that support this approach are flawed and contradicted by others. Also, physical obstruction could be more important in causing postoperative reflux than postoperative ileus in the horse. The antiinflammatory properties of lidocaine and the role of inflammation from intestinal handling in the genesis of postoperative reflux are questionable. Because of cost and questionable efficacy of lidocaine, a well-designed clinical trial is required to support its continued use. However, lidocaine could be given to provide or enhance analgesia in selected cases with postoperative colic.

Cardiac Therapeutics in Horses

Many cardiac therapeutics lack significant evidence of benefit in the horse, and in many cases their use is based on extrapolation of evidence from other species. In recent years there has been a push to develop a better understanding of both the pharmacodynamics and pharmacokinetics of these drugs. Recent data have described the use of antiarrhythmic agents including sotalol, flecainide, and amiodarone. Data about the use of ACE inhibitors in the management of congestive heart failure are encouraging and support their use in certain cases, wheras evidence for other medicines, such as pimobendan, remain speculative.

Cardiac Arrhythmias in Horses

Arrhythmias are common in horses. Sinus arrhythmia and first- and second-degree atrioventricular block are frequently found physiologic arrhythmias, but should immediately disappear after stress or exercise. Atrial premature depolarizations are usually not associated with poor performance, but are a potential trigger for atrial fibrillation. Atrial fibrillation results in an abnormal ventricular response during exercise and poses a risk for collapse in some horses. This arrhythmia can usually be treated by quinidine sulfate or transvenous electrical cardioversion. Ventricular premature depolarizations, especially when associated with structural heart disease, may be a risk factor for ventricular tachycardia or even ventricular fibrillation.

Toxicity and Pharmacokinetic Studies of Lidocaine and Its Active Metabolite, Monoethylglycinexylidide, in Goat Kids

Simple Summary

Disbudding is becoming a routine husbandry procedure in goat farms even though it is a painful procedure without appropriate pain relief. One of the ways to alleviate or minimize the pain associated with disbudding is by using local anesthetics like lidocaine hydrochloride. However, lidocaine hydrochloride has been reported to be toxic in goat kids and there is some data regarding the doses that produce toxicity in goat kids. Therefore, the research team studied the toxicity and pharmacokinetics of lidocaine hydrochloride in goat kids to recommend a safe dose for disbudding.

Abstract

This study determined the convulsant plasma concentrations and pharmacokinetic parameters following cornual nerve block and compared the results to recommend a safe dose of lidocaine hydrochloride for goat kids. The plasma concentrations of lidocaine and monoethylglycinexylidide (MGX) were quantified using liquid chromatography-mass spectrometry. A total dose of 7 mg/kg body weight (BW) was tolerated and should therefore be safe for local and regional anesthesia in goat kids. The mean plasma concentration and mean total dose that produced convulsions in goat kids were 13.59 ± 2.34 µg/mL and 12.31 ± 1.42 mg/kg BW (mean ± S.D.), respectively. The absorption of lidocaine following subcutaneous administration was rapid with C_max and T_max of 2.12 ± 0.81 µg/mL and 0.33 ± 0.11 h, respectively. The elimination half-lives (t_½λz) of lidocaine hydrochloride and MGX were 1.71 ± 0.51 h and 3.19 ± 1.21 h, respectively. Injection of 1% lidocaine hydrochloride (0.5 mL/site) was safe and effective in blocking the nerves supplying horn buds in goat kids.

Successful use of lipid emulsion to resuscitate a foal after intravenous lidocaine induced cardiovascular collapse

BACKGROUND

Lipid emulsion has been reported to be effective for the treatment of local anaesthetic overdoses in rats, dogs and man.

OBJECTIVES

To describe the successful treatment of cardiovascular lidocaine toxicity in a foal with intravenous lipid administration.

STUDY DESIGN

Observational study: case report.

METHODS

An 8-month-old Arabian cross foal was anaesthetised for removal of the right alar fold and nasal plate. Anaesthesia was maintained with isoflurane in oxygen and lidocaine administered with a loading dose followed by a continuous rate infusion (CRI). The anaesthetic period was uneventful and 30 min before expected termination of the procedure lidocaine infusion was stopped. A sudden drop in mean arterial blood pressure was then observed. The ECG signal was lost, the end tidal CO₂ tension dropped from 40 to 10 mmHg, corneal reflex was absent and asystole diagnosed. Cardiopulmonary resuscitation manoeuvres were immediately initiated, but epinephrine and atropine were unsuccessfully administered. Lipid emulsion was administered and the heart rate and arterial blood pressure gradually returned to normal.

RESULTS

The foal recovered consciousness 3 h later, regained its sternal position, was responsive and 20 h later was able to stand up alone.

MAIN LIMITATIONS

It will be necessary to evaluate a greater number of cases to determine the effectiveness of lipids in foals intoxicated with lidocaine.

CONCLUSION

Intravenous lipid emulsion may be helpful in the treatment of potentially lethal cardiotoxicity attributable to lidocaine overdose in the foal.

Comparison of the effects of an intravenous lidocaine infusion combined with 1% isoflurane versus 2% isoflurane alone on selected cardiovascular variables and recovery characteristics during equine general anaesthesia

OBJECTIVES

To compare the effects of a lidocaine constant rate infusion (CRI) combined with 1% isoflurane versus those of 2% isoflurane alone on cardiovascular variables in anaesthetized horses, and to estimate the sample size required to detect a difference in recovery quality.

STUDY DESIGN

Prospective, randomized, blinded, crossover study.

ANIMALS

Twelve healthy experimental horses.

METHODS

Horses were anaesthetized twice using an intravenous (IV) administration of acepromazine, romifidine, diazepam and ketamine. Horses were placed in dorsal recumbency and ventilated mechanically. During the first 10 minutes (P1), anaesthesia was maintained with a 2% inspired isoflurane fraction (FIIso). During the following 20 minutes (P2), horses received IV lidocaine (1.5 mg kg^-1) (group IL) or saline (group I). During the last 60 minutes (P3), group IL received a lidocaine CRI (50 μg kg^-1 minute^-1 IV) and FIIso 1%, whereas group I received a saline CRI and FIIso 2%. Three weeks later, the horses received the alternative treatment. Painful stimuli were induced by introducing an 18 gauge needle intramuscularly. Ketamine and dobutamine requirements and physiological variables were recorded. Recoveries were assessed by two anaesthetists unaware of the treatment. Lidocaine plasma concentrations were measured during recovery. Data were analysed with anova.

RESULTS

During P3, group IL had a lower heart rate (p = 0.002), higher mean arterial pressure (p < 0.001) and lower dobutamine requirement (p < 0.001) than group I. One horse had lidocaine plasma concentrations above toxic levels. Recoveries did not differ significantly between groups. Sample sizes of 208 horses in each group would be necessary to detect a statistically significant difference (85% statistical power) in recovery quality.

CONCLUSIONS AND CLINICAL RELEVANCE

A lidocaine CRI combined with FIIso 1% rather than FIIso 2% alone may improve cardiovascular variables in healthy anaesthetized horses.

Antinociceptive effects of three escalating dexmedetomidine and lignocaine constant rate infusions in conscious horses

Dexmedetomidine and lignocaine IV are used clinically to provide analgesia in horses. The aims of this study were to investigate the antinociceptive effects, plasma concentrations and sedative effects of 2, 4 and 6 µg/kg/h dexmedetomidine IV, with a bolus of 0.96 µg/kg preceding each continuous rate infusion (CRI), and 20, 40 and 60 µg/kg/min lignocaine IV, with a bolus of 550 µg/kg preceding each CRI, in 10 Swiss Warmblood horses. Electrically elicited nociceptive withdrawal reflexes were evaluated by deltoid muscle electromyography. Nociceptive threshold and tolerance were determined by electromyography and behaviour following single and repeated stimulation. Plasma concentrations of drugs were determined by liquid chromatography and mass spectrometry. Sedation was scored on a visual analogue scale. Dexmedetomidine increased nociceptive threshold to single and repeated stimulation for all CRIs, except at 2 µg/kg/h, where no increase in single stimulation nociceptive threshold was observed. Dexmedetomidine increased nociceptive tolerance to single and repeated stimulation at all CRIs. There was large individual variability in dexmedetomidine plasma concentrations and levels of sedation; the median plasma concentration providing antinociceptive effects to all recorded parameters was 0.15 ng/mL, with a range from <0.02 ng/mL (below the lower limit of quantification) to 0.25 ng/mL. Lignocaine increased nociceptive threshold and tolerance to single and repeated stimulation at CRIs of 40 and 60 µg/kg/min, corresponding to plasma lignocaine concentrations >600 ng/mL. Only nociceptive tolerance to repeated stimulation increased at 20 µg/kg/min lignocaine. Lignocaine at 40 µg/kg/min and dexmedetomidine at 4 µg/kg/h were the lowest CRIs resulting in consistent antinociception. Lignocaine did not induce significant sedation.

Partial intravenous anaesthesia in the horse: a review of intravenous agents used to supplement equine inhalation anaesthesia. Part 1: lidocaine and ketamine

OBJECTIVE

To review the literature with regard to the use of different intravenous agents as supplements to inhalational anaesthesia in horses. These drugs include lidocaine, ketamine, opioids and α2 -agonists. The Part 1 of this review will focus in the use of lidocaine and ketamine.

DATABASES USED

Pubmed & Web of Science. Search terms: horse, inhalant anaesthesia, balanced anaesthesia, partial intravenous anaesthesia, lidocaine, ketamine.

CONCLUSIONS

Different drugs and their combinations can be administered systemically in anaesthetized horses, with the aim of reducing the amount of the volatile agent whilst improving the recovery qualities and providing a multimodal analgesic approach. However, full studies as to whether these techniques improve cardiopulmonary status are not always available and potential disadvantages should also be considered.

Cardiorespiratory and antinociceptive effects of two different doses of lidocaine administered to horses during a constant intravenous infusion of xylazine and ketamine

BACKGROUND

This study investigated the antinociceptive effects of a constant rate infusion (CRI) of lidocaine during xylazine and ketamine anesthesia in horses and aimed to correlate these effects with cardiorespiratory variables, bispectral index (BIS) and plasma lidocaine concentrations. Six adult crossbred mares weighing 320-400 kg were anesthetized on three different occasions. Sedation was performed with xylazine (0.75 mg/kg IV) and anesthetic induction with guaifenesin (75 mg/kg IV) and ketamine (2 mg/kg IV). Anesthesia was maintained with 37.5 μg/kg/min of xylazine and 87.5 μg/kg/min of ketamine both administered intravenously for 75 min. The three treatments consisted of: lidocaine (loading dose: 5 mg/kg, CRI: 100 μg/kg/min; THL); lidocaine (loading dose: 2.5 mg/kg; CRI: 50 μg/kg/min: TLL); and saline (TS); all given 15 min after induction and maintained for 1 h. Antinociception was measured by response to electrical stimulation and bispectral index (BIS) was recorded during anesthesia. Parametric and non-parametric data were compared using ANOVA followed by Student-Newman-Keuls and Friedman tests, respectively.

RESULTS

Plasma lidocaine concentrations peaked at the end of lidocaine loading dose and was greater in THL (9.61 ± 2.75 μg/mL) vs TLL (4.50 ± 3.34 μg/mL). Electrical noxious stimulation caused purposeful movement in all horses from TS, but no response in THL. The BIS was decreased in THL only and was less when compared to the other treatments throughout anesthesia. Blood pressure, PaO2 and PaCO2 increased and heart rate (HR), respiratory rate (RR), pH, total plasma protein and temperature decreased during anesthesia in all treatments. PaCO2 and HR were greater and RR and pH less in THL compared to TLL and TS at 30 min during anesthesia. All recoveries were considered excellent. Time to standing was longer after THL (60 ± 20 min) than following TLL and TS (32 ± 17 and 30 ± 15 min, respectively).

CONCLUSIONS

At the highest dose administered (THL) lidocaine CRI during xylazine/ketamine anesthesia decreased BIS and motor response to noxious stimulation, and prolonged recovery time without significant added cardiorespiratory depression.

Apophyseal avulsion fracture of the greater trochanter of the femur in a Thoroughbred filly

The case report of a 14-month-old Thoroughbred filly with acute onset of severe right hindlimb lameness is presented. The horse had a severe and sudden abduction of the hindlimbs due to a side effect of an overdose of lidocaine, which had been administered in a constant rate infusion after a colic surgery. Transcutaneous ultrasonography and standing radiography of the pelvis revealed proximal and cranial displacement of the greater trochanter and free bone fragments consistent with an apophyseal avulsion fracture of the greater trochanter. The complete diagnosis was obtained with the horse in a standing position. The filly was euthanatized because of deterioration resulting from the colic condition and of the poor prognosis of the fracture of the greater trochanter. Postmortem evaluation confirmed an apophyseal avulsion fracture of the right greater trochanter. To the authors' knowledge, ultrasonographic and radiographic findings of this fracture have not been described in the standing horse. The diagnosis was reached quite easily with the horse in a normal standing position when the characteristic ultrasonographic and radiographic findings were detected.

Evaluation of the isoflurane-sparing effects of lidocaine infusion during umbilical surgery in calves

OBJECTIVE

To evaluate the isoflurane-sparing effects of lidocaine administered by constant rate infusion (CRI) during umbilical surgery in calves.

STUDY DESIGN

Randomized 'blinded' prospective clinical study.

ANIMALS

Thirty calves (mean 4.7 ± SD 2.5 weeks old) undergoing umbilical surgery.

METHODS

After premedication with xylazine (0.1 mg kg(-1) , IM), anaesthesia was induced with ketamine (4 mg kg(-1) , IV) and maintained with isoflurane in O(2) administered through a circle breathing system. The calves were assigned randomly to receive a bolus of 2 mg kg(-1) lidocaine IV after induction of anaesthesia, followed by CRI of 50 μg kg(-1) minute(-1) (group L, n=15) or a bolus and CRI of 0.9% sodium chloride (NaCl, group S, n=15). End-tidal isoflurane was adjusted to achieve adequate depth of anaesthesia. Heart rate, direct arterial blood pressure and body temperature were measured intraoperatively. Groups were compared by t- tests, anova or Mann-Whitney rank sum test as appropriate.

RESULTS

The end-tidal concentration of isoflurane (median, IQR) was significantly lower in group L [1.0% (0.94-1.1)] compared to group S [1.2% (1.1-1.5)], indicating a 16.7% reduction in anaesthetic requirement during lidocaine CRI. Cardiopulmonary parameters and recovery times did not differ significantly between groups.

CONCLUSION AND CLINICAL RELEVANCE

Lidocaine CRI may be used as a supplement to inhalation anaesthesia during umbilical surgery in calves in countries where such a protocol would be within the legal requirements for veterinary use in food animals. This study did not show any measurable benefit to the calves other than a reduction in isoflurane requirement.

Neuropathic pain management in chronic laminitis

Managing pain in horses afflicted by chronic laminitis is one of the greatest challenges in equine clinical practice because it is the dreadful suffering of the animals that most often forces the veterinarian to end the battle with this disease. The purpose of this review is to summarize our current understanding of the complex mechanisms involved in generating and amplifying pain in animals with laminitis and, based on this information, to propose a modified approach to pain therapy. Furthermore, a recently developed pain scoring technique is presented that may help better quantify pain and the monitoring of responses to analgesic treatment in horses with laminitis.

Effect of systemic lidocaine on visceral and somatic nociception in conscious horses

REASONS FOR PERFORMING STUDY

Commonly used analgesics (nonsteroidal anti-inflammatory agents, opioids and alpha2-agonists) have unwanted side effects. An effective alternative with minimal adverse effects would benefit clinical equine pain management.

OBJECTIVES

To compare the effect of lidocaine or saline on duodenal and rectal distension threshold pressure and somatic thermal threshold in conscious mature horses.

HYPOTHESIS

Systemically administered lidocaine would increase somatic and visceral nociceptive thresholds.

METHODS

Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min for 2 h) or saline was administered to 6 horses each carrying a permanently implanted gastric cannula, in a randomised, blinded cross-over design. Thermal threshold was measured using a probe containing a heater element placed over the withers which supplied heat until the horse responded. A barostatically controlled intraduodenal balloon was distended until a discomfort response was obtained. A rectal balloon was inflated until extruded or signs of discomfort noted.

RESULTS

Thermal threshold was increased significantly 30 and 90 mins after the start of lidocaine infusion. There was no change in duodenal distension pressure and a small but clinically insignificant change in colorectal distension pressure in the lidocaine group.

CONCLUSIONS

At the dose used, systemically administered lidocaine produced thermal antinociception but minimal changes in visceral nociception.

POTENTIAL RELEVANCE

At these doses, lidocaine may play a role in somatic analgesia in horses.

Effect of a constant rate infusion of lidocaine on the quality of recovery from sevoflurane or isoflurane general anaesthesia in horses

REASONS FOR PERFORMING STUDY

Lidocaine constant rate infusions (CRIs) are common as an intraoperative adjunct to general anaesthesia, but their influence on quality of recovery has not been thoroughly determined.

OBJECTIVES

To determine the effects of an intraoperative i.v. CRI of lidocaine on the quality of recovery from isoflurane or sevoflurane anaesthesia in horses undergoing various surgical procedures, using a modified recovery score system.

HYPOTHESIS

The administration of intraoperative lidocaine CRI decreases the quality of recovery in horses.

METHODS

Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min) or saline was administered for the duration of surgery or until 30 mins before the end of surgery under isoflurane (n = 27) and sevoflurane (n = 27).

RESULTS

Horses receiving lidocaine until the end of surgery had a significantly higher degree of ataxia and a tendency towards significance for a lower quality of recovery. There was no correlation between lidocaine plasma concentrations at recovery and the quality of recovery.

CONCLUSIONS

Intraoperative CRI of lidocaine affects the degree of ataxia and may decrease the quality of recovery.

POTENTIAL RELEVANCE

Discontinuing lidocaine CRI 30 mins before the end of surgery is recommended to reduce ataxia during the recovery period.

Attenuation of ischaemic injury in the equine jejunum by administration of systemic lidocaine

REASONS FOR PERFORMING STUDY

Absorption of endotoxin across ischaemic-injured mucosa is a major cause of mortality after colic surgery. Recent studies have shown that flunixin meglumine retards mucosal repair. Systemic lidocaine has been used to treat post operative ileus, but it also has novel anti-inflammatory effects that could improve mucosal recovery after ischaemic injury.

HYPOTHESIS

Systemic lidocaine ameliorates the deleterious negative effects of flunixin meglumine on recovery of mucosal barrier function.

METHODS

Horses were treated i.v. immediately before anaesthesia with either 0.9% saline 1 ml/50 kg bwt, flunixin meglumine 1 mg/kg bwt every 12 h or lidocaine 1.3 mg/kg bwt loading dose followed by 0.05 mg/kg bwt/min constant rate infusion, or both flunixin meglumine and lidocaine, with 6 horses allocated randomly to each group. Two sections of jejunum were subjected to 2 h of ischaemia by temporary occlusion of the local blood supply, via a midline celiotomy. Horses were monitored with a behavioural pain score and were subjected to euthanasia 18 h after reversal of ischaemia. Ischaemic-injured and control jejunum was mounted in Ussing chambers for measurement of transepithelial electrical resistance (TER) and permeability to lipopolysaccharide (LPS).

RESULTS

In ischaemic-injured jejunum TER was significantly higher in horses treated with saline, lidocaine or lidocaine and flunixin meglumine combined, compared to horses treated with flunixin meglumine. In ischaemic-injured jejunum LPS permeability was significantly increased in horses treated with flunixin meglumine alone. Behavioural pain scores did not increase significantly after surgery in horses treated with flunixin meglumine.

CONCLUSIONS

Treatment with systemic lidocaine ameliorated the inhibitory effects of flunixin meglumine on recovery of the mucosal barrier from ischaemic injury, when the 2 treatments were combined. The mechanism of lidocaine in improving mucosal repair has not yet been elucidated.

Simulation of local anaesthetic nerve block of the infraorbital nerve within the pterygopalatine fossa: anatomical landmarks defined by computed tomography

To provide anaesthesia of the maxillary cheek teeth, a local block of the infraorbital nerve in the pterygopalatine fossa has been suggested. The aim of this study was to re-examine the anatomy of the pterygopalatine fossa, giving special attention to relevant arteries, veins and nerves; simulate the infiltration of an anaesthetic by injecting a contrast medium; improve the injection technique to avoid puncturing of relevant anatomical structures. Five heads and two living horses were investigated using contrast medium injections and computed tomography (CT). Needles were inserted using two insertion techniques: "Palatine Bone Insertion" (PBI) and "Extraperiorbital Fat Body Insertion" (EFBI). Both techniques are suitable for achieving a consistent distribution of contrast medium around the infraorbital nerve. The periorbita prevents the contrast medium from penetrating into the intraperiorbital compartment. The EFBI-technique is most appropriate for providing a sufficient infraorbital nerve block with a minimised risk of complications.