Assessment of the hemodynamic effects of lidocaine administered IV in isofluraneanesthetized cats

2024 RECOVER Guidelines: Advanced Life Support. Evidence and knowledge gap analysis with treatment recommendations for small animal CPR

OBJECTIVE

To systematically review the evidence and devise clinical recommendations on advanced life support (ALS) in dogs and cats and to identify critical knowledge gaps.

DESIGN

Standardized, systematic evaluation of literature pertinent to ALS following Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. Prioritized questions were each reviewed by Evidence Evaluators, and findings were reconciled by ALS Domain Chairs and Reassessment Campaign on Veterinary Resuscitation (RECOVER) Co-Chairs to arrive at treatment recommendations commensurate to quality of evidence, risk:benefit relationship, and clinical feasibility. This process was implemented using an Evidence Profile Worksheet for each question that included an introduction, consensus on science, treatment recommendations, justification for these recommendations, and important knowledge gaps. A draft of these worksheets was distributed to veterinary professionals for comment for 4 weeks prior to finalization.

SETTING

Transdisciplinary, international collaboration in university, specialty, and emergency practice.

RESULTS

Seventeen questions pertaining to vascular access, vasopressors in shockable and nonshockable rhythms, anticholinergics, defibrillation, antiarrhythmics, and adjunct drug therapy as well as open-chest CPR were reviewed. Of the 33 treatment recommendations formulated, 6 recommendations addressed the management of patients with nonshockable arrest rhythms, 10 addressed shockable rhythms, and 6 provided guidance on open-chest CPR. We recommend against high-dose epinephrine even after prolonged CPR and suggest that atropine, when indicated, is used only once. In animals with a shockable rhythm in which initial defibrillation was unsuccessful, we recommend doubling the defibrillator dose once and suggest vasopressin (or epinephrine if vasopressin is not available), esmolol, lidocaine in dogs, and/or amiodarone in cats.

CONCLUSIONS

These updated RECOVER ALS guidelines clarify the approach to refractory shockable rhythms and prolonged CPR. Very low quality of evidence due to absence of clinical data in dogs and cats continues to compromise the certainty with which recommendations can be made.

Antinociceptive and analgesic effect of continuous intravenous infusion of maropitant, lidocaine and ketamine alone or in combination in cats undergoing ovariohysterectomy

Background

Multimodal analgesia consists of the combination of analgesic drugs at low doses to act in different places along the path of pain. Studies with continuous infusion of analgesic drugs in cats are not common. This study aimed to evaluate the analgesic effect of maropitant, lidocaine and ketamine alone or in combination (intravenous bolus + subsequent continuous intravenous infusion) in the management of acute postoperative pain in cats undergoing ovariohysterectomy. Seventy healthy cats undergoing an ovariohysterectomy received a standard anesthetic protocol consisting of acepromazine and morphine, propofol (anesthesia induction), and isoflurane (anesthesia maintenance). The animals were stratified into seven groups (n = 10 in each group): control (CG), maropitant (MG), lidocaine (LG), ketamine (KG), maropitant + lidocaine (LMG), maropitant + ketamine (KMG), and maropitant + lidocaine + ketamine (LKMG). All drugs were injected first as an intravenous bolus and then by continuous intravenous infusion. During surgery, esophageal temperature, respiratory rate, heart rate, oxygen saturation, expired isoflurane concentration, and partial pressure of carbon dioxide at the end of expiration were evaluated at 7 time points. Postoperative pain was evaluated for 6 h after extubation using the visual analogue scale and the UNESP-Botucatu multidimensional composite pain scale for assessing postoperative pain in cats.

Results

Adverse effects related to maropitant, lidocaine and ketamine infusion were not observed. Pain scores were lower in the MG, KG and LG groups when compared to the CG group using both scales. Although pain scores were also lower in all combination groups than CG, more animals in these groups required rescue analgesia compared to MG. This indicates that the postoperative analgesic effect of all drugs, either alone or in combination, confers analgesia, although the combinations did not promote greater analgesia.

Conclusions

Continuous intravenous infusion of maropitant, lidocaine, and ketamine alone induces postoperative analgesic effect in cats undergoing ovariohysterectomy, but combinations of these drugs did not increase the analgesic effect. No adverse effect was observed with any drug or their combination.

Local and Regional Anesthesia in Zoological Companion Animal Practice

Local anesthetics provide analgesia and can be incorporated into multimodal anesthetic protocols. They work by blocking the voltage-dependent sodium ion channels along neurons that mediate nociception. Systemically, these drugs can be cardiotoxic in a dose-dependent manner. Lidocaine and bupivacaine are the most commonly used local anesthetics and their use has been reported in all classes of vertebrates. Despite anecdotal reports to the contrary, zoologic companion animals are unlikely to be more susceptible to the cardiotoxic effects of local anesthetics than domestic small animals. Local anesthetics can be clinically useful for analgesia and anesthesia in zoologic companion animal practice.

Evaluation of the time to desensitization of the larynx of cats following topical lidocaine application

OBJECTIVES

The objective of this study was to evaluate the time to decreased reactivity of the arytenoid cartilages in cats after application of topical lidocaine.

METHODS

One hundred and ten mixed-breed cats were randomly assigned to one of five groups based on the time between application of lidocaine and stimulation of the larynx: 5 (T5), 15 (T15), 30 (T30), 45 (T45) or 60 (T60) s. Cats were premedicated with dexmedetomidine, ketamine and buprenorphine. Anesthesia was induced with propofol to effect. Lidocaine 2% (2 mg/kg) was applied topically to the vocal cords using a catheter attached to a syringe under direct laryngoscopy. After lidocaine application, the designated time elapsed and the vocal cords were stimulated with the patient end of an endotracheal tube. Severity of reaction was reported as none, mild, moderate or severe. All cats were intubated after the reactivity score was recorded. Anesthesia was maintained with isoflurane and 100% oxygen while cats were spayed or castrated. Cats were monitored in recovery for signs of respiratory complications and pain.

RESULTS

There was a significant difference in overall reactivity score between T5 and T45 (P = 0.0038). Also, there was a significant difference in the number of cats with no reaction compared with cats with any reaction between T5 and T30 (P = 0.03), as well as between T5 and T45 (P = 0.0028). No cat had a severe reactivity score at T45 or T60. All cats were successfully intubated. There were no complications during intubation, maintenance of anesthesia or recovery.

CONCLUSIONS AND RELEVANCE

As the lowest overall reactivity score occurred at T45, it is recommended to wait at least 45 s after application of topical lidocaine before attempting tracheal intubation.

Lidocaine administered at a continuous rate infusion does not impair left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam

Lidocaine is a versatile drug that not only provides local anesthesia, but also reduces anesthetic requirements of other agents and has antiarrhythmic, pro-kinetic, anti-inflammatory, antiendotoxemic and antioxidant effects. As it is a drug commonly used in critically ill patients, its safety from the cardiovascular system should be ensured. The aim of this study was to determine the effects of a continuous rate infusion (CRI) of lidocaine on left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam by use of transthoracic echocardiography. Ten New Zealand healthy rabbits were sedated with intramuscular midazolam (1 mg/kg) and enrolled in two experimental treatments (control or lidocaine). The control treatment (CT) comprised an intravenous bolus of 0.9% sodium chloride (0.05 mL/kg) followed by CRI at 5 mL/h, whereas the lidocaine treatment (LT) comprised a bolus of 2% lidocaine without epinephrine at 1 mg/kg followed by CRI at 50 µg/kg/minute. Echocardiographic and hemodynamic variables were studied. Variables were recorded at baseline (TB) and 20, 40 and 60 minutes following start of CRI (T20, T40 and T60, respectively). No differences were found between treatments. The results of this study demonstrate that a continuous rate infusion of lidocaine at 50 µg/kg/minute does not impair echocardiographic indices of left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam.

Evaluation of tumescent local anesthesia in cats undergoing unilateral mastectomy

OBJECTIVE

To evaluate the analgesic efficacy and safety of tumescent local anesthesia (TLA) in cats undergoing unilateral mastectomy.

STUDY DESIGN

Prospective clinical trial.

ANIMALS

A total of 12 ovariohysterectomized female cats.

METHODS

All animals were premedicated with pethidine (4 mg kg^-1) intramuscularly (IM), followed by induction of anesthesia with propofol (5 mg kg^-1) intravenously and maintenance with isoflurane in oxygen. A refrigerated TLA solution (15 mL kg^-1, 8 °C) was injected using a Klein cannula. The solution was composed of 0.5 mL of epinephrine (1 mg mL^-1) and 40 mL of 2% lidocaine added to 210 mL lactated Ringer's solution (final lidocaine concentration 0.32%). Heart and respiratory rates, systolic arterial blood pressure, temperature and oxygen saturation were measured during anesthesia. Blood samples were collected from the jugular vein for measurement of plasma lidocaine concentration using high performance liquid chromatography. Postoperative pain scores were evaluated hourly for 6 hours. Analgesic rescue was performed with tramadol (2 mg kg^-1) IM and meloxicam (0.15 mg kg^-1) subcutaneously.

RESULTS

Plasma lidocaine concentration peaked at 90 minutes after injection of TLA, but no concentration considered toxic for the species was measured. The median postoperative analgesia time was 6 hours after injection of TLA.

CONCLUSIONS

This study found that TLA prevented sympathetic response to noxious stimuli during anesthesia and provided satisfactory postoperative analgesia in cats submitted to total unilateral mastectomy, with no apparent signs of toxicity.

CLINICAL RELEVANCE

TLA can prevent sympathetic stimulation resulting from noxious stimuli during anesthesia, promoting good intraoperative conditions, proving to be a viable addition to analgesia in cats submitted to a total unilateral mastectomy.

Infusão de morfina e cetamina, associada ou não à lidocaína, em gatas submetidas à ovariossalpingo-histerectomia

RESUMO O objetivo deste estudo foi avaliar os efeitos analgésicos transoperatórios da infusão contínua de morfina e cetamina, associada ou não à lidocaína, em gatas submetidas à OSH eletiva. Foram utilizadas 16 fêmeas adultas, hígidas, pré-medicadas com acepromazina (0,1mg/kg) e morfina (0,5mg/kg), ambas pela via intramuscular, induzidas com cetamina (1mg/kg) e propofol (4mg/kg), pela via intravenosa, e mantidas sob anestesia geral inalatória com isoflurano a 1,4 V%. Os animais foram alocados aleatoriamente em dois grupos: grupo morfina, lidocaína e cetamina (MLK, n=8), que recebeu bolus de lidocaína (1mg/kg), pela via IV, seguido de infusão de morfina, lidocaína e cetamina (0,26mg/kg/h, 3mg/kg/h e 0,6mg/kg/h, respectivamente); e grupo morfina e cetamina (MK, n=8), que recebeu bolus de solução salina, seguido de infusão de morfina e cetamina, nas mesmas doses do MLK. Os momentos avaliados foram: M0, basal, cinco minutos após a indução; M1, imediatamente após a aplicação do bolus de lidocaína ou solução salina; M2, M3, M4 e M5, a cada cinco minutos, até completar 20 minutos do início da infusão; M6, após a incisão da musculatura; M7, após pinçamento do primeiro pedículo ovariano; M8, após pinçamento do segundo pedículo ovariano; M9, após pinçamento da cérvix; M10, após sutura da musculatura; M11, ao final da cirurgia; e M12, M13 e M14, intervalos de cinco minutos, até completar uma hora de infusão. A FP no M0 foi maior no MLK quando comparado ao MK. Em ambos os grupos, a PAS foi maior no M7 e no M8 em relação ao M0, porém no MK, além da PAS, a FP foi maior do M7 ao M13, assim como a f. Os animais do MK necessitaram de um número maior de resgates transoperatorios, total de 23, do que o MLK, total de sete. Conclui-se que a adição de lidocaína incrementou a analgesia oferecida, reduzindo o número de resgates analgésicos transoperatórios, a dose total de fentanil, bem como a probabilidade de os animais necessitarem dese tipo de resgate.

AAFP Feline Anesthesia Guidelines

AIM

The overarching purpose of the AAFP Anesthesia Guidelines (hereafter referred to as the 'Guidelines') is to make anesthesia and sedation safer for the feline patient. Scope and accessibility: It is noteworthy that these are the first exclusively feline anesthesia guidelines authored by an expert panel, making them particularly useful as an extensively referenced, practical resource for veterinary practice teams. Because much of the key content is presented in tabular or visual format, the Guidelines have a high level of accessibility and convenience that invites regular usage. While the recommendations in the Guidelines focus primarily on client-owned cats, the content is also applicable to community-sourced animals with an unknown medical history.

State of the art analgesia-Recent developments pharmacological approaches to acute pain management in dogs and cats: Part 2

There has been considerable interest in the area of acute pain management over recent years, focusing on pain assessment, pharmacological and non-pharmacological interventions. The evidence base for our clinical decision making and treatment of patients is ever increasing and becoming more robust. There is still a tendency to base some aspects of pain management on poor quality evidence and this requires further input in years to come. With new literature come new ideas and this review will detail the current knowledge base behind pharmacological management of acute pain in dogs and cats. The known mechanisms of action of each analgesic and its evidence will be considered. The second part of this review will consider the non-traditional analgesics, describing their component drugs individually, thereby focusing on their mechanisms of action and the current evidence for their use in acute pain management.

Retrospective assessment of peripheral nerve block techniques used in cats undergoing hindlimb orthopaedic surgery

OBJECTIVES

The aim of this study was to assess retrospectively the efficacy and complication rate of hindlimb peripheral nerve blocks (PNBs) in cats.

METHODS

Clinical records of cats that received PNBs and underwent hindlimb orthopaedic surgery from February 2010 to October 2014 were examined. Type of PNB, type and dose of local anaesthetic used, end-expiratory fraction of isoflurane (FE'Iso) administered, additional intraoperative analgesia, incidence of hypotension, postoperative opioid requirement, postoperative contralateral limb paralysis and neurological complications at the 6 week re-examination were investigated.

RESULTS

Eighty-nine records were retrieved but only 69 were analysed. Four combinations of PNBs were used: 34 lateral preiliac (LPI) approach to lumbar plexus (LP) associated with lumbar paravertebral approach to sciatic nerve (SN); 20 LPI-LP associated with the lateral approach to SN; three LPI-LP associated with gluteal approach to SN; 12 dorsal-paravertebral (DPV) approach to LP associated with lateral SN. Levobupivacaine was used for the majority of PNBs. The mean intraoperative FE'Iso was 1.15%; hypotension was documented in 55.1% of anaesthetics, while 31.8% of cats received fentanyl and/or ketamine intraoperatively. Postoperatively, 72.7% of cats received at least one dose of opioid, while five cats required further postoperative analgesia (ketamine constant rate infusion and/or gabapentin). No cats showed contralateral limb paralysis and neurological complications at the 6 week re-examination. No differences were found when comparing the different PNBs used.

CONCLUSIONS AND RELEVANCE

PNBs contributed to perioperative anaesthesia/analgesia in cats undergoing hindlimb orthopaedic surgery. However, the clinical relevance of intraoperative hypotension needs further investigation.

[Perioperative pain therapy in dogs and cats - an overview]

Undermanaged pain leads to negative systemic effects that may greatly disturb our patients' welfare. Therefore, a pain assessment tool should be routinely implemented into clinical practice. Validated pain assessment tools are available for dogs and cats. Advanced analgesic therapy follows the principle of a multimodal approach. This means that different analgesic drugs, which act on different targets within the nociceptive pathway, are combined to achieve the desired analgesic effects. In addition to opioids, nonsteroidal anti-inflammatory drugs and local anaesthetics, α2-receptor-agonists, ketamine and gabapentin as well as different nonpharmacologic analgesic techniques are used within the framework of a multimodal analgesic plan.

Analgesia in the Perioperative Period

Untreated or undermanaged perioperative pain has systemic effects that may negatively impact a patient's welfare and return to function. A consistent analgesic plan that assesses a patient's pain and comfort at regular intervals during the perioperative period should be incorporated into practice. Validated pain assessment tools are available for use in dogs and cats. Multimodal analgesic plans should be created for individual patients and modified according to pain assessments. These plans, based on a thorough history, physical examination, and knowledge of the expected pain, should be combinations of an opioid, a nonsteroidal anti-inflammatory drug, a local anesthetic, and nonpharmacologic analgesic techniques.

2015 AAHA/AAFP pain management guidelines for dogs and cats

RATIONALE

The robust advances in pain management for companion animals underlie the decision of the American Animal Hospital Association (AAHA) and American Association of Feline Practitioners (AAFP) to expand on the information provided in the 2007 AAHA/AAFP Pain Management Guidelines. The 2015 Guidelines summarize and offer a discriminating review of much of this new knowledge.

RELEVANCE

Pain management is central to veterinary practice, alleviating pain, improving patient outcomes, and enhancing both quality of life and the veterinarian-client-patient relationship. These Guidelines support veterinarians in incorporating pain management into practice, improving patient care.

APPROACHES

The management of pain requires a continuum of care that includes anticipation, early intervention, and evaluation of response on an individual patient basis. A team-oriented approach, including the owner, is essential for maximizing the recognition, prevention and treatment of pain in animals.

EVIDENCE BASE

The Guidelines include both pharmacologic and non-pharmacologic modalities to manage pain; they are evidence-based insofar as possible and otherwise represent a consensus of expert opinion. Behavioral changes are currently the principal indicator of pain and its course of improvement or progression, and the basis for recently validated pain scores. Post-surgical pain is eminently predictable but a strong body of evidence exists supporting strategies to mitigate adaptive as well as maladaptive forms. Chronic pain is dominated by degenerative joint disease (DJD), which is one of the most significant and under-diagnosed diseases of cats and dogs. DJD is ubiquitous, found in pets of all ages, and inevitably progresses over time; evidence-based strategies for management are established in dogs, and emerging in cats.

Adjunctive, pain-modifying, analgesic drugs

Outside the realm of nonsteroidal antiinflammatory drug(NSAID) and opioid exist a broad range of medications that exert an analgesic effect, or otherwise modify and protect against pain, by manipulating various targets along the nociceptive pathway. Strength of evidence for dogs and cats can vary widely, and this article will review the available literature that may guide clinical usage in these species.

Veterinary and human anaesthesia: an overview of some parallels and contrasts

The history of human and veterinary anaesthesia is both intertwined and parallel. Physicians and anaesthetists often first experimented on animals and developments from human anaesthesia have been incorporated into veterinary medicine. Within veterinary medicine, anaesthesia is a specialty discipline as it is in human medicine. Veterinary anaesthetists undertake additional training and rigorous examinations for a diploma or fellowship. In contrast to human anaesthesia in Australia and New Zealand, veterinary anaesthesia is often performed by non-specialists and by veterinary nurses. Veterinary anaesthesia uses many of the same drugs for premedication, induction and maintenance of anaesthesia as human anaesthesia. However, there are species specific effects of some of the drugs used that differ from the effects in humans. Furthermore, some agents, particularly alpha-2 adrenoreceptor agonists and ketamine, are used very widely in veterinary practice. Also in contrast to most human anaesthesia, in large animal and exotic animal practice the patients can present a physical danger to the anaesthetist. The most notable contrast between human and veterinary anaesthesia is in the reported perioperative complication and mortality rates, with a species dependent perianaesthetic mortality of up to 2% in dogs, cats and horses and greater than 2% in guinea pigs and birds, which is up to 100-fold higher than in human anaesthesia.

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.

Effect of dexmedetomidine on the minimum alveolar concentration of isoflurane in cats

This study reports the effects of dexmedetomidine on the minimum alveolar concentration of isoflurane (MAC(iso) ) in cats. Six healthy adult female cats were used. MAC(iso) and dexmedetomidine pharmacokinetics had previously been determined in each individual. Cats were anesthetized with isoflurane in oxygen. Dexmedetomidine was administered intravenously using target-controlled infusions to maintain plasma concentrations of 0.16, 0.31, 0.63, 1.25, 2.5, 5, 10, and 20 ng/mL. MAC(iso) was determined in triplicate at each target plasma dexmedetomidine concentration. Blood samples were collected and analyzed for dexmedetomidine concentration. The following model was fitted to the concentration-effect data: [Formula in text] where MAC(iso.c) is MAC(iso) at plasma dexmedetomidine concentration C, MAC(iso.0) is MAC(iso) in the absence of dexmedetomidine, I(max) is the maximum possible reduction in MAC(iso), and IC(50) is the plasma dexmedetomidine concentration producing 50% of I(max). Mean ± SE MAC(iso.0), determined in a previous study conducted under conditions identical to those in this study, was 2.07 ± 0.04. Weighted mean ± SE I(max), and IC(50) estimated by the model were 1.76 ± 0.07%, and 1.05 ± 0.08 ng/mL, respectively. Dexmedetomidine decreased MAC(iso) in a concentration-dependent manner. The lowest MAC(iso) predicted by the model was 0.38 ± 0.08%, illustrating that dexmedetomidine alone is not expected to result in immobility in response to noxious stimulation in cats at any plasma concentration.

Rabbit analgesia

With the increasing popularity of rabbits as household pets, the complexity of diagnostic and surgical procedures performed on rabbits is increasing, along with the frequency of routine surgical procedures. More practitioners are faced with the need to provide adequate analgesia for this species. Preemptive analgesia prior to planned surgical interventions may reduce nervous system changes in response to noxious input, as well as reduce postoperative pain levels and analgesic drug requirements. Concurrent administration of analgesic drugs to anesthetized rabbits undergoing painful procedures is warranted both pre- and intraoperatively as well as postoperatively. This article discusses the neuropharmacologic and pharmacologic aspects of pain in rabbits, and reviews current protocols for the use of analgesic drugs.

Clinical evaluation of the anaesthetic sparing effect of brachial plexus block in cats

OBJECTIVE

To evaluate the isoflurane sparing effect and the post-surgical analgesia provided by a brachial plexus block (BPB) in cats undergoing distal thoracic limb surgery.

STUDY DESIGN

Prospective randomized blinded clinical study.

ANIMALS

Twenty client-owned cats.

METHODS

Cats were assigned to receive either no BPB (group NB) or a nerve stimulator guided BPB (group BPB) using lidocaine (3.6 mg kg(-1)) and bupivacaine (1.2 mg kg(-1)). Pre-medication consisted of midazolam and ketamine intravenously (IV). Anaesthesia was induced with propofol IV to effect and maintained with isoflurane delivered in oxygen and a continuous rate infusion of fentanyl (2 microg kg(-1) hour(-1)). End-tidal isoflurane concentration (Fe'ISO) was adjusted every 3 minutes guided by changes in cardiorespiratory parameters and reflexes present, to maintain a stable depth of anaesthesia. Five time points were chosen to record all parameters and compare values between groups. Recovery and post-operative pain assessment were performed using a visual analogue scale (VAS) at 15 and 45 minutes after extubation and thereafter at hourly intervals until 5 hours after placement of the BPB.

RESULTS

No clinically significant differences were seen for heart rate, respiratory rate and non-invasive blood pressure between groups. Mean Fe'ISO was significantly lower in group BPB compared with group NB at all time points. In group NB, all intraoperative measurements of Fe'ISO were significantly higher compared with baseline (3 minutes before start of surgery) measurements. During recovery, VAS scores for group BPB were significantly lower than for group NB. Additional analgesics were needed in all cats within the study period.

CONCLUSION AND CLINICAL RELEVANCE

In cats undergoing orthopaedic surgery of the thoracic limb, BPB reduced intra-operative isoflurane requirement and pain during the early post-operative period when compared with procedures without a BPB. BPB is a useful adjunct to anaesthesia in such cases.

Anesthetic considerations in orthopedic patients with or without trauma

Anesthetic management of orthopedic patients could vary from normal routine management to more challenging critical management depending on the state in which the patient is presented. Multimodal pain management strategies incorporating opioids, which are the mainstay drugs for pain management, along with adjunctive drugs like local anesthetics (eg, lidocaine), dissociative anesthetics (eg, ketamine), and alpha-2 agonists (eg, dexmedetomidine), could improve overall patient comfort and help prevent establishment of chronic pain pathways. Also, use of local nerve blocks can prevent nociception right at the point of origin. Orthopedic patients with multiple organ traumas like head injuries, spinal injuries, pulmonary fat embolism, compartment syndrome, or thoracic injuries are high-risk patients in which any life-threatening organ pathology should be addressed before the patient is put under general anesthesia. Interactions of various drugs like antibiotics and neuromuscular blocking agents used in the perioperative period in orthopedic patients should warrant a careful consideration with respect to their interactions with each other and other anesthetic drugs used.

Long-term pain in cats: how much do we know about this important welfare issue?

PRACTICAL RELEVANCE

Long-term pain in cats is an important welfare issue but is often overlooked and undertreated.

AUDIENCE

All practitioners are faced with cats that require analgesic intervention to improve their quality of life.

PATIENT GROUP

Any cat may potentially experience long-term pain and discomfort. Degenerative joint disease and diabetic-related pain is more common in middle-aged or older individuals, whereas persistent postsurgical pain can occur at any age and is seen in young cats following onychectomy.

EVIDENCE BASE

Robust evidence on long-term pain issues in cats - specifically, relating to prevalence, etiology, and treatment protocols and outcomes - is missing from the veterinary literature. The aim of this review is to summarise the current state of knowledge. In doing so, it takes a practical approach, highlighting the obvious, and some not so obvious, causes of long-term pain in cats; some aspects that warrant closer attention; our ability to recognize pain and monitor how this impacts on quality of life; and today's treatment options.

Adjunctive analgesic therapy in veterinary medicine

Adjunctive analgesic therapies are interventions for pain that involve agents or techniques other than the traditional analgesics (opioids, nonsteroidal anti-inflammatory drugs, and local anesthetics). Adjunctive therapies may be pharmacologic or nonpharmacologic in nature. The focus of this article is on pharmacologic interventions with potential utility as adjunctive analgesics in veterinary medicine. Pharmacology of selected agents, including medetomidine, ketamine, amantadine, gabapentin, systemic lidocaine, and pamidronate, is discussed in addition to evidence for their safety and efficacy and guidelines for their use in veterinary patients.

Analgesia for the critically ill dog or cat: an update

Acute pain reliably accompanies severe illness and injury, and when sufficiently severe, it can complicate the recovery of critically ill patients. Because acute pain is closely tied to the neurologic process of nociception, pharmacologic therapy is often essential and effective. This update focuses on two methods of treatment of acute pain-local anesthetic infusion and continuous intravenous infusion of multimodal agents-that can be layered on top of standard care with other drugs.

Perioperative pain management in veterinary patients

Pain exists; however, we can prevent it, and we can treat it. The fallacy that pain is protective and must be allowed to avoid risk for damage after surgery needs to be eradicated. Preoperative and postoperative analgesia is directed at aching pain, whereas sharp pain associated with inappropriate movements persists. Analgesia provides much more benefit than concern. This article provides suggestions for development of an analgesic plan from the point of admission to discharge. These guidelines can then be adjusted according to the patient's needs and responses.

Pharmacokinetics of lidocaine following the application of 5% lidocaine patches to cats

Lidocaine patches have been used to provide local analgesia in dogs and cats. We conducted this study to assess the systemic and local absorption of lidocaine from topical patches in cats. Eight 2-year-old cats received either intravenous lidocaine at 2 mg/kg or one 700 mg lidocaine patch placed on the lateral thorax for 72 h, in a cross-over randomized repeated measures design. Plasma was collected at specific times and the skin was biopsied at the time of patch removal for the quantitative analysis of lidocaine and its major metabolite, monoethylglycinexylidide (MEGX), by gas chromatography with mass spectrometry. Percent absorption time plots for systemic lidocaine appearance were constructed using the Loo-Riegelman method. Approximately, constant rate absorption was observed from 12-72 h after patch application at a mean +/- SD rate of 109 +/- 49 microg/kg/h, resulting in steady-state lidocaine plasma concentrations of 0.083 +/- 0.032 microg/mL and MEGX concentrations of 0.012 +/- 0.009 microg/mL. Overall bioavailability of transdermal lidocaine was 6.3 +/- 2.7%, and only 56 +/- 29% of the total lidocaine dose delivered by the patch reached systemic circulation. Skin lidocaine concentrations were much higher than plasma concentrations, at 211 +/- 113 microg/g in the thoracic skin beneath the patch and 2.2 +/- 0.6 microg/g in the contralateral thoracic skin without the patch. As both lidocaine and MEGX were recovered from contralateral skin, it is likely that lidocaine accumulated in the skin from low systemic concentrations of circulating lidocaine over the 72-h period of patch application. Plasma lidocaine concentrations remained well below systemically toxic concentrations, and no obvious clinical side effects were observed in any of the cats. The low systemic absorption rate coupled with high local lidocaine concentrations on the skin support the safe use of lidocaine patches in cats.

A clinical comparison of two anaesthetic protocols using lidocaine or medetomidine in horses

OBJECTIVE

To compare the effects of two balanced anaesthetic protocols on end-tidal isoflurane (Fe'ISO), cardiopulmonary performance and quality of recovery in horses.

DESIGN

Prospective blinded randomized clinical study.

ANIMALS

Sixty-nine client-owned horses, American Society of Anesthesiologists category I and II, undergoing elective surgery.

METHODS

The horses were premedicated with acepromazine (0.03 mg kg(-1)) IM 30-60 minutes before induction of anaesthesia and were randomly assigned to one of two treatments: in group L (37 horses) xylazine (1 mg kg(-1)) and in group M (31 horses) medetomidine (7 microg kg(-1)) was administered IV for sedation. Anaesthesia was induced 5 minutes later with ketamine (2.2 mg kg(-1)) and diazepam (0.02 mg kg(-1)) IV and maintained with isoflurane in oxygen/air (initial FIO2 0.40-0.50) and a constant rate infusion (CRI) of either lidocaine (2 mg kg(-1)/15 minutes loading dose followed by 50 microg kg(-1) minute(-1)) (group L) or medetomidine (3.5 microg kg(-1) hour(-1)) (group M). If horses showed movement or nystagmus, additional thiopental or ketamine was administered. Heart rate, mean arterial pressure (MAP), Fe'ISO and arterial blood gases were measured. Cardiac output was measured with the lithium dilution method in 10 (group L) and 11 (group M) horses every 45 minutes. Recovery was scored.

RESULTS

Heart rate and the cardiac index (CI) were significantly higher in group L with changes over time. In group M, MAP was significantly higher during the first 50 minutes. Group L needed more additional ketamine and thiopental to maintain a surgical plane of anaesthesia and Fe'ISO was significantly higher from 70 minutes. Recovery was longer in group M and of better quality. The significance level was set at p < 0.05.

CONCLUSIONS AND CLINICAL RELEVANCE

In group M, maintenance of stable anaesthetic depth was easier and lower Fe'ISO was required to maintain a surgical plane of anaesthesia. Recoveries were longer but of better quality. The CI was higher in group L but cardiovascular function was generally well maintained in both groups.

The effects of ketamine on the minimum alveolar concentration of isoflurane in cats

OBJECTIVES

To determine the minimum alveolar concentration (MAC) of isoflurane during the infusion of ketamine.

STUDY DESIGN

Prospective, experimental trial.

ANIMALS

Twelve adult spayed female cats weighing 5.1 +/- 0.9 kg.

METHODS

Six cats were anesthetized with isoflurane in oxygen, intubated and attached to a circle-breathing system with mechanical ventilation. Catheters were placed in a peripheral vein for the infusion of fluids and ketamine, and the jugular vein for blood sampling for the measurement of ketamine concentrations. An arterial catheter was placed to allow blood pressure measurement and sampling for the measurement of PaCO2, PaO2 and pH. PaCO2 was maintained between 29 and 41 mmHg (3.9-5.5 kPa) and body temperature was kept between 37.8 and 39.3 degrees C. Following instrumentation, the MAC of isoflurane was determined in triplicate using a tail clamp method. A loading dose (2 mg kg(-1) over 5 minutes) and an infusion (23 microg kg(-1) minute(-1)) of ketamine was started and MAC was redetermined starting 30 minutes later. Two further loading doses and infusions were used, 2 mg kg(-1) and 6 mg kg(-1) with 46 and 115 microg kg(-1) minute(-1), respectively and MAC was redetermined. Cardiopulmonary measurements were taken before application of the noxious stimulus. The second group of six cats was used for the measurement of steady state plasma ketamine concentrations at each of the three infusion rates used in the initial study and the appropriate MAC value determined from the first study.

RESULTS

The MAC decreased by 45 +/- 17%, 63 +/- 18%, and 75 +/- 17% at the infusion rates of 23, 46, and 115 microg kg(-1) minute(-1). These infusion rates corresponded to ketamine plasma concentrations of 1.75 +/- 0.21, 2.69 +/- 0.40, and 5.36 +/- 1.19 microg mL(-1). Arterial blood pressure and heart rate increased significantly with ketamine. Recovery was protracted.

CONCLUSIONS AND CLINICAL RELEVANCE

The MAC of isoflurane was significantly decreased by an infusion of ketamine and this was accompanied by an increase in heart rate and blood pressure. Because of the prolonged recovery in our cats, further work needs to be performed before using this in patients.

Effects of intravenous administration of lidocaine on the thermal threshold in cats

OBJECTIVE

To determine the effects of IV administration of lidocaine on thermal antinociception in conscious cats.

ANIMALS

6 cats.

PROCEDURE

2 experiments were performed in each cat (interval of at least 2 months). In experiment 1, lidocaine pharmacokinetics were determined for each conscious cat following IV administration of a bolus of lidocaine (2 mg/kg). In experiment 2, data from experiment 1 were used to calculate appropriate doses of lidocaine that would achieve predetermined plasma lidocaine concentrations in the cats; lidocaine (or an equivalent volume of saline [0.9% NaCl] solution as the control treatment) was administered IV to target pseudo-steady-state plasma concentrations of 0, 0.5, 1, 2, 5, and 8 microg/mL. Skin temperature and thermal threshold were determined at the start of the experiment (baseline) and at each concentration. Samples of venous blood were obtained at each target concentration for plasma lidocaine concentration determination.

RESULTS

In experiment 2, actual plasma lidocaine concentrations were 0.00 +/- 0.00 microg/mL, 0.25 +/- 0.18 microg/mL, 0.57 +/- 0.20 microg/mL, 1.39 +/- 0.13 microg/mL, 2.33 +/- 0.45 microg/mL, and 4.32 +/- 0.66 microg/mL for target plasma concentrations of 0, 0.5, 1, 2, 5, and 8 microg/mL, respectively. Compared with baseline values, no significant change in skin temperature or thermal threshold was detected at any lidocaine plasma concentration (or saline solution equivalent). Skin temperature or thermal threshold values did not differ between lidocaine or control treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that these moderate plasma concentrations of lidocaine did not affect thermal antinociception in cats.