Evaluation of the isoflurane-sparing effects of fentanyl, lidocaine, ketamine, dexmedetomidine, or the combination lidocaine-ketamine-dexmedetomidine during ovariohysterectomy in dogs

Influence of intravenous fentanyl or dexmedetomidine infusions, combined with lidocaine and ketamine, on cardiovascular response, sevoflurane requirement and postoperative pain in dogs anesthetized for unilateral mastectomy

OBJECTIVE

To compare the effects of constant rate infusions (CRI) of fentanyl or dexmedetomidine, combined with lidocaine and ketamine, on cardiovascular response during surgery, sevoflurane requirement and postoperative pain in dogs undergoing mastectomy.

STUDY DESIGN

Prospective, randomized, blinded, clinical trial.

ANIMALS

A total of 29 female dogs with mammary tumors.

METHODS

Premedication consisted of intramuscular acepromazine and morphine. General anesthesia was induced with intravenous propofol and maintained with sevoflurane. Dogs were randomized to be administered intravenous DLK [dexmedetomidine 1 μg kg-1 loading dose (LD) and 1 μg kg-1 hour-1; lidocaine 2 mg kg-1 LD and 3 mg kg-1 hour-1; ketamine 1 mg kg-1 LD and 0.6 mg kg-1 hour-1; n = 14] or FLK (fentanyl 5 μg kg-1 LD and 9 μg kg-1 hour-1; same doses of lidocaine and ketamine; n = 15) during anesthesia. Cardiorespiratory variables and end-tidal sevoflurane (Fe'Sevo) were recorded during surgery. The number of dogs administered ephedrine to treat arterial hypotension [mean arterial pressure (MAP) < 60 mmHg] was recorded. Meloxicam was administered to both groups. Postoperative pain and rescue analgesia requirement were assessed for 24 hours using the short form of the Glasgow Composite Measure Pain Scale. Data were compared using a mixed effects model or a Mann-Whitney test.

RESULTS

More dogs required ephedrine in FLK than in DLK (67% versus 7%). Heart rate was not significantly different between groups, whereas lower values of MAP (p ≤ 0.01) and Fe'Sevo (p = 0.018) were observed in FLK than in DLK. Rescue analgesia was administered to 2/15 dogs in FLK and 0/14 dogs in DLK.

CONCLUSIONS AND CLINICAL RELEVANCE

Based on the cardiovascular response during surgery, intraoperative infusions of FLK and DLK provided adequate antinociception. Infusion of DLK provided greater stability of blood pressure. Both protocols resulted in minimal need for additional analgesia within 24 hours postoperatively.

Randomized clinical trial comparing outcomes after fentanyl or ketamine-dexmedetomidine analgesia in thoracolumbar spinal surgery in dogs

Background

Opioids are widely used for perioperative pain control in dogs undergoing spinal surgery, but alternatives may be required because data suggest that opioids exacerbate inflammation in the injured spinal cord and veterinary access to opioids may become more restricted in the future.

Objectives

To compare recovery of ambulation and other functions between spinal cord‐injured dogs receiving peri‐operative fentanyl and those receiving a ketamine‐dexmedetomidine combination.

Animals

A total of 102 client‐owned dogs undergoing decompressive surgery for thoracolumbar intervertebral disc herniation.

Methods

Randomized clinical trial. Dogs were randomized 1:1 to fentanyl or a ketamine‐dexmedetomidine combination for intra and postoperative analgesia. Primary outcome was time to recovery of ambulation; secondary outcomes were the postoperative Colorado Acute Pain Scale, the short‐form Glasgow Composite Measure Pain Scale, time to recovery of voluntary urination and time to unassisted eating.

Results

No difference was found in time to recovery of ambulation between groups (adjusted sub‐hazard ratio, 0.83; 95% confidence interval [CI], 0.55‐1.24; P = .36) or in pain scores (Colorado: χ² = 14.74; P = .32; Glasgow: χ² = 6.61; P = .76). Differences in time to recovery of eating and urination were small but favored ketamine‐dexmedetomidine (adjusted odds ratios, 3.31; 95% CI, 1.53‐7.16; P = .002 and 2.43; 95% CI, 1.00‐5.96; P = .05, respectively).

Conclusions and Clinical Importance

There was no evidence that, at the doses used, fentanyl impaired ambulatory outcome after surgery for thoracolumbar intervertebral disc herniation in dogs. Pain control appeared similar between groups. Secondary outcomes suggested minor benefits associated with ketamine‐dexmedetomidine. The ketamine‐dexmedetomidine combination appears to be a reasonable alternative to peri‐operative opioids.

Epidural Volume of Injectate Using a Dose Regimen Based on Occipito-Coccygeal Spinal Length (OCL): Randomized Clinical Study Comparing Different Ropivacaine Concentrations, with or without Morphine, in Bitches Undergoing Total Unilateral Mastectomy

A prospective, randomized clinical trial was designed to compare four epidural treatments in dogs undergoing total unilateral mastectomy. The epidural volume of injectate was based on the individual occipito-coccygeal length (OCL) aiming to reach the first thoracic vertebra (T1). The first ten dogs were allocated in a control group (C) and did not receive epidural treatment. Subsequently, forty dogs were randomly allocated in four groups of ten: epidural ropivacaine 0.5% (R0.5%); morphine 0.1 mg kg−1 plus ropivacaine 0.5% (MR0.5%); morphine 0.1 mg kg−1 plus ropivacaine 0.35% (MR0.35%); morphine 0.1 mg kg−1 plus ropivacaine 0.25% (MR0.25%). Intraoperatively, isoflurane requirement (1.3% vs. <1.1% FE’Iso) and fentanyl requirement (9.8 vs. <1.1 µg kg−1 h−1) were significantly higher in C group compared to all epidural groups. Postoperatively, methadone requirement was higher (1.8 mg kg−1 vs. <0.8 mg kg−1) for C group compared to all epidural treatment groups. The ability to walk and to urinate returned 4 h earlier in MR0.35% and MR0.25%. The mean epidural volume of ropivacaine, using a dose regimen based on OCL, to reach T1 was about 0.15 mL cm−1. The addition of morphine further reduced the methadone requirement, without affecting urinary and motor functions.

Target-controlled inhalational anesthesia-isoflurane consumption with adequacy of anesthesia monitoring in conventional and multimodal analgesia – A comparative study

Background:

In a time of increased concern over the environmental impact of chlorofluorocarbons, there is an impetus to minimize inhalational anesthetic consumption. It is possible with multimodal analgesia (MMA) and the use of end-tidal controlled anesthesia (EtCA) which is a low-flow anesthesia technique with adequacy of anesthesia (AoA) monitoring. In MMA, all four elements of pain processing namely transduction, transmission, modulation, and perception are targeted with drugs having a different mechanism of action. In EtCA, anesthetic gases are automatically adjusted for the set minimal alveolar concentration by newer anesthesia work station (GE Healthcare Aisys CS2). AoA is a derived parameter of entropy and surgical pleth index which measures the depth of anesthesia and analgesia, respectively.

Aim:

The aim is to assess the difference in isoflurane consumption between MMA and conventional groups for a given period of time with EtCA and AoA monitoring.

Setting and Design:

This was a prospective randomized controlled trial involving 60 patients undergoing laparoscopic cholecystectomy. They were divided into MMA group and conventional group.

Materials and Methods:

Both the groups received preemptive intravenous diclofenac sodium 75 g and 2% xyloadrenaline infiltration at entry ports. MMA group in addition received paracetamol 1 g and clonidine 0.75 μg.kg^{− 1}. Intraoperatively, patients were on EtCA with AoA monitoring.

Statistical Analysis:

Mean differences in isoflurane consumption between the two groups were compared using an independent t-test. Postextubation adverse effects of analgesic drugs and awareness under general anesthesia were compared using the Chi-square test and presented as numbers and percentages. P < 0.05 was considered a statistically significant.

Results:

Mean isoflurane consumption in the conventional group was 12.7 ± 5.3 mL which was significantly higher than the MMA group which was 8.9 ± 4.1 mL (P = 0.002). The duration of anesthesia between the groups was not significant clinically (P = 0.931).

Conclusion:

EtCA with MMA significantly reduces isoflurane consumption compared to the conventional group of anesthesia.

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.

Efficacy and Safety of Dexmedetomidine Premedication in Balanced Anesthesia: A Systematic Review and Meta-Analysis in Dogs

Simple Summary

Dexmedetomidine, on account of its potent sedative and analgesic properties, is commonly used in balanced anesthesia of small animal anesthesia; however, concerns regarding its cardiovascular effects prevent its full adoption into veterinary clinical practice. We conducted this meta-analysis to determine the effects of dexmedetomidine on sedation, analgesia, cardiovascular and adverse reactions in dogs compared to other premedications. The outcomes included sedation score, pain score, heart rate, systolic arterial blood pressure, mean arterial blood pressure and the incidence of adverse effects. Thirteen studies were included in this meta-analysis. The results showed that dexmedetomidine provides a satisfactory sedative and analgesic effect in balanced anesthesia of dogs. After dexmedetomidine premedication, dogs experienced lower heart rate and higher blood pressure within an acceptable range. The combinations in balanced anesthesia and routes of delivering drugs would affect heart rate, systolic arterial blood pressure, and mean arterial blood pressure of dogs. Before using dexmedetomidine, an animal’s cardiovascular status should be fully considered.

Abstract

Dexmedetomidine is commonly used in small animal anesthesia for its potent sedative and analgesic properties; however, concerns regarding its cardiovascular effects prevent its full adoption into veterinary clinical practice. This meta-analysis was to determine the effects of dexmedetomidine on sedation, analgesia, cardiovascular and adverse reactions in dogs compared to other premedications. Following the study protocol based on the Cochrane Review Methods, thirteen studies were included in this meta-analysis ultimately, involving a total of 576 dogs. Dexmedetomidine administration probably improved in sedation and analgesia in comparison to acepromazine, ketamine and lidocaine (MD: 1.96, 95% CI: [−0.08, 4.00], p = 0.06; MD: −0.95, 95% CI: [−1.52, −0.37] p = 0.001; respectively). Hemodynamic outcomes showed that dogs probably experienced lower heart rate and higher systolic arterial blood pressure and mean arterial blood pressure with dexmedetomidine at 30 min after premedication (MD: −13.25, 95% CI: [−19.67, −6.81], p < 0.0001; MD: 7.78, 95% CI: [1.83, 13.74], p = 0.01; MD: 8.32, 95% CI: [3.95, 12.70], p = 0.0002; respectively). The incidence of adverse effects was comparable between dexmedetomidine and other premedications (RR = 0.86, 95% CI [0.58, 1.29], p = 0.47). In summary, dexmedetomidine provides satisfactory sedative and analgesic effects, and its safety is proved despite its significant hemodynamic effects as part of balanced anesthesia of dogs.

Effect of Fentanyl Infusion on Heart Rate Variability and Anaesthetic Requirements in Isoflurane-Anaesthetized Horses

Controversy continues to surround the use of opioids in equine anaesthesia, with variable effects reported. This blinded clinical study aimed to investigate the influence of a low-dose fentanyl continuous rate infusion (CRI) on isoflurane requirements, parasympathetic tone activity (PTA), and anaesthetic parameters in horses during general anaesthesia. All of the twenty-two horses included in the research underwent a standard anaesthetic protocol. Eleven horses in the fentanyl group (Group F) received a loading dose of fentanyl at 6 µg/kg, followed by a CRI of 0.1 µg/kg/min during anaesthesia. A further 11 horses in the control group (Group C) received equivalent volumes of normal saline. Anaesthetic parameters and PTA index were recorded during anaesthesia. The achieved mean fentanyl plasma concentration was 6.2 ± 0.83 ng/mL. No statistically significant differences between groups were found in isoflurane requirements, MAP values, and mean dobutamine requirements. However, horses in Group F required a significantly lower dose of additional ketamine to maintain a sufficient depth of anaesthesia. Significantly higher PTA values were found in the fentanyl group. Further research is warranted to determine the limitations of PTA monitoring, and the influence of various anaesthetics on its values.

Evaluation of the analgesic effect of fentanyl-ketamine and fentanyl-lidocaine constant rate infusions in isoflurane-anesthetized dogs undergoing thoracolumbar hemilaminectomy

OBJECTIVE

To evaluate anesthetic conditions and postoperative analgesia with the use of intraoperative constant rate infusions (CRIs) of fentanyl-lidocaine or fentanyl-ketamine in dogs undergoing thoracolumbar hemilaminectomy.

STUDY DESIGN

Prospective, randomized, blinded, clinical study.

ANIMALS

A total of 32 client-owned dogs.

METHODS

Dogs were premedicated with fentanyl (5 μg kg^-1) administered intravenously (IV), anesthesia was induced with IV alfaxalone and maintained with isoflurane. Fentanyl (0.083 μg kg^-1 minute^-1) was infused IV with either ketamine (0.5 mg kg^-1; then 40 μg kg^-1 minute^-1; group KF) or lidocaine (2 mg kg^-1; then 200 μg kg^-1 minute^-1; group LF) assigned randomly. Heart rate, noninvasive arterial pressures, respiratory rate, esophageal temperature, end-tidal partial pressure of carbon dioxide and isoflurane concentration were recorded throughout anesthesia. Maintenance of anesthesia, recovery and postoperative pain (Glasgow Composite Pain Scale) were scored. Cardiopulmonary data were analyzed using a two-way anova with repeated measures, demographics of the two groups with a t test, and scores with Mann-Whitney U test, with p < 0.05.

RESULTS

All dogs recovered from anesthesia without complications. No significant difference was found between groups for cardiopulmonary variables, total anesthesia time, sedation score and requirement for postoperative sedation or for rescue analgesia. Anesthetic maintenance score was of lower quality in KF than in LF [median (interquartile range): 0 (0-0.5) versus 0 (0-0); p = 0.032)], but still considered ideal. Recovery score was higher and indicative of less sedation in LF than in KF [1 (1-1.5) versus 0.5 (0-1); p < 0.0001]. Pain score was higher in KF than in LF [2 (1-3) versus 1 (1-2); p = 0.0009].

CONCLUSIONS AND CLINICAL RELEVANCE

Both CRIs of KF and LF provided adequate anesthetic conditions in dogs undergoing thoracolumbar hemilaminectomy. Based on requirement for rescue analgesia, postoperative analgesia was adequate in both groups.

Cardiovascular and renal effects of constant rate infusions of remifentanil, dexmedetomidine and their combination in dogs anesthetized with sevoflurane

We evaluated changes in cardiovascular and renal functions as well as arginine vasopressin (AVP) secretion, with remifentanil and dexmedetomidine administration alone or in combination in sevoflurane-anesthetized dogs. Six healthy adult Beagle dogs received one of the following four treatments in a randomized crossover study: saline (C), remifentanil alone at successively increasing doses (R; 0.15, 0.60, and 2.40 µg/kg/min), dexmedetomidine alone (D; 0.5 µg/kg intravenously for initial 10 min followed by a constant rate infusion at 0.5 µg/kg/hr), and a combination of remifentanil and dexmedetomidine at the above-mentioned doses (RD). Sevoflurane doses were adjusted to 1.5 times of minimum alveolar concentration (MAC) equivalent according to MAC-sparing effects with remifentanil and dexmedetomidine as previously reported. Cardiovascular measurements, renal function data, and plasma AVP concentrations were determined before and every 60 min until 180 min after drug administration as per each treatment. In the R, D and RD, heart rate significantly decreased and mean arterial pressure significantly increased from baseline or with C. Cardiac index significantly decreased and systemic vascular resistance index increased with D and RD. Oxygen extraction ratio, renal blood flow, and glomerular filtration rate were not affected. The plasma AVP concentrations significantly decreased in D and RD, but increased in R. Only in D, the natriuresis was elicited. The combination of remifentanil and dexmedetomidine in sevoflurane-anesthetized dogs was acceptable in terms of the hemodynamics, oxygenation, and renal function. Remifentanil may interfere with dexmedetomidine-induced diuresis and inhibition of AVP secretion.

World Small Animal Veterinary Association Global Dental Guidelines

Dental, oral, and maxillofacial diseases are some of the most common problems in small animal veterinary practice. These conditions create significant pain as well as localized and potentially systemic infection. As such, the World Small Animal Veterinary Association (WSAVA) believes that un- and under treated oral and dental diseases pose a significant animal welfare concern. Dentistry is an area of veterinary medicine which is still widely ignored and is subject to many myths and misconceptions. Effective teaching of veterinary dentistry in the veterinary school is the key to progression in this field of veterinary medicine, and to the improvement of welfare for all our patients globally. These guidelines were developed to provide veterinarians with the information required to understand best practices for dental therapy and create realistic minimum standards of care. Using the three-tiered continuing education system of WSAVA, the guidelines make global equipment and therapeutic recommendations and highlight the anaesthetic and welfare requirements for small animal patients. This document contains information on common oral and dental pathologies, diagnostic procedures (an easily implementable and repeatable scoring system for dental health, dental radiography and radiology) and treatments (periodontal therapy, extractions). Further, there are sections on anaesthesia and pain management for dental procedures, home dental care, nutritional information, and recommendations on the role of the universities in improving veterinary dentistry. A discussion of the deleterious effects of anaesthesia free dentistry (AFD) is included, as this procedure is ineffective at best and damaging at worst. Throughout the document the negative effects of undiagnosed and/or treated dental disease on the health and well-being of our patients, and how this equates to an animal welfare issue, is discussed.

Effects of fentanyl-lidocaine-ketamine versus sufentanil-lidocaine-ketamine on the isoflurane requirements in dogs undergoing total ear canal ablation and lateral bulla osteotomy

OBJECTIVE

To compare the isoflurane-sparing effects of sufentanil-lidocaine-ketamine (SLK) and fentanyl-lidocaine-ketamine (FLK) infusions in dogs undergoing total ear canal ablation and lateral bulla osteotomy (TECA-LBO).

STUDY DESIGN

Randomized blinded clinical study.

ANIMALS

A group of 20 client-owned dogs undergoing TECA-LBO.

METHODS

Intravenous (IV) administration of lidocaine (3 mg kg^-1) and ketamine (0.6 mg kg^-1) with fentanyl (5.4 μg kg^-1; n = 10; FLK group) or sufentanil (0.72 μg kg^-1; n = 10; SLK group) was immediately followed by the corresponding constant rate infusion (CRI) (lidocaine 3 mg kg^-1 hour^-1; ketamine 0.6 mg kg^-1 hour^-1; either fentanyl 5.4 μg kg^-1 hour^-1 or sufentanil 0.72 μg kg^-1 hour^-1). Anaesthesia was induced with propofol 3-5 mg kg^-1 IV and was maintained with isoflurane. End-tidal isoflurane concentration (Fe'Iso) was decreased in 0.2% steps every 15 minutes until spontaneous movements were observed (treated with propofol 1 mg kg^-1 IV) or an increase of > 30% in heart rate or mean arterial pressure from baseline occurred (treated with rescue fentanyl or sufentanil). Quality of recovery and pain were assessed at extubation using the short-form Glasgow Composite Pain Scale (SF-GCPS), Colorado State University Canine Acute Pain scale (CSU-CAP), and visual analogue scale (VAS). Data were analysed with analysis of variance, t tests, Fisher test and Spearman coefficient (p < 0.05).

RESULTS

Fe'Iso decreased significantly in SLK group (45%; p = 0.0006) but not in FLK (15%; p = 0.1135) (p = 0.0136). SLK group had lower scores for recovery quality (p = 0.0204), SF-GCPS (p = 0.0071) and CSU-CAP (p = 0.0273) than FLK at extubation. Intraoperative rescue analgesia and VAS were not significantly different between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with FLK infusion, CRI of SLK at these doses decreased isoflurane requirements, decreased pain scores and improved recovery quality at extubation in dogs undergoing TECA-LBO.

Onset and duration of cis-atracurium neuromuscular block during fentanyl and lidocaine infusions in isoflurane-anaesthetised dogs

BACKGROUND

This retrospective study assessed the onset and duration of the neuromuscular block (NMB) induced by cis-atracurium 0.15 mg/kg intravenously with and without fentanyl or lidocaine infusions in 45 isoflurane-anaesthetised dogs.

METHODS

Dogs with neuromuscular function assessed by a calibrated train-of-four (TOF) monitor with stimulation (every 13 s) of the peroneal nerve were included. The onset and duration of the NMB were defined as the time from cis-atracurium administration until TOF=0 and the time during TOF=0 display, respectively.

RESULTS

The NMB onset was shorter during fentanyl (mean±sd) (1.9±0.7 minutes; P=0.0042) and lidocaine (2.0±0.7 minutes; P=0.0154) compared with control (2.9±0.8 minutes). The NMB duration was shorter in the fentanyl (27.5±7.3 minutes; P=0.0491), but not in the lidocaine group (32.3±6.9 minutes; P=0.0790), compared with control (33.7±9.1 minutes). The NMB onset was poorly but significantly correlated with the dose of fentanyl and lidocaine administered before cis-atracurium (r=-0.3396; P=0.0225). The fentanyl and lidocaine groups received more crystalloid and colloid boluses than the control.

CONCLUSIONS

Fentanyl and lidocaine shortened the NMB onset and the former decreased the NMB duration. Further prospective studies are required to clarify whether this was associated with an indirect decrease in blood pressure or a direct interaction between cis-atracurium and fentanyl and lidocaine.

Recuperação anestésica e analgesia residual da infusão continua intravenosa de fantanil, lidocaína, cetamina e fentanyl-lidocaína-cetamina associados à anesthesia total intravenosa com Propofol em cadelas submetidas à ovariossalpingo-histerectomia eletiva

RESUMO Avaliou-se a recuperação anestésica e a analgesia residual da infusão contínua (IC) de fentanil (F), lidocaína (L), cetamina (K) e fentanil-lidocaína-cetamina (FLK), associados à anestesia total intravenosa com o propofol, em cadelas submetidas à ovariossalpingo-histerectomia. Foram utilizados 32 animais pré-medicados com acepromazina, distribuídos em quatro grupos de acordo com o tratamento analgésico: F: bolus de 0,0036mg/kg de fentanil e IC de 0,0036mg mg/kg/h; L: bolus de 3mg/kg de lidocaína e IC de 3mg/kg/h; K: bolus de 0,6mg/kg de cetamina e IC de 0,6mg/kg/h; e FLK: bolus e IC dos três fármacos nas doses supracitadas. Após o bolus do tratamento analgésico, foi realizada a indução e o início da IC do tratamento analgésico e do propofol. Para avaliação da recuperação anestésica, foram considerados os tempos de extubação, decúbito esternal, posição quadrupedal e os efeitos adversos. A avaliação da analgesia foi realizada por meio da escala visual analógica e modificada de Glasgow, durante seis horas. Os efeitos adversos observados foram vômito, sialorreia e tremor muscular. Receberam analgesia de resgate 100% dos animais do grupo F, 87,5% do K, 50% do L e 12,5% do FLK. O FLK demonstrou maior analgesia, e a recuperação anestésica foi semelhante em todos os grupos.

Adjuvant Analgesics in Acute Pain Management

Adjuvant analgesics (ie, gabapentin, tramadol, and ketamine) are commonly used in small animal practice. Most of these drugs are prescribed for outpatients, when pain is refractory to classic analgesics (ie, local anesthetics, opioids, and nonsteroidal antiinflammatory drugs [NSAIDs]), or when contraindications exist to the administration of other analgesics, including NSAIDs. This article reviews the mechanisms of action, clinical use, potential adverse effects, and current evidence of adjuvant analgesics in the treatment of acute pain in companion animals. These drugs should be considered as alternatives aimed at reducing or replacing opioids.

Efficacy of the Parasympathetic Tone Activity monitor to assess nociception in healthy dogs anaesthetized with propofol and sevoflurane

OBJECTIVE

To compare a Parasympathetic Tone Activity (PTA) monitor with cardiovascular changes in invasive mean arterial pressure (IMAP) and heart rate (HR) when evaluating the response to nociceptive stimuli in anaesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A group of nine (seven male and two female) adult Beagle dogs weighing 13.4 ± 1.5 kg (mean ± standard deviation).

METHODS

Anaesthesia was induced with propofol and maintained with sevoflurane in oxygen. Electrical stimuli of different nociceptive intensities were applied for 30 seconds. Stimuli were classified in each patient according to the response obtained (relevant change ≥ 20%) as low (no response), medium (PTA only) or high (PTA and IMAP/HR). Immediate and averaged values of PTA, IMAP and HR were recorded every second from 60 seconds before to 120 seconds after application of the nociceptive stimulus. Time to nociceptive response and peak response were evaluated with analysis of variance and t test.

RESULTS

Immediate PTA baseline values did not differ significantly before application of the low, medium and high stimuli (73 ± 15, p = 0.966). Immediate PTA response was observed with the medium stimulus at 33 ± 7 seconds with a maximum decrease of 57 ± 13% at 69 ± 5 seconds. With the high stimulus, the immediate PTA response was of a similar magnitude to the medium stimulus with a response at 28 ± 7 seconds (p = 0.221) and a maximum decrease of 68 ± 15% (p = 0.115) at 72 ± 7 seconds (p = 0.436). The cardiovascular change occurred (22 ± 8 seconds) prior to the immediate PTA response (p = 0.032).

CONCLUSIONS AND CLINICAL RELEVANCE

The PTA monitor detected nociceptive stimuli at lower intensities than those eliciting cardiovascular changes. However, nociceptive stimuli of higher intensities provoked cardiovascular changes that occurred before a PTA response was observed.

Comparison of Noninvasive Dynamic Indices of Fluid Responsiveness Among Different Ventilation Modes in Dogs Recovering from Experimental Cardiac Surgery

Background

Fluid resuscitation is a cornerstone of minimizing morbidity and mortality in critically ill patients, but the techniques for predicting fluid responsiveness is still a matter of debate. In this study, we aimed to evaluate the utility of noninvasive stroke volume variation (SVV), pulse pressure variation (PPV), and systolic pressure variation (SPV) as a dynamic predictor for assessing fluid responsiveness during different ventilation modes in anaesthetized, intubated dogs recovering from cardiac surgery.

Material/Methods

Thirty-six adult Beagle dogs undergoing experimental surgery for isolated right ventricular failure were monitored for SVV, PPV, and SPV simultaneously using electrical velocimetry device. The relationships between each indicator and SVI before and after volume loading were compared in 3 ventilatory modes: assist control (A/C), synchronized intermittent mandatory ventilation (SIMV), and continuous positive airway pressure (CPAP). Responders were defined as those whose stroke volume index increased by ≥10%.

Results

In all of the indices, the baseline values were greater in responders than in nonresponders (P<0.01) under A/C and SIMV. Receiver operating curve analysis confirmed the best predictive value during A/C [area under the curve (AUC): SVV, 0.90; PPV, 0.88; SPV, 0.85; P<0.05] followed by SIMV (AUC: SVV, 0.86; PPV, 0.83; CPAP, 0.80; P<0.05), with their sensitivities and specificities of ≥7 5%. By contrast, no statistically significance detected in any parameter during CPAP (AUC: SVV, 0.71; PPV, 0.66; CPAP, 0.65; P>0.05).

Conclusions

SVV, PPV, and SVV are all useful to predict cardiac response to fluid loading in dogs during A/C and SIMV, while their reliabilities during CPAP are poor.

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.

Effect of dexmedetomidine on the minimum infusion rate of propofol preventing movement in dogs

OBJECTIVE

To determine the effect of dexmedetomidine on induction dose and minimum infusion rate of propofol preventing movement (MIR_NM).

STUDY DESIGN

Randomized crossover, unmasked, experimental design.

ANIMALS

Three male and three female healthy Beagle dogs weighing 10.2 ± 2.8 kg.

METHODS

Dogs were studied on three occasions at weekly intervals. Premedications were 0.9% saline (treatment P) or dexmedetomidine (1 μg kg^-1, treatment PLD; 2 μg kg^-1, treatment PHD) intravenously. Anesthesia was induced with propofol (2 mg kg^-1 and then 1 mg kg^-1 every 15 seconds) until intubation. Anesthesia was maintained for 90 minutes in P with propofol (0.5 mg kg^-1 minute^-1) and saline, in PLD with propofol (0.35 mg kg^-1 minute^-1) and dexmedetomidine (1 μg kg^-1 hour^-1), and in PHD with propofol (0.3 mg kg^-1 minute^-1) and dexmedetomidine (2 μg kg^-1 hour^-1). The stimulus (50 V, 50 Hz, 10 ms) was applied to the antebrachium, and propofol infusion was increased or decreased by 0.025 mg kg^-1 minute^-1 based on a positive or negative response, respectively. Data were analyzed using a mixed-model anova and presented as mean ± standard error.

RESULTS

Propofol induction doses were 8.68 ± 0.57 (P), 6.13 ± 0.67 (PLD) and 4.78 ± 0.39 (PHD) mg kg^-1 and differed among treatments (p < 0.05). Propofol MIR_NM values were 0.68 ± 0.13, 0.49 ± 0.16 and 0.26 ± 0.05 mg kg^-1 minute^-1 for P, PLD and PHD, respectively. Propofol MIR_NM decreased 59% in PHD (p < 0.05). Plasma propofol concentrations were 14.04 ± 2.30 (P), 11.30 ± 4.30 (PLD) and 7.96 ± 0.72 (PHD) μg mL^-1 and dexmedetomidine concentrations were 0.68 ± 0.12 (PLD) and 0.89 ± 0.08 (PHD) ng mL^-1 at MIR_NM determination.

CONCLUSIONS AND CLINICAL RELEVANCE

Dexmedetomidine (1 and 2 μg kg^-1) decreased propofol induction dose. Dexmedetomidine (2 μg kg^-1 hour^-1) resulted in a significant decrease in propofol MIR_NM.

Isoflurane minimum alveolar concentration sparing effects of fentanyl in the dog

OBJECTIVE

To characterize the isoflurane-sparing effects of a high and a low dose of fentanyl in dogs, and its effects on mean arterial pressure (MAP) and heart rate (HR).

STUDY DESIGN

Prospective, randomized crossover trial.

ANIMALS

Eight healthy male Beagle dogs weighing 12.1 ± 1.6 kg [mean ± standard deviation (SD)] and approximate age 1 year.

METHODS

Dogs were anesthetized using isoflurane and minimum alveolar concentration (MAC) was determined in duplicate by the bracketing method using an electrical stimulus on the tarsus. Animals were administered fentanyl: low dose (33 μg kg-1 loading dose, 0.2 μg kg-1 minute-1) or high dose (102 μg kg-1 loading dose, 0.8 μg kg-1 minute-1) and MAC was re-determined (MACISO-F). Blood was collected for analysis of plasma fentanyl concentrations before administration and after MACISO-F determination. All values are presented as mean ± SD.

RESULTS

Isoflurane MAC (MACISO) was 1.30 ± 0.23% in the low dose treatment, which significantly decreased to 0.75 ± 0.22% (average MAC reduction 42.3 ± 9.4%). MACISO was 1.30 ± 0.18% in the high dose treatment, which significantly decreased to 0.30 ± 0.11% (average MAC reduction 76.9 ± 7.4%). Mean fentanyl plasma concentrations were 6.2 and 29.5 ng mL-1 for low and high dose treatments, respectively. MAP increased significantly only in the high dose treatment (from 81 ± 8 to 92 ± 9 mmHg). HR decreased significantly in both treatments from 108 ± 25 to 61 ± 14 beats minute-1 with the low dose and from 95 ± 14 to 42 ± 4 beats minute-1 with the high dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl administration resulted in a dose-dependent isoflurane MAC-sparing effect with bradycardia at both doses and an increase in MAP only at high dose. Further evaluation is needed to determine the effects of fentanyl on the overall cardiovascular function.

A retrospective study of anesthesia for subcutaneous ureteral bypass placement in cats: 27 cases

The goals of this retrospective clinical case series study were to describe the management of anesthesia, and to report perioperative complications in cats undergoing subcutaneous ureteral bypass (SUB) placement due to ureteral obstruction. Medical records of client-owned cats with ureteral obstruction and anesthetized for SUB placement between 2012 and 2015 in a veterinary teaching hospital were reviewed. Twenty-seven cases were identified. Duration of anesthesia and surgery (mean ± standard deviation) were 215 ± 42 min and 148 ± 36 min, respectively. Hypothermia was the most common intraoperative complication. Hypotension, hypocapnia, hypertension and bradycardia were also frequently observed. Out of 22 cats who experienced intraoperative hypotension, 17 received inotropes and vasopressors. There was a significant decrease in creatinine (P=0.008) and total solids (P=0.007) after SUB placement when compared with baseline values. Postoperative complications included pain, anorexia, nausea, hypertension, and urinary tract-related problems. No death occurred in the postoperative period. Successful management of anesthesia for SUB placement involves rigorous anesthetic monitoring and immediate treatment of complications. Perioperative complications appear to be common. This study could not identify risk factors associated with this procedure.

Alfaxalone alone or combined with midazolam or ketamine in dogs: intubation dose and select physiologic effects

OBJECTIVE

To determine the intubation dose and select physiologic effects of alfaxalone alone or in combination with midazolam or ketamine in dogs.

STUDY DESIGN

Prospective, clinical study.

ANIMALS

Fifty-three healthy client-owned dogs [mean±standard deviation (SD)] 5.1±1.8 years, 27±15.4 kg, scheduled for elective orthopedic surgery.

METHODS

After premedication with acepromazine (0.02 mg kg^-1) and hydromorphone (0.1 mg kg^-1) intramuscularly, alfaxalone (0.25 mg kg^-1) was administered intravenously over 15 seconds followed immediately by 0.9% saline (AS), midazolam (0.3 mg kg^-1; AM), ketamine (1 mg kg^-1; AK1), or ketamine (2 mg kg^-1; AK2). Additional alfaxalone (0.25 mg kg^-1 increments) was administered as required to permit endotracheal intubation. The incidence of apnea and the time from intubation until spontaneous movement were recorded. Heart rate (HR) and blood pressure were recorded 15 minutes after premedication, after intubation and 2, 5, 10 and 15 minutes thereafter. Blood was collected for measurement of serum glucose and insulin concentrations before induction, after intubation and at 2, 5, 10 and 50 minutes. Data were analyzed by split-plot anova with Bonferroni adjustment for the number of group comparisons.

RESULTS

Mean±SD alfaxalone mg kg^-1 doses required for endotracheal intubation were AS (1.0±0.4), AM (0.4±0.2), AK1 (0.5±0.3) and AK2 (0.5±0.4) (p=0.0005). Differences in cardiopulmonary variables among groups were minor; HR decreased in AS, while in other groups, HR increased transiently postintubation. Incidence of apnea in AS was 54% with no significant difference among groups. Midazolam significantly prolonged time from intubation until spontaneous movement (p<0.002).

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam and ketamine reduced the alfaxalone dose required for endotracheal intubation. Serum glucose and insulin concentrations were not influenced by administration of alfaxalone alone or when administered with midazolam or ketamine.

Effect of fentanyl and lidocaine on the end-tidal sevoflurane concentration preventing motor movement in dogs

OBJECTIVE To determine effects of fentanyl, lidocaine, and a fentanyl-lidocaine combination on the minimum alveolar concentration of sevoflurane preventing motor movement (MAC_NM) in dogs. ANIMALS 6 adult Beagles. PROCEDURES Dogs were anesthetized with sevoflurane in oxygen 3 times (1-week intervals). Baseline MAC_NM (MAC_NM-B) was determined starting 45 minutes after induction of anesthesia. Dogs then received 1 of 3 treatments IV: fentanyl (loading dose, 15 μg/kg; constant rate infusion [CRI], 6 μg/kg/h), lidocaine (loading dose, 2 mg/kg; CRI, 6 mg/kg/h), and the fentanyl-lidocaine combination at the same doses. Determination of treatment MAC_NM (MAC_NM-T) was initiated 90 minutes after start of the CRI. Venous blood samples were collected at the time of each treatment MAC_NM measurement for determination of plasma concentrations of fentanyl and lidocaine. RESULTS Mean ± SEM overall MAC_NM-B for the 3 treatments was 2.70 ± 0.27 vol%. The MAC_NM decreased from MAC_NM-B to MAC_NM-T by 39%, 21%, and 55% for fentanyl, lidocaine, and the fentanyl-lidocaine combination, respectively. This decrease differed significantly among treatments. Plasma fentanyl concentration was 3.25 and 2.94 ng/mL for fentanyl and the fentanyl-lidocaine combination, respectively. Plasma lidocaine concentration was 2,570 and 2,417 ng/mL for lidocaine and the fentanyl-lidocaine combination, respectively. Plasma fentanyl and lidocaine concentrations did not differ significantly between fentanyl and the fentanyl-lidocaine combination or between lidocaine and the fentanyl-lidocaine combination. CONCLUSIONS AND CLINICAL RELEVANCE CRIs of fentanyl, lidocaine, and the fentanyl-lidocaine combination at the doses used were associated with clinically important and significant decreases in the MAC_NM of sevoflurane in dogs.

The effect of multimodal analgesia on minimum alveolar concentration of isoflurane for skin incision at constant bispectral index

Background:

Multimodal analgesia (MMA) by synergy with volatile anesthetics minimizes their use thus decreasing operation theater pollution and greenhouse gas emission.

Aims:

To estimate minimum alveolar concentration (MAC) requirement of isoflurane (ISO) for skin incision with use of MMA in the study group versus conventional regime in the control group for a constant bispectral index (BIS). To observe the side effects of analgesic drugs administered in the study.

Settings and Design:

Forty-two patients of American Society of Anesthesiologist Class I and II scheduled for lumbar spine surgery were included in this prospective, randomized, double-blind, clinical study. They were randomly allocated into two groups of 21 each.

Materials and Methods:

Group A (MMA group/study group) received injections diclofenac sodium, paracetamol, clonidine, and fentanyl and local infiltration (bupivacaine with adrenaline). Group B (conventional regime group/control group) received injections paracetamol and fentanyl and local infiltration (saline with adrenaline). Preemptive analgesia was practiced in the study. The MAC of ISO for skin incision was documented.

Statistical Analysis Used:

Independent sample t-test: To compare MAC_ISO for skin incision between the two groups. One sample t-test: To compare the standard mean concentration with the means of the two groups. Chi-square test: To compare adverse effects between the groups. P < 5% was considered statistically significant.

Results:

The MAC_ISO requirement was significantly lower in the study group at the time of skin incision for BIS of 50–55 compared to the control group (P < 0.001). Post extubation, 43% had nausea and 9% had vomiting in the control group. None of the patients in either group had intraoperative awareness.

Conclusion:

We conclude that preemptive MMA has synergistic effect with ISO. It effectively reduces MAC_ISO to skin incision to a greater degree.

Effect of Acetaminophen Alone and in Combination with Morphine and Tramadol on the Minimum Alveolar Concentration of Isoflurane in Rats

Background

It has been observed that acetaminophen potentiates the analgesic effect of morphine and tramadol in postoperative pain management. Its capacity as an analgesic drug or in combinations thereof to reduce the minimum alveolar concentration (MAC) of inhalational anesthetics represents an objective measure of this effect during general anesthesia. In this study, the effect of acetaminophen with and without morphine or tramadol was evaluated on the isoflurane MAC.

Methods

Forty-eight male Wistar rats were anesthetized with isoflurane in oxygen. MAC_ISO was determined from alveolar gas samples at the time of tail clamping without the drug, after administering acetaminophen (300 mg/kg), morphine (3 mg/kg), tramadol (10 mg/kg), acetaminophen (300 mg/kg) + morphine (3 mg/kg), and acetaminophen (300 mg/kg) + tramadol (10 mg/kg).

Results

The control and acetaminophen groups did not present statistically significant differences (p = 0.98). The values determined for MAC_ISO after treatment with acetaminophen + morphine, acetaminophen + tramadol, morphine, and tramadol were 0.98% ± 0.04%, 0.99% ± 0.009%, 0.97% ± 0.02%, and 0.99% ± 0.01%, respectively.

Conclusions

The administration of acetaminophen did not reduce the MAC of isoflurane and did not potentiate the reduction in MAC_ISO by morphine and tramadol in rats, and therefore does not present a sparing effect of morphine or tramadol in rats anesthetized with isoflurane.

Lidocaine, dexmedetomidine and their combination reduce isoflurane minimum alveolar concentration in dogs

The effects of intravenous (IV) lidocaine, dexmedetomidine and their combination delivered as a bolus followed by a constant rate infusion (CRI) on the minimum alveolar concentration of isoflurane (MAC_ISO) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MAC_ISO/BASAL) was determined after a 90-minute equilibration period. Thereafter, each dog received one of the following treatments (loading dose, CRI): lidocaine 2 mg kg⁻¹, 100 µg kg⁻¹ minute⁻¹; dexmedetomidine 2 µg kg⁻¹, 2 µg kg⁻¹ hour⁻¹; or their combination. MAC was then determined again after 45- minutes of treatment by CRI. At the doses administered, lidocaine, dexmedetomidine and their combination significantly reduced MAC_ISO by 27.3% (range: 12.5–39.2%), 43.4% (33.3–53.3%) and 60.9% (46.1–78.1%), respectively, when compared to MAC_ISO/_BASAL. The combination resulted in a greater MAC_ISO reduction than the two drugs alone. Their use, at the doses studied, provides a clinically important reduction in the concentration of ISO during anaesthesia in dogs.

Anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in isoflurane-anaesthetized sheep

OBJECTIVE

To determine the anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in sheep anaesthetized with isoflurane and undergoing orthopaedic surgery.

STUDY DESIGN

Prospective, randomised, 'blinded' controlled study.

ANIMALS

Twenty healthy sheep (weight mean 41.1 ± SD 4.5 kg).

METHODS

Sheep were sedated with intravenous (IV) dexmedetomidine (4 μg kg(-1) ) and morphine (0.2 mg kg(-1) ). Anaesthesia was induced with propofol (1 mg kg(-1)  minute(-1) to effect IV) and maintained with isoflurane in oxygen and a continuous rate infusion (CRI) of fentanyl 10 μg kg(-1)  hour(-1) (group F) or saline (group P) for 100 minutes. The anaesthetic induction dose of propofol, isoflurane expiratory fraction (Fe'iso) required for maintenance and cardiorespiratory measurements were recorded and blood gases analyzed at predetermined intervals. The quality of recovery was assessed. Results were compared between groups using t-tests or Mann-Whitney as relevant.

RESULTS

The propofol induction dose was 4.7 ± 2.4 mg kg(-1) . Fe'iso was significantly lower (by 22.6%) in group F sheep than group P (p = 0). Cardiac index (mean ± SD mL kg(-1)  minute(-1) ) was significantly (p = 0.012) lower in group F (90 ± 15) than group P (102 ± 35). Other measured cardiorespiratory parameters did not differ statistically significantly between groups. Recovery times and recovery quality were statistically similar in both groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl reduced isoflurane requirements without clinically affecting the cardiorespiratory stability or post-operative recovery in anaesthetized sheep undergoing orthopaedic surgery.

Postoperative analgesic effects of either a constant rate infusion of fentanyl, lidocaine, ketamine, dexmedetomidine, or the combination lidocaine-ketamine-dexmedetomidine after ovariohysterectomy in dogs

OBJECTIVE

To evaluate the postoperative analgesic effects of a constant rate infusion (CRI) of either fentanyl (FENT), lidocaine (LIDO), ketamine (KET), dexmedetomidine (DEX), or the combination lidocaine-ketamine-dexmedetomidine (LKD) in dogs.

STUDY DESIGN

Randomized, prospective, blinded, clinical study.

ANIMALS

Fifty-four dogs.

METHODS

Anesthesia was induced with propofol and maintained with isoflurane. Treatments were intravenous (IV) administration of a bolus at start of anesthesia, followed by an IV CRI until the end of anesthesia, then a CRI at a decreased dose for a further 4 hours: CONTROL/BUT (butorphanol 0.4 mg kg(-1), infusion rate of saline 0.9% 2 mLkg(-1) hour(-1)); FENT (5 μg kg(-1), 10 μg kg(-1) hour(-1), then 2.5 μg kg(-1) hour(-1)); KET (1 mgkg(-1) , 40 μg kg(-1) minute(-1), then 10 μg kg(-1) minute(-1) ; LIDO (2 mg kg(-1), 100 μg kg(-1) minute(-1), then 25 μg kg(-1) minute(-1)); DEX (1 μgkg(-1), 3 μg kg(-1) hour(-1), then 1 μg kg(-1) hour(-1)); or a combination of LKD at the aforementioned doses. Postoperative analgesia was evaluated using the Glasgow composite pain scale, University of Melbourne pain scale, and numerical rating scale. Rescue analgesia was morphine and carprofen. Data were analyzed using Friedman or Kruskal-Wallis test with appropriate post-hoc testing (p < 0.05).

RESULTS

Animals requiring rescue analgesia included CONTROL/BUT (n = 8), KET (n = 3), DEX (n = 2), and LIDO (n = 2); significantly higher in CONTROL/BUT than other groups. No dogs in LKD and FENT groups received rescue analgesia. CONTROL/BUT pain scores were significantly higher at 1 hour than FENT, DEX and LKD, but not than KET or LIDO. Fentanyl and LKD sedation scores were higher than CONTROL/BUT at 1 hour.

CONCLUSIONS AND CLINICAL RELEVANCE

LKD and FENT resulted in adequate postoperative analgesia. LIDO, CONTROL/BUT, KET and DEX may not be effective for treatment of postoperative pain in dogs undergoing ovariohysterectomy.

Effects of lidocaine, dexmedetomidine or their combination on the minimum alveolar concentration of sevoflurane in dogs

The aim of this study was to determine the effects of lidocaine (LIDO) and dexmedetomidine (DEX) or their combination (LIDO-DEX), administered by constant-rate infusion (CRI), on the minimum alveolar concentration (MAC) of sevoflurane in dogs. Seven healthy mongrel dogs were used with a 2-week washout interval between treatments in this study. Anesthesia was induced with propofol and maintained with sevoflurane in oxygen, and MAC of sevoflurane was determined after 90 min equilibration period in the dogs (SEV-MACBASAL). Then, sevoflurane MAC was determined again in the dogs after 45 min equilibration period of one of the following treatments: an intravenous loading dose of lidocaine 2 mg/kg followed by 6 mg/kg/hr CRI (SEV-MACLIDO); an intravenous loading dose of dexmedetomidine 2 µg/kg followed by 2 µg/kg/hr CRI (SEV-MACDEX); or their combination (SEV-MACLIDO-DEX). These SEV-MACs were determined in duplicate. Data were analyzed using ANOVA and post hoc Tuckey test when appropriate. The SEV-MACBASAL was 1.82 ± 0.06%, SEV-MACLIDO was 1.38 ± 0.08%, SEV-MACDEX was 1.22 ± 0.10%, and SEV-MACLIDO-DEX was 0.78 ± 0.06%. The CRI administration of lidocaine, dexmedetomidine and their combination produced a significant reduction in the MAC of sevoflurane by 26.1 ± 9.0% (P<0.0001), 43.7 ± 11.8% (P<0.0002) and 54.4 ± 9.8% (P<0.0001), respectively. The MAC reduction was significantly greater after the CRI combination of lidocaine and dexmedetomidine when compared with lidocaine CRI (P<0.0001) or dexmedetomidine CRI treatments (P<0.025).