Pedal Withdrawal Reflex Research Articles

Total intravenous anesthesia with Ketofol in rabbits: a comparison of the effects of constant rate infusion of midazolam, fentanyl or dexmedetomidine

BackgroundWhen inhalant anesthetic equipment is not available or during upper airway surgery, intravenous infusion of one or more drugs are commonly used to induce and/or maintain general anesthesia. Total intravenous anesthesia (TIVA) does not require endotracheal intubation, which may be more difficult to achieve in rabbits. A range of different injectable drug combinations have been used as continuous infusion rate in animals. Recently, a combination of ketamine and propofol (ketofol) has been used for TIVA in both human patients and animals. The purpose of this prospective, blinded, randomized, crossover study was to evaluate anesthetic and cardiopulmonary effects of ketofol total intravenous anesthesia (TIVA) in combination with constant rate infusion (CRI) of midazolam, fentanyl or dexmedetomidine in eight New Zealand White rabbits. Following IV induction with ketofol and endotracheal intubation, anesthesia was maintained with ketofol infusion in combination with CRIs of midazolam (loading dose [LD]: 0.3 mg/kg; CRI: 0.3 mg/kg/hr; KPM), fentanyl (LD: 6 µg/kg; CRI: 6 µg/kg/hr; KPF) or dexmedetomidine (LD: 3 µg/kg; CRI: 3 µg/kg/hr; KPD). Rabbits in the control treatment (KPS) were administered the same volume of saline for LD and CRI. Ketofol infusion rate (initially 0.6 mg kg− 1 minute− 1 [0.3 mg kg− 1 minute− 1 of each drug]) was adjusted to suppress the pedal withdrawal reflex. Ketofol dose and physiologic variables were recorded every 5 min.ResultsKetofol induction doses were 14.9 ± 1.8 (KPM), 15.0 ± 1.9 (KPF), 15.5 ± 2.4 (KPD) and 14.7 ± 3.4 (KPS) mg kg− 1 and did not differ among treatments (p > 0.05). Ketofol infusion rate decreased significantly in rabbits in treatments KPM and KPD as compared with saline. Ketofol maintenance dose in rabbits in treatments KPM (1.0 ± 0.1 mg/kg/min) and KPD (1.0 ± 0.1 mg/kg/min) was significantly lower as compared to KPS (1.3 ± 0.1 mg/kg/min) treatment (p < 0.05). Ketofol maintenance dose did not differ significantly between treatments KPF (1.1 ± 0.3 mg/kg/min) and KPS (1.3 ± 0.1 mg/kg/min). Cardiovascular variables remained at clinically acceptable values but ketofol infusion in combination with fentanyl CRI was associated with severe respiratory depression.ConclusionsAt the studied doses, CRIs of midazolam and dexmedetomidine, but not fentanyl, produced ketofol-sparing effect in rabbits. Mechanical ventilation should be considered during ketofol anesthesia, particularly when fentanyl CRI is used.

Temperature-induced Artifacts in Tau Phosphorylation: Implications for Reliable Alzheimer's Disease Research.

In preclinical research on Alzheimer's disease and related tauopathies, tau phosphorylation analysis is routinely employed in both cellular and animal models. However, recognizing the sensitivity of tau phosphorylation to various extrinsic factors, notably temperature, is vital for experimental accuracy. Hypothermia can trigger tau hyperphosphorylation, while hyperthermia leads to its dephosphorylation. Nevertheless, the rapidity of tau phosphorylation in response to unintentional temperature variations remains unknown. In cell cultures, the most significant temperature change occurs when the cells are removed from the incubator before harvesting, and in animal models, during anesthesia prior to euthanasia. In this study, we investigate the kinetics of tau phosphorylation in N2a and SH-SY5Y neuronal cell lines, as well as in mice exposed to anesthesia. We observed changes in tau phosphorylation within the few seconds upon transferring cell cultures from their 37°C incubator to room temperature conditions. However, cells placed directly on ice post-incubation exhibited negligible phosphorylation changes. In vivo, isoflurane anesthesia rapidly resulted in tau hyperphosphorylation within the few seconds needed to lose the pedal withdrawal reflex in mice. These findings emphasize the critical importance of preventing temperature variation in researches focused on tau. To ensure accurate results, we recommend avoiding anesthesia before euthanasia and promptly placing cells on ice after removal from the incubator. By controlling temperature fluctuations, the reliability and validity of tau phosphorylation studies can be significantly enhanced.

Mouse isoflurane anesthesia using the drop method.

Anesthesia with isoflurane prior to carbon dioxide euthanasia is recommended as a refinement, but vaporizer access can be limited. An alternative to vaporizers is the 'drop' method, introducing a fixed volume of isoflurane into the induction chamber. Previous work suggests that isoflurane administered at a concentration of 5% via the drop method is effective but aversive to mice; lower concentrations have not been tested. We assessed mouse behavior and insensibility with induction using the drop method for isoflurane concentrations below 5%. Male Crl:CD-1 (ICR) mice (n = 27) were randomly allocated to one of three isoflurane concentrations: 1.7%, 2.7%, and 3.7%. During induction, measures of insensibility and stress-related behaviors were recorded. All mice reached a surgical plane of anesthesia, and mice exposed to higher concentrations did so more quickly; as concentrations increased from 1.7 to 2.7 and 3.7%, the time to recumbency (Least squares means ± SE: 120.5 s ± 8.1, 97.9 s ± 8.1, and 82.8 s ± 8.1, respectively), loss of righting reflex (149.1 s ± 8.5, 127.7 s ± 8.5, and 100.7 s ± 8.5, respectively), and loss of pedal withdrawal reflex (214.5 s ± 8.3, 172.2 s ± 8.3, and 146.4 s ± 8.3, respectively) all declined. Rearing was the most frequently performed stress-related behavior, and was most pronounced immediately following isoflurane administration for all treatments. Our results indicate that the drop method can be used to effectively anesthetize mice with isoflurane concentrations as low as 1.7%; future work should assess mouse aversion.

Stability of unilaterally adrenalectomized rats to anaesthesia using xylazine-ketamine as a model

The stability of every patient to anaesthesia is crucial to a successful surgery and full recovery. This study evaluated the stability of unilaterally adrenalectomized rats to anaesthesia using Xylazine-Ketamine as a model. Twelve female Wistar rats were randomly assigned to two groups of 6 each. Group 1 were the sham group which underwent laparotomy only, while group 2 had their left adrenal glands excised. Three weeks post-adrenalectomy, the animals in both groups were anaesthetized according to standard technique. Anaesthetic parameters assessed include the induction time, time to attain surgical plane of anaesthesia, duration of surgical plane of anaesthesia, duration of anaesthesia, rectal temperature and respiratory rate. Results showed that the mean induction time, time to attain surgical plane of anaesthesia and duration of anaesthesia were not significantly different (p&gt;0.05) between the two groups. The pedal withdrawal reflex (PWR) and the whiskers movement (WM) were used to evaluate the duration of surgical plane of anaesthesia. The duration of surgical plane of anaesthesia determined by the PWR was significantly (p≤0.05) higher in the unilaterally adrenalectomized rats. There were also significant decreases in rectal temperature and respiratory rate when the unilaterally adrenalectomized groups were compared to the controls. From the results, the unilaterally adrenalectomized rats were comparatively as stable to Xylazine-Ketamine anaesthetic protocol as their intact counterparts, at three weeks post-adrenalectomy. However, there may be need to exercise caution when choosing an anaesthetic protocol for unilaterally adrenalectomized animals with special considerations given the depth and duration of anaesthesia required for a procedure and the length of time post-adrenalectomy.

Evaluation of Anesthetic and Cardiorespiratory Effects after Intramuscular Administration of Three Different Doses of Telazol® in Common Marmosets (Callithrix jacchus).

Marmosets' small body size makes anesthesia challenging. Ideally, small volumes of drugs should be administered intramuscularly (i.m.). In addition, dose-dependent sedation and anesthesia are desirable properties for sedatives and anesthetics in marmosets. Telazol® (tiletamine and zolazepam) is highly concentrated, allowing the use of small injection volumes and dose-dependent sedation and anesthesia. A randomized, blinded study with crossover design in ten healthy adult common marmosets (Callithrix jacchus) was performed to evaluate the anesthetic and cardiorespiratory effects of three doses of i.m. Telazol® (respectively, 5, 10, and 15 mg/kg). Depth of anesthesia, cardiorespiratory effects, and induction, immobilization, and recovery times were determined. A significant difference was observed in immobilization time between 5 and 15 mg/kg of Telazol®. In addition, 15 mg/kg of Telazol® resulted in increased recovery times compared to 5 mg/kg. The cardiorespiratory effects during the first 45 min of immobilization were within clinically acceptable limits. The pedal withdrawal reflex was the best indicator of the anesthetic depth.

Comparison of propofol infusion rate required to abolish swallowing or pedal withdrawal reflexes in dogs.

In a prospective, randomized, experimental non-blinded study, the continuous infusions rates of propofol required to prevent swallowing (P-SR) or pedal withdrawal reflex (P-WR) were evaluated in healthy premedicated dogs. Dogs were randomly assigned to one of two treatments at weekly intervals. Following premedication with a combination of acepromazine and methadone, anesthesia was induced with propofol (4.00 mg kg-1 per min) and was maintained for 90 min. The propofol infusion rate was increased or decreased by 0.05 mg kg-1 per min based on positive or negative swallowing (P-SR) or pedal withdrawal reflexes (P-WR). Propofol induction doses were 2.12 ± 0.43 mg kg-1 (P-SR) and 2.14 ± 0.31 mg kg-1 (P-WR), which were not significantly different. The mean (±SD) propofol infusion rate was significantly higher for P-WR (0.26 ± 0.10 mg kg-1 per min) when compared to P-SR (0.22 ± 0.12 mg kg-1 per min). During the last 30 min, the mean propofol infusion rates were 0.09 ± 0.02 and 0.18 ± 0.03 mg kg-1 per min for P-SR and P-WR, respectively. There were no significant differences between treatments with respect to heart rate (HR), respiratory rate, arterial blood pressure, end-tidal CO2 partial pressure, hemoglobin oxygen saturation, partial pressures of oxygen or pH. Transient apnea lasting up to three minutes was observed in three dogs with each treatment. Propofol infusion rate of 0.22 ± 0.12 mg kg-1 per min can be used in premedicated dogs requiring tracheal intubation and undergoing mechanical ventilation, non-painful procedures or painful procedures with local anesthetic techniques.

In Vivo Evaluation of Anti-Nociceptive Effects of Silver Nanoparticles.

Silver nanoparticles (AgNPs) are widely used commercially due to their antimicrobial effects. Little is known about the effect of AgNPs on neural transmission and pain response. The aim of this study was to assess the anti-nociceptive activity of AgNPs. AgNPs were prepared at 16 ug/mL, white albino rats were injected with various doses of AgNPs, and challenged using a hot-plate test and paw withdrawal latency (PWL) was measured. The chronic constriction injury (CCI) model was utilized to evaluate the pedal withdrawal reflex and tail withdrawal reflex. An electrophysiological study was conducted utilizing colon longitudinal muscle strips. AgNPs increased the latency of PWL in a dose-dependent matter over the duration of 6 h. The paw withdrawal threshold in animals with CCI significantly increased after AgNPs administration. In isolated colon longitudinal muscle strips, AgNPs significantly reduced the colonic migrating motor complexes (MMCs) and contraction. This action was completely reversed after removing the AgNPs and adding acetylcholine to the preparation. In this study, AgNPs showed significant anti-nociception properties. To our knowledge, this is the first report to describe this pharmacological action of AgNPs.

Evaluation of alfaxalone total intravenous anesthesia in rabbits (Oryctolagus cuniculus) premedicated with dexmedetomidine or dexmedetomidine and buprenorphine

ObjectiveTo evaluate alfaxalone for total intravenous anesthesia (TIVA) in rabbits premedicated with dexmedetomidine or dexmedetomidine and buprenorphine. Study designCrossover study (part 1) with observational study (part 2). AnimalsA total of eight New Zealand White rabbits (Oryctolagus cuniculus), four female and four male, aged 12–16 weeks and weighing 2.8–3.5 kg in part 1. Separately, four additional rabbits in part 2. MethodsCrossover study design with eight rabbits per treatment. Rabbits were administered treatment D, dexmedetomidine (0.2 mg kg–1), or treatment DB, dexmedetomidine (0.1 mg kg–1) and buprenorphine (0.05 mg kg–1) intramuscularly. Anesthesia was induced with alfaxalone intravenously until a supraglottic airway device was placed to deliver 100% oxygen. Anesthesia was maintained with alfaxalone (TIVA). Infusion rates were adjusted to achieve an absent pedal withdrawal reflex. Heart rate, respiratory rate, noninvasive blood pressure, end-tidal carbon dioxide partial pressure and peripheral hemoglobin oxygen saturation (SpO2) were recorded every 5 minutes. Subsequently, four rabbits underwent ovariohysterectomy using treatment DB and alfaxalone TIVA. ResultsThe mean ± standard deviation alfaxalone infusion rate was 9.6 ± 2.6 and 4.5 ± 1.3 mg kg–1 hour–1 for treatments D and DB, respectively. In both treatments, blood pressure remained within acceptable range and SpO2 was > 95%. Postinduction apnea and respiratory depression were observed in both treatments and managed with manual positive pressure ventilation. Four separate rabbits underwent successful ovariohysterectomy with treatment DB and alfaxalone TIVA. One rabbit required supplementation with inhalant anesthesia; three rabbits were successfully maintained using alfaxalone TIVA alone. Conclusions and clinical relevancePremedication with dexmedetomidine–buprenorphine combined with alfaxalone TIVA may be a viable alternative for performing abdominal surgery in the rabbit. The use of supplemental oxygen and ability to provide respiratory support are advised.

Beyaz Yeni Zelanda Tavşanlarda Farklı Oranlarda Ketamine ve Propofol (Ketofol) Karışımının Anestezi İndüksiyonu Üzerine Etkilerinin Karşılaştırılması

This study was aimed to detect the effects of anesthesia induction with ketamine-propofol (ketofol) admixture in rabbits. Eight, healthy New Zealand white rabbits were randomly received ketofol admixture at the ratio of 1:1, 1:2, and 1:3 with one-week intervals. The length of surgical anesthesia was continuously evaluated until the presence of pedal withdrawal and ear-pinch reflexes. The recovery was assessed by the existence of the righting reflex. The heart rate and respiratory frequency values were recorded at pre-treatment, induction, and two minutes intervals until 20 minutes. There was no statistically significant difference between groups with respect to the ear-pinch reflex and pedal withdrawal reflex. The righting reflex returned earliest at the ratio of 1:1 (8.88 ± 0.63 minutes) which was significantly shorter than the ratio of 1:2 (10.50 ± 0.94 minutes) or 1:3 (13.62 ± 1.93 minutes). The animals receiving ketofol at the ratio of 1:3 had significantly lower respiratory frequency compared to 1:2 and 1:1 ratios at 0, 2, 4, 6, 8, and 12 minutes. The ketofol admixture at the ratio of 1:1 has less respiratory depression effects, and higher doses of propofol in ketofol admixture can be associated with anesthetic complication.

Evaluation of hemodynamic, hematological parameters and the clinical effects of dexmedetomidine-ketamine and xylazine-ketamine anesthesia in rabbits

With this study, it was aimed to assess the effects of experimentally induced dexmedetomidine-ketamine (DK) and xylazineketamine (XK) combinations on clinical parameters and hemodynamic and hematological parameters in rabbits. In the study, 16 male New Zealand breed rabbits were divided into two groups. Group DK (n = 8) was administered dexmedetomidine (25 μg/kg) and ketamine (30 mg/kg) in the same injector, and Group XK (n = 8) was administered xylazine (4 mg/kg) and ketamine (30 mg/kg) in the same injector through the intramuscular (IM) route. Following the injection, the rabbits' reflexes were tested approximately every 30 s. Hemodynamic parameters were determined before the injection (0 min) and 5, 10, 15, 30, 45, 60, 75, 90, 105 and 120 min after the anesthetic combinations were injected. Furthermore, blood gas and electrolyte values were analyzed before, during and after anesthesia. The differences between the groups were not statistically significant in terms of the loss and return times of the righting reflex, ear-pinch reflex and pedal withdrawal reflex (P > 0.05). The mean surgical anesthesia duration was determined as 115 min in the DK group and 116.5 min in the XK group. In both groups, the heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP) and arterial oxygen saturation of hemoglobin (SpO2) decreases. In the statistical analysis, the differences between the groups were statistically significant in terms of HR at the 5th, 10th and 15th min and in terms of SpO2 at the 120th min (P < 0.05). In the DK group, the change in RR based on the pre-injection time (0 min) was found significant (P < 0.05). In the statistical analyses on the arterial blood gases and electrolyte findings, the differences between the DK and XK groups were insignificant in terms of pH, pCO2 and pO2 (P > 0.05) and significant in terms of only glucose (mg/dL) at the 5th min (P < 0.05). Consequently, it was observed that the DK and XK combinations had similar effects in healthy adult rabbits regarding the reflex findings, anesthesia duration and hemodynamic and hematological parameters. It was concluded that, to prevent hypoxemia related to RR decrease in the combination of α2 adrenergic agonists and ketamine, there is a need for oxygen reinforcement starting with the induction of anesthesia, and the DK combination needs to be used carefully in patients with respiratory depression.

Intraperitoneal Alfaxalone and Alfaxalone-Dexmedetomidine Anesthesia in Sprague-Dawley Rats (Rattus norvegicus).

Due to their unpredictability and variable effects, injectable anesthetic regimens in laboratory rodent species warrant refinement. In our study we sought to evaluate alfaxalone, which has gained recent popularity in veterinary medicine, alone and in combination with dexmedetomidine to evaluate their anesthetic ability in Sprague-Dawley rats when administered intraperitoneally. Three doses of alfaxalone only and 4 dose combinations of alfaxalone-dexmedetomidine were tested in males and female rats. The time to induction, anesthetic duration, pulse rate, respiratory rate, temperature, and time to recovery were recorded by a blind observer. The level of anesthesia induced by the various anesthetic protocols was assessed by using pedal withdrawal reflex to a noxious stimulus and scored according to the response. Dependent on the treatment group, atipamezole or saline was administered intraperitoneally once animals reached 60 min of anesthesia. Regardless of the dose, alfaxalone alone achieved only a sedative level of anesthesia, whereas all alfaxalone-dexmedetomidine combinations led to a surgical level of anesthesia in all animals. Anesthesia regimens using alfaxalone alone and in combination with dexmedetomidine demonstrated sex-associated differences, with female rats maintaining longer durations of sedation or anesthesia than their male counterparts. Both male and female rats displayed decreases in physiologic parameters consistent with the effects of dexmedetomidine. Given the results described herein, we recommend 20 mg/kg alfaxalone for sedation and 30 mg/kg alfaxalone combined with 0.05 mg/kg dexmedetomidine for surgical anesthesia in female rats. Appropriate doses of alfaxalone only and alfaxalone-dexmedetomidine for male rats were not determined in this study and need further evaluation.

Population analysis to assess the influence of age and body weight on pharmacokinetics and pharmacodynamics of dexmedetomidine in New Zealand White rabbits.

The purpose of this work was i) to develop a population pharmacokinetic (PK) and pharmacodynamic (PD) model of dexmedetomidine (DEX) in New Zealand White rabbits, ii) to investigate the influence of the age and weight of the animals on the model parameters, and iii) to assess the linearity of DEX PKs in the examined dose range. This was a prospective, crossover study, using a total of 18 New Zealand White rabbits. DEX was administered as a single intravenous bolus injection in the doses from 25 to 300 μg kg-1 . Each New Zealand White rabbit was given the same dose of drug in its three developmental stages. To determine the DEX PK, seven blood samples were taken from each animal. The pedal withdrawal reflex was the PD response used to assess the degree of sedation. Nonlinear mixed effects modelling was used for the population PK/PD analysis. The typical value of elimination clearance was 0.061 L min-1 and was 35% higher in younger New Zealand White rabbits compared with older animals. The PK of DEX was linear in the examined concentration range. Age-related changes in sensitivity to DEX were not detected. The results suggest that due to the pharmacokinetics, younger animals will have lower DEX concentrations and a shorter duration of sedation than older animals given the same doses of DEX per kg of body weight.

Effects of subcutaneous alfaxalone alone and in combination with dexmedetomidine and buprenorphine in guinea pigs (Cavia porcellus)

ObjectiveTo characterize alfaxalone administered subcutaneously (SC) in guinea pigs, both alone and in combination with dexmedetomidine and buprenorphine. Study designProspective, blinded, crossover study. AnimalsA total of 15 healthy female guinea pigs weighing 400–600 g. MethodsAlfaxalone (10, 20 and 40 mg kg−1) was administered SC to three guinea pigs as a pilot dose-finding study. Alfaxalone (20 mg kg−1; A20) was selected for comparison against combination protocols of alfaxalone (15 and 20 mg kg−1) with dexmedetomidine (0.25 mg kg−1) and buprenorphine (0.05 mg kg−1; A15DB, A20DB). Each protocol was randomly administered to 12 guinea pigs separated by ≥7 days. Time and quality of induction and recovery, heart rate, respiratory rate, peripheral hemoglobin oxygen saturation, rectal temperature, pedal withdrawal reflex and adverse effects were recorded. ResultsThe median time to induction for A20, A15DB and A20DB was 6.8–8.0 minutes with no significant difference between treatments. Mean duration of recumbency for A20 was 73.6 ± 19.6 minutes. Recumbency duration for A15DB and A20DB extended to 90 minutes, at which time dexmedetomidine was antagonized using atipamezole (0.025 mg kg−1 SC). Physiological variables were within normal limits with the exception of one animal that died 45 minutes following treatment with A20DB. Pedal withdrawal reflex remained intact with all treatments. Minor side effects such as twitching or bruxism occurred sporadically with treatment A20 but not with A15DB and A20DB. Conclusions and clinical relevanceSC alfaxalone produced uncomplicated sedation that may be recommended for nonpainful procedures that do not require complete immobility. The addition of dexmedetomidine and buprenorphine increased the duration of sedation and immobility, but did not result in general anesthesia. This combination sedation protocol may be useful for nonpainful procedures requiring extended immobility.

Effects of buprenorphine, butorphanol or tramadol premedication on anaesthetic induction with alfaxalone in common marmosets (Callithrix jacchus)

ObjectiveTo investigate the clinical and physiological effects of intravenous (IV) alfaxalone alone or in combination with buprenorphine, butorphanol or tramadol premedication in marmosets. Study designProspective, randomized, blinded, crossover design. AnimalsNine healthy marmosets (391 ± 48 g, 3.7 ± 2.2 years old). MethodsMeloxicam 0.20 mg kg−1 subcutaneously, atropine 0.05 mg kg−1 intramuscularly (IM) and either buprenorphine 20 μg kg−1 IM (BUP-A), butorphanol 0.2 mg kg−1 IM (BUT-A), tramadol 1.5 mg kg−1 IM (TRA-A) or no additional drug (control) were administered to all marmosets as premedication. After 1 hour, anaesthesia was induced with 16 mg kg−1 alfaxalone IV. All animals received all protocols. The order of protocol allocation was randomized with a minimum 28 day wash-out period. During anaesthesia, respiratory and pulse rates, rectal temperature, haemoglobin oxygen saturation, arterial blood pressure, palpebral and pedal withdrawal reflexes and degree of muscle relaxation were assessed and recorded every 5 minutes. Quality of induction and recovery were assessed. Duration of induction, immobilization and recovery were recorded. Blood samples were analysed for aspartate aminotransferase, creatine kinase and lactate dehydrogenase concentrations. The protocols were compared using paired t tests, Wilcoxon's signed-rank test with Bonferroni's corrections and linear mixed effect models where appropriate. ResultsOut of nine animals, apnoea was noted in eight animals administered protocol BUP-A and two animals administered protocol BUT-A. With TRA-A and control protocols, apnoea was not observed. No other significant differences in any of the parameters were found; however, low arterial blood pressures and hypoxia occurred in TRA-A. Conclusions and clinical relevanceOur study employing different premedications suggests that the previously published dose of 16 mg kg−1 alfaxalone is too high when used with premedication because we found a high incidence of complications including apnoea (BUP-A), hypotension and hypoxaemia (TRA-A). Appropriate monitoring and countermeasures are recommended.

Changes in bispectral index score and cardiorespiratory function under constant rate infusion with alfaxalone in dogs

Changes in the cardiovascular and bispectral index score were evaluated in dogs subjected to constant rate infusion (CRI) with alfaxalone. Fifteen dogs were assigned to three groups of 5. Groups and doses of alfaxalone were as follows: group 1, 3 mg/kg for induction and 6 mg/kg/h for CRI; group 2, 3 mg/kg for induction and 8 mg/kg/h for CRI; and group 3, 3 mg/kg for induction and 10 mg/kg/h for CRI. CRI was maintained for 1 h. Respiratory rates and blood pressures showed minimal changes; however, mild tachycardia and mild hypoxemia occurred, especially in group 3. There were some disparities between bispectral index score, electromyography and pedal withdrawal reflex test when measuring anesthetic depth. Additional premedications and/or analgesic agents would be helpful to avoid adverse effects of alfaxalone and provide improved cardiopulmonary functions.

Total intravenous anaesthesia using propofol and sufentanil allows controlled long-term ventilation in rabbits without neuromuscular blocking agents.

The aim of this study was to evaluate a total intravenous anaesthesia (TIVA) protocol using propofol and sufentanil without neuromuscular blocking agents (NBAs) for a non-recovery lung pathology study in rabbits including 10 h of pressure-controlled ventilation. TIVA was started with 20 mg/kg/h propofol and 0.5 µg/kg/h sufentanil. The depth of anaesthesia was assessed by reflex testing and monitoring of spontaneous movements or respiratory efforts. Vital parameters were monitored to assess the effects of the TIVA protocol. The infusion rates were increased whenever reflex testing indicated inadequate depth of anaesthesia, and were reduced when vital parameters indicated unnecessarily deep levels. Median infusion rates of 35 mg/kg/h propofol and 2.0 µg/kg/h sufentanil were needed to ensure an adequate depth of anaesthesia. This protocol suppressed spontaneous movements, breathing and palpebral reflexes, but was unable to suppress corneal and pedal withdrawal reflexes. Since significant drops in arterial blood pressure (ABP) were observed and the animals were not exposed to painful procedures, positive corneal and pedal withdrawal reflexes were tolerated. In conclusion, propofol and sufentanil is a suitable combination for long-term anaesthesia in non-recovery lung pathology models in rabbits without painful procedures. ABP must be monitored carefully because of the circulatory side-effects, but it is an inappropriate surrogate marker for depth of anaesthesia. Due to the lack of neuromuscular blockade this TIVA protocol allows the adjustment of infusion rates based on reflex testing. The resulting decreased risk of unnoticed awareness is a decisive refinement in anaesthesia for similar studies including long-term mechanical ventilation in rabbits.

Injection anaesthesia with fentanyl-midazolam-medetomidine in adult female mice: importance of antagonization and perioperative care.

Injection anaesthesia is commonly used in laboratory mice; however, a disadvantage is that post-anaesthesia recovery phases are long. Here, we investigated the potential for shortening the recovery phase after injection anaesthesia with fentanyl-midazolam-medetomidine by antagonization with naloxone-flumazenil-atipamezole. In order to monitor side-effects, the depth of anaesthesia, heart rate (HR), core body temperature (BT) and concentration of blood gases, as well as reflex responses, were assessed during a 50 min anaesthesia. Mice were allowed to recover from the anaesthesia in their home cages either with or without antagonization, while HR, core BT and spontaneous home cage behaviours were recorded for 24 h. Mice lost righting reflex at 330 ± 47 s after intraperitoneal injection of fentanyl-midazolam-medetomidine. During anaesthesia, HR averaged 225 ± 23 beats/min, respiratory rate and core BT reached steady state at 131 ± 15 breaths/min and 34.3 ± 0.25℃, respectively. Positive pedal withdrawal reflex, movement triggered by tail pinch and by toe pinch, still occurred in 25%, 31.2% and 100% of animals, respectively. Arterial blood gas analysis revealed acidosis, hypoxia, hypercapnia and a marked increase in glucose concentration. After anaesthesia reversal by injection with naloxone-flumazenil-atipamezole, animals regained consciousness after 110 ± 18 s and swiftly returned to physiological baseline values, yet they displayed diminished levels of locomotion and disrupted circadian rhythm. Without antagonization, mice showed marked hypothermia (22 ± 1.9℃) and bradycardia (119 ± 69 beats/min) for several hours. Fentanyl-midazolam-medetomidine provided reliable anaesthesia in mice with reasonable intra-anaesthetic side-effects. Post-anaesthetic period and related adverse effects were both reduced substantially by antagonization with naloxone-flumazenil-atipamezole.

Plasma concentrations and sedative effects of a dexmedetomidine, midazolam, and butorphanol combination after transnasal administration in healthy rabbits.

Plasma concentrations of dexmedetomidine (D=0.1mg/kg), midazolam (M=2mg/kg), and butorphanol (B=0.4mg/kg) were analyzed by liquid chromatography-mass spectrometry (LC-MS/MS) after their simultaneous (DMB) transnasal (TN) administration to healthy rabbits. Time-dependent changes in sedation and antinociception were evaluated by measuring a sedation score based on rabbit's posture, loss of the righting, palpebral and pedal withdrawal reflexes and by instrumental monitoring of rectal temperature, heart rate, arterial blood pressure, pulse-oximetry, and capnometry. The peak plasma concentration (Cmax ) of each drug was reached within 5min (Tmax ) from DMB-TN administration along with deep sedation and analgesia. Such effects subsided after 45min into a moderate sedation and analgesia lasting for additional 15min. All rabbits awakened spontaneously and uneventfully 90min after DMB-TN administration. During the anesthetic procedure, arterial blood pressure markedly decreased and respiratory depression ensued requiring oxygen supplementation. The results of this study show that all three molecules of the DMB combination were absorbed through the TN route, inducing deep sedation and analgesia suitable for minor surgical procedures. Such combination should be used with caution in rabbits bearing cardiovascular or respiratory diseases because of its ability to induce hypotension and respiratory depression.

Chemical restraint of African mole-rats (Fukomys sp.) with a combination of ketamine and xylazine

ObjectiveTo establish an accurate anaesthetic dose for chemical restraint of African mole-rats using ketamine and xylazine. Study designProspective nonrandomized laboratory study. AnimalsSixteen adult Ansell’s mole-rats (Fukomys anselli) and eight giant mole-rats (F. mechowii). MethodsFukomys anselli of different ages, sexes and reproductive status were systematically anaesthetized starting with an intramuscular injection of ketamine (2.5 mg kg−1) and increasing the doses in steps of 0.5 mg kg−1 until loss of the righting reflex (LRR) was observed. Xylazine was added to a constant dose of ketamine, starting at 0.5 mg kg−1 that was increased by 0.5 mg kg−1 in further trials. Once an effective combination was established and evaluated in F. anselli, it was also tested in F. mechowii. Heart and respiratory rates and rectal temperatures were measured during anaesthesia. anova for repeated measures and Student’s t-test were used to compare means. ResultsChemical restraint was accomplished at a dose of 6 mg kg−1 ketamine combined with 2.5 mg kg−1 xylazine. LRR lasted on average mean 56 ± SD 19 minutes (F. anselli) and 140 ± 41 minutes (F. mechowii). Loss of pedal withdrawal reflex (LPR) lasted for 20 ± 15 minutes (F. anselli) and for 29 ± 2 minutes (F. mechowii), respectively. All animals recovered satisfactorily. Heart and respiratory rates were stable during anaesthesia, but rectal temperature fell significantly in F. mechowii after losing the righting reflex (LRR) from T1 (32.6 ± 0.6 °C) to T3 (30.4 ± 0.9 °C). Conclusions and Clinical relevanceAfrican mole-rats (Bathyergidae) live in closed burrow systems under particular conditions (hypercapnia, hypoxia, stable temperature, humidity, darkness) and show several physiological adaptations. Injectable anaesthetics in the dose rates used in other rodents are not appropriate for use in these subterranean species. Here, a reliable protocol for chemical restraint is provided.

Testing three measures of mouse insensibility following induction with isoflurane or carbon dioxide gas for a more humane euthanasia

Laboratory mice are commonly killed via exposure to gradually increasing concentrations of isoflurane and carbon dioxide (CO2) gas. Once rendered insensible using isoflurane or CO2, a high concentration of CO2 is used to decrease time to death. When the switch from isoflurane to a high flow rate of CO2 is made, it is important that the mice are insensible (complete loss of sensation) to prevent conscious exposure to potentially painful and distressing CO2 concentrations (>40%). Currently, no science-based methods exist for users to know when insensibility occurs during isoflurane or CO2 euthanasia protocols. The objective of our study was to examine three measures of insensibility: recumbency onset, loss of the righting reflex and loss of the pedal withdrawal reflex, in mice during euthanasia with 20% gradual-fill CO2 (n=6) or 5% isoflurane using 2L/min oxygen as the carrier gas, followed by CO2 (n=7). In addition to testing for the three insensibility indicators, an ‘escape response’ was recorded if a mouse exhibited leg paddling and forward or lateral movement in response to the experimenter's approaching hand, when about to test for loss of the righting reflex. A ‘purposeful movement’ response was recorded if the animal showed the inability to self-right, but exhibited leg paddling while on its back. The results of this study demonstrated that all isoflurane treatment mice showed an escape response, purposeful movement and a pedal withdrawal response, in comparison to only two, zero and one CO2 mice, respectively. Thus, even after recumbency and loss of the righting reflex, mice showed indications of sensibility, suggesting that these are not reliable indicators of insensibility when using the isoflurane method of euthanasia as outlined in this study. On average (±S.D.) the interval between recumbency onset and loss of the pedal withdrawal reflex was 40 (±13)s for isoflurane versus 16 (±11)s for the CO2 method tested. When using isoflurane induction as described here, we recommend that users wait a minimum of 79s (mean+3 S.D.) after the appearance of recumbency before switching to a high flow rate of CO2. If using the gradual-fill CO2 method as described here, users should wait a minimum of 49s (mean+3 S.D.) before increasing the flow rate of CO2.