Evaluation of cardiovascular effects of intramuscular medetomidine and a medetomidine-vatinoxan combination in Beagle dogs: A randomized blinded crossover laboratory study.

OBJECTIVE: To compare the cardiovascular effects of a combination of medetomidine and vatinoxan (MVX) versus medetomidine (MED) alone administered intramuscularly (IM) and to determine whether heart rate (HR) can be used as a surrogate for cardiac output (CO) after the use of medetomidine with or without vatinoxan. STUDY DESIGN: A randomized, blinded, experimental, crossover study. ANIMALS: A group of eight healthy Beagle dogs aged 4.6 (2.3-9.4) years and weighing 12.9 (9-14.7) kg, median (range). METHODS: Each dog was injected with 1 mg m-2 medetomidine with or without 20 mg m-2 vatinoxan IM with a washout period of 7 days. Cardiovascular data and arterial and mixed venous blood gas samples were collected at baseline, 5, 10, 15, 20, 35, 45, 60, 90 and 120 minutes after treatment administration. CO was measured at all time points via thermodilution. Differences between treatments, period and sequence were evaluated with repeated measures analysis of covariance and the relationship between HR and CO was assessed with a repeated measures analysis of variance; p values < 0.05 were deemed significant. RESULTS: The CO was 47-96% lower after MED than after MVX (p < 0.0001). Increases in systemic, pulmonary arterial and right atrial pressures and oxygen extraction ratio were significantly higher after MED than after MVX (all p < 0.0001). HR was significantly lower after MED and the linear relationship to CO was significant (p < 0.0001). CONCLUSIONS AND CLINICAL RELEVANCE: Overall, MED affected the cardiovascular system more negatively than MVX, and the difference in cardiovascular function between the treatments can be considered clinically relevant. HR was linearly related to CO, and decreases in HR reflected cardiac performance for dogs sedated with medetomidine with or without vatinoxan.

Effects of acepromazine and dexmedetomidine, followed by propofol induction and maintenance with isoflurane anaesthesia, on the microcirculation of Beagle dogs evaluated by sidestream dark field imaging: an experimental trial.

OBJECTIVE: To investigate the effects of intramuscularly administered acepromazine or dexmedetomidine on buccal mucosa microcirculation in Beagle dogs. STUDY DESIGN: Experimental, blinded, crossover study. ANIMALS: A group of seven Beagle dogs aged 7.5 ± 1.4 years (mean ± standard deviation). METHODS: Microcirculation was assessed on buccal mucosa using sidestream dark field videomicroscopy. After baseline measurements, 5 µg kg-1 dexmedetomidine or 30 µg kg-1 acepromazine were administered intramuscularly. After 10, 20 and 30 minutes, measurements were repeated. At 40 minutes after premedication, anaesthesia was induced with propofol intravenously and maintained with isoflurane. Measurements were repeated 50, 60 and 65 minutes after the injection of the investigated drugs. Analysed microcirculatory variables were: Perfused de Backer density, Perfused de Backer density of vessels < 20 µm, Proportion of perfused vessels and Proportion of perfused vessels < 20 µm. Heart rate (HR), systolic, diastolic (DAP) and mean (MAP) arterial pressures were recorded at the same time points. Macro- and microcirculatory variables were analysed using a linear mixed model with baseline as a covariate, treatment, trial period and repetition as fixed effects and time and dog as random effect. Results are presented as effect size and confidence interval; p values < 0.05 were considered significant. RESULTS: After acepromazine, Perfused de Backer density was greater during sedation and anaesthesia [3.71 (1.93-5.48 mm mm-2, p < 0.0001) and 2.3 (0.86-3.75 mm mm-2, p < 0.003)], respectively, than after dexmedetomidine. HR was significantly lower, whereas MAP and DAP were significantly higher with dexmedetomidine during sedation and anaesthesia (p < 0.0001 for all) compared with acepromazine. CONCLUSIONS AND CLINICAL RELEVANCE: The sedative drugs tested exerted a significant effect on buccal mucosal microcirculation with a higher Perfused de Backer density after the administration of acepromazine compared with dexmedetomidine. This should be considered when microcirculation is evaluated using these drugs.

The impact of vatinoxan on microcirculation after intramuscular co-administration with medetomidine in Beagle dogs: a blinded crossover study.

OBJECTIVE: To measure the effects on microcirculation of medetomidine alone (MED) or combined with vatinoxan (MVX). STUDY DESIGN: Randomized, crossover, blinded, experimental study. ANIMALS: A group of eight healthy purpose-bred Beagle dogs. METHODS: Each dog was given 1 mg m-2 MED intramuscularly (IM) or combined with 20 mg m-2 vatinoxan IM (MVX) with a washout period of 7 days. A sidestream dark field (SDF) camera was placed on the buccal mucosa to assess the oral mucosal microcirculation for perfused DeBacker density, proportion of perfused vessels (PPV) (both for all vessels and vessels with a diameter < 20 µm), microvascular flow index (MFI) and heterogeneity index (HI). Videos were recorded at baseline (-5) and 10, 20, 30, 40, 60, 90 and 120 minutes after treatment administration. Linear mixed-effects models were used to assess if microvascular variables were significantly associated with treatment, baseline, and sequence. Results are presented as estimated effect (95% confidence interval), and a p value < 0.05 was considered significant. RESULTS: The interquartile range for baseline measurements was 91.49%-98.42% for PPV, 2.75-3 for MFI and 0-0.36 for HI. Significant effects of treatment and baseline were found. The estimated effect of MED against MVX was -1.98% (-3.53% to -0.42%) for PPV, -0.33 (-0.43 to -0.22) for MFI and 0.14 (0.05 to 0.22) for HI. There were no significant changes seen for perfused DeBacker density, perfused DeBacker density < 20 µm and PPV < 20 µm between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: These results suggest that MVX had significantly fewer effects on buccal mucosal microcirculation than MED. The SDF camera is a useful research tool to assess the microcirculatory status of heavily sedated dogs.

Impact of general anesthesia on rotational thromboelastometry (ROTEM) parameters and standard plasmatic coagulation tests in healthy Beagle dogs.

OBJECTIVE: To assess the influence of general anesthesia on rotational thromboelastometry (ROTEM) and standard coagulation testing in healthy dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: 10 healthy Beagle dogs. METHODS: Dogs were administered methadone (0.2 mg/kg) intramuscularly. Anesthesia was co-induced intravenously 30 min later with midazolam (0.1 mg/kg) and propofol to effect, and maintained with sevoflurane. Crystalloids were administered at 5 ml/kg/h. Blood was sampled by direct venipuncture before induction (T0) and 3.5 h later (T3.5) and ROTEM parameters (ExTEM, InTEM, FibTEM, ApTEM), standard plasmatic coagulation tests (prothrombin time [PT], activated partial thromboplastin time [aPTT], fibrinogen concentration), hematology, ionized calcium, triglycerides, pH, lactate and body temperature were compared over time with Students t - test or Wilcoxon matched pairs signed-rank tests. RESULTS: The following variables dropped significantly between T0 and T3.5: body temperature (p < 0.0001), hematocrit (p < 0.0001), platelet count (p < 0.01), pH (p < 0.01), triglycerides (p < 0.01), fibrinogen concentration (p < 0.01), ExTEM, FibTEM (p < 0.01) and ApTEM (p < 0.05) clotting times. Lactate concentration (p < 0.01), aPTT (p < 0.05) and FibTEM maximum clot firmness increased (p < 0.05). No changes were noted in ionized calcium, PT and InTEM values. CONCLUSION AND CLINICAL RELEVANCE: General anesthesia with concurrent hemodilution and hypothermia induced significant but clinically irrelevant changes in coagulation variables measured at 37 °Celsius. Blood samples from anaesthetized animals can be used for determination of coagulation status in dogs.

Determination of reference intervals and comparison of venous blood gas parameters using standard and non-standard collection methods in 24 cats.

Objectives The aim of this study was to determine in-house reference intervals (RIs) for venous blood analysis with the RAPIDPoint 500 blood gas analyser using blood gas syringes (BGSs) and to determine whether immediate analysis of venous blood collected into lithium heparin (LH) tubes can replace anaerobic blood sampling into BGSs. Methods Venous blood was collected from 24 healthy cats and directly transferred into a BGS and an LH tube. The BGS was immediately analysed on the RAPIDPoint 500 followed by the LH tube. The BGSs and LH tubes were compared using paired t-test or Wilcoxon matched-pairs signed-rank test, Bland-Altman and Passing-Bablok analysis. To assess clinical relevance, bias or percentage bias between BGSs and LH tubes was compared with the allowable total error (TEa) recommended for the respective parameter. Results Based on the values obtained from the BGSs, RIs were calculated for the evaluated parameters, including blood gases, electrolytes, glucose and lactate. Values derived from LH tubes showed no significant difference for standard bicarbonate, whole blood base excess, haematocrit, total haemoglobin, sodium, potassium, chloride, glucose and lactate, while pH, partial pressure of carbon dioxide and oxygen, actual bicarbonate, extracellular base excess, ionised calcium and anion gap were significantly different to the samples collected in BGSs ( P <0.05). Furthermore, pH, partial pressure of carbon dioxide and oxygen, extracellular base excess, ionised calcium and anion gap exceeded the recommended TEa. Conclusions and relevance Assessment of actual and standard bicarbonate, whole blood base excess, haematocrit, total haemoglobin, sodium, potassium, chloride, glucose and lactate can be made based on blood collected in LH tubes and analysed within 5 mins. For pH, partial pressure of carbon dioxide and oxygen, extracellular base excess, anion gap and ionised calcium the clinically relevant alterations have to be considered if analysed in LH tubes.

Cardiopulmonary effects and anaesthesia recovery quality in horses anaesthetized with isoflurane and low-dose S-ketamine or medetomidine infusions.

OBJECTIVES: To evaluate cardiopulmonary effects and anaesthesia recovery quality in horses anaesthetized with isoflurane receiving medetomidine or S-ketamine infusions. STUDY DESIGN: Randomized, blinded, prospective clinical trial. ANIMALS: Fifty horses undergoing elective surgery. METHODS: After acepromazine and flunixin meglumine premedication, horses received medetomidine (7 µg kg-1 ) intravenously (IV). Anaesthesia was induced with midazolam and racemic ketamine (Med treatment group; 2.2 mg kg-1 ; n = 25) or S-ketamine (S-ket treatment group; 1.1 mg kg-1 ; n = 25) IV and maintained with isoflurane in oxygen/air and medetomidine (Med; 3.5 µg kg-1 hour-1 ) or S-ketamine (S-ket; 0.5 mg kg-1 hour-1 ). All horses were mechanically ventilated. Cardiopulmonary variables were evaluated. Isoflurane end-tidal concentrations (Fe'Iso), dobutamine requirements and thiopental boli were recorded. Plasma samples were collected in six horses to evaluate S-ketamine and S-norketamine concentrations. After surgery, medetomidine 2 µg kg-1 was administered IV. Four independent observers scored recovery using a visual analogue scale and a numerical rating scale. RESULTS: Both groups required similar mean Fe'Iso (1%). However, S-ket horses needed more thiopental boli. Median intraoperative cardiac index values were higher with S-ket (4.5 L minute-1  m-2 ) than Med (3.9 L minute-1  m-2 ). Overall, there were no differences in heart rate, blood pressure or dobutamine requirements; however, horses in S-ket showed higher heart rate values at 30 minutes after anaesthesia induction. Compared with Med horses, S-ket horses showed decreased PaO2 and increased pulmonary venous admixture values estimated with the Fshunt calculation. Recoveries were shorter and of poorer quality with S-ket. During infusion, S-ketamine and S-norketamine plasma concentrations lay in the ranges of 0.209-0.917 µg mL-1 and 0.250-0.723 µg mL-1 , respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Despite the higher intraoperative cardiac index with S-ket, both protocols were considered to provide acceptable cardiovascular function. However, recovery quality was significantly better in the Med group.