Dexmedetomidine prevents epinephrine-induced arrhythmias through stimulation of central alpha 2 adrenoceptors in halothane-anesthetized dogs

Dexmedetomidine and magnesium sulfate in preventing junctional ectopic tachycardia after pediatric cardiac surgery

BACKGROUND

Junctional ectopic tachycardia (JET) is a serious tachyarrhythmia following pediatric cardiac surgery. It isn't easy to treat and better to be prevented. This study aimed to examine the prophylactic effects of dexmedetomidine, MgSO4, or their combination in reducing JET following pediatric open cardiac surgery.

METHODS

Hundred and twenty children under 5 years, weighing more than 5 kg, who were scheduled for corrective acyanotic cardiac surgeries were randomized into three groups. Group MD (Dexmedetomidine-MgSO4 group): received dexmedetomidine 0.5 μg/kg IV over 20 min after induction, then infusion 0.5 μg/kg/h for 72 h, and 50 mg/kg bolus of MgSO4 with aortic cross-clamp release, then continued administration for 72 h postoperatively at a dose of 30 mg/kg/day. Group D (the dexmedetomidine group) received the same dexmedetomidine as the MD group in addition to normal saline instead of MgSO4. Group C (control group): received normal saline instead of dexmedetomidine and MgSO4. The primary outcome was the detection of JET incidence; the secondary outcomes were hemodynamic parameters, ionized Mg, vasoactive-inotropic score, extubation time, PCCU and hospital stay, and perioperative complications.

RESULTS

The incidence of JET was significantly reduced in Group MD and Group D (p = .007) compared to Group C. Ionized Mg was significantly higher in Group MD than in Groups D and C during rewarming and in the ICU (p < .001). Better hemodynamic profile in Group MD compared to Group D and Group C throughout surgery and in the ICU, the predictive indexes were significantly better in Group MD than in Groups D and C (p < .001). Including the extubation time, PCCU, and hospital stay.

CONCLUSION

Dexmedetomidine alone or combined with MgSO4 had a therapeutic role in the prevention of JET in children after congenital heart surgery.

Effects of multimodal low-opioid anesthesia protocol during on-pump coronary artery bypass grafting: a prospective cohort study

BACKGROUND

The most favorable anesthesia protocol during on-pump coronary artery bypass grafting (CABG) in patients with coronary heart disease remains unclear, despite previous publications regarding the interaction between anesthesia protocol and postoperative complications. The aim of the study was to compare the effect of a multimodal low-opioid anesthesia protocol (MLOP) on early postoperative complications during on-pump CABG.

METHODS

A single-center prospective cohort study including 120 patients undergoing on-pump CABG aged 18 to 65 years, divided into two groups according to undergoing MLOP or routine-opioid anesthesia protocol (ROP). The analyzed parameters were plasma IL-6 levels, complications, duration of mechanical ventilation, length of intensive care unit stay, and hospitalization.

RESULTS

In the MLOP group, the levels of IL-6 at the end of the surgery were 25.6% significantly lower compared to the ROP group (33.4 ± 9.4 vs. 44.9 ± 15.9, p < 0.0001), the duration of mechanical ventilation was significantly shorter (2.0 (2.0; 3.0) h vs. 4.0 (3.0; 5.0) h, p < 0.001), the incidence of low cardiac output syndrome was almost two and half times lower (7 (11.7%) vs. 16 (26.7%), p = 0.037), and also the incidence of postoperative atrial fibrillation was significantly lower (9 (15.0%) vs. 19 (31.7%), p = 0.031).

CONCLUSION

Our study confirms that using MLOP was characterized by significantly lower levels of IL-6 at the end of surgery and a lower incidence of low cardiac output syndrome and postoperative atrial fibrillation than ROP.

TRIAL REGISTRATION

The study is registered in clinicaltrials.gov №NCT05514652.

Dexmedetomidine Reduces Incidences of Ventricular Arrhythmias in Adult Patients: A Meta-Analysis

Purpose

To assess the antiarrhythmic properties of dexmedetomidine in patients in the intensive care unit.

Methods

A literature review was conducted with Ovid MEDLINE (R), Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Embase, and Scopus. Study Selection. Randomized controlled trials were included, examining the incidence of ventricular arrhythmias, ventricular tachycardia, or ventricular fibrillation with dexmedetomidine compared to placebo or an alternative sedative agent. For each publication that met the selection criteria, the patient demographics, incidence of arrhythmias, mortality, and adverse events were collected. Data extraction was carried out by two authors independently.

Results

We identified 6 out of 126 studies that met the selection criteria for our meta-analysis, all of which focused on the perioperative cardiac surgery period. Patients receiving dexmedetomidine demonstrated a significant reduction of the overall incidence of ventricular arrhythmias (RR 0.35, 95% CI 0.16, 0.76). In particular, dexmedetomidine significantly decreased the risk of ventricular tachycardia compared with control (RR 0.25, 95% CI 0.08, 0.80, I² 0%). Regarding adverse events, dexmedetomidine significantly increased the frequency of bradycardia (RR 2.78 95% CI 2.00, 3.87). However, there was no significant difference in mortality (RR 0.59 95% CI 0.12, 3.02).

Conclusion

From this meta-analysis, we report a decreased incidence of ventricular tachycardia with dexmedetomidine in critically ill patients. This result favors the use of dexmedetomidine for its antiarrhythmic properties.

Effect of Dexmedetomidine on Tachyarrhythmias After Cardiac Surgery: A Systematic Review and Meta-Analysis

ABSTRACT

Tachyarrhythmias after cardiac surgery is a common occurrence in clinical practice, which can be life threatening. We searched 6 databases, including Embase, PubMed, Cochrane, CNKI, Wanfang, and Sinomed, to evaluate the effect of dexmedetomidine on tachyarrhythmias after adult cardiac surgery. The primary end point was the number of patients with atrial fibrillation (AF) after cardiac surgery. The secondary end points included the number of patients with supraventricular tachycardia or with ventricular tachycardia or with ventricular fibrillation or with myocardial infarction or deceased patients, the duration of mechanical ventilation, the intensive care unit stay, hospital stay, and the number of patients with bradycardia and those with hypotension. Among the 1388 retrieved studies, 18 studies (n = 3171 participants) met our inclusion criteria. Dexmedetomidine reduced the incidence of AF by 17% [relative risk (RR) = 0.83; 95% confidence interval (CI), 0.73-0.93; P = 0.002]. Through subgroup analysis, we found that when the maintenance dose of dexmedetomidine was >0.7 µg·kg-1·h-1, the effect of preventing AF was obvious (RR = 0.58; 95%CI 0.43-0.78; P = 0.0003). Dexmedetomidine also reduced the incidence of supraventricular tachycardia by approximately 70% (RR = 0.29; 95% CI, 0.11-0.77; P = 0.01) and the incidence of ventricular tachycardia by approximately 80% (RR = 0.23; 95% CI, 0.08-0.63; P = 0.004) but had no effect on ventricular fibrillation (RR = 1.02; 95% CI, 0.14-7.31; P = 0.99). The major side effect of dexmedetomidine was bradycardia. Dexmedetomidine can reduce the incidence of AF (especially high dosages), supraventricular tachycardia, and ventricular tachycardia after cardiac surgery in adults, but it does not affect the occurrence of ventricular fibrillation.

Influence of doxapram and intermittent 10% carbon dioxide inspiration on cardiovascular and laryngeal functions in anesthetized dogs

OBJECTIVE

To compare the effects of two doses of doxapram intravenous injection and carbon dioxide inhalation on the cardiovascular and laryngeal functions of anesthetized hounds.

STUDY DESIGN

Experimental study.

ANIMALS

Six healthy adult dogs.

METHODS

In a Latin-square design, the mean arterial blood pressure (MABP) and heart rate (HR) were recorded continuously. The inspiratory normalized glottic gap areas (iNGGA) were measured before and after each stimulation with 0.55 mg/kg of doxapram (L-DOX), 2.2 mg/kg of doxapram (H-DOX), or 90 s of inhalation of 10% carbon dioxide in oxygen (I-CO₂ ). The stimulations were tested in duplicate or triplicate. Video clips of the laryngeal movement were scored by board-certified surgeons masked to the treatment.

RESULTS

The MABP increased with L-DOX and H-DOX up to 81% (both p < .001 compared to I-CO₂ ), and persisted during the other stimulations (both p < .001). An intermittent tachycardic effect of up to 79% increase in HR was observed with doxapram. The HR following H-DOX was higher than L-DOX and I-CO₂ (both p < .016). Neither hypertension nor tachycardia was observed with I-CO₂ . The iNGGA increased with all treatments (p < .001). The iNGGA was greater with H-DOX than L-DOX and I-CO₂ (both p < .007). All treatments received higher scores (all p < .001) with acceptable inter- and intra-observers Krippendorff's alphas.

CONCLUSION

All treatments were effective respiratory stimulants in anesthetized dogs; however, doxapram caused hypertension and tachycardia.

CLINICAL SIGNIFICANCE

Carbon dioxide inhalation might improve arytenoid motion without cardiovascular effects in dogs during clinical airway examinations.

Feasibility and postoperative opioid sparing effect of an opioid-free anaesthesia in adult cardiac surgery: a retrospective study

Background

No previous study investigated the dexmedetomidine-based opioid-free anesthesia (OFA) protocol in cardiac surgery. The main objective of this study was to evaluate the feasibility and the postoperative opioid-sparing effect of dexmedetomidine-based OFA in adult cardiac surgery patients.

Methods

We conducted a single-centre and retrospective study including 80 patients above 18 years old who underwent on-pump cardiac surgery between November 2018 and February 2020. Patients were divided into two groups: OFA (lidocaine, ketamine, dexmedetomidine, MgSO4) or opioid-based anaesthesia (remifentanil and anti-hyperalgesic medications such as ketamine and/or MgSO4 and/or lidocaine at the discretion of the anesthesiologist). The primary endpoint was the total amount of opioid consumed in its equivalent of intravenous morphine during the first 48 postoperative hours. Secondary outcomes included perioperative hemodynamics, post-operative maximal pain at rest and during coughing and adverse outcomes. Data are expressed as median [interquartile range].

Results

Patients in the OFA-group had a higher EuroSCORE II, with more diabetes, more dyslipidemia and more non-elective surgery but fewer smoking history. In the OFA group, the median loading dose of dexmedetomidine was 0.6 [0.4–0.6] μg.kg^− 1 while the median maintenance dose was 0.11 μg.kg^− 1.h^− 1 [0.05–0.20]. In 10 (25%) patients, dexmedetomidine was discontinued for a drop of mean arterial pressure below 55 mmHg. The median total amount of opioid consumed in its equivalent of intravenous morphine during the first 48 postoperative hours was lower in the OFA group (15.0 mg [8.5–23.5] versus 30.0 mg [17.3–44.3], p < 0.001). While no differences were seen with rest pain (2.0 [0.0–3.0] versus 0.5 [0.0–5.0], p = 0.60), the maximal pain score during coughing was lower in OFA group (3.5 [2.0–5.0] versus 5.5 [3.0–7.0], p = 0.04). In OFA group the incidence of atrial fibrillation (18% versus 40%, p = 0.03) and non-invasive ventilation use (25% versus 48%, p = 0.04) were lower. The incidence of bradycardia and the intraoperative use of norepinephrine were similar between both groups.

Conclusion

Dexmedetomidine-based OFA in cardiac surgery patients is feasible and could be associated with a lower postoperative morphine consumption and better postoperative outcomes. Further randomized studies are required to confirm these promising results and determine the optimal associations, dosages, and infusion protocols during cardiac surgery.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-021-01362-1.

Dexmedetomidine exhibits antiarrhythmic effects on human-induced pluripotent stem cell-derived cardiomyocytes through a Na/Ca channel-mediated mechanism

Background

Ventricular-like human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) exhibit the electrophysiological characteristics of spontaneous beating. Previous studies demonstrated that dexmedetomidine (DMED), a highly selective and widely used α₂-adrenoceptor agonist for sedation, analgesia, and stress management, may induce antiarrhythmic effects, especially ventricular tachycardia. However, the underlying mechanisms of the DMED-mediated antiarrhythmic effects remain to be fully elucidated.

Methods

A conventional patch-clamp recording method was used to investigate the direct effects of DMED on spontaneous action potentials, pacemaker currents (I_f), potassium (K⁺) channel currents (I_K1 and I_Kr), sodium (Na⁺) channel currents (I_Na), and calcium (Ca²⁺) channel currents (I_Ca) in ventricular-like hiPSC-CMs.

Results

DMED dose-dependently altered the frequency of ventricular-like spontaneous action potentials with a half-maximal inhibitory concentration (IC₅₀) of 27.9 µM (n=6) and significantly prolonged the action potential duration at 90% repolarization (APD₉₀). DMED also inhibited the amplitudes of the I_Na and I_Ca without affecting the activation and inactivation curves of these channels. DMED decreased the time constant of the Na⁺ and Ca²⁺ channel activation at potential –40 to –20 mv, and –20 mv. DMED increased the time constant of inactivation of the Na⁺ and Ca²⁺ channels. However, DMED did not affect the I_K1, I_Kr, I_f, and their current-voltage relationship. The ability of DMED to decrease the spontaneous action potential frequency and the Na⁺ and Ca²⁺ channel amplitudes, were not blocked by yohimbine, idazoxan, or phentolamine.

Conclusions

DMED could inhibit the frequency of spontaneous action potentials and decrease the I_Na and I_Ca of hiPSC-CMs via mechanisms that were independent of the α₂-adrenoceptor, the imidazoline receptor, and the α₁-adrenoceptor. These inhibitory effects on hiPSC-CMs may contribute to the antiarrhythmic effects of DMED.

Evaluation of electrocardiographic repolarization parameters after administration of trimethoprim-sulfadiazine, detomidine, or their combination in horses

OBJECTIVE

To determine whether administration of trimethoprim-sulfadiazine (TMS), detomidine (DET), or TMS plus DET would be associated with changes in ECG repolarization parameters in horses.

ANIMALS

9 healthy adult horses.

PROCEDURES

Each horse received 4 treatments in a blinded, randomized, crossover study design as follows: TMS, 16 to 24 mg/kg, IV; DET, 0.015 to 0.02 mg/kg, IV; TMS plus DET; and saline (0.9% NaCl) solution. Surface ECG traces were obtained over 24 hours, and repolarization parameters were measured at predefined time points after each treatment and compared with a 2-way ANOVA for repeated measures.

RESULTS

Heart rate-corrected QT intervals (QTc) were significantly increased after administration of DET (mean ± SD difference in QTc, 36.57 ± 23.07 milliseconds; increase of 7%) and TMS plus DET (44.96 ± 29.16 milliseconds; increase of 9%), compared with baseline (before treatment) values and values after administration of saline solution. Saline solution and TMS alone did not affect QTc.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of DET or TMS plus DET was associated with a significant and possibly clinically relevant prolongation of QTc, with prolongation of 7% to 9%, a range that is considered as a risk factor for the development of cardiac arrhythmias in people. Results were unexpected because DET is considered to be a safe sedative for horses.

Influence of low-opioid anesthesia in cardiac surgery on dynamics of pro-inflammatory interleukin-6

Introduction

With coronary artery bypass grafting, patients are subjected to additional risk caused by both surgical treatment itself and pathophysiological changes in homeostasis, provoked by the action of anesthetics and cardiopulmonary bypass.

Material and methods

The study involved 60 patients, who had been subjected to coronary artery bypass grafting with cardiopulmonary bypass. All patients were divided into two groups: group I (30 patients) – low-opioid scheme of anesthesia and group II (30 patients) – standard scheme of anesthetic management. Blood interleukin-6 (IL-6) was identified before and after cardiopulmonary bypass using an ELISA test.

Results

Having compared IL-6 values between study groups after completion of cardiopulmonary bypass, it was established that IL-6 levels were 27.51% (p = 0.001) lower in patients of group I compared with the results of patients in group II. Patients in the first group had a significantly shorter time of mechanical ventilation compared to group II (2.1 ±0.7 hours vs. 3.9 ±0.9 hours, p = 0.021). Low cardiac output syndrome was significantly less frequently reported in patients of group I (10.0% vs. 33.3%, p = 0.028). In addition, patients in group I had a significantly shorter time of intensive care unit (ICU) stay (2.5 ±0.7 days vs. 3.5 ±1.0 days, p = 0.044).

Conclusions

Application of multimodal low-opioid anesthesia was associated with significantly lower IL-6 at the end of surgery, shorter mechanical ventilation duration, less frequent low cardiac output syndrome and need for catecholamines, and shorter ICU stays.

Dexmedetomidine is safe and reduces the additional dose of midazolam for sedation during endoscopic retrograde cholangiopancreatography in very elderly patients

Background

Endoscopic retrograde cholangiopancreatography (ERCP) often requires deep sedation. Dexmedetomidine, a highly selective α2-adrenoceptor agonist with sedative activity and minimal effects on respiration, has recently been widely used among patients in the intensive care unit. However, its use in endoscopic procedures in very elderly patients is unclear. In this study, we retrospectively investigated the safety and efficacy of dexmedetomidine sedation during ERCP.

Methods

The study included 62 very elderly patients (aged over 80 years) who underwent ERCP from January 2014, with sedation involving dexmedetomidine (i.v. infusion at 3.0 μg/kg/h over 10 min followed by continuous infusion at 0.4 μg/kg/h) along with midazolam. For comparison, the study included 78 patients who underwent ERCP before January 2014, with midazolam alone. We considered additional administration of midazolam as needed to maintain a sedation level of 3–4, according to the Ramsay sedation scale. The outcome measures were amount of midazolam, adverse events associated with sedation, and hemodynamics.

Results

The incidence of decreased SpO₂ and median dose of additional midazolam were significantly lower in the dexmedetomidine group than in the conventional group. The minimum systolic blood pressure and minimum heart rate during and after examination was significantly lower in the dexmedetomidine group than in the conventional group. However, serious acute heart failure or arrhythmia was not noted.

Conclusions

Dexmedetomidine can decrease the incidence of respiratory complications and the total dose of other sedative agents. It can be used as an alternative to conventional methods with midazolam for adequate sedation during ERCP in very elderly patients.

A clinical study to evaluate the cardiopulmonary characteristics of two different anaesthetic protocols for immobilization of healthy chimpanzees (Pan troglodytes)

OBJECTIVE

To characterize the cardiopulmonary characteristics of two different anaesthetic protocols (tiletamine/zolazepam ± medetomidine) and their suitability for the immobilization of healthy chimpanzees undergoing cardiac assessment.

STUDY DESIGN

Prospective, clinical, longitudinal study.

ANIMALS

Six chimpanzees (Pan troglodytes) aged 4-16 years weighing 19.5-78.5 kg were anaesthetized on two occasions.

METHODS

Anaesthesia was induced with tiletamine/zolazepam (TZ) (3-4 mg kg^-1) or tiletamine/zolazepam (2 mg kg^-1) and medetomidine (0.02 mg kg^-1) (TZM) via blow dart [intramuscular (IM)] and maintained with intermittent boluses of ketamine (IV) or zolazepam/tiletamine (IM) as required. The overall quality of the anaesthesia was quantified based on scores given for: quality of induction, degree of muscle relaxation and ease of intubation. The time to achieve a light plane of anaesthesia, number of supplemental boluses needed and recovery characteristics were also recorded. Chimpanzees were continuously monitored and heart rate (HR), pulse rate (PR), respiratory rate (f_R) oxygen saturation of haemoglobin (SpO₂), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), rectal temperature, mucous membrane colour and capillary refill time recorded. During the first procedure (TZ) animals underwent a 12-channel electrocardiogram (ECG), haematology, biochemistry and cardiac biomarker assessment to rule out the presence of pre-existing cardiovascular disease. A detailed echocardiographic examination was carried out by the same blinded observer during both procedures. Data were compared using Student's paired t-test or Wilcoxon rank tests as appropriate.

RESULTS

There was a significant difference for the area under the curves between anaesthetic protocols for HR, SAP, MAP and f_R. No significant differences in the echocardiographic measurements were evident. Quality of anaesthesia was significantly better with TZM and no additional boluses were required. The TZ protocol required multiple supplemental boluses.

CONCLUSIONS AND CLINICAL RELEVANCE

Both combinations are suitable for immobilization and cardiovascular evaluation of healthy chimpanzees. Further work is required to evaluate the effect of medetomidine in cardiovascular disease.

Comparative evaluation of propofol and ketamine total intravenous anaesthesia (TIVA) with dexmedetomidine and butorphanol in goats

The present study was aimed to compare clinicophysiological, and haemodynamic effects of propofol and ketamine anaesthesia with dexmedetomidine-butorphanol premedication. Prospective, randomized clinical trial, with owner consent was performed on sixteen clinical cases of urolithiasis in goats. After sedation with dexmedetomidine (2.5 μg/kg body wt) and butorphanol (0.05 mg/kg body wt), anaesthesia was induced and maintained with either propofol or ketamine. For maintenance, continuous intravenous infusion (CII) at variable rate was used with respective drug. Infusion rate was adjusted in response to positive reactions to surgical nociceptive stimulation performed during tube cystostomy procedure. Clinicophysiological, and haemodynamic parameters were measured before treatment (baseline), after sedation and during anaesthesia. One way repeated measure analysis was used to compare the mean values at different intervals in each group for non-parametric observations. Mann whitney U test was used to compare median score between groups at corresponding intervals. Compared to baseline, HR (heart rate) improved at 15 min and onwards but remained significantly (P=0.030) lower than the baseline value in both groups. MAP (mean arterial pressure) decreased significantly (P=0.022) up to the end of the observation period in DBP (dexmedetomidine + butorphanol+ propofol); however, in DBK (dexmedetomidine + butorphanol + ketamine) improvement in MAP was observed at 15 min and onwards with significantly (P=0.018) lower values at 15 and 20 min and a non-significantly (P=0.080) lower value at 30 min as compared to the baseline value. Both drug combinations are suitable to induce and maintain anaesthesia for one hour, with good haemodynamic stability and analgesia. However, DBP is related with excellent sedation and muscle relaxation.

Can dexmedetomidine reduce atrial fibrillation after cardiac surgery? A systematic review and meta-analysis

Purpose

Cardiac surgery patients always present with atrial fibrillation (AF) after admission to the intensive care unit, leading to high mortality and lengthy hospitalization. Dexmedetomidine (DEX) is a popular medication used for sedation in the intensive care unit; however, whether it can reduce AF needs to be analyzed.

Materials and methods

Three primary databases, Medline, Embase (Ovid SP) and the Cochrane Central Register of Controlled Trials (CENTRAL), were searched. All English language and randomized control designed clinical publications comparing DEX to control medicines for sedation after elective cardiac surgery were included. Two independent colleagues conducted the data extraction and quality assessments. The subgroup analysis was performed according to the medicine used, age, AF history, and whether previous beta-blocker premedication and cardiopulmonary bypass (CPB) were applied. The overall incidence of AF was analyzed.

Results

A total of 1,295 patients in nine studies met the selection criteria among 2,587 studies screened from the database. After quantitative synthesis, our results revealed that the DEX group was not associated with a decreased incidence of AF compared with the placebo (risk ratio [RR] 0.76, 95% CI 0.37, 1.55, P=0.44) and morphine groups (RR 0.86, 95% CI 0.56, 1.31, P=0.48). Subgroup analysis also indicated that the DEX vs propofol comparison exhibited no difference: 1) for patients of age >60 years (P=0.69) or ≤60 years (P=0.69); 2) under CPB surgery (P=0.45) or without CPB surgery (P=0.88); 3) with beta-blocker premedication (P=0.32) or without beta-blocker premedication (P=0.90); and 4) with AF history (RR 1.07, 95% CI 0.85, 1.36, P=0.57) or without AF history (P=0.30).

Conclusion

This meta-analysis revealed that DEX could not reduce the incidence of AF compared to control medicines following cardiac surgery. DEX may have an increased influence on AF occurrence if patients had a history of AF. However, cautious interpretation should be made due to high clinical heterogeneity.

Does dexmedetomidine have an antiarrhythmic effect on cardiac patients? A meta-analysis of randomized controlled trials

Background

Cardiac surgery patients often experience several types of tachyarrhythmias after admission to the intensive care unit (ICU), which increases mortality and morbidity. Dexmedetomidine (DEX) is a popular medicine used for sedation in the ICU, and its other pharmacological characteristics are gradually being uncovered.

Purpose

To determine whether DEX has an antiarrhythmic effect after cardiac surgery.

Methods

The three primary databases MEDLINE, Embase (OVID SP) and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched, and all English-language and randomized control-designed clinical publications comparing DEX to control medicines for sedation after elective cardiac surgery were included. Two colleagues independently extracted the data and performed other quality assessments. A subgroup analysis was performed according to the different medicines used and whether cardiopulmonary bypass (CPB) was applied. All tachyarrhythmias that occurred in the atria and ventricles were analyzed.

Results

A total of 1295 patients in 9 studies met the selection criteria among 2587 studies that were screened. After quantitative synthesis, our results revealed that the DEX group was associated with a lower incidence of ventricular arrhythmia (VA, OR 0.24, 95% CI 0.09–0.64, I² = 0%, P = 0.005) than the control group. Subgroup analysis did not reveal a significant difference between the DEX and propofol subgroups (OR 0.13, 95% CI 0.03–0.56, I² = 0%, P = 0.007). Additionally, no difference in the incidence of atrial fibrillation (AF) was observed regardless of the different control medicines (OR 0.82, 95% CI 0.60–1.10, I² = 25%, P = 0.19) or whether CPB was applied.

Conclusions

This meta-analysis revealed that DEX has an antiarrhythmic effect that decreases the incidence of VA compared to other drugs used for sedation following cardiac surgery. DEX may not have an effect on AF, but cautious interpretation should be exercised due to high heterogeneity.

Effects of dexmedetomidine on heart arrhythmia prevention in off-pump coronary artery bypass surgery: A randomized clinical trial

Background

Arrhythmia occurring during and after surgery is one of the major complications in open-heart surgery. Dexmedetomidine is an intravenous alpha-2 agonist and very specific short-acting drug to protect the various organs against ischemic injuries and blood reflow. However, the effect of dexmedetomidine for preventing intraoperative heart arrhythmias has not been recognized.

Objective

This study aimed to determine the effect of dexmedetomidine on the incidence rate of heart arrhythmias and anesthetic required in off-pump coronary artery bypass surgery.

Methods

This randomized clinical trial was conducted on patients who were candidates for off-pump coronary artery bypass referring to Imam Reza Hospital of Mashhad, Iran, from July 2016 through January 2017. The patients were randomly assigned to two groups of intervention (infusion of 0.5 mcg/kg/h dexmedetomidine together with induction followed by infusion of 0.5 mcg/kg/h by the end of the surgery) or control (saline infusion). Mean arterial pressure (MAP) and heart rate (HR) were measured before induction, during surgery operation and ICU admission. Data were analyzed by SPSS version 18 using Chi Square and independent-samples t-test.

Results

A total of 76 patients with a mean age of 59.8 ± 8.2 years (in two groups of 38) were studied. The two groups had no statistically significant difference in terms of background variables. The MAP and HR values before induction, during surgery and ICU admission were significantly higher in the control group than in the intervention group (p=0.001). Out of the studied arrhythmias, the values of PAC (55.2% vs. 15.7%), PVC (81.5% vs. 21.0%), AF (26.3% vs. 7.8%), VTAC (21.0% vs. 2.6%) were significantly lower in dexmedetomidine group (p=0.001).

Conclusion

It seems that dexmedetomidine administration during induction and surgery can cause significant reduction in most of the common arrhythmias in off-pump coronary bypass surgery. The use of dexmedetomidine maintains MAP and HR at significantly lower values, and changes compared to the control group as well as reduces the need for anesthetic compounds.

Trial Registration

The present study has been registered at the Iranian Registry of Clinical Trials (www.IRCT.IR) with a code of IRCT2016072413159N9 before starting the study.

Founding

This study was fully sponsored by the Research Deputy at Mashhad University of Medical Sciences, Iran (grant number 941413).

Efficacy of Prophylactic Dexmedetomidine in Preventing Postoperative Junctional Ectopic Tachycardia After Pediatric Cardiac Surgery

BACKGROUND

Postoperative junctional ectopic tachycardia is one of the most serious arrhythmias that occur after pediatric cardiac surgery, difficult to treat and better to be prevented. Our aim was to assess the efficacy of prophylactic dexmedetomidine in preventing junctional ectopic tachycardia after pediatric cardiac surgery.

METHODS AND RESULTS

A prospective controlled study was carried out on 90 children who underwent elective cardiac surgery for congenital heart diseases. Patients were randomized into 2 groups. Group I (dexmedetomidine group): 60 patients received dexmedetomidine; Group II (Placebo group): 30 patients received the same amount of normal saline intravenously. The primary outcome was the incidence of postoperative junctional ectopic tachycardia. Secondary outcomes included bradycardia, hypotension, vasoactive inotropic score, ventilation time, pediatric cardiac care unit stay, length of hospital stay, and perioperative mortality. The incidence of junctional ectopic tachycardia was significantly reduced in the dexmedetomidine group (3.3%) compared with the placebo group (16.7%) with P<0.005. Heart rate while coming off cardiopulmonary bypass was significantly lower in the dexmedetomidine group (130.6±9) than the placebo group (144±7.1) with P<0.001. Mean ventilation time, and mean duration of intensive care unit and hospital stay (days) were significantly shorter in the dexmedetomidine group than the placebo group (P<0.001). However, there was no significant difference between the 2 groups as regards mortality, bradycardia, or hypotension (P>0.005).

CONCLUSION

Prophylactic use of dexmedetomidine is associated with significantly decreased incidence of postoperative junctional ectopic tachycardia in children after congenital heart surgery without significant side effects.

Dexmedetomidine vs propofol sedation reduces delirium in patients after cardiac surgery: A meta-analysis with trial sequential analysis of randomized controlled trials

PURPOSE

It is uncertain whether dexmedetomidine is better than propofol for sedation in postcardiac surgery patients. The purpose of this meta-analysis was to compare the effects of dexmedetomidine and propofol sedation on outcomes in adult patients after cardiac surgery.

METHODS

Randomized controlled trials comparing outcomes in cardiac surgery patients sedated with dexmedetomidine or propofol were retrieved from PubMed, Embase, Web of Science, the Cochrane Library, and Clinicaltrials.Gov until May 23, 2016.

RESULTS

A total of 969 patients in 8 studies met the selection criteria. The results revealed that dexmedetomidine was associated with a lower risk of delirium (risk ratio, 0.40;95% confidence interval [CI], 0.24-0.64; P=.0002), a shorter length of intubation (hours; mean difference, -0.95; 95% CI, -1.26 to -0.64; P<.00001), but a higher incidence of bradycardia (risk ratio 3.17; 95% CI, 1.41-7.10; P=.005) as compared to propofol. There were no statistical differences in the incidence of hypotension or atrial fibrillation, or the length of intensive care unit stay between dexmedetomidine and propofol sedation regimens.

CONCLUSIONS

Dexmedetomidine sedation could reduce postoperative delirium and was associated with shorter length of intubation, but might increase bradycardia in patients after cardiac surgery compared with propofol.

Dexmedetomidine sedation reduces atrial fibrillation after cardiac surgery compared to propofol: a randomized controlled trial

BACKGROUND

Atrial fibrillation occurs frequently in patients following cardiac surgery and can be a cause of increased morbidity and mortality. The use of dexmedetomidine to prevent atrial fibrillation is unclear. The present study was designed to evaluate the effect of dexmedetomidine sedation on the incidence of atrial fibrillation after cardiac surgery.

METHODS

Upon arrival to the intensive care unit (ICU), cardiac surgery patients without prior atrial fibrillation or flutter were randomized to receive either dexmedetomidine (0.2-1.5 μg/kg/h) or propofol (0.3-3 mg/kg/h) open-label titrated to a target Richmond agitation-sedation scale of 0 to -3. Our primary endpoint was the incidence of postoperative atrial fibrillation, and the secondary end points were the length of ICU stay, length of hospital stay, and hospital costs.

RESULTS

Atrial fibrillation occurred in 6 of 44 patients (13.6 %) in the dexmedetomidine group compared to 16 of 44 patients (36.4 %) in the propofol group (odds ratio = 0.28; 95 % confidence interval, 0.10, 0.80; P = 0.025). The median (interquartile range) length of ICU stay in the dexmedetomidine group was significantly lower than in the propofol group (2.9 (2.4-3.5) vs 3.5 (2.7-4.5 days, P = 0.008), with a trend toward a decrease in median hospital costs (86,367 vs 77,874 Chinese yuan; P = 0.068). The incidence of hypotension was higher in the dexmedetomidine group than in the propofol group (25/44 (56.8 %) vs 13/44 (29.5 %); P = 0.017).

CONCLUSIONS

Dexmedetomidine sedation reduced the incidence of new-onset postoperative atrial fibrillation and shortened the length of ICU stay in patients after cardiac surgery compared to propofol sedation. Dexmedetomidine treatment was associated with more episodes of hypotension.

TRIAL REGISTRATION

chictr.org.cn: ChiCTR-IPR-16008231 , retrospectively registered: April 6, 2016. This trial was not prospectively registered due to a lack of importance applied to trial registration.

Electrocardiographic and electrophysiologic effects of dexmedetomidine on children

BACKGROUND

Dexmedetomidine (DEX) is a highly selective alpha-2-adrenergic agonist approved for short-term sedation and monitored anesthesia care in adults. Its effects on the electrocardiography and cardiac conduction tissue are not well described in the literature. Therefore, we aimed to characterize the electrocardiographic and electrophysiologic effects of DEX in children.

METHODS

Twenty children (11 boys and nine girls) between the ages of eight and 17 undergoing electrophysiology study and ablation of the supraventricular tachycardia had hemodynamic and cardiac electrophysiologic variables measured before and during the administration of DEX (1 microgram/kg IV over 10 minutes followed by a 10-minute continuous infusion of 0.5 microgram/kg/h).

RESULTS

A significant decrease in heart rate was seen after the administration of DEX, but the systolic-diastolic-mean arterial pressure, respiratory rate, and end-tidal carbon dioxide did not change. Corrected sinus node recovery times and baseline sinus cycle lengths, which are markers of sinus nodal function, were both lengthened with the administration of DEX. Atrioventricular (AV) nodal function, as evidenced by the Wenckebach cycle length, the ventriculoatrial block cycle length, and AV nodal effective refractory periods, was lengthened significantly. We also found that DEX increased the atrial refractory period and diminished atrial excitability.

CONCLUSIONS

DEX significantly depressed sinus and AV nodal function in pediatric patients without significant electrocardiogram interval changes, other than a trend toward lower heart rates. Although no spontaneous AV nodal block and no clinically significant bradycardia were seen, we recommend that DEX be used with caution in patients at risk for bradycardia and/or AV nodal dysfunction due to its associated comorbidities.

Dexmedetomidine does not reduce atrial fibrillation after lung cancer surgery

OBJECTIVE

To evaluate whether the use of intraoperative dexmedetomidine (DEX) during lung cancer surgery may reduce the incidence of postoperative atrial fibrillation (POAF).

DESIGN

A retrospective study.

SETTING

Academic hospital.

PARTICIPANTS

Seven hundred three adult patients with non-small-cell lung cancer.

MEASUREMENTS AND MAIN RESULTS

Patients younger than 18 years of age with a history of atrial fibrillation were excluded. Episodes of atrial fibrillation were identified from electronic medical records and consisted of cardiology consultations, electrocardiogram records, and use of anti-arrhythmic medications within the postoperative admission time. The Wilcoxon rank sum test was used to evaluate the difference in a continuous variable between patient groups. Fisher's exact test or the chi-square test was used to evaluate the association between 2 categorical variables. Logistic regression models were used for multivariate analysis. Overall POAF incidence was 136 of 703 (19.35%), with a mean onset of 3.01±2.03 days after surgery. Among patients, 204 (29.02%) received DEX intraoperatively. Male gender and age were strong predictors of POAF. POAF incidence was comparable between patients who were (n=93, 21.1%) and were not (n=43, 18.6%) treated with DEX (p=0.46). The mean onset time of arrhythmia was similar in both groups (DEX users: 2.93±2.49 days; non-DEX users: 3.05±1.79 days; p=0.146).

CONCLUSION

These results were similar to those published elsewhere on POAF incidence and risk factors. This study could not confirm the hypothesis that the intraoperative use of DEX is associated with a reduced rate of POAF after thoracic surgery for lung cancer.

Effect of dexmedetomidine on the corrected QT and Tp-e intervals during spinal anesthesia

PURPOSE

The aim of this study is to evaluate the effect of dexmedetomidine on corrected QT (QTc) and Tp-e intervals in patients undergoing spinal anesthesia.

MATERIALS AND METHODS

We studied 50 patients who were scheduled to undergo spinal anesthesia before orthopedic surgeries. Patients were allocated to receive either an infusion of dexmedetomidine or normal saline after spinal anesthesia.

RESULTS

QTc intervals were significantly prolonged after spinal anesthesia, and the prolonged QTc interval returned to baseline values 10 minutes after either normal saline or dexmedetomidine administration in both groups. The QTc interval values after dexmedetomidine administration were significantly shorter compared to the QTc interval values just before dexmedetomidine administration.

CONCLUSION

Dexmedetomidine could promote the return of a prolonged QTc interval induced by spinal anesthesia and might be helpful in patients who have a prolonged QTc interval.

Dexmedetomidine: antiarrhythmic effects in the pediatric cardiac patient

This report aims to provide a general description of the cardiovascular effects of dexmedetomidine, emphasizing its effects on conduction, and to give an evidence-based review of the literature regarding the use of dexmedetomidine to treat and prevent tachyarrhythmias in infants and children. A computerized bibliographic search of the literature on the use of dexmedetomidine to treat and prevent arrhythmias in infants and children was conducted. The cardiovascular effects of dexmedetomidine have been well studied in animal and adult human models. Growing experience, mostly in the pediatric population, has demonstrated the potential therapeutic applications of dexmedetomidine in the acute treatment of arrhythmias. Additionally, its use during cardiac surgery has been associated with a decreased incidence of postoperative ventricular and supraventricular tachyarrhythmias. Although dexmedetomidine is not currently approved by the Food and Drug Administration for the pediatric population, findings have shown it to be effective in various clinical scenarios for sedation. In addition, recent studies show that dexmedetomidine may have promising properties for the acute treatment and prevention of tachyarrhythmias.

Perioperative use of dexmedetomidine is associated with decreased incidence of ventricular and supraventricular tachyarrhythmias after congenital cardiac operations

BACKGROUND

Postoperative tachyarrhythmias remain a common complication after congenital cardiac operations. Dexmedetomidine (DEX), an α-2 adrenoreceptor agonist, can have a therapeutic role in supraventricular tachyarrhythmias for cardioversion to sinus rhythm or heart rate control. Whether routine perioperative use of DEX decreases the incidence of supraventricular and ventricular tachyarrhythmias was studied.

METHODS

In this prospective cohort study, 32 pediatric patients undergoing cardiothoracic operations received DEX and were compared with 20 control patients who did not receive DEX.

RESULTS

Dexmedetomidine was started after anesthesia induction and continued intraoperatively and postoperatively for 38±4 hours (mean dose, 0.76±0.04 μg/kg/h). Ten control patients and 2 DEX patients sustained 16 episodes of tachyarrhythmias (p=0.001), including a 25% vs 0% (p=0.01) incidence of ventricular tachycardia and 25% vs 6% (p=0.05) of supraventricular arrhythmias in the control and DEX group, respectively. Transient complete heart block occurred in 2 control patients and in 1 DEX patient. Control patients had a higher heart rate (141±5 vs 127±3 beats/min, p=0.03), more sinus tachycardia episodes (40% vs 6%; p=0.008), required more antihypertensive drugs with nitroprusside (20±7 vs 4±1 μg/kg; p=0.004) and nicardipine (13±5 vs 2±1 μg/kg; p=0.02), and required more fentanyl (39±8 vs 19±3 μg/kg; p=0.005).

CONCLUSIONS

Perioperative use of dexmedetomidine is associated with a significantly decreased incidence of ventricular and supraventricular tachyarrhythmias, without significant adverse effects.

Medetomidine, an α(2)-adrenergic agonist, activates cardiac vagal nerve through modulation of baroreflex control

BACKGROUND

Although α(2)-adrenergic agonists have been reported to induce a vagal-dominant condition through suppression of sympathetic nerve activity, there is little direct evidence that they directly increase cardiac vagal nerve activity. Using a cardiac microdialysis technique, we investigated the effects of medetomidine, an α(2)-adrenergic agonist, on norepinephrine (NE) and acetylcholine (ACh) release from cardiac nerve endings.

METHODS AND RESULTS

A microdialysis probe was implanted into the right atrial wall near the sinoatrial node in anesthetized rabbits and perfused with Ringer's solution containing eserine. Dialysate NE and ACh concentrations were measured using high-performance liquid chromatography. Both 10 and 100µg/kg of intravenous medetomidine significantly decreased mean blood pressure (BP) and the dialysate NE concentration, but only 100µg/kg of medetomidine enhanced ACh release. Combined administration of medetomidine and phenylephrine maintained mean BP at baseline level, and augmented the medetomidine-induced ACh release. When we varied the mean BP using intravenous administration of phenylephrine, treatment with medetomidine significantly steepened the slope of the regression line between mean BP and log ACh concentration.

CONCLUSIONS

Medetomidine increased ACh release from cardiac vagal nerve endings and augmented baroreflex control of vagal nerve activity.

Effects of dexmedetomidine pretreatment on bupivacaine cardiotoxicity in rats

BACKGROUND AND OBJECTIVE

We evaluated the effects of dexmedetomidine pretreatment on bupivacaine cardiotoxicity in anesthetized rats.

METHODS

Sixteen Wistar-Albino male rats (300-400 g) were anesthetized with ketamine. Electrocardiographic and invasive blood pressure monitoring were performed, and the results were continuously recorded. The rats were randomized into 2 groups. In group D, rats were pretreated with intravenous dexmedetomidine at a dose of 10 Kg/kg (n = 8), whereas in group S, rats were pretreated with intravenous saline (n = 8). Fifteen minutes later, bupivacaine was infused at a rate of 3 mg/kg per minute until cardiac asystole occurred. The timing of specific cardiotoxic events (a 25%, 50%, and 75% reductions of mean arterial pressure and heart rate as well as occurrence of the first arrhythmia and asystole) was recorded.

RESULTS

Dexmedetomidine pretreatment reduced the heart rates and mean arterial pressures of the rats who received it (P G 0.05). Dexmedetomidine pretreatment before bupivacaine administration also significantly increased the time to the 25%, 50%, and 75% reductions in mean arterial pressure and the time to the 25% and 50% reductions in heart rate (P G 0.05). In addition, dexmedetomidine significantly increased the time to first arrhythmia and time to asystole (P G 0.05) in the rats who received it before receiving bupivacaine.

CONCLUSIONS

Dexmedetomidine pretreatment delays the effects of bupivacaine cardiotoxicity.

The antiarrhythmic effect of centrally administered rilmenidine involves muscarinic receptors, protein kinase C and mitochondrial signalling pathways

BACKGROUND AND PURPOSE

We have previously demonstrated that stimulation of imidazoline receptors in the CNS prevented halothane-adrenaline arrhythmias during halothane anaesthesia and that stimulation of the vagus nerve may be critical to this effect. However, details of the mechanism(s) involved are not yet available. The present study was designed to examine the role of muscarinic receptors, protein kinase C (PKC), ATP-sensitive potassium channels (K(ATP)) and the mitochondrial permeability transition pore (MPTP) in the antiarrhythmic effect of rilmenidine, an imidazoline receptor agonist.

EXPERIMENTAL APPROACH

Rats were anaesthetized with halothane and monitored continuously for arterial blood pressure and premature ventricular contractions. The arrhythmogenic dose of adrenaline was defined as the lowest dose producing three or more premature ventricular contractions within a 15-s period. We confirmed that centrally administered rilmenidine prevented halothane-adrenaline arrhythmias and then examined the antiarrhythmic effect of rilmenidine in the presence of atropine methylnitrate, a muscarinic receptor antagonist, calphostin C, a PKC inhibitor, HMR-1098, a sarcolemmal K(ATP) inhibitor, 5-hydroxydecanoic acid, a mitochondrial K(ATP) inhibitor or atractyloside, an MPTP opener.

KEY RESULTS

The antiarrhythmic effect of rilmenidine was significantly inhibited by atropine methylnitrate, calphostin C, 5-hydroxydecanoic acid and atractyloside, but the effects of HMR-1098 in our model were not clear.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that muscarinic receptors, PKC, mitochondrial K(ATP) channels and MPTP may be crucial components of the mechanism involved in the antiarrhythmic effect of rilmenidine given into the CNS.

Management and complications of anesthesia for transvenous electrical cardioversion of atrial fibrillation in horses: 62 cases (2002-2006)

OBJECTIVE

To describe management of anesthesia for transvenous electrical cardioversion (TVEC) in horses and report perianesthetic complications.

DESIGN

Retrospective case series.

ANIMALS

62 horses with atrial fibrillation and without underlying cardiac disease and 60 horses without atrial fibrillation.

PROCEDURES

Medical records of horses with atrial fibrillation anesthetized for TVEC were reviewed, as were records of horses without atrial fibrillation anesthetized for magnetic resonance imaging (MRI). The TVEC group horses were compared with MRI group horses for incidence of intraoperative bradycardia and use of inotropic drugs. Data obtained included patient signalment, weight, duration of anesthesia, heart rate and arterial blood pressure during anesthesia, anesthetic drugs administered, mode of ventilation, perioperative complications, and quality of recovery.

RESULTS

The TVEC group horses were > 1 year of age and were predominantly Standardbreds. The TVEC group horses underwent a total of 76 anesthetic episodes. For 40 (52.6%) anesthetic episodes, horses received xylazine only for premedication, and for 26 (34.2%) anesthetic episodes, horses received xylazine and butorphanol. Induction of anesthesia consisted of ketamine administration in various combinations with diazepam and guaifenesin for 74 (97.4%) anesthetic episodes and ketamine alone for 2 (2.6%). Bradycardia in horses was encountered during 15 of 76 (19.7%) anesthetic episodes. Minor signs of possible postanesthetic myopathy occurred following 6 (7.9%) anesthetic episodes. No significant difference was found between TVEC and MRI group horses regarding incidence of bradycardia and inotropic drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Short-duration anesthesia for TVEC of atrial fibrillation in horses without underlying cardiac disease was a safe procedure.

Effects of dexmedetomidine on cerebral circulation and systemic hemodynamics after cardiopulmonary resuscitation in dogs

PURPOSE

Our purpose was to examine the effect of dexmedetomidine, when used with phenylephrine during cardiopulmonary resuscitation (CPR), on the cerebral and systemic circulations.

METHODS

In pentobarbital-anesthetized, mechanically ventilated dogs, we evaluated pial vessel diameters, cerebral oxygen extraction, and systemic hemodynamics before and after cardiac arrest (5 min) and resuscitation, in the presence or absence of dexmedetomidine (n = 7 each; dexmedetomidine or control group).

RESULTS

In both groups: (a) pial arterioles were dilated at 5 and 15 min after CPR, and had returned to baseline diameters at 30 min; (b) sagittal sinus pressure was significantly raised at 5 and 15 min after CPR; and (c) cerebral oxygen extraction was decreased at 5, 15, and 30 min after CPR, and had returned to baseline level at 60 min after CPR. We could find no differences between the two groups in the cerebral circulation after CPR. However, the number of defibrillation electric shocks required to restore spontaneous circulation (5.5 vs 3.6; P < 0.05), the dose of phenylephrine used for CPR (1193 microg vs 409 microg; P < 0.01), and the number of postresuscitation ventricular ectopic beats observed during the first 120 min after successful resuscitation (1606 vs 348; P < 0.05) were all significantly lower in the dexmedetomidine group.

CONCLUSION

Although intravenous dexmedetomidine, as used for CPR, does not have a beneficial effect on either cerebral vessels or cerebral oxygen extraction, it may reduce the number of defibrillation shocks needed and the number of postresuscitation ventricular ectopic beats, and help to bring about stable systemic circulation after CPR.

Dexmedetomidine or medetomidine premedication before propofol-desflurane anaesthesia in dogs

The objective of this study was to evaluate dexmedetomidine as a premedicant in dogs prior to propofol-desflurane anaesthesia, and to compare it with medetomidine. Six healthy dogs were anaesthetized. Each dog received intravenously (i.v.) five preanaesthetic protocols: D1 (dexmedetomidine, 1 microg/kg, i.v.), D2 (dexmedetomidine, 2 microg/kg, i.v.), M1 (medetomidine, 1 microg/kg, i.v.), M2 (medetomidine, 2 microg/kg, i.v.), or M4 (medetomidine, 4 microg/kg, i.v.). Anaesthesia was induced with propofol (2.3-3.3 mg/kg) and maintained with desflurane. The following variables were studied: heart rate (HR), mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, respiratory rate (RR), arterial oxygen saturation, end-tidal CO2, end-tidal concentration of desflurane (EtDES) required for maintenance of anaesthesia and tidal volume. Arterial blood pH (pHa) and arterial blood gas tensions (PaO2, PaCO2) were measured during anaesthesia. Time to extubation, time to sternal recumbency and time to standing were also recorded. HR and RR decreased significantly during sedation in all protocols. Cardiorespiratory variables during anaesthesia were statistically similar for all protocols. EtDES was significantly different between D1 (8.1%) and D2 (7.5%), and between all doses of medetomidine. Desflurane requirements were similar for D1 and M2, and for D2 and M4 protocols. No statistical differences were observed in recovery times. The combination of dexmedetomidine, propofol and desflurane appears to be effective for induction and maintenance of general anaesthesia in healthy dogs.

Medetomidine and dexmedetomidine: a review of cardiovascular effects and antinociceptive properties in the dog

Alpha(2)-adrenoreceptor agonists (alpha(2)-agonists) are commonly used in small animal anaesthesia for their potent sedative and analgesic properties, although concerns about their cardiovascular effects have prevented their full adoption into veterinary practice. Research into alpha(2) adrenoreceptor agonists and their clinical use is extensive, therefore this review focuses on the use of dexmedetomidine and medetomidine in dogs. Emphasis is given to the cardiovascular effects and antinociceptive action of these agents.

Evaluation of the sedative and cardiorespiratory effects of dexmedetomidine, dexmedetomidine-butorphanol, and dexmedetomidine-ketamine in cats

OBJECTIVE

To determine sedative and cardiorespiratory effects of dexmedetomidine alone and in combination with butorphanol or ketamine in cats.

DESIGN

Randomized crossover study.

ANIMALS

6 healthy adult cats.

PROCEDURES

Cats were given dexmedetomidine alone (10 microg/kg [4.5 mg/lb], IM), a combination of dexmedetomidine (10 microg/kg, IM) and butorphanol (0.2 mg/kg [0.09 mg/lb], IM), or a combination of dexmedetomidine (10 microg/kg, IM) and ketamine (5 mg/kg [2.3 mg/lb], IM). Treatments were administered in random order, with > or = 1 week between treatments. Physiologic variables were assessed before and after drug administration. Time to lateral recumbency, duration of lateral recumbency, time to sternal recumbency, time to recovery from sedation, and subjective evaluation of sedation, muscle relaxation, and auditory response were assessed.

RESULTS

Each treatment resulted in adequate sedation; time to lateral recumbency, duration of lateral recumbency, and time to recovery from sedation were similar among treatments. Time to sternal recumbency was significantly greater after administration of dexmedetomidine-ketamine. Heart rate decreased significantly after each treatment; however, the decrease was more pronounced after administration of dexmedetomidine-butorphanol, compared with that following the other treatments. Systolic and diastolic blood pressure measurements decreased significantly from baseline with all treatments; 50 minutes after drug administration, mean blood pressure differed significantly from baseline only when cats received dexmedetomidine and butorphanol.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that in cats, administration of dexmedetomidine combined with butorphanol or ketamine resulted in more adequate sedation, without clinically important cardiovascular effects, than was achieved with dexmedetomidine alone.

24-hour Holter-monitoring in the perianaesthetic period in dogs premedicated with dexmedetomidine

Baseline and perianaesthetic 24-hour Holter recordings were carried out in six healthy beagles. After dexmedetomidine premedication anaesthesia was induced with propofol and maintained with propofol infusion or isoflurane for one hour. Dexmedetomidine alone was used as control. The recordings were analysed for ventricular premature complexes (VPC), atrioventricular (AV) blocks and mean heart rate/hour (HR). In most recordings, no ventricular arrhythmias were detected, the maximum frequency being two VPCs/24 h. VPCs were not seen during anaesthesia or during the recovery period. The development of second-degree AV-blocks varied from dog to dog. Most of the heart blocks were seen during the premedication period when bradycardia was most prominent. During the subsequent night, HR was similar between treatments and did not differ from that seen on the baseline recordings. In beagles treated with dexmedetomidine alone or combined with propofol or propofol/isoflurane, ventricular arrhythmias were not detected more frequently than those reported in healthy non-anaesthetised dogs.

Minimal alveolar concentration of desflurane in combination with an infusion of medetomidine for the anaesthesia of ponies

The minimum alveolar concentration of desflurane when combined with a continuous infusion of medetomidine at 3.5 microg/kg/hour was measured in seven ponies. Anaesthesia was induced with medetomidine (7 microg/kg intravenously) followed by ketamine (2 mg/kg intravenously) and maintained with desflurane in oxygen. The infusion of medetomidine was started 20 minutes after the induction of anaesthesia. The electrical test stimulus was applied at the coronary band (50 V, 10 ms bursts at 5 Hz for one minute), and heart rates and rhythms, arterial blood pressures, and arterial blood gas tensions were measured at intervals, just before the application of the stimulus. The mean (sd) minimum alveolar concentration of desflurane was 5.3 (1.04) per cent (range 3.2 to 6.4 per cent), 28 per cent less than the previously published value for desflurane alone after the induction of anaesthesia with xylazine and ketamine. The cardiopulmonary parameters remained stable throughout the period of anaesthesia. The mean (sd) time taken by the ponies to stand after the administration of desflurane ceased was 16.5 (6.17) (range 5.8 to 26) minutes, and the quality of recovery was good or excellent. However, one pony died shortly after standing; a postmortem examination revealed that it had chronic left atrial dilatation.

Pros and cons of using alpha-2 agonists in small animal anesthesia practice

The alpha-2 agonists have been used in veterinary practice for over 30 years following the introduction of xylazine (ROMPUN, Bayer Corp., Shawnee Mission, KS) in 1962. The decision to use alpha-2 agonists in anesthesia practice should be based on factors including patient disposition, presenting complaint, type of procedure, and the veterinarian's familiarity with the drug. Controversy surrounds the issue of using anticholinergic agents concurrent with the alpha-2 agonists. Patient selection and procedure type can aid in determining when use of an anticholinergic with the alpha-2 agonist is advantageous. Antagonism of alpha-2 agonists can be readily accomplished. Commonly, alpha-2 agonists are used in combination with other agents to provide neuroleptanalgesia or sedation prior to general anesthesia.

alpha-2 and imidazoline receptor agonists. Their pharmacology and therapeutic role

Clonidine has proved to be a clinically useful adjunct in clinical anaesthetic practice as well as in chronic pain therapy because it has both anaesthetic and analgesic-sparing activity. The more selective alpha-2 adrenoceptor agonists, dexmedetomidine and mivazerol, may also have a role in providing haemodynamic stability in patients who are at risk of peri-operative ischaemia. The side-effects of hypotension and bradycardia have limited the routine use of alpha-2 adrenoceptor agonists. Investigations into the molecular pharmacology of alpha-2 adrenoceptors have elucidated their role in the control of wakefulness, blood pressure and antinociception. We discuss the pharmacology of alpha-2 adrenoceptors and their therapeutic role in this review. The alpha-2 adrenoceptor agonists are agonists at imidazoline receptors which are involved in central blood pressure control. Selective imidazoline agonists are now available for clinical use as antihypertensive agents and their pharmacology is discussed.

Mivazerol, a new alpha 2-adrenergic agonist, blunts cardiovascular effects following surgical stress in pentobarbital-anesthetized rats

BACKGROUND

Mivazerol is a new and selective alpha 2-adrenoceptor agonist, devoid of hypotensive effects, which has been designed to prevent adverse cardiac outcome in perioperative patients with, or at risk coronary artery disease.

METHODS

In the present study, the effects of mivazerol on hemodynamic changes induced by trachea-exposure surgery stress were investigated in pentobarbital-anesthetized rats, and compared to those of dexmedetomidine.

RESULTS

Intravenous infusion of 3 different doses of mivazerol (3.75, 7.5 and 15 micrograms.kg-1.h-1) did not significantly alter BP but caused a dose-related decrease in HR. The maximal decrease in HR was approximately 87 beats/min. Contrary to mivazerol, dexmedetomidine (7.5 micrograms.kg-1.h-1, i.v.) decreased both BP (11 +/- 3.2 mmHg) and HR. The maximum decrease in HR was approximately 104 beats/min. Surgical stress produced a rapid increase in BP (maximal increase of 50 mmHg) and HR (maximal increase of 100 beats/min), which lasted for at least 15 min. Constant infusion of mivazerol, at dose of 15 micrograms.kg-1.h-1, beginning 20 min prior to surgery and lasting for 35 min, significantly inhibited surgical stress-induced increases in BP (P < 0.05) and HR (P < 0.001). Dexmedetomidine, at a dose which produced hypotension and profound bradycardia prior to surgery, did not have any effect on the surgical stress-induced elevation in BP (P > 0.05), but prevented the increase in HR (P < 0.05). Pretreatment with the alpha 2-adrenoceptor antagonist rauwolscine (0.5 mg/kg, i.v.) blocked the bradycardia induced by mivazerol as well as the inhibitory effect of mivazerol on surgical stress-induced elevations in HR and BP.

CONCLUSION

Mivazerol attenuates surgical stress-induced elevations in BP and HR during pentobarbital anesthesia in rats, and these effects are mediated by stimulation of alpha 2-adrenoceptors. Unlike dexmedetomidine, mivazerol does not reduce BP, and is also more potent than dexmedetomidine in blunting surgical stress-induced increases in BP in pentobarbital-anesthetized rats.

The involvement of pertussis toxin-sensitive G proteins in the post receptor mechanism of central I1-imidazoline receptors

1. To elucidate the possible involvement of pertussis toxin (PTX)-sensitive G proteins in the post receptor mechanism of alpha 2-adrenoceptors and imidazoline receptors, we examined the effect of pretreatment of the central nervous system with PTX on the antidysrhythmic effect of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, and rilmenidine, a selective I1-imidazoline receptor agonist on halothane-adrenaline dysrhythmias in rats. 2. Dexmedetomidine (0, 1.0, 2.0, 5.0 micrograms kg-1 min-1.i.v.) and rilmenidine (0, 1.0, 3.0, 10, 20 micrograms kg-1, i.v.) prevented the genesis of halothane-adrenaline dysrhythmias in a dose-dependent fashion. Both idazoxan (10, 20 micrograms kg-1, intracerebroventricularly (i.c.v.)), an alpha 2-adrenoceptor antagonist with high affinity for imidazoline receptors, and rauwolscine, (40 micrograms kg-1, i.c.v.), an alpha 2-adrenoceptor antagonist with low affinity for imidazoline receptors inhibited the action of dexmedetomidine (5.0 micrograms kg-1, min-1, i.v.), but the inhibitory potency of idazoxan was much greater than that of rauwolscine. While the pretreatment with PTX (0.1, 0.5, 1.0 micrograms kg-1, i.c.v.) did not change the dysrhythmogenecity of adrenaline, this treatment completely blocked the antidysrhythmic property of rilmenidine (20 micrograms kg-1, i.v.) as well as dexmedetomidine (5.0 micrograms kg-1 min-1, i.v.). 3. It is suggested that central I1-imidazoline receptors as well as alpha 2-adrenoceptors may be functionally coupled to PTX-sensitive G proteins.

Antiarrhythmic action of rilmenidine on adrenaline-induced arrhythmia via central imidazoline receptors in halothane-anaesthetized dogs

1. To elucidate the role of central imidazoline receptors in the genesis of adrenaline-induced arrhythmias under halothane anaesthesia, we investigated the effects of rilmenidine, a selective agonist at imidazoline receptors, on this type of arrhythmia in dogs. Rilmenidine (1, 3, 10 micrograms kg-1, i.v.) did not affect basal haemodynamic parameters (heart rate and blood pressure), but dose-dependently inhibited adrenaline-induced arrhythmias under halothane anaesthesia. 2. Although, rilmenidine has a weak affinity for alpha(2)-adrenoceptors, pretreatment with idazoxan (10 micrograms kg-1, intracisternally i.c.), an imidazoline receptor antagonist which has also alpha(2)-adrenoceptor blocking potency, blocked the antiarrhythmic effect of rilmenidine (10 micrograms kg-1, i.v.). In contrast, pretreatment with rauwolscine (20 micrograms kg-1, i.c.), a classical alpha(2)-adrenoceptor antagonist with little affinity for imidazoline receptors, did not affect the effect of rilmenidine (10 micrograms kg-1, i.v.). Furthermore, bilateral vagotomy completely blocked the antiarrhythmic action of rilmenidine (10 micrograms kg-1, i.v.). 3. It is suggested that the antiarrhythmic action of rilmenidine is due to the activation of central imidazoline receptors and that vagal tone is critical for this action of rilmenidine.