α2-Adrenoceptor agonists in anaesthesia: a new paradigm

Electrical stimulation of the ventral tegmental area restores consciousness from sevoflurane-, dexmedetomidine-, and fentanyl-induced unconsciousness in rats

BACKGROUND

Dopaminergic neurons in the ventral tegmental area (VTA) are crucially involved in regulating arousal, making them a potential target for reversing general anesthesia. Electrical deep brain stimulation (DBS) of the VTA restores consciousness in animals anesthetized with drugs that primarily enhance GABAA receptors. However, it is unknown if VTA DBS restores consciousness in animals anesthetized with drugs that target other receptors.

OBJECTIVE

To evaluate the efficacy of VTA DBS in restoring consciousness after exposure to four anesthetics with distinct receptor targets.

METHODS

Sixteen adult Sprague-Dawley rats (8 female, 8 male) with bipolar electrodes implanted in the VTA were exposed to dexmedetomidine, fentanyl, ketamine, or sevoflurane to produce loss of righting, a proxy for unconsciousness. After receiving the dopamine D1 receptor antagonist, SCH-23390, or saline (vehicle), DBS was initiated at 30 μA and increased by 10 μA until reaching a maximum of 100 μA. The current that evoked behavioral arousal and restored righting was recorded for each anesthetic and compared across drug (saline/SCH-23390) condition. Electroencephalogram, heart rate and pulse oximetry were recorded continuously.

RESULTS

VTA DBS restored righting after sevoflurane, dexmedetomidine, and fentanyl-induced unconsciousness, but not ketamine-induced unconsciousness. D1 receptor antagonism diminished the efficacy of VTA stimulation following sevoflurane and fentanyl, but not dexmedetomidine.

CONCLUSIONS

Electrical DBS of the VTA restores consciousness in animals anesthetized with mechanistically distinct drugs, excluding ketamine. The involvement of the D1 receptor in mediating this effect is anesthetic-specific.

Postoperative Delirium after Dexmedetomidine versus Propofol Sedation in Healthy Older Adults Undergoing Orthopedic Lower Limb Surgery with Spinal Anesthesia: A Randomized Controlled Trial

BACKGROUND

Delirium is a critical postoperative complication in older patients. Based on the hypothesis that intraoperative dexmedetomidine sedation would lower postoperative delirium than propofol sedation would, the authors compared the incidence of postoperative delirium in older adults, using the mentioned sedatives.

METHODS

This double-blinded, randomized controlled study included 748 patients, aged 65 yr or older, who were scheduled for elective lower extremity orthopedic surgery, between June 2017 and October 2021. Patients were randomized equally into two groups in a 1:1 ratio according to the intraoperative sedative used (dexmedetomidine vs. propofol). The postoperative delirium incidence was considered the primary outcome measure; it was determined using the confusion assessment method, on the first three postoperative days. The mean arterial pressure and heart rate were evaluated as secondary outcomes.

RESULTS

The authors enrolled 732 patients in the intention-to-treat analyses. The delirium incidence was lower in the dexmedetomidine group than in the propofol group (11 [3.0%] vs. 24 [6.6%]; odds ratio, 0.42; 95% CI, 0.201 to 0.86; P = 0.036). During sedation, the mean arterial pressure (median [interquartile range] mmHg) was higher in the dexmedetomidine group (77 [71 to 84]) than in the propofol group (74 [69 to 79]; P < 0.001); however, it significantly fell lower (74 [68 to 80]) than that of the propofol group (80 [74 to 87]) in the postanesthesia care unit (P < 0.001). Lower heart rates (beats/min) were recorded with the use of dexmedetomidine than with propofol, both during sedation (60 [55 to 66] vs. 63 [58 to 70]) and in the postanesthesia care unit (64 [58 to 72] vs. 68 [62-77]; P < 0.001).

CONCLUSIONS

Dexmedetomidine showed a lower incidence of postoperative delirium than propofol in healthy older adults undergoing lower extremity orthopedic surgery.

EDITOR’S PERSPECTIVE

Tasipimidine-the pharmacological profile of a novel orally active selective α2A-adrenoceptor agonist

The pharmacological profile of tasipimidine, a novel orally active α₂-adrenoceptor agonist developed for situational anxiety and fear in dogs, was studied in various in vitro and in vivo models. In the cell assays, tasipimidine demonstrated binding affinity and full agonism on the human α_2A-adrenoceptors with a pEC50 of 7.57, while agonism on the α_2B-and α_2C-adrenoceptors and the rodent α_2D-adrenoceptor was weaker, resulting in pEC50 values of 6.00, 6.29 and 6.56, respectively. Tasipimidine had a low binding affinity on the human α₁-adrenoceptors. It had no functional effects in the LNCaP cells expressing endogenously the human α_1A-adrenoceptors but was a weak agonist in the Chem-1 cells coexpressing Gα15 protein and α_1A-adrenoceptors. In the recombinant CHO cells, although tasipimidine was a weak partial agonist in the inositol monophosphate accumulation assay, it was a full agonist in the intracellular [Ca²⁺] assay. No functional effects were observed on the human α_1B-adrenoceptor, whereas in the rat α_1A and α_1B-adrenoceptors, tasipimidine was a weak partial agonist. In the rat vas deferens preparations, tasipimidine was a full agonist on the α_2D-adrenoceptor but weak partial agonist on the α₁-adrenoceptor. The receptor profile of tasipimidine indicated few secondary targets, and no functional effects were observed. Sedative effects of tasipimidine were demonstrated in vivo by the reduced acoustic startle reflex in rats with subcutaneous doses and decreased spontaneous locomotor activity in mice with subcutaneous and higher oral doses. It may be concluded that tasipimidine is an orally active and selective α_2A-adrenoceptor agonist.

Return of the Righting Reflex Does Not Portend Recovery of Cognitive Function in Anesthetized Rats

As the number of individuals undergoing general anesthesia rises globally, it becomes increasingly important to understand how consciousness and cognition are restored after anesthesia. In rodents, levels of consciousness are traditionally captured by physiological responses such as the return of righting reflex (RORR). However, tracking the recovery of cognitive function is comparatively difficult. Here we use an operant conditioning task, the 5-choice serial reaction time task (5-CSRTT), to measure sustained attention, working memory, and inhibitory control in male and female rats as they recover from the effects of several different clinical anesthetics. In the 5-CSRTT, rats learn to attend to a five-windowed touchscreen for the presentation of a stimulus. Rats are rewarded with food pellets for selecting the correct window within the time limit. During each session we tracked both the proportion of correct (accuracy) and missed (omissions) responses over time. Cognitive recovery trajectories were assessed after isoflurane (2% for 1 h), sevoflurane (3% for 20 min), propofol (10 mg/kg I.V. bolus), ketamine (50 mg/kg I.V. infusion over 10 min), and dexmedetomidine (20 and 35 μg/kg I.V. infusions over 10 min) for up to 3 h following RORR. Rats were classified as having recovered accuracy performance when four of their last five responses were correct, and as having recovered low omission performance when they missed one or fewer of their last five trials. Following isoflurane, sevoflurane, and propofol anesthesia, the majority (63-88%) of rats recovered both accuracy and low omission performance within an hour of RORR. Following ketamine, accuracy performance recovers within 2 h in most (63%) rats, but low omission performance recovers in only a minority (32%) of rats within 3 h. Finally, following either high or low doses of dexmedetomidine, few rats (25-32%) recover accuracy performance, and even fewer (0-13%) recover low omission performance within 3 h. Regardless of the anesthetic, RORR latency is not correlated with 5-CSRTT performance, which suggests that recovery of neurocognitive function cannot be inferred from changes in levels of consciousness. These results demonstrate how operant conditioning tasks can be used to assess real-time recovery of neurocognitive function following different anesthetic regimens.

Comparison of Intra and Post-operative Sedation efficacy of Dexmedetomidine-Midazolam and Dexmedetomidine-Propofol for Major Abdominal Surgery

BACKGROUND

The effectiveness and side effects of dexmedetomidine (DEX) in combination with midazolam and propofol have not been comparatively studied in a single clinical trial as sedative agents to general anesthesia before.

OBJECTIVE

The objective of this study is to compare intra and post-operative sedation between DEX-Midazolam and DEX-Propofol in patients who underwent major abdominal surgery on the duration of general anesthesia, hemodynamic and sedation effect.

METHOD

This prospective, randomized, double-blinded clinical trial included 50 patients who were 20 to 60 years of age and admitted for major abdominal surgery. The patients were randomly assigned by a computer-generated random numbers table to sedation with DEX plus midazolam (DM group) (n=25) or DEX plus propofol (DP group) (n=25). In the DM group, patients received a bolus dose of 0.1 mg/kg of midazolam and immediately initiated the intravenous (i.v.) infusion of DEX 1 µg/kg over a 10 min and 0.5 µg/kg/hr by continuous i.v. infusion within operation period. In the DP group, patients received pre-anesthetic i.v. DEX 1 µg/kg over 15 min before anesthesia induction and 0.2-1 µg/kg/hr by continuous i.v. infusion during the operative period. After preoxygenation for at least 2 min, during the surgery, patients received propofol infusion dose of 250 μg/kg/min for 15 min then a basal infusion dose of 50 μg/kg/min. The bispectral index (BIS) value, as well as mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), oxygen saturation (SaO2), percutaneous arterial oxygen saturation (SpO2) and end-tidal carbon dioxide tension (ETCO2) were recorded before anesthesia (T0), during anesthesia (at 15-min intervals throughout the surgical procedure), by a blinded observer. Evidence of apnea, hypotension, hypertension and hypoxemia were recorded during surgery.

RESULTS

The hemodynamic changes, including HR, MAP, BIS, VT, SaO2, and RR had a downward tendency with time, but no significant difference was observed between the groups (P>0.05). However, the two groups showed no significant differences in ETCO2 and SPO2 values in any of the assessed interval (P>0.05). In this study, the two groups showed no significant differences in the incidence of nausea, vomiting, coughing, apnea, hypotension, hypertension, bradycardia and hypoxemia (P>0.05). Respiratory depression and serious adverse events were not reported in either group. Extubation time after surgery was respectively 6.3 ± 1.7 and 5.8 ± 1.4 hr. in the DM and DP groups and the difference was not statistically significant (P= 0.46).

CONCLUSION

Our study showed no significant differences between the groups in hemodynamic and respiratory changes in each of the time intervals. There were also no significant differences between the two groups in the incidence of complication intra and post-operative. Further investigations are required to specify the optimum doses of using drugs which provide safety in cardiovascular and respiratory system without adverse disturbance during surgery.

Toxin-Induced Coma and Central Nervous System Depression

Many medications and toxins may induce central nervous system (CNS) depression. Even when the intention is to induce CNS depression, other nervous system adverse effects may occur, such as with anesthetics. Pain medications produce characteristic CNS toxicities. Sedative hypnotics may induce altered mentation among systemic toxicities. Stimulants may mimic coma when discontinued abruptly. Acute and chronic carbon monoxide poisoning can lead to altered mental status and prolonged cognitive difficulties. Some medications and environmental toxins can mimic brain death. High clinical suspicion and early recognition of these effects is vital to treatment, most of which is supportive.

Intranasal dexmedetomidine combined with local anesthesia for conscious sedation during breast lumpectomy: A prospective randomized trial

Breast lumpectomy is usually performed under general or local anesthesia. To the best of our knowledge, whether conscious sedation with intranasal dexmedetomidine and local anesthesia is an effective anesthetic technique has not been studied. Thus, the present study aimed to investigate the effectiveness of conscious sedation with intranasal dexmedetomidine combined with local anesthesia in breast lumpectomy, and to identify its optimal dose. A prospective randomized, double-blinded, placebo-controlled, single-center study was designed, and patients undergoing breast lumpectomies were recruited based on the inclusion and exclusion criteria. All patients were randomly allocated to four groups: i) Local anesthesia with 0.9% intranasal saline (placebo); local anesthesia with ii) 1 µg.kg⁻¹; iii) 1.5 µg.kg⁻¹; or iv) 2 µg.kg⁻¹ intranasal dexmedetomidine. The sedation status, pain relief, vital signs, adverse events, and satisfaction of patient and surgeon were recorded. Patients in the three dexmedetomidine groups were significantly more sedated and experienced less pain compared with the placebo group 45 min after intranasal dexmedetomidine administration and during 30 min in the post-anesthesia care unit. Patients in the 1.5 µg.kg⁻¹ group were more sedated compared with the 1 µg.kg⁻¹ group (without reaching statistical significance), whereas the 1.5 µg.kg⁻¹ group exhibited a similar level of sedation 45 min after intranasal dexmedetomidine administration compared with the 2 µg.kg⁻¹ group. In addition, patients in the 1 and 1.5 µg.kg⁻¹ group experienced no adverse hemodynamic effects. Patient and surgeon satisfaction were greater in the 1.5 µg.kg⁻¹ group compared with the 1 and 2 µg.kg⁻¹ groups. Taken together, the results of the present study suggested that conscious sedation with intranasal dexmedetomidine and local anesthesia may be an effective anesthetic for breast lumpectomy surgery, and that the optimal dose for intranasal dexmedetomidine administration may be 1.5 µg.kg⁻¹, as it resulted in good sedation and patient satisfaction without adverse effects.

Opioid-free anesthesia within an enhanced recovery after surgery pathway for minimally invasive lumbar spine surgery: a retrospective matched cohort study

OBJECTIVE

Enhanced recovery after surgery (ERAS) and multimodal analgesia are established care models that minimize perioperative opioid consumption and promote positive outcomes after spine surgery. Opioid-free anesthesia (OFA) is an emerging technique that may achieve similar goals. The purpose of this study was to evaluate an OFA regimen within an ERAS pathway for lumbar decompressive surgery and to compare perioperative opioid requirements in a matched cohort of patients managed with traditional opioid-containing anesthesia (OCA).

METHODS

The authors performed a retrospective analysis of prospectively collected data. They included 36 patients who underwent lumbar decompression under their ERAS pathway for spinal decompression between February and August 2018. Eighteen patients who received OFA were matched in a 1:1 ratio to a cohort managed with a traditional OCA regimen. The primary outcome was total perioperative opioid consumption. Postoperative pain scores (measured using the numerical rating scale [NRS]), opioid consumption (total morphine equivalents), and length of stay (time to readiness for discharge) were compared in the postanesthesia care unit (PACU). The authors also assessed compliance with ERAS process measures and compared compliance during 3 phases of care: pre-, intra-, and postoperative.

RESULTS

There was a significant reduction in total perioperative opioid consumption in patients who received OFA (2.43 ± 0.86 oral morphine equivalents [OMEs]; mean ± SEM), compared to patients who received OCA (38.125 ± 6.11 OMEs). There were no significant differences in worst postoperative pain scores (NRS scores 2.55 ± 0.70 vs 2.58 ± 0.73) or opioid consumption (5.28 ± 1.7 vs 4.86 ± 1.5 OMEs) in the PACU between OFA and OCA groups, respectively. There was a clinically significant decrease in time to readiness for discharge from the PACU associated with OFA (37 minutes), although this was not statistically significantly different. The authors found high overall compliance with ERAS process measures (91.4%) but variation in compliance according to phase of care. The highest compliance occurred during the preoperative phase (94.71% ± 2.88%), and the lowest compliance occurred during the postoperative phase of care (85.4% ± 5.7%).

CONCLUSIONS

OFA within an ERAS pathway for lumbar spinal decompression represents an opportunity to minimize perioperative opioid exposure without adversely affecting pain control or recovery. This study reveals opportunities for patient and provider education to reinforce ERAS and highlights the postoperative phase of care as a time when resources should be focused to increase ERAS adherence.

Dexmedetomidine versus propofol at different sedation depths during drug-induced sleep endoscopy: A randomized trial

OBJECTIVES/HYPOTHESIS

The aim of this study was to compare the effect of dexmedetomidine and propofol on airway dynamics, cardiorespiratory system, and emergence following drug-induced sleep endoscopy (DISE).

STUDY DESIGN

Prospective, randomized, single-blinded study.

METHODS

Sixty patients age 18 to 65 years in American Society of Anesthesiologists physical status groups 1 and 2 scheduled to undergo DISE were randomly allocated to either Group P (N = 30; receiving propofol infusion at 50-150 μg/kg/min) or Group D (N = 30; receiving dexmedetomidine bolus of 1 μg/kg followed by infusion at 0.5-1.0 μg/kg/hr). DISE was done at light sleep and deep sleep. Airway obstruction at tongue base was recorded as primary outcome. Airway obstruction at velum, oropharyngeal lateral wall, and epiglottis level during light and deep sedation, hemodynamic and respiratory parameters, time to attain sufficient sedation, time for emergence from sedation, and any adverse events during DISE with the two study drugs were recorded as secondary outcomes.

RESULTS

There was a greater degree of obstruction at the tongue base level (P = 0.001) and Oropharynx level (P = 0.017) in Group P compared with Group D during deep sedation. Increase in airway obstruction from light to deep sleep was seen with propofol at the oropharynx (P = 0.0185) and tongue base (P = 0.0108) levels. Two patients (6.6%) in Group D and 10 patients (33.3%) in Group P showed oxygen saturation below the minimum oxygen saturation recorded during polysomnography. Time to open eyes to call after stopping sedation was significantly less in Group P (P = 0.005).

CONCLUSIONS

Dexmedetomidine shows a lesser degree of airway collapse and higher oxygen saturation levels at greater sedation depth during DISE. Propofol has a faster onset and emergence from sedation.

LEVEL OF EVIDENCE

1b Laryngoscope, 130:257-262, 2020.

Identifying binding modes of two synthetic derivatives of adrenalin to the α2C-adrenoceptor by using molecular modeling; insights into the α2C-adrenoceptor activation

Although, α2C adrenergic receptor (AR) mediates a number of physiological functions in vivo and has great therapeutic potential, the absence of its crystal structure is a major difficulty in the activation mechanism studies and drug design endeavors. Here, a homology model of α2C AR has been presented by means of multiple sequence alignment. The used templates were the latest crystal structures of the other ARs (Protein Data Bank IDs: 2R4R, 2RH1, 4GPO, 3P0G, 4BVN and 4LDO) that have 38.4% identity with the query. We then conducted docking simulations to understand and analyze the binding of noradrenaline (NOR), and its derivatives, namely arachidonoyl adrenalin (AA-AD) and arachidonoyl noradrenalin (AA-NOR) to the receptor. The existence of H-bonds between the ligands and SER218 residue implies the same binding site of derivatives with respect to the NOR. AA-AD and AA-NOR bind to the receptor with the larger binding affinities. The presence of salt bridge between ARG149 and GLU377 in the free receptor, obtained from molecular dynamics studies proved that the receptor still is in its basal state before binding process take places. The activation process is characterized by increasing in the RMSD values of the backbone receptor in the bound state, increasing the RMSF of the transmembrane involved in the activation process and the disappearance of the ARG149-GLU377 salt bridge.

The Effect of Dexmedetomidine on Middle Ear Pressure

OBJECTIVE: Dexmedetomidine is a preferred anesthetic agent in otological surgery because it provides controlled hypotension and good surgical field visibility. The aim of this study was to evaluate the influence of this novel agent on middle ear pressure.

STUDY DESIGN AND SETTING: This prospective clinical trial was performed in 60 patients who were scheduled for elective surgery. They received dexmedetomidine or saline infusion for 20 minutes before induction of anesthesia. Tympanometric measurements were recorded for both ears at preoperative, intraoperative, and postoperative states.

RESULTS: Mean difference of tympanometric peak pressure from baseline was statistically significant between dexmedetomidine and control group at the 30th minute of operation (24.8 daPa, P = 0.003 for right ear; 20.5 daPa, P = 0.02 for left ear) and at the end of the operation (25.8 daPa, P = 0.01 for right ear; 28.1 daPa, P = 0.004 for left ear).

CONCLUSIONS: Dexmedetomidine anesthesia raises the tympanometric parameters, but they never exceed the limits of normal.

α2-Adrenergic Receptor and Isoflurane Modulation of Presynaptic Ca2+ Influx and Exocytosis in Hippocampal Neurons

BACKGROUND

Evidence indicates that the anesthetic-sparing effects of α2-adrenergic receptor (AR) agonists involve α2A-AR heteroreceptors on nonadrenergic neurons. Since volatile anesthetics inhibit neurotransmitter release by reducing synaptic vesicle (SV) exocytosis, the authors hypothesized that α2-AR agonists inhibit nonadrenergic SV exocytosis and thereby potentiate presynaptic inhibition of exocytosis by isoflurane.

METHODS

Quantitative imaging of fluorescent biosensors of action potential-evoked SV exocytosis (synaptophysin-pHluorin) and Ca influx (GCaMP6) were used to characterize presynaptic actions of the clinically used α2-AR agonists dexmedetomidine and clonidine, and their interaction with isoflurane, in cultured rat hippocampal neurons.

RESULTS

Dexmedetomidine (0.1 μM, n = 10) or clonidine (0.5 μM, n = 8) inhibited action potential-evoked exocytosis (54 ± 5% and 59 ± 8% of control, respectively; P < 0.001). Effects on exocytosis were blocked by the subtype-nonselective α2-AR antagonist atipamezole or the α2A-AR-selective antagonist BRL 44408 but not by the α2C-AR-selective antagonist JP 1302. Dexmedetomidine inhibited exocytosis and presynaptic Ca influx without affecting Ca coupling to exocytosis, consistent with an effect upstream of Ca-exocytosis coupling. Exocytosis coupled to both N-type and P/Q-type Ca channels was inhibited by dexmedetomidine or clonidine. Dexmedetomidine potentiated inhibition of exocytosis by 0.7 mM isoflurane (to 42 ± 5%, compared to 63 ± 8% for isoflurane alone; P < 0.05).

CONCLUSIONS

Hippocampal SV exocytosis is inhibited by α2A-AR activation in proportion to reduced Ca entry. These effects are additive with those of isoflurane, consistent with a role for α2A-AR presynaptic heteroreceptor inhibition of nonadrenergic synaptic transmission in the anesthetic-sparing effects of α2A-AR agonists.

Emergency Corrective Surgery of Congenital Diaphragmatic Hernia With Pulmonary Hypertension: Prolonged Use of Dexmedetomidine as a Pharmacologic Adjunct

INTRODUCTION

Underdevelopment of the lung parenchyma associated with abnormal growth of pulmonary vasculature in neonates with congenital diaphragmatic hernia results in pulmonary hypertension which mandates smooth elective mechanical ventilation in postoperative period, for proper alveolar recruitment and oxygenation, allowing lungs to mature enough for its functional anatomy and physiology. Dexmedetomidine is sympatholytic, reduces pulmonary vascular resistance and exerts sedative and analgesic property to achieve stable hemodynamics during elective ventilation. Neonatal experience with dexmedetomidine has been predominately in the form of short term or procedural use as a sedative.

CASE PRESENTATION

The preliminary clinical experience with pre-induction to 48 hours postoperative use of dexmedetomidine infusion as a pharmacologic adjunct in the emergency corrective surgery of three such neonates are presented.

CONCLUSIONS

Hemodynamics remained virtually stable during the whole procedure and post-operative pain relief and recovery profile were satisfactory. The prolonged infusion was well tolerated with a gradual trend towards improved oxygen saturation. Careful planning of the anesthetic management and the ability to titrate the adjunct utilized for smooth postoperative ventilation are the keys to ameliorate the complications encountered and favorable outcomes achieved in such patients.

Variable Findings for Drug-Induced Sleep Endoscopy in Obstructive Sleep Apnea with Propofol versus Dexmedetomidine

OBJECTIVE

To compare VOTE classification findings (velum, oropharyngeal-lateral walls, tongue base, and epiglottis) for drug-induced sleep endoscopy (DISE) among patients with obstructive sleep apnea (OSA) using 2 sedation protocols.

STUDY DESIGN

Case series with chart review.

SETTING

Single tertiary institution.

SUBJECTS

Patients with OSA who underwent DISE.

METHODS

A total of 216 patients underwent DISE between November 23, 2011, and May 1, 2015. DISE findings based on VOTE classification were compared between patients receiving the propofol- and dexmedetomidine-based sedation protocols.

RESULTS

Patients with OSA (N = 216; age, 44.3 ± 11.7 years; body mass index, 27.9 ± 4.8 kg/m(2)) underwent DISE with intravenous administration of propofol (n = 52) or dexmedetomidine (n = 164). There were no statistically significant differences between the 2 groups in baseline apnea-hypopnea index, oxygen desaturation index, Mallampati score, tonsil size, Epworth Sleepiness Scale score, peripheral oxygen saturation nadir, age, sex, or body mass index. Patients in the propofol group had a significantly increased likelihood of demonstrating complete tongue base obstruction (75%, 39 of 52) versus partial or no obstruction (25%, 13 of 52) in the anterior-posterior dimension, as compared with the dexmedetomidine group (complete obstruction: 42.7%, 70 of 164; partial or no obstruction: 57.3%, 94 of 164; odds ratio: 4.0; 95% confidence interval: 2.0-8.1; P = .0001). Obstruction of other airway subsites was not significantly different.

CONCLUSION

Use of propofol versus dexmedetomidine to induce sedation may have a significant effect on the pattern of upper airway obstruction observed during DISE. Randomized prospective studies are indicated to confirm these initial findings.

Safety and analgesic efficacy of intravenous dexmedetomidine in arthroscopic knee surgery

Context:

Dexmedetomidine, a highly selective alpha-2 agonist has been used as an adjuvant analgesic in vascular, bariatric, and thoracic surgery. We assessed the efficacy of intravenous dexmedetomidine as an analgesic adjunct to local anesthetic infiltration for control of postoperative pain in arthroscopic knee surgery.

Settings and Design:

This was a randomized control study performed in a Tertiary Care Hospital.

Materials and Methods:

Forty-five adult patients scheduled for anterior/posterior cruciate ligament reconstruction were randomized into three groups. Group B (bupivacaine group) received bupivacaine intraarticularly and normal saline by the intravenous route. Group D (dexmedetomidine group) received Intravenous dexmedetomidine and normal saline intraarticularly. Group BD (bupivacaine + dexmedetomidine group) received a combination of intravenous dexmedetomidine and intraarticular bupivacaine. Patient's cardiorespiratory parameters, time to first rescue, total rescue analgesic consumption in first 24 h, visual analog scale for pain were assessed.

Statistical Analysis:

The data were analyzed using analysis of variance and Chi-square test.

Results:

The time to first request for rescue analgesia was significantly prolonged in Group D and Group BD patients (P < 0.05) compared to Group B. Total rescue analgesic consumption was least in Group BD. Group D and Group BD patients had lower heart rate and systolic and diastolic blood pressure values.

Conclusion:

Intravenous dexmedetomidine in combination with intraarticular bupivacaine decreased perioperative analgesic requirement in patients undergoing arthroscopic knee surgery. However, monitoring and vigilance are essential if dexmedetomidine is used as part of a multimodal analgesic regimen in view of its hemodynamic side effects.

A comparison of propofol vs. dexmedetomidine for sedation, haemodynamic control and satisfaction, during esophagogastroduodenoscopy under conscious sedation

WHAT IS KNOWN AND OBJECTIVE

Esophagogastroduodenoscopy (EGD) is a common diagnostic procedure which requires sedation for most patients. We undertook a prospective, randomized, double-blinded study to compare the effect of propofol vs. dexmedetomidine on the sedation of outpatients during EGD.

METHODS

Prior to the procedure, outpatients received either propofol at 0·6 mg/kg, with additional doses of 10-20 mg until the Observer's Assessment of Alertness/Sedation Scale (OAA/S) score reached 2-4, or dexmedetomidine at a loading dose of 1 μg/kg over a 10-min period followed by a 0·5 μg/kg/h infusion until the OAA/S score reached 2-4. Vital signs, sedation level, adverse events, patients' and endoscopist's satisfaction score, and an evaluation of the recovery time were assessed.

RESULTS AND DISCUSSION

Negligible haemoglobin oxygen saturation (SpO2 ) and respiratory rate variations were observed in both groups, although respiratory depression occurred in two cases (5·9%) in the propofol group. Mean arterial pressure (MAP) in the propofol group decreased during the procedure compared with baseline (P < 0·05) and was also lower in comparison with the dexmedetomidine group (P < 0·05). Heart rate (HR) decreased after the loading dose in the dexmedetomidine group (P < 0·05). More patients in the propofol group underwent deeper sedation at the beginning of the procedure (P < 0·05), although the recovery time was comparable between the two groups (P > 0·05). Three cases (9·1%) in the dexmedetomidine group were delayed because of dizziness, bradycardia and nausea. There was a higher satisfaction score among patients in the propofol group (P < 0·05), although the endoscopist's satisfaction score was comparable between the two groups (P > 0·05).

WHAT IS NEW AND CONCLUSION

Propofol and dexmedetomidine provide a relatively satisfactory level of sedation without clinically notable adverse effects during EGD. In addition, patients preferred propofol administration for the deeper sedation and rapid recovery, and dexmedetomidine exhibited minimal adverse effects on respiratory function.

Analysis of functional selectivity through G protein-dependent and -independent signaling pathways at the adrenergic α(2C) receptor

Although G protein-coupled receptors (GPCRs) are traditionally categorized as Gs-, Gq-, or Gi/o-coupled, their signaling is regulated by multiple mechanisms. GPCRs can couple to several effector pathways, having the capacity to interact not only with more than one G protein subtype but also with alternative signaling or effector proteins such as arrestins. Moreover, GPCR ligands can have different efficacies for activating these signaling pathways, a characteristic referred to as biased agonism or functional selectivity. In this work our aim was to detect differences in the ability of various agonists acting at the α2C type of adrenergic receptors (α2C-ARs) to modulate cAMP accumulation, cytoplasmic Ca(2+) release, β-arrestin recruitment and receptor internalization. A detailed comparative pharmacological characterization of G protein-dependent and -independent signaling pathways was carried out using adrenergic agonists (norepinephrine, phenylephrine, brimonidine, BHT-920, oxymetazoline, clonidine, moxonidine, guanabenz) and antagonists (MK912, yohimbine). As initial analysis of agonist Emax and EC50 values suggested possible functional selectivity, ligand bias was quantified by applying the relative activity scale and was compared to that of the endogenous agonist norepinephrine. Values significantly different from 0 between pathways indicated an agonist that promoted different level of activation of diverse effector pathways most likely due to the stabilization of a subtly different receptor conformation from that induced by norepinephrine. Our results showed that a series of agonists acting at the α2C-AR displayed different degree of functional selectivity (bias factors ranging from 1.6 to 36.7) through four signaling pathways. As signaling via these pathways seems to have distinct functional and physiological outcomes, studying all these stages of receptor activation could have further implications for the development of more selective therapeutics with improved efficacy and/or fewer side effects.

Dexmedetomidine ameliorates monitored anaesthesia care

Background and Aims:

Monitored anaesthesia care (MAC) is meant for procedures under local anaesthesia. Various drugs have been used for this purpose. The recently introduced alpha2 agonist, dexmedetomidine provides “conscious sedation” with adequate analgesia and minimal respiratory depression. Hence, the safety and efficacy of two doses of dexmedetomidine for sedation and analgesia were evaluated.

Methods:

A total of 90 patients were distributed in three groups of 30 each: Dexmedetomidine 0.5 μg/kg (DL), dexmedetomidine 1.0 μg/kg (DH) and normal saline (C). The initial loading dose was followed by maintenance infusion of 0.2-0.7 μg/kg/h of dexmedetomidine or equivalent volume of saline. Study drug was started at least 15 min before placement of local anaesthesia. Drugs were titrated to a target level of sedation (=3 on Ramsay sedation scale [RSS]). Midazolam 0.02 mg/kg for RSS < 3 and fentanyl 0.5 μg/kg were supplemented as required. The statistical analysis was performed using Chi-square test and mean and anova analysis.

Results:

In groups DL and DH fewer patients required supplemental midazolam, 56.7% (17/30) and 40% (12/30), compared with control, where 86.7% (26/30)needed midazolam supplements. P = 0.000. Both groups DL and DH required significantly less fentanyl (84.8 and 83.9 μg) versus control (144.2 μg). There was significantly increased ease of achieving and maintaining targeted sedation and analgesia in both dexmedetomidine groups when compared with placebo (P = 0.001). Adverse events observed with dexmedetomidine were bradycardia and hypotension.

Conclusions:

Dexmedetomidine in the doses studied was considered safe and effective sedative and analgesic for patients undergoing procedures under MAC.

Dexmedetomidine decreases requirement of thiopentone sodium and pentazocine followed with improved recovery in patients undergoing laparoscopic cholecystectomy

Background:

Pain relief remains the most fundamental and consequential aspect of surgery for patients throughout perioperative period. Dexmedetomidine has created an interest in α2-adrenoceptor agonists in the management of pain and hence the aim of this study was to evaluate the effectiveness of the drug in hilly population of North India.

Materials and Methods:

Patients, irrespective of gender, were randomly allocated to two groups, control and test, each having 30 patients. Test group received an infusion of dexmedetomidine at a rate of 0.5 μg/kg/h 30 min before induction and 0.6 μg/kg/h after inducing anesthesia. Control patients received a volume-matched infusion of normal saline as placebo. Approximately 2 min before induction, analgesia was provided in the form of pentazocine, 0.5 mg/kg in control and 0.3 mg/kg in the test group. Induction was performed by 2 mg/kg thiopentone sodium supplemented with intravenous boluses of 25 mg thiopentone sodium every 15 s until loss of eyelid reflex (determined every 15 s). Induction dose of thiopentone sodium and total pentazocine dose were recorded. Recovery was assessed on the clinical recovery score (CRS) scale.

Results:

Infusion of dexmedetomidine decreased the induction dose of thiopentone approximately by 33% and of pentazocine dose by approximately 39% in patients undergoing laparoscopic cholecystectomy. Moreover, incidence of pain was also decreased significantly. Improved CRS from 4.33 to 6.87 was noticed immediately post-operatively in dexmedetomidine group of patients.

Conclusion:

Infusion of dexmedetomidine during the laparoscopic cholecystectomy decreases the requirement of thiopentone sodium and pentazocine and leads to early recovery of patients.

Improved quality of surgical field during endoscopic sinus surgery after clonidine premedication--a pilot study

BACKGROUND

Inadequate surgical field visualization due to intraoperative bleeding during endoscopic sinus surgery (ESS) can cause major complications. The aim of this prospective study was to compare the effect of preoperative administration of clonidine and melatonin on the quality of the surgical field visualization and selected aspects of presurgical premedication.

METHODS

Twenty-six patients undergoing ESS for chronic sinusitis and polyp removal were enrolled and randomly assigned to receive either oral clonidine or melatonin as preoperative premedication. During the operation, the quality of the surgical field was assessed and graded using the scale proposed by Boezaart. The evaluations were done at 15, 30, and 60 minutes after incision. The effect of this premedication choice on the intraoperative and postoperative hemodynamic profile was examined in each group. Anxiolytic effects of both premedication agents were assessed using the visual analogue scale for anxiety (VAS-A). Propofol dose and induction time (the time for bispectral index [BIS] to reach 45), anesthesia and surgical procedures time, and recovery time (the time for BIS to reach 90) were assessed in both groups as well.

RESULTS

The quality of the surgical field was consistently better in 2 of 3 time points in the clonidine group. Perioperative mean arterial pressure and intraoperative heart rate had a more favorable profile in patients premedicated with clonidine. There were no differences in other measured parameters between groups.

CONCLUSION

Premedication with clonidine before ESS provides better quality of surgical field and more favorable hemodynamic profile as compared to melatonin.

The effect of dexmedetomidine continuous infusion as an adjuvant to general anesthesia on sevoflurane requirements: A study based on entropy analysis

Background:

Dexmedetomidine, a α2 agonist as an adjuvant in general anesthesia, has anesthetic and analgesic-sparing property.

Aims:

To evaluate the effect of continuous infusion of dexmedetomidine alone, without use of opioids, on requirement of sevoflurane during general anesthesia with continuous monitoring of depth of anesthesia by entropy analysis.

Materials and Methods:

Sixty patients were randomly divided into 2 groups of 30 each. In group A, fentanyl 2 mcg/kg was given while in group B, dexmedetomidine was given intravenously as loading dose of 1 mcg/kg over 10 min prior to induction. After induction with thiopentone in group B, dexmedetomidine was given as infusion at a dose of 0.2-0.8 mcg/kg. Sevoflurane was used as inhalation agent in both groups. Hemodynamic variables, sevoflurane inspired fraction (FI_sevo), sevoflurane expired fraction (ET_sevo), and entropy (Response entropy and state entropy) were continuously recorded. Statistical analysis was done by unpaired student's t-test and Chi-square test for continuous and categorical variables, respectively. A P-value < 0.05 was considered significant.

Results:

The use of dexmedetomidine with sevoflurane was associated with a statistical significant decrease in ET_sevo at 5 minutes post-intubation (1.49 ± 0.11) and 60 minutes post-intubation (1.11 ±0.28) as compared to the group A [1.73 ±0.30 (5 minutes); 1.68 ±0.50 (60 minutes)]. There was an average 21.5% decrease in ET_sevo in group B as compared to group A.

Conclusions:

Dexmedetomidine, as an adjuvant in general anesthesia, decreases requirement of sevoflurane for maintaining adequate depth of anesthesia.

A Comparison of the Effects of Esmolol and Dexmedetomidine on the Clinical Course and Cost for Controlled Hypotensive Anaesthesia

OBJECTIVE

To compare the effects of esmolol (β-blocker) and dexmedetomidine (α-2-agonist) on patients' clinical course and cost of application of controlled hypotension during middle-ear surgery.

METHODS

Fifty ASA I-II patients scheduled for tympanomastoidectomy were enrolled in the study and were randomized into two groups. Bispectral Index (BIS) and neuromuscular monitoring (TOF GUARD-SX) were applied to all patients. In group E (n=25), 0.5 mg kg(-1) min(-1) esmolol was infused over 1 min before induction and titrated over a range of 10-200 μg kg(-1) min(-1); in group D (n=25), 0.5 μg kg(-1) dexmedetomidine was infused over 10 minutes before induction, and then titrated over a range of 0.2-0.7 μg kg(-1) hr(-1) to maintain mean arterial pressure (MAP) between 55 and 65 mmHg and BIS 40-50 after induction. In both groups, 0.25 μg kg(-1) min(-1) remifentanil infusion was used for anaesthesia maintenance. Maintaining end-tidal CO2 (EtCO2) at 35-40, using 1 MAC sevoflurane in 50% O2-air mixture, mechanical ventilation was started. The effects of both agents on hemodynamic conditions [(heart rate (HR), mean arterial pressure (MAP)], neuromuscular blockage [onset of action (OA), duration of clinical action (DCA), recovery index (RI)], amount of bleeding, surgeon satisfaction, and total dexmedetomidine and esmolol doses used during the intervention were recorded and costs were compared between the groups.

RESULTS

No significant difference was present in hemodynamic conditions, bleeding scores or surgeon satisfaction between groups. Although OA was similar in both groups, DCA and RI were significantly higher in group D. Cost was significantly higher with esmolol than dexmedetomidine.

CONCLUSION

We conclude that although both agents are feasible in inducing hypotensive anaesthesia, while neuromuscular block time prolonged by using dexmedetomidine, higher costs were observed with esmolol.

Dexmedetomidine: current role in anesthesia and intensive care

BACKGROUND AND OBJECTIVES

To update and review the application of dexmedetomidine in anesthesia and intensive care. This study is a comprehensive review of clinical uses, pharmacology, pharmacokinetics, mechanism of action and adverse effects of dexmedetomidine.

CONTENT

The effective use of sedative-hypnotic agents and analgesics is an integral part of comfort and safety of patients. Dexmedetomidine is a potent and highly selective α-2 adrenoceptor agonist with sympatholytic, sedative, amnestic, and analgesic properties, which has been described as a useful and safe adjunct in many clinical applications. It provides a unique "conscious sedation", analgesia, without respiratory depression. The current reviewed uses include sedation at Intensive Care Unit-ICU (both adult and pediatric), emergency department, regional and general anesthesia, neurosurgery, sedation for pediatric procedures, awake fiber-optic intubation, cardiac surgery and bariatric surgery.

CONCLUSIONS

Dexmedetomidine offers a unique ability of providing both sedation and analgesia without respiratory depression. It is a new agent with a wide safety margin, excellent sedative capacity and moderate analgesic properties. Although its wide use is currently in patients of surgical and non-surgical intensive care units, dexmedetomidine seems to have promising future applications in neuroprotection, cardioprotection and renoprotection. More detailed studies are required to define its role as sedative in critical, neurosurgical and pediatric patients, as anesthesia adjunct and sedative during procedures.

Are the pharmacology and physiology of α₂ adrenoceptors determined by α₂-heteroreceptors and autoreceptors respectively?

α(2)-Adrenoceptors are important mediators of physiological responses to the endogenous catecholamines noradrenaline and adrenaline. In addition, α(2)-adrenoceptors are pharmacological targets for the treatment of hypertension, sympathetic overactivity and glaucoma. α(2)-Adrenoceptors are also targeted to induce sedation and analgesia in anaesthesia and intensive care. α(2)-Adrenoceptors were first described as presynaptic receptors inhibiting the release of various transmitters from neurons in the central and peripheral nervous systems. In addition to these presynaptic neuronal receptors, α(2)-adrenoceptors were also identified in many non-neuronal cell types of the body. Gene-targeting in mice provided a comprehensive assignment of the physiological and pharmacological functions of these receptors to specific α(2A)-, α(2B) - and α(2C)-adrenoceptor subtypes. However, the specific cell types and signalling pathways involved in these subtype-specific α(2)-adrenoceptor functions were largely unexplored until recently. This review summarizes recent findings from transgenic mouse models, which were generated to define the role of α(2)-adrenoceptors in adrenergic neurons, that is, α(2)-autoreceptors, versus α(2)-adrenoceptors in non-adrenergic neurons, termed α(2)-heteroreceptors. α(2)-Autoreceptors are primarily required to limit release of noradrenaline from sympathetic nerves and adrenaline from adrenal chromaffin cells at rest. These receptors are desensitized upon chronic activation as it may for instance occur due to enhanced sympathetic activity during chronic heart failure. In contrast, pharmacological effects of acutely administered α(2)-adrenoceptor agonist drugs essentially require α(2)-heteroreceptors in non-adrenergic neurons, including analgesia, sedation, hypothermia and anaesthetic-sparing as well as bradycardia and hypotension. Thus a clear picture has emerged of the significance of auto- versus heteroreceptors in mediating the physiological functions of α(2)-adrenoceptors and the pharmacological functions of α(2)-adrenoceptor agonist drugs respectively.

Sedation with dexmedetomidine in the intensive care setting

Dexmedetomidine is an α-2 agonist that produces sedation and analgesia without compromising the respiratory drive. Use of dexmedetomidine as a sedative in the critically ill is associated with fewer opioid requirements compared with propofol and a similar time at goal sedation compared with benzodiazepines. Dexmedetomidine may produce negative hemodynamic effects including lower mean heart rates and potentially more bradycardia than other sedatives used in the critically ill. Recent studies have demonstrated that dexmedetomidine is safe at higher dosages, but more studies are needed to determine whether the efficacy of dexmedetomidine is dose dependent. In addition, further research is required to define dexmedetomidine’s role in the care of delirious critically ill patients, as many, but not all, studies have indicated favorable outcomes.

Comparative pharmacology of adrenergic alpha(2C) receptors coupled to Ca(2+) signaling through different Galpha proteins

Adrenergic alpha(1), alpha(2) and beta receptors are members of the G-protein-coupled receptor families (GPCRs) mediating physiological responses to adrenaline (epinephrine) and noradrenaline (norepinephrine). Since GPCRs are major targets for potential therapeutic agents, development of robust, reliable and cost effective functional screening methods for these receptors is in the focus of pharmacological research. For this reason, the aim of the present study was to develop an intracellular calcium assay for investigating the pharmacology of the alpha(2C) type of adrenergic receptors (alpha(2C)-AR). Although activation of alpha(2C)-AR is not linked to calcium mobilization, co-expression of these receptors with the chimeric Galpha(qi5) protein, containing the five carboxyl-terminal amino acids from G(i), or promiscuosus Galpha(16) protein can divert receptor signaling to the G(q) pathway generating Ca(2+) release from intracellular stores. In order to assess the functional potency of alpha(2)-AR agonists and antagonists, we established a fluorometric Ca(2+) assay using cell lines stably and constitutively co-expressing alpha(2C)-AR and Galpha(qi5) or Galpha(16) proteins (Galpha(qi5)/alpha(2C) and Galpha(16)/alpha(2C)). As part of the pharmacological characterization, we measured the changes in cytoplasmic Ca(2+) levels due to activation of the chimeric Galpha(qi5) or Galpha(16) coupled recombinant alpha(2C) receptors as a function of increasing concentration of several agonists (noradrenaline, brimonidine, oxymetazoline, clonidine, moxonidine) and antagonists (MK912, yohimbine). The binding affinities of alpha(2)-AR agonist and antagonists and the inhibition of the forskolin-stimulated cAMP accumulation in alpha(2C)-AR expressing cells were also measured. These results confirmed that the Galpha(qi5)/alpha(2C) and Galpha(16)/alpha(2C) recombinant systems can be useful for modelling the native G(i)-coupled system. Our results indicate that a plate-reader based fluorometric Ca(2+) assay may be suitable in high-throughput screening for alpha(2C)-AR ligands as well.

Intravenous dexmedetomidine as an adjunct for labor analgesia and cesarean delivery anesthesia in a parturient with a tethered spinal cord

For parturients desiring labor analgesia who have contraindications to neuraxial techniques, intravenous opioid-based patient-controlled analgesia (IVPCA) offers a reasonable alternative, although incomplete analgesia and maternal and neonatal respiratory depression can occur. Dexmedetomidine, a highly selective alpha(2) agonist with negligible placental transfer, may be a valuable adjunct to IVPCA by providing additional analgesia without the respiratory depression associated with increasing opioid usage. The successful use of a dexmedetomidine infusion as an adjunct to unsatisfactory fentanyl IVPCA is reported in a 31-year-old parturient with spina bifida occulta and a tethered spinal cord reaching L5-S1. Dexmedetomidine significantly improved the analgesic quality; increased sedation was observed, but the patient was easily rousable to verbal stimuli. No episodes of maternal hypotension or bradycardia, or fetal heart rate irregularities occurred. Cesarean delivery was required for prolonged first stage of labor and presumed chorioamnionitis; it was conducted under general anesthesia during which the dexmedetomidine infusion was continued. A healthy baby boy was delivered with normal Apgar scores and no discernible neurobehavioral or other deficits.

Delirium in the acute care setting: characteristics, diagnosis and treatment

Delirium is a neurobehavioral syndrome caused by the transient disruption of normal neuronal activity secondary to systemic disturbances. It is also the most common psychiatric syndrome found in the general hospital setting, its prevalence surpassing better known psychiatric disorders. This article reviews the published literature on delirium and addresses the epidemiology, known etiologic factors, presentation and characteristics of delirium, while emphasizing what is known about treatment strategies and prevention. Given increasing evidence that delirium is not always reversible and the many sequelae associated with its development, physicians must do everything possible to prevent its occurrence or shorten its duration, by recognizing its symptoms early, correcting underlying contributing causes, and using treatment strategies proven to help recover functional status.

Clinical analgesic efficacy and side effects of dexmedetomidine in the early postoperative period after arthroscopic knee surgery

STUDY OBJECTIVES

To determine the analgesic efficacy of dexmedetomidine in the early postoperative period.

DESIGN

Randomized, double-blind, double placebo-controlled clinical trial.

SETTING

University medical center.

PATIENTS

30 ASA physical status I, II, and III patients with cruciate ligament lesion and joint fibrosis who were scheduled for knee arthroscopy.

INTERVENTIONS

Patients were prospectively randomized to receive dexmedetomidine one mcg/kg(-1) intravenously (IV), for 10 minutes followed by dexmedetomidine 0.3 mcg/kg(-1) for 50 minutes or propacetamol two g, IV, for 10 minutes.

MEASUREMENTS

Pain scores, time to onset analgesia, and morphine consumption were measured. Open-label rescue morphine 5 mg IV was available as needed during the postdosing evaluation period of 8 hours. Hemodynamic data, sedation scores, and renal and hepatic function were assessed for control of adverse events.

MAIN RESULTS

Pain scores with dexmedetomidine and propacetamol were similar. There were no differences in the number of patients who required supplemental rescue analgesia (7/15 vs 4/15; P = 0.44), but total morphine requirements were higher with dexmedetomidine (45 mg) versus propacetamol (20 mg) in the 8-hour follow-up (P < 0.05). The most frequent adverse events with dexmedetomidine were bradycardia and hypertension.

CONCLUSIONS

Dexmedetomidine provides a modest analgesic effect after knee arthroscopy, but the side effects of this drug, such as hypertension and bradycardia, may restrict the use of large bolus doses.

Sedation and analgesia in the intensive care unit

PURPOSE OF REVIEW

Sedation and analgesia are important means of providing care for the critically ill patient.

RECENT FINDINGS

It is now clear that posttraumatic stress disorders resulting from an intensive care unit stay may be prevented by the right level of sedation. New drug developments but also recent findings in new ventilation strategies allow for a sedation management that is better tailored to an individual's need. Most importantly, regular definition of the appropriate level of sedation and analgesia as well as monitoring of the desired level will help to avoid over- and undersedation and may ultimately improve the outcome of the patient and reduce costs.

SUMMARY

Sedation and analgesia are now regarded as an integral part of treatment on the intensive care unit instead of being an unpleasant but necessary and minor issue. The importance of monitoring the level of sedation and analgesia has only recently been realized. It remains to be shown that new management strategies including an evaluation of the patient, planned interventions and the choice of drugs will further improve the care for the critically ill.

Effect of dexmedetomidine on bleeding during tympanoplasty or septorhinoplasty

BACKGROUND AND OBJECTIVE

The aim of this study was to evaluate the efficacy of dexmedetomidine, an alpha(2)-adrenoceptor agonist, on intraoperative bleeding, anaesthetic drug requirement and postoperative pain.

METHODS

Forty patients scheduled for elective tympanoplasty and septorhinoplasty operations under general anaesthesia were included in the study. The patients were randomly assigned to receive either a dexmedetomidine 1 microg kg(-1) bolus 10 min before induction of anaesthesia plus 0.5 microg kg(-1) h(-1) infusions during maintenance or placebo. Mean arterial pressure was maintained between 60 and 80 mmHg. Perioperative mean arterial pressure, heart rate, time to extubation and time to awakening were recorded. Bleeding during surgery was assessed by the surgeon, blinded to the study drugs, both intraoperatively and postoperatively as a final personal opinion about the whole surgical process.

RESULTS

The heart rate and mean arterial pressure were significantly lower during induction, operation and extubation in the dexmedetomidine group (P < 0.05). Blood losses were lower in the dexmedetomidine group (P < 0.05). Propofol dose required for induction, and fentanyl and isoflurane consumption were significantly reduced in the dexmedetomidine group (P < 0.05). The total amounts of nitroglycerin and meperidine used were higher in the control group (P < 0.05).

CONCLUSIONS

Dexmedetomidine decreased bleeding, postoperative analgesic requirements and intraoperative anaesthetic requirements and was associated with more stable haemodynamic responses to anaesthesia. We conclude that dexmedetomidine is a useful adjuvant to decrease bleeding when a bloodless surgical field is requested.

Dexmedetomidine: an updated review

OBJECTIVE

To review recent literature on the safety and efficacy of dexmedetomidine.

DATA SOURCES

Articles were identified through searches of MEDLINE (1966-January 2007). Key words included dexmedetomidine, medetomidine, alpha(2)-agonist, and sedation. References from selected articles were reviewed for additional references.

STUDY SELECTION AND DATA EXTRACTION

Experimental and observational studies that focused on the safety and efficacy of dexmedetomidine in humans were selected.

DATA SYNTHESIS

Dexmedetomidine is an alpha(2)-agonist for short-term sedation in critically ill patients. In postoperative patients, dexmedetomidine produced similar levels of sedation and times to extubation, with less opioid requirements compared with propofol. Dexmedetomidine has also been studied for sedation in critically ill medical and pediatric patients, as adjunct to anesthesia, and for procedural sedation. Hypotension, hypertension, and bradycardia are common adverse effects. Although dexmedetomidine is labeled only for sedation less than 24 hours, it has been administered for longer than 24 hours without apparent development of rebound hypertension and tachycardia.

CONCLUSIONS

Dexmedetomidine is a safe and effective agent for sedation in critically ill patients. Further, well designed studies are needed to define its role as a sedative for critically ill medical, neurosurgical, and pediatric patients, as an adjunct to anesthesia, and as a sedative during procedures.

Balanced anaesthesia today

An 'ideal' anaesthetic can be approached by using a combination of different compounds. A variety of anaesthetic techniques has been described to ensure safe administration and an early recovery with high patient satisfaction. In particular, the inhalational anaesthetics desflurane and sevoflurane, with their rapid pharmacokinetics, re-established the notion of balanced anaesthesia as an equivalent, well-controllable technique. With the choice of anaesthetics and anaesthetic adjuvants clinically available today, especially the combination of a volatile anaesthetic with a short-acting opioid, balanced anaesthesia represents a big step towards an ideal anaesthetic.

Dexmedetomidine in anaesthesia

PURPOSE OF REVIEW

The development of dexmedetomidine, a potent and highly selective alpha2-adrenoceptor agonist, has created new interest in the use of alpha2-adrenoceptor agonists, and has led to its evaluation in various yet non-approved perioperative settings. The current review focuses on the usefulness of dexmedetomidine in anaesthesia practice.

RECENT FINDINGS

Recently acquired knowledge and experience with dexmedetomidine in perioperative use will be presented and discussed in the context of known pharmacological properties.

SUMMARY

Dexmedetomidine offers beneficial pharmacological properties, providing dose-dependent sedation, analgesia, sympatholysis and anxiolysis without relevant respiratory depression. The side-effects are predictable from the pharmacological profile of (2-adrenoceptor agonists. In particular, the unique sedative properties of dexmedetomidine resulted in several interesting applications in anaesthesia practice, promising benefits in the perioperative use of this compound. However, dexmedetomidine was approved for sedation in the intensive care unit in the USA in 1999, and administration in anaesthesia practice remains an 'off-label' use. Further studies are needed to establish the role of dexmedetomidine in the perioperative period.

Analgesie und Sedierung in der Intensivmedizin

Sedation and analgesia are relevant aspects for the adequate treatment of patients in an intensive care unit. Recent drug developments and new strategies for ventilation provide improved sedation management allowing better adaptation to the clinical background and individual needs of the patient. This article provides an overview on the application of different substance groups. Focus is placed on newly developed pharmaceuticals such as dexmedetomidine. Another aspect is scoring system-related and EEG-based monitoring of depth of sedation. Modern concepts of analgesia and sedation for ICU patients have been developed based on the interaction of different parameters such as adaptive sedation and analgesia management (ASAM).

Cellular mechanisms in sympatho-modulation of the heart

Cardiovascular function relies on complex servo-controlled regulation mechanisms that involve both fast-acting feedback responses and long-lasting adaptations affecting the gene expression. The adrenergic system, with its specific receptor subtypes and intracellular signalling cascades provides the major regulatory system, while the parasympathetic system plays a minor role. At the molecular level, Ca(2+) acts as the general signal trigger for the majority of cell activities including contraction, metabolism and growth. During recent years, important new results have emerged allowing an integrated view of how the multifarious Ca(2+)-signalling mechanisms transmit adrenergic impulses to intracellular target sites. These insights into cellular and molecular mechanisms are pivotal in improving pharmacological control of the sympathetic responses to surgical trauma and perioperative stress. They are examined in detail in this review, with particular emphasis being given to the differences in intracellular signalling between cardiomyocytes and vascular smooth muscle cells.

Treatment of persistent tachycardia with dexmedetomidine during off-pump cardiac surgery

IMPLICATIONS

After unsuccessful treatment of intraoperative tachycardia with esmolol during off-pump revascularization, heart rate was successfully reduced with a bolus and infusion of dexmedetomidine.

Physiological significance of alpha(2)-adrenergic receptor subtype diversity: one receptor is not enough

Alpha(2)-adrenergic receptors mediate part of the diverse biological effects of the endogenous catecholamines epinephrine and norepinephrine. Three distinct subtypes of alpha(2)-adrenergic receptors, alpha(2A), alpha(2B), alpha(2C), have been identified from multiple species. Because of the lack of sufficiently subtype-selective ligands, the specific biological functions of these receptor subtypes were largely unknown until recently. Gene-targeted mice carrying deletions in the genes encoding for individual alpha(2)-receptor subtypes have added important new insight into the physiological significance of adrenergic receptor diversity. Two different strategies have emerged to regulate adrenergic signal transduction. Some biological functions are controlled by two counteracting alpha(2)-receptor subtypes, e.g., alpha(2A)-receptors decrease sympathetic outflow and blood pressure, whereas the alpha(2B)-subtype increases blood pressure. Other biological functions are regulated by synergistic alpha(2)-receptor subtypes. The inhibitory presynaptic feedback loop that tightly regulates neurotransmitter release from adrenergic nerves also requires two receptor subtypes, alpha(2A) and alpha(2C). Similarly, nociception is controlled at several levels by one of the three alpha(2)-receptor subtypes. Further investigation of the specific function of alpha(2)-subtypes will greatly enhance our understanding of the relevance of closely related receptor proteins and point out novel therapeutic strategies for subtype-selective drug development.