Alpha 2-adrenergic agents in anaesthesia

Efficacy and safety of sedation with dexmedetomidine in adults undergoing gastrointestinal endoscopic procedures: systematic review and meta-analysis of randomized controlled trials

Background: The sedative role of dexmedetomidine (DEX) in gastrointestinal endoscopic procedures is unclear. We performed this systematic review and meta-analysis to assess the efficacy and safety of sedation with DEX during gastrointestinal endoscopic procedures with a view to providing evidence-based references for clinical decision-making. Methods: The PubMed, Embase, Cochrane Library, Web of Science, and ClinicalTrials.gov databases were searched for randomized controlled trials (RCTs) that compared DEX with different sedatives comparators (such as propofol, midazolam, and ketamine) for sedation in a variety of adult gastrointestinal endoscopic procedures from inception to 1 July 2022. Standardized mean difference (SMD) and weighted mean difference (WMD) with 95% confidence interval (CI) or pooled risk ratios (RR) with 95% CI were used for continuous outcomes or dichotomous outcomes, respectively, and a random-effect model was selected regardless of the significance of the heterogeneity. Results: Forty studies with 2,955 patients were assessed, of which 1,333 patients were in the DEX group and 1,622 patients were in the control (without DEX) group. The results suggested that the primary outcomes of sedation level of DEX are comparable to other sedatives, with similar RSS score and patient satisfaction level, and better in some clinical outcomes, with a reduced risk of body movements or gagging (RR: 0.60; 95% CI: 0.37 to 0.97; p = 0.04; I2 = 68%), and a reduced additional requirement for other sedatives, and increased endoscopist satisfaction level (SMD: 0.41; 95% CI: 0.05 to 0.77; p = 0.03; I2 = 86%). In terms of secondary outcomes of adverse events, DEX may benefit patients in some clinical outcomes, with a reduced risk of hypoxia (RR:0.34; 95% CI: 0.20 to 0.55; p < 0.0001; I2 = 52%) and cough (RR: 0.25; 95% CI: 0.12 to 0.54; p = 0.0004; I2 = 0%), no significant difference in the risk of hypotension, while an increased risk of bradycardia (RR: 3.08; 95% CI: 2.12 to 4.48; p < 0.00001; I2 = 6%). Conclusion: This meta-analysis indicates that DEX is a safe and effective sedative agent for gastrointestinal endoscopy because of its benefits for patients in some clinical outcomes. Remarkably, DEX is comparable to midazolam and propofol in terms of sedation level. In conclusion, DEX provides an additional option in sedation for gastrointestinal endoscopic procedures. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/#searchadvanced.

Comparative Study of Gabapentin, Clonidine and Placebo in Alleviating the Hemodynamic Changes Due to Tracheal Intubation and Laryngoscopy

INTRODUCTION

Hemodynamic changes during laryngoscopy and tracheal intubation must be reduced for safe and effective anesthesia. The present study was conducted to compare the efficacy of oral clonidine, gabapentin and placebo in alleviating the hemodynamic changes due to tracheal intubation and laryngoscopy.

METHODS

This was a double-blinded randomized controlled trial conducted on 90 patients who were undergoing elective surgery and were randomized into three groups. Group I (n=30) received a placebo, group II (n=30) received gabapentin and group III (n=30) received clonidine as premedication before anesthesia induction. Patient heart rate and pressor response were recorded periodically and compared between the groups.

RESULTS

There was no significant difference in the baseline heart rate (HR) and mean arterial pressure (MAP) between the groups. HR elevation was observed in all three groups and found to be significant (p=0.0001) but the increase was higher in the placebo (15 min: 80.80± 15.41) and lower in the clonidine group (15 min: 65.53± 12.43). The elevation in systolic and diastolic blood pressure was least and transient in the gabapentin group, as compared to placebo and clonidine group. Intra-operatively, the requirement of opioids was higher in the placebo as compared to clonidine and gabapentin (p < .001).

CONCLUSION

Clonidine and gabapentin were effective in reducing the hemodynamic changes during laryngoscopy and intubation.

Indoleamine-2,3-Dioxygenase as a Perioperative Marker of the Immune System

Indoleamine-2,3-dioxygenase (IDO) is the “rate-limiting” enzyme in the kynurenine (Kyn) pathway of the tryptophan (Trp) catabolism. By its immune-modulatory effect, IDO initiates changes to the physiologically balanced immune state and plays a key role in the pathogenesis of various diseases, as well as in the perioperative setting during surgery. In autoimmune processes, highly malignant cancers such as glioblastoma or organ transplantation, IDO’s involvement has been studied extensively. However, in severe systemic infections, as present in sepsis, it is not yet completely understood. Hereafter, in this narrative review, we present the current knowledge of IDO’s implication on such complex immune-related processes. Moreover, we address the role of IDO as a predictive biomarker as well as a therapeutic target for immune-mediated diseases. Finally, we discuss IDO in the setting of surgical trauma-induced stress and highlight its promising use as a biomarker in the pre-operative setting for all disciplines involved in the decision-making process and treatment of patients undergoing surgery.

Effects of fadolmidine, an α2 -adrenoceptor agonist, as an adjuvant to spinal bupivacaine on antinociception and motor function in rats and dogs

α2 -Adrenoceptor agonists such as clonidine and dexmedetomidine are used as adjuvants to local anesthetics in regional anesthesia. Fadolmidine is an α2 -adrenoceptor agonist developed especially as a spinal analgesic. The current studies investigate the effects of intrathecally administered fadolmidine with a local anesthetic, bupivacaine, on antinociception and motor block in conscious rats and dogs. The antinociceptive effects of intrathecal fadolmidine and bupivacaine alone or in combination were tested in the rat tail-flick and the dog's skin twitch models. The durations of motor block in rats and in dogs were also assessed. In addition, the effects on sedation, mean arterial blood pressure, heart rate, respiratory rate and body temperature were evaluated in telemetrized dogs. Concentrations of fadolmidine in plasma and spinal cord were determined after intrathecal and intravenous administration in rats. Co-administration of intrathecal fadolmidine with bupivacaine increased the magnitude and duration of the antinociceptive effects and prolonged motor block without hypotension. The interaction of the antinociceptive effect was synergistic in its nature in rats. Concentration of fadolmidine in plasma was very low after intrathecal dosing. Taken together, these studies show that fadolmidine as an adjuvant to intrathecal bupivacaine provides enhanced sensory-motor block and enables a reduction of the doses of both drugs. The results indicate that co-administration of fadolmidine with intrathecal bupivacaine was able to achieve an enhanced antinociceptive effect without hypotension and could thus represent a suitable combination for spinal anesthesia.

Effects of dexmedetomidine on blood coagulation: an in vitro study using rotational thromboelastometry

PURPOSE

To assess the effects of various concentrations of dexmedetomidine on the human blood coagulation profile using rotational thromboelastometry (ROTEM).

METHODS

Venous blood samples were collected from 11 healthy volunteers and divided into four specimen bottles; dexmedetomidine was added to attain final sample concentrations of 0, 0.5, 1.0, and 1.5 ng/mL. ROTEM was performed on each study sample.

RESULTS

The concentration of dexmedetomidine increased, and the ROTEM values showed a hypercoagulable state. The change in clotting time (CT) for INTEM was larger in samples with a dexmedetomidine concentration of 1.5 ng/mL (- 34%) than in the 0.5 ng/mL samples (- 16%) (P = 0.010). The change in clot formation time (CFT) for INTEM was greater in 1.5 ng/mL samples (- 16%) than in 0.5 ng/mL samples (- 4%) (P = 0.004). A greater decrease in CT for EXTEM was identified in the 1.0 ng/mL and 1.5 ng/mL samples (- 36% and - 37%, respectively) than in the 0.5 ng/mL samples (- 12%) (P = 0.003 for both categories). The change in CFT for EXTEM was greater in the 1.0 ng/mL and 1.5 ng/mL samples (- 11% and - 13%, respectively) than in the 0.5 ng/mL samples (- 4%) (P = 0.006 and P = 0.001, respectively). A bigger change in maximum clot firmness (MCF) for EXTEM was observed in the 1.5 ng/mL samples (4%) than in the 0.5 ng/mL samples (0%) (P = 0.002). The change in MCF for FIBTEM was greater in the 1.5 ng/mL samples (19%) than in the 0.5 ng/mL samples (5%) (P = 0.001).

CONCLUSIONS

All coagulation pathways showed a hypercoagulable state as the concentration of dexmedetomidine increased. Nevertheless, most of the values of ROTEM were maintained within the reference ranges. Clinical Trial NCT04269278.

Pharmacodynamics of intrathecal and epidural fadolmidine, an α2-adrenoceptor agonist, after bolus and infusion in dogs-comparison with clonidine

An α₂-adrenoceptor agonist, clonidine, is extensively used in both anesthesia and intensive care medicine. However, clonidine may produce pronounced hemodynamic side effects such as hypotension and bradycardia which may limit its usefulness in certain conditions. Fadolmidine is a potent α₂-adrenoceptor agonist with different physicochemical properties than clonidine. Here, the effects of fadolmidine and clonidine on analgesia (an increase in thermal skin twitch response latency), sedation, blood pressure, heart rate, respiratory rate, and body temperature were evaluated either up to 8 h after either intrathecal or epidural bolus injections or during a 24-h continuous intrathecal infusion at equipotent analgesic doses in non-anesthetized Beagle dogs. Fadolmidine and clonidine produced a dose-dependent and equipotent maximal antinociception after intrathecal bolus injection (ED₅₀: 67 μg and 78 μg, respectively), but the duration of action of fadolmidine was more long-lasting. During the intrathecal infusion, fadolmidine achieved a good analgesic effect without evoking cardiovascular side effects, e.g., hypotension; these were evident during clonidine infusion. Epidurally, the antinociceptive potency of fadolmidine was weaker (ED₅₀: 128 μg) than when intrathecally administered and weaker than that of epidural clonidine (ED₅₀: 51 μg). At analgesic doses, fadolmidine injection induced moderate initial hypertension concomitantly with a decrease in heart rate whereas clonidine evoked hypotension and bradycardia. These results suggest that especially when non-opioid long-term pain relief is needed, an intrathecal infusion of fadolmidine can provide long-term antinociception with less of the known use-limiting adverse effects associated with clonidine.

Effects of Dexmedetomidine on Blood Glucose and Serum Potassium Levels in Children Undergoing General Anesthesia: A Secondary Analysis of Safety Endpoints During a Randomized Controlled Trial

BACKGROUND

Dexmedetomidine is a highly selective α2-adrenergic agonist, which is increasingly used in pediatric anesthesia and intensive care. Potential adverse effects that have not been rigorously evaluated in children include its effects on blood glucose and serum potassium concentrations, which are relevant due to the associations of derangements of both parameters with undesired outcomes. We investigated the effects of 3 different doses of dexmedetomidine on these outcomes in a randomized controlled trial in children undergoing elective surgery.

METHODS

Sixty-four American Society of Anesthesiologists I-II children were randomized to receive either dexmedetomidine 0.25 µg/kg, dexmedetomidine 0.5 µg/kg, dexmedetomidine 0.75 µg/kg, or 0 µg/kg (control), as a bolus administered over 60 seconds after induction of anesthesia. Changes in plasma glucose and serum potassium concentrations were measured in venous blood sampled before and at 15 and 30 minutes after study drug administration. Data were plotted within and between groups and analyzed using a constrained longitudinal data approach.

RESULTS

Forty-nine children completed the study. Mean glucose levels at 15 and 30 minutes were elevated with estimated changes from baseline of 0.37 mmol/L (95% CI, 0.29-0.45 mmol/L) and 0.05 mmol/L (95% CI, 0.00-0.10 mmol/L), respectively. At 15 minutes, there was a linear dose-response relationship (1.07 mmol/L/μg/kg [95% CI, 0.57-1.58 mmol/L/μg/kg]), but there was no appreciable effect of dexmedetomidine at 30 minutes (0.15 mmol/L/μg/kg [95% CI, -0.40 to 0.70 mmol/L/μg/kg]). Potassium levels were depressed relative to baseline, with a mean difference at 15 minutes of -0.20 mEq/L (95% CI, -0.28 to -0.12 mEq/L) and at 30 minutes of -0.12 mEq/L (95% CI, -0.15 to -0.08 mEq/L), but there was no appreciable effect of dexmedetomidine at either time.

CONCLUSIONS

Small elevations in glucose and decreases in potassium were observed after induction of anesthesia in children. The elevation in glucose at 15 minutes depended on the dose of dexmedetomidine administered. These preliminary data warrant further investigation.

Discharge Readiness after Propofol with or without Dexmedetomidine for Colonoscopy

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Enhanced recovery protocols employ various approaches to minimize detrimental side effects of anesthetizing agents. The authors tested the hypothesis that adding low-dose dexmedetomidine to propofol for anesthesia in ambulatory colonoscopies, compared with propofol alone, would lower the propofol requirement, improve the intra-procedure hemodynamic state, and not increase time-to-discharge.

Methods

In this noninferiority, double-blind, randomized controlled trial, patients having colonoscopies received total IV anesthesia either with propofol and placebo (n = 50), or propofol and a bolus dose of dexmedetomidine, 0.3 μg/kg (n = 51). Additional propofol was administered to maintain a Bispectral Index score of 60. Following the procedure, readiness for discharge was assessed regularly using the Modified Post Anesthetic Discharge Scoring System until discharge criteria were met. The primary outcome was the percentage of patients meeting discharge criteria within 30 min from procedure end-time.

Results

Twenty-six of 51 (51%) patients receiving propofol-dexmedetomidine were ready for discharge by 30 min from procedure end time, compared with 44 of 50 (88%) receiving propofol (P &lt; 0.001). Propofol consumption was lower in subjects receiving propofol–dexmedetomidine (140 μg · kg-1 · min-1) compared to those receiving propofol (180 μg · kg-1 · min-1) with P = 0.011. The lowest mean arterial pressure decreased further from baseline in those receiving propofol–dexmedetomidine (−30%; mean decrease −30 ±10.5 mmHg) compared to propofol (−21%; mean decrease, −22 ± 14.2 mmHg) with P = 0.003. There was no difference in incidence of bradycardia, with sustained bradycardia occurring in 3 of 51 (6%) patients receiving propofol–dexmedetomidine compared to 1 of 50 (2%) patients receiving propofol (P = 0.62). No apnea episodes requiring positive-pressure ventilation occurred in either group.

Conclusions

For anesthesia in ambulatory colonoscopy, combining low-dose dexmedetomidine with propofol delayed discharge readiness and provoked hypotension compared to propofol alone.

Perianal Block: Is It as Good as Spinal Anesthesia for Closed Hemorrhoidectomies?

Background and Aims:

This study compared if perianal block using ropivacaine and dexmedetomidine was as good as spinal anesthesia (SA) using bupivacaine (heavy) for closed hemorrhoidectomies.

Methods:

A prospective randomized study was conducted in sixty patients who underwent closed hemorrhoidectomy. Thirty patients of Group A received SA. Thirty patients in Group B received local perianal block. Patients were evaluated for onset of the block, total pain-free period, and time to ambulation. Patient satisfaction in terms of pain during injection and satisfaction with the anesthesia technique was assessed after 2-week telephonically. Data were statistically analyzed using unpaired t-test for the continuous variables and Fischer's exact test for categorical variables.

Results:

Onset of anesthesia was significantly earlier in Group B, mean (standard deviation [SD]) value being 3.17 (1.28) min as compared to Group A, 6.24 (4.28) min (P = 0.0004). Total pain-free period (mean [SD]) in minute was longer in Group B, 287 (120) min as compared to Group A, 128 (38) min. Time to ambulation was significantly earlier in Group B, 22.83 (29.32) min as compared to Group A 302 (92.41) min. Pain during injection between the two groups was comparable. However, more patients in Group B (60%) were satisfied with the anesthesia technique as compared to Group A (27.5%).

Conclusion:

Perianal block for hemorrhoidectomy with ropivacaine 0.2% using dexmedetomidine as an adjuvant is an effective and reliable technique which is as effective as SA. It provides prolonged postoperative analgesia and early ambulation.

Efficacy and Safety of Clonidine as an Adjuvant to Bupivacaine for Caudal Analgesia in Paediatric Infra-Umbilical Surgeries

INTRODUCTION

Caudal analgesia, has gained popularity in paediatric intraoperative and postoperative pain management, more so with the use of adjuvants to prolong its duration, each of them having various results. Clonidine, an alpha2-adrenergic agonist is being used for its analgesic effects in various doses with 0.25% Bupivacaine.

AIM

The study was conducted to compare the analgesic efficacy, haemodynamic safety and side effects of 1 μg/kg Clonidine added to 1 ml/kg of 0.125% Bupivacaine solution for caudal analgesia.

MATERIALS AND METHODS

A prospective, randomised, double-blind, controlled study was carried out in 60 children of ASA Physical Status I, aged 1-10 years, scheduled for infraumbilical operations in a tertiary care centre. They were randomly assigned for caudal analgesia, to either group B: 1ml/kg of 0.125% Bupivacaine solution or group BC: 1ml/kg of 0.125% Bupivacaine and preservative free Clonidine 1μ/kg. All were premedicated with midazolam 0.75 mg/kg orally 30 minutes prior to induction of anaesthesia. Heart rate (HR), Mean Arterial blood Pressure (MAP) and oxygen saturation (SpO2) were monitored. General anaesthesia was induced with thiopentone (1.25%) 5mg/kg and inhalation of oxygen, nitrous oxide and sevoflurane. Postoperative pain, sedation and motor block was assessed by the various scores and patients were monitored for adverse effects.

RESULTS

The mean duration of postoperative analgesia was 3 times longer in group BC. Group B received significantly more doses of rescue analgesic than group BC (p-value of 0.004). There was no significant bradycardia, hypotension, sedation or urinary retention in either of the groups. There was no residual motor blockade at 6 hours. Incidence of vomiting was similar in both the groups.

CONCLUSION

Caudal Clonidine in the dose of 1 μg/kg in children is a satisfactory and efficacious adjuvant to caudal Bupivacaine for producing prolonged postoperative analgesia with minimum side effects.

Prospective multicentre randomised, double-blind, equivalence study comparing clonidine and midazolam as intravenous sedative agents in critically ill children: the SLEEPS (Safety profiLe, Efficacy and Equivalence in Paediatric intensive care Sedation) study

BACKGROUND

Children in paediatric intensive care units (PICUs) require analgesia and sedation but both undersedation and oversedation can be harmful.

OBJECTIVE

Evaluation of intravenous (i.v.) clonidine as an alternative to i.v. midazolam.

DESIGN

Multicentre, double-blind, randomised equivalence trial.

SETTING

Ten UK PICUs.

PARTICIPANTS

Children (30 days to 15 years inclusive) weighing ≤ 50 kg, expected to require ventilation on PICU for > 12 hours.

INTERVENTIONS

Clonidine (3 µg/kg loading then 0-3 µg/kg/hour) versus midazolam (200 µg/kg loading then 0-200 µg/kg/hour). Maintenance infusion rates adjusted according to behavioural assessment (COMFORT score). Both groups also received morphine.

MAIN OUTCOME MEASURES

Primary end point Adequate sedation defined by COMFORT score of 17-26 for ≥ 80% of the time with a ± 0.15 margin of equivalence. Secondary end points Percentage of time spent adequately sedated, increase in sedation/analgesia, recovery after sedation, side effects and safety data.

RESULTS

The study planned to recruit 1000 children. In total, 129 children were randomised, of whom 120 (93%) contributed data for the primary outcome. The proportion of children who were adequately sedated for ≥ 80% of the time was 21 of 61 (34.4%) - clonidine, and 18 of 59 (30.5%) - midazolam. The difference in proportions for clonidine-midazolam was 0.04 [95% confidence interval (CI) -0.13 to 0.21], and, with the 95% CI including values outside the range of equivalence (-0.15 to 0.15), equivalence was not demonstrated; however, the study was underpowered. Non-inferiority of clonidine to midazolam was established, with the only values outside the equivalence range favouring clonidine. Times to reach maximum sedation and analgesia were comparable hazard ratios: 0.99 (95% CI 0.53 to 1.82) and 1.18 (95% CI 0.49 to 2.86), respectively. Percentage time spent adequately sedated was similar [medians clonidine 73.8% vs. midazolam 72.8%: difference in medians 0.66 (95% CI -5.25 to 7.24)]. Treatment failure was 12 of 64 (18.8%) on clonidine and 7 of 61 (11.5%) on midazolam [risk ratio (RR) 1.63, 95% CI 0.69 to 3.88]. Proportions with withdrawal symptoms [28/60 (46.7%) vs. 30/58 (52.6%)] were similar (RR 0.89, 95% CI 0.62 to 1.28), but a greater proportion required clinical intervention in those receiving midazolam [11/60 (18.3%) vs. 16/58 (27.6%) (RR 0.66, 95% CI 0.34 to 1.31)]. Post treatment, one child on clonidine experienced mild rebound hypertension, not requiring intervention. A higher incidence of inotropic support during the first 12 hours was required for those on clonidine [clonidine 5/45 (11.1%) vs. midazolam 3/52 (5.8%)] (RR 1.93 95% CI 0.49 to 7.61).

CONCLUSIONS

Clonidine is an alternative to midazolam. Our trial-based economic evaluation suggests that clonidine is likely to be a cost-effective sedative agent in the PICU in comparison with midazolam (probability of cost-effectiveness exceeds 50%). Rebound hypertension did not appear to be a significant problem with clonidine but, owing to its effects on heart rate, specific cardiovascular attention needs to be taken during the loading and early infusion phase. Neither drug in combination with morphine provided ideal sedation, suggesting that in unparalysed patients a third background agent is necessary. The disappointing recruitment rates reflect a reluctance of parents to provide consent when established on a sedation regimen, and reluctance of clinicians to allow sedation to be studied in unstable critically ill children. Future studies will require less exacting protocols allowing enhanced recruitment.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN02639863.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 18, No. 71. See the NIHR Journals Library website for further project information.

Comparative Evaluation of Bolus Administration of Dexmedetomidine and Fentanyl for Stress Attenuation During Laryngoscopy and Endotracheal Intubation

BACKGROUND

Laryngoscopy and endotracheal intubation can cause hypertension and tachycardia which can result in myocardial ischemia or stroke in vulnerable people. The objective of our study was to compare the efficacy of bolus dose of dexmedetomidine and fentanyl in attenuating haemodynamic stress responses following laryngoscopy and intubation.

MATERIALS AND METHODS

Sixty patients who were fixed to undergo elective surgeries under general anaesthesia were randomly divided into 2 groups. Group 1 received 1 mcg/kg of dexmedetomidine over 10 minutes and group 2 received fentanyl 2mcg/kg before induction. Anaesthesia was standardized in both the groups and vital parameters were recorded for up to 10 minutes after intubation.

RESULTS

Dexmedetomidine in a dose of 1mcg/kg prevented an increase in heart rate following laryngoscopy when compared to fentanyl group. This effect lasted for 10 minutes after intubation is performed. Though dexmedetomidine prevented an increase in blood pressure, this effect was statistically significant only for 2 minutes after intubation when compared to fentanyl group.

CONCLUSION

Attenuation of rise in heart rate and blood pressure following laryngoscopy and endotracheal intubation was better with 1mcg/kg of dexmedetomidine when compared to fentanyl.

Attenuation of sympathoadrenal responses and anesthetic requirement by dexmedetomidine

Context:

During induction of general anesthesia hypertension and tachycardia caused by tracheal intubation may lead to cardiac ischemia and arrhythmias. Dexmedetomidine attenuates the hemodynamic response to endotracheal intubation and reduces anesthetic requirement.

Aims:

The purpose of this study was to evaluate the effect of a single pre-induction intravenous dose of dexmedetomidine 1 μg/kg on cardiovascular response resulting from laryngoscopy and endotracheal intubation and need for anesthetic agent.

Materials and Methods:

Fifty patients scheduled for elective major surgery were randomized into two groups each having twenty five patients-dexmedetomidine group (Group 1) and control group (Group 2). Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP) and Ramsay sedation score were recorded at 1, 2 and 5 min after completion of administration of study drug. Fentanyl 2 μg/kg was administered to all patients and propofol was given until loss of verbal contact. Intubation was facilitated with vecuronium 0.1 mg/kg i.v. Anesthesia was maintained with oxygen (O₂) and nitrous oxide (N₂O) 33%: 67% and isoflurane. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP) was noted at 1 min, 2 min and 5 min after intubation.

Statistical Analysis Used:

For statistical analysis of the clinical data obtained, the analysis of variances (ANOVA) with paired t-test was used.

Results:

Pretreatment with dexmedetomidine 1 ug/kg attenuated, but did not totally abolish the cardiovascular and catecholamine responses to tracheal intubation after induction of anesthesia. In our present study, HR, SBP, DBP all increased after intubation at 1, 2, 3 and 5 min in both the groups, but the rise was significantly less in the dexmedetomidine group. Requirement of propofol was significantly less in the dexmedetomidine group.

Conclusions:

Preoperative administration of a single dose of dexmedetomidine blunted the hemodynamic responses during laryngoscopy, and reduced anesthetic requirements.

Intranasal dexmedetomidine in combination with patient-controlled sedation during upper gastrointestinal endoscopy: a randomised trial

BACKGROUND

Sedation using intranasal dexmedetomidine is a convenient and well-tolerated technique. This study evaluated the sedative efficacy of intranasal dexmedetomidine in combination with patient-controlled sedation (PCS) for upper gastrointestinal endoscopy.

METHODS

In this double-blind, randomised, controlled trial, 50 patients received either intranasal dexmedetomidine 1.5 μg/kg (dexmedetomidine group) or intranasal saline (placebo group) 1 h before the procedure. PCS with propofol and alfentanil was provided for rescue sedation. Additional sedative consumption, perioperative sedation scores using Observer's Assessment of Alertness/Sedation (OAA/S) scale, recovery, vital signs, adverse events and patient satisfaction were assessed.

RESULTS

Total consumption of PCS propofol and alfentanil was significantly less in the dexmedetomidine than placebo group with a mean difference of -13.8 mg propofol (95% confidence interval -27.3 to -0.3) and -34.5 μg alfentanil (95% confidence interval -68.2 to -0.7) at the completion of the procedure (P = 0.044). Weighted areas under the curve (AUCw ) of OAA/S scores were significantly lower in the dexmedetomidine group before, during and after procedures (P < 0.001, P = 0.024 and P = 0.041 respectively). AUCw of heart rate and systolic blood pressure were also significantly lower during the procedure (P = 0.007 and P = 0.022 respectively) with dexmedetomidine. There was no difference in recovery, side effects or satisfaction.

CONCLUSION

Intranasal dexmedetomidine with PCS propofol and alfentanil confers deeper perioperative clinical sedation with significantly less use of additional sedatives during upper gastrointestinal endoscopy.

Caudal ropivacaine-clonidine: A better post-operative analgesic approach

The aim was to determine qualitative and quantitative aspects of caudal block, haemodynamic effects, and post-operative pain relief of ropivacaine 0.25% versus ropivacaine 0.25% with clonidine for lower abdominal surgeries in paediatric patients. A double-blind study was conducted among 44 paediatric patients in the Department of Anaesthesiology and Intensive Care of our institute. A total of 44 ASA-I paediatric patients between the ages of 1 and 9 years, scheduled for elective hernia surgery, were enrolled in this randomised double-blind study. The caudal block was administered with ropivacaine 0.25% (Group I) and ropivacaine 0.25% and clonidine 2 µg/kg (Group II) after induction with general anaesthesia. Haemodynamic parameters were observed before, during and after the surgical procedure. Post-operative analgesic duration, total dose of rescue analgesia, pain scores and any side effects were looked for and recorded. All the results were tabulated and analysed statistically. The variables in the two groups were compared using the non-parametric tests. For all statistical analyses, the level of significance was P < 0.05. Forty-four patients were enrolled in this study and their data were subjected to statistical analysis: 22 patients in both the groups were comparable with regard to demographic data, haemodynamic parameters and other vitals and were statistically non-significant (P>0.05). The duration of analgesia was significantly prolonged in Group II (P<0.05). The dose requirement for post-operative pain relief was also significantly lesser in Group II. The incidences of side effects were almost comparable and non-significant. A caudal block with 0.25% of isobaric ropivacaine combined with 2 µg/kg of clonidine provides efficient analgesia intra-operatively and prolonged duration of analgesia post-operatively.

Effect of dexmedetomidine on the minimum alveolar concentration of isoflurane in cats

This study reports the effects of dexmedetomidine on the minimum alveolar concentration of isoflurane (MAC(iso) ) in cats. Six healthy adult female cats were used. MAC(iso) and dexmedetomidine pharmacokinetics had previously been determined in each individual. Cats were anesthetized with isoflurane in oxygen. Dexmedetomidine was administered intravenously using target-controlled infusions to maintain plasma concentrations of 0.16, 0.31, 0.63, 1.25, 2.5, 5, 10, and 20 ng/mL. MAC(iso) was determined in triplicate at each target plasma dexmedetomidine concentration. Blood samples were collected and analyzed for dexmedetomidine concentration. The following model was fitted to the concentration-effect data: [Formula in text] where MAC(iso.c) is MAC(iso) at plasma dexmedetomidine concentration C, MAC(iso.0) is MAC(iso) in the absence of dexmedetomidine, I(max) is the maximum possible reduction in MAC(iso), and IC(50) is the plasma dexmedetomidine concentration producing 50% of I(max). Mean ± SE MAC(iso.0), determined in a previous study conducted under conditions identical to those in this study, was 2.07 ± 0.04. Weighted mean ± SE I(max), and IC(50) estimated by the model were 1.76 ± 0.07%, and 1.05 ± 0.08 ng/mL, respectively. Dexmedetomidine decreased MAC(iso) in a concentration-dependent manner. The lowest MAC(iso) predicted by the model was 0.38 ± 0.08%, illustrating that dexmedetomidine alone is not expected to result in immobility in response to noxious stimulation in cats at any plasma concentration.

Sedation in the bariatric patient

Obesity is a significant health problem that has assumed epidemic proportions. A durable reduction in weight and improved morbidity and mortality have been realized with the introduction of various bariatric surgical procedures. It is unknown how safe the current practices of sedation for endoscopic procedures are in bariatric patients. Morbid obesity can result in pulmonary hypertension, obstructive sleep apnea, and restrictive lung disease. This article explores these issues and how they may impact the risk profile of current standards for endoscopic sedation.

Sedation, analgesia, and delirium in the critically ill patient

Most critically ill patients receive a myriad of psychoactive medications during their hospital stay. An understanding of the pharmacology of the more commonly used sedative and analgesic therapies enables the clinician to aptly utilize these medications and limit toxicity. A key to the appropriate provision of sedative and analgesic pharmacotherapy is a thorough patient assessment, use of validated monitoring tools, and defined therapeutic goals. Limiting these therapies while optimizing patient comfort has been shown to reduce the duration of mechanical ventilation and reduce intensive care unit (ICU) and hospital length of stay and should be the aim of the multidisciplinary medical team. This review is intended to provide the reader with a fundamental understanding of how to facilitate comfort of the mechanically ventilated critically ill adult patients and how to minimize medication-related toxicities.

A comparison of dexmedetomidine versus midazolam for sedation, pain and hemodynamic control, during colonoscopy under conscious sedation

OBJECTIVE

The intent of our study was to compare the effects of dexmedetomidine versus midazolam on perioperative hemodynamics, sedation, pain, satisfaction and recovery scores during colonoscopy.

MATERIAL AND METHODS

A total of 60 ASA I-II patients, between 20 and 80 years of age were included in the study. Patients were randomly assigned to two groups. Midazolam 0.05 mg kg(-1) and fentanyl citrate 1 microg kg(-1) were administered intravenously to cases in Group I (n = 30). An initial loading dose of 1 microg kg(-1) dexmedetomidine was administered intravenously in 10 min to cases in Group II (n = 30) before the procedure and as a continuous infusion dose of 0.5 microg kg(-1) h(-1) just before the procedure started. Also 1 microg kg(-1) fentanyl citrate was administered intravenously immediately before the procedure. Peripheral oxygen saturation (S(pO2)), mean arterial pressure (MAP), heart rate (HR), Ramsay Sedation Scale (RSS), Numeric Rating Scale (NRS) scores and colonoscopist satisfaction scores of the cases were recorded.

RESULTS

Although statistically significant values were not detected between the two groups with regard to mean arterial pressure, in Group I heart rates were higher and S(pO2) scores were lower in a statistically significant manner. When the groups were compared with regard to RSS, the RSS scores of Group I at the 10th and 15th minutes were significantly lower than Group II. There was no statistically significant difference between the two groups when compared with regard to NRS scores. Satisfaction scores were significantly lower in Group II.

CONCLUSION

Dexmedetomidine provides more efficient hemodynamic stability, higher Ramsay sedation scale scores, higher satisfaction scores and lower NRS scores in colonoscopies. According to our results we believe that dexmedetomidine can be used safely as a sedoanalgesic agent in colonoscopies.

[Quality of premedication and patient satisfaction after premedication with midazolam, clonidine or placebo : Randomized double-blind study with age-adjusted dosage]

BACKGROUND

Premedication aims at alleviating preoperative anxiety and nervousness and also at minimizing adverse effects. To our knowledge there is no study comparing efficacy and patient satisfaction of different premedications in age-adjusted dosage.

METHODS

In 139 patients anxiety, sedation and adverse effects were measured at 6 consecutive perioperative time points after administration of midazolam, clonidine or a placebo.

RESULTS

Midazolam showed the strongest sedative and anxiolytic effects, clonidine less and placebo none. Clonidine and midazolam reduced the risk of postoperative nausea and vomiting (PONV). Midazolam showed minimal adverse effects and the best patient satisfaction.

CONCLUSION

Midazolam was the most anxiolytic, sedative and favored premedication with the least adverse effects. Most patients would choose midazolam next time.

Procedural sedation and obesity: waters left uncharted

BACKGROUND

Moderate sedation during endoscopy may pose increased risks among obese patients.

OBJECTIVE

To review the literature that considers aspects of sedation within the obese population and to identify gaps in our knowledge.

DESIGN

Literature-based review.

RESULTS

There may be increased risks among obese patients undergoing moderate sedation. In particular, the presence of obstructive sleep apnea may identify a subset of patients at higher risk for complications.

LIMITATIONS

English language literature only.

CONCLUSIONS

Although obesity may be associated with increased risks of procedural sedation, future studies should better clarify such risks to better inform clinical decision making.

Anesthesia for gastrointestinal endoscopic procedures

Traditionally, sedation for gastrointestinal endoscopic procedures was provided by the gastroenterologist. Increasingly, however, complex procedures are being performed on seriously ill patients. As a result, anesthesiologists now are providing anesthesia and sedation in the gastrointestinal endoscopy suite for many of these patients. This article reviews the challenges encountered in this environment and anesthetic techniques that can be used successfully for these procedures.

The effect of the novel alpha-2-adrenoceptor agonist naphthylmedetomidine on pulse rate, arterial blood pressure and sedation in rabbits

OBJECTIVE

The aim of this study was to investigate the effect of a novel alpha-2-adrenoceptor (alpha(2)-AR) agonist, naphthylmedetomidine, on cardiorespiratory function and sedation in rabbits in comparison with medetomidine.

STUDY DESIGN

Prospective, randomized, experimental trial.

ANIMALS

Forty-two chinchilla rabbits of both sexes, weighing 2.5-4.5 kg.

METHODS

The rabbits received 350 microg kg(-1) naphthylmedetomidine (n = 21) or medetomidine (n = 21) intramuscularly according to a randomization scheme. Arterial blood pressure (AP), oxygen saturation of haemoglobin (SpO(2)), pulse rate (PR) and righting reflex were monitored for 20 minutes after injection.

RESULTS

Both drugs significantly decreased PR. The effect of medetomidine was significantly greater than that of naphthylmedetomidine and was evident within 1 minute. The decrease in PR after naphthylmedetomidine administration first appeared after 4 minutes. Medetomidine decreased the SpO(2) after 3 minutes but there was no effect after naphthylmedetomidine. Medetomidine decreased the mean, systolic and diastolic AP within 5 minutes of administration but naphthylmedetomidine had no effect. The mean time to loss of righting reflex was 185 and 714 seconds after the administration of medetomidine and naphthylmedetomidine respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

These results provide the first description of the effects of naphthylmedetomidine on cardiovascular and psychomotor functions in rabbits. Further work is required to reveal the anaesthetic sparing, analgesic or sedative effect of partial naphthylmedetomidine.

Desipramine potentiation of the acute depressant effects of ethanol: modulation by alpha2-adrenoreceptors and stress

Ethanol exerts effects on the brain noradrenergic system, and these are thought to contribute to the sedative/hypnotic (depressant) effects of ethanol. Recent studies suggest that the norepinephrine transporter (NET) plays an important role in modulating ethanol's depressant effects. The aim of the present study was to further characterize this role. Transporter blockers with varying affinity for NET versus the serotonin transporter (desipramine>fluoxetine>citalopram) were tested for their ability to alter ethanol's depressant effects, and for comparison, hypothermic effects. Effects of desipramine on another depressant, pentobarbital, were examined. Desipramine potentiation of ethanol's depressant effects was assessed following depletion of brain norepinephrine via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) treatment, or depletion of brain 5-HT via para-chlorophenylalanine methyl ester hydrochloride (PCPA) treatment. The effects of co-administration of either the selective alpha2-adrenoreceptor agonist (dexmedetomidine) or the selective alpha2-adrenoreceptor antagonist (atipamezole) on desipramine's effect on ethanol's depressant effects were examined. Given the close link between stress, ethanol and norepinephrine, desipramine potentiation of ethanol's depressant effects was tested following repeated forced swim stress. Results showed that desipramine, but not SERT-selective doses of citalopram or fluoxetine, strongly potentiated the depressant (not hypothermic) effects of ethanol. These effects were mimicked by dexmedetomidine and blocked by atipamezole, but not by depletion of either norepinephrine or 5-HT. Desipramine potentiation of ethanol's depressant effects was abolished following repeated stress. Present findings further support a major role for NET and the alpha2-adrenoreceptor in modulating the depressant effects of ethanol, with possible implications for understanding the role of noradrenergic dysfunction in stress-related alcoholism.

The comparison of dexmedetomidine and midazolam used for sedation of patients during upper endoscopy: A prospective, randomized study

The aim of the present prospective, randomized study was to investigate and compare the safety and efficacy of dexmedetomidine versus midazolam in providing sedation for gastroscopy. A total of 50 adult patients (25 patients receiving dexmedetomidine and 25 patients receiving midazolam), 18 to 60 years of age, and rated I and II on the American Society of Anesthesiologists physical status classification system were included. A brief questionnaire was used to collect demographic data; patients were asked to rate anxiety, satisfaction with care to date and expected discomfort on a visual analogue scale. The following parameters were measured continuously and recorded every minute: heart rate, mean arterial pressure, hemoglobin oxygen saturation and respiratory rate. The two groups were similar with regard to age, body mass index, sex, education, duration of endoscopy, and ethanol or tobacco use. After the procedure, full recovery time, mean arterial pressure, heart rate, respiratory rate and hemoglobin oxygen saturation levels were similar in both groups. Both groups also had low levels of perceived procedural gagging, discomfort and anxiety scores (P > 0.05), and high satisfaction levels (90.1+/-3.0 for dexmedetomidine versus 84.9+/-4.5 for midazolam; P > 0.05). Retching and endoscopist satisfaction were significantly different in patients receiving dexmedetomidine versus those receiving midazolam (88.8+/-6.5 versus 73.5+/-16.4, P < 0.05; and 20.6+/-4.4 versus 45.2+/-6.0; P < 0.001). In the midazolam group, the number of patients who had adverse effects was higher than the dexmedetomidine group (P < 0.05). As a result, dexmedetomidine performed as effectively and safely as midazolam when used as a sedative in upper gastroscopy; it was superior to midazolam with regard to retching, rate of side effects and endoscopist satisfaction. It was concluded that dexmedetomidine may be a good alternative to midazolam to sedate patients for upper endoscopy.

Noradrenergic pain modulation

Norepinephrine is involved in intrinsic control of pain. Main sources of norepinephrine are sympathetic nerves peripherally and noradrenergic brainstem nuclei A1-A7 centrally. Peripheral norepinephrine has little influence on pain in healthy tissues, whereas in injured tissues it has variable effects, including aggravation of pain. Its peripheral pronociceptive effect has been associated with injury-induced expression of novel noradrenergic receptors, sprouting of sympathetic nerve fibers, and pronociceptive changes in the ionic channel properties of primary afferent nociceptors, while an interaction with the immune system may contribute in part to peripheral antinociception induced by norepinephrine. In the spinal cord, norepinephrine released from descending pathways suppresses pain by inhibitory action on alpha-2A-adrenoceptors on central terminals of primary afferent nociceptors (presynaptic inhibition), by direct alpha-2-adrenergic action on pain-relay neurons (postsynaptic inhibition), and by alpha-1-adrenoceptor-mediated activation of inhibitory interneurons. Additionally, alpha-2C-adrenoceptors on axon terminals of excitatory interneurons of the spinal dorsal horn possibly contribute to spinal control of pain. At supraspinal levels, the pain modulatory effect by norepinephrine and noradrenergic receptors has varied depending on many factors such as the supraspinal site, the type of the adrenoceptor, the duration of the pain and pathophysiological condition. While in baseline conditions the noradrenergic system may have little effect, sustained pain induces noradrenergic feedback inhibition of pain. Noradrenergic systems may also contribute to top-down control of pain, such as induced by a change in the behavioral state. Following injury or inflammation, the central as well as peripheral noradrenergic system is subject to various plastic changes that influence its antinociceptive efficacy.

Effect of romifidine on the nociceptive withdrawal reflex and temporal summation in conscious horses

OBJECTIVE

To investigate the action of a single IV administration of romifidine on the thresholds of the nociceptive withdrawal reflex (NWR) and temporal summation in conscious horses.

ANIMALS

10 adult horses.

PROCEDURE

Single electrical stimulations were applied on the digital nerves to evoke NWR from the left forelimb and hind limb. Repeated electrical stimulations (10 stimuli, 5 Hz) were given to obtain temporal summation. Surface electromyographic reflex activity was recorded from the common digital extensor and cranial tibial muscles. After baseline assessment of NWR and temporal summation thresholds, romifidine (80 microg x kg(-1), IV) was administered. Successive determinations of NWR and temporal summation thresholds were performed 5, 25, and 55 minutes after administration.

RESULTS

Romifidine significantly increased the current intensities necessary to evoke NWR and temporal summation in forelimbs and hind limbs of horses. Values were significantly higher than baseline values 55 minutes after romifidine administration. After administration of romifidine, a facilitation of reflex components of tactile origin was observed when repeated stimulations were applied.

CONCLUSIONS AND CLINICAL RELEVANCE

Results confirm antinociceptive activity of romifidine and may represent an objective demonstration of the well-known hypersensitivity to tactile stimuli observed in horses receiving alpha2-adrenoreceptor agonists in clinical practice. Romifidine can be included in analgesic and anesthetic protocols to provide additional analgesia in horses.

The role of α2-agonists in neurosurgery

Alpha2-agonists have been extensively used and studied in anaesthesia and intensive care medicine. A list of benefits includes anxiolysis, blood pressure stabilization, analgesia, anaesthetic sparing effects and sedation without respiratory depression or significant cognitive impairment. Fear of inadvertent hypotension, bradycardia or post-operative sedation, and the variability of the haemodynamic response to different doses or rates of administration, have meant that universal acceptance in clinical practice has not yet been seen. Recently, the actions of these agents on the alpha2-adrenoreceptor and the imidazoline receptor have been more accurately identified, helping to explain the differences between the actions of various agents. The two readily available agents, clonidine and dexmedetomidine have already been used in many different anaesthetic situations, for a wide variety of surgical procedures. We believe that both of these alpha2-agonists are useful adjuncts for the management of the neurosurgical patient during surgery, and in the intensive care unit.

Romifidine-Ketamine Anaesthesia in Atropine and Triflupromazine Pre-medicated Buffalo Calves

The study was conducted on 10 buffalo calves with a weight of 98.5 +/- 3.9 kg and age 9.7 +/- 1.3 months. Ten trials of two treatments were carried out using a randomized block design. Atropine at the dose of 0.02 mg/kg bodyweight was administered in both the groups. The animals of group I received romifidine at the dose of 10 microg/kg i.v., 10 min after atropine administration, whereas, animals of group II received triflupromazine at the dose of 0.3 mg/kg i.m. and 10 min later romifidine at the dose of 10 microg/kg i.v. immediately followed by ketamine at the dose of 5 mg/kg i.v. The onset of action of romifidine in group I occurred within 2 min and the animals remained under mild sedation for 31 +/- 4.8 min. In group II, the triflupromazine-romifidine-ketamine combination induced anaesthesia for 14 +/- 2.3 min. Hypothermia, significant bradycardia and respiratory depression was noticed in both groups at different time intervals.

Clonidine as a pre-anesthetic agent for flexible bronchoscopy

Several drugs have been employed for sedation during flexible fiberoptic bronchoscopy (FOB). Clonidine attenuates stress-induced sympathoadrenal responses and has sedative properties. We investigate the effects of clonidine premedication on hemodynamic and comfort parameters of patients submitted to FOB under airway topical anesthesia only. Patients received placebo (n = 22; men = 16; median age = 50.5 years) or intravenous clonidine (3 microg/kg; n = 20; men = 15; median age = 46.0 years) 15 min before FOB. Blood pressure (BP), heart rate (HR), plasma norepinephrine (nor) and cortisol levels were measured before, during, and 1 h after FOB. Comfort was assessed by the examiner and by the patients using a visual numerical scale (0-10). The placebo group showed significant increases in systolic BP, HR, and nor levels during FOB (SBP = 125 mmHg x 145 mmHg; HR = 74 bpm x 85 bpm; nor = 316.2 pg/dl x 483.1 pg/dl), whereas clonidine group did not display such changes. Clonidine group showed a lower frequency of cardiac arrhythmias than the placebo group during and after FOB (supraventricular = 39% x 50%; ventricular = 22% x 40%). Levels of comfort were high and comparable in both groups. We concluded that although clonidine led to a somewhat better hemodynamic profile, it did not contribute to better comfort in this setting.

Effect of Oral Tizanidine on Local-anesthetic Infiltration Pain during Epidural Catheterization

PURPOSE

Tizanidine is a clonidine derivative and has the same effects, such as sedation, anxiolysis and analgesic response. We evaluated the effect of tizanidine on infiltration pain during epidural catheterization.

METHODS

Forty patients scheduled to undergo epidural anesthesia in elective surgery were randomly allocated into two groups. The control group received placebo 60 minutes before arrival in the operating room, and the tizanidine group received 3 mg of oral tizanidine as premedication 60 minutes before arrival in the operating room. Every patient was measured heart rate and blood pressure before receiving placebo or premedication and after arrival in the operating room. After an epidural catheter was indwelled, the patients were questioned about the infiltrating pain of local anesthetic, and the degree was assessed by means of visual analog scale score (VAS score, 0 to approximately 100 mm).

RESULTS

Blood pressure in the operating room was significantly attenuated in the tizanidine group compared to the control group (148 +/- 21 mmHg vs 130 +/- 15 mmHg). Heart rate was not significantly different between the two groups. Rate-pressure product was significantly lower in the tizanidine group (11282 +/- 2960 vs 9592 +/- 2632). VAS score in the tizanidine group was significantly lower than that in the control group (P <0.001).

CONCLUSION

It was possible to reduce the infiltration pain of local anesthetic during epidural catheterization by oral administration of 3 mg of tizanidine as premedication. Blood pressure and rate-pressure product in the operating room were also attenuated by receiving tizanidine. Therefore, we recommend premedication with tizanidine for patients undergoing epidural catheterization.

Regional distribution of alpha(2C)-adrenoceptors in brain and spinal cord of control mice and transgenic mice overexpressing the alpha(2C)-subtype: an autoradiographic study with [(3)H]RX821002 and [(3)H]rauwolscine

Behavioral studies on gene-manipulated mice have started to elucidate the neurobiological functions of the alpha(2C)-adrenoceptor (AR) subtype. In this study, we applied quantitative receptor autoradiography to investigate the potential anatomical correlates of the observed functional effects of altered alpha(2C)-AR expression. Labeling of brain and spinal cord sections with the subtype non-selective alpha(2)-AR radioligand [(3)H]RX821002 and the alpha(2C)-AR-preferring ligand [(3)H]rauwolscine revealed distinct binding-site distribution patterns. In control mice, [(3)H]rauwolscine binding was most abundant in the olfactory tubercle, accumbens and caudate putamen nuclei, and in the CA1 field of the hippocampus. A mouse strain with overexpression of alpha(2C)-AR regulated by a gene-specific promoter showed approximately two- to four-fold increased levels of [(3)H]rauwolscine binding in these regions. In addition, dramatic increases in [(3)H]rauwolscine binding were seen in the nerve layer of the olfactory bulb, the molecular layer of the cerebellum, and the ventricular system of alpha(2C)-AR-overexpressing mice, representing "ectopic" alpha(2C)-AR expression. Competition-binding experiments with several alpha(2)-AR ligands confirmed the alpha(2C)-AR identity of these sites. Our results provide quantitative evidence of the predominance of the alpha(2A)-AR subtype in most regions of the mouse CNS, but also disclose the wide distribution of alpha(2C)-AR in the normal mouse brain, although at relatively low density, except in the ventral and dorsal striatum and the hippocampal CA1 area. alpha(2C)-AR are thus present in brain regions involved in the processing of sensory information and in the control of motor and emotion-related activities such as the accumbens and caudate putamen nuclei, the olfactory tubercle, the lateral septum, the hippocampus, the amygdala, and the frontal and somatosensory cortices. The current results may help in specifying an anatomical framework for the functional roles of the alpha(2A)- and alpha(2C)-AR subtypes in the mouse CNS.

New agents for sedation in the intensive care unit

Several advances are likely to benefit the ICU patient requiring sedation, analgesia, and anxiolysis. The cooperative sedation induced by dexmedetomidine is a unique and valuable state that allows patients to be aroused easily and interferes little with ventilation. Remifentanil is the prototype of short-acting drugs, providing fast onset and offset; its relatively high cost may be balanced by limiting the risk for long-lasting respiratory depression. Lorazepam seems to be finding more proponents, especially in long-term ICU sedation where the costs of the newer agents may be prohibitive.

Chronic subordination stress in male tree shrews: replacement of testosterone affects behavior and central alpha(2)-adrenoceptors

Subordination stress induced by social defeat in male animals is known to inhibit gonadal functions and it has been discussed whether the resulting deficit in testosterone might play a role in subordination behavior. One of the major transmitter systems involved in regulation of behavior is the noradrenergic system. To analyze whether a testosterone replacement can alter subordination behavior and whether this might be related to changes in the brain noradrenergic system, we quantified alpha(2)-adrenoceptors (alpha(2)-ARs) in the central nervous system of male tree shrews. Animals were submitted to chronic subordination stress and received testosterone at the same time. Behavior was monitored during all phases of the experiment: the control period of 10 days, the period of social stress lasting 10 days when subordinates were confronted daily with a dominant male, and, subsequently, the stress and treatment period of 18 days when in parallel to the stress, animals received either injections of testosterone or vehicle. Brain alpha(2)-ARs were quantified by in vitro receptor autoradiography using the antagonist ligand (3)H-RX821002. Locomotor activity decreased significantly during the stress period and was not re-normalized by testosterone. In contrast, testosterone re-normalized scent marking behavior and autogrooming, parameters that had both been reduced due to the subordination stress. Vehicle injections improved none of these behaviors. In 8 of 10 brain regions that were analyzed, numbers of alpha(2)-adrenergic binding sites were increased in stressed animals that received vehicle injections, but a difference between testosterone and vehicle injected animals was only observed in five regions. These brain regions are all known to be involved in emotional behavior (anterior hypothalamus, medial nucleus of the amygdala, cingulate cortex) or autonomic regulation, respectively (solitary tract nucleus, dorsal motor nucleus of vagus). Therefore, our data show that testosterone influences behavior of male subordinates and modulates alpha(2)-AR expression in their brains. Androgen-mediated alterations in receptors occur in brain regions that are known to be involved in emotionality, e.g., in the anterior hypothalamus which regulates aggressive behavior. One can therefore conclude that alpha(2)-ARs contribute to neuronal functions that are responsible for subordination of stress behavior, and that testosterone-induced receptor changes are related to the partial restoration of normal behavior.

Sedation in outpatient bronchoscopy

Bronchoscopy is a procedure that is likely to provoke anxiety as the patient is surrounded by monitoring and bronchoscopy equipment, and care is administered by strangers who perform intimate, invasive, and sometimes, painful procedures. Sedation is needed, therefore, to allay anxiety and reduce stress, improve patient comfort and co-operation, provide amnesia and facilitate the bronchoscopic procedure. In this review we try to summarize the current knowledge on currently used sedation protocols with special reference to the commonly used pharmacological agents. We believe sedation should be used routinely in fiberoptic bronchoscopy in order to achieve a safe and pleasant procedure for both the patient and the pulmonologist.

The effect of clonidine premedication on hemodynamic responses to microlaryngoscopy and rigid bronchoscopy

The usual hemodynamic response to laryngoscopy and bronchoscopy is an increase in heart rate and arterial blood pressure. Previous work has reported that 10%-18% of the patients develop ischemic ST segment changes during the procedure. Therefore, we performed a prospective, randomized, double-blinded study in 36 patients scheduled for elective microlaryngeal and bronchoscopic surgical procedures to evaluate the effects of 300-microg oral clonidine premedication (n = 18) or placebo (n = 18) on the hemodynamic alterations and the incidence of perioperative myocardial ischemic episodes. Myocardial ischemia was assessed by using continuous electrocardiographic monitoring, beginning 30 min before, and lasting until 24 h after the operation. During the procedure, patients receiving placebo exhibited a significant increase (mean +/- SD) in arterial blood pressure (the systolic increasing from 137+/-11 to 166+/-17 mm Hg, the diastolic increasing from 80+/-11 to 97+/-14 mm Hg) and heart rate (increasing from 79+/-15 to 97+/-12 bpm) compared with the baseline and with the clonidine group. A dose of 300-microg clonidine blunted the hemodynamic response to endoscopy. Ventricular arrhythmias were more frequent in patients who were not premedicated with clonidine. Two patients in the control group, but none in the clonidine group, had evidence of myocardial ischemia. These data should encourage routine premedication with clonidine in patients undergoing microlaryngoscopic and bronchoscopic procedures.

The TASK-1 two-pore domain K+ channel is a molecular substrate for neuronal effects of inhalation anesthetics

Despite widespread use of volatile general anesthetics for well over a century, the mechanisms by which they alter specific CNS functions remain unclear. Here, we present evidence implicating the two-pore domain, pH-sensitive TASK-1 channel as a target for specific, clinically important anesthetic effects in mammalian neurons. In rat somatic motoneurons and locus coeruleus cells, two populations of neurons that express TASK-1 mRNA, inhalation anesthetics activated a neuronal K(+) conductance, causing membrane hyperpolarization and suppressing action potential discharge. These membrane effects occurred at clinically relevant anesthetic levels, with precisely the steep concentration dependence expected for anesthetic effects of these compounds. The native neuronal K(+) current displayed voltage- and time-dependent properties that were identical to those mediated by the open-rectifier TASK-1 channel. Moreover, the neuronal K(+) channel and heterologously expressed TASK-1 were similarly modulated by extracellular pH. The decreased cellular excitability associated with TASK-1 activation in these cell groups probably accounts for specific CNS effects of anesthetics: in motoneurons, it likely contributes to anesthetic-induced immobilization, whereas in the locus coeruleus, it may support analgesic and hypnotic actions attributed to inhibition of those neurons.

Antagonism of antinociception produced by intrathecal clonidine by ketorolac in the rat: the role of the opioid system

The management of severe pain may require "balanced analgesia," involving the use of analgesics with different modes of action. Clonidine, an alpha(2)-adrenoreceptor agonist produces analgesia by itself as well as when given with morphine and local anesthetics. Ketorolac is indicated for the management of moderately severe acute pain and causes analgesia equivalent to morphine. This study was designed to investigate whether the addition of ketorolac promotes antinociception produced by intrathecal administration of clonidine in male Sprague-Dawley rats. Intrathecal injection of clonidine (1-30 microg) induced a dose-dependent increase in antinociception as measured by the tail flick (TF) and hot plate tests. Ketorolac alone (150-600 microg) increased the antinociception by 50%-60% only in the TF test. Ketorolac (10 microg) decreased clonidine (10 microg)-induced antinociception from 69.1% +/- 7.8% to 23.5% +/- 1. 6% (P < 0.05) in the TF test and 35.7% +/- 4.7% to 4.5% +/- 0.1% (P < 0.05) maximum possible effect in the hot plate test. Ketorolac also antagonized the effect of 30 microg of clonidine. The opioid receptor antagonist naloxone antagonized the antinociceptive effect of clonidine and ketorolac, indicating the involvement of the opioid system in the antinociception produced by clonidine or ketorolac. However, neither clonidine nor ketorolac (10(-8) to 10(-3) M) inhibited the binding of specific ligands to mu-, delta-, and kappa-opioid receptors, indicating a lack of direct interaction of clonidine and ketorolac with opioid receptors. These results suggest that intrathecal injection of ketorolac antagonizes the antinociception produced by clonidine.

Effect of clonidine premedication on haemodynamic responses to fibreoptic bronchoscopy

The usual haemodynamic response to fibreoptic bronchoscopy is an increase in heart rate and blood pressure. We therefore compared, in a prospective, randomised, double-blind study, the effect of two doses of oral clonidine premedication (150 microg or 300 microg) with placebo (control group) on the haemodynamic alterations in 62 patients who underwent elective fibreoptic bronchoscopy. Significant increases in blood pressure and heart rate were observed during fibreoptic bronchoscopy only in the control group. Clonidine 150 microg blunted the haemodynamic response to fibreoptic bronchoscopy (p < 0.05). Significant decreases in systolic blood pressure (< 90 mmHg) were observed in all patients premedicated with 300 microg clonidine. Throughout the study nine patients (75%) in the 300 microg clonidine group were treated at least once for hypotension. Compared with the control group, time to awakening was significantly longer only in patients premedicated with 300 microg clonidine. In conclusion, premedication with 150 microg oral clonidine attenuates haemodynamic responses to fibreoptic bronchoscopy, without causing excessive haemodynamic depression and sedation. These data encourage the administration of clonidine as premedication in patients undergoing fibreoptic bronchoscopy, particularly in those with, or at risk for, coronary artery disease.

Regulation of monoamine receptors in the brain: dynamic changes during stress

Monoamine receptors are membrane-bound receptors that are coupled to G-proteins. Upon stimulation by agonists, they initiate a cascade of intracellular events that guide biochemical reactions of the cell. In the central nervous system, they undergo diverse regulatory processes, among which are receptor desensitization, internalization into the cell, and downregulation. These processes vary among different types of monoamine receptors. alpha 2-Adrenoceptors are often downregulated by agonists, and beta-adrenoceptors are internalized rapidly. Others, such as serotonin1A-receptors, are controlled tightly by steroid hormones. Expression of these receptors is reduced by the "stress hormones" glucocorticoids, whereas gonadal hormones such as testosterone can counterbalance the glucocorticoid effects. Because of this, the pattern of monoamine receptors in certain brain regions undergoes dynamic changes when there are elevated concentrations of agonists or when the hormonal milieu changes. Stress is a physiological situation accompanied by the high activity of brain monoaminergic systems and dramatic changes in peripheral hormones. Resulting alterations in monoamine receptors are considered to be in part responsible for changes in the behavior of an individual.

Effects of cortisol on brain alpha2-adrenoceptors: potential role in stress

It has been proposed that behavioural changes induced by chronic psychosocial stress in male tree shrews might be related to alterations in the central nervous alpha2-adrenoceptor system. In the noradrenergic centres of the brain, alpha2-adrenoceptors function as autoreceptors regulating noradrenaline release. Chronic stress downregulates these receptors in several brain regions. Since during stress, the activity of the hypothalamus-pituitary-adrenal axis is increased leading to high concentrations of plasma glucocorticoids, we investigated whether the effects of chronic stress can be mimicked by cortisol treatments. Two experiments were performed: a short-term treatment (males were injected i.v. with 1.5 mg cortisol and brains were dissected 2 h later) and a long-term treatment (animals received the hormone in their drinking water for 5 days; daily uptake 3-7 mg). The short-term treatment (injection), similar to the stress effects, downregulated alpha2-adrenoceptors in several brain regions. In contrast, the long-term oral treatment induced regional receptor upregulation. These data show: (i) that glucocorticoids regulate alpha2-adrenoceptors in the brain; (ii) that the duration and/or the route of cortisol application determines the results: and (iii) that chronic stress effects are not only due to the long-term glucocorticoid exposure, but also to other elements of the stress response.