Respiratory effects of clonidine alone and combined with morphine, in humans

Risk assessment and optimization strategies to reduce perioperative respiratory adverse events in Pediatric Anesthesia-Part 2: Anesthesia-related risk and treatment options

Perioperative respiratory adverse events are the most common cause of critical events in children undergoing anesthesia and surgery. While many risk factors remain unmodifiable, there are numerous anesthetic management decisions which can impact the incidence and impact of these events, especially in at-risk children. Ongoing research continues to improve our understanding of both the influence of risk factors and the effect of specific interventions. This review discusses anesthesia risk factors and outlines strategies to reduce the rate and impact of perioperative respiratory adverse events with a chronologic based inquiry into anesthetic management decisions through the perioperative period from premedication to postoperative disposition.

Pharmacological Management of Paroxysmal Sympathetic Hyperactivity: A Scoping Review

Paroxysmal sympathetic hyperactivity (PSH) occurs in ∼10% of patients following acute severe brain injury. While PSH is associated with worse outcomes, there are no clinical practice guidelines to inform treatment. We aimed to systematically review the literature on the pharmacological management of PSH. MEDLINE, Embase, and Cochrane library databases were searched from inception to August 2020. Eligible studies met the following criteria: 1) randomized controlled trials, non-randomized controlled trials (case control or controlled cohort), observational studies, case series, and case reports; 2) study population of adult and pediatric patients; 3) exposure to an acute neurological insult complicated by PSH (or historic synonym); 4) description of pharmacological treatment of PSH. Our search retrieved 2729 citations with 83 articles assessed for inclusion. After full text extraction, 56 manuscripts inclusive of 459 patients met eligibility criteria. We identified 31 case reports, 15 case series (152 patients), seven retrospective case control or cohort studies (212 patients), and three prospective observational studies (52 patients). Traumatic brain injury was the most common precipitating insult (407 patients), followed by hypoxic encephalopathy (72 patients) and intracranial hemorrhage (10 patients). There were 48 drugs from 22 classes prescribed for the management of PSH. The most frequently prescribed agents were benzodiazepines, β-blockers, opioids, α-2 agonists, and baclofen. However, route and dose of drug and subsequent outcome were inconsistently reported, such that no summary was possible. While a wide variety of drugs have been reported to treat PSH, there is a lack of even moderate-quality evidence to inform clinical decision making.

Safety of clonidine used for long-term sedation in paediatric intensive care: A systematic review

AIM

Although not approved, the α-adrenoceptor agonist clonidine is considered an option for long-term sedation protocols in paediatric intensive care. We reviewed adverse effects of clonidine occurring in this indication.

METHODS

Relevant literature was systematically identified from PubMed and Embase. We included interventional and observational studies on paediatric patients admitted to intensive care units and systemically long-term sedated with clonidine-containing regimes. In duplicates, we conducted standardised and independent full-text assessment and extraction of safety data.

RESULTS

Data from 11 studies with 909 patients were analysed. The studies were heterogeneous regarding patient characteristics (age groups, comorbidity, or comedication) and sedation regimes (dosage, route, duration, or concomitant sedatives). Just four randomised controlled trials (RCTs) and one observational study had comparison groups, using placebo or midazolam. For safety outcomes, our validity evaluation showed low risk of bias only in three studies. All studies focused on haemodynamic problems, particularly bradycardia and hypotension. Observed incidences or subsequent interventions never caused concerns. However, only two RCTs allowed meaningful comparisons with control groups. Odds ratios showed no significant difference between the groups, but small sample sizes (50 and 125 patients) must be considered; pooled analyses were not reasonable.

CONCLUSION

All evaluated studies concluded that the use of clonidine in paediatric intensive care units is safe. However, a valid characterisation of the safety profile remains challenging due to limited, biased and heterogeneous data and missing investigation of long-term effects. This evaluation demonstrates the lack of data, which prevents reliable conclusions on the safety of clonidine for long-term sedation in critically ill children. For an evidence-based use, further studies are needed.

Clinical Practice: Should we Radically Alter our Sedation of Critical Care Patients, Especially Given the COVID-19 Pandemics?

The high number of patients infected with the SARS-CoV-2 virus requiring care for ARDS puts sedation in the critical care unit (CCU) to the edge. Depth of sedation has evolved over the last 40 years (no-sedation, deep sedation, daily emergence, minimal sedation, etc.). Most guidelines now recommend determining the depth of sedation and minimizing the use of benzodiazepines and opioids. The broader use of alpha-2 adrenergic agonists ('alpha-2 agonists') led to sedation regimens beginning at admission to the CCU that contrast with hypnotics+opioids ("conventional" sedation), with major consequences for cognition, ventilation and circulatory performance. The same doses of alpha-2 agonists used for 'cooperative' sedation (ataraxia, analgognosia) elicit no respiratory depression but modify the autonomic nervous system (cardiac parasympathetic activation, attenuation of excessive cardiac and vasomotor sympathetic activity). Alpha-2 agonists should be selected only in patients who benefit from their effects ('personalized' indications, as opposed to a 'one size fits all' approach). Then, titration to effect is required, especially in the setting of systemic hypotension and/or hypovolemia. Since no general guidelines exist for the use of alpha-2 agonists for CCU sedation, our clinical experience is summarized for the benefit of physicians in clinical situations in which a recommendation might never exist (refractory delirium tremens; unstable, hypovolemic, hypotensive patients, etc.). Because the physiology of alpha-2 receptors and the pharmacology of alpha-2 agonists lead to personalized indications, some details are offered. Since interactions between conventional sedatives and alpha-2 agonists have received little attention, these interactions are addressed. Within the existing guidelines for CCU sedation, this article could facilitate the use of alpha-2 agonists as effective and safe sedation while awaiting large, multicentre trials and more evidence-based medicine.

Postoperative Analgesia in Neonates and Infants Using Epidural Chloroprocaine and Clonidine

INTRODUCTION

In neonates and infants, epidural analgesia has gained popularity as a means of providing postoperative analgesia, limiting opioid-related adverse effects and improving the postoperative course. In addition to a local anesthetic agent, adjunctive agents may be added to further augment analgesia. Clonidine is an α2-adrenergic agonist that is frequently added to single-shot caudal analgesia, but there are limited data regarding its use in a continuous epidural infusion, especially in patients ≤12 months of age.

METHODS

We retrospectively reviewed the hospital records of neonates and infants who received postoperative epidural infusions with 2-chloroprocaine, and clonidine was identified over a 4-year period.

RESULTS

The study cohort included 52 neonates and infants ranging in age from 0 to 12 months and in weight from 2.1 to 10.1 kilograms. The catheters were dosed with either 1.5% 2-chloroprocaine (n=47) or 3% 2-chloroprocaine (n=5) with clonidine (median concentration 0.2 µg/mL) infused at a median rate of 0.72 mL/kg/hour. Pain scores were uniformly ≤3 at all evaluation points during the first 72 postoperative hours with a limited need for supplemental systemic opioids. No serious adverse effects were noted.

CONCLUSION

With the recognized limitations of a retrospective study, these preliminary data demonstrate the safety of adding clonidine to an epidural infusion of 2-chloroprocaine in neonates and infants less than 12 months of age. Future studies are needed to determine its analgesic efficacy compared to 2-chloroprocaine alone and the optimal clonidine concentration for postoperative epidural infusions.

A Comparative Study of Midazolam Alone or in Combination with Dexmedetomidine or Clonidine for Awake Fiberoptic Intubation

Background:

Awake fiberoptic intubation (AFOI) is the gold standard technique for managing patients with anticipated difficult airway. Conscious sedation is desirable, not only to make the procedure more tolerable and comfortable for the patient but also to ensure optimal intubating conditions. Ideal sedation regime for AFOI should provide comfort, cooperation, hemodynamic stability, and amnesia along with maintenance of spontaneous respiration. Several sedative agents have been assessed over the past two decades for this purpose but α2 agonists appear to be the favorable choice owing to its sedative, analgesic, amnestic, and sympatholytic properties along with good hemodynamic profile.

Aims:

The present study has been aimed to recognize the characteristics of dexmedetomidine, clonidine, and midazolam and to compare their efficacy in providing optimal intubating conditions as well as hemodynamic stability during AFOI.

Settings and Design:

A prospective double-blind randomized study done in tertiary care hospital.

Materials and Methods:

Sixty patients of American Society of Anesthesiologists physical status Classes I and II aged 18–60 years with anticipated difficult airway were randomly allocated into three groups. All the patients received injection midazolam bolus followed by sedation infusion of midazolam, dexmedetomidine, and clonidine according to the allocated group. Primary outcome includes the time to achieve Ramsay Sedation Score (RSS) ≥2, time taken in intubation, intubation score, comfort score for fiberoptic insertion and intubation, and patient tolerance after intubation. The secondary outcome was hemodynamic, and respiratory variables include changes in heart rate (HR), mean arterial pressure (MAP), oxygen saturation (SpO₂), and respiratory rate during the procedure.

Statistical Analysis:

All data were recorded, summarized, tabulated, and statistically analyzed using SPSS 16.0 version (Chicago, Inc., USA). The data were presented in mean ± standard deviation. P < 0.05 was considered as statistically significant.

Results:

All the three groups were comparable in terms of demographic profile. Time to achieve RSS ≥2 and mean intubation time was significantly less in Groups D and C as compared to Group M (P < 0.001). Among groups, Group D took least time to achieve RSS ≥2 (5.53 ± 0.74) and mean intubation time (4.53 ± 0.91). Similarly, overall intubation score, comfort, and patient tolerance score were significantly more in Group M as compared to Groups D and C (P < 0.001). Among the groups, Group D achieved least intubation score (3.80 ± 0.67) and comfort score (2.53 ± 0.74). Although Groups D and C have a lower mean HR and MAP during the procedure and intubation compared to Group M, the incidence of SpO₂ is most frequent with clonidine.

Conclusions:

Patients who received α2 agonist were calmer and cooperative with less pain and discomfort than the patients who received midazolam. Dexmedetomidine allows better endurance, stable hemodynamics, and patent airway as compared to clonidine.

Psychotropic drug therapy in patients in the intensive care unit - usage, adverse effects, and drug interactions: a review

Managing psychological problems in patients admitted to intensive care unit (ICU) is a big challenge, requiring pharmacological interventions. On the other hand, these patients are more prone to side effects and drug interactions associated with psychotropic drugs use. Benzodiazepines (BZDs), antidepressants, and antipsychotics are commonly used in critically ill patients. Therefore, their therapeutic effects and adverse events are discussed in this study. Different studies have shown that non-BZD drugs are preferred to BZDs for agitation and pain management, but antipsychotic agents are not recommended. Also, it is better not to start antidepressants until the patient has fully recovered. However, further investigations are required for the use of psychotropic drugs in ICUs.

Building on the Shoulders of Giants: Is the use of Early Spontaneous Ventilation in the Setting of Severe Diffuse Acute Respiratory Distress Syndrome Actually Heretical?

Acute respiratory distress syndrome (ARDS) is not a failure of the neurological command of the ventilatory muscles or of the ventilatory muscles; it is an oxygenation defect. As positive pressure ventilation impedes the cardiac function, paralysis under general anaesthesia and controlled mandatory ventilation should be restricted to the interval needed to control the acute cardio-ventilatory distress observed upon admission into the critical care unit (CCU; "salvage therapy" during "shock state"). Current management of early severe diffuse ARDS rests on a prolonged interval of controlled mechanical ventilation with low driving pressure, paralysis (48 h, too often overextended), early proning and positive end-expiratory pressure (PEEP). Therefore, the time interval between arrival to the CCU and switching to spontaneous ventilation (SV) is not focused on normalizing the different factors involved in the pathophysiology of ARDS: fever, low cardiac output, systemic acidosis, peripheral shutdown (local acidosis), supine position, hypocapnia (generated by hyperpnea and tachypnea), sympathetic activation, inflammation and agitation. Then, the extended period of controlled mechanical ventilation with paralysis under general anaesthesia leads to CCU-acquired pathology, including low cardiac output, myoneuropathy, emergence delirium and nosocomial infection. The stabilization of the acute cardio-ventilatory distress should primarily itemize the pathophysiological conditions: fever control, improved micro-circulation and normalized local acidosis, 'upright' position, minimized hypercapnia, sympathetic de-activation (normalized sympathetic activity toward baseline levels resulting in improved micro-circulation with alpha-2 agonists administered immediately following optimized circulation and endotracheal intubation), lowered inflammation and 'cooperative' sedation without respiratory depression evoked by alpha-2 agonists. Normalised metabolic, circulatory and ventilatory demands will allow one to single out the oxygenation defect managed with high PEEP (diffuse recruitable ARDS) under early spontaneous ventilation (airway pressure release ventilation+SV or low-pressure support). Assuming an improved overall status, PaO₂/FiO₂≥150-200 allows for extubation and continuous non-invasive ventilation. Such fast-tracking may avoid most of the CCU-acquired pathologies. Evidence-based demonstration is required.

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

The Role of the α2-Adrenoceptor Agonist Dexmedetomidine in Postsurgical Sedation in the Intensive Care Unit

Dexmedetomidine was evaluated for sedation of 401 postsurgical patients in this double-blind, randomized, placebocontrolled, multicenter trial. Dexmedetomidine or saline was started on arrival in the intensive care unit (ICU) (1.0 mcg/kg for 10 minutes), then titrated at 0.2 to 0.7 mcg/kg/h to effect. Patients could be given propofol if necessary. Morphine was administered for pain. Sixty percent of the dexmedetomidine patients required no other sedative to maintain an RSS ≥ 3; 21% required < 50 mg propofol. In contrast, 76% of the control group received propofol; 59% required ≥ 50 mg. Dexmedetomidine patients required significantly less morphine for pain relief (P < .001). Continuously given throughout the ICU stay, dexmedetomidine had no effect on respiratory rate, oxygen saturation, duration of weaning, or times to extubation. Nurses judged the dexmedetomidine patients were easier to manage. Later, fewer dexmedetomidine patients remembered pain or discomfort. The majority of dexmedetomidine patients maintained blood pressures within normal range, without rebound. Hypertension, atelectasis, and rigors occurred more frequently in the control group, while hypotension and bradycardia occurred more frequently in the dexmedetomidine group. Preoperative cardiovascular conditions were not risk factors for dexmedetomidine patients.

Comparison of lumbar epidural bupivacaine with fentanyl or clonidine for postoperative analgesia in children with cerebral palsy after single-event multilevel surgery

AIM

To compare diazepam use, muscle spasm, analgesia, and side effects when clonidine or fentanyl are added to epidural bupivacaine in children with cerebral palsy after multilevel orthopaedic surgery.

METHOD

Fifty children were prospectively randomized to receive clonidine (n=24, mean age 10y 10mo [SD 2y 11mo]) or fentanyl (n=26, mean age 10y 11mo [SD 2y 10mo]).

RESULTS

There was no difference in primary outcome measures: median diazepam use (fentanyl 0, interquartile range [IQR] 0-0; clonidine 0, IQR 0-0; p=0.46), any muscle spasm (no muscle spasms in: fentanyl, 36%; clonidine, 62%; p=0.11), painful muscle spasm (fentanyl 40%; clonidine 25%; p=0.46), or pain score ≥6 (none: fentanyl 44%; clonidine 42%; p=0.29). There were differences in secondary outcome measures: no vomiting (clonidine 63%; fentanyl 20%); vomiting occurred more frequently with fentanyl (32% vomited more than three times; clonidine none; p=0.001). Fentanyl resulted in more oxygen desaturation (at least two episodes: fentanyl 20%; clonidine 0; p<0.001). Clonidine resulted in lower mean (SD) area under the curve for systolic blood pressure (fentanyl 106.5 [11.0]; clonidine 95.7mmHg [7.9]) and heart rate (fentanyl 104.9 beats per minute [13.6]; clonidine 85.3 [11.5]; p<0.001).

INTERPRETATION

Clonidine and fentanyl provide adequate analgesia with low rates of muscle spasm, resulting in low diazepam use. The choice of epidural additive should be based upon the most tolerable side-effect profile.

Alpha-2 agonists for long-term sedation during mechanical ventilation in critically ill patients

BACKGROUND

Sedation reduces patient levels of anxiety and stress, facilitates the delivery of care and ensures safety. Alpha-2 agonists have a range of effects including sedation, analgesia and antianxiety. They sedate, but allow staff to interact with patients and do not suppress respiration. They are attractive alternatives for long-term sedation during mechanical ventilation in critically ill patients.

OBJECTIVES

To assess the safety and efficacy of alpha-2 agonists for sedation of more than 24 hours, compared with traditional sedatives, in mechanically-ventilated critically ill patients.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, Issue 10, 2014), MEDLINE (1946 to 9 October 2014), EMBASE (1980 to 9 October 2014), CINAHL (1982 to 9 October 2014), Latin American and Caribbean Health Sciences Literature (1982 to 9 October 2014), ISI Web of Science (1987 to 9 October 2014), Chinese Biological Medical Database (1978 to 9 October 2014) and China National Knowledge Infrastructure (1979 to 9 October 2014), the World Health Organization international clinical trials registry platform (to 9 October 2014), Current Controlled Trials metaRegister of controlled trials active registers (to 9 October 2014), the ClinicalTrials.gov database (to 9 October 2014), the conference proceedings citation index (to 9 October 2014) and the reference lists of included studies and previously published meta-analyses and systematic reviews for relevant studies. We imposed no language restriction.

SELECTION CRITERIA

We included all randomized and quasi-randomized controlled trials comparing alpha-2 agonists (clonidine or dexmedetomidine) versus alternative sedatives for long-term sedation (more than 24 hours) during mechanical ventilation in critically ill patients.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study quality and extracted data. We contacted study authors for additional information. We performed meta-analyses when more than three studies were included, and selected a random-effects model due to expected clinical heterogeneity. We calculated the geometric mean difference for continuous outcomes and the risk ratio for dichotomous outcomes. We described the effects by values and 95% confidence intervals (CIs). We considered two-sided P < 0.05 to be statistically significant.

MAIN RESULTS

Seven studies, covering 1624 participants, met the inclusion criteria. All included studies investigated adults and compared dexmedetomidine with traditional sedatives, including propofol, midazolam and lorazepam. Compared with traditional sedatives, dexmedetomidine reduced the geometric mean duration of mechanical ventilation by 22% (95% CI 10% to 33%; four studies, 1120 participants, low quality evidence), and consequently the length of stay in the intensive care unit (ICU) by 14% (95% CI 1% to 24%; five studies, 1223 participants, very low quality evidence). There was no evidence that dexmedetomidine decreased the risk of delirium (RR 0.85; 95% CI 0.63 to 1.14; seven studies, 1624 participants, very low quality evidence) as results were consistent with both no effect and appreciable benefit. Only one study assessed the risk of coma, but lacked methodological reliability (RR 0.69; 95% CI 0.55 to 0.86, very low quality evidence). Of all the adverse events included, the most commonly reported one was bradycardia, and we observed a doubled (111%) increase in the incidence of bradycardia (RR 2.11; 95% CI 1.39 to 3.20; six studies, 1587 participants, very low quality evidence). Our meta-analysis provided no evidence that dexmedetomidine had any impact on mortality (RR 0.99; 95% CI 0.79 to 1.24; six studies, 1584 participants, very low quality evidence). We observed high levels of heterogeneity in risk of delirium (I² = 70%), but due to the limited number of studies we were unable to determine the source of heterogeneity through subgroup analyses or meta-regression. We judged six of the seven studies to be at high risk of bias.

AUTHORS' CONCLUSIONS

In this review, we found no eligible studies for children or for clonidine. Compared with traditional sedatives, long-term sedation using dexmedetomidine in critically ill adults reduced the duration of mechanical ventilation and ICU length of stay. There was no evidence for a beneficial effect on risk of delirium and the heterogeneity was high. The evidence for risk of coma was inadequate. The most common adverse event was bradycardia. No evidence indicated that dexmedetomidine changed mortality. The general quality of evidence ranged from very low to low, due to high risks of bias, serious inconsistency and imprecision, and strongly suspected publication bias. Future studies could pay more attention to children and to using clonidine

Adjuncts should always be used in pediatric regional anesthesia

A number of different adjuncts to local anesthetics can be used to prolong and optimize postoperative pain relief following regional anesthesia in children. The present text provides a slightly opinionated but evidence-based argument in favor of this practice.

Suppression of the cough reflex by α 2-adrenergic receptor agonists in the rabbit

The α₂-adrenergic receptor agonist clonidine has been shown to inhibit citric acid-induced cough responses in guinea pigs when administered by aerosol, but not orally. In contrast, oral or inhaled clonidine had no effect on capsaicin-induced cough and reflex bronchoconstriction in humans. In addition, intravenous administration of clonidine has been shown to depress fentanyl-induced cough in humans. We investigated the effects of the α₂-adrenergic receptor agonists, clonidine and tizanidine, on cough responses induced by mechanical and chemical (citric acid) stimulation of the tracheobronchial tree. Drugs were microinjected (30–50 nL) into the caudal nucleus tractus solitarii (cNTS) and the caudal ventral respiratory group (cVRG) as well as administered intravenously in pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bilateral microinjections of clonidine into the cNTS or the cVRG reduced cough responses at 0.5 mmol/L and abolished the cough reflex at 5 mmol/L. Bilateral microinjections of 0.5 mmol/L tizanidine into the cNTS completely suppressed cough responses, whereas bilateral microinjections of 5 mmol/L into the cVRG only caused mild reductions in them. Depressant effects on the cough reflex of clonidine and tizanidine were completely reverted by microinjections of 10 mmol/L yohimbine. Intravenous administration of clonidine (80–120 μg/kg) or tizanidine (150–300 μg/kg) strongly reduced or completely suppressed cough responses. These effects were reverted by intravenous administration of yohimbine (300 μg/kg). The results demonstrate that activation of α₂-adrenergic receptors in the rabbit exerts potent inhibitory effects on the central mechanism generating the cough motor pattern with a clear action at the level of the cNTS and the cVRG.

Is there a place for pressure-support ventilation and high positive end-expiratory pressure combined to alpha-2 agonists early in severe diffuse acute respiratory distress syndrome?

Acute respiratory distress syndrome (ARDS) is associated with a high mortality linked primarily to co-morbidities (sepsis, cardiac failure, multiple organ failure, etc.). When the lung is the single failing organ, quick resolution of ARDS should skip some complications arising from a prolonged stay in the critical care unit. In severe ARDS (PaO2/FIO2=P/F<100 with positive end-expiratory pressure (PEEP) ≥ 5 cm H2O), current recommendations are to intubate the trachea of the patient and use mechanical ventilation, low tidal volume, high PEEP, prone positioning and possibly neuromuscular blockade in association with intravenous sedation. Another strategy is possible. Firstly, spontaneous ventilation (SV) coupled with pressure support (PS) ventilation and high PEEP is possible from tracheal intubation onwards, with the possible exception of the short period following immediately tracheal intubation. Secondly, using alpha-2 adrenergic agonists (e.g. clonidine, dexmedetomidine) can provide first-line sedation from the beginning of mechanical ventilation, as they preserve respiratory drive, lower oxygen consumption and pulmonary hypertension and increase diuresis. Alpha-2 agonists are to be supplemented, if appropriate, by drugs devoid of effect on respiratory drive (neuroleptics, etc.). The expected benefits would be to prevent acquired diaphragmatic weakness, accumulation of sedation, cognitive dysfunction, and presumably improved outcome. This hypothesis should be tested in a double blind randomized controlled trial.

A prospective, randomized, double blind and placebo-control study comparing the additive effect of oral midazolam and clonidine for postoperative nausea and vomiting prophylaxis in granisetron premedicated patients undergoing laparoscopic cholecystecomy

Background:

Reduction of postoperative nausea and vomiting (PONV) continues to be a major challenge in perioperative care in spite of introduction of newer antiemetics with better efficacy and safety profiles. Therefore, we evaluated the additive effect of oral midazolam and clonidine for PONV prophylaxis in granisetron premedicated patients undergoing laparoscopic cholecystectomy.

Materials and Methods:

In a prospective, randomized fashion, 120 selected cases were randomized into three groups: I, II or III to receive a tablet of midazolam (15 mg, n = 36), clonidine (150 mcg, n = 40), or glucose as placebo (5 g, n = 44) orally, 1 h before anesthesia. Occurrence of PONV along with need for rescue antiemetic during the first postoperative day was compared between groups as a primary outcome.

Results:

Episodes of PONV reduced significantly in Group II (15%) as compared to group I and III (22.2%, 59%) at various time points during the period of observation (P = 0.002). Need for rescue antiemetic was significantly lower in group I (13.88%) and II (5%) as compared to group III (52.27%, P < 0.001).

Conclusion:

Oral clonidine is better adjuvant for PONV prophylaxis, as compared to midazolam, in granisetron premedicated patients undergoing laparoscopic cholecystectomy.

[Dexmedetomidine and clonidine: a review of their pharmacodynamy to define their role for sedation in intensive care patients]

Alpha-2 adrenergic agonists ("alpha-2 agonists") present multiple pharmacodynamic effects: rousable sedation, decreased incidence of delirium in the setting of critical care, preservation of respiratory drive, decreased whole body oxygen consumption, decreased systemic and pulmonary arterial impedance, improved left ventricular systolic and diastolic function, preserved vascular reactivity to exogenous catecholamines, preserved vasomotor baroreflex with lowered set point, preserved kidney function, decreased protein catabolism. These pharmacodynamic effects explain the interest for these drugs in the critical care setting. However, their exact role for sedation in critically ill-patients remains open for further studies. Given the few double-blind randomized multicentric trials available, the present non exhaustive analysis of the literature aims at presenting the utilization of alpha-2 agonists as potential first-line sedative agents, in the critical care setting. Suggestions regarding the use of alpha-2 agonists as sedatives are detailed.

[Effects of intravenous clonidine on recovery and postanaesthetic analgesic requirements.]

Pain and pain-related sympathoadrenergic reactions (hypertension, tachycardia) accompanied by nausea, vomiting and shivering are the most common side effects of recovery from anaesthesia. The alpha(2)agonist clonidine acts as a sedative, anxiolytic, antihypertensive, antiemetic, antisialogogue and decreases the incidence of shivering. Thus, we studied the effects of intraoperatively administered clonidine on the recovery period and the postoperative analgesic requirements in patients undergoing maxillofacial surgery.

METHODS

After approval by the local Ethics Commitee and after informed consent had been given, 40 patients scheduled for elective maxillofacial surgery were included in this double-blind, randomized study. As a supplement to standardized general anaesthesia (isoflurane, N(2)O), the patients received either clonidine 5 mug/kg or placebo during the last hour of the operation. Blood pressure, heart rate, time of recovery, and sedation and pain scores were measured postoperatively. The occurrence of nausea, vomiting or shivering was noted, as were the requirements of piritramide for analgesia, which was administered on demand in titrating dosages, and of nifedipine for systolic blood pressure exceeding 180 mm Hg.

RESULTS

The two groups were comparable regarding biometric parameters, ASA-classification and duration of anaesthesia. Clonidinetreated patients were later in opening their eyes (22.5+/-11.9 min vs 17.9+/-10.9; n.s.) and the ability to state their dates of birth returned later (32.2+/-11.6 min vs. 25.7+/-12.8;P<0.05). Pain was more frequent in the placebo group (P<0.05 after 30 min), and there-fore, these patients required much more piritramid (P<0.01). The sedation scores showed no significant differences. No vomiting occurred in the clonidine group, and shivering was less frequent (P<0.01). The placebo group received more nifedipine (P<0.05) because the rate-pressure product was higher (P<0.01).

DISCUSSION

Opiates are frequently used as analgesics after maxillofacial surgery, even though their most common side effect-respiratory depression, nausea and vomiting-are particularly dangerous in these patients because of the obstruction of the upper respiratory tract. Self-titration of the opiate dosage on demand can decrease the incidence of serious side effects. Clonidine administered intraoperatively caused a profound reduction in analgesic requirements in this study. Additional opiate administration in the postoperative period was unnecessary in nearly all clonidine-treated patients. The attenuating effect on sympathoadrenergic reactions leads to lowering of the rate-pressure product and may be of advantage for patients suffering from arterial hypertension, angina pectoris or bronchial asthma. The slower emergence from anaesthesia following clonidine administration is probably caused by double-blind study properties preventing full consideration of the decreased isoflurane requirements after clonidine.

[Systemic clonidine versus opioids in postoperative analgesia-A randomized double-blind study.]

INTRODUCTION

alpha(2)-Adrenozeptoragonisten agonists have shown antinociceptive and analgesic effects, which are not antagonized by naloxone. Therefore, the mechanism of action should be independent of opioid receptors. Most studies on this topic have been performed using clonidine. Experimentally the analgesic effect of clonidine can be suppressed by the inhibition of central adrenergic receptors. Furthermore, clonidine has analgesic effects at the spinal level. During recent years numerous studies have shown the analgesic effect of spinally or epidurally administered clonidine in humans. However, only very few studies have investigated the analgesic effect of parenterally administered clonidine in humans.

METHODS

After the approval of the local ethical committee had been obtained, 60 patients (ASA I-III, age 18-65 years) scheduled for elective orthopaedic procedures were included in this double-blind randomized study. All patients gave their written consent on the day before the operation. Premedication was standardized and involved benzodiazepines. Isoflurane was used as the sole anaesthetic. Postoperatively the pain level of the patients was controlled by a visual analogue scale (VAS 0-10). When the VAS reached at least 5 and the patients requested an analgesic, they were randomly assigned to either the morphine, tramadol or clonidine group. Twenty patients received 5 mg morphine i.v., 20 patients received 50 mg tramadol and 20 patients received 150 clonidine i.v. If the analgesic effect was insufficient, the above-mentioned dosage was repeated after 30 min. The therapy was classified as a failure if no sufficent analgesia could be achieved within 60 min. These patients received 7.5 mg piritramide i.v. VAS and sedation were measured at 10-min intervals during the 1 st h and at 15-min intervals during the following 2h. Heart rate, blood pressure and oxygen saturation were measured at 5-min intervals during the whole study period. Statistical analysis of the data was performed by ANOVA, Wilcoxon test, Student'st-test and chi-square test using a level of significance ofP<0.05.

RESULTS

All groups were comparable as regards their basic clinical parameters. Morphine, tramadol and clonidine significantly reduced the VAS within 20 min. During the whole study period the analgesic effect of clonidine was comparable with that of morphine and tramadol. No significant differences were observed in the number of repetitions after 30 min or in the failure rate. After 2 h sedation was significantly higher in the morphine group. No clinically relevant cardiovascular or respiratory side-effects were observed in any of the patients.

DISCUSSION

In our study the analgesic effect of 150 mug clonidine i.v. was equivalent to that of 5 mg morphine i.v. and 50 mg tramadol. Our results in humans confirm the dosage relationship of 1ratio30 found by Eisenach in sheep. Further studies on the use of parenteral clonidine for postoperative analgesia seem to be warranted.

Dexmedetomidine and clonidine induce long-lasting activation of the respiratory rhythm generator of neonatal mice: possible implication for critical care

Dexmedetomidine and clonidine are alpha-2 adrenoceptor agonists increasingly used in the critical care unit as sedative agents for their benzodiazepine-sparing effects and their limited depressing effect on breathing. However adverse effects on breathing have been also reported with alpha-2 adrenoceptor agonists and their central effects on the respiratory rhythm generator are poorly known. We therefore examined the effects of dexmedetomidine, clonidine, the alpha-2 adrenoceptor antagonist yohimbine and the benzodiazepine midazolam on the activity of the isolated respiratory rhythm generator of neonatal mice using medullary preparations where the respiratory rhythm generator continued to function in vitro. For the first time, we showed that 5min bath applications of dexmedetomidine or clonidine activated the respiratory rhythm generator for periods over than 30min. Second, we showed that the long-lasting effect of dexmedetomidine implicated receptors other than alpha-2 adrenoceptors as it persisted after their blockade with yohimbine. Third, we reported that 5min bath applications of the benzodiazepine midazolam significantly depressed the respiratory rhythm generator, and that this depression was prevented by pre-treatment with either dexmedetomidine or clonidine. Although further experiments are still required to identify the mechanisms through which dexmedetomidine and clonidine activate the respiratory rhythm generator, our current in vitro results in neonatal mice support the use of dexmedetomidine and clonidine in the critical care unit.

Anesthetic considerations and surgical caveats for awake airway surgery

The evolution of novel techniques for the treatment of laryngeal pathology has led to a significant expansion of the role of diagnostic assessment and the range of laryngeal procedures performed. These procedures typically benefit from an anesthetic approach that diverges from a standard general endotracheal or laryngeal mask airway-based inhalational anesthetic. The shared airway, need for intraoperative assessment of vocal cord function, risk of airway fire, and desire for rapid emergence and discharge are all important factors. In this article the authors undertake a collaborative anesthesia-surgical discussion of anesthetic management for airway procedures that are optimally performed with a spontaneously breathing, cooperative patient. An overview of pharmacologic approaches to airway anesthesia and cooperative sedation, followed by a discussion on the surgical requirements and anesthetic goals of commonly performed procedures, are presented.

Scale exponents of blood pressure and heart rate during autonomic blockade as assessed by detrended fluctuation analysis

How the autonomic nervous system influences the fractal dynamics of heart rate (HR) and blood pressure (BP) remains unclear. The purpose of our study was to separately assess cardiac vagal and sympathetic (cardiac vs. vascular) influences on fractal properties of HR and BP as described by scale exponents of detrended fluctuation analysis (DFA). R-R intervals, systolic and diastolic BP were measured in nine supine volunteers before and after administration of autonomic blocking agents (atropine, propranolol, atropine+propranolol, clonidine). Spectra of DFA scale exponents, α(t), were calculated for scales between 5 and 100 s. HR and BP scale structures differed at baseline, being α(t) of HR <1, with a minimum between 10 and 20 s followed by a higher plateau between 40 to 80 s, while α(t) of BP decreased with t from values >1. Comparison of atropine and propranolol with baseline and combined cardiac parasympathetic and sympathetic blockade (atropine+propranolol) indicated opposite influences of vagal and cardiac sympathetic outflows on HR exponents. The vagal outflow adds white-noise components, amplifying differences with BP exponents; the cardiac sympathetic outflow adds Brownian motion components at short scales and contributes to the plateau between 40 and 80 s. Overall sympathetic inhibition by clonidine decreased short- and long-term exponents of HR, and short-term exponents of BP, so that their α(t) spectra had different means but similar profiles. Therefore, cardiac vagal, cardiac sympathetic and vascular sympathetic outflows contribute differently to HR and BP fractal structures. Results are explained by different distribution and dynamics of acetylcholine receptors and of α- and β-adrenergic receptors between heart and vasculature.

A comparison of intravenous sedation with two doses of dexmedetomidine: 0.2 µg/kg/hr Versus 0.4 µg/kg/hr

The present study investigated the physiologic and sedative effects between two different continuous infusion doses of dexmedetomidine (DEX). Thirteen subjects were separately sedated with DEX at a continuous infusion dose of 0.2 µg/kg/hr for 25 minutes after a loading dose of 6 µg/kg/hr for 5 minutes (0.2 group) and a continuous infusion dose of 0.4 µg/kg/hr for 25 minutes after a loading dose of 6 µg/kg/hr for 5 minutes (0.4 group). The recovery process was then observed for 60 minutes post infusion. The tidal volume, mean arterial pressure, and heart rate in both groups decreased significantly during infusion, but they were within a clinically acceptable level. A Trieger dot test plot error ratio in the 0.4 group was significantly higher than that in the 0.2 group until 15 minutes post infusion. Sedation appears to be safe at the infusion doses of DEX studied. However, increasing maintenance infusion doses of DEX from 0.2 µg/kg/hr to 0.4 µg/kg/hr delays some recovery parameters.

Respiratory Depression in Young Prader Willi Syndrome Patients following Clonidine Provocation for Growth Hormone Secretion Testing

Objectives. To determine the sedative and respiratory effects of clonidine when used to evaluate growth hormone (GH) secretion in children with Prader Willi Syndrome (PWS). Methods. The study prospectively evaluated children with PWS who received clonidine (0.15 mg/m²) to assess GH responsiveness. Patients were studied up to four times over three years. Vital signs, oxygen saturation, and sedation level were recorded at baseline and every five minutes following clonidine. Changes between baseline and post-clonidine were evaluated using a repeated measurement analysis. Results. Sixty studies were performed on 17 patients, mean age 30.4 ± 15.0 months. The mean ± SD dose of clonidine was 0.074 ± 0.027 mg (5.3 ± 1.72 mcg/kg). All patients achieved a sedation score of 4 to 5 (drowsy to asleep). Mean declines in respiratory rate (7.5 ± 6.1 breaths/min; P < .001), and oxygen saturation (2.2 ± 2.0%; P < .001) occurred following clonidine. Five patients (29%) experienced oxygen saturations ≤94% on nine occasions. Three oxygen desaturations were accompanied by partial airway obstruction. Conclusions. Clonidine doses to assess GH secretion often exceed doses used for sedation and result in significant respiratory depression in some children with PWS. There was no association between oxygen desaturation and BMI.

Intravenous Sedation with Low-Dose Dexmedetomidine: Its Potential for Use in Dentistry

This study investigated the physiologic and sedative parameters associated with a low-dose infusion of dexmedetomidine (Dex). Thirteen healthy volunteers were sedated with Dex at a loading dose of 6 mcg/kg/h for 5 minutes and a continuous infusion dose of 0.2 mcg/kg/h for 25 minutes. The recovery process was observed for 60 minutes post infusion. The tidal volume decreased significantly despite nonsignificant changes in respiratory rate, minute ventilation, oxygen saturation, and end-tidal carbon dioxide. The mean arterial pressure and heart rate also decreased significantly but within clinically acceptable levels. Amnesia to pin prick was present in 69% of subjects. A Trieger dot test plot error ratio did not show a significant change at 30 minutes post infusion despite a continued significant decrease in bispectral index. We conclude that sedation with a low dose of Dex appears to be safe and potentially efficacious for young healthy patients undergoing dental procedures.

Respiratory, metabolic and hemodynamic effects of clonidine in ventilated patients presenting with withdrawal syndrome

OBJECTIVE

To investigate the respiratory, metabolic and hemodynamic effects of clonidine in ventilated patients presenting with withdrawal syndrome after sedation interruption.

DESIGN

Prospective, interventional, single-center study in 30 ventilated ICU patients.

INTERVENTIONS

Metabolic [oxygen consumption (VO(2)), CO(2) production (VCO(2)), resting energy expenditure (REE)], respiratory [minute ventilation (V (E)), tidal volume (V (T)), respiratory rate (RR)] and hemodynamic (HR, SAP, MAP) parameters were measured in 30 ventilated ICU patients. Measurements were performed first under sedation with remifentanil-propofol, then after sedation interruption, and finally after clonidine administration (0.9-1.8 mg of clonidine in two doses of 10 min interval).

RESULTS

Sedation interruption produced significant increases in the hemodynamic parameters (SAP and MAP by 33%, HR by 37%), and metabolic rate (increase in VO(2) by 70%, VCO(2) by 88% and REE by 74%), leading to high respiratory demands (increase in V (E) from 9 to 15 l/min). The V (E) was increased due to a twofold increase in the RR; V (T) remained constant. In 25 out of 30 patients, clonidine administration decreased the hemodynamic (SAP, MAP and HR), metabolic (VO(2), VCO(2), REE) and respiratory parameters to values close to those observed with sedation. Clonidine induced mild sedation and patients became more cooperative with the ventilator. All patients responding to clonidine were weaned from the ventilator in 2 days (median, range 1-18 days).

CONCLUSION

Patients with withdrawal syndrome had significantly elevated hemodynamic, metabolic and respiratory demands. Clonidine significantly decreased these demands, induced mild sedation and facilitated patient cooperation with the ventilator, enabling ventilator weaning.

Intravenous clonidine infusion in infants after cardiovascular surgery

BACKGROUND

The aim of this study was to investigate the hemodynamic profile and heart rhythm in infants who were given intravenous clonidine infusion after prolonged analgesia/sedation following cardiac surgery.

METHODS

This is a single center retrospective review. A total of 542 cardiovascular surgical procedures in infants aged 0-24 months with congenital heart disease were performed between 01/2003 and 12/2005 at the Deutsches Herzzentrum in Berlin. The majority received no long-term analgesia/sedation, but 50 (9%) of these infants received clonidine (dosed at 0.18-3.6 microg.kg(-1).h(-1)) for sedation and to reduce withdrawal symptoms such as CNS hyperactivation, hypertension, tachycardia, and fever. The hospital records of these infants were studied.

RESULTS

Fifty infants (median age 5.0 months, median body weight 5.3 kg, 32 males/18 females) received prolonged analgesia/sedation to ensure hemodynamic stability. Clonidine infusion started on day 5 (median) after surgery. During clonidine treatment we found an age-related normalized profile of hemodynamic parameters with a reduction of heart rate and mean arterial pressure from the upper norm to the mean within 24 h (P < 0.001). In no case did clonidine cause low blood pressure resulting in additional therapy to reach the target blood pressure. There were no adverse effects on cardiac rhythm, especially no onset of atrioventricular block. Midazolam, fentanyl, and other opioids could be ended on day 4 of clonidine treatment.

CONCLUSIONS

Although off-label, it is feasible to use clonidine infusions in infants in the PICU setting after cardiac surgery without hemodynamic problems arising.

Neuraxial drug administration: a review of treatment options for anaesthesia and analgesia

Neuraxial drug administration describes techniques that deliver drugs in close proximity to the spinal cord, i.e. intrathecally into the CSF or epidurally into the fatty tissues surrounding the dura, by injection or infusion. This approach was initially developed in the form of spinal anaesthesia over 100 years ago. Since then, neuraxial drug administration has evolved and now includes a wide range of techniques to administer a large number of different drugs to provide anaesthesia, but also analgesia and treatment of spasticity in a variety of acute and chronic settings. This review concentrates on the pharmacological agents used and the clinical basis behind currently utilised approaches to neuraxial drug administration. With regard to local anaesthetics, the main focus is on the development of the enantiomer-specific compounds ropivacaine and levobupivacaine, which provide similar efficacy to bupivacaine with a reduced risk of severe cardiotoxicity. Opioids are the other group of drugs widely used neuraxially, in particular to provide analgesia alone or more commonly in combination with other agents. The physicochemical properties of the various opioids explain the main differences in efficacy and safety between these drugs when used intrathecally, of which morphine, fentanyl and sufentanil are most commonly used. Another group of drugs including clonidine, dexmedetomidine and epinephrine (adrenaline) provide neuraxial analgesia via alpha-adrenergic receptors and are used mainly as adjuvants to local anaesthetics and opioids. Furthermore, intrathecal baclofen is in routine clinical use to treat spasticity in a number of neurological conditions. Beside these established approaches, a wide range of other drugs have been assessed for neuraxial administration to provide analgesia; however, most are in various early stages of investigation and are not used routinely. These drugs include neostigmine, ketamine, midazolam and adenosine, and the conotoxin ziconotide. The latter is possibly the most unusual compound here; it has recently gained registration for intrathecal use in specific chronic pain conditions.

A comparison of epidural bupivacaine-fentanyl and bupivacaine-clonidine in children undergoing the Nuss procedure

The administration of epidural opioids, though effective for producing analgesia, has severe side effects in most patients. It is unknown whether clonidine can effectively replace opioids and cause fewer side effects. We compared, in this randomized trial, the incidence of vomiting and pruritus as well as the analgesic profile of three different combinations of bupivacaine, fentanyl, and clonidine administered epidurally in patients undergoing the Nuss procedure: bupivacaine + fentanyl, bupivacaine + clonidine, bupivacaine + fentanyl + clonidine. The incidence of side effects was significantly less in the bupivacaine + clonidine group (33%) compared with the bupivacaine + fentanyl (92%) and bupivacaine + fentanyl + clonidine (73%) groups (P = 0.004). Quality of postoperative analgesia was similar in the three groups. No significant complications were observed. In conclusion, clonidine is an effective and safe alternative to epidural opioids.

Anesthesia and analgesia during and after surgery in neonates

BACKGROUND

Historically, the use of anesthetics and analgesics in neonates and infants has been based on extrapolations from studies performed in adults and older children. Over the past 20 years, there has been a growing body of research on the clinical pharmacology and clinical outcomes of these agents in neonates and infants.

OBJECTIVE

This article summarizes clinical pharmacology and clinical outcomes studies of opioids, opioid antagonists, sedative-hypnotics, nonsteroidal anti-inflammatory drugs and acetaminophen, and local anesthetics in neonates and infants to highlight gaps in the available knowledge, review some concerns about study design, and identify drugs that should receive high priority for future study.

METHODS

Relevant studies were identified through a search of MEDLINE and a review of textbooks, conference proceedings, and abstracts. The available literature was subjected to expert committee-based review.

CONCLUSIONS

There is a growing body of information on analgesic and anesthetic pharmacokinetics, pharmacodynamics, and clinical outcomes in neonates and infants, permitting safe and effective use in some clinical settings. Major gaps in knowledge persist, however. Future research may involve a combination of clinical trials and preclinical studies in suitable infant animal surrogate models.

Clonidine: an alternative to benzodiazepines for premedication in children

PURPOSE OF REVIEW

The aim of this review is to summarize the use of clonidine for paediatric premedication and to make a comparison with benzodiazepines. A routine clonidine premedication protocol is also presented.

RECENT FINDINGS

In the US 50% of young children undergoing surgery receive premedication and midazolam is the most frequently used drug. The number of trials that compare midazolam with active controls are few and this premedicant is not adequately validated. Clonidine is still used as premedication in a small number of centres but the literature on paediatric use of clonidine is steadily growing. A recent review article has concluded that the use of clonidine does enhance the quality of perioperative management in infants and children and more recent publications support the use of clonidine for premedication. Its effect on the circulation is mild but routine atropine administration is recommended. Contraindications to the use of clonidine are few. Apart from a general overview on the effects of clonidine this article will also summarise the published trials that have compared clonidine with benzodiazepines for premedication in children.

SUMMARY

Midazolam the most commonly used drug for paediatric premedication worldwide. Despite having a number of beneficial effects it is far from an ideal premedicant, especially concerning its effect on cognition/amnesia, confusion and long-term behavioural disturbances. Clonidine lacks the majority of the negative effects associated with midazolam and is associated with a number of beneficial perioperative effects. Our clinical experience of replacing midazolam with clonidine as premedicant in children, including also outpatients, has been favourable.

Clonidine in paediatric anaesthesia: review of the literature and comparison with benzodiazepines for premedication

BACKGROUND

Children undergoing anaesthesia and surgery can experience significant anxiety and distress during the peri-operative period, but whether routine premedication is necessary is currently debated. Benzodiazepines are the most frequently used drugs as premedication in paediatric anaesthesia. In the US, 50% of young children undergoing surgery receive premedication and midazolam is the most frequently used drug in this context (1). Nishina and coworkers (2) concluded in a review article in 1999 that clonidine, administered via an oral, rectal, or caudal route, is a promising adjunct to anaesthetics and analgesics to enhance quality of peri-operative management in infants and children. Later publications also support the use of clonidine for premedication (3-6). The aim of this communication is to review the use of clonidine in paediatric anaesthesia and to propose clonidine as a promising alternative to midazolam. Clonidine is associated with a number of beneficial effects in the context ofanaesthesia both in adults and children. Why clonidine is not routinely use in clinical practice despite the massive publication list is to a large extent due to the lack of marketing efforts from the pharmaceutical industry since multiplegeneric preparations are now readily available on most markets. Midazolam is also associated with a number of beneficial effects, but is far from an ideal premedicant in children, especially with regards to the amnesia, confusion and long term behavioural disturbances. Clonidine has contrary to midazolam no effect on respiration. We believe that clonidine is a good alternative to midazolam as premedication in infants and children.

Long-term use of clonidine in a critically-ill infant

We report the use of clonidine in an infant as an adjunct to sedation and analgesia for 4.5 months in the critical care setting. Advantages, potential side effects, and dosing for multiple modes of delivery are discussed.

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.

Oral clonidine does not change ventilatory response to carbon dioxide in sevoflurane-anesthetized children

BACKGROUND

Clonidine is a useful premedicant for pediatric anesthesia. The drug has potential for ventilatory depression. The aim of the current study was to determine the effects of clonidine premedication on the ventilatory response to hypercapnia during sevoflurane anesthesia using the carbon dioxide (CO(2)) steady state method.

METHODS

Sixty children (3-13 yr) were assigned to receive clonidine 4 microg x kg(-1) or placebo. Anesthesia was maintained with spontaneous breathing and 2% sevoflurane. Minute ventilation (VE), respiratory rate (RR), endtidal CO(2) pressure (P(ECO(2)), and arterial hemoglobin oxygen saturation (SpO2) were measured with a facemask tightly fitted before and during 7% CO(2) inhalation.

RESULTS

Compared with placebo, oral clonidine failed to reduce VE volume before CO(2) loading under general anesthesia with 2% sevoflurane. Inhalation of CO(2) increased VE. Oral clonidine did not attenuate the increase in VE induced by hypercapnic challenge under sevoflurane anesthesia. There were no differences in RR, P(ECO(2), or SpO2 between the placebo and clonidine groups before and during CO(2) loading.

CONCLUSION

These data suggest that oral clonidine is a suitable premedication for sevoflurane anesthesia under spontaneous breathing conditions in children.

Postoperative pain relief following intrathecal bupivacaine combined with intrathecal or oral clonidine

BACKGROUND

The purpose of the present study was to evaluate the postoperative analgesic and adverse effects of equal doses of oral or intrathecal clonidine in spinal anaesthesia with bupivacaine plain.

METHODS

Forty-five ASA I-III orthopaedic patients scheduled for osteosynthesis of a traumatic femur fracture were randomised in a double-blind fashion to one of 3 groups. Patients received 15 mg of plain bupivacaine intrathecally (group B) or an intrathecal mixture of bupivacaine 15 mg and clonidine 150 mg (group CIT). In group CPO oral clonidine 150 mg was administered 60 min before intrathecal injection of bupivacaine 15 mg.

RESULTS

Oral and intrathecal clonidine prolonged the time until the first request for analgesics, 313 +/- 29 and 337 +/- 29 min, respectively, vs. 236 +/- 27 min in group B (P < 0.01). The total 24- h PCA morphine dose was significantly lower in group CIT(19.3 +/- 1.3 mg) compared to groups B and CPO(33.4 +/- 2.0 and 31.2 +/- 3.1 mg). MAP was decreased significantly during the first hour after intrathecal clonidine(14%) and during the first 5 h after oral clonidine(14-19%). HR decreased in CIT during the 5th and 6th postoperative hours(7-9%) and during the first 2 h(9%) in CPO (P < 0.01). The degree of sedation was more pronounced in group CPO during the first 3 h. Four patients had pruritus in group B.

CONCLUSIONS

Addition of intrathecal clonidine prolonged analgesia and decreased morphine consumption postoperatively more than oral clonidine. Hypotension was more pronounced after oral than after intrathecal clonidine. Intrathecal clonidine is therefore recommended.

Effect of in vivo treatment of clonidine on ATP-ase's enzyme systems of synaptic plasma membranes from rat cerebral cortex

The effects on energy-consuming ATP-ases were studied in two types of synaptic plasma membranes from rat cerebral cortex after in vivo injection of clonidine. To study the mechanism of action of clonidine at subcellular level, the enzyme activities of Na+, K+-ATP-ase, Ca2+, Mg2+-ATP-ase, Low- and High-affinity Ca2+-ATP-ase, and Mg2+-ATP-ase were evaluated on synaptic plasma membranes of control and treated animals with clonidine (5 microg x kg(-1); i.p. 30 minutes). Acute treatment with clonidine decreased the catalytic activity of Ca2+, Mg2+-ATP-ase and of low-affinity Ca2+-ATP-ase only in synaptic plasma membranes of II type, that is the fraction enriched in synaptic plasma membranes. The decreases of these enzymatic activities are related to the interference of the drug on Ca2+ homeostasis in synaptoplasm. The reductions of these enzyme-consuming ATP-ases give further evidence that clonidine has not only neuroreceptorial effects, but that the drug also affects the energy metabolism of cerebral tissue, improving the knowledges about the pharmacology of clonidine. Because the elevation of [Ca2+]i, during ischemia/hypoxia contributes to cellular injury, these findings may suggest that the prevention of calcium overload may be the key mechanism of protection by alpha2-agonist.

Effects of xylazine hydrochloride during isoflurane-induced anesthesia in horses

OBJECTIVE

To quantitate dose- and time-related anesthetic-sparing effects of xylazine hydrochloride (XYL) during isoflurane-induced anesthesia in horses and to characterize selected physiologic responses of anesthetized horses to administration of XYL.

ANIMALS

6 healthy adult horses.

PROCEDURE

Horses were anesthetized 2 times to determine the minimum alveolar concentration (MAC) of isoflurane in O2 and to characterize the anesthetic-sparing effect (MAC reduction) after IV administration of XYL (0.5 and 1 mg/kg of body weight, random order). Selected measures of cardiopulmonary function, blood glucose concentrations, and urinary output also were measured during the anesthetic studies.

RESULTS

Isoflurane MAC (mean +/- SEM) was reduced by 24.8 +/- 0.5 and 34.2 +/- 1.9% at 42 +/- 7 and 67 +/- 10 minutes, respectively, after administration of XYL at 0.5 and 1 mg/kg. Amount of MAC reduction by XYL was dose- and time-dependent. Overall, cardiovascular and respiratory values varied little among treatments. Administration of XYL increased blood glucose concentration; the magnitude of change was dose- and time-dependent. Urine volume increased but not significantly.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of XYL reduced the anesthetic requirement for isoflurane in horses. The magnitude of the decrease is dose- and time-dependent. Administration of XYL increases blood glucose concentration in anesthetized horses in a dose-related manner.