Cardiopulmonary effects of dexmedetomidine in sevoflurane-anesthetized sheep with and without nitric oxide inhalation

Comparing the effects of intravenous injection and intranasal atomisation of detomidine in sheep

BACKGROUND

Detomidine is an α-2 agonist sedative drug which reduces the release of norepinephrine in nerves. Administering this drug through intranasal (IN) route could cause direct transmission to the central nervous system. Therefore, IN administration of detomidine would decrease the side effects and the onset of sedation.

OBJECTIVES

In this study, IN administration of detomidine in sheep through an atomiser was compared to its IV administration.

METHODS

Fifteen mature female sheep with an approximate weight of 49.53 ± 1.72 kg were used. They were randomly divided into three groups: (1) atomising 10 μg/kg (IND₁₀ ); (2) IV 10 μg/kg (IVD) and (3) atomising 30 μg/kg (IND₃₀ ). Following administration, vital signs, electrocardiographic components, sedative score and biochemistry profile were measured after 15, 30 and 60 min, which were compared with the baseline measures.

RESULTS

Bradycardia and the percentage of reduction from the baseline value in the respiratory rate were lower in the IND₁₀ group compared to those in the IVD group. There was no significant difference in terms of the temperature and blood oxygen saturation (SpO₂ ) among all the groups (p > 0.05). The level of cortisol declined in all the groups, and in the IND₃₀ (60 min), it was significantly different with the baseline value. The level of glucose increased in all the groups compared to the baseline, which was not significant. Insulin concentration was reduced in all the groups, and in the IND₃₀ group, it changed significantly 60 min after the drug administration. Sedation onset time was faster in the IV group. However, sedation scores between the two administration methods were not different, and only a dose-dependent increase was found in the sedation score in the atomisation group.

CONCLUSIONS

Our findings revealed that IN atomisation of detomidine triggers similar sedation as its IV administration, which could be used as an alternative method.

ONE-LUNG VENTILATION PATIENTS: CLINICAL CONTEXT OF ADMINISTRATION OF DIFFERENT DOSES OF DEXMEDETOMIDINE

Background

Open and endoscopic thoracic surgeries improve surgical exposure by One-lung ventilation (OLV). The aim of this study was to investigate the effects of different doses of dexmedetomidine on inflammatory response, oxidative stress, cerebral tissue oxygen saturation (SctO2) and intrapulmonary shunt in patients undergoing one-lung ventilation (OLV).

Methods

Seventy-five patients undergoing open pulmonary lobectomy in our hospital from January 2016 to December 2017 were enrolled and randomly divided into high-dose dexmedetomidine group (group D1, 1 mg/kg, n=25), low-dose dexmedetomidine group (group D2, 0.5 mg/kg, n=25) and control group (group C, n=25). Then, arterial blood and internal jugular venous blood were taken before anesthesia induction (T0) and at 15 min after twolung ventilation (T1) and 5 min (T2) and 30 min (T3) after OLV for later use. Next, the changes in hemodynamic parameters [mean arterial pressure (MAP), heart rate (HR) and pulse oxygen saturation (SpO2)] of patients were observed in each group. Enzyme-linked immunosorbent assay (ELISA) was carried out to detect serum inflammatory factors such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) and oxidative stress indicators [superoxide dismutase (SOD) and malondialdehyde (MDA)]. The changes in SctO2, arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt Qs/Qt (a measurement of pulmonary shunt: right-to-left shunt fraction) were observed. Additionally, the changes in lung function indicators like lung dynamic compliance (Cdyn) and airway peak pressure (P_peak) were determined.

Results

There were no statistically significant differences in the MAP, HR and SpO2 among three groups at each observation time point (P>0.05). At T2 and T3, the levels of serum IL-6, TNF-α and IL-8 were obviously decreased in group D1 and D2 compared with those in group C (P<0.05), and the decreases in group D1 were overtly larger than those in group D2, and the decreases at T3 were markedly greater than those at T2 (P<0.05). In comparison with group C, group D1 and D2 had notably reduced levels of serum reactive oxygen species (ROS) and MDA (P<0.05) and remarkably increased SOD content (P<0.05) at T2 and T3, and the effects were markedly better in group D1 than those in group D2. Besides, they were significantly superior at T3 to those at T2 (P<0.05). The SctO2 in group D1 and D2 was evidently lowered at T2 and T3 compared with that at T0, and the decrease in group D1 was distinctly smaller than that in group D2 (P<0.05). The Qs/Qt was significantly lower in group D1 and D2 than that in group C at T2 and T3 (P<0.05), while the PaO2 content was notably raised (P<0.05), and the decrease and increase were significantly larger in group D1 than those in group D2, and they were obviously greater at T3 to those at T2 (P<0.05). At T0 and T1, no significant differences were detected in the Cdyn, Pplat and Ppeak among three groups. At T2 and T3, the Cdyn was significantly elevated, while the Pplat and Ppeak overtly declined (P<0.05), and group D1 had greater changes in comparison with group D2, and the changes were obviously more evident at T3 to those at T2 (P<0.05).

Conclusions

Dexmedetomidine effectively ameliorates inflammatory response and oxidative stress, lowers oxygenation, Qs/Qt and the decrease in SctO2 and improves lung function during OLV, with good efficacy.

Comparison of pulmonary function in isoflurane anaesthetized ventilated sheep (Ovis aries) following administration of intravenous xylazine versus medetomidine

Alpha2 receptor agonists (alpha2-agonists) are useful sedative and analgesic agents in sheep, but have adverse pulmonary effects, which are reportedly similar between different alpha2-agonists. This randomized crossover study compared pulmonary function after intravenous administration of an alpha2-agonist, either xylazine or an equipotent dose of medetomidine in 34 female sheep anaesthetized twice. Pulmonary function was assessed using spirometry, volumetric capnography, arterial blood gas analysis 1 min prior to, and 5 and 10 min after administration of the allocated alpha 2 agonist drug. Pulmonary structural changes were subsequently assessed using computed tomography (CT). Tachypnoea or hypoxaemia prompted reversal with atipamezole and exclusion of data. Data were analysed for a fixed effect of drug using a mixed effect linear model with significance set at p < 0.05. Ten sheep administered xylazine required atipamezole while none of sheep receiving medetomidine did. Xylazine produced significantly higher respiratory frequency, airway pressures, airway resistance and arterial carbon dioxide (CO2), and lower dynamic compliance, tidal volume, CO2 elimination and end tidal CO2 tension and arterial oxygen tension than medetomidine. This was associated with a significantly lower % of aerated tissue and higher % poorly and non-aerated tissue in CT images of sheep receiving xylazine versus medetomidine. In conclusion, xylazine administration produced marked decreases in pulmonary function, in ventilated isoflurane anaesthetized sheep, when compared to an equipotent dose of medetomidine when administered as an intravenous bolus supporting the use of medetomidine when alpha2-agonists are required.

Application of α2 -adrenergic agonists combined with anesthetics and their implication in pulmonary intravascular macrophages-insulted pulmonary edema and hypoxemia in ruminants

Alpha₂ -adrenergic agonists have been implicated in the development of pulmonary edema (PE) and sustained hypoxemia that lead to life-threatening pulmonary distress in ruminants, especially with sensitive and compromised animals. Recently, there is limited understanding of exact mechanism underlying pulmonary alterations associated with α₂ -adrenergic agonist administration. Ruminants have a rich population of pulmonary intravascular macrophages (PIMs) in the pulmonary circulation, which may be involved in the development of pulmonary alveolo-capillary barrier damage. Hence, the central thesis of this review is overviewing the literatures regarding the systemic use of α₂ -adrenergic agonists in domestic ruminants, focusing on their pulmonary side effects, especially on the influence of PIMs on the lung. At this moment, further studies are needed to provide a clear emphasis and better understanding of the potential role of PIMs in the lung pathophysiology associated with α₂ -adrenergic agonists. These preliminary studies would be potentially to develop future medications and intervention targets that may be helpful to alleviate or prevent the critical striking pulmonary effects, and thereby improving the safety of α₂ -agonist application in ruminants.

Cardiopulmonary effects of vatinoxan in sevoflurane-anaesthetised sheep receiving dexmedetomidine

The effects of pre-treatment with vatinoxan (MK-467) on dexmedetomidine-induced cardiopulmonary alterations were investigated in sheep. In a crossover study design with a 20-day washout, seven sheep were anaesthetised with sevoflurane in oxygen and air. The sheep were ventilated with the pressure-limited volume-controlled mode and a positive end-expiratory pressure of 5cmH₂O. Peak inspiratory pressure (PIP) was set at 25cmH₂O. The sheep received either 150μg/kg vatinoxan HCl (VAT+DEX) or saline intravenously (IV) 10min before IV dexmedetomidine HCl (3μg/kg, DEX). Cardiopulmonary variables were measured before treatments (baseline), 3min after vatinoxan or saline, and 5, 15 and 25min after dexmedetomidine. Computed tomography (CT) of lung parenchyma was performed at baseline, 2min before dexmedetomidine, and 10, 20 and 30min after DEX. Bronchoalveolar lavage (BAL) was performed after the last CT scan and shortly before sheep recovered from anaesthesia. After VAT, cardiac output significantly increased from baseline. DEX alone significantly decreased partial arterial oxygen tension, total dynamic compliance and tidal volume, whereas PIP was significantly increased. With VAT+DEX, these changes were minimal. No significant changes were detected in haemodynamics from baseline after DEX. With VAT+DEX, mean arterial pressure and systemic vascular resistance were significantly decreased from baseline, although hypotension was not detected. On CT, lung density was significantly increased with DEX as compared to baseline. No visual abnormalities were detected in bronchoscopy and no differences were detected in the BAL fluid after either treatment. The pre-administration of vatinoxan alleviates dexmedetomidine-induced bronchoconstriction, oedema and hypoxaemia in sevoflurane-anaesthetised sheep.

Use of Dexmedetomidine in Cardiothoracic and Vascular Anesthesia

Dexmedetomidine is a highly selective α₂-adrenergic agonist with analgesic and sedative properties. In the United States, the Food and Drug Administration approved the use of the drug for short-lasting sedation (24 h) in intensive care units (ICUs) in patients undergoing mechanical ventilation and endotracheal intubation. In October 2008, the Food and Drug Administration extended use of the drug for the sedation of nonintubated patients before and during surgical and nonsurgical procedures. In the European Union, the European Medicine Agency approved the use of dexmedetomidine in September 2011 with a single recognized indication: ICU adult patients requiring mild sedation and awakening in response to verbal stimulus. At present, the use of dexmedetomidine for sedation outside the ICU remains an off-label indication. The benefits of dexmedetomidine in critically ill patients and in cardiac, electrophysiology-related, vascular, and thoracic procedures are discussed.

Sedative and cardiorespiratory effects of detomidine constant rate infusion in sheep

The use of sheep in experiments is widespread and is increasing worldwide, and so is the need to develop species-specific anaesthetic techniques to ensure animal safety. Previous studies have mentioned several protocols involving the administration of alpha-2 adrenergic agonists in sheep; however, assessment of the efficacy and safety of these infusion techniques is still relatively new. Thus, the aim of the present study is to assess the effectiveness of detomidine constant rate infusion (CRI) in sheep by measuring the cardiovascular and respiratory parameters, blood gas variables and sedation scores. Eight adult female Santa Inês sheep received 20 µg/kg of detomidine hydrochloride intravenously as a bolus loading dose, followed by an infusion rate of 60 µg/kg/h. The heart rates and respiratory rates changed continuously during the CRI period. No arrhythmias were observed. The reduction in arterial partial pressure of oxygen (PaO₂) was not significant, but one animal showed signs of hypoxaemia (minimum PaO₂ of 66.9 mmHg). The arterial partial pressure of carbon dioxide (PaCO₂) increased, but the animals did not become hypercapnic. The bicarbonate (HCO^3-), pH and base excess (BE) tended towards metabolic alkalosis. The cardiac output (CO), stroke volume (SV), cardiac index (CI) and ejection fraction (EF%) showed no significant changes. The fractional shortening (FS%) decreased slightly, starting at T_45min. Sedation scores varied between 3 (0/10) after sedation and during recovery and 7 (0/10) during CRI. We concluded that administering detomidine at an infusion rate of 60 µg/kg/h in Santa Inês sheep is a simple technique that produces satisfactory sedation for minimally invasive procedures.

The effect of epidural dexmedetomidine on oxygenation and shunt fraction in patients undergoing thoracotomy and one lung ventilation: A randomized controlled study

Background and Aims:

Role of epidural dexmedetomidine in providing analgesia is well documented, but its effect on oxygenation and shunt fraction is not well established. We studied the hypothesis that epidural dexmedetomidine may improve oxygenation and shunt fraction during one-lung ventilation (OLV).

Material and Methods:

After taking Institutional Ethics Committee approval, sixty patients undergoing thoracotomy and OLV were randomized to receive epidural ropivacaine with saline (RS group) or epidural ropivacaine with dexmedetomidine (RD group). Group RS received 7 ml of ropivacaine 0.5% with 1.5 ml normal saline (NS) bolus while RD group received 7 ml of 0.5% ropivacaine with 1 mcg/kg dexmedetomidine reconstituted in 1.5 ml NS. This was followed by infusion of 5 ml/h of 0.5% ropivacaine in RS group and 5 ml/h of 0.5% ropivacaine containing 0.2 mcg/kg of dexmedetomidine in RD group. Arterial and central venous blood gas parameters were obtained 15 minutes after intubation during two lung ventilation (TLV15), 15 and 45 min after OLV (OLV15, OLV45) and 15 minutes after reinstitution of two lung ventilation (ReTLV).

Results:

RD group had better oxygenation (254.2 ± 72.3 mmHg, 240.60 ± 59.26 mmHg) as compared to RS group (215.2 ± 64.3 mmHg, 190.7 ± 61.48 mmHg) at OLV15 (P – 0.04) and OLV45 (P – 0.004) respectively. Shunt fraction in RD group was (30.31 ± 7.89%, 33.76 ± 8.89%) and (35.14 ± 7.58%, 39.57 ± 13.03%) in RS group at OLV15 and OLV45, respectively. The increase in the shunt fraction from TLV15 was significantly greater in RS group than RD group both at OLV15 (P – 0.03) and OLV45 (P – 0.03). The sevoflurane and fentanyl requirement was lower in RD group.

Conclusion:

Epidural dexmedetomidine improves oxygenation and reduces shunt fraction during OLV, in patients undergoing thoracotomy. It also reduces intraoperative anesthetic and analgesic requirement.

Anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in isoflurane-anaesthetized sheep

OBJECTIVE

To determine the anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in sheep anaesthetized with isoflurane and undergoing orthopaedic surgery.

STUDY DESIGN

Prospective, randomised, 'blinded' controlled study.

ANIMALS

Twenty healthy sheep (weight mean 41.1 ± SD 4.5 kg).

METHODS

Sheep were sedated with intravenous (IV) dexmedetomidine (4 μg kg(-1) ) and morphine (0.2 mg kg(-1) ). Anaesthesia was induced with propofol (1 mg kg(-1)  minute(-1) to effect IV) and maintained with isoflurane in oxygen and a continuous rate infusion (CRI) of fentanyl 10 μg kg(-1)  hour(-1) (group F) or saline (group P) for 100 minutes. The anaesthetic induction dose of propofol, isoflurane expiratory fraction (Fe'iso) required for maintenance and cardiorespiratory measurements were recorded and blood gases analyzed at predetermined intervals. The quality of recovery was assessed. Results were compared between groups using t-tests or Mann-Whitney as relevant.

RESULTS

The propofol induction dose was 4.7 ± 2.4 mg kg(-1) . Fe'iso was significantly lower (by 22.6%) in group F sheep than group P (p = 0). Cardiac index (mean ± SD mL kg(-1)  minute(-1) ) was significantly (p = 0.012) lower in group F (90 ± 15) than group P (102 ± 35). Other measured cardiorespiratory parameters did not differ statistically significantly between groups. Recovery times and recovery quality were statistically similar in both groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl reduced isoflurane requirements without clinically affecting the cardiorespiratory stability or post-operative recovery in anaesthetized sheep undergoing orthopaedic surgery.

Predominant role of vasoconstrictors over dilatators derived from arachidonic acid in hypoxic pulmonary vasoconstriction

Prostanoids derived from arachidonic acid (AA) have been shown to play a permissive role in the regulation of vascular tone and wall tension. Conventionally, epoxyeicosatrienoic acids (EETs) and prostacyclin have been considered as dilatators, whereas thromboxane (TX) and hydroxyeicosatetraenoic acid (HETE) were considered as vasoconstrictors. However, the role of these prostanoids in the mediation of acute hypoxic pulmonary vasoconstriction is not yet clearly understood. In the present study, the role of prostanoids in the acute hypoxic response in rat isolated intrapulmonary arteries (IPAs) was investigated. Exogenous AA directly caused vasoconstriction, but exerted a significant inhibition on hypoxic vasoconstriction. The vasoconstriction by AA was mediated by the endothelium. AA metabolites from lipoxygenase (LOX) had no effect on vascular tone or hypoxic vasoconstriction. Consistent results from the blockage of cytochrome P450 (CYP) or CYP epoxide hydrolase showed that HETE contributed to endothelium‑independent hypoxic vasoconstriction. EET via epoxygenase exerted no effect on 80 mM KPSS‑induced vessel contraction or hypoxic vasoconstriction. In addition, prostacyclin also failed to inhibit hypoxic pulmonary vasoconstriction (HPV). However, blockage of thromboxane A2/prostanoid (TP) receptors almost eliminated hypoxic vasoconstriction, suggesting the primary role of TP receptors in the regulation of the hypoxic response in rat IPAs. In conclusion, the current data indicate the predominant role of vasoconstrictors instead of dilatators in mediating HPV. These data also highlight a pivotal role for voltage‑independent Ca2+ entry in pulmonary hypoxic response and suggest that modulation of these channels by prostanoids underlies their regulatory mechanisms.

Effects of dexmedetomidine on oxygenation during one-lung ventilation for thoracic surgery in adults

STUDY OBJECTIVE

To evaluate the effects of dexmedetomidine on hypoxic pulmonary vasoconstriction (HPV) and oxygenation during one-lung ventilation (OLV) in adults undergoing thoracic surgery.

DESIGN

Prospective, randomized, double-blinded trial.

SETTING

Tertiary care, University-based hospital.

PATIENTS

Nineteen adult patients undergoing thoracic surgery requiring OLV.

INTERVENTIONS

During inhalational anesthesia with desflurane, patients were randomized to receive either dexmedetomidine (bolus dose of 0.3 μg/kg followed by an infusion of 0.3 μg/kg/hr) or saline placebo.

MEASUREMENTS

Three arterial blood gas samples (ABG) were obtained to evaluate the effects of dexmedetomidine on oxygenation. Secondary outcomes included differences in hemodynamic parameters (heart rate and mean arterial pressure), end-tidal desflurane concentration required to maintain the bispectral index (BIS) at 40-60, supplemental fentanyl to maintain hemodynamic stability, and phenylephrine to keep the mean arterial pressure (MAP) within 10% of baseline values.

MAIN RESULTS

Oxygenation during OLV did not change following the administration of dexmedetomidine (PaO2/FiO2 ratio of 188 ± 115 in dexmedetomidine patients versus 135 ± 70 mmHg in placebo patients). There were no differences in hemodynamic variables or depth of anaesthesia between the two groups. With the administration of dexmedetomidine, there was a decrease in the expired concentration of desflurane required to maintain the BIS at 40-60 when compared with the control group (4.5 ± 0.8% versus 5.1 ± 0.8%). In patients receiving dexmedetomidine, fentanyl requirements were decreased when compared to placebo (2.7 μg/kg/patient versus 3.1 μg/kg/patient). However, more patients receiving dexmedetomidine required phenylephrine to maintain hemodynamic stability (6 of 9 patients versus 3 of 10 patients) and the total dose of phenylephrine was greater in patients receiving dexmedetomidine when compared with placebo 10.3 μg/kg/patient versus 1.1 μg/kg/patient).

CONCLUSION

Dexmedetomidine does not adversely affect oxygenation during OLV in adults undergoing thoracic surgical procedures. The improvement in oxygenation in the dexmedetomidine patients may be related to a decrease in the requirements for inhalational anaesthetic agents thereby limiting its effects on HPV.

Evaluation of a ketamine-propofol drug combination with or without dexmedetomidine for intravenous anesthesia in cats undergoing ovariectomy

OBJECTIVE

To evaluate the use of a ketamine-propofol combination, with or without dexmedetomidine, in cats undergoing ovariectomy and to assess Heinz body formation following administration of these drugs.

DESIGN

Randomized clinical trial.

ANIMALS

15 client-owned female cats.

PROCEDURES

Anesthesia was induced with a ketamine (2.0 mg/kg [0.91 mg/lb])-propofol (2.0 mg/kg) combination with (n = 7) or without (8) dexmedetomidine (0.003 mg/kg [0.0013 mg/lb]) and was maintained via continuous IV infusion of a 1:1 ketamine-propofol combination (administration rate for each drug, 10.0 mg/kg/h [4.54 mg/lb/h]). Cats underwent ovariectomy; duration of infusion was 25 minutes. Physiologic variables were measured at predetermined time points. Heinz bodies were quantified via examination of blood smears. Numeric scales were used to assess quality of recovery, degree of sedation, and signs of pain after surgery.

RESULTS

The ketamine-propofol group had a significantly higher mean heart rate at several time points during drug infusion, a significantly shorter time from the end of infusion to extubation (7 vs 29 minutes), and significantly lower sedation scores for the first hour after surgery than did the ketamine-propofol-dexmedetomidine group. Other variables were similar between groups; recovery was smooth, and anesthesia and postoperative analgesia were deemed adequate for all cats. The number of RBCs with Heinz bodies was not increased after surgery, compared with values immediately after anesthetic induction.

CONCLUSIONS AND CLINICAL RELEVANCE

Total IV anesthesia with a ketamine-propofol combination, with or without dexmedetomidine, appeared to be effective in healthy cats. These short-term infusions produced smooth recovery and adequate analgesia during the postoperative period.

Dexmedetomidine: applications for the pediatric patient with congenital heart disease

This study aimed to provide a general description of the cardiovascular and hemodynamic effects of dexmedetomidine and an evidence-based review of the literature regarding its use in infants and children with congenital heart disease (CHD). A computerized bibliographic search of the literature on dexmedetomidine use in infants and children with CHD was performed. The cardiovascular effects of dexmedetomidine have been well studied in animal and adult human models. Adverse cardiovascular effects include occasional episodes of bradycardia, with rare reports of sinus pause or cardiac arrest. Both hypotension and hypertension also have been reported. The latter is related to peripheral α(2B) agonism leading to vasoconstriction. No adverse effects on the pulmonary vasculature have been noted even in patients with preexisting pulmonary hypertension. Although there are no direct effects on myocardial function, decreased cardiac output may result from changes in heart rate or increases in afterload. Although not currently Food and Drug Administration (FDA)-approved for the pediatric population, findings have shown dexmedetomidine to be effective in various clinical scenarios of patients with CHD including sedation during mechanical ventilation, prevention of procedure-related anxiety, prevention of emergence delirium and shivering after anesthesia, and treatment of withdrawal. Although dexmedetomidine may have limited utility for painful or invasive procedures, preliminary data suggest that the addition of ketamine to the regimen may offer benefits. When used during the perioperative period, additional benefits include blunting of the sympathetic stress response with a reduction of endogenous catecholamine release, a decrease in intraoperative anesthetic requirements, and a limitation of postoperative opioid requirements.

Acute hemodynamic changes after rapid intravenous bolus dosing of dexmedetomidine in pediatric heart transplant patients undergoing routine cardiac catheterization

BACKGROUND

Dexmedetomidine is a highly selective α(2)-adrenoceptor agonist with sedative, anxiolytic, and analgesic properties that has minimal effects on respiratory drive. Its sedative and hypotensive effects are mediated via central α(2A) and imidazoline type 1 receptors while activation of peripheral α(2B)-adrenoceptors result in an increase in arterial blood pressure and systemic vascular resistance. In this randomized, prospective, clinical study, we attempted to quantify the short-term hemodynamic effects resulting from a rapid i.v. bolus administration of dexmedetomidine in pediatric cardiac transplant patients.

METHODS

Twelve patients, aged 10 years or younger, weighing ≤40 kg, presenting for routine surveillance of right and left heart cardiac catheterization after cardiac transplantation were enrolled. After an inhaled or i.v. induction, the tracheas were intubated and anesthesia was maintained with 1 minimum alveolar concentration of isoflurane in room air, fentanyl (1 μg/kg), and rocuronium (1 mg/kg). At the completion of the planned cardiac catheterization, 100% oxygen was administered. After recording a set of baseline values that included heart rate (HR), systolic blood pressure, diastolic blood pressure, central venous pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and thermodilution-based cardiac output, a rapid i.v. dexmedetomidine bolus of either 0.25 or 0.5 μg/kg was administered over 5 seconds. The hemodynamic measurements were repeated at 1 minute and 5 minutes.

RESULTS

There were 6 patients in each group. Investigation suggested that systolic blood pressure, diastolic blood pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and systemic vascular resistance all increased at 1 minute after rapid i.v. bolus for both doses and decreased significantly to near baseline for both doses by 5 minutes. The transient increase in pressures was more pronounced in the systemic system than in the pulmonary system. In the systemic system, there was a larger percent increase in the diastolic pressures than the systolic pressures. Cardiac output, central venous pressure, and pulmonary vascular resistance did not change significantly. HR decreased at 1 minute for both doses and was, within the 0.5 μg/kg group, the only hemodynamic variable still changed from baseline at the 5-minute time point.

CONCLUSION

Rapid i.v. bolus administration of dexmedetomidine in this small sample of children having undergone heart transplants was clinically well tolerated, although it resulted in a transient but significant increase in systemic and pulmonary pressure and a decrease in HR. In the systemic system, there is a larger percent increase in the diastolic pressures than the systolic pressures and, furthermore, these transient increases in pressures were more pronounced in the systemic system than in the pulmonary system.

Cesarean section and primary pulmonary hypertension: the role of intravenous dexmedetomidine

Primary pulmonary hypertension is a fatal disease that frequently becomes evident in pregnancy. The management of pregnant women with primary pulmonary hypertension poses a number of difficult problems, especially where regional anesthesia is considered to be contraindicated. A 30-year-old woman who developed primary pulmonary hypertension at 23 weeks of pregnancy was transferred to our hospital. Systolic pulmonary artery pressure and plasma brain natriuretic peptide levels were markedly elevated. Nitric oxide inhalation and prostacyclin prevented the progression of cardiac failure and reduced both plasma brain natriuretic peptide and pulmonary artery pressure. Cesarean section was performed at 32 weeks under general anesthesia. A combination of nitric oxide, prostacyclin, nitroglycerin, and dobutamine were administered during surgery. Intravenous dexmedetomidine was specifically used during emergence and recovery from anesthesia. This provided effective pain relief and hemodynamic stability. Throughout the clinical course, brain natriuretic peptide levels was monitored and used as an indicator of cardiac failure.

Deep sedation with dexmedetomidine in a porcine model does not compromise the viability of free microvascular flap as depicted by microdialysis and tissue oxygen tension

BACKGROUND

Deep sedation is often necessary after major reconstructive plastic surgery in the face and neck regions to prevent sudden spontaneous movements capable of inflicting mechanical injury to the transplanted musculocutaneous flap(s). An adequate positioning may help to optimize oxygenation and perfusion of the transplanted tissues. We hypothesized that dexmedetomidine, a central alpha2-agonist and otherwise potentially ideal postoperative sedative drug, may induce vasoconstriction in denervated flaps, and thus increase the risk of tissue deterioration.

METHODS

Two symmetrical myocutaneous flaps were raised on each side of the upper abdomen in 12 anesthetized pigs. The sympathetic nerve fibers were stripped from the arteries in one of the flaps (denervated flap), while nerve fibers were kept untouched in the other (innervated flap). After simulation of ischemia and reperfusion periods, the animals were randomized to deep postoperative sedation with either propofol (n = 6) or dexmedetomidine (n = 6). Flap tissue metabolism was monitored by microdialysis and tissue-oxygen partial pressure. Glucose, lactate, and pyruvate concentrations were analyzed from the dialysate every 30 min for 4 h.

RESULTS

Mean arterial blood pressure was higher in the dexmedetomidine group (P = 0.036). Flap tissue metabolism remained stable throughout the experiment as measured by lactate-pyruvate and lactate-glucose ratios (median ranges 14.3-24.5 for lactate-pyruvate and 0.3-0.6 for lactate-glucose) and by tissue-oxygen partial pressure, and no differences were found between groups.

CONCLUSIONS

Our data suggest that dexmedetomidine, even if used for deep sedation, does not have deleterious effects on local perfusion or tissue metabolism in denervated musculocutaneous flaps.

Dexmedetomidine: applications in pediatric critical care and pediatric anesthesiology

OBJECTIVE

To provide a general descriptive account of the end-organ effects of dexmedetomidine and to provide an evidence-based review of the literature regarding its use in infants and children.

DATA SOURCE

A computerized bibliographic search of the literature regarding dexmedetomidine.

MAIN RESULTS

The end-organ effects of dexmedetomidine have been well studied in animal and adult human models. Adverse cardiovascular effects include occasional episodes of bradycardia with rare reports of sinus pause or cardiac arrest. Hypotension has also been reported as well as hypertension, the latter thought to be due to peripheral alpha2B agonism with peripheral vasoconstriction. Although dexmedetomidine has no direct effects on myocardial function, decreased cardiac output may result from changes in heart rate or increases in afterload. There are somewhat conflicting reports in the literature regarding its effects on ventilatory function, with some studies (both human and animal) suggesting a mild degree of respiratory depression, decreased minute ventilation, and decreased response to CO2 challenge whereas others demonstrate no effect. The central nervous system effects include sedation and analgesia with prevention of recall and memory at higher doses. Dexmedetomidine may also provide some neuroprotective activity during periods of ischemia. Applications in infants and children have included sedation during mechanical ventilation, prevention of emergence agitation following general anesthesia, provision of procedural sedation, and the prevention of withdrawal following the prolonged administration of opioids and benzodiazepines.

CONCLUSIONS

The literature contains reports of the use of dexmedetomidine in approximately 800 pediatric patients. Given its favorable sedative and anxiolytic properties combined with its limited effects on hemodynamic and respiratory function, there is growing interest in and reports of its use in the pediatric population in various clinical scenarios.

Dexmedetomidine-induced pulmonary alterations in sheep

Alpha(2) agonist-induced pulmonary oedema in sheep might be related to alterations in pulmonary haemodynamics and/or activation of inflammatory processes. In seven sevoflurane-anaesthetized sheep pulmonary haemodynamics, arterial oxygen tensions, nitric oxide and prostaglandin E(2) concentrations were determined before and after intravenous dexmedetomidine (2microg kg(-1)). In a second trial, lung tissue was sampled for histopathology and quantitative real-time PCR for IL-1beta and iNOS mRNA in a control sheep and 2, 10 and 30min after dexmedetomidine. Computer tomography of the lung under sevoflurane anaesthesia before and after dexmedetomidine was performed. Two minutes after dexmedetomidine mean pulmonary artery pressure, pulmonary arterial occlusion pressure and estimated capillary pressurewere significantly increased to 34.5mmHg, 22.2mmHg and 27.1mmHg, respectively. On computer tomography, lung density increased immediately after dexmedetomidine, with maximal density occurring between 9 and 12min. Histopathology was consistent with vascular congestion followed by protein and erythrocyte extravasation into alveoli. Increased iNOS mRNA levels were detected in sevoflurane anaesthetized animals only. An IL-1beta signal occurred after morphological changes had occurred in lung tissue. These findings support hydrostatic stress as the underlying cause of alpha(2) agonist-induced pulmonary oedema in sheep.