Carboxymethyl-γ-cyclodextrin, a novel selective relaxant binding agent for the reversal of neuromuscular block induced by aminosteroid neuromuscular blockers: an ex vivo laboratory study.

BACKGROUND: Residual neuromuscular block at the end of surgery may compromise the patient's safety. The risk of airway complications can be minimized through monitoring of neuromuscular function and reversal of neuromuscular block if needed. Effective reversal can be achieved with selective relaxant binding agents, however, sugammadex is the only clinically approved drug in this group. We investigated the concentration-response properties of a novel selective relaxant binding agent, carboxymethyl-γ-cyclodextrin for the reversal of neuromuscular block. We evaluated the hypothesis that it is equally potent for reversing neuromuscular block as sugammadex. METHODS: Phrenic nerve - hemidiaphragm tissue preparations were isolated from male Wistar rats and suspended in a tissue holder allowing electrical stimulation of the nerve and monitoring of muscle contraction force. Concentration-response relationships were constructed for the neuromuscular blocking agents rocuronium, pipecuronium, and vecuronium. The half-effective concentrations of sugammadex and carboxymethyl-γ-cyclodextrin for reversal of neuromuscular block were determined. RESULTS: The half effective concentrations (95% confidence interval, CI) were 7.50 (6.93-8.12) µM for rocuronium, 1.38 (1.33-1.42) µM for pipecuronium, and 3.69 (3.59-3.80) µM for vecuronium. The half effective concentrations (95% CI) of carboxymethyl-γ-cyclodextrin and sugammadex were 35.89 (32.67-39.41) µM and 3.67 (3.43-3.92) µM, respectively, for the reversal of rocuronium-induced block; 10.14 (9.61-10.70) µM and 0.67 (0.62-0.74) µM, respectively, for the reversal of pipecuronium-induced block; and 376.1 (341.9-413.8) µM and 1.45 (1.35-1.56) µM, respectively, for the reversal of vecuronium-induced block. CONCLUSIONS: Carboxymethyl-γ-cyclodextrin is an effective, but less potent agent for reversal of neuromuscular block than sugammadex.

Ipsilateral and Simultaneous Comparison of Responses from Acceleromyography- and Electromyography-based Neuromuscular Monitors.

BACKGROUND: The paucity of easy-to-use, reliable objective neuromuscular monitors is an obstacle to universal adoption of routine neuromuscular monitoring. Electromyography (EMG) has been proposed as the optimal neuromuscular monitoring technology since it addresses several acceleromyography limitations. This clinical study compared simultaneous neuromuscular responses recorded from induction of neuromuscular block until recovery using the acceleromyography-based TOF-Watch SX and EMG-based TetraGraph. METHODS: Fifty consenting patients participated. The acceleromyography and EMG devices analyzed simultaneous contractions (acceleromyography) and muscle action potentials (EMG) from the adductor pollicis muscle by synchronization via fiber optic cable link. Bland-Altman analysis described the agreement between devices during distinct phases of neuromuscular block. The primary endpoint was agreement of acceleromyography- and EMG-derived normalized train-of-four ratios greater than or equal to 80%. Secondary endpoints were agreement in the recovery train-of-four ratio range less than 80% and agreement of baseline train-of-four ratios between the devices. RESULTS: Acceleromyography showed normalized train-of-four ratio greater than or equal to 80% earlier than EMG. When acceleromyography showed train-of-four ratio greater than or equal to 80% (n = 2,929), the bias was 1.3 toward acceleromyography (limits of agreement, -14.0 to 16.6). When EMG showed train-of-four ratio greater than or equal to 80% (n = 2,284), the bias was -0.5 toward EMG (-14.7 to 13.6). In the acceleromyography range train-of-four ratio less than 80% (n = 2,802), the bias was 2.1 (-16.1 to 20.2), and in the EMG range train-of-four ratio less than 80% (n = 3,447), it was 2.6 (-14.4 to 19.6). Baseline train-of-four ratios were higher and more variable with acceleromyography than with EMG. CONCLUSIONS: Bias was lower than in previous studies. Limits of agreement were wider than expected because acceleromyography readings varied more than EMG both at baseline and during recovery. The EMG-based monitor had higher precision and greater repeatability than acceleromyography. This difference between monitors was even greater when EMG data were compared to raw (nonnormalized) acceleromyography measurements. The EMG monitor is a better indicator of adequate recovery from neuromuscular block and readiness for safe tracheal extubation than the acceleromyography monitor.

International survey of neuromuscular monitoring in two European countries: a questionnaire study among Hungarian and Romanian anaesthesiologists.

BACKGROUND: Accumulating evidence indicates that objective neuromuscular monitoring and pharmacological reversal of neuromuscular block reduces the occurrence of residual muscle paralysis in the acute postoperative phase. However, objective neuromuscular monitoring is not a routine habit in anaesthesia. In order to change this situation, we wished to find out, as a first step to improvement, the current use of neuromuscular monitors and the custom of anaesthetists for reversal of neuromuscular block before tracheal extubation. METHODS: A ten-point questionnaire was available via the Surveymonkey website and the link was sent to 2202 Hungarian and Romanian anaesthetists by email. RESULTS: Three hundred and two (13.7%) of the 2202 registered anaesthetists responded. Less than 10% of them regularly use neuromuscular monitors. They underestimated the occurrence of residual block; only 2.2% gave a correct answer. Neuromuscular monitors are available in 74% of hospitals but are scarcely used. One third of anaesthetists rarely or never use reversal; approximately 20% regularly reverse before extubation. The responders typically believe that clinical signs of residual block are reliable. Instead of monitoring, they use the "timing methods" for tracheal extubation such as time elapsed from last dose, the duration of action of relaxant, the number of top-up doses, the cumulative dose, the return of adequate respiratory tidal volume and the ability to sustain a 5 s head lift. CONCLUSIONS: We concluded that neuromuscular monitoring in these two European countries is suboptimal as is the reversal strategy. Given the fact that monitors are available in the hospitals, the mentality should be changed towards evidence based practice.

The effect of magnesium on the reversal of rocuronium-induced neuromuscular block with sugammadex: an ex vivo laboratory study.

BACKGROUND: Magnesium dose-dependently potentiates the effect of non-depolarizing neuromuscular blocking agents. We investigated whether the potentiation of rocuronium-induced blockade by magnesium reduces the effect of sugammadex in an ex-vivo environment and how this influences the safety margin of reversal. METHODS: Phrenic nerve - hemidiaphragm tissue preparations were isolated from male Wistar rats. The specimens were suspended in a tissue holder that allowed registering muscle contraction amplitude following electrical stimulation of the nerve. Concentration-response relationships were elucidated for magnesium, as well as for rocuronium and sugammadex. RESULTS: The mean (95% confidence interval [CI]) half effective concentrations (EC50) of rocuronium in the presence of magnesium 1 mM or 1.5 mM were 7.50 µM (6.97-8.07 µM) and 4.25 µM (4.09-4.41 µM), respectively (p < 0.0001). Increasing magnesium from 1 mM to 1.5 mM during reversal of rocuronium-induced block increased the mean (95% CI) EC50 of sugammadex from 3.67 µM (3.43-3.92 µM) to 5.36 µM (5.18-5.53 µM), whereas mean (95% CI) effective concentrations for 95% effect (EC95) were not significantly different at 7.22 µM (6.09-8.54 µM) and 7.61 µM (7.05-8.20 µM), respectively (p = 0.542). When rocuronium-induced block was reversed to a train-of-four (TOF) ratio > 0.9, but with still visible fade, increasing magnesium from 1 mM to 2 mM decreased the TOF ratio to below 0.9. If there was no visible fade after reversal, increasing magnesium concentration did not reduce the TOF ratio. CONCLUSIONS: Magnesium potentiates the neuromuscular effect of rocuronium and shifts the concentration-response curve to the left. Magnesium decreases the safety margin of reversal of rocuronium-induced neuromuscular block with sugammadex.

Reversal of Deep Pipecuronium-Induced Neuromuscular Block With Moderate Versus Standard Dose of Sugammadex: A Randomized, Double-Blind, Noninferiority Trial.

BACKGROUND: Certain surgical interventions may require a deep neuromuscular block (NMB). Reversal of such a block before tracheal extubation is challenging. Because anticholinesterases are ineffective in deep block, sugammadex 4 mg/kg has been recommended for the reversal of rocuronium- or vecuronium-induced deep NMB. However, this recommendation requires opening 2 vials of 200 mg sugammadex, which results in an increase in drug costs. Therefore, we sought a less expensive solution for the induction and reversal of deep NMB. Although the optimal dose of sugammadex for antagonism of deep block from pipecuronium has not been established, data pertaining to moderate block are available. Accordingly, we hypothesized that sugammadex 2 mg/kg would be a proper dose to reverse deep pipecuronium block, enabling us to avoid cost increases. In the present study, we compared sugammadex 2 mg/kg with the standard dose of 4 mg/kg for reversal of deep block from pipecuronium. METHODS: This single-center, randomized, double-blind, 2 parallel-arms, noninferiority study comprised 50 patients undergoing general anesthesia with propofol, sevoflurane, fentanyl, and pipecuronium. Neuromuscular monitoring was performed with acceleromyography (TOF-Watch SX). Noninferiority margin was specified beforehand as an increase in reversal time of no >10% (corresponding to 1 minute for the primary outcome). When the block spontaneously recovered to posttetanic count 1, the patients randomly received sugammadex 2 or 4 mg/kg, and the time from the injection to the train-of-four (TOF) ratio of 1.0 was measured. Primary outcome was the time to achieve the normalized TOF ratio of 0.9 in a particular patient. Residual or recurrent postoperative NMB was additional end point. RESULTS: Each patient recovered to the normalized TOF ratio of 0.9. In the 2 mg/kg group, reversal time was 1.73 ± 1.03 minutes (95% confidence interval [CI], 1.33-2.13; n = 25), and in the 4 mg/kg group, reversal time was 1.42 ± 0.63 minutes (mean ± standard deviation) (95% CI, 1.17-1.67; n = 25). The mean difference in reversal times between the 2 groups was 0.31 minutes (95% CI, -0.18 to 0.8), and the upper limit of CI was below the noninferiority margin of 1 minute. Postoperative block did not occur. CONCLUSIONS: The effect of sugammadex 2 mg/kg was noninferior to that of 4 mg/kg in reversing posttetanic count-1 degree pipecuronium block. Sugammadex reversal of deep pipecuronium block appears to be effective.

Reversal of Vecuronium-induced Neuromuscular Blockade with Low-dose Sugammadex at Train-of-four Count of Four: A Randomized Controlled Trial.

BACKGROUND: Rocuronium-induced neuromuscular block that spontaneously recovered to a train-of-four count of four can be reversed with sugammadex 0.5 or 1.0 mg/kg. We investigated whether these doses of sugammadex can also reverse vecuronium at a similar level of block. METHODS: Sixty-five patients were randomly assigned, and 64 were analyzed in this controlled, superiority study. Participants received general anesthesia with propofol, sevoflurane, fentanyl, and vecuronium. Measurement of neuromuscular function was performed with acceleromyography (TOF-Watch-SX, Organon Teknika B.V., The Netherlands ). Once the block recovered spontaneously to four twitches in response to train-of-four stimulation, patients were randomly assigned to receive sugammadex 0.5, 1.0, or 2.0 mg/kg; neostigmine 0.05 mg/kg; or placebo. Time from study drug injection to normalized train-of-four ratio 0.9 and the incidence of incomplete reversal within 30 min were the primary outcome variables. Secondary outcome was the incidence of reparalysis (normalized train-of-four ratio less than 0.9). RESULTS: Sugammadex, in doses of 1.0 and 2.0 mg/kg, reversed a threshold train-of-four count of four to normalized train-of-four ratio of 0.9 or higher in all patients in 4.4 ± 2.3 min (mean ± SD) and 2.6 ± 1.6 min, respectively. Sugammadex 0.5 mg/kg reversed the block in 6.8 ± 4.1 min in 70% of patients (P < 0.0001 vs. 1.0 and 2.0 mg/kg), whereas neostigmine produced reversal in 11.3 ± 9.7 min in 77% of patients (P > 0.05 vs. sugammadex 0.5 mg/kg). The overall frequency of reparalysis was 18.7%, but this incidence varied from group to group. CONCLUSIONS: Sugammadex 1.0 mg/kg, unlike 0.5 mg/kg, properly reversed a threshold train-of-four count of four vecuronium-induced block but did not prevent reparalysis.

Design and evaluation of artificial receptors for the reversal of neuromuscular block.

Applying patient friendly and cost-efficient medications in healthcare will be a real challenge in the 21st century. Sugammadex is a selective, yet expensive agent used for the post-surgical reversal of neuromuscular block since 2008. A wide library of cyclodextrin-based follow-ups, having potentially similar affinity towards target aminosteroid type neuromuscular blocking agents has been established. Almost 20 compounds were assessed with respect to in vitro affinity against three commonly applied drugs. Based on the capillary electrophoretic screening, carboxymethylated and sulfobutylated gamma-cyclodextrin derivatives have the potential to be promising lead molecules for their affinity towards pipecuronium was identical or even superior to Sugammadex. Carboxymethylated gamma-cyclodextrin showed efficient and complete reversal of the pipecuronium induced neuromuscular block in an ex vivo rat diaphragm experiment.

Impact of reversal strategies on the incidence of postoperative residual paralysis after rocuronium relaxation without neuromuscular monitoring: A partially randomised placebo controlled trial.

BACKGROUND: Electronic neuromuscular monitoring is not widely used to determine either the reversal requirements for neuromuscular block before extubation of the trachea, or to determine if there is any subsequent postoperative residual neuromuscular block (PORNB). OBJECTIVES: To investigate the incidence of PORNB using acceleromyography after spontaneous recovery of rocuronium-induced block and to compare this with the administration of sugammadex, neostigmine or a placebo. DESIGN: Partially randomised, partially randomised, placebo-controlled, double-blind, four-group parallel-arm study. SETTING: Single-centre study performed between October 2013 and December 2015 in a university hospital. PATIENTS: Of the 134 eligible patients, 128 gave their consent and 125 of these completed the study. INTERVENTIONS: Patients received general anaesthesia with propofol, sevoflurane, fentanyl and rocuronium. Neuromuscular transmission was measured by acceleromyography (TOF-Watch-SX; Organon Teknika B.V., Boxtel, the Netherlands) but the anaesthetist was blind to the results. If the anaesthetist deemed pharmacological reversal to be necessary before extubation of the trachea then patients were assigned randomly to receive either sugammadex (2.0 mg kg), neostigmine (0.05 mg kg) or a placebo. In the postanaesthesia care unit, an independent anaesthetist, unaware of the treatment given, assessed the neuromuscular function using acceleromyography. MAIN OUTCOME MEASURES: The incidence of a normalised train-of-four ratio less than 0.9 on arrival in the recovery room. RESULTS: In total, 125 patients were recruited. Neuromuscular block was allowed to recover spontaneously in 50 patients, whereas the remainder received either sugammadex (27), neostigmine (26) or placebo (22). The number of cases with PORNB were one (3.7%), four (15%), 13 (26%) and 10 (45%) after sugammadex, neostigmine, spontaneous recovery and placebo, respectively. Sugammadex and neostigmine were more effective than placebo [odds ratio (OR): 0.05, 95% confidence interval (CI): 0.005 to 0.403, P = 0.005; OR: 0.22, 95% CI: 0.056 to 0.85, P = 0.028, respectively]. Sugammadex performed better than spontaneous recovery (OR: 0.11, 95% CI: 0.014 to 0.89, P = 0.039) unlike neostigmine (OR: 0.52, 95% CI: 0.15 to 1.79, P = 0.297). Yet, antagonism (pooled data) was more effective than spontaneous recovery (OR: 0.3, 95% CI: 0.1 to 0.9, P = 0.03). CONCLUSION: Although pharmacological reversal based on clinical signs was superior to spontaneous recovery it did not prevent PORNB, irrespective of the reversal agent. TRIAL REGISTRATION: The study is registered under EUDRACT number 2013-001965-17.

Reversal of Pipecuronium-Induced Moderate Neuromuscular Block with Sugammadex in the Presence of a Sevoflurane Anesthetic: A Randomized Trial.

BACKGROUND: Pipecuronium is a steroidal neuromuscular blocking agent. Sugammadex, a relaxant binding γ-cyclodextrin derivative, reverses the effect of rocuronium, vecuronium, and pancuronium. We investigated whether sugammadex reverses moderate pipecuronium-induced neuromuscular blockade (NMB) and the doses required to achieve reversal. METHODS: This single-center, randomized, double-blind, 5-group parallel-arm study comprised 50 patients undergoing general anesthesia with propofol, sevoflurane, fentanyl, and pipecuronium. Neuromuscular monitoring was performed with acceleromyography (TOF-Watch SX) according to international standards. When the NMB recovered spontaneously to train-of-four count 2, patients randomly received 1.0, 2.0, 3.0, or 4.0 mg/kg of sugammadex or placebo. Recovery time from sugammadex injection to normalized train-of-four (TOF) ratio 0.9 was the primary outcome variable. The recovery time from the sugammadex injection to final T1 was the secondary end point. Postoperative neuromuscular functions were also assessed. RESULTS: Each patient who received sugammadex recovered to a normalized TOF ratio of 0.9 within 5.0 minutes (95% lower confidence interval for the lowest dose 70.1%; for all doses 90.8%) and 79% of these patients reached a normalized TOF ratio 0.9 within 2.0 minutes (95% lower confidence interval for the lowest dose 26.7%; for all doses 63.7%). T1 recovered several minutes after the TOF ratio. No residual postoperative NMB was observed. CONCLUSIONS: Sugammadex adequately and rapidly reverses pipecuronium-induced moderate NMB during sevoflurane anesthesia. Once the train-of-four count has spontaneously returned to 2 responses following pipecuronium administration, a dose of 2.0 mg/kg of sugammadex is sufficient to reverse the NMB.

Efficacy of sugammadex for the reversal of moderate and deep rocuronium-induced neuromuscular block in patients pretreated with intravenous magnesium: a randomized controlled trial.

BACKGROUND: Magnesium enhances the effect of rocuronium. Sugammadex reverses rocuronium-induced neuromuscular block. The authors investigated whether magnesium decreased the efficacy of sugammadex for the reversal of rocuronium-induced neuromuscular block. METHODS: Thirty-two male patients were randomized in a double-blinded manner to receive magnesium sulfate (MgSO4) 60 mg/kg or placebo intravenously before induction of anesthesia with propofol, sufentanil, and rocuronium 0.6 mg/kg. Neuromuscular transmission was monitored using TOF-Watch SX acceleromyography (Organon Ltd., Dublin, Ireland). In 16 patients, sugammadex 2 mg/kg was administered intravenously at reappearance of the second twitch of the train-of-four (moderate block). In 16 further patients, sugammadex 4 mg/kg was administered intravenously at posttetanic count 1 to 2 (deep block). Primary endpoint was recovery time from injection of sugammadex to normalized train-of-four ratio 0.9. Secondary endpoint was recovery time to final T1. RESULTS: Average time for reversal of moderate block was 1.69 min (SD, 0.81) in patients pretreated with MgSO4 and 1.76 min (1.13) in those pretreated with placebo (P = 0.897). Average time for reversal of deep block was 1.77 min (0.83) in patients pretreated with MgSO4 and 1.98 min (0.58) in those pretreated with placebo (P = 0.572). Times to final T1 were longer compared with times to normalized train-of-four ratio 0.9, without any difference between patients pretreated with MgSO4 or placebo. CONCLUSION: Pretreatment with a single intravenous dose of MgSO4 60 mg/kg does not decrease the efficacy of recommended doses of sugammadex for the reversal of a moderate and deep neuromuscular block induced by an intubation dose of rocuronium.

Reversal of neuromuscular blockade with sugammadex at the reappearance of four twitches to train-of-four stimulation.

BACKGROUND: Doses of sugammadex required to reverse deep, moderate, and shallow rocuronium-induced neuromuscular blockade have been established. However, no adequate doses for the reversal of reappearance of four twitches of train-of-four (TOF) stimulation (threshold TOF-count-four) have been established. METHODS: This single-center, randomized, controlled, double-blind, four-groups parallel-arm study included 80 patients undergoing general anesthesia with propofol, sevoflurane, fentanyl, and rocuronium. Neuromuscular monitoring was performed with calibrated acceleromyography. Once rocuronium-induced neuromuscular blockade recovered spontaneously to threshold TOF-count-four, patients randomly received 0.5, 1.0, 2.0 mg/kg of sugammadex or 0.05 mg/kg of neostigmine. The time between study drug injection and reversal of TOF ratios to 1.0 was measured. Rapid reversal (≤2.0 min average, upper limit of 5.0 min) was the primary endpoint and slower reversal (≤5.0 min average, upper limit of 10 min) was the secondary endpoint of the study. RESULTS: Sugammadex, in doses of 1.0 and 2.0 mg/kg, reversed threshold TOF-count-four to TOF ratios of 1.0 in 2.1±0.8 min (mean±SD) and 1.8±0.9 min, respectively. Sugammadex, 0.5 mg/kg, induced a similar degree of reversal in 4.1±1.9 min (P<0.001 vs. 1.0 and 2.0 mg/kg). Neostigmine, 0.05 mg/kg, reversed TOF ratios to 1.0 in 8.5±3.5 min (P<0.001 vs. sugammadex groups). CONCLUSION: Sugammadex, 1.0 mg/kg, rapidly and effectively reverses rocuronium-induced block that has recovered spontaneously to a threshold TOF-count-four. A dose of 0.5 mg/kg was equally effective, but satisfactory antagonism took as long as 8 min to take place.

Low concentrations of ketamine initiate dendritic atrophy of differentiated GABAergic neurons in culture.

Administration of subanesthetic concentrations of ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) type of glutamate receptors, is a widely accepted therapeutic modality in perioperative and chronic pain management. Although extensive clinical use has demonstrated its safety, recent human histopathological observations as well as laboratory data suggest that ketamine can exert adverse effects on central nervous system neurons. To further investigate this issue, the present study was designed to evaluate the effects of ketamine on the survival and dendritic arbor architecture of differentiated gamma-aminobutyric acidergic (GABAergic) interneurons in vitro. We show that short-term exposure of cultures to ketamine at concentrations of > or =20 microg/ml leads to a significant cell loss of differentiated cells and that non-cell death-inducing concentrations of ketamine (10 microg/ml) can still initiate long-term alterations of dendritic arbor in differentiated neurons, including dendritic retraction and branching point elimination. Most importantly, we also demonstrate that chronic (>24 h) administration of ketamine at concentrations as low as 0.01 microg/ml can interfere with the maintenance of dendritic arbor architecture. These results raise the possibility that chronic exposure to low, subanesthetic concentrations of ketamine, while not affecting cell survival, could still impair neuronal morphology and thus might lead to dysfunctions of neural networks.

Effect of ketamine on dendritic arbor development and survival of immature GABAergic neurons in vitro.

Ketamine, a noncompetitive antagonist of the N-methyl-D-aspartate type of glutamate receptors, was reported to induce neuronal cell death when administered to produce anesthesia in young rodents and monkeys. Subanesthetic doses of ketamine, as adjuvant to postoperative sedation and pain control, are also frequently administered to young children. However, the effects of these low concentrations of ketamine on neuronal development remain unknown. The present study was designed to evaluate the effects of increasing concentrations (0.01-40 microg/ml) and durations (1-96 h) of ketamine exposure on the differentiation and survival of immature gamma-aminobutyric acidergic (GABAergic) interneurons in culture. In line with previous studies (Scallet et al., 2004), we found that a 1-h-long exposure to ketamine at concentrations > or = 10 microg/ml was sufficient to trigger cell death. At lower concentrations of ketamine, cell loss was only observed when this drug was chronically (> 48 h) present in the culture medium. Most importantly, we found that a single episode of 4-h-long treatment with 5 microg/ml ketamine induced long-term alterations in dendritic growth, including a significant (p < 0.05) reduction in total dendritic length and in the number of branching points compared to control groups. Finally, long-term exposure (> 24 h) of neurons to ketamine at concentrations as low as 0.01 microg/ml also severely impaired dendritic arbor development. These results suggest that, in addition to its dose-dependent ability to induce cell death, even very low concentrations of ketamine could interfere with dendritic arbor development of immature GABAergic neurons and thus could potentially interfere with the development neural networks.

Clinically relevant concentrations of propofol but not midazolam alter in vitro dendritic development of isolated gamma-aminobutyric acid-positive interneurons.

BACKGROUND: Recent laboratory studies showed that exposure to supraclinical concentrations of propofol can induce cell death of immature neurons. However, no data are available regarding the effects of clinically relevant concentrations of this agent on neuronal development. The authors addressed this issue by evaluating the effect of propofol on dendritic growth and arbor expansion of developing gamma-aminobutyric acid-positive (GABAergic) interneurons. METHODS: Immature neuroblasts were isolated from the newborn rat subventricular zone and differentiated into GABAergic interneurons in culture. In addition to cell death, the effects of increasing concentrations and durations of propofol exposure on neuronal dendritic development were evaluated using the following morphologic parameters: total dendritic length, primary dendrites, branching point, and Scholl analysis. RESULTS: The authors demonstrate that propofol induced cell death of GABAergic neurons at concentrations of 50 microg/ml or greater. As little as 1 microg/ml propofol significantly altered several aspects of dendritic development, and as little as 4 h of exposure to this agent resulted in a persistent decrease in dendritic growth. In contrast, application of midazolam did not affect neuronal development. CONCLUSION: Short-term exposure of immature developing GABAergic neurons to clinically relevant concentrations of propofol can induce long-term changes in dendritic arbor development. These results suggest that propofol anesthesia during central nervous system development could interfere with the molecular mechanisms driving the differentiation of GABAergic neurons and thus could potentially lead to impairment of neural networks.

Effect of magnesium, high altitude and acute mountain sickness on blood flow velocity in the middle cerebral artery.

Cerebral blood flow is thought to increase at high altitude and in subjects suffering from acute mountain sickness (AMS); however, data from the literature are contentious. Blood flow velocity in the middle cerebral artery (MCAv) may be used as a proxy measure of cerebral blood flow. Using transcranial Doppler sonography, MCAv was measured during normo- and hyper-ventilation in subjects who participated in a trial that tested the effect of magnesium supplementation on the prevention of AMS. First, MCAv was recorded at 353 m (baseline). Subjects were then randomized to receive oral magnesium citrate and matching placebo. A second measurement was taken after a 24 +/- 2 h ascent from 1130 m to 4559 m (altitude I), and a third after a 20-24 h stay at 4559 m (altitude II). Using multivariate linear regression, an association was sought between MCAv and magnesium supplementation, subjects' age and gender, altitude itself, a temporary stay at altitude, and the presence of AMS (Lake Louise Score >6 with ataxia, nausea and/or headache). Subjects with AMS had additional Doppler recordings immediately before and after rescue medication (oxygen, dexamethasone and acetazolamide). Forty-seven subjects had measurements at baseline, 39 (21 receiving magnesium and 18 placebo) at altitude I and 26 (13 receiving magnesium and 13 placebo) at altitude II. During hyperventilation, MCAv decreased consistently (for each measurement, P<0.001). Magnesium significantly increased MCAv by 8.4 cm.s(-1) (95% confidence interval, 1.8-15), but did not prevent AMS. No other factors were associated with MCAv. Eleven subjects had severe AMS [median score (range), 11 (8-16)] and, after rescue medication, the median score decreased to 3 (range, 0-5; P=0.001), but MCAv remained unchanged (65 +/- 18 cm.s(-1) before compared with 67 +/- 16 cm.s(-1) after rescue medication; P=0.79). MCAv was increased in subjects who received magnesium, but was not affected by exposure to high altitude or by severe AMS.

Magnesium for the prevention and treatment of acute mountain sickness.

Magnesium is a physiological N-methyl-D-aspartate (NMDA) antagonist. The NMDA receptor may be involved in the pathogenesis of acute mountain sickness (AMS). In the present study, healthy subjects were randomized to receive either 400 mg of oral magnesium citrate (16 mmol) or matching placebo every 8 h for 5 days (prevention trial). Subjects then climbed to 4559 m in approx. 24 h and stayed there for 48 h. A Lake Louise Score <3 at any time was defined as the absence of AMS, whereas a score >6 (with ataxia, headache and nausea) was defined as a prevention failure. In a subsequent trial (treatment trial), subjects with a Lake Louise Score >6 (with ataxia, headache and/or nausea) were randomized to receive either 4 g of intravenous magnesium sulphate (16 mmol) or matching placebo. A decrease in the score >50% within 60 min was regarded as a treatment success. Dichotomous data were analysed using relative risk (RR) or odds ratio (OR), and continuous data using Student's t test or Wilcoxon's rank-sum test. In the prevention trial, data from 61 subjects (30 receiving magnesium and 31 placebo) were analysed. With oral magnesium, 20% of subjects had no AMS compared with 16.1% in the placebo group [RR (95% CI), 1.2 (0.4-3.6); where CI is confidence interval]. With magnesium, 40% were prevention failures compared with 35.5% in the placebo group [RR (95% CI), 1.13 (0.59-2.15)]. The mean time to failure and severity of AMS was similar between the two groups. With magnesium, 38.2% had loose stools compared with 11.8% in placebo group [RR (95% CI), 3.25 (1.18-8.97)]. In the treatment trial, 12 subjects received magnesium and 13 received the placebo. With intravenous magnesium, 25% were regarded as treatment successes compared with none in the placebo group [OR (95% CI), 9.71 (0.91-103.4)]. With magnesium, mean (+/- S.D.) scores decreased from 11.6 +/- 1.7 before treatment to 9.0 +/- 3.5 after treatment (P=0.009); scores remained unchanged in the placebo group. With magnesium, 75% of subjects experienced a transient flushing compared with 7.7% in the placebo group [RR (95% CI), 0.05 (0.01-0.25)]. In conclusion, oral magnesium does not prevent AMS. In subjects with established AMS, intravenous magnesium reduces the severity of symptoms to some extent, but this effect is of no clinical importance.