Lithospheric folding by flexural slip in subduction zones as source for reverse fault intraslab earthquakes.

Subduction requires the permanent generation of a bend fold in the subducting slab which mechanics is not well understood. Lithospheric bending of subducting slabs was traditionally considered to be accommodated by orthogonal flexure, generating extensional outer rise earthquakes responsible of the external arc elongation during folding. Here we explore the possibility of lithospheric flexure being accommodated through simple shear deformation parallel to the slab (folding by flexural slip) and evaluate this process as source of earthquakes. The seismicity predicted by flexural slip dominated slab bending explains a significant amount of intermediate earthquakes observed in subduction zones with different degrees of coupling. This mechanism predicts the generation of intraslab thrust earthquakes with fault planes subparallel to the slab top. Being the orientations of the fault planes the same for the interface thrust earthquakes and the flexural-slip intraslab earthquakes, the amount of seismic moment liberated by the interface could be significantly lower than considered before. This proposed seismic source should be taken into account in models and hazard studies of subduction zones. Determining the seismic generating processes in subduction zones and their characteristics is a fundamental issue for the correct assessment of the associated seismic and tsunami risk.

[Efficacy of sugammadex in the reversal of neuromuscular blockade induced by rocuronium in long-duration surgery: under inhaled vs. intravenous anesthesia]. / Eficacia de la reversión con sugammadex del bloqueo neuromuscular inducido por rocuronio en cirugía de larga duración. Comparación del efecto de la anestesia inhalatoria frente a intravenosa.

BACKGROUND AND OBJECTIVE: Sugammadex reverses neuromuscular blockade induced by aminosteroid agents by encapsulating these agents. The objective of this study was to compare the efficacy and safety of sugammadex to reverse a rocuronium-induced neuromuscular blockade in long-duration surgery in association with inhaled or intravenous anesthesia. PATIENTS AND METHODS: We performed a randomized, double-blind, multicenter trial of 20 ASA 1-3 patients aged between 18 and 69 years and scheduled for elective surgery lasting at least 120 minutes. Anesthesia was induced with remifentanil and rocuronium at a dosage of 0.6 mg x kg(-1), and neuromuscular function was monitored by means of acceleromyography. After randomization, anesthesia was maintained with sevoflurane or with propofol for total intravenous anesthesia. Patients in both groups also received an infusion of remifentanil for analgesia and rocuronium to maintain a block of greater than 90%. After surgery, sugammadex was administered at a dosage of 2 mg x kg(-1) on reappearance of the second train-of-four (TOF) twitch (T2) and the times until recovery of T4/T1 ratios of 0.7, 0.8, and 0.9 (main endpoints). Mean arterial pressure and heart rate were recorded at baseline and after 2, 5, 10, and 30 minutes (secondary outcome measures). RESULTS: Although less rocuronium was consumed in the sevoflurane group than in the propofol group and the time between the start of sugammadex administration until recovery of a TOF ratio of 0.9 was shorter for the sevoflurane group than for propofol group (mean [SD], 1.46 [0.30] minutes and 1.89 [0.62] minutes, respectively), these differences were not significant. No signs of recurarization or associated adverse effects were observed. CONCLUSIONS: Sugammadex effectively and safely reverses a rocuronium-induced neuromuscular blockade in less than 2 minutes in long-duration surgery performed under both inhaled and intravenous anesthesia. The interaction of neuromuscular blocking agents with sevoflurane appears not to affect the reversal time of sugammadex in such operations.

Sugammadex, una revolución en farmacología neuromuscular / Suggammadex, a revolutionary new drug to reverse neuromuscular block

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The cuff method: a pilot study of a new method of monitoring neuromuscular function.

BACKGROUND: A new method of monitoring neuromuscular blockade based on a modified blood pressure cuff that incorporates stimulating electrodes was compared with mechanomyography (MMG) ('gold standard'). METHODS: Forty adults and 20 children (ASA I-II) underwent neuromuscular blockade monitoring on the contralateral arms and on the same arm using the new cuff method and MMG. Only train-of-four (TOF) ratios > 0.1 and T(1) heights > 0 were studied. Supramaximal stimulation was also assessed. A device based on a PC with an analogue-to-digital conversion card was used to control and synchronize MMG and the cuff method. The agreement between both methods was assessed using the statistical method of Bland and Altman. RESULTS: When TOF ratios were >0.7, the bias between the two methods was -0.04 with the limits of agreement ranging from -0.21 to -0.12 (95% CI -0.06 to -0.02). The T(1) > 0 heights bias was -0.01 with the limits of agreement ranging from -0.26 to 0.24 (95% CI -0.02 to -0.003). The sensitivity of the cuff method was 88%, with a specificity of 85% and an accuracy of 86%. CONCLUSION: This pilot study indicates that the cuff method could be useful to monitor neuromuscular blockade according to the bias and limits of agreement compared with MMG, particularly when the degree of blockade was evaluated by TOF ratios > 0.7. The new cuff method is easy and simple to use. However, further studies in a larger number of patients are necessary to confirm these favourable preliminary results.

[Rocuronium]. / Rocuronio.

Rocuronium is a new nondepolarizing neuromuscular blocking agent (NDNMBA) that has recently been introduced for clinical use. Its main advantage over other such agents is its rapid onset of action, which may lead to its use as the relaxant of choice when rapid intubation is required. An additional advantage is that, unlike other amino-steroidal NDNMBAs, rocuronium does not produce active metabolites. The potency of rocuronium is five times lower than that of vecuronium and its half life at its place of effect is shorter. Selectivity for the laryngeal muscle system is greater, possibly explaining the rapid onset observed. Hemodynamic stability, along with the absence of histamine release even at doses as high as 4 to 5 ED95, allow it to be used in high risk patients. Successful use has been reported in emergency surgery in patients with full stomachs, in cesarean deliveries, in cardiovascular surgery, and in liver, kidney and other transplants. Rocuronium administered in repeated doses or in continuous infusion provides adequate muscle relaxation over the required period, with predictable reversibility of effects.

Pharmacokinetics and pharmacodynamics of rocuronium bromide in adult patients.

In seven patients (M/F: 4:3) rocuronium 0.6 mg kg-1 was given after the induction of anaesthesia with propofol, and during maintenance with N2O/O2, halothane 0.5% and alfentanil 60-90 micrograms kg-1 h-1. Intubation conditions were scored at 60 s and lag time, onset time, maximal block achieved, recovery to 25% of T1, and Recovery Index, were measured using a Relaxograph. Blood samples were taken over a 300 min period and analysed for rocuronium. Intubating conditions at 60 s were excellent in all patients. Mean clearance was 5.2 ml kg-1 min-1, the terminal half-life was 69 min and distribution volume at steady state was 0.22 litre kg-1. Cumulative urinary excretion was around 18% within 24 h.

[Speed of intubation using a new neuromuscular blocker. Rocuronium bromide (ORG 9426)]. / Rapidez de intubación de un nuevo bloqueador neuromuscular. Bromuro de rocuronio (ORG 9426).

OBJECTIVES: To compare intubation conditions and neuromuscular parameters, patency time, maximum level of block, time and clinical duration of effect for rocuronium bromide 0.6 mg/kg (ORG 9426) versus equally potent doses of vecuronium and atracurium under similar experimental conditions. PATIENTS AND METHODS: Sixty patients were divided into three groups of twenty. Intubation conditions were scored on a scale of 3-12 points based on relaxation of the vocal cords, presence of cough and ease of laryngoscopy after 60 or 90 sec. Neuromuscular parameters were obtained by integrated electromyography of the thenar and hypothenar muscle structure, evoked by supramaximal stimuli of the cubital nerve in train of four (2 Hz in 2 sec). The shape of the electrocardiographic curve, heart rate and mean arterial pressure measured non-invasively were recorded throughout the surgical procedure. RESULTS: Means of onset times and times of effect for rocuronium (33 and 135 sec) were significantly lower than those obtained with vecuronium and atracurium. Clinical duration, free of hemodynamic changes, was similar in the three groups. Rocuronium produces excellent intubation conditions 60 sec after administration, although at this point peripheral muscle block was only partial. Rocuronium may be superior to other neuromuscular blockers available today as a result of the speed with which it affords excellent intubation conditions.

[Comparison of the effects of midazolam and thiopental on the neuromuscular response of vecuronium, atracurium, and pancuronium]. / Comparación de los efectos del midazolam y del tiopental en la respuesta neuromuscular del vecuronio, atracurio y pancuronio.

To assess the possible interactions of midazolam and thiopental with the muscular relaxants vecuronium (0.08 mg/kg), atracurium (0.5 mg/kg), and pancuronium (0.1 mg/kg), a comparative analysis was undertaken in two groups of 18 and 32 patients treated respectively with midazolam (0.3 mg/kg) and thiopental (5 mg/kg). The beginning of the effect, maximal blockade, duration of the clinical response, and the spontaneous recovery index were measured on electromyographic recordings of action potentials evoked by train of four supramaximal stimuli delivered every 20 sec on the ulnar nerve. Conditions for intubation were assessed 2 minutes after administration of muscular relaxant. There were no significant differences in neuromuscular parameters in either of the two groups of patients treated with midazolam or with thiopental independently of the relaxant drug administered.

[Use of vecuronium and atracurium in continuous infusion. A comparative study using electromyography and accelerometry]. / Utilización del vecuronio y atracurio en infusión continua. Estudio comparativo con electromiografía y acelerometría.

Vecuronium and atracurium, muscle relaxant agents of intermediate action, were administered in continuous infusion to 175 patients undergoing prolonged surgical operations with the purpose of achieving serum concentrations inducing maintained blocking of neuromuscular function. We used a 0.08 mg/kg or 0.5 mg/kg bolus intubation dose followed by a continuous infusion of vecuronium (72 patients) or atracurium (103 patients) 10 minutes after, at the necessary pace to maintain inhibition of neuromuscular transmission over 90%. Monitoring of relaxation was done by means of four supramaximal stimuli trains which were repeated every 20 seconds and applied to the cubital nerve. Composite electromyogram (electromyography) and thumb acceleration (mechanomyography-accelerometry) were simultaneously recorded. Infusion was interrupted 15 minutes before ending the operation; reversion occurred spontaneously in 143 patients and 32 patients had to be reversed with neostigmine. Beginning of action, total duration of infusion, infusion speed, and 25-75 spontaneous and after decurarization recovery index were measured. Initial dose allowed an easy tracheal intubation and the constant relaxation achieved with 0.068 mg/kg/h and 0.46 mg/kg/h infusion of vecuronium and atracurium was adequate for all operations. Spontaneous recovery is often adequate at the end of operations in carefully monitored patients. Both monitoring methods are useful for clinical evaluation of neuromuscular transmission.

[A tiapride and ketamine combination in short duration anesthesia]. / Asociación de tiapride y ketamina en anestesia de corta duración.

Tiapride was used as premedication on a series of 16 patients subsequently submitted to general anesthesia with ketamine. In order to compare the effects of tiapride on the incidence of visionary dreams, hallucinations and dyslepsic syndrome brought about by, this series was compared with 2 further series of patients premedicated with dihydrobenzoperidol plus fentanyl (15 patients) and diazepam plus haloperidol (11 patients). Effectiveness was evaluated by means of a 10 point recovery scale (1: rate of sedation; 2: anterior amnesia; 3: comprehensiveness and collaboration test; 4: space sense and time orientation; 5: Bender test; 6: dysleptic syndrome; 7: sick feeling and vomit; 8: subjective status; 9: recovery quality; 10: dreams and hallucinations) at 15, 30 and 60 minutes after the administration of the different premedications. General tolerance was evaluated by continuous quantification of vital signs: pulse rate, EKG and systolic, diastolic and mean blood pressures. The effects were analysed with ANOVA one-way, Newman-Keuls and t-paired tests. Premedication with 7.5 mg/kg of tiapride significantly reduced the incidence of dreaming, provided the necessary sedation and appropiate postoperative analgesia and rapid recovery of psychomotor coordination with no obvious alterations in haemodynamic parameters attributable to the selective blocking action of the dopaminergic receptors. The association tiapride-ketamine may be useful in anesthesia for day-case surgery.

Prolonged suxamethonium-induced neuromuscular blockade associated with organophosphate poisoning.

We report a patient, exposed to Malathion during agricultural work, who suffered a prolonged apnoea after the administration of suxamethonium. He had a normal phenotype (E1u E1u), but an extremely low plasma cholinesterase activity. The diagnosis was made by assaying cholinesterase activity and analysing the enzymic components by electrophoresis on polyacrylamide gel slabs. The results indicated that the apnoea was a result of the low activity of plasma cholinesterase induced by Malathion.