Effect of Magnesium on Deterioration and Symptomatic Hemorrhagic Transformation in Cerebral Ischemia: An Ancillary Analysis of the FAST-MAG Trial.

BACKGROUND: Magnesium (Mg) is a neuroprotectant in preclinical models. Lower serum Mg levels have been associated with symptomatic hemorrhagic transformation (HT) in patients with ischemic stroke. Early treatment of acute ischemic stroke with Mg may reduce rates of symptomatic HT. METHODS: In this post hoc study of the Field Administration of Stroke Therapy Magnesium (FAST-MAG) trial, 1,245 participants with a diagnosis of cerebral ischemia received 20 g of Mg or placebo initiated in the prehospital setting. Posttreatment serum Mg level was measured for 809 participants. Cases of clinical deterioration, defined as worsening by ≥4 points on the National Institute of Health Stroke Scale (NIHSS), were imaged and evaluated for etiology. Symptomatic HT was defined as deterioration with imaging showing new hemorrhage. RESULTS: Clinical deterioration occurred in 187 and symptomatic HT in 46 of 1,245 cases of cerebral ischemia. Rates of deterioration and symptomatic HT were not significantly lower in those who received Mg (15.7% vs. 14.4%, p = 0.591; 2.8% vs. 4.6%, p = 0.281). In cases where serum Mg level was obtained posttreatment, lower serum Mg level (<1.7 mg/dL) was associated with significantly higher rates of deterioration and symptomatic HT (27.5% vs. 15.5%, p = 0.0261; 11.6% vs. 3.65%, p = 0.00819). CONCLUSIONS: Treatment with Mg did not significantly reduce rates of clinical deterioration or symptomatic HT. Future analysis should address whether treatment with Mg could have influenced the subgroup with low serum Mg at baseline.

A Normalized Model of a Microelectromechanical Relay Calibrated by Laser-Doppler Vibrometry.

This work presents a behavioral model for a microelectromechanical (MEM) relay for use in circuit simulation. Models require calibration, and other published relay models require over a dozen parameters for calibration, many of which are difficult to extract or are only available after finite element analysis. This model improves on prior work by taking advantage of model normalization, which often results in models that require fewer parameters than un-normalized models. This model only needs three parameters extracted from experiment and one dimension known from device fabrication to represent its non-contact behavior, and two additional extracted parameters to represent its behavior when in contact. The extracted parameters-quality factor, resonant frequency, and the pull-in voltage-can be found using laser Doppler vibrometry. The device dimension is the actuation gap size, which comes from process data. To demonstrate this extraction process, a series of velocity step responses were excited in MEM relays, the measured velocity responses were used to calibrate the model, and then then simulations of the model (implemented in Verilog-A) were compared against the measured data. The error in the simulated oscillation frequency and peak velocity, two values selected as figures of merit, is less than 10% across many operating voltages.

Direct Endoscopic Visualization Combined with Ultrasound Guided Access during Percutaneous Nephrolithotomy: A Feasibility Study and Comparison to a Conventional Cohort.

PURPOSE: Percutaneous nephrolithotomy access may be technically challenging and result in significant radiation exposure. In an attempt to reduce percutaneous nephrolithotomy radiation exposure, a novel technique combining ultrasound and direct ureteroscopic visualization was developed and reviewed. MATERIALS AND METHODS: Ureteroscopy without fluoroscopy was used to determine the optimal calyx for access, which was punctured with a Chiba needle under percutaneous ultrasound guidance. Next a wire was passed into the collecting system and ureteroscopically pulled into the ureter using a basket. Tract dilation and sheath and nephrostomy tube placement were performed under direct ureteroscopic visualization. Twenty consecutive patients undergoing this novel technique were reviewed and compared to 20 matched patients treated with conventional percutaneous nephrolithotomy. Mann-Whitney U and Pearson chi-square tests were used for comparisons with p <0.05 considered significant. RESULTS: Using this novel technique mean fluoroscopy access time was 3.5 seconds (range 0 to 27.9) and mean total fluoroscopic time was 8.8 seconds (range 0 to 47.1). Mean operative time was 232 minutes (range 87 to 533), estimated blood loss was 111 ml, the stone-free rate was 65% and the complication rate was 25%. Compared to 20 matched conventional percutaneous nephrolithotomy cases, there was no difference in operative time (p=0.76), estimated blood loss (p=0.64), stone-free rate (p=0.50) or complications (p=1.00). However, the novel technique resulted in a significant reduction in fluoroscopy access time (3.5 vs 915.5 seconds, p <0.001) and total fluoroscopy time (8.8 vs 1,028.7 seconds, p <0.001). CONCLUSIONS: This study demonstrates the feasibility of combined ultrasound and ureteroscopic assisted access for percutaneous nephrolithotomy. A greater than 99% reduction in fluoroscopy time was achieved using this technique.

Percutaneous Externally Assembled Laparoscopic Instruments: Creation of a New Surgical Paradigm.

OBJECTIVES: Laparoendoscopic single-site surgery (LESS) and natural orifice transluminal endoscopic surgery (NOTES) produce excellent cosmetic outcomes, but are technically challenging. The objective of this study was to test the functionality and feasibility of a novel minimally invasive surgical paradigm, which maintains triangulation but uses special externally assembled instruments to minimize the postoperative cosmetic impact. METHODS: Percutaneous Externally Assembled Laparoscopic (PEAL) instruments have specialized 2.96-mm shafts with interchangeable 5-mm working tips that are assembled externally. First, 5-mm laparoscopic, PEAL, and 2-mm needlescopic instruments were tested to determine piercing force on fresh human cadaver organs. In a bench-top study, 20 subjects assembled and used PEAL instruments in five different skills tests that were also compared with the same tasks using conventional laparoscopic instruments. Finally, PEAL instrument functionality was tested in a four-porcine nephrectomy feasibility study. RESULTS: PEAL (2.80 lbF) and 5-mm laparoscopic instruments (2.28 lbF) had a significantly higher mean organ piercing perforation force compared with needlescopic instruments (1.39 lbF, p < 0.05). Average assembly time of PEAL instruments was 31.08 seconds (range: 19.83-43.85). There were no significant differences in the amount of time needed for completion of the bench-top tasks between laparoscopic and PEAL instruments (p > 0.05 for all tasks). Four-porcine PEAL nephrectomies were completed with no complications and minimal blood loss (mean 7.5 mL). Mean operative time was 98.25 minutes (range 79-116). CONCLUSION: PEAL tools are easily assembled, have similar safety and efficacy compared with standard laparoscopic tools, and are less likely to injure organs compared with needlescopic instruments. They function well during laparoscopic nephrectomy and may decrease the invasiveness of conventional laparoscopic instrumentation.