Potency and time course of mivacurium block during sevoflurane, isoflurane and intravenous anesthesia

PURPOSE: To determine the potency and time course of action of mivacurium neuromuscular block under routine clinical conditions during sevoflurane, isoflurane and intravenous anesthesia. METHOD: Patients were anesthetized with nitrous oxide 66% in oxygen and 1.5 MAC sevoflurane or isoflurane or a propofol infusion, neuromuscular block being monitored using mechanomyography. Potency was determined using administration of single doses of mivacurium of 40-100 micrograms.kg-1 and construction of dose-response curves (n = 72). The onset and duration of action were determined following a bolus dose of 0.2 mg.kg-1 of mivacurium (n = 30). RESULTS: The ED50 and ED95 (with 95% confidence limits) were estimated to be 42 (35-51) and 86 (74-98) micrograms.kg-1, 52 (45-60) and 89 (72-110) micrograms.kg-1, and 53 (45-62) and 95 (81-112) micrograms.kg-1 during sevoflurane, isoflurane and propofol anesthesia respectively (P < 0.05 between sevoflurane and propofol). Following administration of the 0.2 mg.kg-1 dose, neither the times (mean +/- SD) to maximum block (1.6 +/- 0.31, 1.7 +/- 0.21 and 1.6 +/- 0.45 min, respectively) nor the times to 25 and 90% recovery of T1 (20 +/- 4.5 and 33 +/- 8.8 min, 21 +/- 3.8 and 33 +/- 6.5 min, and 18 +/- 4.1 and 28 +/- 5.8 min respectively) were different among groups. The times to recovery of TOF ratio to 0.8 were 40 +/- 10.0, 36 +/- 8.5 and 29 +/- 5.5 min in the sevoflurane, isoflurane and propofol groups respectively (P = 0.017 between the sevoflurane and propofol groups). CONCLUSIONS: Under usual conditions of clinical anesthesia the potency of mivacurium was slightly enhanced during sevoflurane compared with intravenous anesthesia but the duration of action was only minimally prolonged during sevoflurane and isoflurane anesthesia.     

Robotic-Assisted Minimally Invasive Central Pancreatectomy: Technique and Outcomes

Background

Central pancreatectomy is a definitive treatment for low-grade tumors of the pancreatic neck that preserves pancreatic and splenic function at the potential expense of postoperative pancreatic fistula. We analyzed outcomes after robot-assisted central pancreatectomy (RACP) to reexamine the risk–benefit profile in the era of minimally invasive surgery.

Methods

Retrospective analysis of nine RACP performed between August 2009 through June 2010 at a single institution.

Results

The average age of the cohort was 64 (range 18–75 years) with six women (67 %). Indications for surgery included: five benign cystic neoplasm and four pancreatic neuroendocrine tumor. Median operative time was 425 min (range 305–506 min) with 190 ml median blood loss (range 50–350 ml) and one conversion to open due to poor visualization. Median tumor size was 3.0 cm (range 1.9–6.0 cm); all patients achieved R0 status. Pancreaticogastrostomy was performed in seven cases and pancreaticojejunostomy in two. The median length of hospital stay was 10 days (range 7–19). Two clinically significant pancreatic fistulae occurred with one requiring percutaneous drainage. No patients exhibited worsening diabetes or exocrine insufficiency at the 30-day postoperative visit.

Conclusions

RACP can be performed with safety and oncologic outcomes equivalent to published open series. Although the rate of pancreatic fistula was high, only 22 % had clinically significant events, and none developed worsening pancreatic endocrine or exocrine dysfunction.     

Biomechanical evaluation of a low profile, anchored cervical interbody spacer device in the setting of progressive flexion-distraction injury of the cervical spine

Introduction

Anterior cervical decompression and fusion is a well-established procedure for treatment of degenerative disc disease and cervical trauma including flexion-distraction injuries. Low-profile interbody devices incorporating fixation have been introduced to avoid potential issues associated with dissection and traditional instrumentation. While these devices have been assessed in traditional models, they have not been evaluated in the setting of traumatic spine injury. This study investigated the ability of these devices to stabilize the subaxial cervical spine in the presence of flexion-distraction injuries of increasing severity.

Methods

Thirteen human cadaveric subaxial cervical spines (C3–C7) were tested at C5–C6 in flexion–extension, lateral bending and axial rotation in the load-control mode under ±1.5 Nm moments. Six spines were tested with locked screw configuration and seven with variable angle screw configuration. After testing the range of motion (ROM) with implanted device, progressive posterior destabilization was performed in 3 stages at C5–C6.

Results

The anchored spacer device with locked screw configuration significantly reduced C5–C6 flexion–extension (FE) motion from 14.8 ± 4.2 to 3.9 ± 1.8°, lateral bending (LB) from 10.3 ± 2.0 to 1.6 ± 0.8, and axial rotation (AR) from 11.0 ± 2.4 to 2.5 ± 0.8 compared with intact under (p < 0.01). The anchored spacer device with variable angle screw configuration also significantly reduced C5–C6 FE motion from 10.7 ± 1.7 to 5.5 ± 2.5°, LB from 8.3 ± 1.4 to 2.7 ± 1.0, and AR from 8.8 ± 2.7 to 4.6 ± 1.3 compared with intact (p < 0.01). The ROM of the C5–C6 segment with locked screw configuration and grade-3 F-D injury was significantly reduced from intact, with residual motions of 5.1 ± 2.1 in FE, 2.0 ± 1.1 in LB, and 3.3 ± 1.4 in AR. Conversely, the ROM of the C5–C6 segment with variable-angle screw configuration and grade-3 F-D injury was not significantly reduced from intact, with residual motions of 8.7 ± 4.5 in FE, 5.0 ± 1.6 in LB, and 9.5 ± 4.6 in AR.

Conclusions

The locked screw spacer showed significantly reduced motion compared with the intact spine even in the setting of progressive flexion-distraction injury. The variable angle screw spacer did not sufficiently stabilize flexion–distraction injuries. The resulting motion for both constructs was higher than that reported in previous studies using traditional plating. Locked screw spacers may be utilized with additional external immobilization while variable angle screw spacers should not be used in patients with flexion-distraction injuries.     

A method for the direct electrical stimulation of the auditory system in deaf subjects: a functional magnetic resonance imaging study

PURPOSE: To develop a safe functional magnetic resonance imaging (fMRI) procedure for auditory assessment of deaf subjects. MATERIALS AND METHODS: A gold-plated tungsten electrode has been developed which has zero magnetic susceptibility. Used with carbon leads and a carbon reference pad, it enables safe, distortion-free fMRI studies of deaf subjects following direct electrical stimulation of the acoustic nerve. Minor pickup of the radio frequency (RF) pulses by the electrode assembly is difficult to eliminate, and a SPARSE acquisition sequence is used to avoid any effects of unintentional auditory nerve stimulation. RESULTS: The procedure is demonstrated in a deaf volunteer. Activation is observed in the contralateral but not the ipsilateral primary auditory cortex. This is in sharp contrast to studies of auditory processing in hearing subjects, but consistent with the small number of previous positron emission tomography (PET) and MR studies on adult deaf subjects. CONCLUSION: The fMRI procedure is able to demonstrate whether the auditory pathway is fully intact, and may provide a useful method for preoperative assessment of candidates for cochlear implantation.     

Plantar pressures and relative lesser metatarsal lengths in older people with and without forefoot pain

Forefoot pain is a common problem in older people. We determined whether plantar pressures during gait and the relative lengths of the lesser metatarsals differ between older people with and without plantar forefoot pain. Dynamic plantar pressure assessment during walking was undertaken using the Tekscan MatScan® system in 118 community‐dwelling older people (44 males and 74 females), mean age 74 (standard deviation = 5.9) years, 43 (36%) of whom reported current or previous plantar forefoot pain. The relative lengths of metatarsals 1–5 were determined from weightbearing X‐rays. Participants with current or previous plantar forefoot pain exhibited significantly (p = 0.032) greater peak plantar pressure under metatarsal heads 3–5 (1.93 ± 0.41 kg/cm² vs. 1.74 ± 0.48 kg/cm²). However, no differences were found in relative metatarsal lengths between the groups. These findings indicate that older people with forefoot pain generate higher peak plantar pressures under the lateral metatarsal heads when walking, but do not exhibit relatively longer lesser metatarsals. Other factors may be responsible for the observed pressure increase, such as reduced range of motion of the metatarsophalangeal joints and increased stiffness of plantar soft tissues. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 427–433, 2013