Standard Insertion Research Articles

Decreasing MRSA Infections

INVASIVE INFECTIONS WITH METHICILLIN-RESISTANT STAPHYlococcus aureus (MRSA) have become a focus of national attention over the past several years due to their potentially lethal complications and reports indicating that their frequency is on the rise in most US hospitals. Hospitalizations with infections due to MRSA steadily increased between 2000 and 2005, nearly doubling in many areas of the country. Klevens et al estimated that up to 18 650 deaths in the United States in 2005 may have been associated with invasive MRSA infection. These statistics coupled with the increasing number of outbreaks of MRSA infections in community settings have helped ignite a contentious public debate about the best means of control, including calls for increased surveillance for MRSA infections, new prevention activities such as screening of all patients admitted to hospitals to detect colonization with MRSA (universal screening), and public reporting of hospitalacquired MRSA infections. Now amidst this alarm, the report by Burton and colleagues in this issue of JAMA documents decreases in the rate of MRSA-related central line–associated bloodstream infections (CLABSI) in hospitals participating in a voluntary surveillance network. This network was initially known as the National Nosocomial Infection Surveillance system (NNIS, 1997-2004) and later as the National Healthcare Safety Network (NHSN, 2006-2007). Facilities participating in NNIS/NSHN report to the Centers for Disease Control and Prevention (CDC) all health care–acquired infections detected during prospective surveillance in a variety of units. The current report details the experience with MRSA CLABSI in intensive care units (ICUs) from 1997 to 2007 and demonstrates that despite an overall increase in the incidence of MRSA infections, the rate of MRSA CLABSI decreased 49.6% at NNIS/NSHN hospitals. Four types of ICUs (surgical, cardiothoracic, coronary, and medical/surgical without a major teaching affiliation) initially experienced an increase in MRSA CLABSI lasting until 2001, but this was followed by declining rates through 2007. All units, except pediatric ICUs, experienced an overall decline in infections from 2002-2007. Moreover, both the overall rate of CLABSI and methicillin-sensitive S aureus (MSSA) CLABSI showed steady declines from 1997 to 2007 among all types of ICUs. Although the report by Burton et al suggests ICUs are having increasing success limiting the spread of MRSA, the study is not without limitations. The first concern is the dynamic nature of NNIS/NHSN. Fewer than 6% of ICUs in the current study participated in the NNIS/NHSN for the entire 11-year study interval. A large number of hospitals entered the network for the first time in 2007 prompted by mandatory public reporting requirements in many states, highlighting the changing nature of the network and challenging its description as a voluntary, hospital-based reporting system. In addition, although the authors contend that voluntary self-reporting was most likely accurate, it has not been validated since 1998. The accuracy of selfreporting may be an important issue in the upcoming era of mandatory public reporting and increased scrutiny of hospital-acquired infections by regulatory agencies. The study also leaves the unsettling realization that the observed reductions in infection cannot be attributed to any particular intervention. Previous reports from NNISparticipating ICUs have demonstrated reductions in bloodstream infections, ventilator-associated pneumonias, and catheter-associated urinary tract infections. These reports have led to the conclusion that prospective surveillance followed by careful local risk assessment and adoption of interventions that include best practices can be used to reduce hospital-acquired infection rates. It is likely that the reductions in infections reported by Burton et al were related to a range of interventions that have been implemented during the last decade including better hand hygiene practices, adoption of standardized line insertion and care practices, proper barrier precautions, improved catheter technology, and shorter periods of indwelling catheter use in patients. Thus, it is impossible to determine which practices had the greatest effect or even which were implemented by participating ICUs. Can the end be justified by the means, when the means are unknown?

Randomized clinical trial of a modified Seldinger technique for open central venous cannulation for implantable access devices

Totally implantable access ports (TIAPs) are often used for patients who need permanent venous access. The primary success rate using direct open insertion is about 80 per cent, so rescue strategies are needed. This study compared the primary success rates of standard open insertion and a modified Seldinger technique. This randomized trial recruited 164 patients scheduled for primary implantation of a TIAP and compared two interventions. The primary endpoint was the success rate of the implantation technique. The primary success rates were similar: 66 (80 per cent) of 82 patients who had standard open insertion versus 69 (84 per cent) of 82 patients undergoing the modified Seldinger method (P = 0.686). A logistic mixed regression analysis including treatment group, age, Karnofsky index, body mass index and surgeon's experience showed no advantage for the Seldinger method: odds ratio 1.30 (95 per cent confidence interval 0.62 to 2.70). TIAPs were eventually implanted successfully in 163 (99.4 per cent) of 164 patients. In 11 patients randomized to standard surgery, the Seldinger method was a successful rescue strategy. The primary success rate was similar for both open insertion methods. The modified Seldinger method is useful if standard open insertion fails. ISRCTN 52368201 (http://www.controlled-trials.com).

Partial and Double-Array Implantation of the Ossified Cochlea

To review our experience with partial standard and double-array cochlear implantation in the ossified cochlea. Retrospective case review. Tertiary referral center. Twenty cochleae in 19 adult and pediatric patients with ossified cochleae. Patients underwent either partial insertion of a standard electrode array or double-array electrode insertion for their cochlear implantation. Number of electrodes inserted, number of active electrodes at follow-up, and open-set speech performance. Twelve patients (four children and eight adults) had partial insertion of standard array electrode. The mean number of electrodes inserted and active at follow-up was 14.8 and 11.3, respectively. Eight patients (four children and four adults) had a double-array electrode implanted. The mean number of electrodes inserted and active at follow-up was 18.1 and 16.3, respectively. Open-set speech recognition was better in children regardless of duration of deafness. There were no complications. These findings suggest that the double array allows for more usable electrodes than in partially inserted cochlear implant. Compared with adults, children with ossified cochlea do well both in partial standard and double-array insertion. Both insertion techniques are safe, with no complications occurring in our patients. Straight and double arrays should be available in the operating suite for any patient in whom suspected cochlear ossification is confronted.

Wang-Zwische Double Lumen Cannula—Toward a Percutaneous and Ambulatory Paracorporeal Artificial Lung

We are developing a high performance double lumen cannula (DLC) for a minimally invasive, ambulatory and percutaneous paracorporeal artificial lung (PAL). The Wang-Zwische (W-Z) DLC was designed for percutaneous insertion into the Internal Jugular (IJ) vein with a drainage lumen open to both the superior vena cava (SVC) and the inferior vena cava (IVC) maximizing venous drainage. A separate collapsible but nondistensible membrane infusion lumen open to the right atrium (RA) achieves minimal recirculation allowing for total gas exchange. The W-Z DLC prototypes are made by a proprietary dip molding process with the "molded in" flat wire spiral stainless steel spring resulting in a flexible yet kink resistant thin wall (0.1 mm) outer cannula with one piece construction. With the ultra thin membrane infusion lumen collapsed, an introducer shaft fits tightly within the drainage lumen to facilitate insertion with placement at the SVC-RA-IVC junction. The W-Z DLC prototypes were tested while connected to a compact pump-gas exchanger circuit in three sheep (2 acute and one 15 day performance study). Insertion was simple, using standard percutaneous insertion techniques. Recirculation was as low as 2%. The 15 day performance study demonstrated our prototype 26 Fr W-Z DLC can achieve 2 L/min blood flow with minimal recirculation. The W-Z DLC design minimizes recirculation rate, maximizes flow lumen cross-sectional area, and maximizes achievable blood flow to enhance gas exchange performance allowing for one site percutaneous venovenous support.

A New Punctal Plug Insertion Technique to Prevent Intracanalicular Plug Migration

To evaluate the intracanalicular migration rate during plug insertion with a new plug insertion technique compared with a standard technique. Interventional, nonrandomized, comparative study. Forty-five patients with dry eye syndrome underwent a punctal plug insertion with the new technique, and 33 patients underwent a punctal plug insertion with a standard technique at the dry eye subspecialty outpatient clinic of the Department of Ophthalmology at Keio University. Tear function examinations and ocular surface evaluations, including the Schirmer test, tear film breakup time, fluorescein and Rose Bengal vital staining scores, were performed before punctal plug insertion. Super Flex Punctum Plugs (Eagle Vision, Memphis, Tennessee, USA; Softplug-Oasis Medical Inc, Glendora, California, USA) were implanted in all subjects with both techniques. In total, 120 procedures were carried out with the new technique and 132 procedures with the standard technique. There were no statistical differences between the two groups in tear function and ocular surface staining scores (P > .05). There was no intracanalicular plug migration with the new insertion technique, whereas there were 18 incidents of intracanalicular migration of 132 standard plug insertion procedures (13.6%). The new plug insertion technique seems to be effective in eliminating intracanalicular plug migration during the insertion procedure.

The Feasibility of Comprehensive IMRT Verification using Novel 3D Dosimetry Techniques Compatible with the RPC Head and Neck Phantom

The Feasibility of Comprehensive IMRT Verification using Novel 3D Dosimetry Techniques Compatible with the RPC Head and Neck Phantom

SU‐GG‐T‐135: Evaluation of PRESAGE/optical‐CT 3D Dosimetry for Commissioning a Linac for IMRT

Purpose: PRESAGE is a novel radiochromic plastic which, in combination with optical‐CT imaging, has been shown to have outstanding potential for high‐resolution three‐dimensional (3D) dosimetry. Here, the first application of PRESAGE/optical‐CT to commissioning a new accelerator for IMRT treatment.is presented. Commissioning was achieved using a modified Radiological Physics Center (RPC) IMRT credentialing phantom that enabled 3D dosimetry. Method and Materials: The RPC phantom was CT scanned twice, first with the standard insert and second with the modified PRESAGE insert. A 9‐field IMRT plan was created in the Eclipse planning system to meet the credentialing requirements on the standard CT‐scan, and to deliver 6.6Gy to the primary PTV. This plan was then recalculated on the second CT scan incorporating the PRESAGE insert. In the latter case, the prescription dose was reduced to 4Gy to avoid over‐exposing the dosimeter. Consistent relative fluence between the plans was verified by MapCHECK and DynaLog file analysis. After irradiation, evaluation of the PRESAGE/optical‐CT system was performed by comparison with the independent film and TLD measurements made at the RPC. Profile comparisons and gamma maps were generated to compare both sets of measurements with the eclipse planning dose distribution. Results: An improved acquisition technique led to high quality low noise 3D data (<1%rms) achieved using the PRESAGE/optical‐CT system. Excellent agreement was observed (gamma criteria of 3%, 2mm) between the PRESAGE and the Eclipse distributions. Similar agreement was observed between the corresponding EBT and Eclipse distributions. Conclusion: Prior studies from the RPC have shown IMRT commissioning is non‐trivial and prone to error. This work demonstrates successful integration of PRESAGE/optical‐CT dosimetry in the RPC IMRT credentialing phantoms. The high quality of the 3D dosimetry data (noise ∼1%, accurate to within 3%) represents a significant improvement over previous work with PRESAGE, and a new tool for comprehensive verification of IMRT treatments.

Nanoscale adaptive meshing for rapid STM imaging

The numerical evaluation of individual tunnel currents (pixels) constitutes the bottleneck of fast scanning tunneling microscopy (STM) imaging. The number and the position of grid points where the current is punctually evaluated have to be judiciously chosen to reveal the most important contrasts. In this note, we present an adaptive meshing approach that significantly accelerates the computation time to produce STM images by reducing the number of pixels to evaluate without affecting the final image resolution. This method iteratively reveals the STM image by selecting new probing locations that improves the image quality at each step. A straightforward method to compute a STM image is to send a high resolution square grid to a solver that will return a pixel color intensity for each node [1,2]. Since pixel calculation is the most time consuming step but is independent of the grid quality, redefining the surface discretization will reduce the amount of computed pixels and thus the time required to compute an image. This process is a step by step image analysis in which zones of interest, such as contrasts related to adsorbed molecules or structural defects, are identified. Contrarily to mesh modeling where one creates an optimized mesh from a high resolution solution, here we want to iteratively build an optimized mesh from a coarse and previous solution. A Delaunay triangulation has been used to efficiently generate optimized meshes from high resolution images [3], and a similar discretization scheme is used in the present work. During mesh generation, standard point insertion algorithms [4] are favored over methods that enable coarsening and smoothing operations [5], since displacing or removing already computed pixels will results in undesirable exclusion of already computed data.

Suture-Assisted vs Forceps-Assisted Insertion of the Donor Lenticula during Descemet Stripping Automated Endothelial Keratoplasty

To compare a new insertion method using a suture with the standard forceps-assisted insertion of the lamellar corneal graft in Descemet stripping automated endothelial keratoplasty (DSAEK). Interventional, comparative case series. DSAEK was performed on 28 consecutive eyes of 28 patients (mean age +/- standard deviation, 72.5 +/- 9.7 years; 12 males). The donor tissue was prepared using the Moria automated lamellar therapeutic keratectomy microkeratome head with a 300-mm blade depth on a Moria artificial anterior chamber (Moria, Antony, France). The central 9 mm of the recipient's Descemet membrane were stripped through a superior limbal incision. In eight consecutive unselected patients, a 10-0 monofilament suture on a long straight needle was used to insert the folded donor lenticula into the recipient's eye, whereas in the other 20 patients, a standard insertion forceps was used. During the suture insertion, an anterior chamber maintainer was used to fill the anterior chamber continuously with balanced salt solution to prevent its collapse. Suture-assisted DSAEK did not differ significantly from forceps-assisted DSAEK in any of the preoperative parameters. No significant differences were noted in the intraoperative or postoperative complications. Six months after surgery, there were no significant differences in endothelial cell counts (1804 vs 1935 cells/mm(2), respectively), visual acuity (20/40 vs 20/36, respectively), or refraction (spherical equivalent, 0.93 vs 1.05 diopters, respectively). Suture-assisted DSAEK is a valid alternative to forceps insertion; however, it does not seem to offer a significant advantage.

Endovascular coils as lung tumour markers in real-time tumour tracking stereotactic radiotherapy: preliminary results

To evaluate the use of endovascular coils as markers for respiratory motion correction during high-dose stereotactic radiotherapy with the CyberKnife, an image-guided linear accelerator mounted on a robotic arm. Endovascular platinum embolisation coils were used to mark intrapulmonary lesions. The coils were placed in subsegmental pulmonary artery branches in close proximity to the target tumour. This procedure was attempted in 25 patients who were considered unsuitable candidates for standard transthoracic percutaneous insertion. Vascular coils (n = 87) were succesfully inserted in 23 of 25 patients. Only minor complications were observed: haemoptysis during the procedure (one patient), development of pleural pain and fever on the day of procedure (one patient), and development of small infiltrative changes distal to the vascular coil (five patients). Fifty-seven coils (66% of total inserted number) could be used as tumour markers for delivery of biologically highly effective radiation doses with automated tracking during CyberKnife radiotherapy. Endovascular markers are safe and allow high-dose radiotherapy of lung tumours with CyberKnife, also in patients who are unsuitable candidates for standard transthoracic percutaneous marker insertion.

Tips for intubation with the Pentax‐AWS® Rigid Indirect Laryngoscope in morbidly obese patients

Tips for intubation with the Pentax‐AWS^® Rigid Indirect Laryngoscope in morbidly obese patients

Micro injection molding for mass production using LIGA mold inserts

Micro molding is one of key technologies for mass production of polymer micro parts and structures with high aspect ratios. The authors developed a commercially available micro injection molding technology for high aspect ratio microstructures (HARMs) with LIGA-made mold inserts and pressurized CO2 gasses. The test inserts made of nickel with the smallest surface details of 5 μm with structural height of 15 μm were fabricated by using LIGA technology. High surface quality in terms of low surface roughness of the mold inserts allowed using for injection molding. Compared to standard inserts no draft, which is required to provide a proper demolding, was formed in the inserts. To meet higher economic efficiency and cost reduction, a fully electrical injection molding machine of higher accuracy has been applied with dissolving CO2 gasses into molten resin. The gasses acts as plasticizer and improves the flowability of the resin. Simultaneously, pressurizing the cavity with the gasses allows high replication to be obtained. Micro injection molding, using polycarbonate as polymer resins, with the aspect ratio of two was achieved in the area of 28 × 55 mm2 at the cycle time of 40 s with CO2 gasses, in contrast to the case of the aspect ratio of 0.1 without the gasses.

Experience of anesthesiologists with percutaneous nonangiographic venous access

Study Objective To compare percutaneous nonangiographic insertion of a venous access device with a standard surgical cutdown insertion technique. Design Prospective, controlled, randomized study. Setting Operating room and anesthesia induction room of a university hospital. Patients 100 consecutive oncology patients scheduled for intravenous chemotherapy. Interventions Patients were randomized to two groups: (1) The percutaneous group received implantation through the internal jugular vein by experienced anesthesiologists, whereas (2) the surgical group received venous cutdown insertion through the cephalic or subclavian vein by surgeons (n = 50 for each group). Measurements Duration of procedure, long-term device function, complications such as hematoma formation, infection, hemothorax, pneumothorax, and patients' satisfaction with the placement procedure at two months of follow-up were all measured and recorded. Main Results The percutaneous technique was found to have several advantages, including reduced time for insertion and greater patient satisfaction with procedure. The percutaneously implanted devices also had fewer insertion-associated complications. Conclusion The simplified, percutaneous, nonangiographic technique is as effective as the traditional venous cutdown technique and can be safely done by surgeons as well as by experienced physicians who are not surgeons.

Disposable laryngeal tube suction—A randomized comparison of two insertion techniques performed by novice users in anaesthetised patients

Laryngeal tubes are supraglottic airway devices that can be used in alternative to a tracheal tube to provide ventilation during cardiopulmonary resuscitation. The product line has recently been expanded by the disposable laryngeal tube suction (LTS-D). We tested the hypothesis that, with a modified insertion technique (MIT), the rate of correct placement attempts within 45 s could be significantly increased compared to the standard insertion technique (SIT) recommended by the manufacturer. Fifty-four adult patients undergoing trauma surgery under general anaesthesia had an LTS-D inserted by first-time users, randomly assigned to the SIT or a MIT. A brief manikin-based demonstration of the device and the assigned technique was given before insertion. In the MIT the tip of the LTS-D was rotated by 180 degrees prior to insertion. Forced chin lift to create sufficient retropharyngeal space was performed with the other hand. Introduced to one-third of its length, the LTS-D was again rotated by 180 degrees and pushed down the pharynx. The rate of successful tube placements within 45 s was the main outcome variable. Insertion took 73+/-41 s (SIT) and 40+/-8s (MIT, P<0.01). Insertion within 45 s was possible in n=7/27 patients (26%, SIT) and in n=20/27 patients (74%, MIT, P<0.01). In one patient of the MIT group, placement failed. Non-anaesthesia personnel, such as nurses and emergency medical technicians (n=27), performed comparably to board-certified anaesthesiologists or those in training (n=27). Applying a MIT significantly reduced the time for successful insertion of an LTS-D by first-time users. Insertion within 45 s was significantly more frequent with this technique. Further studies need to be conducted to determine if the LTS-D can be recommended as a first-line airway during cardiopulmonary resuscitation.

Glide insertion technique for donor cornea lenticule during Descemet's stripping automated endothelial keratoplasty

We describe a simple technique for inserting the donor corneal lenticule in Descemet's stripping automated endothelial keratoplasty. Unlike the standard insertion method, which requires folding the donor lenticule, this technique uses a modified intraocular lens (IOL) glide to guide the unfolded donor lenticule through the small incision with an intraocular forceps. This prevents significant endothelial trauma and surgical difficulties when the lenticule is unfolded. Additional endothelial protection is provided by an ophthalmic visco-surgical device on the IOL glide, which protects the donor endothelium from the corneal wound edge and prevents iris prolapse during insertion.

Cochlear Implant Electrode Insertion: The Round Window Revisited

To examine aspects of round window (RW) anatomy that are relevant to its use as a portal for atraumatic insertion of cochlear implant electrodes. Anatomic study using human cadaveric temporal bones. A series of 30 temporal bones was dissected to permit microscopic study of the RW region. The bony overhangs of the RW niche limit visibility of the RW membrane during surgery. Measurements of RW membrane area visible through a facial recess opening before and after drilling the overhangs in 15 temporal bones showed that RW membrane visibility is typically increased by a factor of 1.5 to 3 times after drilling and by as much as 13 times when the opening of the RW niche is relatively small. Observations from within the scala tympani in 15 cochlear dissections showed substantial variability in size of the RW opening available for electrode insertion. Area measurements of the portion of the RW covered by the vertical segment of the RW membrane ranged from 0.8 to 1.75 mm2 in these specimens. In addition, irregularities in contour of the RW margin may make insertion challenging, which may necessitate drilling the anterior-inferior margin of the RW. Drilling in this region should be approached with care because of the close proximity of the cochlear aqueduct opening. RW insertion can be performed in a manner that is potentially less traumatic than the standard cochleostomy insertion. It may therefore be advantageous in cases in which hearing preservation is the goal.

Effects of Inner Ear Trauma on the Risk of Pneumococcal Meningitis

To examine the risk of pneumococcal meningitis in healthy rats that received a severe surgical trauma to the modiolus and osseous spiral lamina or the standard insertion technique for acute cochlear implantation. Interventional animal studies. Fifty-four otologically normal adult Hooded-Wistar rats. Fifty-four rats (18 of which received a cochleostomy alone; 18, a cochleostomy and acute cochlear implantation using standard surgical techniques; and 18, a cochleostomy followed by severe inner ear trauma) were infected 4 weeks after surgery with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges in cochlear implant recipients with meningitis. Severe trauma to the osseous spiral lamina and modiolus increased the risk of pneumococcal meningitis when the bacteria were given via the middle or inner ear (Fisher exact test, P<.05). However, the risk of meningitis did not change when the bacteria were given via the hematogenous route. Acute electrode insertion did not alter the risk of subsequent pneumococcal meningitis for any route of infection. Severe inner ear surgical trauma to the osseous spiral lamina and modiolus can increase the risk of pneumococcal meningitis. Therefore, every effort should be made to ensure that cochlear implant design and insertion technique cause minimal trauma to the bony structures of the inner ear to reduce the risk of pneumococcal meningitis.

CFD Modelling of Turbulent Drop Breakage in a Kenics Static Mixer and Comparison with Experimental Data

This study has investigated drop breakage in liquid–liquid systems by means of advanced numerical modelling tools based on computational fluid dynamics (CFD). A static mixer with 24 standard Kenics inserts was analysed with the volume fraction of dispersed phase equal to 0.1%. Four superficial velocities were used resulting in Reynolds numbers of 12 000, 15 000, 18 000 and 21 000, respectively. To simulate the evolution of the drop size distribution (DSD), the population balance equation (PBE) was coupled with the multi-phase description and added to the standard equations in the CFD code with proper kinetic expressions for the breakage rate. Instead of solving the original PBE, transport equations for the moments of the DSD were solved and the closure problem was overcome by using the quadrature method of moments (QMOM). As expected, the predicted drop size decreased along the mixer and pressure drop, final size distribution and Sauter mean drop diameters, d 32, all agreed well with data reported in a previous experimental study, the best agreement for d 32 being from −10% to +9%, obtained with the finest mesh, 927 k.

Effect of Impact on Chondrocyte Viability During Insertion of Human Osteochondral Grafts

Osteochondral grafts, used to treat chondral and osteochondral defects, require high insertional forces that may affect the viability of chondrocytes in the graft. The objectives of this study were to (1) measure the loading impact during insertion of osteochondral grafts, (2) evaluate the effect of insertional loading on chondrocyte viability, and (3) assess this effect on chondrocyte apoptosis and activation of caspase-3. The distal parts of twelve fresh femora from six adult human cadavers were harvested within seventy-two hours after the death of the donor. From each femur, four 15-mm-diameter cylindrical osteochondral grafts were isolated; two of these grafts (a total of twenty-four grafts in the study) were transplanted with standard impact insertion into recipient sockets in the other condyle of the ipsilateral femur. The other two grafts served as unloaded controls. Loads were measured during the insertion of ten of the twenty-four transplanted grafts. Full-thickness cartilage disks were then removed from the grafts, incubated for up to forty-eight hours, and analyzed for cell viability, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling)-positive reactivity, and caspase-3 activation, each as a function of the depth from the articular surface. The insertion of an osteochondral graft was characterized, on the average (and standard deviation), by 10 +/- 4 impacts, each generating 2.4 +/- 0.9 kN of load and 13.3 +/- 4.9 MPa of stress for a duration of 0.57 +/- 0.13 ms with a 0.62 +/- 0.25 N.s impulse. Impact insertion increased cell death in the superficial 500 mum to 21% at one hour (p < 0.001) and 47% at forty-eight hours (p < 0.001) and also increased cell death in deeper layers at forty-eight hours. Some cell death was due to apoptosis, as indicated by an increase in caspase-3 activation at eight hours (p < 0.01) and TUNEL-positive cells at forty-eight hours (p < 0.05) in the superficial 500 mum of impacted cartilage. Impact insertion of osteochondral grafts generates damaging loads that cause chondrocyte death, particularly in the superficial zone, mainly as a result of apoptosis mediated by the activation of caspases. Chondrocyte death that occurs during impact insertion of osteochondral grafts may lead to compromised function. Understanding the mechanisms and consequences of such impact loading may provide insights into potential therapeutic interventions, or lead to changes in the insertion technique, to decrease the cell injury associated with impact loading.

Is Low-current Search a Risk Factor in Peripheral Nerve Localization?

We thank Dr. Al-Nasser for the attentive reading of our article regarding the use of continuous peripheral nerve blocks after orthopedic surgery.1We understand and accept some remarks regarding the possible risk of neuropathy for intensities lower than 0.5 mA during the nerve stimulation procedure. Dr. Al-Nasser's concerns, which have already been evoked by Auroy et al. ,2are supported by recent articles reporting that for low-intensity and short-duration nerve stimulation (&lt; 0.5 mA, 0.1 ms), needle–nerve contact can be obtained without any muscle movement3or pain.4However, some points must be clarified: Research of a minimal intensity during nerve stimulation was not a part of our study design; all of the studies reported by Al-Nasser were related to single-shot blocks and not continuous peripheral nerve blocks; the authors do not decide, regardless of whether it seems important, that one element or another is a risk factor—rather, the multivariate analysis by logistic regression concludes that; the authors5,6who reported the vicinity of nerve and needle tip for values less than 0.5 mA used theoretical biophysics data but did not check their data in clinical practice (ultrasound studies) or in animals; and it was recently reported that signs of nerve inflammation after a peripheral nerve block appeared only after a minimal low-intensity threshold value of 0.2 mA.7The stimulating current at which a needle is sufficiently close for a successful block but still at a safe distance from the nerve to avoid injury is unknown.8In our study, the placement of the needle was considered successful when a specific muscle contraction was obtained at a current output of less than 0.5 mA (1 Hz and impulse duration of 0.1 ms). The current was then gradually decreased until the muscle twitch stopped between 0.4 and 0.2 mA. Nerve stimulation below 0.2 mA was never sought. Intensity of less than 0.5 mA did not seem to be a risk factor. Several elements might explain that: All continuous peripheral nerve blocks were performed by highly trained anesthesiologists following standardized insertion techniques; the nerve stimulators, which delivered the dialed current, were regulated to deliver the actual current; the catheters were inserted for values between 0.2 and 0.5 mA; and there was no motor response for intensity of less than 0.2 mA.Most importantly, the risk of nerve lesion increases when a physician uses an old nerve stimulator that reports only the theoretical current and not the current actually delivered, which can be lower. If anesthesiologists use this standard of nerve stimulator, they should not set their threshold at 0.5 mA, but invest in a new nerve stimulator to limit the risk of nerve injury.*Lapeyronie University Hospital, Montpellier, France. x-capdevila@chu-montpellier.fr