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Purpose: Numerous navigation devices for percutaneous, CT-guided interventions exist and are, due to their advantages, increasingly integrated into the clinical workflow. However, effective training methods to ensure safe usage are still lacking. This study compares the potential of an augmented reality (AR) training application with conventional instructions for the Cube Navigation System (CNS), hypothesizing enhanced training with AR, leading to safer clinical usage., Methods: An AR-tablet app was developed to train users puncturing with CNS. In a study, 34 medical students were divided into two groups: One trained with the AR-app, while the other used conventional instructions. After training, each participant executed 6 punctures on a phantom (204 in total) following a standardized protocol to identify and measure two potential CNS procedural user errors: (1) missing the coordinates specified and (2) altering the needle trajectory during puncture. Training performance based on train time and occurrence of procedural errors, as well as scores of User Experience Questionnaire (UEQ) for both groups, was compared., Results: Training duration was similar between the groups. However, the AR-trained participants showed a 55.1% reduced frequency of the first procedural error (p > 0.05) and a 35.1% reduced extent of the second procedural error (p < 0.01) compared to the conventionally trained participants. UEQ scores favored the AR-training in five of six categories (p < 0.05)., Conclusion: The AR-app enhanced training performance and user experience over traditional methods. This suggests the potential of AR-training for navigation devices like the CNS, potentially increasing their safety, ultimately improving outcomes in percutaneous needle placements., Competing Interests: Declarations. Conflict of interest: The authors TS, QL, and MM declare no conflict of interest. SM, AU, RH, and SW are employees of and/or shareholders in Medical Templates. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. Ethical approval: All studies have been approved and performed in accordance with ethical standards. Informed consent: This article does not contain patient data. Informed consent was obtained from all participants included in the study., (© 2024. The Author(s).)

Background: We aimed to introduce the puncture technique based on a novel device for preperitoneal tunneling in laparoscopic PD catheter placement and to evaluate the safety and efficacy of this technique., Methods: This novel device was used in our center from May 2016. We conducted a retrospective analysis of patients undergoing laparoscopic PD catheter placement. The traditional method was performed in 20 patients and the novel procedure in 18 patients. A straight Tenckhoff PD catheter was placed in all patients., Results: No intraoperative complications were encountered in both groups. Compared the traditional technique group, the procedure based on the novel device had a shorter operative time (49.2 ± 11.8 vs 53.9 ± 12.5). One patient in the traditional tunneling group underwent catheter obstruction. There were no pericatheter leakage, exit site and subcutaneous infection, hernia and peritonitis in the early postoperative days. No mortality was observed in these patients. The 6-month survival rate of the catheter was 100%., Conclusions: Laparoscopic preperitoneal tunneling technique is an effective way to implant intra-abdominal catheter. Our method based on a novel puncture device for preperitoneal tunneling is safe and efficient.

Image-guided surgery is growing in importance with each year. Various imaging technologies are used. The objective of this study was to test whether a new mixed reality navigation system (MRNS) improved percutaneous punctures. This system allowed to clearly visualize the needle tip, needle orientation, US probe and puncture target simultaneously with an interactive 3D computer user inferface. Prospective pre-clinical comparative study. An opaque ballistic gel phantom containing grapes of different sizes was used to simulate puncture targets. The evaluation consisted of ultrasound-guided (US-guided) needle punctures divided into two groups, standard group consisted of punctures using the standard approach (US-guided), and assisted navigation group consisted of punctures using MRNS. Once a puncture was completed, a computed tomography scan was made of the phantom and needle. The distance between the needle tip and the center of the target was measured. The time required to complete the puncture and puncture attempts was also calculated. Total participants was n = 23, between surgeons, medical technicians and radiologist. The participants were divided into novices (without experience, 69.6%) and experienced (with experience > 25 procedures, 30.4%). Each participant performed the puncture of six targets. For puncture completion time, the assisted navigation group was faster (42.1%) compared to the standard group (57.9%) (28.3 s ± 24.7 vs. 39.3 s ± 46.3-p 0.775). The total punctures attempts was lower in the assisted navigation group (35.4%) compared to the standard group (64.6%) (1.0 mm ± 0.2 vs. 1.8 mm ± 1.1-p 0.000). The assisted navigation group was more accurate than the standard group (4.2 ± 2.9 vs. 6.5 ± 4.7-p 0.003), observed in both novices and experienced groups. The use of MRNS improved ultrasound-guided percutaneous punctures parameters compared to the standard approach.

Purpose: Percutaneous needle insertion procedures are commonly used for diagnostic and therapeutic purposes. Although current technology allows accurate localization of lesions, they cannot yet be precisely targeted. Lung cancer is the most common cause of cancer-related death, and early detection reduces the mortality rate. Therefore, suspicious lesions are tested for diagnosis by performing needle biopsy., Methods: In this paper, we have presented a novel computed tomography (CT)-compatible needle insertion device (NID). The NID is used to steer a flexible needle (φ0.55 mm) with a bevel at the tip in biological tissue. CT images and an electromagnetic (EM) tracking system are used in two separate scenarios to track the needle tip in three-dimensional space during the procedure. Our system uses a control algorithm to steer the needle through a combination of insertion and minimal number of rotations., Results: Noise analysis of CT images has demonstrated the compatibility of the device. The results for three experimental cases (case 1: open-loop control, case 2: closed-loop control using EM tracking system and case 3: closed-loop control using CT images) are presented. Each experimental case is performed five times, and average targeting errors are 2.86 ± 1.14, 1.11 ± 0.14 and 1.94 ± 0.63 mm for case 1, case 2 and case 3, respectively., Conclusions: The achieved results show that our device is CT-compatible and it is able to steer a bevel-tipped needle toward a target. We are able to use intermittent CT images and EM tracking data to control the needle path in a closed-loop manner. These results are promising and suggest that it is possible to accurately target the lesions in real clinical procedures in the future.

2D Ultrasound (US) is becoming the preferred modality for image-guided interventions due to its low cost and portability. However, the main limitation is the limited visibility of surgical tools. We present a new sensor technology that can easily be embedded on needles that are used for US-guided interventions. Two different types of materials are proposed to be used as sensor--co-polymer and PZT. The co-polymer technology is particularly attractive due to its plasticity, allowing very thin depositions (10-20 μm) on a variety of needle shapes. Both sensors receive acoustic energy and convert it to an electrical signal. The precise location of the needle can then be estimated from this signal, to provide real-time feedback to the clinician. We evaluated the feasibility of this new technology using (i) a 4DOF robot in a water tank; (ii) extensive ex vivo experiments; and (iii) in vivo studies. Quantitative robotic studies indicated that the co-polymer is more robust and stable when compared to PZT. In quantitative experiments, the technology achieved a tracking accuracy of 0.14 ± 0.03mm, significantly superior to competing technologies. The technology also proved success in near-real clinical studies on tissue data. This sensor technology is non-disruptive of existing clinical workflows, highly accurate, and is cost-effective. Initial clinician feedback shows great potential for large scale clinical impact.

With real-time instrument tracking and in-situ guidance projection directly integrated in a handheld ultrasound imaging probe, needle-based interventions such as biopsies become much simpler to perform than with conventionally-navigated systems. Stereo imaging with needle detection can be made sufficiently robust and accurate to serve as primary navigation input. We describe the low-cost, easy-to-use approach used in the Clear Guide ONE generic navigation accessory for ultrasound machines, outline different available guidance methods, and provide accuracy results from phantom trials.

This paper presents a real-time segmentation method for curved needles in biological tissue based on analysis of B-mode and power Doppler images from a tracked 2D ultrasound transducer. Mechanical vibration induced by an external voice coil results in a Doppler response along the needle shaft, which is centered around the needle section in the ultrasound image. First, B-mode image analysis is performed within regions of interest indicated by the Doppler response to create a segmentation of the needle section in the ultrasound image. Next, each needle section is decomposed into a sequence of points and transformed into a global coordinate system using the tracked transducer pose. Finally, the 3D shape is reconstructed from these points. The results of this method differ from manual segmentation by 0.71 ± 0.55 mm in needle tip location and 0.38 ± 0.27 mm along the needle shaft. This method is also fast, taking 5-10 ms to run on a standard PC, and is particularly advantageous in robotic needle steering, which involves thin, curved needles with poor echogenicity.

Background: Endosonography (EUS)-guided transmural pseudocyst drainage is a multistep procedure currently performed with different "off-the-shelf" accessories developed for other applications. Multiple device exchanges over-the-wire is time consuming and risks loss of wire access. This report describes the technical feasibility and outcomes for EUS-guided drainage of pancreatic fluid collections using a novel exchange-free device developed for translumenal therapy., Methods: Between April and November 2010, 14 patients (9 men; mean age, 49.9 years) with pancreatic fluid collection (mean size, 102 mm) underwent 16 EUS-guided drainage procedures using the exchange-free access device at a single tertiary care center. The trocar of the exchange-free device was used to gain pseudocyst access. The dual-balloon catheter then was advanced over the trocar, followed by inflation of the (first) anchor balloon. Cyst contents were sampled, and contrast was injected to define the pseudocyst anatomy. The first guidewire was inserted into the cyst cavity. The cystenterostomy tract was dilated to 10 mm with the (second) dilation balloon, followed by a second guidewire insertion. The exchange-free access device was removed, leaving the two guidewires in place for two double-pigtail stents., Results: The procedure was technically successful for all the patients. No acute procedure-related complications occurred. Late complications included a symptomatic leak in a patient who underwent drainage of a pancreatic uncinate pseudocyst from the second duodenum, a self-limited transfusion-dependent bleed after transbulbar drainage, and symptomatic pseudocyst infection., Conclusion: Pseudocyst access, cystenterostomy tract dilation, and placement of two guidewires for dual stent drainage are technically feasible using an exchange-free access device. The device has the potential to standardize, simplify, and streamline EUS-guided pseudocyst drainage with a single instrument. Comparative studies with alternative tools and methods for pseudocyst drainage are warranted.

Purpose: Patients undergoing left atrial ablation require transseptal puncture, which can be challenging, even for experienced physicians. This study compared the efficacy and safety of radiofrequency (RF) energy transseptal punctures to conventional approach., Methods: Patients requiring transseptal puncture for left atrial access were included using either conventional approach or the NRG™ RF transseptal needle as first attempt. Procedure time for transseptal access, fluoroscopy time, crossover, and safety of both techniques were compared., Results: A total of 241 transseptal punctures were performed in 148 consecutive patients (114 men, 54 ± 10 years, left atrial volume 32 ± 10 ml/m(2)) who underwent 157 procedures with left atrial access, mainly for atrial fibrillation. It was a repeat transseptal procedure in 49 patients. Procedures were guided by transesophageal echocardiography. RF transseptal puncture was planned in 119 procedures. RF was delivered in 98 procedures (82%) for 139/187 punctures: 48 punctures did not require RF, including 25 punctures performed by exposing the needle tip, 22 through patent foramen ovale, and 1 RF delivery failure by the generator. Average time for RF transseptal was 4.8 ± 2.8 min compared to 7.5 ± 8.5 min for conventional approach (p = 0.045). Fluoroscopy time was 1.8 ± 1.3 min for RF transseptal and 2.9 ± 2.8 min for standard approach (p = 0.043). Four patients required crossover to RF transseptal needle in the conventional group (p = 0.003). One tamponade occurred at the end of procedure in a patient using the RF needle, and one interatrial septum dissection with aortic root hematoma occurred in the conventional group., Conclusions: Transseptal needle puncture using RF energy can be performed safely and quickly under imaging guidance.

Arthrocentesis, injection and infiltration of joints and soft tissues belong to the basic procedures in rheumatology. The indications and the practical performance are based on experience and tradition. Nowadays, a crucial reappraisal and adaption of indications and technical aspects appear important in the light of new evidence and technical developments. The main indications for puncture remain the search of an infectious arthritis and reduction of intra-articular pressure due to effusion. Good indications for the injection of glucocorticoids are inflammation in sterile joints and activated osteoarthritis. The local infiltration with corticosteroids in mechanically induced enthesopathies at the lateral epicondyle of the humerus or at the plantar fascia have to be questioned in the light of recent publications which show that this common practice is associated with a poorer outcome than without injection.

Mechanical pressure applied to a Brockenbrough needle at the fossa ovalis is the standard transseptal puncture technique. Circumstances where the fossa ovalis is thick or aneurysmal can make this method challenging. In this case, we illustrate the use of a radiofrequency powered transseptal needle to cross the fossa ovalis.

Introduction: An increasing number of patients undergo left atrial ablation procedures, since several approaches have proven efficacy in the treatment of atrial fibrillation. Although transseptal catheterization was generally shown be a safe technique, it harbors the principal risk of cardiac injury. Therefore, there is a need for a safe and effective tool to enable transseptal puncture in difficult cases as well., Methods and Results: In 158 consecutive patients, a transseptal puncture was intended for mapping and ablation of left atrial tachycardias. In seven patients of this series transseptal puncture using different sheaths and needle designs, the operators failed to cross the interatrial septum as a result of severe tenting. Three patients were known to have a septal aneurysm; a redo procedure was performed in two patients. In the remaining patients, there was no obvious explanation for the difficulty in crossing the interatrial septum conventionally. In all seven patients, a 120-cm-long nitinol guidewire ("needle wire") with a 0.014-inch diameter was used to cross the atrial septum with the following idea: after tenting the fossa ovalis with the transseptal dilator and the Brockenbrough needle positioned just inside the tip, effortless advancement of the needle wire perforates the membranous fossa. Unsupported by the needle and dilator, the tip of the wire immediately assumes a "J" shape, rendering it incapable of further tissue penetration after its entry into the left atrium. In all seven patients, the needle wire could be placed into a left pulmonary vein. In five patients, a single attempt was sufficient to reach the left atrium with the wire, two patients needed two and three attempts, respectively. No complications occurred., Conclusions: Additional use of a needle wire to perform transseptal puncture in a subset of patients at higher risk for complications appears safe and effective.

Background: The implantation of a Port-A-Cath (PAC) is a common surgical procedure usually done under guidance with techniques such as fluoroscopy, ultrasound, or intravenous electrocardiography. PAC implantation without guidance avoids radiation exposure and decreases time, expense, and complexity. The purpose of this study was to analyze the success rate, and operation-related and postoperative complications of PAC implantation without intraoperative guidance., Methods: Between July 2004 and June 2007, 1,070 PACs were implanted in 1,025 patients receiving chemotherapy. All PACs were placed via the subclavian vein by percutaneous puncture. The catheter length was precalculated for each patient. Postoperative chest radiography was immediately performed to check the catheter position. All data on outcome of the implantations were reviewed retrospectively., Results: The catheter tip was correctly placed at the cavoatrial junction without complications in 1,055/1,070 (98.6%) of the implants. Surgery-related complications occurred in 15 (1.4%) implantations: 9 malposition, 3 pneumothorax, 2 hematoma, and 1 catheter kinking. Two patients underwent PAC removal due to hematoma with subsequent wound infection in one and catheter occlusion by kinking in the other. There were 86 (8.0%) postoperative complications that resulted in PAC removal: catheter occlusion in 24 (2.2%), pocket infection in 22 (2.1%), catheter rupture in 11 (1.0%), venous thrombosis in 9 (0.8%), port exposure in 9 (0.8%), catheter fracture in 6 (0.6%), infraclavicular pain in 3 (0.3%), catheter migration in 1 (0.1%), and extraportal injection in 1 (0.1%)., Conclusions: PACs can be safely and accurately placed using percutaneous puncture of the subclavian vein without intraoperative guidance.

This paper presents a new modeling method for the insertion of needles and more generally thin and flexible medical devices into soft tissues. Several medical procedures rely on the insertion of slender medical devices such as biopsy, brachytherapy, deep-brain stimulation. In this paper, the interactions between soft tissues and flexible instruments are reproduced using a set of dedicated complementarity constraints. Each constraint is positionned and applied to the deformable models without requiring any remeshing. Our method allows for the 3D simulation of different physical phenomena such as puncture, cutting, static and dynamic friction at interactive frame rate. To obtain realistic simulation, the model can be parametrized using experimental data. Our method is validated through a series of typical simulation examples and new more complex scenarios.

Background: Minimally invasive surgery (MIS) in preschool children (<5 years of age) is not common yet, and few reports evaluating typical complications are available. Trocar site hernias are well described in adult patients but also have been reported for preschool children. The goal of our study was to determine incidence and relevance of trocar site hernias as complications of minimally invasive surgery in preschool children., Methods: Retrospective analysis of all pediatric patients who underwent minimally invasive surgery at a single institution. Review of the literature., Results: Trocar site hernias are significantly more frequent in preschool children than in older ones (p = 0.006). Complication rates at all are not significantly different. Trocar site hernias in infants are mainly of type 3 (omental protrusion) and occur within the first postoperative week., Conclusion: Meticulous suturing of all layers (particularly the peritoneum) even in small incisions (2 mm) is recommended to prevent omental protrusion at trocar site in children up to 5 years of age.

We have previously proposed a computer guidance system for liver punctures designed for intubated (free breathing) patients. The lack of accuracy reported (1 cm) was mostly due to the breathing motion that was not taken into account. In this paper we modify our system to synchronise the guidance information on the expiratory phases of the patient and present an evaluation on 6 patients of our respiratory gated system. Firstly, we show how a specific choice of patient allows us to rigorously and passively evaluate the system accuracy. Secondly, we demonstrate that our system can provide a guidance information with an error below 5 mm during expiratory phases.

A commercially available camera trocar diminishes the working space because of its high profile and is not proof against blood stain. The authors designed a new camera trocar for gasless endoscopic thyroid surgery. The new trocar consists of a shaft for a 5-mm endoscope as well as a disc 18 mm in diameter and 2 mm thick. The trocar is inserted from an adjacent 3-cm working port, pushed out to an incision for a 5-mm endoscope, and placed with the shaft up and the disc down. Because of its disc, the trocar is designed to be proof against blood stain and to maintain more working space. The newly designed trocar might be very useful for gasless endoscopic thyroid surgery as well as other gasless surgical procedures.

We have extended the real-time tomographic reflection display of the Sonic Flashlight to a laser guidance system that aims to improve safety and accuracy of needle insertion, especially for deep procedures. This guidance system is fundamentally different from others currently available. Two low-intensity lasers are mounted on opposite sides of a needle aimed parallel to the needle. The needle is placed against a notch in the Sonic Flashlight mirror such that the laser beams reflect off the mirror to create bright red spots on the flat panel display. Due to diffuse reflection from these spots, the virtual image created by the flat panel display contains the spots, identifying the projected destination of the needle at its actual location in the tissue. We have implemented our design and validated its performance, identifying several areas for potential improvement.

Percutaneous Vertebroplasty (PVP) is an effective and less invasive medical treatment for vertebral osteoporotic compression fractures. However, this operative procedure is quite difficult because an arcus vertebra, which is narrow, is needled with accuracy, and an operator's hand is exposed to X-ray continuously. We have developed a needle insertion robot for Percutaneous Vertebroplasty. Its experimental evaluation on the basic performance of the system and needle insertion accuracy are presented. A needle insertion robot is developed for PVP. This robot can puncture with accuracy and an operator does not need to be exposed to X-ray. The mechanism of the robot is compact in size (350 mm x D 400 mm x H270 mm, weight: 15 kg) so that the robot system can be inserted in the space between C-arm and the patient on the operating table. The robot system is controlled by the surgical navigation system where the appropriate needle trajectory is planned based on pre-operative three-dimensional CT images. The needle holding part of the robot is X-ray lucent so that the needle insertion process can be monitored by fluoroscopy. The position of the needle during insertion process can be continuously monitored. In vitro evaluation of the system showed that average position and orientation errors were less than 1.0 mm and 1.0 degree respectively. Experimental results showed that the safety mechanism called mechanical fuse released the needle holding disk properly when excessive force was applied to the needle. These experimental results demonstrated that the developed system has the satisfactory basic performance as needle insertion robot for PVP.

Background: It is technically difficult to puncture deep-seated hepatic tumors by conventional laparoscopic ultrasonography with a linear-array probe. We have developed a laparoscopic ultrasonography system with a convex-array probe., Methods: The laparoscopic system used had a fixed forward-viewing convex-array transducer, and a guide groove for puncture was added to the back of the unit. These characteristics enabled us to continuously monitor the position of the needle tip on the ultrasonographic image immediately after puncturing on the liver surface. We attempted tumor puncture in 11 patients with hepatocellular carcinoma under a new probe guidance., Results: The mean puncturing distance up to the tumors was 38.7 mm. All punctures were successful on the first pass and the tumors were treated with radiofrequency ablation., Conclusion: Using this new equipment, puncturing hepatic tumors for treatment is relatively easy, irrespective of the position of the tumor.

Over a period of 5 years 81 vascular complications after 15,460 catheterizations of the femoral artery for diagnostic (n = 11,883) or therapeutic (n = 3577) procedures were registered. The following complications were observed in declining frequency: 1. False aneurysm (n = 65), 2. arterial occlusion (dissection, embolia, thrombosis) (n = 8), 3. vascular lesion causing profuse bleeding (n = 7), 4. AV-fistula (n = 1). The total complication rate was 0.52%. The complication rate was significantly higher in therapeutical procedures (1,03%) than in diagnostic investigations (0.37%). Pseudoaneurysms were complicated by thrombosis of the femoral vein (n = 3), lymphatic fistula (n = 3) and deep wound infection (n = 9); secondary complication rate 18.5%. Risk factors for local vascular complications are old age, female gender, high grade arteriosclerosis at the puncture site, overweight, manifest arterial hypertension and medication with cumarin, acetylsalicylic acid or heparin. Further complicating factors are connected with technical risks such as duration of the procedure. French size of the catheter, the catheter sheath and multiple punctures. Vascular repair was performed by simple angiography in most cases, but in 14.8% more extensive surgical procedures were required. In patients with signs of occlusive vascular disease the external iliac artery was replaced by a PTFE-vascular access graft in 4 cases and an arterioplasty of the deep femoral artery was performed in 2 patients. 36% of the operations were undertaken as emergencies. Reintervention was necessary for a postoperative bleeding complication in 1 case (surgical complication rate 1.2%). A female patient suffering from aortic valve stenosis died during emergency operation due to massive retroperitoneal hemorrhage after cardiac catheterization (mortality rate 1.2%). Over a median follow-up period of 37 months no late complications of the intervention were recorded, nor recurrences of peripheral arterial occlusive disease.

Since the first report of successful percutaneous endoscopic gastrostomy placement by Gauderer and Ponsky in 1981 [Surg. Gynecol. Obstet. 152: 83-85], many modifications of the original technique have been published. Each reports easier and safer placement of the gastrostomy tube, but all have the same inherent flaw: Access to the gastric lumen is accomplished by a blind needle puncture of the anterior abdominal wall. A new technique, utilizing a newly available microendoscope (Origin Medsystems), is described. Using the microendoscope, direct visualization of the stomach and left upper quadrant of the abdomen allows safer access to the gastric lumen for subsequent tube placement without the need for additional incisions or punctures. The procedure can still be performed with local infiltrative anesthesia and systemic intravenous sedation.

Electrosurgical energy may be utilized as an adjunct to mechanical force for insertion of laparoscopic trocars. The advantage of this approach may be better operator control of insertion, with less risk of intraperitoneal and retroperitoneal injury. To assess the safety and efficacy of electrosurgical trocars, we compared them to mechanical trocars in clinical and animal trials. During 100 trocar introductions in 25 laparoscopic cholecystectomies, insertion force was measured. In contrast to mechanical trocars, which required progressively more force to insert as size increased, electrosurgical trocars required the same low insertion force regardless of size. No wound complications occurred. In animal experiments, wound healing (measured histologically and by bursting strength) was normal and equivalent for mechanical and electrosurgical insertions. We conclude that electrosurgical trocars require less force for insertion and do not impair wound healing. Electrosurgical trocars may thus offer important safety advantages over mechanical trocars.

In order to avoid invasive procedures (transfrontal, transcallosal) in the surgical treatment of colloid cysts the stereotactic aspiration technique was introduced by Bosch, Rähn and Backlund in 1978. The viscosity of the intracystic colloid and the displacement of the cyst away from the aspiration needle are possible reasons for unsuccessful aspiration. GT-guided stereotactic endoscopic technique gives the opportunity to fenestrate the cyst wall under direct visual control. After CT-guided stereotactic puncture of the right lateral ventricle with the foramen of Monro as target a steerable endoscope is introduced and the foramen of Monro is passed. The wall of the cyst is fenestrated and coagulated by means of monopolar (or laser) coagulation. Using this technique we have treated four patients with colloid cysts. Immediately postoperatively all of them were relieved of their complaints and have been symptom-free for a mean follow up period of twelve months. Studies of cerebrospinal fluid flow patterns, performed prior to and every six months after the endoscopic intervention, confirmed a remarkable reduction of foraminal obstruction.

An electrode is presented which permits in vivo PCO2 measurements using a micropuncture technique. The tip diameter of the electrode is only a few microns, the tip is specially designed for measuring PCO2 in small tissue compartements.