Localization of epidural space: A review of available technologies

Ultrasound-Guided Epidural Anaesthesia in a 73-Year-Old Female With Bilateral Osteoarthritis and a History of Difficult Epidural Placement: A Case Report

Osteoarthritis (OA) of the knee is highly prevalent in the elderly population and generally causes disabling pain and dysfunction. Thus, knee OA has become one of the most common indications for total knee replacement (TKR) surgery. Neuraxial anaesthesia management in patients could be very challenging when there is a previous history of difficult epidural placements. The anatomical deformities and degenerative changes can limit the precise positioning of needles and increase the complication rates. This is a case of ultrasound-guided epidural and spinal anaesthesia administration in a 73-year-old female with a history of bilateral OA of the knee with previous difficult epidural placement. The patient had severe OA with severe pain and significant limitations in function. Epidural catheter placement was difficult in a prior bilateral tibial fracture repair, and she needed general anaesthesia for the procedure. Preoperative imaging showed significant degenerative change and decreased intervertebral spaces, which could compromise the accuracy of conventional epidural placement techniques. Real-time ultrasound was used for both epidural and spinal anaesthesia. Intraoperative and postoperative analgesia was provided with bolus doses of bupivacaine following the test dose that confirmed correct catheter placement. On the third postoperative day, the patient was discharged with oral analgesics. This report describes the use of ultrasound guidance to overcome the anatomical obstacles and challenges in epidural and spinal anaesthesia. The use of ultrasound guidance can contribute to a decrease in the complication rate, ensure adequate analgesia, and increase the accuracy of epidural treatment.

Pilot epinephrine dose-finding study to counter epidural-related blood pressure reduction

OBJECTIVE

An unwanted side effect associated with epidural analgesia is the reduction in blood pressure (BP) due to the sympathetic blockade. This study evaluated the hemodynamic effects of adding different epinephrine concentrations to epidurally injected local anesthetic solution to counteract sympathectomy. We hypothesized that epinephrine could mitigate the decrease in BP possibly caused by the local anesthetic, specifically decreasing the incidence of hypotension.

METHODS

Sixty-six patients were enrolled in a randomized, controlled, quadruple-blinded prospective study into three groups: epidural ropivacaine 0.2% without epinephrine (control) or with 2 µg/mL or 5 µg/mL epinephrine. Our primary outcome was the assessment of differences in hypotension between groups, defined as a >20% decrease in hypotension from baseline to the end of the intraoperative period.

RESULTS

Forty-seven patients completed the study, and 19 were withdrawn. Fifteen patients were in the control group, while 16 patients received 0.2% ropivacaine +2 µg/mL epinephrine, and 16 received 0.2% ropivacaine +5 µg/mL epinephrine. The overall rate of hypotension was 21.3% (10/47). There were no statistically significant differences in hypotension rates between the control group (33%) and groups receiving either +2 µg/mL (13%, p=0.165) or +5 µg/mL (19%, p=0.353) of epinephrine. In secondary analyses, respiratory rate showed greater decreases in control groups across the perioperative period compared with treatment groups (p=0.016) CONCLUSION: Adding epinephrine to the epidural local anesthetic did not significantly decrease the rate of hypotension. However, epinephrine mitigated decreases in respiratory rate across the perioperative period. Future studies will focus on increasing group size and higher epinephrine concentrations (10 µg/mL).

TRIAL REGISTRATION NUMBER

NCT02722746.

The Power of Color Flow Doppler Ultrasonography Versus Blind Technique in Localization of Epidural Catheter: A Randomized Prospective Study

Background

The success of epidural analgesia hinges on the precise insertion of the needle within the epidural space; failure rates have been reported to reach 32%.

Objectives

We report a new method using color Doppler to help verify the accurate location of the epidural needle tip.

Methods

This is a randomized prospective study. Sixty patients undergoing hysterectomy were enrolled, with 30 patients in each group. Color flow Doppler (CFD) ultrasonography was employed to guide epidural catheter placement. The ultrasound-guided epidural technique was used for patients where challenges in identifying traditional landmarks for epidural space localization were anticipated. The procedure commenced with a spinal epidural technique. After sterile preparation and draping of the area, a curvilinear ultrasound transducer, encased in a sterile sheath, was used to locate the interspinous space. The primary outcome measure focused on flow visualization at different insertion levels. Secondary outcome measures included the duration of catheter implantation, intervertebral level of insertion, and dermatome sensory levels. The study also assessed the quality of epidural analgesia and patients' assessment of analgesic quality using a Verbal Numerical Rating Scale.

Results

The study reported a successful and predominantly safe outcome, with high success rates in flow visualization and effective anesthesia coverage. Flow visualization at the insertion and surrounding levels demonstrated a 100% success rate at all observed points. The Visual Numeric Rating Scale (VNRS) results indicated a median pain score of 2 with an interquartile range (IQR) of 2 - 3, showcasing a generally low level of post-procedural pain among the subjects, reflecting good quality post-operative analgesia. Regarding dermatome sensory levels after 2 hours, the distribution across various levels, including T4, T6, T7, T8, T10, and T12, exhibited a favorable outcome. The highest proportion was observed at T10 (68.3%), suggesting effective anesthesia coverage in the targeted areas. The study demonstrated comparable efficiency between the CFD-guided and blind techniques in terms of procedural aspects. However, notable distinctions were observed in patients' reported pain levels, with the CFD group experiencing lower pain compared to the blind technique group. Additionally, the study highlighted the association between CFD and improved procedural accuracy and safety.

Conclusions

This study advocates for the integration of CFD into routine clinical practice to enhance procedural outcomes and patient safety during hysterectomy surgeries.

Spontaneous epidural and subdural hematomas of the spine: Review of anatomy and imaging findings

Spontaneous epidural (SEH) and subdural hematomas (SSH) of the spine are a rare cause of spinal injury and morbidity. They often present in the emergency setting, though magnetic resonance imaging is the gold-standard for diagnosis. Knowledge of anatomy, and in particular of the dural layers of the spine, is crucial to understand the location of SEH and SSH and their relationship with spinal structure. In this pictorial review, we aim to explain imaging features of the SEH and SSH, and to rule out their main differential diagnosis.

Evaluation of a modified ultrasound-assisted technique for mid-thoracic epidural placement: a prospective observational study

BACKGROUND

Although mid-thoracic epidural analgesia benefits patients undergoing major surgery, technical difficulties often discourage its use. Improvements in technology are warranted to improve the success rate on first pass and patient comfort. The previously reported ultrasound-assisted technique using a generic needle insertion site failed to demonstrate superiority over conventional landmark techniques. A stratified needle insertion site based on sonoanatomic features may improve the technique.

METHODS

Patients who presented for elective abdominal or thoracic surgery requesting thoracic epidural analgesia for postoperative pain control were included in this observational study. A modified ultrasound-assisted technique using a stratified needle insertion site based on ultrasound images was adopted. The number of needle passes, needle skin punctures, procedure time, overall success rate, and incidence of procedure complications were recorded.

RESULTS

One hundred and twenty-eight subjects were included. The first-pass success and overall success rates were 75% (96/128) and 98% (126/128), respectively. In 95% (122/128) of patients, only one needle skin puncture was needed to access the epidural space. The median [IQR] time needed from needle insertion to access the epidural space was 59 [47-122] seconds. No complications were observed during the procedure.

CONCLUSIONS

This modified ultrasound-assisted mid-thoracic epidural technique has the potential to improve success rates and reduce the needling time. The data shown in our study may be a feasible basis for a prospective study comparing our ultrasound-assisted epidural placements to conventional landmark-based techniques.

Confirming identification of the epidural space: a systematic review of electric stimulation, pressure waveform analysis, and ultrasound and a meta-analysis of diagnostic accuracy in acute pain

To review the use of epidural electric stimulation test, pressure waveform analysis, and ultrasound assessment of injection as bedside methods for confirming identification of the epidural space in adults with acute pain, the PubMed database was searched for relevant reports between May and August 2022. Studies reporting diagnostic accuracy with conventional Touhy needles and epidural catheters were further selected for meta-analysis. Sensitivity and specificity were estimated using univariate logistic regression for electric stimulation and pressure analysis, and pooling of similar studies for ultrasound. Risk of bias and applicability was assessed using QUADAS-2. For electric stimulation, pressure waveform analysis, and ultrasound, respectively 35, 22, and 28 reports were included in the review and 9, 9, and 7 studies in the meta-analysis. Electric stimulation requires wire-reinforced catheters and an adequate nerve stimulator, does not reliably identify intravascular placement, and is affected by local anaesthetics. Sensitivity was 95% (95% CI 93-96%, N = 550) and specificity unknown (95% CI 33-94%, N = 44). Pressure waveform analysis is unaffected by local anaesthetics, but does not identify intravascular nor intrathecal catheters. Sensitivity was 90% (95% CI 72-97%, N = 694) and specificity 88% (95% CI 78-94%, N = 67). B-mode, M-mode and doppler ultrasound may be challenging, and data is still limited. Risk of bias was significant and accuracy estimates must be interpreted with caution. Electric stimulation and pressure waveform analysis seem clinically useful, although they must be interpreted cautiously. In the future, clinical trials in patients with difficult anatomy will likely be most useful. Ultrasound requires further investigation.

Vasovagal Pre-Syncope Induced by Epidural Electrical Stimulation Test: A Rare Case Report in a 61-Year-Old Woman Undergoing Ventral Hernia Repair

BACKGROUND Thoracic epidural analgesia is a commonly applied technique for perioperative pain management in major thoraco-abdominal surgery, but is complicated by high failure rates. The epidural electrical stimulation test (EEST) or "Tsui test" is a safe and effective method whereby low electrical current is used to confirm correct epidural catheter position and decrease the variability in analgesic effectiveness of the neuraxial technique. CASE REPORT We present the case of a 61-year-old woman with no prior cardiac or pulmonary comorbidities who was scheduled to undergo a ventral and parastomal hernia repair with component separation. The patient was offered a low thoracic epidural for perioperative analgesia. Technical aspects of the siting of the epidural catheter were uneventful and a confirmatory Tsui test was planned. At the initiation of electrical stimulation via the epidural catheter to confirm optimal catheter positioning, the patient experienced symptomatic bradycardia and hemodynamic instability that persisted despite terminating the electrical stimulation, and required pharmacologic intervention. CONCLUSIONS This report describes a rare case of vasovagal pre-syncope associated with the EEST or Tsui test. Although vasovagal reactions can be commonly associated with neuraxial procedures due to augmented venous return or severe emotional stress, we raise the possibility that through direct electrical stimulation in the epidural space, the EEST may have the potential to trigger such a physiologic response.

Recent Advances in Smart Epidural Spinal Needles

Lumbar puncture is a minimally invasive procedure that utilizes a spinal needle to puncture the lumbar epidural space to take a sample from the cerebrospinal fluid or inject drugs for diagnostic and therapeutic purposes. Physicians rely on their expertise to localize epidural space. Due to its critical procedure, the failure rate can reach up to 28%. Hence, a high level of experience and caution is required to correctly insert the needle without puncturing the dura mater, which is a fibrous layer protecting the spinal cord. Failure of spinal anesthesia is, in some cases, related to faulty needle placement techniques since it is blindly inserted. Therefore, advanced techniques for localization of the epidural space are essential to avoid any possible side effects. As for epidural space localization, various ideas were carried out over recent years to provide accurate identification of the epidural space. Subsequently, several methodologies based on mechanical and optical schemes have been proposed. Several research groups worked from different aspects of the problem, namely, the clinical and engineering sides. Hence, the main goal of this paper is to review this research with the aim of remedying the gap between the clinical side of the problem and the engineering side by examining the main techniques in building sensors for such purposes. This manuscript provides an understanding of the clinical needs of spinal needles from an anatomical point of view. Most importantly, it discusses the mechanical and optical approaches in designing and building sensors to guide spinal needles. Finally, the standards that must be followed in building smart spinal needles for approval procedures are also presented, along with some insight into future directions.

Inadvertent Placement of Thoracic Epidural Catheter in Pleural Cavity: A Case Report and Review of Published Literature

Thoracic epidural placement is considered the gold standard for pain management for abdominal or thoracic surgery. It provides analgesia superior to that provided by opioids with a decreased risk of pulmonary complications. Insertion of a thoracic epidural catheter requires the knowledge and expertise of an anesthetist; epidural catheter insertion may be challenging especially when sited in the higher thoracic region, in patients with unusual neuraxial anatomy, patients unable to position adequately for insertion or morbidly obese patients. Postoperatively the anesthetic team is required to look after the patient and assess for any complications such as hypotension. Even though the incidence of complications may be low; however, some of these could have detrimental consequences for the patients such as epidural abscess, hematoma formation, and temporary or permanent neurological damage. In this case report, we will discuss a patient who underwent a three-stage esophagectomy for esophageal squamous cell carcinoma under general anesthesia with epidural analgesia. The epidural catheter (Portex® Epidural Minipack System with NRFit® connector, ICUmedical, USA) was found in the intrapleural space during video-assisted thoracoscopy for the thoracic part of esophagectomy. To facilitate surgical access, the catheter was removed immediately, and the patient was given patient-controlled analgesia with morphine for postoperative pain control.

Ligamentum Flavum Rupture by Epidural Injection Using Ultrasound with SMI Method

The loss of resistance (LOR) method has been used exclusively to identify epidural space. It is difficult to find the epidural space without the risk of dural puncture. Various devices have been developed to improve the accuracy of the LOR method; however, no method has overcome the problems completely. Therefore, we devised a ligamentum flavum rupture method (LFRM) in which the needle tip is placed only on the ligamentum flavum during the epidural injection, and the injection pressure is used to rupture the ligamentum flavum and spread the drug into the epidural space. We confirmed the accuracy of this method using ultrasound with superb microvascular imaging (SMI) to visualize the epidural space. Here, we report two cases of 63-year-old and 90-year-old males. The 63-year-old patient presented with severe pain in his right buttock that extended to the posterior lower leg. The 90-year-old patient presented with intermittent claudication every 10 min. LFRM was performed, and SMI was used to confirm that the parenteral solution had spread into the epidural space. Our results indicate that LFRM can be used for interlaminar lumbar epidural steroid injections.

Neuraxial labor analgesia: Initiation techniques

The ideal technique for labor analgesia would have a quick onset, predictable quality, and adjustable depth and duration. Moreover, it would be easy to perform and have minimal maternal and fetal side effects. A catheter-based neuraxial approach encompasses these desirable characteristics and includes the epidural, combined spinal epidural, dural puncture epidural, and intrathecal catheter techniques. In this review, we outline the unique technical considerations, analgesic characteristics, and side effect profiles for each technique that can ultimately impact the maternal-fetal dyad. The selection of neuraxial analgesia techniques should consider the patient and team's goals and expectations, the clinical context, and the institutional culture. Labor analgesic techniques that initiate with an intentional dural puncture component have a faster onset, greater bilateral and sacral spread, and lower rates of epidural catheter failure. Further elucidation of the mechanisms, benefits, and risks of each neuraxial initiation technique will continue to benefit patients and care providers.

Comparison of landmark and real-time ultrasound-guided epidural catheter placement in the pediatric population: a prospective randomized comparative trial

Background

Epidural block placement in pediatric patients is technically challenging for anesthesiologists. The use of ultrasound (US) for the placement of an epidural catheter has shown promise. We compared landmark-guided and US-guided lumbar or lower thoracic epidural needle placement in pediatric patients.

Methods

This prospective, randomized, comparative trial involved children aged 1–6 years who underwent abdominal and thoracic surgeries. Forty-five children were randomly divided into two groups using a computer-generated random number table, and group allocation was performed by the sealed opaque method into either landmark-guided (group LT) or real-time ultrasound-guided (group UT) epidural placement. The primary outcome was a comparison of the procedure time (excluding US probe preparation). Secondary outcomes were the number of attempts (re-insertion of the needle), bone contacts, needle redirection, skin-to-epidural distance using the US in both groups, success rate, and complications.

Results

The median (interquartile range) time to reach epidural space was 105.5 (297.0) seconds in group LT and 143.0 (150) seconds in group UT (P = 0.407). While the first attempt success rate was higher in the UT group (87.0% in UT vs. 40.9% in LT; P = 0.004), the number of bone contacts, needle redirections, and procedure-related complications were significantly lower.

Conclusions

The use of US significantly reduced needle redirection, number of attempts, bone contact, and complications. There was no statistically significant difference in the time to access the epidural space between the US and landmark technique groups.

A comparative study of ultrasound assisted versus landmark technique for combined spinal-epidural anaesthesia in patients undergoing lower limb orthopaedic surgery

Background and Aims:

Spinal anatomy is better visualised in the para sagittal oblique view with the aid of ultrasonography. The present study was undertaken to investigate whether preprocedural ultrasonography can facilitate the ease of establishing combined spinal epidural (CSE) via paramedian approach versus landmark approach in patients undergoing lower limb orthopaedic surgery.

Methods:

This prospective randomised study was conducted in 100 American Society of Anesthesiologists (ASA) grade I-II patients, aged 18-60 years requiring CSE and randomly divided into two groups: Ultrasound-assisted (USG) group (n = 50) and Surface landmark (SLG) group (n = 50). The primary outcome was to compare the first pass needle success rate to establish CSE and the secondary outcomes were to compare the number of needle puncture attempts, time to establish landmarks (t1), time to accomplish CSE (t2) and complications.

Results:

First pass needle success rate in USG group was 43 (86.0%) versus 36 (60.0%) in SLG group (P = 0.001). Number of attempts taken to establish CSE was lower in USG group as compared to SLG group (P = 0.023). t1 was greater in USG group (1.45 ± 0.47) minutes as compared to (0.79 ± 0.34) minutes in SLG group (P = 0.003). t2 was reduced in USG group (1.47 ± 0.55) minutes versus (2.73 ± 1.36) minutes in SLG group (P = 0.005).

Conclusion:

Preprocedural USG for CSE via paramedian approach increases first pass needle success rate and reduces needle puncture attempts in patients undergoing lower limb orthopaedic surgery.

Epidural Needle Guidance Using Viscoelastic Tissue Response

Objective: We designed, prototyped, and tested a system that measures the viscoelastic response of tissue using nondestructive mechanical probing, with the goal of aiding clinical providers during epidural needle placement. This system is meant to alert clinicians when an epidural needle is about to strike bone during insertion. Methods: During needle insertion, the system periodically mechanically stimulates and collects viscoelastic response information data from the tissue at the needle’s tip using an intra-needle probe. A machine-learning algorithm detects when the needle is close to bone using the series of observed stimulations. Results: Tests run on ex vivo pig spine show that the system can reliably determine if the needle is pointed at and within 3 mm of bone. Conclusion: Our technique can successfully differentiate materials at and in front of the needle’s tip. However, it does not provide the 5 mm of forewarning that we believe would be necessary for use in clinical epidural needle placement. The technique may be of use in other applications requiring tissue differentiation during needle placement or in the intended application with further technical advances. Clinical and Translational Impact Statement: This Early/Pre-Clinical Research evaluates the feasibility of a method for helping clinical providers receive feedback during epidural needle insertion—thereby reducing complication rates—without significant alterations from current workflow.

Pneumomediastinum: A Rare Complication of Epidural Analgesia

Pneumomediastinum is a rare complication following epidural block using the loss of resistance (LOR) technique with air. It is speculated to result from the opening of potential space connecting the epidural space and the posterior mediastinum via intervertebral foramina through fascial planes. To date, only two cases of pneumomediastinum after epidural block have been reported. An incidental finding of pneumomediastinum two days after the procedure has not been reported before. Epidural block as a cause should be considered among multiple causes while interpreting the imaging of this life-threatening complication in the postoperative period.

Soft System Based on Fiber Bragg Grating Sensor for Loss of Resistance Detection during Epidural Procedures: In Silico and In Vivo Assessment

Epidural analgesia represents a clinical common practice aiming at pain mitigation. This loco-regional technique is widely used in several applications such as labor, surgery and lower back pain. It involves the injections of anesthetics or analgesics into the epidural space (ES). The ES detection is still demanding and is usually performed by the techniques named loss of resistance (LOR). In this study, we propose a novel soft system (SS) based on one fiber Bragg grating sensor (FBG) embedded in a soft polymeric matrix for LOR detection during the epidural puncture. The SS was designed to allow instrumenting the syringe's plunger without relevant modifications of the anesthetist's sensations during the procedure. After the metrological characterization of the SS, we assessed the capability of this solution in detecting LOR by carrying it out in silico and in clinical settings. For both trials, results revealed the capability of the proposed solutions in detecting the LOR and then in recording the force exerted on the plunger.

Current Status of Neuraxial and Paravertebral Blocks for Adult Cardiac Surgery

Cardiac surgeries are known to produce moderate to severe pain. Pain management has traditionally been based on intravenous opioids. Poorly controlled pain can result in increased incidence of respiratory complications such as atelectasis and pneumonia leading to prolonged intubation and intensive care unit length of stay and subsequent prolonged hospital stay. Adequate perioperative analgesia improves hemodynamics and immunologic responses, which would result in better outcomes after cardiac surgery. Opioid sparing "Enhanced Recovery After Surgery" protocols are increasingly being incorporated into cardiac surgeries. This will reduce opioid requirements and opioid-related side effects and facilitate fast-tracking of patients. Regional analgesia can be provided by neuraxial blocks, fascial plane blocks, peripheral nerve blocks, or simply by the infiltration of the wound with local anesthetics for cardiac surgery. Neuraxial analgesia is provided through epidural, spinal, and paravertebral routes. Though they are being replaced by peripheral fascial plane blocks, epidural and spinal analgesia are still being used in some centers. In this article, neuraxial forms of analgesia are focused. We sought to review epidural analgesia and its impact in suppressing hemodynamic stress response, reducing pulmonary complications, and development of chronic pain. The relationship between intraoperative heparinization and potential neuraxial hematoma is discussed. Other neuraxial options such as spinal and paravertebral analgesia and their usefulness, benefits, and limitations are also reviewed.

Automatic Midline Identification in Transverse 2-D Ultrasound Images of the Spine

Effective epidural needle placement and injection involves accurate identification of the midline of the spine. Ultrasound, as a safe pre-procedural imaging modality, is suitable for epidural guidance because it offers adequate visibility of the vertebral anatomy. However, image interpretation remains a key challenge, especially for novices. A deep neural network is proposed to automatically classify the transverse ultrasound images of the vertebrae and identify the midline. To distinguish midline images from off-center frames, the proposed network detects the left-right symmetric anatomic landmarks. To assess the feasibility of the proposed method for midline detection, a data set of ultrasound images was collected from 20 volunteers, whose body mass indices were less than 30. The data were split into two segments, for training and test. The performance of the proposed method was further evaluated using fourfold cross validation. Moreover, it was compared against a state-of-the-art deep neural network. Compared with the gold standard provided by an expert sonographer, the proposed trained network correctly classified 88% of the transverse planes from unseen test patients. This capability supports the first step of guiding the placement of an epidural needle.

Pain management during labor and vaginal birth

Neuraxial analgesia provides excellent pain relief in labor. Optimizing initiation and maintenance of neuraxial labor analgesia requires different strategies. Combined spinal-epidurals or dural puncture epidurals may offer advantages over traditional epidurals. Ultrasound is useful in certain patients. Maintenance of analgesia is best achieved with a background regimen (either programmed intermittent boluses or a continuous epidural infusion) supplemented with patient-controlled epidural analgesia and using dilute local anesthetics combined with opioids such as fentanyl. Nitrous oxide and systemic opioids are also used for pain relief. Nitrous oxide may improve satisfaction despite variable effects on pain. Systemic opioids can be administered by healthcare providers or using patient-controlled analgesia. Appropriate choice of drug should take into account the stage and progression of labor, local safety protocols, and maternal and fetal/neonatal side effects. Pain in labor is complex, and women should fully participate in the decision-making process before any one modality is selected.

Optical fiber technology enables smart needles for epidurals: an in-vivo swine study

Nowadays, epidural space identification is made by using subjective and manual techniques characterized by failure rates up to 7%. In this work, we propose a fiber optic sensor technology based needle guidance system, that is directly inspired by the most common technique currently used for epidurals; through real-time strain measurements, the fiber Bragg grating integrated inside the needle lumen is able to effectively perceive the typical force drop occurring when the needle enters the epidural space. An in vivo swine study demonstrates the validity of our approach, paving the way for the development of lab-in-a-needle systems.

Epidural electrical stimulation test versus local anesthetic test dose for thoracic epidural catheter placement: a prospective observational study

PURPOSE

This study examined the concordance between epidural electrical stimulation test (EEST) and local anesthetic (LA) test dose to indicate correct thoracic epidural catheter position. The relationship between the test results and epidural postoperative analgesia was also assessed.

METHODS

This prospective observational cohort study was done in patients receiving thoracic epidural analgesia for abdominal surgery. After insertion, the epidural catheter was tested using a nerve stimulator to elicit a motor response. The LA test dose was then administered, and sensory block to ice and pinprick was assessed. The primary outcome was the presence/absence of motor response to EEST and sensory block to test dose. Concordance of responses was assessed using kappa statistics, and their predictive power of postoperative epidural analgesia was evaluated.

RESULTS

Sixty-eight thoracic epidural catheters were inserted, of which 62 were used perioperatively. The kappa agreement between EEST and LA test dose responses was moderate at 0.42 (95% confidence interval [CI], 0.18 to 0.67). Positive responses to EEST and LA test dose were observed in 62 (100%) and 50 (81%) patients, respectively, while 52 patients (84%) showed adequate analgesia postoperatively. The sensitivity (95% CI) of EEST and LA test dose to predict adequate postoperative epidural analgesia was 1 (0.93 to 1) and 0.79 (0.65 to 0.89), respectively, and the positive predictive values (95% CI) of EEST and LA test dose were 0.84 (0.75 to 0.93) and 0.82 (0.71 to 0.92), respectively.

CONCLUSION

Following thoracic epidural catheter insertion, the responses to the EEST and LA test dose showed "moderate" agreement. The EEST has a higher sensitivity than the LA test dose to predict adequate epidural analgesia following abdominal surgery, however, both tests have a comparable positive predictive value.

Smart Optical Catheters for Epidurals

Placing the needle inside the epidural space for locoregional anesthesia is a challenging procedure, which even today is left to the expertise of the operator. Recently, we have demonstrated that the use of optically sensorized needles significantly improves the effectiveness of this procedure. Here, we propose an optimized configuration, where the optical fiber strain sensor is directly integrated inside the epidural catheter. The new design allows the solving of the biocompatibility issues and increases the versatility of the former configuration. Through an in vivo study carried out on a porcine model, we confirm the reliability of our approach, which also opens the way to catheter monitoring during insertion inside biological spaces.