Infectious meningitis. Why are the leptomeninges preferentially involved? Electron microscopic insights.

In infectious meningitis, pathogens preferentially attack the leptomeninges (pia mater and arachnoid) rather than the pachymeninges (dura mater). This study aims to provide ultra-anatomical insights from our extensive collection of electron microscopy images and propose mechanisms, highlighting structures that favor the introduction, adherence, colonization, and proliferation of microorganisms leading to spinal meningitis. Over several years, we analyzed an extensive collection of transmission and scanning electron microscopy images of human spinal meninges captured in our laboratories. Upon examining 378 of those images, we identified potential sites for the iatrogenic or hematogenic introduction and adherence of microorganisms, as well as sites for their colonization and proliferation. These included the outer surface of the spinal dural sac, structures within the epidural space, and the spinal dural sac itself, which comprises compact dura mater with interwoven collagen fibers and tightly bound arachnoid cells. Also, the subdural (extra-arachnoid) compartment, consisting of fragile neurothelial cells prone to rupture under force, formed an acquired spinal subdural space, a new subarachnoid compartment, limited by arachnoid trabeculae, that surrounded the nerve roots and spinal cord and the pia mater. Macrophages, fibroblasts, mast cells, and plasma cells were also observed within the dura mater, arachnoid layer, arachnoid trabeculae, and pia mater. These images illustrate how the characteristics of the meningeal layers could contribute to bacterial adhesion and proliferation at various locations, inducing selective inflammation during (iatrogenic) spinal meningitis. In addition, the images help to explain why magnetic resonance imaging enhancement appears preferentially at specific sites.

Anatomical study with clinical significance of communicating and visceral branching of the cervical and upper thoracic sympathetic trunk.

Current advances in the management of the autonomic nervous system in various cardiovascular diseases, and in treatments for pain or sympathetic disturbances in the head, neck, or upper limbs, necessitate a thorough understanding of the anatomy of the cervicothoracic sympathetic trunk. Our objective was to enhance our understanding of the origin and distribution of communicating branches and visceral cervicothoracic sympathetic nerves in human fetuses. This was achieved through a comprehensive topographic systematization of the branching patterns observed in the cervical and upper thoracic ganglia, along with the distribution of communicating branches to each cervical spinal nerve. We conducted detailed sub-macroscopic dissections of the cervical and thoracic regions in 20 human fetuses (40 sides). The superior and cervicothoracic ganglia were identified as the cervical sympathetic ganglia that provided the most communicating branches on both sides. The middle and accessory cervical ganglia contributed the fewest branches, with no significant differences between the right and left sides. The cervicothoracic ganglion supplied sympathetic branches to the greatest number of spinal nerves, spanning from C5 to T2. The distribution of communicating branches to spinal nerves was non-uniform. Notably, C3, C4, and C5 received the fewest branches, and more than half of the specimens showed no sympathetic connections. C1 and C2 received sympathetic connections exclusively from the superior ganglion. Spinal nerves that received more branches often did so from multiple ganglia. The vertebral nerve provided deep communicating branches primarily to C6, with lesser contributions to C7, C5, and C8. The vagus nerve stood out as the cranial nerve with the most direct sympathetic connections. The autonomic branching pattern and connections of the cervicothoracic sympathetic trunk are significantly variable in the fetus. A comprehensive understanding of the anatomy of the cervical and upper thoracic sympathetic trunk and its branches is valuable during autonomic interventions and neuromodulation. This knowledge is particularly relevant for addressing various autonomic cardiac diseases and for treating pain and vascular dysfunction in the head, neck, and upper limbs.

The size, number, and distribution of nerve endings around and within the human epiglottis, focusing on tracheal intubation maneuvers.

The aim of this study was to examine the distribution of nerve endings in the mucosa, submucosa, and cartilage of the epiglottis and the vallecula area and to quantify them. The findings could inform the choice of laryngoscope blades for intubation procedures. Fourteen neck slices from seven unembalmed, cryopreserved human cadavers were analyzed. The slices were stained, and cross and longitudinal sections were obtained from each. The nerve endings and cartilage were identified. The primary metrics recorded were the number, area, and circumference of nerve endings located in the mucosa and submucosa of the pharyngeal and laryngeal sides of the epiglottis, epiglottis cartilage, and epiglottic vallecula zone. The length and thickness of the epiglottis and cartilage were also measured. The elastic cartilage of the epiglottis was primarily continuous; however, it contained several fragments. It was covered with dense collagen fibers and surrounded by adipose cells from the pharyngeal and laryngeal submucosa. Nerve endings were found within the submucosa of pharyngeal and laryngeal epiglottis and epiglottic vallecula. There were significantly more nerve endings on the posterior surface of the epiglottis than on the anterior surface. The epiglottic cartilage was twice the length of the epiglottis. The study demonstrated that the distribution of nerve endings in the epiglottis differed significantly between the posterior and anterior sides; there were considerably more in the former. The findings have implications for tracheal intubation and laryngoscope blade selection and design.

Human lumbar sympathetic blockade: An anatomical study to address potential block failure.

The lumbar sympathetic block is often used to treat complex regional pain syndrome, but it seems to have a high failure rate. This study seeks anatomical explanations for this apparent failure in order to refine our block procedure. Two simulated sympathetic trunk blocks were carried out on four fresh, cryopreserved unembalmed human cadavers under fluoroscopic control at the L2 vertebral body level, followed by two further simulated blocks at the L4 vertebral body level on the other side. Dye was injected, and the areas were dissected following a specific protocol. We then describe the anatomy and the spread of the dye compared to the spread of the contrast medium on fluoroscopy. The ganglia were differently located at different vertebral levels, and differed among the cadavers. Following this anatomical clarification, we now prefer to perform lumbar sympathetic blocks at the fourth lumbar vertebra level, using an extraforaminal approach at the caudal end of ​​the vertebra, avoiding the anterolateral margin of the vertebral body at the midpoint.

Innervation of the heart: Anatomical study with application to better understanding pathologies of the cardiac autonomics.

Current advances in management of the cardiac neuroaxis in different cardiovascular diseases require a deeper knowledge of cardiac neuroanatomy. The aim of the study was to increase knowledge of the human fetal extrinsic cardiac nervous system. We achieved this by systematizing the origin and formation of the cardiac nerves, branches, and ganglia and their sympathetic/parasympathetic connections. Thirty human fetuses (60 sides) were subjected to detailed sub-macroscopic dissection of the cervical and thoracic regions. Cardiac accessory ganglia lying on a cardiac nerve or in conjunction with two or more (up to four) nerves before entering the mediastinal cardiac plexus were observed in 13 sides. Except for the superior cardiac nerve, the sympathetic cardiac nerves were individually variable and inconstant. In contrast, the cardiac branches of the vagus nerve appeared grossly more constant and invariable, although the individual cardiac branches varied in number and position of origin. Each cervical cardiac nerve or cardiac branch of the vagus nerve could be singular or multiple (up to six) and originated from the sympathetic trunk or the vagus nerve by one, two, or three roots. Sympathetic nerves arose from the cervical-thoracic ganglia or the interganglionic segment of the sympathetic trunk. Connections were found outside the cardiac plexus. Some cardiac nerves were connected to non-cardiac nerves, while others were connected to each other. Common sympathetic/parasympathetic cardiac nerve trunks were more frequent on right (70%) versus left sides (20%). The origin, frequency, and connections of the cardiac nerves and branches are highly variable in the fetus. Detailed knowledge of the normal neuroanatomy of the heart could be useful during cardiac neuromodulation procedures and in better understanding nervous pathologies of the heart.

Early reduction in postoperative pain is associated with improved long-term function after shoulder arthroplasty: a retrospective case series.

PURPOSE: Mixed modalities are frequently utilized in total shoulder arthroplasty (TSA) to control pain, improve patient satisfaction, reduce narcotics use and facilitate earlier discharge. We investigate the relationship between early postoperative pain control and long-term functional outcomes after shoulder arthroplasty. METHODS: A retrospective review identified 294 patients (314 shoulders) who underwent anatomic or reverse TSA and received a continuous cervical paravertebral nerve block perioperatively. Opioid and non-opioid analgesics were also available to the patients in an "as needed" capacity to augment perioperative pain control. In addition to demographic and surgical characteristics, the impact on functional outcomes of relative pain (i.e., a patient's subjective pain relative to the entire cohort), pain gradient (i.e., the slope of a patient's subjective pain), and opioid consumption during the first 24 h postoperatively were assessed. Shoulder function was assessed using validated outcome measures collected at 2 year follow-up. Outcomes were measured using American Shoulder and Elbow Surgeons questionnaire (ASES), Shoulder Pain and Disability Index (SPADI), SPADI-130, Raw and Normalized Constant Score, SST-12 and UCLA score. RESULTS: Patients younger than 65, females, reverse TSA, revisions, and preoperative opioid users had worse functional outcomes. On univariate analysis, increased pain perioperatively (> 50% percentile relative pain) was associated with decreased function at 2 years when analyzed with all seven outcome scores (P < .001 for all), reaching minimal clinically important difference (MCID) using the Constant Score. On multivariate analysis, increased pain in the first 24 h postoperatively (assessed on a continuous scale) was independently associated with worse ASES, SPADI, and SPADI-130 scores. Intraoperative ketamine administration and opioid consumption in the 24 h postoperative period did not influence long-term shoulder function. CONCLUSION: Patients reporting reduced pain after TSA demonstrated improved shoulder function with the Constant score at 2 years postoperatively in both univariate and multivariate analysis. Larger-scale investigation may be warranted to see if this is true for other functional outcome measures. LEVEL OF EVIDENCE: III, treatment study.

Microscopy of structures surrounding typical acupoints used in clinical practice and electron microscopic evaluation of acupuncture needles.

Although the general functionality and structures of acupoints have been studied, there has been little insight into their underlying morphology and physical characteristics. We describe the microanatomical structures surrounding acupoints, the electron microscopic appearance of the needles, and the physical effects of acupuncture needling on the fascia. We injected heparinized blood solution through thin needles at seven known and commonly used "sweat acupoints" in eight fresh, unembalmed, cryopreserved human cadavers to mark the needle positions, and later, during histological examination, to identify them. After the solution was injected, samples were dissected and prepared for histological examination. We examined 350 cross-sections of five different paraffin wax sections from each acupoint microscopically. Acupuncture needles were photographed and superimposed on the cross-sectioned tissues at similar magnifications. Needles were also examined under a scanning electron microscope to judge the roughness or smoothness of their surfaces. A greater conglomeration of nerve endings surrounded the acupoints than in tissues more than 1-3 cm distant from them. Nerve endings and blood vessels were in close contact with a complex network of membranes formed by interlacing collagen fibers, and were always enclosed within those collagen membranes. Nerve endings were found within hypodermis, muscles, or both. Scanning electron microscopy demonstrated the three-dimensional shapes and sizes of the needles, and the degree of roughness or smoothness of their polished external surfaces. We demonstrate a delicate arrangement of nerve endings and blood vessels enclosed within complex collagen membrane networks at acupoints within the hypodermis and muscle. This arrangement could explain why needling is an essential step in the acupuncture process that provides favorable outcomes in clinical practice.

Spinal arachnoid sleeves and their possible causative role in cauda equina syndrome and transient radicular irritation syndrome.

INTRODUCTION: We have previously described arachnoid sleeves around cauda equina nerve roots, but at that time we did not determine whether injections could be performed within those sleeves. The purpose of this observational study was to establish whether the entire distal orifice of a spinal needle can be accommodated within an arachnoid sleeve. MATERIALS AND METHODS: We carefully dissected the entire dural sacs off four fresh cadavers, opened them by longitudinal incision, and immersed them in saline. Under direct vision, we penetrated the cauda equina roots nerves traveling almost vertically downward at 30 locations each with a 27- and a 25-G pencil-point needle (60 punctures total). We captured the images with a stereoscopic camera. RESULTS: The nerve root offered no noticeable resistance to needle entry. Although the arachnoid sleeves could not be identified with the naked eye, they were translucent but visible under microscopy. In 21 of 30 attempts with a 27-gauge needle, and in 20 of 30 attempts with a 25-gauge needle, the distal orifice of the spinal needle was completely within the arachnoid sleeve. CONCLUSION: It seems possible to accommodate the distal orifice of a 25- or a 27-gauge pencil-point spinal needle completely within the space of the arachnoid sleeve. An injection within this sleeve could potentially lead to a neurological syndrome, as we have previously proposed.

A reliable septum exists between the lateral cord and medial and posterior cords in the costoclavicular region: Clinical and microanatomical considerations in brachial plexus anesthetic blockade.

BACKGROUND AND OBJECTIVES: The ultrasound-guided proximal infraclavicular costoclavicular block (PICB) appears popular but its results are inconsistent. We sought an accurate demonstration of septae formed between the brachial plexus cords. METHODS: We performed in-plane, lateral-to-medial PICBs on 120 patients and recorded images. Once the most superficial lateral cord component was entered, a 0.4-0.6 mA current was applied to confirm needle placement; 5 ml of local anesthetic (LA) solution was then injected and its spread was observed and recorded. As the needle was advanced, the presence or absence of a hyperechoic linear structure was noted before the deeper compartment was reached, specifically looking for the possible displacement of such a septum. RESULTS: Upon initial scanning, a septum was observed in 67 of the 120 patients (46.2%). However, there was clear displacement of a linear septum between the lateral cord compartment and the medial and posterior cord compartments that prevented spread between the compartments in 94.16% of patients. Piercing the septum evoked motor responses from the medial or posterior cord. The same anatomical regions were studied microanatomically by analyzing cross-sections obtained with the same approach angle as the ultrasound probe. CONCLUSIONS: Intraplexus fascial septae that bundled the medial and posterior cords into one compartment and separated them from the lateral cord were demonstrated and confirmed microanatomically. This suggests the need for two separate injections (or two separate catheter placements for continuous peripheral nerve blockade) into the superficial and deep compartments to ensure LA spread around all three cords of the brachial plexus at this level.

Case series of fluoroscopic findings and 3D reconstruction of human spinal MRIs of the space of Okada.

OBJECTIVE: To better understand the unexpected spread of contrast medium observed by conventional fluoroscopic X-ray images during standard neuraxial techniques used in the treatment of pain. The support of 3D reconstruction of MRI images of structures within the lumbar spine was used to better understand the space of Okada. METHODS: Lumbar facet joint and epidural corticosteroid injections in five patients under fluoroscopic guidance with loss of resistance to air or saline to identify the facet joints or epidural space. Next, in a retrospective study, the authors examined the retrodural space of Okada and the neighboring tissues with 3D reconstruction of spinal MRIs of seven patients without any demonstrable spinal pathology to better understand the characteristics of the space of Okada. RESULTS: Contrast medium spread to the ipsilateral and contralateral sides was observed in five patients. The contralateral spread was thought to be through the retrodural space of Okada, which is a potential space between the anterior surface of the vertebral lamina and the posterior surface of the ligamentum flavum. It facilitates communication between the contralateral articular facet joints of the spine. CONCLUSIONS: This study provides new evidence for the existence of the space of Okada where an unexpected contralateral spread occurred following facet joint and attempted epidural injection. The 3D reconstructions of MRIs may help us better understand the nature of the retrodural space of Okada and its clinical implications.

Revision Arthroplasty Does Not Require More Opioids Than Primaries: A Review of Prescribing Practices After Implementation of a Structured Perioperative Pain Management Strategy.

BACKGROUND: There is a growing body of literature on opioid mitigation strategies following total joint arthroplasty. However, these have almost exclusively been studied in populations undergoing primary procedures, with revision arthroplasty historically thought to be more resistant due to procedural variability and complexity. We report on opioid utilization for revision arthroplasty following implementation of a structured, standardized opioid reduction strategy. METHODS: Beginning January 2015, a comprehensive multidisciplinary pain protocol was developed and applied universally to all patients undergoing hip and knee arthroplasty, including revisions, without exclusion. We performed a retrospective review of opioid prescription trends for the revision arthroplasty subgroup between January 2014 and July 2018, with the first year serving as a baseline for comparison. Inpatient and outpatient opioid prescription data, inpatient satisfaction scores, and quality metrics were also reviewed. RESULTS: We identified 1273 revision arthroplasty cases in the study period. There was a significant reduction in average oral morphine equivalents utilized per procedure when comparing preintervention and postimplementation values. Overall, inpatient prescriptions decreased 24.1% and outpatient utilization decreased 62.4% over the study period. Significant reductions were seen in both the total hip (60.6%) and total knee (64.0%) subgroups. Although revision arthroplasty patients were prescribed 32.5% more oral morphine equivalents at baseline, at year 5 there was no significant difference in outpatient prescriptions between primary and revision subgroups. CONCLUSION: At our institution, a standardized opioid reduction strategy has resulted in marked reduction in opioid prescriptions for revision arthroplasty patients in line with generally successful reductions for primary arthroplasty. More importantly, with this approach, revision arthroplasty patients required no more outpatient opioids than their primary counterparts. LEVEL OF EVIDENCE: Level III, Retrospective cohort study.

Another (Internal) Epineurium: Beyond the Anatomical Barriers of Nerves.

The epineurium has been accepted as the outer anatomical barrier of the peripheral nerves. Our objective was to characterize the microanatomy of the layers surrounding nerves using different tissue-specific staining methods. Two hundred forty-two cross sections of human sciatic and median nerves, and brachial plexuses of eight fresh unembalmed cadavers, were examined. The samples were fixed in formaldehyde solution and stained with hematoxylin-eosin, Masson's trichrome, or epithelial membrane antigen under standard conditions. Because epithelial membrane antigen only stains the perineurium, we demonstrated using hematoxylin-eosin and Masson's trichrome that there were different collagen layers inside and outside the nerves. All fascicles had a collagen layer that surrounded the perineurium and were in close contact with it, with no adipose tissue between them. Unlike the perineurium, this layer, an "internal epineurium," contained no cells, and it surrounded one or a small group of fascicles. Bundling these fascicles or small groups of fascicles together was the true epineurium, and between the true and internal epineurium, we consistently found an adipose-containing compartment. More proximal to this, the tibial and common peroneal nerves were bundled together by another collagen layer, the circumneurium, which also had a fat-cell-containing compartment deep to it. There were scattered collagen fibers among the adipocytes. Using tissue-specific staining, we were able to demonstrate a collagen layer, the "internal epineurium." Outside the nerves, we identified several fat-containing concentric compartments. Those compartments were limited by collagen fiber layers that were also similar to the epineurium. Clin. Anat. 33:199-206, 2020. © 2019 Wiley Periodicals, Inc.

Extrafasicular and Intraperineural, but No Endoneural, Spread after Deliberate Intraneural Injections in a Cadaveric Study.

BACKGROUND: There is confusion regarding the spread of intraneurally injected local anesthetic agents during regional anesthesia. The aim of this research was to deliberately inject a marker that does not leave the neural compartment into which it is injected, and then to study the longitudinal and circumferential spread and possible pathways of intraneural spread. METHODS: After institutional review board approval, we intraneurally injected 20 and 5 ml of heparinized blood solution under ultrasound guidance into 12 sciatic nerves in the popliteal fossa and 10 median nerves, respectively, of eight fresh, unembalmed cadavers using standard 22-gauge "D" needles, mimicking the blocks in clinical conditions. Ultrasound evidence of nerve swelling confirmed intraneural injection. Samples of the nerves were then examined under light and scanning electron microscopy. RESULTS: Extrafascicular spread was observed in all the adipocyte-containing neural compartments of the 664 cross-section samples we examined, but intrafascicular spread was seen in only 6 cross-sections of two nerves. None of the epineurium, perineurium, or neural components were disrupted in any of the samples. Spread between the layers of the perineurium was a route of spread that included the perineurium surrounding the fascicles and the perineurium that formed incomplete septa in the fascicles. Similar to the endoneurium proper, subepineural compartments that did not contain any fat cells did not reveal any spread of heparinized blood solution cells. No "perineural" spaces were observed within the endoneurium. We also did not observe any true intrafascicular spread. CONCLUSIONS: After deliberate intraneural injection, longitudinal and circumferential extrafascicular spread occurred in all instances in the neural compartments that contained adipocytes, but not in the relatively solid endoneurium of the fascicles.

The Posterior Lumbar Epidural Space: Three-Dimensional Reconstruction of High-Resolution MRI: Real and Potential Epidural Spaces and Their Content In Vivo.

OBJECTIVE: Our aim was to study the posterior lumbar epidural space with 3D reconstructions of magnetic resonance images (MRIs) and to compare and validate the findings with targeted anatomic microdissections. DESIGN: We performed 3D reconstructions of high-resolution MRIs from seven patients and normal-resolution MRIs commonly used in clinical practice from 196 other random patients. We then dissected and photographed the lumbar spine areas of four fresh cadavers. RESULTS: From the 3D reconstructions of the MRIs, we verified that the distribution of the posterior fat pad had an irregular shape that resembled a truncated pyramid. It spanned between the superior margin of the lamina of the caudad vertebra and beyond the inferior margin to almost halfway underneath the cephalad lamina of the cranial vertebra, and it was not longitudinally or circumferentially continuous. The 3D reconstructions of the high-definition MRI also consistently revealed a prelaminar fibrous body that was not seen in most of the usually used low-definition MRI reconstructions. Targeted microdissections confirmed the 3D reconstruction findings and also showed the prelaminar tissue body to be fibrous, crossing from side to side anterior to the cephalad half of each lamina, and spanning from the dural sac to the laminae. CONCLUSIONS: Three-dimensional reconstructions and targeted microdissection revealed the unique appearance of posterior fat pads and a prelaminar fibrous body. The exact consistency, presence, prevalence with age, presence in other regions, and function of this body are unknown and require further research.

Early Experience with Bilateral Continuous Femoral Nerve Block and Single-Injection Spinal Anesthesia for Bilateral Total Knee Arthroplasty: A Case Series.

Objective: Total knee arthroplasty (TKA) is a commonly performed surgery in the United States, with demand for unilateral and simultaneous bilateral TKAs (BTKAs) expected to increase significantly over the coming decades. This study reports the authors' early experience in a consecutive series of simultaneous BTKAs performed under regional anesthesia and mild sedation. Methods: In this retrospective case series, the authors examined all simultaneous BTKAs performed over two years by a single surgeon. Only patients receiving bilateral continuous femoral nerve blockade (CFNB) and single-injection sciatic nerve blockade in combination with single-injection subarachnoid block were included in the study. Of the 32 patients who underwent BTKAs during this period, 25 met the inclusion criteria. The patient's anesthesia records, physician notes, nursing notes, pharmacy records, and physical therapy records were then reviewed systematically to create a database of information. Results: Only one of 25 patients required conversion to general anesthesia during surgery. There were no major perioperative complications. The average Defense and Veterans Pain Rating Scale score immediately postoperation was 0.6/10, and the average daily score remained below 3.5/10 throughout the hospital stay. The use of bilateral CFNB did not prevent patients from ambulating during physiotherapy. Conclusions: This early retrospective case series suggests that it is feasible to effectively manage the postoperative pain associated with BTKA with staged bilateral CFNB and single-injection sciatic nerve blockage in combination with single-injection subarachnoid block as the sole anesthetic technique without negatively influencing early ambulation.

A novel marker for identifying and studying the membranes, barriers, and compartments surrounding peripheral nerves microscopically.

Recent anatomical discoveries indicate the importance of identifying membranes and compartments surrounding peripheral nerves into which local anesthetic agents can be injected and continuous nerve block catheters placed during regional anesthetic procedures. However, current markers used in anatomical studies have multiple drawbacks, specifically extravasation into noninjected locations, which can result in inadequate treatment. We studied a readily-available new marker, heparinized blood solution (HBS), which is easy to identify by microscopy and can remain in the nerve compartment into which it is deposited without distorting the tissue. We collected blood from 22 patients and prepared it as HBS. This was then injected into four fresh cadavers as in routine clinical practice for ultrasound-guided nerve blocks to form a so-called "doughnut" by "hydro-dissecting" at 32 sites. All samples, including nerves and neighboring tissues, were then prepared and examined by light microscopy. Although no deliberate intraneural injection was attempted, the marker was identified inside all the nerve compartments except the fascicles. Apart from leaking through the needle entry site in some instances, there was no extravasation of the HBS into neighboring nerve compartments in either direction. The tissues were not distorted and the erythrocytes did not form a thrombus. Nerve membranes and compartments could be clearly identified with routine staining. This technique enabled us to study the longitudinal and circumferential spread in all nerve compartments and to collect data for better interpretation of factors influencing an anesthetic nerve block and situations in which complications could possibly arise. HBS seemed superior to other markers because it did not leave the compartments into which it had been injected, did not distort the tissue, and was easily visible under the light microscope. Clin. Anat., 31:1050-1057, 2018. © 2018 Wiley Periodicals, Inc.

Teaching a Machine to Feel Postoperative Pain: Combining High-Dimensional Clinical Data with Machine Learning Algorithms to Forecast Acute Postoperative Pain.

BACKGROUND: Given their ability to process highly dimensional datasets with hundreds of variables, machine learning algorithms may offer one solution to the vexing challenge of predicting postoperative pain. METHODS: Here, we report on the application of machine learning algorithms to predict postoperative pain outcomes in a retrospective cohort of 8,071 surgical patients using 796 clinical variables. Five algorithms were compared in terms of their ability to forecast moderate to severe postoperative pain: Least Absolute Shrinkage and Selection Operator (LASSO), gradient-boosted decision tree, support vector machine, neural network, and k-nearest neighbor (k-NN), with logistic regression included for baseline comparison. RESULTS: In forecasting moderate to severe postoperative pain for postoperative day (POD) 1, the LASSO algorithm, using all 796 variables, had the highest accuracy with an area under the receiver-operating curve (ROC) of 0.704. Next, the gradient-boosted decision tree had an ROC of 0.665 and the k-NN algorithm had an ROC of 0.643. For POD 3, the LASSO algorithm, using all variables, again had the highest accuracy, with an ROC of 0.727. Logistic regression had a lower ROC of 0.5 for predicting pain outcomes on POD 1 and 3. CONCLUSIONS: Machine learning algorithms, when combined with complex and heterogeneous data from electronic medical record systems, can forecast acute postoperative pain outcomes with accuracies similar to methods that rely only on variables specifically collected for pain outcome prediction.

Acute Pain Medicine in the United States: A Status Report.

BACKGROUND: Consensus indicates that a comprehensive,multimodal, holistic approach is foundational to the practice of acute pain medicine (APM),but lack of uniform, evidence-based clinical pathways leads to undesirable variability throughout U. S. healthcare systems. Acute pain studies are inconsistently synthesized to guide educational programs. Advanced practice techniques involving regional anesthesia assume the presence of a physician-led, multidisciplinary acute pain service,which is often unavailable or inconsistently applied.This heterogeneity of educational and organizational standards may result in unnecessary patient pain and escalation of healthcare costs. METHODS: A multidisciplinary panel was nominated through the APM Shared Interest Group of the American Academy of Pain Medicine. The panel met in Chicago, IL, in July 2014, to identify gaps and set priorities in APM research and education. RESULTS: The panel identified three areas of critical need: 1) an open-source acute pain data registry and clinical support tool to inform clinical decision making and resource allocation and to enhance research efforts; 2) a strong professional APM identity as an accredited subspecialty; and 3) educational goals targeted toward third-party payers,hospital administrators, and other key stake holders to convey the importance of APM. CONCLUSION: This report is the first step in a 3-year initiative aimed at creating conditions and incentives for the optimal provision of APM services to facilitate and enhance the quality of patient recovery after surgery, illness, or trauma. The ultimate goal is to reduce the conversion of acute pain to the debilitating disease of chronic pain.

Regional anesthesia does not consistently block ischemic pain: two further cases and a review of the literature.

OBJECTIVE: Ischemic pain is complex and poorly understood. There is controversy regarding whether or not regional anesthetic techniques block ischemic pain. We present two further cases where regional anesthesia did not block ischemic pain despite adequate motor and sensory block. CASE REPORT 1: A 29-year-old healthy male underwent elective right lateral ankle ligament reconstruction for ankle instability with single-injection femoral and sciatic nerve blocks as the sole anesthetic. He reported no pain during or after surgery; approximately 90 min after the cast dressing was applied, he complained of severe pain in his medial ankle despite persistent complete sensory and motor blockade. The cast was removed, and he had immediate and complete resolution of his pain, which was thought to be due to ischemia. CASE REPORT 2: A 45-year-old female with a history of diabetes mellitus, hypertension, and 30 pack-year smoking history presented with increasingly cold, cyanotic, and painful fingers in her right hand. She suffered necrotic lesions of her 4th and 5th fingers accompanied by severe ischemic type pain. A continuous C7 cervical paravertebral block was placed. Despite dense sensory and motor blockade, she still reported excruciating pain that ultimately required amputation after developing demarcated gangrene. CONCLUSION: The two cases support the growing body of evidence that ischemic pain is largely unaffected by regional anesthesia, even with adequate sensory and motor block. The prevailing understanding regarding peripheral nerve blocks in patients in danger of developing compartment syndrome should be reconsidered.