Ultrasound Assisted Neuraxial Blockade in Obstetric Anesthesia

Central Neuraxial Blocks (CNBs) relevant to the practice of obstetric anesthesia and analgesia are spinal, epidural and combined spinal-epidural injections. These techniques are routinely used for cesarean deliveries and labor pain relief. Traditionally, CNBs are performed using surface anatomical landmarks. In the first instance the highest point of each iliac crest is identifies. The imaginary line connecting these points allegedly passes through the L4 vertebral body in non-pregnant women, and L3 vertebral body in pregnant women [1]. Based on this, the operator palpates and counts the spinous processes and decides on the needle entry point. Although this technique is widely accepted as relatively reliable, the correlation is inconsistent even in non-complicated cases. Obesity, tissue edema, pelvic rotation, limited ability to bend forward, hyperlordosis, labor pain, underlying spinal deformity or previous back surgery and instrumentation pose additional difficulty for anesthesiologists to correctly locate the intervertebral levels.

Limited Chest Ultrasound to Replace CXR in Diagnosis of Pneumothorax Post Image-Guided Transthoracic Interventions

Purpose: To assess the diagnostic accuracy of limited chest ultrasound in detecting pneumothorax following percutaneous transthoracic needle interventions using chest X-ray (CXR) as the reference standard. Methods: With IRB approval, after providing consent, asymptomatic patients after percutaneous transthoracic needle interventions were enrolled to undergo limited chest ultrasound in addition to CXR. A chest Radiologist blinded to the patient’s prior imaging performed a bedside ultrasound, scanning only the first 3 anterior intercostal spaces. Pneumothorax diagnosed on CXR was categorized as small or large and on ultrasound as grades 1, 2, or 3 when detected in 1, 2, or 3 intercostal spaces, respectively. Results: 38 patients underwent 36 biopsies (34 lungs, 1 pleura, and 1 mediastinum) and 2 coil localizations. CXR showed pneumothorax in 13 patients. Ultrasound was positive in 10 patients, with 9 true-positives, 1 false-positive, 4 false-negatives, and 24 true-negatives. The false positive results were due to apical subpleural bullae. The false-negative results occurred in 2 small apical and 2 focal pneumothoraces at the needle entry sites. Four pneumothoraces were categorized as large on CXR, all of which were categorized as grade 3 on ultrasound. Sensitivity and specificity of US for detection of pneumothorax of any size were 69.23% (95%CI 38.6%, 90.1%) and 96.0% (95%CI 79.6%, 99.9%), and for detection of large pneumothorax were 100% (95%CI 39.8%, 100%) and 100% (95%CI 89.7%, 100%). Conclusions: Results of this prospective study is promising. Limited chest ultrasound could potentially replace CXR in the management of postpercutaneous transthoracic needle intervention patients.

O49 The use of augmented reality for surgical guidance: an assessment of the human error

Introduction Microsoft HoloLens® is an augmented-reality headset which is increasingly used for surgical guidance. This headset allows the overlay of patient-specific virtual models obtained from medical images onto the patient’s body surface using automatic marker-based alignment. This can guide surgeons during certain surgical tasks, e.g. determining biopsy needle entry points. This study aims to measure the human error in the localisation of virtual models with the headset and discuss its surgical implications. Method 59 adults were recruited between the ages of 20–59 years. A 12 cm2 digital marker was displayed on a monitor in 9 different positions, one at a time. This was repeated 3 times, resulting in 27 markers shown to each participant. Once a marker was detected by the headset’s camera, a virtual hexagon was rendered on the headset’s transparent lenses. Participants were tasked to click on the hexagon’s vertices using a mouse. The clicks’ coordinates were recorded by the system and compared to the predicted coordinates. This allowed for the calculation of the vertex localisation error. Result The mean vertex localisation error was found to be 5.19 mm (±3.56) with a range from 0.08 to 29.77 mm. There was a significant difference between marker positions as determined by a one-way ANOVA (P < 0.001). Conclusion This study suggests that the error in the localisation of virtual models depends on the position of the markers relative to the user wearing the headset. Further research is required to explore whether training can reduce the human error with this headset. Take-home Message The range of the human error in localising virtual models via the Microsoft HoloLens® headset is large and may be dependent on the position of the marker relative to the user of the headset. Further research is needed to investigate whether training with the headset can improve human performance.

Intracardiac Self Insertion of a Darning Needle in a Psychiatric Patient

Objective: We report a case of self inserted needle into the left ventricle of the heart and a description of our surgical intervention in a psychiatric patient without decision-making capacity. We discuss issues regarding obtaining consent in this patient with a sub-acute presentation, report our operative approach, and summarize a treatment approach based on a review of current literature. Methods: A PubMed search using terms “needle, “heart”, “insertion”, “intracardiac foreign object”, yielded 69 relevant papers. 67 of these were case reports yielding 72 individual cases. Age, gender, cause of the needle entry (Accidental Plus (A+), Intravenous Drug User [IVDU], Self-inflicted (SI)), type of needle, location in heart, neuropsychiatric history, treatment, and outcome were documented. Results: Within the SI category, there were a total of 28 cases, 89.3% had a neuropsychiatric history whereas only there were only 2 such patients in both the IVDU and A+ group. The location of the needle in the heart in all 72 cases was as follows: right ventricle 40.3%, other 20.8%, left ventricle 19.4 %, ventricle and interventricular septum 16.7% and the right and left atrium were each 1.4 %. In all three groups (n=72), 77.8% of patients underwent surgery, with 92.9% having a stable outcome. Conclusion: Our case and review demonstrates that management of such cases, particularly when active mental health issues are present, requires a case-by-case evaluation and treatment as a specific standard of care has not been established. Surgical intervention appears to be the preferred management regardless of presentation with good outcomes. Running Title: Intracardiac Self Insertion of a Darning Needle in a Psychiatric Patient