HoloLens: an Objective Alternative to the Operator's Memory

US guidance for epidural anesthesia is yet challenging due to anatomical and technical restrictions which are rely on the operator's memory to imitate accurate needle trajectory. To address the problem, the study investigators designed and developed the first model of a live anatomical holographic marking system using Microsoft HoloLens, an augmented reality technology tool, to provide a superimposed US image as an objective alternative to the operator's memory. In this study, the proposed methodology will be used to accurate and ease directing the needle insertion thereby leading to the success of the epidural placement and decrease in procedure time. Based on previously published and data from the SHSC institution, mean thoracic epidural analgesia placement required 10 minutes with a standard deviation of 3 minutes. A reduction in procedure time will reduce patient discomfort, increase block and operating rooms efficiency thereby reducing hospital costs as well as used for anatomically challenging patients.

The investigators hypothesize that using augmented reality through HoloLens will lead to implementation of a newly developed virtual holographic 'see-through' tool for neuraxial anesthetic techniques that will increase needle accuracy and decrease procedure time.

The main question of the study is to assess the accuracy of the developed application. In particular, the study will determine if a holographic marking of the site of needle insertion and optimal angulation will increase needle accuracy and reduce procedure time by increasing first past success when compared to traditional ultrasound land-mark based techniques.

The methodology proposed in this study is truly innovative in medical content, involves a partnership with software and engineering experts. The study will lead to implementation of a new objective tool, validation of which will create an accessible, cost-effective piece of technology that will reduce patient morbidity and increase procedure success rate. This 'state-of-the-art' technology can be used for alternate procedures such as peripheral nerve block in patients that cannot be easily positioned for live US techniques. Also, this study will generate a knowledge-based approach that can be used as a teaching and clinical tool locally at institutions presented with anatomically difficult population (e.g. trauma, obstetric patients) at Sunnybrook Health Sciences Centre and around the world, where resources are at a minimum.

This is a prospective cohort randomized trial. With institutional ethical approval and having obtained both, written informed consent and verbal assent from participants, 84 thoracic epidural events will be assessed. A thoracic spine US 3D Phantom model utilizing open source BodyParts3D library anatomy files constructed by group of software and engineering experts, and accessible for practice to anesthetists. Our 3D Phantom model has similar palpation characteristics to a patient mimicking a standard loss of resistance to saline that occurs on entrance of a needle to the spinal canal cavity. The holographic mapping methodology will be practiced by anesthetists on the Phantom model until they feel comfortable with the system prior the study start. Participants will be recruited from the pre-anesthesia clinic. Only participants who meet inclusion criteria will be approached for participation in this study (Table 1,inclusion/exclusion criteria, study protocol). The anesthetists will be randomized to: Group1, landmark based thoracic epidural technique(control) or, Group 2, HoloLens-assisted thoracic epidural technique(intervention), where the needle will be inserted using instantly created holographic trajectory. SHS centre has a dedicated regional block room and four regional expert anesthetists in the US-guided thoracic epidural technique and are comfortable with the HoloLens. Prior to the study start, anesthetists will practice needle insertion on the phantom model by attempting needle insertion 20Xeach, or until they felt comfortable with the tool, while wearing HoloLens. Other aspects of patient care will follow the standard of care at the centre. Data will be collected by anesthetists and include patients surgical/abdominal pain assessment during epidural procedure and post-operatively, and questionnaire about their experience using the HoloLens.

Data will be validated to enable optimization and further implementation of novel technology.

• Inclusion Criteria/Anesthetists:

• Trained in US-guided epidural technique with fellowship
• Performed >100 thoracic US-guided epidural procedures
• Exclusion Criteria/Patients:

• age >18
• Lack of verbal patient assent after study introduction

The control group will be required to determine if hologram mapping and methodology indeed provide an accuracy of the holographic trajectory and create a live road map for the needle path hidden under the patient's skin. Study participants will be withdrawn from the study at their request at any time.

To address this study specific objectives of whether the HoloLens application, that is designed to allow a holographic marking of the needle insertion site and optimal angulation would 1) decrease procedure time by increasing first past success when used as a guide to the thoracic epidural space; and 2) increase needle accuracy when compared to traditional ultrasound landmark based techniques, an observer (i.e. anesthesiologist) will document following:

• the time to procedure completion starting from skin puncture to time at which the Tuohy needle is withdrawn;
• the number of a needle movements (in any direction/re-direction)
• number of skin punctures made;
• patients' pain score during the procedure and post-operatively using the numeric rating scale (NRS);
• any complications during the procedure such as paresthesias, dural punctures;
• the need for patient controlled analgesia (PCA) in PACU (constituting failure of epidural).

Inclusion criteria

• Trained in US-guided epidural technique with fellowship
• Performed >100 thoracic US-guided epidural procedures

Exclusion criteria

• Age <18
• Lack of verbal patient assent after study introduction