Using Augmented Reality to 3D Map Needle Pathways in Real Time to Enhance Neuraxial Anesthesia
Phase: NA
Conditions: Virtual Reality, Anesthesia, Epidural
Sponsor: Sunnybrook Health Sciences Centre

 
 
 
 
 
 
 
Using Augmented Reality to 3D Map Needle Pathways in 
Real Time to Enhance Neuraxial Anesthesia 
 
 
 
Co-Principal Investigators: 
 
Dr. Fahad Alam (MD, FRCPC, MHSc) 
 
Dr. Julian Wiegelmann (MD, FRCPC) 
 
Co-Investigators: 
Dr. Oskar Singer 
Dr. Stephen Choi 
Dr. Paul McHardy 
Dr. Shelly Au 
Dr. Lilia Kaustov 
 

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Background: 
Neuraxial anesthesia (spinal and epidural) has traditionally been a ‘blind’ technique. The subarachnoid or 
epidural space is identified via anatomical landmarks, relying on operators’ feel and skill, both are 
subjective, lack complete accuracy and highly influenced by patient body habitus where obese patients or 
those with anatomical variations, or spinal abnormalities are shown to be quite challenging1,2. Neuraxial 
anesthesia is not a benign procedure as multiple attempts or inaccurate trajectories of the needle can not 
only be anxiety provoking and cause patient discomfort but can also lead to patient morbidity in the form 
of spinal/epidural hematomas, infection, dural puncture headaches and nerve injury3.  
The use of ultrasound (US) has become routine for peripheral nerve blocks as it allows for real-time views 
of needle position for peripheral blocks to achieve higher rates of success, fewer complications, reduced 
patient discomfort, and quicker procedural times4. The needle and/or target structures are kept in constant 
view with the use of ultrasound during the block procedure to allow for higher accuracy. As such, US 
guidance has become the de facto standard of care for peripheral nerve blocks and in fact, is now 
mandated by the Royal College of Physicians of the United Kingdom for central line insertion5.  
Though increasing in popularity, US guidance for neuraxial procedures is still relatively uncommon due to 
technical challenges of real-time guidance in conjunction with the difficulties of US imaging of bony 
structure6. However, different from US-guided peripheral nerve blocks, the common technique for US use 
in neuraxial anesthesia is to provide pre-procedure landmarks so the operator has an accurate prediction 
for the placement of the needle tip, depth and trajectory before actual needle insertion. Anatomical 
landmarks are visualized using the US along multiple viewing planes and skin markings are made based on 
these images. The US probe is then placed at rest and subsequent needle insertion is done in a semi-blind 
manner based on the skin markings and knowledge of approximate depth and trajectory from memory.  
Multiple reviews have been published recently detailing the procedure of US-guided spinal and epidural 
anesthesia at the lumbar spine, though not in real time6,7. They have shown that US reduces procedure 
time, number of needle passes, needle contact with bone, and other complications compared to traditional 
placement techniques based on operator feel7,8. Despite this, the process of placing the US probe at rest 
and then moving forward with the procedure based on skin markings has the downfall of trying to imitate 
accurate needle trajectory beneath the skin based on the operator’s memory9. This may also lead to 
multiple attempts at needle placement or failure of the procedure, challenges that are important to 
consider when attempting thoracic spine neuraxial techniques. Notably, due to the steep angulation of the 
spinous processes at the thoracic level, achieving needle trajectory to get to the epidural space can prove 
to be quite challenging10.  
In contrast to lumbar epidurals where a midline approach is used, the common technique for thoracic 
epidurals is a ‘paramedian’ approach. This involves purposely contacting lamina with the needle and 
continuously adjusting in a cephalad/midline direction to ensure that the operator is walking up the bone 
until the epidural space is entered. The paramedian approach mitigates having to navigate the difficult 
bony landmarks at the thoracic level. However, hitting bone with the needle can cause patient discomfort. 
While US landmarks can be done with thoracic epidurals, the needle trajectory is of greater difficulty to 
predict if the insertion is made solely on memory from the US images. Hence, US is yet to be commonly 
adopted as an approach for thoracic epidurals unlike lumbar spine neuraxial techniques. 
To address the problem, we propose to use augmented reality technology as a tool to provide a 
superimposed US image as an objective alternative to the operator’s memory. Microsoft HoloLens is a head 
mounted augmented reality device, which allows for overlaying computer-generated elements to the real 

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world. Notably, this technology presents a unique opportunity where we will be able to combine the US 
image and angulation of the US probe to instantly create, in real time, spatially stable holograms overlaying 
the patient’s anatomy in the user’s field of view. Thus, when the operator locates the anatomical 
landmarks using an US for a neuraxial technique, a holographic needle trajectory can be instantaneously 
generated and remains on the patient even after the US probe is placed at rest.  
 
The model we propose in this project is truly innovative in medical content and involves a partnership with 
software and engineering experts. In collaboration with our partners, we have recently designed and 
developed the first model of a live holographic anatomical marking system using Microsoft HoloLens. We 
aim to pilot the prototype on a three-dimensional (3D) printed see-through thoracic spine phantom by four 
experienced staff regional-anesthesiologists to determine the accuracy of the holographic trajectory. We 
strongly believe, that using augmented reality, it will be possible to provide an accurate live road map for 
the needle path hidden under the patient’s skin. Also, this alongside 3D object recognition will bring in a 
variety of potential uses in anaesthesiology.  
Overall Aims and Objectives: 
 
Our goal is to combine academic, medicinal and industrial expertise in a partnership to create a new 
technique for use in medicine. This partnership will strengthen the important area of human health, 
neuraxial anesthesia, and ultimately, will better facilitate the translation of research discoveries into 
applied therapies.  
The objectives of this study are to assess whether the use of augmented reality in the form of creating a 
holographic marking of the site of needle insertion and optimal angulation will 1) reduce 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.  
 
Hypothesis: 
 
We hypothesize that using augmented reality through HoloLens, the creation of a newly developed 
holographic tool for neuraxial anesthetic techniques will increase needle accuracy thereby decreasing 
procedure time. 
 
Methodology, Experimental Design and Evaluation 
The 3D Phantom model. A thoracic spine ultrasound phantom (Figure 1) was constructed utilizing open 
source BodyParts3D library anatomy files. This library was created based on whole body MRI images with 
2mm slice thickness of a healthy male volunteer11. A container and associated parts were designed and 3D 
printed using AutoDesk Fusion 360 and a Creality CR-10S from PLA, respectively. When filled with 
compatible gel and covered with a layer of surgical glove material (to obscure the location of the spine with 
the opaque gel12 ), the model has interlaminar acoustic windows and depth characteristics compatible with 
population averages when viewed with a portable ultrasound13. The phantom has similar palpation 
characteristics to a patient, and a standard loss of resistance to saline occurs on entrance of a needle to the 
spinal canal cavity. 

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Figure 1: 3D Model of Thoracic Spine Ultrasound Phantom 
 
Study design and workflow.  
Local research ethics approval will be sought prior to study participant’s recruitment. Only participants who 
meet inclusion/exclusion criteria (Table 1) will be approached for participation in this study.  
We aim to study 84 sequential thoracic epidural events and randomize them to one of two study groups: 
Group 1, landmark based thoracic epidural technique (control) or, Group 2, HoloLens-assisted thoracic 
epidural technique (intervention). Sunnybrook Health Sciences has a dedicated regional block room and 
four experienced regional anesthetists that are trained and experienced in the thoracic epidural technique 
and will perform thoracic epidurals for this study (see Table 1 for inclusion criteria). Prior to the start of the 
study, the four expert anesthesiologists will practice needle insertion on the above described phantom 
model by attempting needle insertion 20 times each, or until they felt comfortable with the system, while 
wearing the Microsoft HoloLens. The anesthesiologist performing the thoracic epidural insertion procedure 
will be randomized to either study Group 1, or 2. 
 

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In Group 1 (control), the staff anesthesiologist will follow the traditional technique for US-guided thoracic 
epidural insertion. Briefly, the anesthesiologist will use the US to identify and mark the appropriate spot for 
placement of the thoracic epidural catheter. The US probe is then placed at rest and the anesthesiologist 
will proceed with thoracic epidural needle insertion following standard techniques. 
In Group 2 (intervention), the staff anesthesiologist will use the HoloLens tool to assist with the traditional 
technique as described above for Group 1. In combination with the US, a hologram image of the trajectory 
towards the epidural space will be generated, thereby mitigating the need to walk off the lamina. The 
holographic system will mark the appropriate spot for placement of the thoracic epidural catheter. Then, 
the needle will be inserted following the holographic trajectory overlaid on the patient’s back. The hand 
movements and realtime ultrasound images of the small portion of the patient’s spine with no visually 
identifying features will be recorded during procedure. The anesthesiologists’ hands and needle movement 
will be captured and will be used post-procedure as a back-up to real-time assessments by 
anesthesiologists and research assistants to confirm the procedure time and needle movements. The 
recordings and ultrasound images will be stored in a de-identified manner.  
 
 
Inclusion Criteria:  
Anesthetists 
 
Exclusion Criteria:  
Patients  
 
 
Trained in US-guided epidural technique with fellowship 
 
Performed >100 thoracic US-guided epidural procedures 
 
 
Age <18 
 
Lack of verbal patient assent 
after study introduction 
 
Table 1. HoloLens study participants inclusion and exclusion criteria. 
 
Sample Size Calculation and Statistical analysis: 
A previous published studies have revealed that mean thoracic epidural catheter placement using 
traditional palpation and landmark guidance requires 10 minutes with a standard deviation of 3 min14,15.  
Therefore, having 2 minutes reduction in procedure time (i.e. 20% relative reduction) will be considered a 
meaningful in the context of patient comfort and operating room efficiency. Considering a 2-sided type I 
error rate of 5% and power of 80%, 36 participants will be required per group, and 72 participants will be 
required to complete the study. Assuming possible participants withdrawal from the study, we will recruit 
84 study subjects to compensate for an expected 15% withdrawal rate. Each of the four anesthesiologists 
will complete an equal number of thoracic epidurals. 
Secondary outcomes that are continuous in nature (e.g. number of skin punctures, number of needle 
movements, procedural pain score) will be analyzed in the same manner. For binary outcomes 
(parasthesias, dural puncture, PCA in PACU) the Chi square test (or Fisher’s exact when expected cell 
counts are less than 5) will be utilized. To account for multiple comparisons, we will use the Holm-
Bonferroni method and an adjusted p<0.05 will be considered significant.  
Expected Outcomes measures: 

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To address our specific objectives of whether the HoloLens tool and methodology, 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, we will ask an 
observer (i.e. anesthesiologist) to document following: 
A. the time to procedure completion starting from skin puncture to time at which the Tuohy needle is 
withdrawn; 
B. the number of  needle movements (in any direction/re-direction); 
C. number of skin punctures made; 
D. patients’ pain score during the procedure using the numeric rating scale (NRS); 
E. any complications during the procedure such as paresthesias, dural punctures;  
F. the need for patient controlled analgesia (PCA) in PACU (constituting failure of epidural). 
Lastly, the patient will be asked to rate their level of overall discomfort during the procedure on a scale of 
0-10 (0 – being no pain/no discomfort and 10 being worst possible pain/extreme discomfort) at its 
conclusion. Similarly, the regional anesthesiologists will be given a questionnaire regarding ease of use and 
limitations of the technique. Our survey strategy will help to validate study results, and enable optimization 
and implementation of the novel technology. 
 
Knowledge Translation 
 
The success of this proposal will lead to implementation of a new objective tool, validation of which will 
create an accessible, low-cost 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 ultrasound techniques (e.g. 
trauma patients). The HoloLens can be applied at institutions with a unique but potentially anatomically 
difficult population such as the obstetric and trauma population. Specifically, at the outset, we aim to apply 
HoloLens locally at Trauma Bay, Sunnybrook Health Sciences Centre. In aggregate, the proposed study will 
generate a knowledge-based cost-effective approach that can be used as a teaching and clinical tool 
around the world where resources are at a minimum. 
 
 
 

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