**1. Introduction**

386 Practical Applications in Biomedical Engineering

[152] Zhong X, Spottinswoode BS, Meyer CH, Kramer CM, Epstein FH. Imaging threedimensional myocardial mechanics using navigator-gated volumetric spiral cine

DENSE MRI. Magn Reson in Med 2010; 64(4):1089-1097.

The application of engineering techniques into biomedical procedures has proved extremely beneficial in many areas of medicine. A developing area is in epidural analgesia and anaesthesia, a technique employed for the relief of pain in both acute and chronic, and for anaesthesia to enable pain-free surgery. The aim of this chapter is to demonstrate several specific areas of research and how biomedical engineering techniques are used to improve and enhance the experience and training in the epidural procedure. The overall goal is to reduce the risks and subsequent morbidity in patients using advanced technologies to recreate the epidural procedure replicating as far as possible the in-vivo procedure. This would allow anaesthetists to practice the procedure in a safe and controlled environment without risk to patients. This could be achieved by recreating the sensation of the needle passing through the tissues and ligaments and by the generation of forces that match exactly those felt in-vivo. Epidural simulators are currently used as a training aid for anaesthetists, however existing simulators lack realism to various degrees and their operation is not based on measured invivo data that can accurately simulate the procedure. The techniques of advanced simulation and biomedical engineering detailed in this chapter can provide a solution.

Haptic devices have been used previously to reproduce needle forces but the forces are often not based on measured data. Needle insertion forces in-vivo are largely unknown as there are few studies in this specific area. Without accurate measurement of resultant pressure on the syringe plunger of the epidural needle, as the needle passes through the various ligaments and tissues of the spine, it is difficult to create accurate simulation of the epidural procedure. The ideal model would require other features such as a palpable spine, ability to accommodate for patient variation, 3D graphics visualisation and an adjustable needle insertion point. Techniques in biomedical engineering can provide solutions through

© 2012 Dubey et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Dubey et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the design of devices capable of making precise measurements and utilising them in a novel high fidelity epidural simulator. Adequate training on an advanced simulator will help alleviate the risks of epidural failures from inaccurate placement and also reduce potential morbidity to patients thereby improving the safety of the procedure.

Biomedical Engineering in Epidural Anaesthesia Research 389

interspinous ligaments, ligamentum flavum and then to the epidural space. Epidural needle insertion is essentially a blind procedure, but utilises a well-known technique referred to as "loss of resistance" (LOR). LOR essentially involves identification of the epidural space by compression of either fluid or air as the epidural needle encounters the various ligaments of the lumbar vertebral column [1]. Initially, the back of the patient is palpated, and using surface landmarks such as the iliac crests, an assessment is made of suitable intervertebral spaces and of midline. For lumbar epidurals, this may be between lumbar vertebra 3 (L3) and lumbar vertebra 4 (L4) for instance. The epidural or Tuohy needle, as it is commonly called, is inserted into the interspinous ligament and a syringe filled with saline is attached to the end of the needle. These LOR syringes are specially manufactured so that there is less friction between the plunger and the inner wall of the LOR syringe. A constant or intermittent force is then applied to the plunger by the operator's thumb as the needle is slowly advanced forward. As the tougher and more fibrous ligamentum flavum is encountered, a higher resistive force to injection is encountered. Once the needle tip traverses the ligamentum flavum, the epidural space is then entered into and saline can be quite easily injected, hence the phenomenon of LOR. It is this haptic perception that informs the operator of needle location within the various tissue layers, obstruction from bone and loss of resistance from potential spaces such as those between the ligaments. Combining this with the creation in one's mind of a three-dimensional image of lumbar spinal anatomy

The ideal epidural simulator should be capable of replicating the above procedure and aim to recreate as far as possible the in-vivo procedure. A real Tuohy needle could be inserted at any intervertebral space in the lumbar or thoracic region using the midline or paramedian approach [2]. It would contain a force feedback haptic device, with force data originating from measured Tuohy needle insertions from patients. Using measured in-vivo data from patients and integrating this into the epidural simulator software, the resistance would automatically adjust to give patient variation on weight, height and body shape. This could simulate random patients or match measurements from a specific patient. The 3D virtual patient and virtual vertebrae can also be adjusted in size and shape to match measurements from actual patients. As the needle advances, the resultant force should represent each tissue layer and a LOR on reaching the epidural space. Once the epidural space is reached, saline would be released. During the entire insertion, a 3D virtual spine could be displayed on the monitor showing the trajectory of the needle in real time. The manikin could bend forwards to mimic spinal flexion to increase spacing between the vertebrae or alternatively bend backwards (extension) to simulate increased difficulty in locating the interspinous

Variation in patient size, height, weight and other characteristics should be possible based upon actual patient measurements. Currently, most simulators have only two or three options such as obese, elderly and normal [3-6] which is perhaps not enough to encapsulate reality and could therefore be improved. Simulators could have unlimited patient variation by including parameters such as height, weight, body shape, age, obesity which could be adjustable. Ideally, the settings should match measurements from real patient data. The

enables successful placement of an epidural catheter.

space for training purposes.

This chapter is laid out in various sections to illustrate different aspects of current epidural anaesthesia research. Section 2 describes the actual epidural procedure and its challenges. Section 3 discusses the needle insertion forces in epidurals. Section 4 describes an interspinous pressure measurement device for wireless data collection during needle insertion leading to a porcine trial discussed in Section 5. Section 6 describes an image processing technique for non-contact needle depth measurement that could be used in conjunction with pressure measurement for fully characterising the needle insertion. In Section 7, 3D-modelling of spine with bending and flexing is discussed for flexibility of patient's positions together with heterogeneous volumetric modelling of spinal ligaments in Section 8. Stereo 3D visualisation for depth perception of epidural procedure has been discussed in Section 9. Section 10 applies a haptic force feedback device configured with the measured force data to create an electronic human–computer interface which is described in Section 11. Finally, section 12 brings all these technologies together and demonstrates the complete system that makes up our current epidural simulator prototype with conclusions provided in section 13.
