WO2007068050A1 - Simulator and method - Google Patents

Abstract

One aspect of the invention relates to a haptic simulation apparatus having a moveable shaft restrained within a bearing, a force reflecting device acting on (5) one end of the shaft with the other end of the shaft being manipulated by a user, and a control means for controlling the reflected force applied to an end of the shaft. In another aspect of the invention there is provided a loss of resistance (10) simulation system including a gas passage connectable to a syringe, pressure sensing means for sensing gas pressure in the gas passage, and means for increasing or decreasing the gas pressure in the air passage in response to changes in pressure in the passage. The invention also concerns a method of simulating a medical or surgical procedure, computer software for use with a (15) medical simulation device and an interactive simulation system configured to provide interactive training for learning a complete procedure, particularly an epidural anaesthesia, including dextrous and non-dextrous steps.

Description

SIMULATOR AND METHOD

Field of the Invention

The present invention relates to a simulator and method, more particularly it relates to a haptic simulation apparatus and a method of teaching a medical or surgical procedure. It will be convenient to describe the invention with particular reference to a haptic simulation apparatus and interface used to simulate an epidural anaesthesia and teaching of epidural anaesthesia and procedure although the invention may have wider application.

Background to the Invention

Epidural injection is commonly performed as part of a procedure for anaesthesia. It is commonly used during surgery or during childbirth to relieve pain and restrict sensation below a location on the spinal cord. Epidural injections and associated procedural steps require a high level of precision and skill from the administering clinician. A needle is inserted into the epidural space and once in the epidural space, a cannula is inserted and the needle retracted. Anaesthetic may then be administered through the cannula. While inserting the needle into the epidural space, the clinician must be careful so as not to perforate the dura matter, a layer that covers and protects the spinal cord and its nerves. Perforation of the dura matter may lead to complications such as leakage of cerebro-spinal fluid which may result in headache or more serious complications.

Most epidural anaesthesia is administered in the lumbar region. As the needle passes through the ligaments in the lumbar region, tactile clues are generated by the different tissue layers between the skin and the epidural space. These clues must then be interpreted to successfully navigate the needle tip into the epidural space, while avoiding contact with bone or penetrating too deeply and puncturing the dural membrane. Once the epidural space is located, a catheter is inserted to deliver a suitable anaesthetic into the epidural space to effect analgesia. Various tissue layers to be traversed to reach the epidural space include the epidermis and dermis layers, subcutaneous fat, the supraspinous ligament, the interspinous ligament and finally the ligamentum flavum.

Other than using imaging technology, the technique which is used to locate the epidural space is termed the "loss of resistance" technique. This technique relies on the density and toughness characteristics of the interspinous ligament and the ligamentum flavum, the latter being the last layer of resistance before the epidural space is penetrated, and their effect in blocking the end of the epidural needle and thus providing resistance felt through the loss of resistance device.

The actual procedure utilises a specially designed needle with a slight curve at the end called a Tuohy needle. Once a Tuohy needle is firmly anchored in the interspinous ligament, a "loss of resistance" ("LOR") device filled with saline or air is attached to the hub of the needle. This device is specifically designed for the loss of resistance technique of epidural injection and has a freely moving plunger which gives the clinician a greater level of haptic (force) feedback. If the needle tip is correctly located in the interspinous ligament or the ligamentum flavum, then no fluid or air can be discharged from the device, thus by pressing on the device plunger a resistance will be felt.

Whilst the needle is being inserted through the interspinous ligament and ligamentum flavum, the user will apply a light pressure to the plunger of the LOR device. The two main techniques to identify the loss of resistance, one using saline in the LOR device, and the other using air in the device have slightly different actions. When using air, it is normal for the user to oscillate the plunger pressure slightly. When using saline, normally a constant pressure is applied. While the tip of the needle is embedded within the ligaments, there is (generally) no, or little loss of resistance in the device, ie: pressure is not lost in the device barrel. When the tip of the needle enters the epidural space, there is a sudden loss of resistance to injection and the air or saline in the device passes freely into the space as if the space were empty. Forward motion of the needle is then immediately stopped. The device is removed from the epidural needle and a catheter is threaded into the epidural space via the needle and by observing the depth to which the needle has penetrated. The needle is then also removed and anaesthetic can be continuously or repeatedly administered for as long as required through the catheter.

Patients undergoing epidural anaesthesia are generally positioned either in a sitting position bent forwards, or lying down in a curled position, so that spacing between spinous processes is increased.

There are few ways that a trainee can practice the complete procedure of administering epidural anaesthesia before attempting it on a patient. Non- human animals, cadavers or rubber models may be used, but these are not a particularly good substitute. As a result, trainees gain most of their experience from performing epidural procedures on actual patients under the supervision of an expert. This type of training has a very high risk associated with it, as there is little margin for error, and no real ability to repeat the procedure again in a short timeframe to improve skills. Further there is no way for a trainee to see exactly where the needle is located so as to directly correlate the haptic sensation they are experiencing with various anatomical structures.

Haptic feedback apparatus designed to simulate the force profiles and loss of resistance sensations experienced during an actual procedure are known. These apparatus may simulate the saline technique by having saline or water injected into the apparatus, and the loss of resistance is simulated by release of a valve.

Because the apparatus used in haptic feedback simulators contains sensitive electronic equipment it would be desirable to avoid the use of fluids such as saline or water in such simulators to avoid the risk of leakage causing damage to other parts of the simulator and to avoid the need to purge fluids injected into the simulator when the simulator is no longer in use. It would further be desirable for a simulator to be capable of simulating the loss of resistance technique for both air and saline techniques.

It would also be desirable to provide a haptic simulation apparatus which is readily portable.

It would further be desirable to provide a haptic simulation apparatus in which a force reflecting device only needs to be able to measure position and apply forces in 3 degrees of freedom.

It would also be desirable to provide a method of teaching a medical or surgical procedure which provides an environment for the user to practice all relevant aspects of a procedure, including aspects other than dextrous skills.

Summary of the Invention

In one aspect of the invention there is provided a haptic simulation apparatus including a shaft having a longitudinal axis, the shaft being moveable through a range of motion and having first and second ends; a bearing between said first and second ends restraining said shaft in one or more ranges of motion; force reflecting device acting on said second end; control means for controlling the reflected force applied to said second end by said force reflecting device for locations and orientations of the shaft within the range of motion.

The haptic simulation apparatus may have a notional outside, which may be representative of the outside of the body which would be experienced by a clinician, and a notional inside which would correspond to the inside of the body, and the bearing represents the location at the surface of a body where an injecting needle is to be inserted.

Preferably the bearing is a gimbal slide bearing having a centre point which is designed to allow the shaft to slide back and forth along its longitudinal axis and to pivot in 2 angular directions (pitch and yaw) about the center point of the bearing. In a preferred embodiment the shaft is hollow to allow the flow of fluid from said first end towards said second end, or to allow fluid pressure to be communicated between said first and second ends.

The shaft may include at its first end a device attachment means, such as a luer fitting which provides a fluid-tight attachment point for a device. Preferably, the device attachment means is adapted to receive a "Loss of Resistance" device which has a corresponding fitting, such as a luer fitting, for example. The first end of the shaft may include a flange, such as luer wings which may provide a leverage point for the user when manipulating the shaft. The device attachment means and/or flange may have a secondary function in acting to limit the depth which the shaft can be inserted into the bearing.

The second end of the shaft is associated with the force reflecting device such that the force or motion of the second end of the shaft is detected by and may be opposed by the force reflecting device. The second end may be pivotably connected to the force reflecting device by a coupling.

Preferably, the coupling is attached to a wrist of the force reflecting device such that it allows the shaft to rotate freely to at least a limited degree about the shaft's longitudinal axis.

In a preferred embodiment there is also provided a calibration means associated with the second end of the shaft. This may be in the form of a calibration ring proximate the coupling. The calibration means may act in conjunction with a calibration stop located proximate the bearing on the second end side of the bearing. The calibration means may act by forcing the shaft to a known location and orientation when the shaft is fully retracted, whereby the force reflecting device can be primed with this known position and orientation.

In one embodiment, the calibration means additionally constrains the retraction of the shaft from the bearing as the first end is drawn back form the bearing and the second end is drawn towards the bearing. Thus travel of the shaft may be limited by the contact of the calibration means upon the calibration stop. There may be provided additional shaft restraint means, which are preferably located on the second end side of the bearing, ie on the inside of the apparatus. The shaft restraint means may include an abutment surface which restricts the possible pitch and yaw angulation of the shaft at various degrees of insertion into the bearing. Preferably the abutment surface is conical, and which radiates out from the bearing on the inside of the apparatus. The shaft may be constrained to, for example, approximately + or -20 degrees in each of the pitch and yaw rotation directions by the contact of the calibration means with the inside conical abutment surface. Constraining of the range of motion of the shaft through the bearing, particularly the fixed location in space of a pivot point for the shaft, ensures that the force reflecting device needs to be able to measure position and apply forces in only 3 degrees of freedom. For convenience, if the force reflecting device resolves these degrees of freedom to Cartesian coordinates, the orientation of the shaft (and by inference, the orientation of the needle in the patient which the apparatus may be attempting to simulate) can be calculated using the vectorial difference between the current cartesian position of the force reflecting device (or rather the reference point on the device) and the cartesian position of the bearing.

Without constraining the shaft, the force reflecting device would need to be capable of rendering forces and measuring position in at least 5 degrees of freedom, in order to simulate a fixed needle entry point and torsional stiffness of a needle as it sits deep within the ligaments of a patient.

The second end of the shaft may be connected or connectable to a fluid conduit which may be associated with a loss of resistance (LOR) simulator, such as the LOR simulator described below. Preferably, the coupling includes a fluid passage connection means such as a nipple for making a fluid connection from the shaft to the LOR simulator, capable of forming a fluid-tight passage from the LOR device when connected to the first end of the shaft to the LOR simulator.

The bearing may be located in a housing. The housing may include a skin plate mounted on a substantially vertical plane which is adapted to represent the skin of a patient surrounding the simulated injection site. Near the center of the skin plate there may be an opening and the bearing may be mounted concentrically within the opening.

The force reflecting device senses the 3 dimensional position of its wrist (or reference point) and sends this data back to the control means. The control means will generally be a computer. Preferably the data is sent to the computer at high frequency (typically 1 kHz or greater). From this data, the software computes the angular orientation of the shaft and the depth to which the shaft has protruded through the bearing, which may be past a nominal point near the surface of the skin plate.

The software then uses this calculated data to represent what would be the needle depth and orientation of the simulated epidural injection procedure and preferably performs a ray trace of a simulated 3 dimensional anatomical model representing the anatomy of the patient. The ray may be traced in the same direction as the instantaneous needle direction. The intersection of this ray with the surface topology of the 3D anatomical model is compared to the needle depth data and a force vector is calculated. This force vector is a 3D vector representing the magnitude and the direction of a force to be reflected by the force reflecting device at this instant, in order for the user to experience a force on the needle which is consistent with what the user would feel as a resistive force on the needle if she was performing the procedure on a live patient of the same anatomy and the needle was at exactly the same depth, insertion point and orientation.

As the shaft is pushed deeper through the bearing, the reflected forces rise and fall to simulate the resistance of each of the layers of tissue and ligaments encountered during a "real" epidural injection procedure.

In one embodiment of the invention there is provided a loss of resistance simulator connectable to the shaft where fluid pressure in the fluid conduit is passively controlled by a valve, such as a solenoid or pinch valve, that blocks or impedes fluid flow in the fluid passage when closed, and allows fluid flow when open. In this embodiment of the LOR simulator, the valve is kept shut throughout the needle insertion portion of the epidural procedure, until the epidural space is reached, ie while the shaft is being inserted into the bearing to the modelled position. The control means then commands the valve to open, thus allowing fluid to flow from a LOR device connected to the first end of the shaft, through the shaft, through the fluid conduit and into the atmosphere. This embodiment can be used to simulate the saline LOR technique by priming the mechanism with water or saline, or to simulate the air technique by priming the mechanism with air. As air is compressible ,but liquid such as saline or water is not compressible, the pressures and changes of pressures experienced using the two techniques will be different. The main disadvantage of this embodiment for simulating the saline technique is that it introduces liquid in an unsealed manner, to the device operation. Since, ideally, the LOR device should be attached to the first end of the shaft part way through the procedure (as is practiced in the real procedure), the liquid path is not closed and sealed. This introduces the possibility that liquid may spill out of the system and cause a potential electrical, corrosion or safety hazard.

Thus according to another aspect of the present invention there is provided a loss of resistance simulation system including: an air passage connectable directly or indirectly to a LOR device; pressure sensing means for sensing air pressure in said air passage; air pressure varying means for increasing or decreasing the air pressure in said air passage in response to changes in air pressure in said passage.

Significantly, it is the use of a gas as a force transmission medium for the simulation of a liquid containing system and the control method used to infer the plunger displacement Ds and apply a force F to the plunger in response to this displacement. This arrangement can use a standard, unadapted LOR device (ie: without plunger position feedback) and uses the same apparatus for simulating both the air and saline LOR techniques without the use of messy fluids. Preferably the air passage is directly or indirectly connectable to a loss of resistance device. Such connection may be via a shaft as described above, preferably with a luer type fitting.

The air passage may be a flexible conduit such as a catheter which preferably has sufficiently inextensible sidewalls to resist being expanded or inflated upon increased air pressure therein. In one embodiment one end of the air passage is connected to the coupling decribed above.

Preferably, the means for increasing and decreasing the pressure in the air passage includes a ram, for example a piston in a cylinder, which may be driven in directions to either increase or decrease the pressure in the air passage. The ram may be located in a chamber with a volume such that retraction of the ram from the chamber increases the volume of the chamber and thus proportionately decreases the pressure of air in the chamber, or insertion of the ram in the chamber decreases the volume in the chamber such that the pressure proportionately increases. The chamber will be connected with the air passage so that the changes in pressure in the chamber are communicated to the air passage. The ram may be actuated by, for example, a motor, a solenoid, or by other means. Other means for increasing and decreasing the pressure in the air passage other than use of a ram or piston may be used.

In this embodiment of the LOR simulation system, there may be two distinct modes of operation, air simulation mode and saline simulation mode. In air simulation mode, the ram may be positioned stationary at minimum volume Vm in the chamber, until the second end of the shaft is advanced to a position which equates to when the epidural space is reached, at which time the ram partially retracts quickly from the chamber to increase the volume Vm in the chamber, thus decreasing the pressure in the air passage and consequently, allowing the pressure applied by the user to the device plunger to cause the device plunger to move inward, thus simulating the loss of resistance. The less preferred alternative to using an air pressure varying means which can increase and decrease the pressure in the air passage is simply to use a valve, such as a solenoid valve, which can only decrease the pressure in the air passage by venting air from the air passage.

A significant advantage in using the air pressure varying means is found in the saline simulation mode of the LOR simulation system. In this mode, the system does not actually contain any liquid. The main characteristic of using saline as a medium for the LOR technique in a real procedure is that saline is substantially less compressable than air. This is manifested to the user as a much higher stiffness to pressure applied by the user to the device plunger. In practice, the user usually leaves a bubble of air in the device, thus providing a small amount of compressibility. Experiments suggest that the stiffness of a saline primed device is at least 50 times higher than that of an air primed device. In this embodiment, as the user applies pressure to the device plunger, the pressure in the air passage rises. A sensor for detecting the pressure in the air passage detects this rise in pressure and signals to the control means (and its embedded software) which, by utilizing this pressure value and the known volume of the chamber Vm, infers a particular quantifyable movement in the device plunger. In response, the air pressure varying means is commanded to move inward, thus decreasing Vm by a known amount and consequently further increasing the pressure in the air passage. This increase in pressure is felt by the user as greater stiffness in movement of the plunger. This control loop may be repeated at very high frequency, typically 1 kHz. With sufficiently high stiffness, the user will perceive the response of the system to pressure applied to the device plunger, to be similar to what she would feel when using saline in a real procedure.

In the saline simulation mode, loss of resistance is simulated by rapid movement of the air pressure varying means to reduce the air pressure in the air passage, such as withdrawing the ram in the chamber, thus decreasing the volume Vm in the chamber and dropping the pressure quickly in a similar way to the air simulation mode.

The air ram embodiment has other significant advantages over the valve embodiment of the LOR simulation system. The embedded software running in the control means may continuously monitor the air pressure and consequently, can continuously infer the position of the device plunger within the barrel of the LOR device and the force being applied by the user to the device plunger. This information can be logged and analyzed to assess the correctness of the user's LOR device handling technique. Typical metrics measured might include; too much force applied, too little force applied, uneven force applied, too much oscillation in applied force, not enough oscillation in applied force. Furthermore, the actual responsiveness of the control software can be adjusted to simulate different physiological effects. For example, a slow leak in pressure above a threshold or a partial loss of resistance, whereby only a small amount of pressure is lost before the system returns to it's normal closed response, both simulate abnormalities in anatomy and physiology. Simulating, measuring and assessing the user's responses to abnormal cases is highly advantageous for a medical procedure simulator such as this invention, since this helps ensure the clinician is practiced in a wider range of cases she will encounter in real practice.

Good epidural injection technique requires that the penetration force is produced substantially by applying force to the needle luer rather than the LOR device plunger, which should be pressurized independently. This minimizes the risk that a sudden LOR in the device or a posterial movement by the patient will translate into uncontrolled needle penetration. The air ram embodiment of the LOR simulation system can measure this by combining the penetration force as applied by the force reflecting device at each point of needle penetration with the pressure applied to the needle plunger, as measured by the control means to calculate the penetration force applied to the needle luer since the applied penetration force will be equal to the force applied by the user to the needle luer plus the force applied to the LOR device plunger, which can be deduced from the pressure and the volume Vm in the chamber. Thus, the distribution of force applied by the user between needle luer and LOR device plunger can be continuously measured, monitored and assessed.

Another advantage of the air ram embodiment is that because the position of the plunger can be continuously calculated, this information can be used by the system software to animate a 3D graphical representation of the device and plunger on screen, in time with the user's oscillations on the plunger, thus increasing the fidelity of the simulation session.

The ability to provide a portable simulation system is important to allow the system to be used where it is most needed at the hospital or elsewhere where training may occur. The invention may include a mechanism for securing the moving parts of the system during transit and which in one embodiment may also double as an optimal in-use positioning gauge and securing mechanism to stop the apparatus from moving during use. The apparatus may include a housing in which the shaft, bearing, force reflecting device, LOR simulating system and other componentry may be located. The housing may include a travel flap which is moveable between closed position, where it covers the first end of the shaft and protects it from damage, and an open position. When the apparatus is in use, the travel flap may be lowered from a substantially vertical closed position to an open horizontal position and which may rest on the benchtop or other surface on which the apparatus is positioned. The travel flap preferably includes a bench lock adapted to rest over the lip of the bench and therefore provide resistance to any backward force that is applied to the apparatus during normal use. Preferably the bench lock is a tab or flap that may fall down from the travel flap under gravity when the travel flap is lowered to its opened position. The size of the travel flap and the location of the bench lock are preferably designed to set the apparatus back from the edge of the bench top a distance suitable for optimal use of the apparatus and also to provide protection for the shaft and connected device from accidentally being knocked by people walking past the apparatus.

When the apparatus is being prepared for transit, the shaft is pushed as far into the bearing as possible and the travel flap is closed and secured by a latch. The travel flap may be associated with a travel locking means which is adapted to securely retain the free end or wrist of the sensitive force reflecting device. As the travel flap is closed, it may actuate a mechanism to cause the travel means to securely engage with a portion of the shaft or features associated with the shaft such as the coupling to lock the shaft, force reflecting device and bearing securely in place. This may be achieved by causing the coupling to be held against the shaft restraint means. Similarly, when the travel flap is moved to an open position the travel locking means may disengage the shaft, force reflecting device and/or coupling. Locking of the shaft may also be achieved by positioning a locking plate over the shaft between the travel flap end and the body of the device.

When the apparatus is first set up for use in a training session, the force reflecting device must be calibrated. Calibration may be performed by the user retracting the shaft fully out so that the first end is retracted as far away as possible from the bearing and the second end is drawn as close to the bearing as possible. The calibration means may centre the shaft to a perpendicular orientation by the engagement of the calibration means to a mating surface behind the bearing on the inside of the apparatus. When the shaft is in position, the user may press a button on screen and the software configures the force reflecting device to identify it's current position as this preconfigured, known position.

During the insertion of the shaft through the bearing as simulating the insertion of a virtual epidural needle, a 3D anatomical model may be displayed on a visual display unit (VDU) and the shaft may be represented as a needle animated to inject into the 3D model, reflecting the actual position of the shaft in the apparatus. The anatomy of the 3D model may be displayed in a variety of ways including; with opaque skin so the virtual needle disappears beneath the surface of the skin; with translucent skin and tissue layers so that the progression of the virtual needle through each layer can be seen; and additionally shown in cross section.

In cross-sectional view, the virtual needle may be shown penetrating a cross sectional view of the tissue layers. In a preferred aspect of the invention the cross sectional viewing planes are adjusted axial and sagittal planes. Since the user may pitch or yaw the shaft and hence the virtual needle during insertion, if the cross-sectional views were purely axial or sagittal views, the needle would not be visible in the cross sectional view since it would generally not lie exactly within the plane. In the present invention, the axial and sagittal views may be adjusted to track pitch and yaw so that the needle is always fully visible within both views. The adjusted sagittal plane is the sagittal plane, pivoted by "yaw" degrees about the vertical axis running through the skin insertion point. The adjusted axial view is the axial plane, pivoted by a number of degrees of pitch about the horizontal axis running through the notional skin insertion point. Pitch and yaw are determined from the orientation of the shaft as detected by the force reflecting device.

By rotating the 3D anatomical models 90 degrees, the simulator can be used to simulate the epidural injection procedure on a patient that is lying down, rather than the more common sitting position. This patient orientation presents a higher level of difficulty for the clinician because the needle must be angulated left and right to pitch it vertically within the spinal column. Since the simulator provides this function entirely in software, no mechanical changes are required and the apparatus previously described and the apparatus can be used for the lying position procedure and the sitting position procedure without modification or adjustment.

Patient model variation is an important aspect of a medical simulator. This allows the clinician to train on a wide variety of cases for increased proficiency. The present invention may accommodate patient model variation by including several different 3D anatomical models with different sizes of critical anatomical features (eg: thicker fat layer), narrower epidural space etc. Further patient variation may be obtained by scaling aspects of the haptic response curves (eg: skin penetration force) depending on which model is selected. Also, specific patient histories can be programmed for specific models and consequently modify the complications that may appear in the simulation and alter the assessment algorithms to account for those different histories.

In yet another aspect of the present invention there is provided a method of simulating a medical or surgical procedure including the steps of: (a) receiving from a user inputs corresponding to dexterous and non- dexterous steps required to perform the procedure being simulated; (b) providing the user with haptic feedback corresponding to the dextrous steps of the procedure being simulated; and

(c) providing the user with non-haptic feedback indicative of the progress of the simulated procedure.

In another aspect of the present invention there is provided a computer software product for use with a simulation device, the computer software product configured to perform steps in a method of simulating a medical or surgical procedure, the method including: (a) receiving inputs corresponding to non-dexterous steps selected by a user performing the procedure being simulated;

(b) maintaining a log of received inputs; and

(c) providing the user with feedback on their performance of the simulated procedure, including selection of non-dexterous steps involved in the procedure.

The computer software product according to the invention may be configured to simulate patients having a range of different anatomical characteristics such as skin type, age, size, weight, fat content and pre-existing conditions. It may also include analysis algorithms for tracking and assessing steps performed in the procedure being simulated and may further include a force scaling module for scaling software anatomical models of different virtual patients and virtual tools and combinations thereof.

In another aspect of the invention there is provided an interactive simulation system for simulating one or more medical or surgical procedures, the simulation system configured to provide an interactive training environment for learning the complete procedure including dexterous and non-dexterous steps, the system including an interface with a mechanical device for performing one or more dexterous steps, and visual display device presenting a user with options for performing non-dexterous steps.

Many people consider the dexterous step of inserting the needle tip into the tissue of the spine and locating the epidural space to be the most complex and difficult to learn aspect of an epidural needle insertion procedure. Methods exist for training clinicians in performing this aspect of the procedure and some of these methods have been described above. However, in addition to these specific dextrous steps, other steps, which may include a dextrous component such as palpation of the spine, preparation of an injection site, etc., must also be performed to satisfactorily complete the procedure. These steps are classified herein as "non-dextrous" steps even though they may involve a dextrous aspect.

Non-dextrous steps involved in successful completion of an epidural needle insertion procedure include, but are not limited to: communicating with the patient, a carer and/or other clinicians, sterilising the needle insertion site, administering local anaesthetic prior to inserting the needle, administering the correct analgesic dose, testing for adequate analgesia, appropriately discarding biologically contaminated disposables and completing the necessary documentation after the needle has been inserted. Follow up with the patient after the insertion procedure may also be important particularly if there have been complications during the needle insertion.

However, due to the complexity of the needle insertion aspect of the procedure, clinicians sometimes forget to attend adequately to the other "non-dexterous" steps involved. This can lead to various complications and can result in patient discomfort, infection and confusion resulting from incomplete or inaccurate patient records.

To minimise the risk of these occurrences, an aspect of the present invention provides an interactive simulation system providing a fully integrated training and simulation environment for learning a full medical or surgical procedure such as an Epidural Labour Analgesia (ELA) procedure. The system has the ability to improve and preferably test a user's knowledge of all steps involved in the procedure including dexterous and non-dexterous steps, and the order in which they must be performed.

Thus, the inventive system is a full-procedure simulator configured to provide, in its preferred embodiment, interactive learning content describing the full procedure as well as demonstration, practice, testing and assessment platforms. This system helps users learn and perfect technical aspects of the procedure as well as less technical aspects such as patient communication and documentation which are rarely formally "learnt". The system also helps the user understand how s/he is progressing in their knowledge and skill of the procedure.

Preferably, the interactive simulation system has four modules, generally described as "WATCH", "LEARN", "PRACTICE" and "TEST" although it is to be understood that variations upon these modules may be made to incorporate greater complexity or simplicity, depending on the procedure being simulated.

The "WATCH" module provides video footage of an actual procedure from start to finish to provide users an indication of the steps involved. In most cases, the video footage is accompanied by a narrative which gives audible cues and learning content along the way. Preferably, the "WATCH" module is configured to present a range of different video clips representing some of the variations which may occur from one procedure to the next. For example, for an ELA procedure, the "WATCH" module may present footage of a procedure with a patient in a sitting position or lying down, or may show a paediatric or elderly patient as well as for example, showing the clinician obtaining informed consent from the patient for the procedure to commence.

The "LEARN" module provides the user with information for learning about the procedure and how to perform it. Preferably, the "LEARN" module includes information about both the dexterous and non-dexterous steps required to successfully complete the procedure. The "LEARN" module may be embodied in a suite of interactive computer-based tutorials, or in a single tutorial to be completed by the user. Preferably, the "LEARN" module guides the user sequentially through each step in the procedure being learnt.

The "PRACTICE" module enables the user to practice all the steps required to successfully complete the procedure, including both dextrous (i.e. technical) and non-dexterous steps. As part of this module, the user is presented with one or more menus of possible steps or actions which may be selected during procedure simulation. The dexterous (i.e. technical) steps include, for an ELA procedure, aspects such as "Insert Epidural Needle" and "Attach LOR device". Non-dexterous steps include "Check patient history", "Monitor Oxygen Saturation", and "Scrub" to name a few. When completing this module, the user selects items from the one or more menus in the order s/he feels they should be performed and at the appropriate stages of the procedure.

It should be noted, that some actions could be considered dexterous steps or non-dexterous steps depending on the fidelity of the simulation system and the manual aspects of the procedure that are important to the learning and assessment of the procedure. For example, the step "Scrub" would probably be considered a non-dexterous step for ELA, since it assumed to be a previously acquired skill of the clinician, however, for a basic surgical skills training full procedure simulator, "Scrub" could be considered a dexterous step if the various manual skills involved in good scrubbing technique are being taught and assessed using the simulator.

At the stage of the procedure where manual dexterous skill needs to be practiced (e.g. "Insert Epidural Needle") a 3D model of a patient is presented to the user on a visual display unit and the user performs the needle insertion process using a needle insertion station (NIS) which is enabled with a haptic feedback mechanism such as the one described above. Upon finishing the complete procedure (i.e. dexterous and non-dexterous steps) the user will have a better understanding of both the dexterous and non-dexterous skills required to successfully perform the procedure.

The "TEST" module incorporates the features of the "PRACTICE" module with the additional features of being able to track and assess the steps performed by the user. That is, as the simulation is being completed by the user who selects steps to complete along the way, the steps and the order in which they have been selected are logged. In some embodiments, it may be desirable that the "PRACTICE" module also log and track steps performed. At the conclusion of the simulation when the user considers the procedure to be complete, the system performs data analysis and provides a report on how well the user performed. In the "TEST" module this may also include a grading or score.

The report may include information such as the steps selected by the user which were correct, steps which were performed out of order and steps which were omitted. Preferably, the report also provides quantitative measures of the user's skill on the dexterous components of the procedure.

In a preferred embodiment, the "PRACTICE" and "TEST" modules are embodied in a computer software product for use with a simulation device which receives inputs corresponding to non-dexterous steps selected by the user in performing the procedure. The software product is configured in such a way that it helps trainee clinicians learn the entire procedure and not just the steps which require finely tuned dexterous skills. It also provides a testing platform for assessing how well a clinician has performed the simulated procedure and enable clinicians to improve their skills in a low-risk environment. The software also maintains a log of the received inputs and at completion of the simulation, provides the user with feedback on their performance of the simulated procedure.

The simulator does not just test the user's skill at inserting the epidural needle, though this is a very important skill to test. The simulator also provides an environment for the user to practice and test herself on all aspects of the procedure from patient communication, through asepsis, technical aspects, documentation etc. The full procedure simulator (FPS) comprises software and a GUI that includes lists of actions that can be performed by the user during the procedure. Each action is grouped under icons that relate to specific domains of action (eg: Communicate, Needle and Catheter, Position Patient, Drugs etc.). During FPS practice, the user must select from the menus (or palette) each action she would perform, and select or enter the value of any parameters required for that action (eg: drug dosage).

The simulator software will keep track of every action the user performed and the order in which they are performed. Some actions will be acted upon immediately by the simulator software, to provide guidance and feedback to the user as she performs the simulated procedure (eg: simulate "ouch" if the epidural needle is advanced through the skin without a local anesthetic having been applied beforehand). At the end of the simulated procedure, the simulator software scans through a log of every action taken by the user during the procedure and a written report is generated, detailing how well the user performed with respect to nominally well performed procedures as determined by experts in the epidural procedure.

Metrics measured may include, but not be limited to; essential steps omitted, incorrect steps performed, incorrect settings within a step, dangerous combinations of steps, steps performed out of order, management of complications encountered during the procedure, instrument handling skills etc

It will now be convenient to describe the invention with reference to a preferred embodiment illustrated in the accompanying drawings. It is to be understood that the drawings and following description relate to a preferred embodiment only and are not intended to limit the scope of the invention. In the description which follows, the procedure being simulated is the ELA procedure. However the procedure may be any medical or surgical procedure in which non- dexterous skills (as well as dextrous skills) are required to successfully complete the procedure. Thus it is to be understood that the principles of the simulation system and software aspects of the present invention are applicable to teaching, learning and simulation of a range of different procedures and the present invention is not to be limited to the specific examples or procedures described herein.

Figure 1 is a front isometric view of a haptic simulation apparatus of the present invention with a front flap shown in an open position.

Figure 2 is a front isometric view of the shaft insertion section of the apparatus of Figure 1 . Figure 3 is a rear isometric view of the haptic simulation apparatus of Figure 1 with the housing removed.

Figure 4 is a rear isometric view of the haptic simulation apparatus of claim 1 not depicting selected componentry.

Figure 5 is a schematic diagram of an air ram arrangement used to simulate loss of resistance in the present invention.

Figure 6 illustrates an example of a graphical user interface suitable for use with embodiments of the present invention.

None of Figures 1 to 5 depict a computer or computer monitor which would be associated with the simulation apparatus.

Figure 7 illustrates an example list of options associated with a step selected by the user.

Figure 8 illustrates a virtual patient using a view presenting translucent skin and tissue layers.

In Figure 1 , haptic simulation apparatus 1 includes a housing 3, a base plate 5, a carry handle 7 and a travel flap 9. Travel flap 9 is hinged to base plate 5 and is moveable between an open position as shown in Figure 1 and a closed position when apparatus 1 is to be transported or is not in use. Electrical connection panel 1 1 includes data jacks 13 and 15 for connection to a computer or other device, and power jack 14 for connection to a power source. Travel flap 9 includes a bench lock 17 which has an abutment face 19. When apparatus 1 is placed on a benchtop and travel flap 9 is opened, bench lock 17 which is hinged to travel flap 9 may drop down to expose an abutment face 19. Apparatus 1 may then be moved until abutment face 19 comes into contact with an edge of the bench top to prevent apparatus 1 from inadvertently being pushed across the benchtop when in use. Front face 21 of apparatus 1 , which can represent the lumbar region of a notional patient includes a skin plate 23, which may be made from a resilient material which may resemble human skin. Skin plate 23 may provide a person using apparatus 1 with a surface on which to rest the user's non-dominant hand to stabilise against sudden forward motion.

Towards the centre of skin plate 23 there is an opening 25 which simulates an insertion point to a patient. First end 27 of shaft (not shown in this figure) includes a luer fitting 29 and luer wings 31 and 33 at the base 35 of luer fitting 29.

Turning to Figure 2, shaft 37 passes through opening 25 and into gimbal bearing 39. Opening 25 is large enough to allow shaft 37 to be pivoted about gimbal bearing 39 in a range of pitch 41 and yaw 43 motions. Shaft 37 has an elongate axis 45 and shaft 37 may also be moved into apparatus 1 or out from apparatus 1 along axis 45 through gimbal bearing 39. A loss of resistance (LOR) device 47 having a device body 49, a plunger 51 inserted into device body 49 and a luer fitting 53 which is insertable into luer fitting 29 to form a fluid tight seal. The LOR device 47 is attachable and detachable by the user during normal operation.

Latch 53 may be engaged by travel flap 9 when the travel flap 9 is in a closed position.

Luer wings 31 and 33 will abut region 55 surrounding opening 25 when shaft 37 is inserted to a maximum extent into gimbal bearing 39. Thus, luer wings 31 and 33 against region 55 provide a stop to restrict the extent to which shaft 37 can be inserted into apparatus 1 along axis 45.

In Figure 3, second end 57 of shaft 37 is shown associated with a calibration ring 59. Shaft 37, which is hollow, has its second end 57 associated with a coupling 61 and coupling 61 is connected to wrist 63 of force reflecting device 65. The force reflecting device 65 shown in Figure 3 is a phantom® desktop™ haptic device manufactured by SensAble Technologies, Inc., although other haptic devices of different geometric configurations may equally be used. Force reflecting device 65 has, in addition to other rotatable joints, a waist joint 67 rotatable relative to base 5 in a substantially vertical axis. As a preferred feature of the present invention, movement of shaft 37 along axis 45 causes force reflecting device 65 to rotate predominantly about waist joint 67. Because the greatest force likely to be applied by a user to shaft 37 is along axis 45, it is preferable that the force reflecting device is oriented relative to such axis so that the device's greatest force reflecting capacity is utilized. Force reflecting device 65 is capable of exterting its maximum exertable force against rotation of the device about waist joint 67. In this way, a force reflecting device with a lower maximum extertable force may be utilized than if movement of the shaft were to move the force reflecting device in another range of motions.

Coupling 61 includes a fitting (not shown) on which is connected an air pipe 69 in communication with device 47. End 71 of air pipe 69 is connected to a cylinder 73 of air ram 75. Although not shown, a t-junction between end 71 and cylinder 73 would normally be provided, the third arm of the t-junction leading to a pressure transducer which is electrically connected to electronic circuitry. Air ram 75 includes a motor 77 which drives a piston 79 in cylinder 73 along guide 81 . Driving piston 79 into cylinder 73 toward cylinder end 83 will increase the air pressure in air pipe 69, and that air pressure will be transmitted along air pipe 69 and shaft 37 to be felt at plunger 51 . When motor 77 withdraws piston 79 away from cylinder end 83 this will decrease the air pressure in air pipe 69.

Latch 85 has an arm 87 which rotates about pivot 89 between an unlatched position, as shown in Figures 3 and 4 when the apparatus 1 has travel flap 9 in an open position. When travel flap 9 is moved to a closed position when the apparatus 1 is no longer in use and/or is to be transported, actuating means (not shown) associated with travel flap 9 causes latch 85 to rotate about pivot 89 so that arm 87 engages and holds coupling 61 against gimbal angle restrictor 91 , thus securing the force reflecting device 65. Return spring (not shown) biases latch 85 to closed position when the travel flap 9 is closed. Alternative locking mechanisms may equally be employed.

In Figure 4, gimbal angle restrictor 91 is shown having a frusto conical surface 93 which radiates outwardly away from gimbal bearing 39. Adjacent gimbal bearing 39 is calibration face plate 95 which is a substantially annular surface against which calibration surface 97 of calibration ring 59 may abut when shaft 37 is withdrawn from gimbal bearing 39 to a maximum extent. Calibration ring 59 includes annular restrictor surface 99, part of which will abut on part of frusto conical surface 93 if the pitch or yaw of shaft 37 relative to axis 45 reaches a predetermined limit. Preferably surface 93 is contacted by restrictor surface 99 at an angle of about 20° deviation from axis 45. In other words, frusto conical surface prevents needle 37 from being angled to a greater extent than about 20° from a normal axis.

In use with travel flap 9 opened and abutment face 19 of bench lock 17 abutting the front of a desktop, and with appropriate electrical and data connections made to a power source and to a computer, with appropriate software running, a user will first withdraw shaft 37 from gimbal bearing 39 by grasping luer fitting 29 or luer wing 31 or 33 until calibration surface 97 of calibration ring 59 comes into contact with calibration face plate 95. When calibration face plate 95 and calibration surface 97 abut properly, shaft 37 should be oriented along normal axis 45. In this position, the user will trigger a calibration step to be performed by the computer, whereby the orientation of the components of force reflecting device 65, and in particular, the position of wrist 63 is noted electronically. Alternatively, it will be appreciated that electronic means, such as limit switches or proximity sensors, for detecting this calibration position could replace this manual user step of acknowledging the calibration position to provide an automatic calibration mechanism.

In Figure 5, device 102 includes plunger 103 which is actuated by user 104 and barrel 105. The volume Vs represents the air volume in device 102. Passage 107 represents the hollow shaft and air pipe depicted in the previous figures. Air ram 109 includes piston 1 1 1 which is driven by motor 1 13. Volume Vm represents the volume of air in air ram 109.

T-junction 1 15 has branch 1 17 to static chamber 1 19 and is associated with a pressure transducer P. Motor 1 13 is connected to piston 1 1 1 by a lead screw (or ball screw) 1 12 and lead nut (or ball nut) 1 14. Rotary motion of the motor is converted to linear motion of the piston 1 1 1 which results in increasing or decreasing of Vm under programmatic control of the controlling electronics / software. The position of the piston Dm within the air ram 109 is determined by either measuring the position of the motor using an optical encoder 1 16 connected to the motor shaft or by interrogating the commanded position of the controlling electronic circuit.

Since the position of the piston 1 1 1 is known, Vm is known. If the starting volume of the device 102 is known Vs(O) at the beginning of the LOR procedure, then using the basic thermodynamic equation PV = nRT, the volume Vs can be calculated for any detected pressure P and known volume Vm provided that the temperature T does not appreciably change between the calibration of the system and the measurement of P.

Vs(O) is calibrated once at the beginning of each LOR procedure, by asking the user to connect the device 102 to the needle luer fitting 29 with the plunger 103 prepositioned to a point midway along the barrel 105 of the device 102.

Given then, that the volume Vs of the device 102 is continually calculated, since the geometry of the barrel 105 of the device 102 is known and essentially cylindrical, Vs is proportional to the displacement Ds of the plunger 103 within the barrel 105.

The control software therefore calculates Ds continuously or at high frequency, based on the variable elements Dm, and P.

A force can be applied to the plunger 103 to resist forward motion by the user by moving the motor 1 13 forward, thereby decreasing Dm and consequently Vm, which results in a known rise in pressure P and consequently, a known increase in force F applied to the plunger 103 by the air pressure in the device 102. Knowing Ds, a spring damper model can be applied to the control software such that the force F which results upon the plunger 103 is generally proportional to the displacement of the plunger 103 and has a high spring stiffness constant, thus simulating the stiffness of a largely incompressible fluid, such as is used when performing the saline LOR technique (whereby the barrel 105 is mostly filled with saline and a small amount of air). In addition, a damping component can be included in the control software's spring damper model that adjusts the applied force F in proportion to and in the opposite direction to the velocity of the plunger 103, thus damping out oscillations that may otherwise be induced by the spring component of the model.

When the shaft has been advanced in the simulator to a location which corresponds to an epidural space and the loss of resistance cue is applicable, a controller may activate motor 1 13 to retract piston 1 1 1 from chamber 1 10 so that the air pressure in air ram 109 decreases as Vm increases. This reduction in pressure should be felt by user 104 through plunger 103 of device 102 as a sudden movement of the plunger 103 into the device barrel 105, thus simulating the loss of resistance experienced in the saline LOR technique.

Referring to Figure 6, there is shown a graphical user interface (GUI) 201 suitable for use with a device for simulating the ELA procedure. The GUI is preferably embodied in software, and it is to be understood that various back- end software modules may be used to simulate a range of different medical or surgical procedures. GUI 201 is made visible on a visual display unit such as a computer screen and presents to the user various icons and indicators.

Buttons 207a,b,c,d are selectable by the user to activate either the "WATCH", "LEARN", "PRACTICE" or" TEST" modules as described above. Icons 203a,b,c,d,e,f,g,h correspond to different skill areas in which dextrous and non- dextrous steps are required to successfully complete the procedure being simulated. Preferably, the icons include a graphic component which is indicative of the skill area to which the icon relates, although any other selectable indicator may be used.

In Figure 6, icon 203a represents "COMMUNICATION", icon 203b represents OBTAIN INFORMATION", icon 203c represents "SAFETY CHECKS", icon 203d represents "MAINTAIN ASEPSIS", icon 203e represents "NEEDLE & CATHETER", icon 203f represents "POSITION PATIENT", icon 203g represents "DRUGS", icon 203h represents "DOCUMENTATION" and icon 203i represents "STOP PROCEDURE". The icons may be selected by the user operating a mouse or other selection device to "click" on the icon or by using a touch screen in which the icon can be selected directly with the user's finger, thumb or knuckle. Selection of one of the icons 203a-h opens drop-down list of the possible steps which may be performed in a particular skill area. Accordingly, each of the skill areas represented by icons 203a-h has a related drop-down or expanding list (205a,b,c,d,e,f,g,h) not shown.

During use of the simulator and system only one icon 203 is selected at a time hence only one list 205 is presented at any one time. Table 1 indicates, for an ELA, examples for skill areas represented by icons 203a-h and possible steps which may be presented in related lists 205a-h.

The lists may be arranged in such a way that the order in which the steps must be performed is not immediately clear to the user. Lists may also include inappropriate steps or actions which will be checked for in assessment. Thus, the user will need to apply their knowledge of the procedure to ensure that the required non-dexterous steps are performed, along with the dexterous steps, and that the steps are performed in order.

Whilst it is not shown in Table 1 , lists 205a-h may be structured in a cascaded manner, wherein one or more steps in a list have one or more related steps or prompts. For example, the step "select needle gauge" may have a related list in which the clinician is presented with a range of needle sizes of which one must be selected. This aspect of the invention provides a realistic simulation environment since in reality, not all patients have the same presentation, medical history or tissue characteristics so a single needle gauge will not be suitable for all cases. In this regard it is to be understood that the simulator may also be configured to simulate medical or surgical procedures for patients having different characteristics such as age, weight, size, fat layers, pre-existing conditions or taking into consideration individual medical histories.

Table 1

Returning to the selection of steps in the simulated procedure, selection of a needle size suitable for the virtual patient provides a more immersive and realistic simulation.

Another step which may have cascaded or related steps or prompts is "clarify midwife will perform monitoring" which appears in list 205c. In the embodiment illustrated in Figure 6, selection of this step reveals a list of prompts as presented at 221 in Figure 7. The training clinician selects various physiological parameters which s/he desires to be monitored while the epidural is in use. As is the case with the other steps selected during the simulation, selection of parameters in Figure 7 is logged and tracked by the simulation system for subsequent use in assessment and reporting. In a real needle insertion situation, the patient may be sitting or lying down, depending on the circumstances in which the procedure is being performed, and the condition of the patient. Again, simulation of this aspect of the procedure provides a more realistic simulation.

Preferably, the inventive simulator has the ability to simulate a needle injection procedure for patients in both the sitting and lying positions without the need to adjust the mechanical aspects of the simulation system. Accordingly, the visual representation of the virtual patient is augmented to show the patient in the sitting or lying position, and control software for the haptic reverses the pitch and yaw aspects of the haptic device if the patient is lying down. This provides an advantage over prior art systems which either do not facilitate simulation in both the sitting and lying positions, or which require adjustment to the mechanical components of the simulator to "reposition" the patient.

Figure 6 also shows viewing panel 209 in which one or more views of the virtual patient are presented. In a preferred embodiment, the GUI software is configured to provide a range of different three dimensional anatomical views of the virtual patient. In one embodiment, the visual display provides a view of the virtual patient similar to what the user would see in a real procedure. In another view, the user is presented with a view in which the 3D virtual patient has translucent skin, ligaments, tissues and other anatomical features of the spinal column, and the user is able to see the virtual needle penetrating the various layers in the region in which the needle is being inserted. An example of a view showing translucent skin and tissue layers is presented in Figure 8. This is advantageous as it enables the user to connect the haptic cues indicating the amount of force to be applied with the anatomical structure of the patient and the tissue layer being penetrated.

In another view, or in combination with the translucent view, the user may be presented with cross sectional anatomical views of the patient. The sections may be in the sagittal or axial planes. Preferably, the GUI software is configured to adjust the plane of the sectional views in real time to track the angle of attack of the needle. This enables the needle to remain in view throughout the simulation. The viewing panel 209 may present one view to the user, or may be divided into 3 panels in which 3 different views are presented to the user, i.e. 3D view of patient plus axial section view plus sagittal section view. This is advantageous because it enables the user to connect simultaneously the haptic cues generated by the mechanical simulator with the virtual patient's surface anatomy, and anatomical tissue layers.

Future patent applications may be filed in Australia or overseas on the basis of or claiming priority from the present application. It is to be understood that the following (provisional) claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the (provisional) claims at a later date so as to further define or re-define the invention or inventions.

Claims

The claims defining the invention are as follows:

1 . A haptic simulation apparatus including a shaft having a longitudinal axis, the shaft being moveable through a range of motion and having first and second ends; a bearing between said first and second ends constraining said shaft in one or more ranges of motion; force reflecting device acting on said second end; control means for controlling the reflected force applied to said second end by said force reflecting device for locations and orientations of the shaft within the range of motion.

2. A haptic simulation apparatus according to claim 1 wherein said bearing constrains said shaft at a point at or about said bearing.

3. A haptic simulation apparatus according to claim 1 or 2 wherein said bearing is a gimbal slide bearing and said shaft is capable of moving about said bearing along its longitudinal axis and to pivot in two angular directions about a centre point of the bearing.

4. A haptic simulation apparatus according to any one of claims 1 to 3 having cooperable calibration members associated with said bearing and said second end of said shaft such that the location and orientation of said shaft can be determined when said members cooperate.

5. A haptic simulation apparatus according to claim 4 wherein said calibration members act together to constrain movement of said shaft in one or more degrees of freedom beyond a predetermined range.

6. A haptic simulation apparatus according to claim 4 or 5 wherein said calibration members cooperate when the second end of said shaft is proximate said bearing.

7. A haptic simulation apparatus according to any one of claims 1 to 6 wherein there is provided shaft restraint means for limiting the range of motion of said shaft in pitch and yaw.

8. A haptic simulation apparatus according to claim 7 wherein said shaft restraint means includes an abutment surface to limit the range of motion of said shaft.

9. A haptic simulation apparatus according to claim 8 wherein at least a portion of said abutment surface is substantially conical.

10. A haptic simulation apparatus according to any one of claims 7 to 9 wherein said shaft restraint means limits the range of motion of said shaft in pitch and yaw to + or - 20°.

1 1 . A haptic simulation apparatus according to any one of claims 1 to 10 wherein said simulation apparatus simulates a medical procedure.

12. A haptic simulation apparatus according to claim 1 1 wherein said medical procedure is an epidural anaesthesia.

13. A haptic simulation apparatus according to any one of claims 1 to 12 wherein said bearing is located in a housing at the surface of said apparatus.

14. A loss of resistance ("LOR") simulation system including: a gas passage connectable directly or indirectly to a device having a plunger; pressure sensing means for sensing gas pressure in said gas passage; gas pressure varying means for increasing or decreasing the gas pressure in said gas passage in response to changes in gas pressure in said passage.

15. A LOR simulation system according to claim 14 wherein the gas is air.

16. A LOR simulation system according to claim 14 or 15 wherein the system can simulate LOR of a liquid filled system and a gas filled system.

17. A LOR simulation system according to any one of claims 14 to 16 wherein said gas pressure varying means includes means for varying the volume of gas in a chamber.

18. A LOR simulation system according to claim 17 wherein said gas pressure varying means includes a cylinder containing a volume of gas in communication with said gas passage, and a ram moveable in said cylinder increase or decrease the volume of gas in said cylinder to increase or decrease the pressure of said gas in said gas passage.

19. A LOR simulation system according to claim 18 wherein said ram is actuated by a solenoid or a motor.

20. A LOR simulation system according to any one of claims 14 to 19 wherein said gas pressure varying means may be controlled to increase said gas pressure in said gas passage in response to an increase in gas pressure by actuation of said device.

21 . A LOR simulation system according to any one of claims 14 to 20 including a pressure sensor in said gas passage, and control means responsive to said pressure sensor to control said means for varying the volume of gas in said chamber.

22. A LOR simulation system according to any one of claims 14 to 21 wherein said pressure sensor sends data to a processor to log pressure in said gas passage.

23. A LOR simulation system according to claim 22 wherein the position of said plunger in said device when connected to said gas passage can be calculated by said processor.

24. A LOR simulation system according to claim 22 or 23 wherein the force applied to said plunger when said device is connected to said gas passage can be calculated by said processor.

25. A haptic simulation apparatus according to claim 25 wherein said loss of resistance simulator is a LOR simulator according to any one of claims 14 to 24.

26. A method of simulating a medical or surgical procedure including the steps of: (a) receiving from a user inputs corresponding to dexterous and non- dexterous steps required to perform the procedure being simulated.

(b) providing the user with haptic feedback corresponding to the dextrous steps of the procedure being simulated; and

(c) providing the user with non-haptic feedback indicative of the progress of the simulated procedure.

27. A method of simulating a medical or surgical procedure according to claim 26 wherein the dextrous steps include insertion of an epidural needle.

28. A method of simulating a medical or surgical procedure according to claim 26 or claim 27 wherein the non-dextrous steps include one or more of communication, asepsis of medical/surgical site, administration of pain relief, patient comfort, documentation and post-procedure follow up.

29. A method of simulating a medical or surgical procedure according to any on of claims 26 to 28 wherein the non-haptic feedback includes one or more visual feedback and audible feedback.

30. A method of simulating a medical or surgical procedure according to claim 29 wherein the visual feedback includes a graphical representation of a virtual tool and a virtual patient on which the simulated procedure is being performed.

31 . A method of simulating a medical or surgical procedure according to claim 29 or claim 30 wherein visual feedback is provided at completion of the simulation and includes a report indicative of the success of the simulated procedure.

32. A method according to claim 26 wherein the haptic feedback is provided by a haptic simulation apparatus according to any one of claims 1 to 13 or claim 25.

33. A computer software product for use with a simulation device, the computer software product including rules for performing steps in a method of simulating a medical or surgical procedure, the method including: (a) receiving from a user performing the procedure being simulated inputs corresponding to non-dextrous steps of the procedure; (b) maintaining a log of received inputs; and

(c) providing the user with feedback on performance of the simulated procedure, including performance of non-dextrous steps involved in the procedure.

34. A computer software product according to claim 33 wherein the non- dextrous steps include one or more of communication, asepsis of medical/surgical site, administration of pain relief, documentation and postprocedure follow up.

35. A computer software product according to claim 33 or 34 wherein the method further includes receiving user inputs corresponding to dextrous steps performed during the procedure.

36. A computer software product according to any one of claims 33 to 35 wherein the log further maintains a record of an order in which the inputs are received from the user.

37. A computer software product according to any one of claims 33 to 36 wherein the method further includes the step of generating a report at completion of the simulated procedure, the report being indicative of the user's ability to perform the complete procedure, including non-dextrous steps.

38. A computer software product according to any one of claims 33 to 37 further including a learning module providing information pertaining to the procedure being simulated.

39. A computer software product according to any one of claims 33 to 38 further including a demonstration module configured to demonstrate to the user how to perform the procedure successfully.

40. A computer software product according to claim 39 wherein the demonstration module presents visual footage of a medical or surgical procedure to the user.

41 . A computer software product according to any one of claims 33 to 40 wherein said product presents an audible narrative of a medical or surgical procedure to the user.

42. A computer software product according to any one of claims 33 to 41 further including a testing module for testing a user's ability to complete the procedure successfully, including dextrous and non-dextrous steps.

43. A computer software product according to claim 42 wherein the testing module provides a grading of the user's ability to perform the procedure.

44. A computer software product according to any one of claims 33 to 43 configured to simulate patients having a range of different anatomical characteristics including one or more of skin type, age, weight, fat content and pre-existing medical conditions and medical history.

45. A computer software product according to any one of claims 33 to 44 further configured to present the user with a visual representation of a virtual patient and a virtual tool for performing the procedure, wherein the visual representation can be selected to present one or more of the following view types:

(a) opaque skin;

(b) translucent skin;

(c) axial cross section; and

(d) sagittal cross section.

46. A computer software product according to claim 45 wherein the axial and sagittal cross sectional views are adjusted in real time to track the virtual tool so that it remains in view during simulation of the procedure.

47. A computer software product according to any one of claims 33 to 46 further including analysis algorithms for tracking and assessing steps performed in the procedure being simulated.

48. A computer software product according to any one of claims 33 to 47 further including a force scaling module for scaling software anatomical models of different virtual patients and virtual tools and combinations thereof.

49. An interactive simulation system for simulating one or more medical or surgical procedures, the simulation system configured to provide an interactive training environment for learning the complete procedure including dexterous and non-dexterous steps, the system including an interface with a mechanical device for performing one or more dexterous steps, and visual display device presenting a user with options for performing non-dexterous steps.

50. A simulation system according to claim 49 configured to operate with the computer software product according to any one of claims 33 to 48.

51 . A computer software product according to claim 33 for use with a simulation device according to any one of claims 1 to 13.

52. A haptic simulation system substantially as hereinbefore described with reference to any one of the drawings.

53. A loss of resistance simulation system as hereinbefore described with reference to any one of the drawings.

54. A method substantially as hereinbefore described with reference to the example.

55. A computer software product substantially as hereinbefore described with reference to the example.