GB2369714A - An epidural simulator device. - Google Patents

Abstract

The device is based on a sheet of high-density polyethylene. The closed cell architecture of these materials makes them resistant to the injection of air and saline. The foam is used to simulate the interspinous ligaments of the lumbar spine. Foam of different characteristics may be heat laminated together. The foam (15cm*15cm*3.5cm) is held in a torso shaped frame. The frame can be fixed in the 'sitting' and 'lateral' position by an adjustable clamp. A drawing of the bony anatomy of the pelvis and lumbar spine is applied to the frame. The foam is sandwiched between the frame and 4mm sheet of Perspex with a midline 4cm wide slot. An epidural needle is introduced into the foam through holes cut in the frame corresponding to the S1/L5 to L1/L2 lumbar interspace.

Description

Ail epidural simulator device for training practitioners in the anaesthetic technique of epidural injection Epidural anaesthesia is an anaesthetic technique where a specialised needle (Tuohy needle) is introduced through the interspinous ligaments of a patient's back into the epidural space. A syringe containing air or saline is attached to the needle as the needle is advanced through these ligaments. The operator applies force to the plunger of the syringe to put the contents of the syringe under pressure, either manually or by a simple pressuring device. The dense interspinous ligaments offer great resistance to the injection of air or saline. When the Tuohy needle enters the epidural space there is a sudden loss of resistance and air and saline can be injected freely into the tissues.

The needle can be then used to inject drugs into the epidural space or introduce a catheter for repeat injection of drugs. There is a risk of damaging the patient if the needle is advanced to far. The depth of the epidural space is about 3-6mm and introducing a needle into this space safely requires a degree of expertise. However it remains the norm for anaesthetists to acquire this skill by practice on patients.

Training is often the limited to see-one do-one method. Performing the technique for the first time on a patient, under the gaze of a senior anaesthetist, is often the single most stressful personal experience in training. This practice is at least unfair to all those involved: patient; trainee and trainer, and is perhaps unethical. To master the technique there is no substitute for hands-on experience with real patients. However the basic manual skills of holding the needle, advancing the needle under control, pressurising the syringe and recognising the end-point can be acquired first on a model. Bromage recommended this approach over twenty years ago (1), but there is no training device for the acquisition of the basic'needle'skills in general use. The use of a potato (2) and a banana (3) and two simple inanimate devices (4) (5) as training aids have been described. Portex (6) marketed an interesting mechanical device based on a modified Tuohy needle, spring-loaded friction plates and a solenoid valve to trigger loss of resistance. But none of these devices has gained widespread acceptance.

I have experimented with different types of foam to simulate the interspinous ligaments, and found high-density polyethylene foams have the right'feel'. These foam are used in industry as packaging materials. The closed cell architecture of these materials makes them resistant to deformation and the injection of air and saline.

Polyethylene foam is produced in a range of densities (18K. g/m-120Kg/m) and 'hardness'and foams of different nature may be heat laminated together.

Experienced practitioners of epidural injection recognise changes in resistance as the needle is advanced. Also patients differ and classes of patients have different characteristics: old, children, pregnant. Foams with different characteristics may thus be bonded together in layers to resemble the ligaments of different classes of patients.

I have found a 3.5cm sheet ofEvazote EV50 (50Kg/m3) most closely resembles the feel of the interspinous ligaments for an'average'patient.

My aim was to develop a device that could be used as a training aid in epidural anaesthesia for the novice practitioner to acquire the basic manual skills of epidural injection. The unique features of this device are: 1. The use of high density polyethylene foam to simulate the interspinous ligaments 2. The bonding of layers of polyethylene foam of different characteristics to simulate the changes in the interspinous ligament with advance of a Touhy needle A novel feature of the device is the use of a patient shaped frame with some added anatomical features to produce a sense of realism.

The model is based on a laminated sheet of high-density polyethylene foam used in industry for packaging (Manufacturer, BP Chemical Ltd; local supplier TDK Cosyfoam, Co Durham). The sheet of foam (15cm*15cm*3. 5cm) is held in a torso shaped frame of marine plywood. This frame can be fixed by an adjustable clamp to any thickness of work surface in the'sitting' (leaning forward at an angle of 150 to the vertical) and'lateral'position. Laminated to the frame is a drawing of the bony anatomy of the pelvis and lumbar spine. The foam is sandwiched between the frame and 4mm sheet of Perspex with a midline 4cm wide slot and fixed by four bolts.

Holes are cut in the frame at the Sil/15 through to L1/L2 interspaces corresponding to the bony margins of the epidural'window'detailed in the schematic drawing (pedicles, spinous process and lamina). The Tuohy needle can be inserted into the foam through any one of these holes, and the foam is used to simulate the passage of the needle through the interspinous ligaments and ligamentum flavum. Intrusion of the Tuohy needle into the'epidural'space can be judged by inspecting the inner surface of the foam through the midline slot in the sheet of Perspex. When the foam becomes exhausted from multiple punctures the bolts holding down the Perspex sheet can be loosened and the foam moved.

1. Bromage PR Epidural analgesia. Philidelphia, WB Saunders Co 1978; 716-19 2. Tuckey J The epidural potato! Anaesthesia 1998; 53: 1232-3 3. Leighton B. A Green grocers model of the epidural space. Anaesthesiology 1989; 70: 386-9 4. Meek T An epidural training simulator International Journal of Obstetric Anaesthesia 1998; 7: 282 5. Paw HGW A trainer for identification of the epidural space Anaesthesia 1995 50: 914

6. Daykin AP, Bacon RJ An epidural injection simulator Anaesthesia 1990 ; 45 : 23536

Claims (8)

1. Claims 1. A device to train novice anaesthetists in the clinical skill of epidural cannulation based on a sheet of high density of polyethylene foam to replicate the interspinous ligaments held in a torso shaped frame detailing the bony anatomical landmarks.
2. 2. Lamination of foam of different characteristics (density and hardness) to replicate changes in the interspinous ligaments in different patient populations and depth of injection
3. 3. A novel clamp detailed in the photograph allowing the device to be fixed to any work surface without damage.
4. 4. The ability to position the device in the'sitting'and'lateral' (laying on side) position adds value as a training aid
5. 5. The anatomical drawing adds value as a training aid.
6. 6. The torso shaped frame adds value as a training aid (suspension of disbelief : adds a sense reality)
7. 7. The device is simple in construction so as to be inexpensive and thus present no fiscal constraints on users. To be useful as a training aid the device must be readily available at the site of training. Training takes place at the site of clinical activity that in practice is widely dispersed in terms of place (operating theatres maternity suite) and each hospital would need several devices to fulfil this training need.
8. 8. Simplicity of design and practicality also differentiates this device from other devices described in the literature (see bibliography).