The creation of a stoma, an opening from the inside of an organ to the outside, is an increasingly common surgical intervention in the management of a large variety of clinical conditions. In most cases it provides a means of diverting bowel or bladder fluid/content from diseased/infected tissue and enables its collection externally through a suitable catheter or pouch appliance system. The most common interventions relate to the bladder (urostomy), small bowel (ileostomy) or colon (colostomy) and can be introduced as an acute or long term measure to patients who range in age from neonates to the elderly.Control over bladder and bowel function is a social norm and any deviation from this can lead to stigma and social isolation. Sadly, the introduction of a stoma removes this control as a consequence of bypassing the sphincter muscles. In such situations, the bladder/bowel content will be collected in a disposable/drainable pouch which covers the surgical outlet and is adhered to the skin through an adhesive flange. The seal between the pouch and the skin can be compromised as a consequence of the exuded fluid undermining the adhesive and can lead to failure of the device. This can have significant ramifications for the psychological wellbeing of the patient – whether compromising the personal dignity of the immobile or elderly or leading to severe distress and debilitating embarrassment for ambulatory patients when occurring in public settings.
The project relates to the design and production of an early warning system that can be used to alert the patient to the impending advent of a leak and allow sufficient time for remedial action to be taken. It will provide the patient with a higher degree of confidence in the pouch system which will allow patients to lead a normal life without the fear of uncontrollable bladder/bowel leakage. The project will take a prototype system developed by the principal applicant and optimise the design/operation/production factors necessary for it to progress towards commercialisation. At present, there are no competing technologies and the device meets a clear demand, has sufficient market potential for both personal and institutional (hospital/residential home) use and is easily integrated with existing pouch systems irrespective of size, shape or function.
The primary aim is to optimise the design and operation of a leak detection system that will improve the quality of life for patients living with a stoma. The device is a two part system in which a detector circuit is married to a disposable probe that can be integrated within existing pouch appliance systems.
The initial foundations of the project arose from an EPSRC sponsored project which focused on the design and development of sensor probes for insertion within catheters. This work involved the laser patterning of polymer encased conductive paths to create nano and micro sized pores that could later be functionalised to detect the presence of bacteria within the catheter and thus provide prevent infection. The principles needed to fabricate the sensing probes have been used to functionalise the leak detection probes which are pivotal to the present application. The probes outlined in the following section are a translational spin off from that grant funding.
The research team led by the Principal Applicant took the probe and developed a prototype leak detection system for stoma pouches. The prototype employs a conductivity circuit connected to a vibration alarm. A coated copper probe is used as a loop encircling the flange of the stoma pouch and sits between skin and the adhesive layer. Fluid draining from the pouch has a tendency to undermine this adhesive layer and if left untreated would lead to the failure of the pouch and the release of bowel or bladder contents. The copper probe sits near the periphery of the flange such that upon contact with the fluid, the electrolyte completes the detection circuit and activates the vibration device which provides a discrete alarm to inform the patient that the pouch needs to be changed.
The system is applies an innovative detection probe which consists of two intertwined polymer coated copper wires which have been laser treated to provide periodic etching in the insulating polymer coat. The result is the production of nanoscale factures in the film through which the stoma fluid can permeate and hence enable charge transfer between the two wires – thus completing the circuit raising the alarm. The bulk of the coating however is complete – preventing circuit shorting and avoids direct contact of the copper wire with the skin and overcomes issues with biocompatibility and peristomal irritation. A polyester wick is also entwined with the two wires. This increases the sensitivity of the device such that upon a leak emerging at a discrete point – the fluid is transported along the wire network by capillary action and activates a greater proportion of nano fractures and thus increases the sensitivity of the detector.
The detection circuit is based on an oscillating conductivity detector. In normal operation two spatially separate probes would be used and the conductivity between the two measured. Such systems are routinely used as leak detectors in conventional water storage systems but these types of device are unsuitable for use as stoma detectors. The placement of the two electrodes would be difficult when trying to ensure that circuit shorting does not occur – complicated by the fact that the electrodes have to encircle the stoma. A critical issue in the application of the stoma pouch relates to the fact that the flange must be sited relatively quickly – bladder / bowel fluid will continue to exude from the stoma and thus any wetting of the skin surrounding the stoma will prevent an adequate seal from being achieved. The critical / competitive advantages of the device are that the probe is:
1. coiled into a single length which is easily manufactured
3. easily/speedily positioned onto the flange
4. flexible/mouldable and can follow the perimeter of the existing flanges
5. user positioned to adjust warning time
6. small and does not compromise the flange seal
Normally, the probes would consist of noble metals – principally platinum. In this case, the Principal Applicant has developed an innovative method through which to use inexpensive copper wire. While the latter have been used as probes for simple leak detection systems they are generally unsuitable for use in the present context – acid from the stoma fluid will corrode the wire if placed directly in contact with the skin and thus lead to copper(II) ion being mobilised. The nanoscale cracks allow the permeation of the stoma fluid through to the underlying copper, hence enabling the charge to transfer between the two electrode probes. The polymer layers are however still intact and thus prevents the copper from coming into direct contact with one another and with the patient’s skin. The surface area of copper exposed is minimal and transport through the factures of any mobilised copper ion would be significantly restricted and thus unlikely to cause any irritation issues. As soon as the stoma fluid contacts the electrodes the alarm will be raised and the probe changed.
Polymer coated copper is a commercial product used in conventional electrical/electronic engineering where the polymer coating prevents electrical shorting within devices. This also allows the wires to be intertwined in the present case without shorting. This however creates a problem in that the unmodified insulating layer also prevents the probe from working – the two underlying wires MUST be able to contact the solution (in this case the stoma output) for a signal to be generated. If the holes are too large then there is a possibility of a false positive as the two wires come into direct contact and hence complete (short) the circuit.
The fractures are created by rastering across the polymer coated copper wire using a 25W carbon dioxide laser to create 25 micron troughs at intervals of 2mm along the length of the probe and which partially exposes the underlying metal. After removing one segment – the laser is repositioned to remove another however the transmission of heat along the length of the wire however results in the partial melting of the polymer surrounding the previously ablated segment which recovers the metal with molten polymer. When cool, fractures arise as a consequence of the previous thermal stress. The copper wires are then intertwined with a polyester thread (to create a wick) and the final assembly serves as a two electrode probe which can be placed onto the periphery of the pouch flange. The flange plus probe can then be placed directly over the stoma onto the skin and the probe connections attached to the meter. As fluid is released from the stoma – some will begin to seep under the flange and will gradually undermine the adhesive seal. The detector is activated when the fluid reaches the probe and effectively completes the circuit. The degree of warning can be controlled by the user through the placement of the probe – the closer to the flange periphery the shorter the period before warning and flange failure
At present there are no technologies that can alert the patient an impending leak. The most common recourse is to apply additional tape around the stoma flange as an additional barrier to extend the lifetime of the pouch appliance. The latter however does nothing to prevent a leak. Sadly leaks are inevitable and can be exacerbated in individuals who have a high stoma fluid output or are physically active. The stoma is usually sited on the abdomen around the waist (surgically the most accessible site) but this region is prone to skin creasing when a person bends and it is the creasing of the skin below the flange which can accelerate the failure of the appliance. In most cases the patient will be unaware as to the impending failure and hence the consequences of a leak occurring in public can often increase the patient’s social isolation. The proposed device address a pressing need and can be delivered at a cost that will be little different from the cost of applying adhesive layers. Critically the device would provide an inconspicuous alert to the patient which will enable them to alter their present activity and repair/replace the failing flange without the crippling embarrassment that unexpected failure would cause. The device would therefore provide patients with participation.greater confidence and facilitate an improvement in their quality of life through enabling normal social activities.
The device also meets and important clinical need where it could alert the care staff to the impending leak and thus enable replacement of the device. This would save time and costs associated with the replacement of the bed linen and clean up of the patient and laundry of the linen. More importantly, it prevents patient distress and could help preserve a degree of personal dignity which is often sacrificed when control over bowel / bladder is lost. The device is capable of continuous monitoring and thus will remotely and discretely inform the care staff.
School of Engineering
University of Ulster