MICA: iTraXS (intra Tracheal Multiplexed Sensing): an optical sensor equipped endotracheal tube

In health, people keep their airway clear by coughing and keeping a resting "tone" in the muscles of the throat and tongue. Seriously ill or anaesthetized patients however cannot do this, so clinicians often use an endotracheal tube (ETT) in the trachea (windpipe) to maintain an open airway. The tube has an inflatable "cuff", which sits inside the trachea and forms a gas-tight seal preventing gas leaks and protecting the lungs from soiling by vomit or blood which can lead to ventilator associated pneumonia. The cellular lining (mucosa) of the trachea is easily injured when pressure from the cuff squeezes oxygen carrying blood out of the tissues. To minimize injury, it is important that this pressure is kept at the minimum necessary to avoid leaks and to protect the lungs from contamination. Unfortunately, clinical staff don't routinely measure pressure, and dangerously high readings are commonplace, resulting in a range of tracheal injuries. Injuries range from moderate to severe sore throat in half of all patients after surgery (500,000 per year in the UK), to lifelong tracheal narrowing (Post Intubation Tracheal Stenosis - PITS) which occurs in around 2000 patients per year in England. Our survey of PITS patients revealed a pattern of delayed diagnosis and significantly reduced physical activity from breathlessness.

Our group recently developed a new prototype tube (iTraXS- intra Tracheal Multiplexed Sensing) which uses fine optical fibre sensors in the cuff. In addition to blood flow, oxygenation and temperature measurement, contact pressure with the tracheal wall is measured by the change in wavelength (colour) of light reflected from the sensor. This enables the cuff to be inflated to the most appropriate pressure in order to achieve a gas seal but not to occlude blood flow in the mucosa. This project aims to extend the sensing ability and make clinically compliant versions of our laboratory hardware and software which measure the wavelength changes. We will test the new system in preclinical studies at the University of Nottingham. At the end of this project the device will be ready for clinical trials.

We think iTraXS is capable of improving the everyday experience of surgery for patients worldwide and significantly reduce the suffering and costs associated with PITS at low cost to purchasers. In addition, we think that iTraXS will demonstrate the potential of emerging optical sensor technology to enable sensing of the internal environment of patients in real time, providing previously unavailable data to aid clinical decision making. In addition to standard academic dissemination, our partners P3 Medical and Gill Research and Development will provide valuable manufacturing experience and trade exposure. The iTraXS prototype was runner up at the 2018 Innovation Awards of the Association of Anaesthetists of Great Britain and Ireland, which we expect will help us with industry and clinician awareness. Activities conducted in this project such as end user engagement, health economic modelling and market research will help to support the business case.

Incorrect endotracheal tube (ETT) cuff inflation pressure causes a number of significant problems for intubated patients. If pressure is too high this can result in tracheal injury. Around 3% of intensive care patients intubated for >48hrs suffer tracheal stenosis due to the cuff impairing mucosal perfusion, resulting in 1900 tracheal resections/yr (UK). Tracheal inflammation by the same mechanism results in moderate to severe sore throat and voice change in ~50% of all intubated patients (0.5m/yr UK). If cuff pressure is too low this causes harm through increased pulmonary aspiration of fluid materials, a major contributing factor in ventilator associated pneumonia (VAP). Tracheal pressure injury is avoidable if contact pressure and its effect on mucosal perfusion are monitored, enabling appropriate cuff inflation and personalised care. We prototyped the world's first optical fibre sensor equipped tracheal tube: iTraXS to address this unmet clinical need. We successfully demonstrated simultaneous measurement of mucosal contact pressure and perfusion in animals and conscious human volunteers using sensors incorporated into an ETT. Contact pressure and ischaemia were measurable for different cuff inflation levels. The prototype comprises: a disposable sensorized tube measuring pressure and perfusion at a single position; an electronic unit containing light sources and signal interrogators; a display/user interface and operating software. The system has MHRA no objection but is not fully CE compliant with medical device regulations or usable by clinicians independent of engineer support.
Our aim is to develop this device to be ready for clinical trials. This project will expand the number and functionality of sensors; develop regulatory compliant software and hardware; investigate mass manufacturing processes; validate performance in the laboratory and an animal model; obtain MHRA no objection; develop health economic and commercial models; and capture additional IP

Incorrect cuff inflation pressure causes a number of significant problems for intubated patients. If the cuff pressure is too high this can result in tracheal injury. Around 3% of intensive care patients intubated for >48 hours suffer tracheal stenosis due to the high contact pressure from the inflatable cuff impairing mucosal perfusion. 1900 patients/yr require tracheal resection in the UK alone. Tracheal inflammation by the same mechanism results in moderate to severe sore throat and voice change in ~50% of all intubated patients (500,000/yr in UK). This is an avoidable form of hospital acquired pressure injury, for which litigation is increasing and reimbursement is being removed or reduced.
If the cuff pressure is too low then this causes harm through increased pulmonary aspiration of fluid materials, a major contributing factor in ventilator associated pneumonia (VAP). VAP occurs in 8-28% of ventilated ICU patients. On average, VAP increases length of stay by 6 days, and mortality by up to 50%. Each episode costs the NHS ~£12,000 ($25-40,000 in the US).
There is the potential to significantly reduce these conditions using the iTraXS device. Monitoring contact pressure and perfusion at the cuff/trachea interface will allow the appropriate inflation to provide a gas seal for effective ventilation while avoiding occlusion of the blood flow in the mucosal tissue.