Engineering Insight

Respiratory rate monitoring is vital in perioperative surgery. Traditionally, nurses primarily check chest movement to identify breathing. That technique is inadequate if a patient is suffering from a blockage, for example, or if there is chest movement for a reason that is not associated with breathing. Respiratory rate is the vital sign that is recorded least often, yet it is one of the most sensitive to problems and could be the first indicator that something is wrong with a patient.

Applying moisture sensor technology
With nothing on the market to automate the process of directly measuring respiratory rate, medical electronics company Anaxsys (Send, UK; www.anaxsys.co.uk) saw an opportunity to apply moisture sensor technology to a standard oxygen mask. Anaxsys had developed and patented advanced sensor technology capable of profiling moisture levels in inhaled breath. Integrating the sensor into a mask, however, introduced new challenges, because it is essential that patients are not exposed to cross-infection at the interface of the connector and mask-mounted sensor. With this challenge in mind, Anaxsys engaged in hospital studies with nurses in postoperative care and initiated discussions on product concepts with a Cambridge-based consultancy.

It soon became clear that there was an overwhelming preference for one particular design approach, both for the breath rate sensor and the visible/audible monitor and alarm. User trials with an early prototype also confirmed this preference and identified the need for continuous monitoring of the respiratory rate and for both upper and lower respiratory-rate alarms.
After early user trials and identification of additional features that would be required, Anaxsys held a design review of the user-requirement specification. As Anaxsys had limited electronics and software development resources, it engaged the skills of Ashford-based instrumentation design consultancy and manufacturer, Integrated Technologies Ltd (ITL). Initially handling the sensor housing, alarm functionality and digital interface, the ITL team later took on all aspects of algorithm development, prototyping and design for manufacture.

To solve the cross-infection potential identified during risk analysis, the sensor housing was completely redesigned by ITL. There was also an issue with noise pick-up in the screened cable connecting the mask-mounted sensor and monitor unit because of the low signal levels involved. The ITL team came up with a digital solution by developing a dedicated and low-cost analogue to digital convertor that is incorporated into the cable connector of the mask. With the research complete, the business model in place and the engagement of ITL, respiR8 was born.

The launch of respiR8
RespiR8 received the CE mark and was launched in October 2010. It consists of a low-cost, disposable, specially adapted oxygen mask fitted with a sensor. The respiR8 has a robust reusable electronic monitor that can be used throughout the duration of a patient’s stay and provides a clear digital display of real-time respiratory rate. One of the major factors appreciated by users in the concept trials was the active matrix organic light-emitting diode screen, legible from almost any angle. This technology was adopted in the design with special attention to its procurement, as this is a relatively high-cost display option.

Any significant change in respiratory rate trips an integral alarm, allowing healthcare professionals to make an immediate intervention. The high-low alarm conforms fully to EU regulatory and safety standards. Respiratory history is stored in memory and can be viewed using a second display mode, identifying respiratory rate trends during the monitoring period.
From a commercial perspective, volume revenue comes from the sensor being fitted in the mask: one sensor per mask and one mask per patient delivers high volumes but at a relatively low margin. The reusable high-quality monitor is manufactured in lower volumes but at a higher cost and higher margin.

RespiR8 is mains powered, uses a rechargeable battery that allows patients to be monitored while they are moved and can be rapidly deployed for use with any existing bed-head array system.