Introduction and objectives For people with MND who might benefit from home non-invasive ventilation (NIV), current NICE guidance recommends 3-monthly surveillance visits with review of respiratory symptoms, lung function and daytime SpO2. In previous work we have found these recommended parameters poorly predict an elevated arterial CO2 (PaCO2) and the 3 month intervals can be too long as patients die unexpectedly between appointments. We are developing a home-monitoring approach, using personalised capnometry-derived indices, to try to identify developing ventilatory failure, potentially improving on current management pathways. We present initial findings from our pilot study.
Methods Patients with MND attending routine clinics have been invited to use a novel LED-based capnometer 3 times daily at home for up to 52 weeks. At 3-monthly clinic visits, participants perform capnometry and have arterial blood gases (measuring PaCO2) along with daytime SpO2 and lung function tests. The primary study aim was to assess agreement between values for CO2 from capnometry and PaCO2. Secondary aims include an examination of changes in a number of mathematically extracted features of capnometry over time to discover if any predict clinical deterioration.
Results We have recruited 28 participants for home capnometry. Data for PaCO2 from clinic visits (n=39) and paired measures from capnometry were analysed for correlation. The strongest relationship was for the maximum expired (MaxEx) CO2 but even for this r was just 0.4 (p=0.01). Bland-Altmann analysis confirms that agreement between capnometry and PaCO2 was weak with a trend towards an offset with capnometry under calling the PaCO2. However early analysis of home monitoring over several weeks shows potential for differentiating between stable and deteriorating patients. The attached figure shows plots of 7 day rolling average MaxExCO2 for a clinically stable participant and one who deteriorated and required NIV.
Conclusions Preliminary data show weak agreement between selected capnometry parameters and PaCO2 in clinic. Changes over time in extracted data suggest that home monitoring with capnometry may differentiate stable and deteriorating patients. This might be a trigger for clinical review in a timely fashion while reducing unnecessary clinic visits.
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