Monitoring vital instability in patients outside high care facilities

Complications that are associated with surgery and hospitalization cannot be entirely ruled out. To prevent patients from experiencing addi­tional harm, it is essential that complications during hospitalization are recognized and treated adequately. A patient’s respiratory sta­tus can provide us with valuable information about the presence and progression of these complications. Unfortunately, respiratory assessment is still infrequently performed and technical solutions for (continuous) respiratory monitoring are generally not available outside high care facilities. This thesis aims to provide a strong basis for future development of continuous monitoring strategies outside high care facilities.

The implementation of a system for continuous respiratory monitoring in order to im­prove patient outcomes is a ‘complex intervention’. That is illustrated by our systematic review as incomplete and suboptimal implementation of one of the components of the monitoring strategy jeopardizes the success of the complete monitoring strategy. The first of those components is the sensor technology. It is essential for success to de­velop sensor technologies that are explicitly suitable for the low care clinical setting. The frequency-modulated continuous wave radar that monitors respiratory rate would fit the low care requirements, as it operates in a non-invasive wireless, and contactless mode. However, a monitoring strategy is more than just the sensor technology. The success of a moni­toring strategy depends on several other components, including signal analysis, alarm strate­gy, as well as the diagnostic and treatment algorithms used. Illustrated by the clinical evaluations of the radar and capnograph sensor technology in this thesis. The radar prototype signal analysis was not sophisticated enough to recognize voluntary movement, that resulted in artifacts and limited the diagnostic accuracy. The additive value of monitoring with a capnograph during procedural sedation depends on the therapeutic interventions and choices that interact with the monitoring strategy. In this example, something elementary as the administration of supplemental oxygen makes the difference.

Successful development of continuous respiratory monitoring strategies for use outside high care facilities also depends on the methodology that is used to study them. We compared three statistical methods to derive limits of agreement in method comparison studies in a simulation study and found that it does indeed matter which statistical method is used to determine the accuracy of monitoring devices. Furthermore, we studied the association between the duration of vital instability before intensive care unit (ICU) admissions and mortality. Our findings suggest that ICU admission should be cautiously used as surrogate endpoint in studies evaluating a monitoring strategy to detect deteriorating patients.

Based on the find­ings of our clinical studies and systematic review implementation of routine continuous non-in­vasive respiratory monitoring on general hospital wards cannot yet be advocated, however the monitoring strategy should be intensified, and this thesis reveals that technical monitoring solutions are getting closer.