In-hospital Patient Mobilization Quantification After Cardiac Surgery Using Accelerometers: What do Patients do?

Objectives: After heart surgery patients stay for 4 – 7 days in the hospital and start their rehabilitation the day after surgery with physiotherapy training. Patients infrequently mobilize during their surgical ward stay, as patients are unaware why mobilization is important. Furthermore, patients’ progress of mobilization activities is not available. The aim of the MOV_EM_ENTT study was to use accelerometers with artificial intelligence algorithms for quantification of in-hospital mobilization after cardiac surgery.

Methods: Patient activities lying in bed, sitting in a chair, standing, walking, cycling on an exercise bike, and walking the stairs were defined to measure patient mobilization. An accelerometer (AX3, Axivity) was postoperatively placed on both the upper arm and upper leg. An artificial neural network algorithm classified the activities. The primary endpoint was each activity duration performed between 7 a.m. and 11 p.m. Secondary endpoints were intensive care unit and surgical ward stay. A subgroup analysis was performed for male and female patients.

Results: 29 cardiac surgery patients were classified with an intensive care unit stay of 1 (1–2) night and surgical ward stay of 5 (3–6) nights. Patients spent 41 (20–62) min less time in bed for each following hospital day (p<0.001). Although patients practiced in the morning, they laid more in bed in the afternoon. Standing (p=0.004), walking (p<0.001), and walking the stairs (p=0.001) increased during hospital stay. No differences between men (n=22) and women (n=7) were observed for all endpoints.

Conclusion: The approach presented in this study is applicable for measuring all six activities and for monitoring postoperative recovery of cardiac surgery patients. A next step is to provide remote monitoring with wearable sensors to guide patient-specific cardiac rehabilitation.