We sincerely thank Fuchita et al. for their interests and excellent comments on our article. We conducted a subanalysis of 673 patients enrolled in two trials who were recovering from abdominal surgery. Posture and movement were continuously monitored from postanesthesia care unit admission until 48 postoperative hours using ViSi Mobile devices (Sotera Wireless, Inc., USA) that categorize posture as upright 90 degrees, upright 45 degrees, lying supine, lying on one side, walking, and fallen. Our primary outcome was duration of mobilization, defined as minutes sitting (upright 90 degrees) or standing per monitoring hour.
As Fuchita et al. note our ViSi sensors could not distinguish sitting on the edge of a bed from sitting in a chair, but the positions seem comparable from a physiologic perspective. Our definition of mobilization, which distinguishes lying in bed from more active positions, is consistent with most enhanced recovery pathways that recommend 2 h out of bed on the day of surgery and 6 h/day thereafter.
We agree that many accelerometers lack validation in hospitalized populations. However, the ViSi Mobile monitoring system is cleared by the Food and Drug Administration (Silver Spring, Maryland) for noninvasive continuous vital sign monitoring. It includes an embedded torso accelerometer and adaptive posture algorithms that measure spine angle within 1° ± 9º and correctly identified 99 out of 102 postures. Mobility data were missing for a median of just 4.3 h (interquartile range, 0.4 to 9.6 h) during the initial 48 postoperative hours, after accounting for patients who were discharged early. While speculative, it seems likely that disconnections were more common in active patients, thereby underestimating the actual difference in mobilization between active and sedentary patients.
Overall, our results demonstrate that better analgesia is associated with increased mobility, independent of opioid consumption. Although we found a strong inverse association between postoperative complications and mobilization, we cannot exclude reverse causation since patients who are sicker or have postoperative complications surely move less than those recovering smoothly. It was nonetheless remarkable that all 17 complications occurred in the 50% of patients who mobilized less than 2 h/day—and the relationship was all the more striking since our definition of mobilization included sitting.