Physical Activity of ICU Survivors during Acute Admission: Agreement of the activPAL with Observation

Abstract

We estimated the agreement of a thigh-worn accelerometer, the activPAL, used to measure activity and sedentary parameters, with observed mobility assessments of intensive care unit (ICU) survivors. We prospectively compared activPAL measurements with direct observation during assessments at discharge from the ICU or acute hospital in eight participants with a median age of 56 (1st-3rd quartile 48-65) years and an Acute Physiology and Chronic Health Evaluation II score of 23 (1st-3rd quartile 17-24). Frequency of sit-to-stand transitions; time spent standing, stepping, upright (standing and stepping), and sedentary (lying/sitting); and total steps were described; analysis was performed using Bland-Altman plots and calculating the absolute percent error. All sit-to-stand transitions were accurately detected. The mean difference on the Bland-Altman plots suggested an overestimation of standing time with the activPAL of 31 (95% CI: -9, 71) seconds and underestimation of stepping time by 25 (95% CI: -47, -3) seconds. The largest median absolute percent errors were for standing time (21.9%) and stepping time (18.7%); time spent upright (1.7%) or sedentary (0.3%) was more accurately estimated. The activPAL underestimated total steps per session, achieving the largest percent error (70.8%). Because it underestimated step count, the activPAL likely incorrectly recorded stepping time as standing time, so that time spent upright was the measure of activity with the smallest error. Sedentary behaviour, including frequency of transitions, was validly assessed.

A study investigating the validity of an accelerometer in quantification of step count in adult hospital inpatients recovering from critical illness

“…This finding concurs with other studies which have investigated the validity of a thigh-mounted accelerometer (activPAL) in quantification of step count in critical care survivors, hospitalised older adults, patients with advanced cancer (in-and outpatient) and outpatients with rheumatoid arthritis. 2,7,10,11 Absolute percentage error was reduced when the accelerometer was mounted on the non-affected limb in hospitalised acute stroke patients and community-based patients post hip fracture. 7 The excellent results found for the ankle-mounted GT3X concur with a study by Edbrooke et al, 1 who investigated the validity of the ankle-mounted AMP 331 accelerometer in hospitalised adults recovering from critical illness.…”

“…5 Thigh and ankle placement sites have previously undergone investigation of their validity in quantification of step count in both acutely hospitalised older adults and critical illness survivors. [1][2][3]6,7 When participants undertook the walking aspect of the protocol, a single observer (the chief investigator) walked with them, counting their steps until participants decided to stop. The duration of the walk was noted to the second, using a Precision ™ radio-controlled alarm clock (Model AP004; Peers Hardy Group, Solihull).…”

“…1 However, a thigh-mounted activPAL accelerometer underestimated steps in hospitalised critical illness survivors, with a median (interquartile range) absolute percentage error for a total step count of 70.1% (28.6%). 2 Other ankle-mounted accelerometers, such as the ActiGraph GT3X+, have demonstrated validity in quantification of step count in hospitalised elderly populations who walk at slow speeds, when the low-frequency extension data filter is activated. 3 When this filter is activated, sensitivity of the accelerometer to low-intensity movements is increased.…”

“…Two studies have investigated the validity of accelerometry to quantify step count in critical illness survivors, comparing accelerometer-quantified step count to observed step count. 1,2 A mean difference of 0.92 steps (95% limits of agreement −3.27 to 5.11 steps) was determined for the ankle-mounted AMP 331 accelerometer. 1 However, a thigh-mounted activPAL accelerometer underestimated steps in hospitalised critical illness survivors, with a median (interquartile range) absolute percentage error for a total step count of 70.1% (28.6%).…”

Validation of a wireless patch sensor to monitor mobility tested in both an experimental and a hospital setup: A cross-sectional study

“…Validation of those two wireless monitors is promising, though validation was not the primary aim of the study and therefore performed in a very small sample (n = 6) on limited data (lying 42 minutes, sitting/standing 30 minutes, walking 18 minutes). In addition, Baldwin et al [ 26 ] assessed validity outcomes of the activPAL in patients after intensive care unit discharge. They present similar results to the current study as Bland-Altman analysis reflects an overestimation of the time standing and underestimation of walking.…”