Elsevier

Gait & Posture

Volume 39, Issue 1, January 2014, Pages 118-123
Gait & Posture

Low cost and batteryless sensor-enabled radio frequency identification tag based approaches to identify patient bed entry and exit posture transitions

https://doi.org/10.1016/j.gaitpost.2013.06.009Get rights and content

Highlights

  • We investigate a batteryless sensor enabled RFID tag for falls prevention near beds.

  • We study two algorithms for automatic detection of bed entry and exits in real-time.

  • The sensor on the sternum method performed better than the sensor on mattress.

  • A study showed sensitivity to be 90.4% for bed exit using the sensor on sternum.

  • A study showed specificity to be 93.80% for bed exit using the sensor on sternum.

Abstract

Introduction

Falls in hospitals and residential care facilities commonly occur near the bed. The aim of this study was to investigate the accuracy of a continuously wearable, batteryless, low power and low cost monitoring device (Wearable Wireless Identification and Sensing Platform) with a single kinematic sensor capable of real-time monitoring to automatically detect bed entry and exit events.

Materials and methods

Three dimensional acceleration readings and the strength of the transmitted signal from the WISP was interpreted to identify bed exit events and sensitivity, specificity and Receiving Operator Curves (ROC) were determined.

Results

The sensor located over sternum method performed best with sensitivity and specificity values of 92.8% and 97.5% respectively for detecting bed entry and values of 90.4% and 93.80% respectively for bed exit. On the other hand, the sensor-on-mattress algorithm achieved sensitivity and specificity values of 84.2% and 97.4% respectively for bed entry and 79% and 97.4% for bed exit detection.

Conclusion

The WISP located over the sternum method is the preferred method to detect bed entry and exit. However, further work in frail older people is required to confirm the performance of this method.

Introduction

Falls occur commonly in residential care and hospital settings where older people are major consumers of care. In both hospitals and residential care facilities, falls commonly occur around the bed [1], [2]. In one acute care study, 65.9% of falls occurred in the bedroom with 80.1% of these falls occurring around the bed [2]. We undertook an audit of falls in our hospital (unpublished data) and found that in almost 50% of cases, falls occurred in patients with documented confusion. Falls commonly occurred between 5 pm and 7 am, in the room, and when staffing levels are lower with 13% of falls related to getting in and out of bed. Bed exiting detection systems are one approach being employed clinically, and trialled in research to provide staff with warning that patients with increased risk of falls (often older patients with cognitive impairment and multiple comorbidities) are about to get up from the bed or chair without the required supervision or assistance [5], [6], [7]. An older underpowered study (n = 70) in a geriatric hospital ward found no reduction in falls or falls related injury with pressure sensor bed exist alarms [3]. Similarly, a more recent, larger cluster randomized control trial did not find a reduction in falls rate even though there was increased use of pressure sensor alarms [4]. A variety of sensing systems attached to the body, bed and floor exist in the market despite the lack of evidence [3], [5], [6], [7], [8] and a recent evaluation of 16 devices reported that only three pressure sensor alarm systems were acceptable for use [8]. The presence of multiple bed exit alarm devices in the market is evidence that clinicians are searching for methods to alert them to patients or residents trying to get out of bed so that they might be able to intervene with the hope of possibly preventing a fall.

Wireless Identification and Sensing Platform (WISP) devices are batteryless, low power and low cost, capable of continuous wear, contain a kinematic sensor and are suitable for real-time monitoring of static postures and posture transitions. In this paper, our aim was to investigate the accuracy of two new technological approaches using WISP devices to automatically identify posture transitions associated with bed exiting with the hope that this would provide caregivers with the opportunity to intervene earlier [9]. The two different technological methods evaluated are: (i) WISP located over sternum; and (ii) WISP attached to mattress on the lateral side away from the entry or exit side.

Section snippets

The technology

The technological backbone of this study is the application of an acceleration sensor enabled passive (batteryless) radio-frequency identification (RFID) device, a wireless technology capable of precise and automatic identification of objects or people without requiring sight of the device [10], [11], [12]. The proposed system consists of: (i) a WISP for activity monitoring and identification [13]; (ii) RFID readers and antennas infrastructure for reading WISPs; and (iii) Patient Monitoring

Results

Subjects performed over 180 PTs including standing-to-sitting, sitting-to-lying, lying-to-sitting and sitting-to-standing for the WISP attached a body trunk algorithm and 100 PTs for the algorithm based on the WISP sensor attached to mattress including, sitting, standing (implying bed empty) and lying. The results (Table 1) suggest that the WISP over the sternum method demonstrated higher sensitivity in detecting entry into and exit out of bed when compared to the WISP on mattress method.

Discussion

The main finding of this study was that a single WISP placed over the sternum accurately identified movement into and out of bed. The small, battery free and low cost nature of WISPs are an advantage, especially in settings where there is significant risk of infection such as hospitals where the device offers both disposability and user-friendliness. The WISP located over the sternum method performed better with few false negatives and positives with bed exits. These low error rates are likely

Acknowledgements

This research was supported by a grant from the Hospital Research Foundation (THRF), South Australia and the Australian Research Council (DP130104614). The volunteers consented to participate in this study. This study has been reviewed by the Human Research Ethics Committee TQEH/LMH/MH and no ethical matters of concerns were identified.
Conflict of interest

There are no conflicts of interest to declare.

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