Validity of an under-mattress sensor for objective sleep measurement in critically ill patients: a prospective observational study

Nagatomo et al. Journal of Intensive Care https://doi.org/10.1186/s40560-020-0433-x (2020) 8:16 RESEARCH Open Access Validity of an under-mattress sensor for objective sleep measurement in critically ill patients: a prospective observational study Kanae Nagatomo1* , Tomoyuki Masuyama2, Yusuke Iizuka1, Jun Makino3, Junji Shiotsuka1 and Masamitsu Sanui1 Abstract Background: Considering the adverse effects of sleep disturbance in critical care settings, accurate assessment could aid therapy; however, methodological inadequacies mean that no viable option is currently available. Research in healthy population has recently shown that a non-wearable sleep measurement device placed under the mattress of the bed could be beneficial in intensive care settings. Therefore, we aimed to validate this device compared with polysomnography (PSG) and to assess how it related to subjective sleep evaluations. Methods: This observational study measured the sleep of critically ill adult patients. The primary goal was to validate the Nemuri SCAN (NSCAN; Paramount Bed Co., Ltd., Tokyo, Japan) against the reference standard PSG for 24 h. The secondary goal was to evaluate the association between the objective parameters obtained from NSCAN and PSG and the subjective report data obtained using the Richards–Campbell Sleep Questionnaire (RCSQ) for the nighttime. Results: Eleven participants were evaluated. The median of the total sleep time scored by PSG was 456.0 (353.0–517.5) min during the nighttime and 305.0 (186.2–542.5) min during the daytime. PSG over 24 h revealed significant decreases in restorative sleep, with excessive daytime sleep, but with a normal quantity of nighttime sleep. The agreement, sensitivity, and specificity rates (with 95% confidence intervals) for the NSCAN compared with PSG were 68.4% (67.9– 69.0%), 90.1% (89.7–90.6%), and 38.7% (37.9–39.7%), respectively. The median RCSQ value when subjectively evaluating nighttime sleep was 68.0 (26.3–83.5); this showed no correlation with the NSCAN sleep parameters, despite a positive correlation with the ratio of the stage N2 isolated or combined with restorative sleep in the PSG assessment. Conclusions: NSCAN had moderate agreement, high sensitivity, and poor specificity in intensive care settings, which is most likely due to its inability to identify immobile wakefulness often observed in critically ill patients or sleep depth. This remains a barrier to its use in the assessment of subjective sleep quality. Trial registration: This investigation was part of an interventional trial registered with the University Hospital Medical Information Network Individual Clinical Trials Registry (UMIN000026350, http://www.umin.ac.jp/icdr/index-j.html) on March 1, 2017. Keywords: Critically ill patients, Sleep evaluation, Polysomnography, Sleep measurement, Richards–Campbell Sleep Questionnaire * Correspondence: 1 Department of Anesthesiology and Critical Care Medicine, Jichi Medical University Saitama Medical Center, 1-847 Amanuma-cho, Omiya-ku, Saitama-shi, Saitama 330-8503, Japan Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Nagatomo et al. Journal of Intensive Care (2020) 8:16 Background Sleep disturbance, which is a common and negative experience for patients in the intensive care unit (ICU) [1–9], could exacerbate the disease condition and increase the risk of cognitive function deterioration [1–7]. It is also associated with the post-intensive care syndrome that has a significant long-term impact on survivors [10, 11]. The characteristic sleep architectures of this population when measured by polysomnography (PSG) include a reduction in restorative sleep (i.e., rapid eye movement (REM) sleep and slow wave sleep) and severe fragmentation from frequent arousals and awakenings within the normal range of the total sleep time (TST) [1–7], with an abnormality in the day–night sleep cycle [1, 4, 5]. Sleep should be appropriately promoted in critical care settings; however, to date, the factors affecting sleep in the ICU are not completely understood [3, 4, 11]. Furthermore, methodological issues of sleep measurement remain practical barriers [2, 6]. Although PSG is the standard objective method for measuring sleep quality and quantity, its technical difficulty, high cost, and intolerability to patients make it impractical for its routine implementation in the ICU [11, 12]. Although several studies have sought to report alternative methods of sleep monitoring, they have not yet been established [12–15]. The Richards–Campbell Sleep Questionnaire (RCSQ) is one of the simplest methods of subjective evaluation [3, 12, 16] and has been shown to correlate with PSG parameters [17]. However, the reliability of such subjective evaluation is not always assured, particularly in patients with cognitive impairments [3, 6, 12, 18]. Nemuri SCAN (NSCAN; Paramount Bed Co., Ltd., Tokyo, Japan) is a non-wearable sleep monitor placed under a mattress and can automatically identify sleep–wake cycles and whether a patient is in bed by assessing the body motions, respiratory, and heartbeat movements, which has previously been validated in healthy subjects [19]. To date, NSCAN has not been assessed in critically ill patients. Therefore, in this study, we aimed to validate NSCAN against 24-h PSG as a tool for sleep measurement in patients in the ICU and to identify its association with subjective sleep evaluated by the RCSQ. We test a hypothesis that NSCAN is expected to offer the valid precision of detecting patients’ sleep compared with the reference standard PSG for 24 h. The primary outcome variable is patients’ sleep defined by PSG. The primary analysis of the study is agreement, sensitivity, and specificity rates of the patients’ sleep between NSCAN and PSG. We hypothesize that NSCAN is expected to offer an option for sleep evaluation in the ICU. Methods Study setting and sample This prospective observational study was part of a larger interventional trial approved by the Institutional Review Page 2 of 8 Board of Jichi Medical University Saitama Medical Center (S17–134). It was conducted in the general 8-bed ICU at Jichi Medical University Saitama Medical Center, a 600bed tertiary teaching hospital in Saitama, Japan, from March 2017 to October 2017. The staff in the ICU primarily treated perioperative patients (particularly (...truncated)