A pilot study of high frequency accelerometry-based sedation and agitation monitoring in critically ill patients

Abstract

Objective: The degree of sedation or agitation in critically ill patients is typically assessed with the Richmond Agitation and Sedation Scale (RASS). However, this approach is intermittent and subject to unrecognised variation between assessments. High frequency accelerometry may assist in achieving a quantitative and continuous assessment of sedation while heralding imminent agitation.

Design: We undertook a prospective, observational pilot study.

Setting: An adult tertiary intensive care unit in Melbourne, Australia.

Participants: 20 patients with an admission diagnosis of trauma.

Main outcome measures: Accelerometers were applied to patients' wrists and used to continuously record patient movement. Video data of patient behaviour were simultaneously collected, and observers blinded to accelerometry data were adjudicated the RASS score every 30 seconds. Exploratory analyses were undertaken.

Results: Patients were enrolled for a median duration of 9.7 hours (interquartile range [IQR], 0-22.8) and a total of 160 hours. These patients had a median RASS score of 0 (IQR, -4 to 0). A 2-minute moving window of amplitude variance was seen to reflect contemporaneous fluctuations in motor activity and was proportional to the RASS score. Furthermore, the moving window of amplitude variance was observed to spike immediately before ≥ 2 point increases in the RASS score.

Conclusions: We describe a novel approach to the analysis of wrist accelerometry data in critically ill patients. This technique not only appears to provide novel and continuous information about the depth of sedation or degree of agitation, it is also notable in its aptitude to anticipate impending transitions to higher RASS values.

Figure 1

A frequency histogram of the observed Richmond Agitation and Sedation Scale (RASS) scores

Figure 2

Examples of accelerometry versus time at Richmond Agitation and Sedation Scale (RASS) scores –4, 0 and 4

Figure 3

Population mean acceleration at a given Richmond Agitation and Sedation Scale (RASS) score (with variance) (A). Average 2-minute moving window mean at a given RASS score (B). Overall population variance at a given RASS score (C). Average 2-minute moving window variance at a given RASS score (D)

Figure 4

An example of a patient’s data showing Richmond Agitation and Sedation Scale (RASS) scores, acceleration, and moving window variance over about 10 minutes. A patient is observed to transition from across a range of RASS scores. The accelerometry power output is depicted in the middle graph and the 30-second moving window variance on top. The amplitude is proportional to the RASS score and the moving window variance presages an increase in agitation

Figure 5

Mean variance in acceleration around a jump in the Richmond Agitation and Sedation Scale (RASS) score of at least 2 points (A), with standard deviation (B)