Assessment of the feasibility of an ultra-low power, wireless digital patch for the continuous ambulatory monitoring of vital signs

Abstract

Background and objectives: Vital signs are usually recorded at 4-8 h intervals in hospital patients, and deterioration between measurements can have serious consequences. The primary study objective was to assess agreement between a new ultra-low power, wireless and wearable surveillance system for continuous ambulatory monitoring of vital signs and a widely used clinical vital signs monitor. The secondary objective was to examine the system's ability to automatically identify and reject invalid physiological data.

Setting: Single hospital centre.

Participants: Heart and respiratory rate were recorded over 2 h in 20 patients undergoing elective surgery and a second group of 41 patients with comorbid conditions, in the general ward.

Outcome measures: Primary outcome measures were limits of agreement and bias. The secondary outcome measure was proportion of data rejected.

Results: The digital patch provided reliable heart rate values in the majority of patients (about 80%) with normal sinus rhythm, and in the presence of abnormal ECG recordings (excluding aperiodic arrhythmias such as atrial fibrillation). The mean difference between systems was less than ±1 bpm in all patient groups studied. Although respiratory data were more frequently rejected as invalid because of the high sensitivity of impedance pneumography to motion artefacts, valid rates were reported for 50% of recordings with a mean difference of less than ±1 brpm compared with the bedside monitor. Correlation between systems was statistically significant (p<0.0001) for heart and respiratory rate, apart from respiratory rate in patients with atrial fibrillation (p=0.02).

Conclusions: Overall agreement between digital patch and clinical monitor was satisfactory, as was the efficacy of the system for automatic rejection of invalid data. Wireless monitoring technologies, such as the one tested, may offer clinical value when implemented as part of wider hospital systems that integrate and support existing clinical protocols and workflows.

Keywords: GENERAL MEDICINE (see Internal Medicine).

Figure 1

The end-to-end monitoring system for wireless continuous monitoring of vital signs.

Figure 2

Comparison of heart and respiratory rate data between the wireless, digital patch monitoring system and the reference bedside monitor during a 2 h monitoring period in patients who had undergone elective surgery (group 1 patients).

Figure 3

Comparison of heart and respiratory rate data between the wireless, digital patch monitoring system and the reference bedside monitor during a 2 h monitoring period in patients with low voltage/variable QRS morphology (A) and patients with atrial fibrillation (B).

Figure 4

Comparison of heart and respiratory rate data between the wireless, digital patch monitoring system and the reference bedside monitor during a 2 h monitoring period in patients with a high body mass index (>30 kg/m²; A) and patients with diabetes (B).