Introduction
The COVID-19 pandemic has created an unprecedented need for remote patient monitoring.
At the time of writing this article, the majority of countries worldwide are on lockdown
to minimize the spread of the virus, and most of the patients who tested (or are suspected
to be) positive for COVID-19 are in self-isolation at home. Even robust healthcare
systems are facing a shortage of healthcare professionals, personal protective equipment,
beds, and mechanical ventilators in intensive-care-units (ICU) (Kissler et al., 2020),
thus highlighting the need for alternative medical solutions, including remote patient
monitoring (Alwashmi, 2020; FDA, 2020; Ohannessian et al., 2020). New policies have
therefore been introduced to promote the development of monitoring devices (FDA, 2020),
thus creating favorable opportunities to improve the remote monitoring of some overlooked
vital signs. This is especially the case for respiratory rate (RR), which is currently
poorly recorded despite its relevance in the context of COVID-19.
Current COVID-19 guidelines suggest measuring resting RR to inform triage decisions,
diagnosis, prognosis, and as a criterion for ICU admission and for the early recognition
of COVID-19 patient deterioration. The World Health Organization indicates that a
resting value of RR > 30 breaths/min is a critical sign for the diagnosis of severe
pneumonia in adults, while the cut-off value for children varies according to age
(World Health Organization, 2020). At triage, RR values are used to support the assignment
of patients to different categories and to make decisions on the use of supplemental
oxygen (Ayebare et al., 2020; Italian Thoracic Society Italian Respiratory Society,
2020). The treatment of patients affected by acute respiratory insufficiency from
COVID-19 is also tailored considering RR values (Italian Thoracic Society Italian
Respiratory Society, 2020). Furthermore, RR helps with the timely recognition of COVID-19
patient deterioration, thus contributing to the implementation of early intervention
strategies (Sun et al., 2020). Resting RR values also contribute to the prognosis
of COVID-19 patients as ICU admission and mortality are associated with significantly
higher RR values compared to non-ICU patients and survivors (Huang et al., 2020; Zhou
et al., 2020). Besides, the normalization of resting RR is among the signs used to
quantify the time to clinical recovery from COVID-19 infection (Al-Tawfiq et al.,
2020).
The clinical relevance of RR mandates the improvement of the accuracy of RR measurements
in response to the COVID-19 pandemic. RR measurements too often rely on manual counting
in the clinical setting and are often poorly performed out of the hospital. For instance,
guidelines for telephone consultation of COVID-19 patients recognize the fundamental
role of RR in the assessment of patients, but propose unsatisfying solutions for its
remote assessment (Greenhalgh et al., 2020). Since patients usually have no direct
access to respiratory devices, RR is self-reported by answering the question “Is your
breathing faster, slower, or the same as normal?” (Greenhalgh et al., 2020). However,
experimental data discourage the self-report of RR and highlight how measurement awareness
affects resting RR values (Hill et al., 2018). On the other hand, several sensors
and techniques can be used for the accurate remote monitoring of RR; some of these
are ready-to-use in the face of the COVID-19 challenge, while others deserve further
consideration in the future.
Technological Solutions for Remote Respiratory Rate Monitoring
The abundance of techniques currently available can satisfy the various needs of COVID-19
patients with different severities of symptoms (see Figure 1). We can differentiate
techniques for patients that need (1) periodic short-term screening or (2) continuous
monitoring. The majority of COVID-19 patients have mild symptoms and can be screened
periodically (e.g., twice a day) for vital signs. These patients can take advantage
of emerging technologies exploiting built-in cameras of smartphones, tablets, and
laptops to record RR from the respiratory-induced chest wall movements or superficial
changes in face perfusion (Poh et al., 2011; Brüser et al., 2015). By registering
a short video capturing the torso area or the face of the seated patient, RR (and
other vital signs like heart rate) can be streamed to healthcare professionals using
an internet connection (Brüser et al., 2015). This technique is discreet, available
in the market, and shows medical-grade accuracy (error <1 breaths/min) when the patient
is stationary (Massaroni et al., 2019a). The wide spread use of smart devices makes
camera-based solutions immediately available, relatively low-cost, and user friendly.
Furthermore, the availability of smart devices is becoming fundamental in the time
of COVID-19, and healthcare systems can benefit from it.
Figure 1
Technological solutions that can be used for the remote RR monitoring of COVID-19
patients. (A) The built-in camera of a smart device can be used to record RR from
the respiratory-induced chest wall movements or superficial changes in face perfusion
of a seated patient. (B) The built-in microphone of a smartphone can be used to record
RR from the breathing sounds of the patient. (C) An instrumented mattress can be adopted
for continuous RR monitoring by registering the breathing-related chest wall movements
of the patient. (D) Radio wave or Wi-Fi signal sources and receivers can be used for
registering RR values through the modulation of the transmitted signals by respiratory-related
thoracic movements (no body sensors are needed). (E) A smart garment (e.g., a strap
with conductive strain sensors) can be used to record RR continuously from the respiratory-related
periodic changes in chest wall circumference, even during daily activities (e.g.,
walking).
For patients needing continuous monitoring (e.g., older adults, patients with comorbidities
or more severe symptoms), prolonged acquisition through camera-based methods is not
recommended given the higher amount of data to be processed. In these cases, smart
devices offer another ready-to-use technological solution, i.e., the recording of
breathing sounds using built-in microphones (Brüser et al., 2015; Nam et al., 2015).
Currently available systems have implemented this technology for continuous RR monitoring
and unobtrusive sleep apnea detection in quiet environments, with good results in
terms of accuracy (error <1%) (Nam et al., 2015). Other solutions available in the
market monitor RR continuously with strain or pressure sensors installed underneath
mattresses, under bedposts, and on the seating area and backrest of chairs (Watanabe
et al., 2005; Brüser et al., 2015). These solutions are discreet, relatively low-cost
(~100€), and show medical grade-accuracy (error <2 breaths/min) (Brüser et al., 2015).
Furthermore, promising technologies for continuous RR monitoring exploit the modulation
of radio waves and Wi-Fi signals by respiratory-related thoracic movements (Lai et
al., 2011; Abdelnasser et al., 2015). These waves or signals can be generated by radio
sources or traditional modems for internet connection, and have been used to monitor
the RR of patients in different postures (seated, standing and lying on the bed) (Brüser
et al., 2015). Some of these technological solutions are incredibly small, but are
still under development and unavailable in the market (Brüser et al., 2015).
Patients that need continuous vital sign monitoring, even during everyday-life activities,
can be equipped with wearable devices like smart garments (e.g., t-shirts or chest
bands embedding sensors) (Massaroni et al., 2019b). Unlike most of the aforementioned
technologies, smart garments may provide accurate and robust RR values even during
daily activities. Several commercial solutions are available in the market with prices
around 300€, although further efforts are required to advance the field of respiratory
monitoring with wearable devices (Massaroni et al., 2019b). Altogether, a variety
of technological solutions are already available for the accurate remote monitoring
of RR, and a multidisciplinary approach is required to implement these techniques
effectively in medical surveillance programs.
Discussion
Accurate remote RR monitoring is expected to play an important role in the context
of the COVID-19 pandemic. It may facilitate healthcare assistance for self-isolated
COVID-19 patients as well as for all patients that have restricted access to medical
services in this time of crisis. The improvement of remote patient monitoring would
also favor the implementation of timely and cost-effective healthcare services, including
the early warning of patient deterioration, remote triage, and home monitoring of
COVID-19 patients discharged from hospitals. This would help mitigate the burden on
hospitals, decrease the risk of infection for healthcare professionals, and thus reduce
virus transmission. The availability of a large number of accurate RR data will also
contribute to improving the development of predictive models for the risk of hospital
admission, and the development of diagnostic and prognostic models. Finally, we argue
that an accurate remote monitoring of RR is essential and should be performed alongside
the monitoring of other vital signs. Ready-to-use technological solutions are available
to accomplish this goal. Effective RR monitoring would be an important contribution
to facing the current COVID-19 crisis and managing similar scenarios that may possibly
occur in the next months or years (Kissler et al., 2020).
Author Contributions
CM, AN, ES, and MS contributed to the conception and design of the work, manuscript
writing, critical revision of the article, and approval of the final version of the
article.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial
or financial relationships that could be construed as a potential conflict of interest.