WEARABLE SENSORS TO IMPROVE DETECTION OF PATIENT DETERIORATION

Meera Joshi, Hutan Ashrafian, Lisa Aufegger, Sadia Khan, Sonal Arora, Graham Cooke & Ara Darzi

Abstract

Introduction

Monitoring a patient’s vital signs forms a basic component of care, enabling the identification

of deteriorating patients and increasing the likelihood of improving patient outcomes. Several

paper-based track and trigger warning scores have been developed to allow clinical

evaluation of a patient and guidance on escalation protocols and frequency of monitoring.

However, evidence suggests that patient deterioration on hospital wards is still missed, and

that patients are still falling through the safety net. Wearable sensor technology is currently

undergoing huge growth, and the development of new light-weight wireless wearable sensors

has enabled multiple vital signs monitoring of ward patients continuously and in real time.

Areas covered

In this paper, we aim to closely examine the benefits of wearable monitoring applications that

measure multiple vital signs; in the context of improving healthcare and delivery. A review of

the literature was performed.

Expert commentary

Findings suggest that several sensor designs are available with the potential to improve

patient safety for both hospital patients and those at home. Larger clinical trials are required

to ensure both diagnostic accuracy and usability.

Word Count 185

Key Words: Continuous monitoring, Patient deterioration, Hospital, Vital signs, Ward

patients, Wearable sensors.

1

Introduction

1.1 The need for continuous monitoring

Monitoring of a patient’s observations forms a basic component of clinical care.

National Confidential Enquiry into Patient Outcome and Death (NCEPOD) data shows that

clinical deterioration may present several hours prior to an adverse event(1). Unfortunately,

unwell patients are still currently falling through the ‘safety net(2). Some 39% of acute

emergency patients admitted to the Intensive Therapy Unit (ITU) are referred late(3). A

measurement of a patient’s vital signs is often the first step in assessing for any acute

deterioration in their clinical condition(4)(5).

1.2 Recording of vital signs

Essential vital signs that are routinely captured are: temperature, heart rate (HR), blood

pressure, respiratory rate (RR), oxygen saturations and level of consciousness. Vital signs

inform and guide clinicians on how the patients are progressing during hospital admissions,

and alert in cases of patient deterioration. A measurement of a patient’s vital signs is often the

first step in assessing for any acute deterioration in their clinical condition(4) (5). An acute

deterioration in patient’s condition is accompanied by changes in their physiological

parameters first(6)(7). The vital signs can help detect several problems such as cardiac,

respiratory, shock and sepsis. A patient’s vital signs are crucial to ensure an earlier detection

of sepsis(8)(9). If these changes are not detected and treated there is a risk of cardio-

respiratory arrest(10) (11). With stretched resources and a busy ward the opportunity to

identify deteriorating patients early can be easily missed. Consequently, acute wards with a

high turnover of patients are most at risk and admit sicker patients.

For ward patients, most hospitals offer intermittent monitoring. A range of observation

machines are available and vary depending on the NHS trust. The most commonly used

observation machines in the NHS are the Dinamap Vital Signs Monitor(12) and the Welch

Allyn Spot Vital Signs® Device (13). Most observation machines provide a local display for

the healthcare professional reviewing the observations and it is not common practice

currently for their integration into electronic health records or alerting through mobile

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devices. During the time of monitoring a physical check on the patient is performed by a

healthcare assistant or junior nurse. This normally takes around 5-10 minutes and a portable

observation machine is used. The observation machines are connected to the patient through

several ways.

The blood pressures is measured by using an appropriately sized blood pressure cuff which is

attached to the patient during the monitoring process, this often takes a few minutes to

calculate and gives both a systolic and diastolic reading. A finger based probe measures the

oxygen saturations and heart rate. The temperature is often recorded using a portable

tympanic probe. There are other routes of recording temperature that are less common such

as; axillary, oral and rectal. In most hospitals, the observation machines have a local display

and this is copied onto the paper based observation chart by the healthcare staff member that

is taking the observation. The way that vital signs are obtained in healthcare has not changed

for several decades with often a single ward nurse managing many patients. Currently in most

hospitals the monitoring of respiratory rate is not automated and cannot be calculated by the

observation machine itself. Instead, the respiratory rate is measured by the healthcare

professional counting the breaths over a time period either for a full minute or for 30 seconds

and multiplying it by two. The current way of measuring respiratory rate has been shown to

highly inaccurate and poorly reported(14). Level of cognition is assessed by healthcare staff

at the bedside and is currently not automated. It is normally measured through simple scales

such as AVPU whereby the patient is Alert or responds to Voice or responds to Pain, or is

Unresponsive.

The common practice for measuring a patients vital signs as recommended by The National

Institute for Health and Care Excellent (NICE) is all patients have their vital signs recorded

every 12 hours as a minimum(2). Every 4-6 hours are when ward observations are typically

taken although overnight they may be very infrequent. The frequency of monitoring is

depended on each individual trust policy and may be increased in certain clinical

circumstances such as very unwell patients or those with a head injury for example that

require more frequent monitoring. The limitations to current monitoring practice is that

deterioration between these time periods of monitoring may easily be missed.

Several paper track and trigger warning scores have been developed to allow clinical

evaluation of a patient and guidance on escalation protocols and frequency of monitoring.

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One such score that is most frequently used in the National Health Service (NHS) is the

National Early Warning Score (NEWS)(15). The Royal College of Physicians recommends

that the minimum frequency of monitoring should be every 12 hours (15). The frequency of

observations are increased to 4-6 hours for those with a NEWS of 1-4, hourly for a NEWS of

5-7 and continuously for patients with a NEWS of 7 or greater(15). An increased frequency

of monitoring is required for acutely unwell patients.

The reporting of vital signs in their current form has been prone to errors for several reasons.

Firstly there may be an inadequate monitoring frequency for some patients(16) (17) (18). The

calculation of the early warning score itself may be inaccurate(19)(20)(21)(22)(23). Paper

based observation charts have been used over the last 50 years and are still the most common

way to record observations in most NHS hospitals. Most causes of error arise from the use of

paper based observation charts. The paper charts that have been traditionally used are placed

at the patient’s bedside. Any damage to the paper chart due to spillage for example or poor

documentation may leave them to be illegible and lead to false interpretation(24) (25).

1.3 Continuous monitoring of vital signs

For decades, the way vital signs are measured have not changed. They are taken at static

moments in time. Wearable sensors will cause a huge paradigm change. There will be a

dramatic change in the landscape of assessment of vital sign observations as these new

technologies develop further. Patients will be continuously monitored which in turn will be

combined with real time analytics helping to identify unwell or deteriorating patients much

sooner than current technologies. The use of these sensors in high-risk patients and acutely

unwell patients will be an early source of interest.

Continuous monitoring of vital signs through the latest wearable sensors may help in the

early identification of patient deterioration. Fortunately, to tackle the above challenges, there

have been significant developments of wearable sensors in recent years (26)(27)(28)(29)(30)

(31)(32)(33). It has been possible to develop smaller, light-weight sensors, with greater

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sampling frequency that can relay information wirelessly ensuring that patient mobility is not

compromised and the sensors will be well tolerated.

The continuous monitoring of heart rate and respiratory rate can predict and reduce the

occurrence of potentially adverse events such as cardiac arrest and respiratory failure. It has

been shown that respiratory function deteriorates in a significant number of patients prior to

an ITU admission(34). As well as the standard vital signs mentioned above newer wearable

sensors may be able to measure the ‘physiological signal’ which may represent the

complexity of the integrated compensatory responses that change early in the clinical process

rather than outcome variables such as vital signs(35). Newer markers such as age combined

with traditional vital signs may help better triaging of patients than traditional vital signs (36).

Whilst vital signs are useful in detection of patient deterioration it should be noted that

normal physiological processes are in place to help compensate when patients become

unwell. At times, vital signs do not change until quite late until the progression of the

patient’s condition particularly in shock(35). Patients use compensatory physiological

mechanisms (such as vasoconstriction, tachycardia and deep inspiration) to help maintain the

consistency of blood pressure(37)(38)(36)(39).

A range of options are used to transmit the data from the sensor wirelessly including

Bluetooth, radiofrequency and Wi-Fi signal. The wearable sensor technology can transmit

data back to the clinicians via alerting through a centralised monitoring system, integrating

into electronic health records and alerting to mobile applications for portable hand held

devices such as smart phones and Personal Digital Assistant (PDA).

With faster and better prediction of patient deterioration through proactive monitoring of a

patient’s vital signs it is likely patient outcomes will improve and make substantial

improvements to patient safety. Whilst it is likely that wearable sensors will improve patient

safety and patient outcomes the use of wearable sensors in clinical practice is currently very

novel. Consequently, there are very few high-quality studies or randomised controlled trials

thus far reviewing patient outcomes. The benefit of continuous monitoring must be offset by

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both practical and economic considerations of running a well-controlled large trial in high

risk patients.

Early studies on outcomes have found promising results. Several studies have shown

wearable sensors to improve a diverse range of patient outcomes from; reduced pressure

sores(40), a reduction in the number of total days spent on an Intensive Care unit(41),

reduction in hospital stay (42), a greater diagnosis of heart arrhythmias such as atrial

fibrillation (43),

However, the results may be conflicting, a randomised control trial has found continuous

monitoring to have no effect on adverse events and mortality. Only 16% of patients were

monitored for 72 hours as intended and thus the study was significantly underpowered(44).

Patients on high dependency units and intensive care often require continuous monitoring as

small changes in physiology may have a profound effect on patient outcomes. This

monitoring is impractical for ambulating ward patients as existing systems are often heavy,

expensive and require indwelling lines and or additional wires. One of the key strengths in

the use of wearable sensors is the encouragement of patients to ambulate early in hospital.

There is significant data which shows the benefits of early ambulation in hospitalised patients

and an improvement in recovery. Much of this work started in the 1990s when the concept of

enhanced recovery after surgery was first proposed(45). Early mobilisation of surgical

patients is one of the pillars in the Enhanced Recover After Surgery (ERAS) programme

which has been widely adopted worldwide. Improved adherence to ERAS is associated with

improved clinical outcomes after patients undergo major colorectal surgery(46). As well as

the benefit in surgical patient’s early mobilisation has also been encouraged for medical

patients. Early physical rehabilitation has been shown to reduce hospital length of stay in

medical patients such as those with acute respiratory failure(47). Early mobilisation after an

intensive care unit admission have been shown to improve neuromuscular weakness and

physical function(48).

The current forms of monitoring used on the wards are often bulky and have lots of wires

restricting the movement of patients. Whilst they are useful for patients confined to bed, most

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patients are ambulating on the ward and would be severely restricted if such monitoring was

continuous. In additional there is the potential that current monitoring used continuously may

inadvertently slow recovery by reducing mobility. Performing manual observations on

patients can take between 5-10 minutes per patient and can be time consuming for staff. The

use of automatic monitoring systems such as wearable sensors can free up staff to perform

other tasks. The way that observations are taken currently is open to user interpretation,

whereas wearable sensors will help to reduce any bias in recording observations.

The newer wearable sensors that have been developed offer several advantages to current

monitoring. They are often wireless enabling greater movement and less restrictions than

current monitoring. The sensors are lighter and smaller in size and so can be worn more

discretely by patients. They offer more comfort than current forms of bedside monitoring.

Respiratory rate is manually counted by a nurse at the bedside and is not currently automated.

Data shows that respiratory rate is repeatedly the vital sign where documentation is poor(49)

and often inaccurately calculated and recorded(50). Automated ways of calculating

respiratory rate through wearable sensors aim to provide greater accuracy and greater

documentation. Additionally vital sign data from wearable technology can be used in the

development of ‘automated health event prediction, prevention and intervention’(51).

Continuous monitoring has the potential to be a great benefit in identifying patients with

sepsis where deterioration can be very rapid (52). Additionally, identifying the

‘normalisation’ of patients earlier may result in earlier discharges, reducing both length of

stay and costs. With the growing elderly population and more patients with chronic disease

being managed in the community there is an increasing role for continuous monitoring at

home too.

1.4 Latest wearable sensors

The wearable sensor market is rising rapidly and driven by major technology companies

(Google and Apple) as well as those specialising in sports clothing (Nike and Adidas). This is

a huge industry with an expected market worth of $2.86 billion dollars by 2025(53). There is

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currently no out right leader in the field. The key factors in wearable sensor growth are a

combination of higher user demand, advancement in sensor technologies resulting in

miniaturisation, reduced production costs, coupled with both wireless communication streams

and a longer battery life.

Wearable bio sensors are non-invasive devices that capture, transmit and process health

related data(54). Ideal sensors should be low cost, reliable, light weight, easy to wear, easy to

use, have a long battery life and allow the wearer to ambulate normally. Thus, far there is

little in the literature for wearable sensor use in routine ward-based patient care.

This paper reviews wearable sensors that can measure multiple vital signs continuously.

Whilst most available sensors are consumer graded there are a few manufacturers that have

obtained European Conformity (CE) and or Food and Drug Administration (FDA) approvals

for use in hospital settings. Whilst this was not a systematic review our search strategy used

Ovid, Medline and Google. Only those wearables that have both FDA and CE marking

approvals will be described. The search was reviewed by both authors MJ and HS.

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2. Expert commentary – continuous wearable sensors measuring multiple parameters

2.1 Early Sense Monitoring System

The Early Sense Monitoring System measures HR, beat-to-beat fluctuations (i.e. RR

intervals) and bed motion. The sensor is placed under the patient’s mattress and is a non-

disposable sensor. It is attached to the bedside monitor and display centre for healthcare

professionals via a wire (26). The system consists of a sensor under the bed, a bedside

monitor, a central display station and software. As the sensor is attached to a mains power

supply the battery life of the sensor is not a factor. The system can alert to a bedside unit,

central display station and a mobile device. As this sensor is not directly attached to the

patient there are no concerns about the weight of the sensor. The sensor can only be used

when the patient is in bed (55). The Early Sense system is perhaps the most researched

monitoring system to date; it has been tested on patients and has both FDA and CE marking

approvals. In a study involving a 316-bed community hospital two models were constructed.

Model A was a care based model in which the estimated total cost savings of intervention

effects were reviewed. Whilst model B was a conservative model in which only the direct

variable cost component for the final day of length of stay and treatment of pressure ulcers

was included (56).When evaluating the costs of the system both cost models found a positive

return on investment when used in both surgical and medical wards(56).

Its use on medical and surgical wards has shown to significantly reduce both the length of

stay and Intensive Care Unit days for transferred patients(41). The estimated reduction in

length of stay is likely to be attributable to the continuous monitoring of vital signs reflecting

the earlier detection and more effective intervention for clinical problems which are known to

prolong both ICU and hospital stay(41). Thus, far to our knowledge this has mainly been

used for research purposes as opposed to routine clinical care. The main limitations of the

system are that it is only of use whilst the patient is in bed and is currently unable to interface

with the electronic medical record.

2.2 Vital Connect HealthPatch™

The Vital Connect HealthPatch™ is an alternative light weight sensor that monitors a total of

eight vital signs; single lead Electrocardiography (ECG), HR, HR variability, RR, skin

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temperature, body posture, fall detection and activity (57). There is a wireless adhesive sensor

that is placed on the patient’s chest. The patch is disposable with a battery life of 4 days and

has been tested on patients (57). The specifications are a weight of 11grams and size of 11.5

x 3.6 x 0.8 cm. The vital connect sensor transmits signals via Bluetooth to a centralised

monitoring device and via text to a mobile device. It is both FDA approved and CE marked.

Like similar sensors described above it can transmit real time continuous observation data at

a sampling frequency of 125Hz(27). The patch was validated in health individuals

undergoing various physiological assessments such as exercising. A comparison was made

between the patch and standard reference monitoring and 3 patches were placed on each

patient (27). The patches were placed in three possible locations: (1) in a modified lead-II

configuration on the left midclavicular line over intercostal space (ICS) 2, (2) vertically over

the upper sternum, or (3) horizontally on the left midclavicular line over ICS 6(27). The

monitoring used was a Actiheart device for heart rate, oxygen cannula attached to an Oridion

Capnostream capnography monitor for respiratory rate and two pedometers (Omron and

FitBit) for measuring steps(27). The patch was proven to be accurate. In comparison to the

reference monitoring the heart rate measurement had a mean absolute error (MAE) of less

than 2 bpm(27). Respiratory rate had an MAE of 1.1 breaths per minute during metronome

breathing(27). The posture detection had an accuracy of over 95% in two of the three patch

locations, steps were counted with an absolute error of less than 5%, and falls were detected

with a sensitivity of 95.2% and specificity of 100%(27). However, there was a very small

sample size of 25 healthy participants. The patch was tested in well elderly subjects with

various medical co-morbidities over 50 consecutive days in their homes(58). The patch

sensor was paired to a smart phone in which data streams could be reviewed in real-time. HR,

RR and skin temperature estimated the mean absolute errors to be <3 beats/min, <3

breaths/min and <1.2 ◦C, compared to reference monitoring(58). This data suggests that it

may be possible to use such a patch at home for monitoring of both elderly and vulnerable

patients.

2.3 Sotera Wireless VisiMobile System

The ViSiMobile System continuously measures HR, ECG, RR, oxygen saturation level, skin

temperature and non-invasive blood pressure(28). The sensor is worn around the wrist and

has a thumb sensor for oxygenation saturation. The main unit of the sensor weights 110

grams. The size dimensions are; 2.6 cm in height x 4.9 cm in width x 9.4 cm in length. The

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battery life for this system is between 12-14 hours before it needs to be recharged. It uses Wi-

Fi technology, can integrate into the electronic health systems and send alerts to tablets or

smartphones for significant changes in vital signs. The ViSiMobile System has been FDA

approved and CE marked. It has been used in a study at the John Hopkins Hospital for

patients on a surgical ward (59). This was run as a quality improvement pilot study, the

results of which are currently being analysed. The early results from this study are

encouraging. The 3-month surveillance has identified patients with pulmonary emboli, the

early stage sepsis, myocardial infarction and atrial fibrillation. On discharge 98% of patients

showed satisfaction with the system. The satisfaction from nursing staff was recorded at 70-

75%. A concern for multi parameter continual vital sign monitoring is the risk of alarm

fatigue; which occurs when one is exposed to frequent alarms they can become desensitised.

This system in particular has been shown to have low rates of alarm fatigue(60).

2.4 Sensium Vitals Monitoring Technology

This is a wearable, wireless, continuous monitoring device for inpatients in a ward setting. It

is able to measure HR, RR and axillary temperature(29). It is a low cost, single use, low

powered device with near real time vitals every 2 minutes and a battery life of 5 days. The

patch is attached to the patient’s chest via ECG electrodes and a wire is attached around the

patients back with a sensor measuring axillary temperature. The battery life for this sensor is

up to 5 days. The lower power consumption is a real strength of this product over its

competitors. The data from the sensor is transmitted via radiofrequency to a centralised

monitoring device or smartphone. The sensor is both FDA approved and CE marked. The

patch has been tested in 60 patients and has been shown to have reliable heart rate values(61).

The study was performed in recovery after patients underwent routine surgery and on a

general ward. The wearable patch has ambulatory algorithms which insure that noisy or

irregular signals are not reported to ensure a reduction in false alerts and alert fatigue(29)(62).

2.5 Philips Bio Sensor

The Philips Bio Sensor is small light weight sensor measuring HR, RR, skin temperature,

body posture, fall detection, single lead ECG, RR-interval and step count(30). It is a wireless

self-adhesive sensor worn on the chest. It weighs 12 grams and the size dimensions are 1cm x

3.6cm x 0.8 cm. During a normal ECG waveform, the R interval equates to a point

corresponding to the peak of the QRS complex. The RR-interval in this context is the interval

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between successive R peaks on an ECG. The Philips Bio Sensor is disposable and has a

battery life of 4 days. The sensor technology is ECG electrodes that detect heart rate, a

thermistor to detect skin temperature and 3 axis accelerometer to detect motion(30). The

patient data is transmitted via Bluetooth to an IntelliVue Guardian Software tool which can

integrate into electronic medical records and alert to smart phone devices. The sensor is both

FA approved and CE marked. There are currently no research papers with the use of the

sensor on the wards for continuous monitoring.

2.6 Isansys Lifetouch Sensors

The Lifetouch manufactured by Isansys and is a small light weight wireless wearable sensor

that examines the ECG trace to extracts the HR, RR, and heart rate variability before relaying

information to a central server(31). The Life touch weighs 7 grams and sensor dimensions for

a small sensor are 14cm x 4.7cm x 0.95cm. It is attached to the patient’s chest via ECG

electrodes(31).This sensor battery life is between 4- 6 days as a maximum(31). It transmits

data via Bluetooth and can be transferred into electronic health systems. This is FDA and CE

marked. There is another sensor they have called Lifetemp which sticks to the body by using

silicone gel adhesive and is normally placed in the axilla(31). It can continuously measure

relative skin temperature from patients and transmit readings wirelessly to a blue tooth

enabled receiver. There are currently no research papers with the use of the sensor on the

wards for continuous monitoring.

2.7 Zephyr Bio-HarnessTM

The Bio-HarnessTM has been used predominantly for commercial purpose, it has been tested

in fields such as sport and the military(32). The sensor can measure HR, HR Variability, RR,

temperature, posture and accelerometry data. HR is captured through electrode sensors within

the chest strap and reported as beats per minute(63). RR is measured using a capacitive

pressure sensor that detects expansion and contraction of the torso and gives an output of

breaths per minute(63). Triaxial accelerometry uses piezoelectric technology and reports 1Hz

per second(63). There is also a micro electro-mechanical sensor accelerometer with a

12

capacitive measurement scheme and is sensitive along 3 orthogonal axes (vertical, sagittal

and lateral)(63). The skin temperature is measured using an infrared sensor through a clear

window at the apex of the device(63). These parameters were tested using a repeated,

discontinuous incremental treadmill protocol(63). The coefficient of variation was low for

HR, accelerometery, posture and skin temperature(63). RR was less reliable(63). This is a

wearable sensor with an elasticated belt that is typically worn around the chest(32). The

sensor is non disposable with a battery life of 24 hours. The data is transmitted via ECHO or

Bluetooth to a centralised display. The sensor is both FA approved and CE marked. There are

currently no research papers with the use of the sensor on the wards for continuous

monitoring.

2.8 Advanced Medical mONitoring (AMON) Wearable Sensor

Advanced Medical mONitoring (AMON) is a wearable sensor that can continuously measure

HR, oxygen saturations and temperature of a patient (33). It is a wrist worn sensor and

weighs 286 grams. The sensor is a non-disposable sensor with a variable battery life

depending on power consumption. The data is uploaded via Wi-Fi to centralised monitoring

and can incorporate into electronic health records. In addition, it can measure the level of

physical activity, blood pressure and one lead ECG when necessary. This sensor has both

FDA approval and CE marking. Automatic alerts can be sent to the healthcare team if any

deviations are found in measurements. In a study of 33 healthy volunteers the accuracy of

the device when compared to manual observations was questioned(33). There was initially a

design flaw in the pulse algorithm; once corrected 85% had a difference of less than 5 beats

per minute(33). There was unfortunately great deviation in the oxygen saturations measured

and there was no ECG concordance apart from HR(33). There are currently no research

papers with the use of the sensor on the wards for continuous monitoring.

A summary of each wearable sensor and the vital signs measured can be found in table 1.

A further description of each wearable sensor can be found in table 2.

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Conclusions

3.1 Comparison of the sensors described

A range of sensors measuring a variety of vital signs have been described above and the

results are encouraging. Wearable sensors and digital technology have the potential to

improve patient safety for both hospital patients and those at home. Several sensor designs

are available. The Early Sense monitoring system sensor is placed under the mattress.

Although useful for some patients those that are ambulating on the wards or in a chair next to

the bed for example would not receive monitoring. Several sensors were placed on the chest

either through adhesives or ECG electrodes (Vital Connect, Sensium, Philips and Isansys).

These can easily be worn under the patient’s clothes and are unobtrusive. The wrist worn

sensors were the Amon and VisiMobile ones whilst the Zephyr sensor is worn around the

chest. All the sensors described above measure HR which is the most commonly measured

vital sign. Respiratory rate and temperature were the second most commonly measured vitals.

No system yet exists that can perform all routine observations. For example, assessing

cognitive levels are difficult to assess using wearable sensors. In addition, there is yet

insufficient data to allow wearable sensors to replace routine ward observations.

The power consumption of the sensors is quite variable; the VisiMobile system battery life

was 12-14 hours whilst the Sensium vitals patch could be worn for up to 5 days. All sensors

reviewed in this study had a combination of FDA and or CE marking approvals. Due to the

nature of a google search there may be potential bias in the selection of sensors.

3.2 Future challenges

Future challenges of using sensor technology to measure vital signs is the need for sensors

and data transmission to be reliable, accurate, as well as to ensure that the collected patient

data is securely saved (64). Accuracy compares sensor readings to the current gold standard

of ward observations to see how close together the readings are. Whilst reliability ensures

that the sensor will calculate the correct vital signs all the time. For widespread wearable

sensor use they must be both accurate and reliable. The combination of battery life, size,

accuracy and reliability of a sensor in practice will determine its usage. There is a need to

reduce power consumption of the sensor electronics to extend the battery life. If the battery

life is poor and needs constant replacement this would cause a significant inconvenience for

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patients and healthcare staff alike, reducing user satisfaction and sensor uptake. Large heavy

sensors will inevitably reduce usability for end users. There are a few trials that have used

wearable sensors in a hospital setting but these have small numbers of patients (61)(65)(66).

Non-industry led larger trials are needed to ensure independent accuracy and reliability.

Once reliability and accuracy are proven more widespread sensor use can take place. There is

the potential for use in the community by patients with chronic medical conditions or high

risk patients at risk of deterioration such as the elderly. If there is suitable safe monitoring in

the home environment clinicians may be more likely to discharge patients sooner from

hospital. A centralised review of the data could be carried out by outreach services such as

hospital at home. The costs of outreach services, sensors and supporting software require

must be reviewed. There is little in the literature thus far on the economics of sensor use.

Some of the newer wearable sensors have the potential to be used at home. The monitoring of

vital signs at home has been shown to reduce resource utilisation and facilitate the

management of patients with heart failure in the community(67). A wearable sensor patch

worn by patients at home has been show to detect irregular heartbeats such as atrial

fibrillation(68). This can be reassuring for both patients and hospital staff. A typical example

of potential home sensor use is patients’ post-surgery, where complications may develop

several days after the patient has been discharged. At home monitoring of a patient’s vital

signs may alert staff at the hospital if the patient becomes unwell. Additionally, a patient with

normal observations can be more reassuring. At home monitoring of both HR and RR has

been performed previously(69). It is hoped in the future that other vital signs such as level of

cognition may be measured through wearable sensors allowing for more a complete vital

signs assessment that can be used to populate scoring systems such as NEWS.

As well as vital signs, it is possible that wearable sensors can measure other parameters such

as accelerometer data. These sensors may be useful to monitor patients with mobility

difficulties such as those with Parkinson’s disease and facilitate the titration of medication in

the late stages of disease(70). Unintentional falls can cause significant injury in elderly

patients. It may be possible to use non-invasive wireless sensors worn around the waist to

detect a fall occurrence and the location of the person with a fall(71).

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3.3 Sensor integration and training

However great the sensor technology is, it is reliant on the way it is delivered to the medical

team. It must be delivered to the clinicians in an easy user friendly format to encourage use.

Newer sensor technology enables digital alerts to be sent to hand held devices such as smart

phones. The smart phone technology is readily available and often used by many in their

everyday lives. In this way, it may be easily co-ordinated into the healthcare professional’s

lifestyle without the need for extensive training which occurs with alternative technology.

The network capacity in sensor technology must with stand the large amounts of data

generated both from the sensors and the communication device used to relay this information.

Whilst having FDA approval and CE marking is required sensor integration in a clinical

setting is often challenging. The sensors described in this review measure vital signs which

are routinely measured in a clinical setting. Other types of sensor may measure physiological

‘signals’ and these may be difficult to interpret in clinical practice. The workload after the

introduction of sensors may change due to the use of wearable sensors and digital alerting.

Clinicians may not have the time to measure large quantities of data on a daily basis and a

‘data deluge’ effect may occur(72). Therefore ‘Intelligent’ data processing systems are

required to support healthcare staff and allow for predictive monitoring of patients to identify

those patients most at risk (72). Successful implementation of wearable sensors may rely on

good integration with current clinical systems and processes. Currently many NHS trusts are

adopting electronic health records. Data from the wearable sensors should be easily

incorporated into electronic health records. In a clinical study of patients using wearable

sensors in real ward settings, patient wearing the ECG sensor found it too uncomfortable for

prolonged use. In addition, data dropout was a huge challenge due to infrastructure problems

(interruptions in Wi-Fi) and expired sensor batteries (72). Prior to widespread

implementation the hospital infrastructure should be developed enough to support the new

technology. It is not just the sensors themselves but the way that the data from the sensor is

received handled and processed in the most effective way. Strategies for interruptions in Wi-

Fi for example should be developed and readily available at the start of the project. Whilst it

may be useful to have alerting within centralised electronic health records these would

require the clinical staff to be at a work station a majority if the time. There must be sufficient

work stations in all clinical areas for healthcare staff to use as well as more portable systems

for when staff are not at their desk. This would include alerts being sent to smart phones and

16

personal device assistants.

There are currently many innovative technological tools flooding healthcare. There are

several strategies that have been suggested to improve successful implementation particularly

in the acute setting. These include; early input from staff on the new technology, appropriate

education, accessibility to the technology combined with early evaluation and feedback to

staff(73). The adoption of any new technologies relies on successful staff engagement. There

are several strategies in place that can help. One of the key factors in workforce engagement

methodology is to enable involvement in the decision making process(74). In addition all

roles within the hospital should be considered and adequate training provided(74).

Overall wearable sensors create an exciting opportunity to improve patient safety both in the

hospital and for users at home. An engaged healthcare work force is vital to ensuring their

success. Larger studies are required in a hospital setting and a good evidence base needed

before large scale roll out.

4. Five-year view

It is anticipated that wearable sensors are the future and will form an integral aspect of patient

care both in hospital and at home. As reliability and diagnostic accuracy are established and

enhanced, their use will become increasingly widespread. It is anticipated that over the next 5

years much of the focus of work will be in the hospital setting and follow-up and post-

discharge settings or for at risk patients within the community. Those new acutely unwell

patients admitted to the hospital might be the individuals that may benefit most from these

technologies in their early distribution. In addition, high risk groups of patients such as those

on immunosuppressive treatments may routinely have a wearable sensor as standard care.

The wearable sensor technologies will only be adopted if they are adequately supported by

evidence with appropriate and safe training of all staff and patients using these devices.

17

5. Key messages

5.1 Further larger scale studies are required in patients to review the effects of

wearable sensors.

5.2 Wearable sensor technology should have the ability to integrate into electronic

health records.

5.3 Ideally wearables should be able to measure multiple vital sign parameters

simultaneously.

5.4 Healthcare work force engagement in sensor technology is vital to ensuring their

success.

5.5 Sensors need to have a high diagnostic accuracy (and low number of false

positives) results to ensure healthcare engagement.

5.6 The cost-effectiveness of wearable sensors and potential costs savings should be

reviewed.

18

6 Expert Commentaries

6. 1 Key weaknesses in management so far

It is known that patients admitted to general wards are still falling through the safety nets.

Whilst there have been substantial improvements in patient safety; patient deterioration is

often missed and referrals and escalation to more intense levels (such as ITU) are late. Some

patient groups are typically presenting to hospital later and more unwell; the elderly

population is increasing and many patients have multiple co-morbidities. The acute admitting

wards such as the acute medical and surgical wards have a high turnover of patients with

altered physiology and rapid patient deterioration. This is coupled with increased pressures

on nursing staff and high numbers of temporary staff. These factors can make the

identification of early patient deterioration particularly challenging. Whilst the track and

trigger approach to care has been helpful, the actual way that the vital signs are measured has

not changed significantly over several decades and could benefit from fundamental

enhancement.

6.2 Potential Goal of the future

Continuous monitoring through wearable sensor technologies may help provide some of the

solutions to offer closer monitoring for patients. Wearable sensors have undergone a huge

recent growth. The newer sensors are smaller, lighter, wireless, have longer battery lives and

more processing power than their predecessors. The goal is for all patients that show signs of

deterioration to be identified early so they can be given treatment sooner. This may help to

prevent some of the adverse outcomes associated with delayed identification. Whilst the

sensors in this paper have focused on the traditional vital signs it may be that newer sensors

which measure arterial pressure and flow waveforms may be the future.

6.3 Ultimate goals

The goal is to have a discrete wearable sensor that is well tolerated by all patients and staff

which correctly identifies acute deteriorating patients in real time. The sensor ideally should

be able to measure all vital signs. Developing a sensor that can measure real time blood

pressure and level of cognition is a real challenge for the future. The first goal is to ensure

19

that the sensors are reliable by independent researchers in large-scale high quality trials with

appropriate clinical endpoints.

6.4 Expected Challenges

The expected challenges are several fold. The first are the sensors themselves; they may need

to be smaller still with longer battery lives, with good reliability and accuracy. They also

must have great diagnostic accuracy to reduce the number of false alerts and the potential for

alert fatigue, and should, ideally measure all vital signs including blood pressure and level of

cognition so track and trigger scores can be calculated. The integration of them into the

existing medical health record is essential for long-term uptake. All sensors should be used as

an adjunct to care and not limit the staff and patient interaction. A proactive risk assessment

for the implementation of wearable sensors has been suggested(75). A carefully designed

implantation will help ensure successful integration into clinical workflows preventing

problems and potential harm to patients(75). An evaluation would be performed focusing on

the normal procedures and actions required for sensor use. In this way potential challenges

hope to be identified and addressed (75). A proactive assessment can help address which

patients will wear the wearable sensors and which clinical areas may require them the most

(75). Lastly, the economic costs of the sensors must be reviewed and should be cost effective

prior to wide scale roll out.

6.5 Areas of interest

Ultimately these sensors with provide a whole new archetype of real-time continuous patient

physiological assessment; these will link into the digital and big-data analytical platforms for

the next-generation of healthcare where they will act as a catalyst for even better early

diagnostics, preventions and cures.

20

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Table 1.: Is a summary of each wearable sensor and the vital signs measured.

28

Device Heart

Rate

Heart Rate

Variability/ RR

Interval

Single Lead

Electrocardiography

Respiratory

Rate

Skin

Temperature

Bed Motion Body

Posture

Fall

Detection

Activity Oxygen

Saturations

Non-invasive

Blood

Pressure

Current Monitoring

Devices

Yes Yes Yes Yes

Early Sense

monitoring (26)

Yes Yes Yes

Vital Connect (27) Yes Yes Yes Yes Yes Yes Yes Yes

VisiMobile System

(28)

Yes Yes Yes Yes Yes Yes

Sensium Vitals (29) Yes Yes Yes

Philips Bio

Sensor (30)

Yes Yes Yes Yes Yes Yes Yes Yes

Isansys Life Touch

Sensor (31)

Yes Yes Yes

Zephyr Wearable

Sensor (32)

Yes Yes Yes Yes Yes Yes

Amon wearable

Sensor (33)

Yes Yes, measured 3

times a day or on

request

Yes Yes Yes Yes, measured

3 times a day

or on request

29

Table 2.: A description of each wearable sensor.

Device Description of sensor Duration

/ sensor use

Disposable Tested on Patients

Approval EHR Integration Mechanisms of alerting

Early Sense monitoring (26)

Sensor placed under patient’s mattress N/A No Yes FDA Approved + CE marked

No Centralised

Vital Connect (27) Wireless adhesive sensor placed on the chest 4 days Patch disposable, Sensor not disposable

Yes FDA Approved + CE marked

Yes Centralised & Mobile Device

VisiMobile System (28)

Sensor worn around the wrist to measure BP, a chest sensor to measure HR, RR and skin temperature, a thumb sensor for oxygen saturation

Battery Life 12-14 hours

No Yes FDA Approved + CE marked

Yes Centralised & Mobile Device

Sensium Vitals (29) Adhesive sensor on the chest attached via ECG electrodes 5 days Yes Yes FDA Approved + CE marked

Yes Centralised & Mobile Device

Philips Bio Sensor (30) Self-adhesive sensor worn on the chest 4 days Yes Yes FDA Approved + CE marked

Yes Centralised & Mobile Device

Isansys Life Touch Sensor (31)

Adhesive sensor on the chest attached via ECG electrodes 4-6 days Yes Yes FDA Approved + CE marked

Yes Centralised & Mobile Device

Zephyr Wearable Sensor (32)

Sensor worn in a belt, typically around the chest 24 hours No Yes FDA Approved + CE marked

Unknown Centralised

Amon wearable Sensor (33)

Wrist worn sensor Variable depending on power consumption

No Yes FDA Approved + CE marked

Yes Centralised

BP = Blood pressure, HR = Heart Rate, RR = Respiratory Rate, ECG = Electrocardiography, CE = Conformity European (CE), FDA = Food and Drug Administration

30