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Technology Assessment: Early Sense for Monitoring Vital Signs in Hospitalized Patients

In: VA Evidence Synthesis Program Evidence Briefs [Internet]. Washington (DC): Department of Veterans Affairs (US); 2011–.
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Technology Assessment: Early Sense for Monitoring Vital Signs in Hospitalized Patients

Mark Helfand et al.
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The EarlySense Monitoring System has been developed to provide continuous monitoring of heart rate (HR), respiration rate (RR), and bed motion for patients in medical/surgical, oncology, orthopedics, isolation, post-partum, skilled nursing facilities, long term acute care, and rehabilitation settings. The VA Office of the Deputy Under Secretary for Health for Policy and Services (10P) requested an independent evaluation from the VA Evidence-based Synthesis Program (ESP) to help guide the field as to EarlySense's monitoring capabilities, benefits and harms, impact on nurse staffing, and the overall effectiveness of the system. The USH seeks to better understand how this technology is being used in similar hospital settings in the US, what kinds of VA patients would be best served by it, and whether there are particular types of units or distribution of beds within those units for which this technology would be best suited. The ESP review team searched for and critically appraised relevant studies and systematic reviews and interviewed key informants, including VA nurses who have experience with the EarlySense system. In addition, we requested a Product Brief from the ECRI Institute, which is intended to serve as a companion to our report.

WHAT IS EARLYSENSE?: EarlySense is a low-acuity continuous monitor. As shown in the figure below, EarlySense consists of (1) a sensor that is placed under the patient's mattress, (2) a bedside monitor, (3) a central display station, and (4) proprietary analytic software that runs on a PC (not shown). The system is based on a piezoelectric sensor, sensitive to applied mechanical strains. The system differs from other patient monitoring systems in that it is a contactless device which eliminates the use of telemetry leads. While the patient is lying flat in bed, the system continuously records heart rate (HR), respiration rate (RR), and bed motion. Low-acuity systems do not provide cardiac waveforms (rhythm strips). They can display oxygen saturation if that is monitored using a separate system. EarlySense does not interface with the electronic medical record. Every 0.5 seconds, an updated HR reading is established based on analysis of the heart pulse pattern for the last 8 seconds, and an updated RR reading based on analysis of the last 1 minute of the respiration pattern. The system provides alerts if any of the parameters exceed predefined thresholds, which can be customized. Alerts can also be sent directly to nurses' mobile phones or pagers. EarlySense also provides bed exit alerts for patients at risk of falls, and includes a timer to remind nurses to turn patients (to help prevent the development of pressure ulcers). EarlySense can monitor up to 40 beds at one time. EarlySense received FDA 510(K) clearance as a Class II device based on demonstration that it was equivalent to devices that are used to monitor vital signs in patients undergoing sleep studies and in ambulatory patients. FDA clearance permits marketing in the US but does not mean that the FDA has found the device to have clinical efficacy. Rather, clearance means that EarlySense is equivalent to older devices in its ability to measure respiration rate and heart rate.

PREDICTING CLINICAL DETERIORATION: Research conducted in the 1990s suggested that, among patients on general hospital wards, delays in treatment can lead to clinical deterioration and changes in vital signs and mental function that precede deterioration are often missed.. These observations led to the development of “rapid response teams” (RRTs) that are activated when a patient fulfills predefined criteria. The criteria are based on vital signs checks and assessment of mental status. Some systems also include decreased urinary output, oxygen saturation, difficulty breathing, increase in supplemental oxygen dose, and subjective concern detected by the nurse at the bedside. The Early Warning Scoring Systems (EWS), Modified EWS (MEWS), and the National EWS (NEWS) are commonly used sets of criteria. These systems are widely used in VA. In addition to indicating when to call the RRT, the systems also incorporate recommendations for the frequency of bedside assessment. In 2014, a systematic review from the VA Evidence-based Synthesis Program found that EWS/NEWS have strong predictive value for cardiac arrest and patient death and their use increases RRT calls, but the impact of EWS/NEWS on preventing patient mortality, transfers to the ICU, or length of hospital stay is uncertain. The ability to predict which patients are most likely to deteriorate has not been established. DeVita et al (2010) argue that while analyses of cardiac arrests and deaths indicate that most are preceded by vital signs lying outside normal ranges, most studies are retrospective, and because the total number of clinical deteriorations has not been determined, the ability of physiological abnormalities to predict risk of a serious event is unknown. Thus, in many circumstances, clinicians cannot predict which patients are most likely to deteriorate. In addition, lack of data prevents any estimate of how often severe deterioration leads to clinically adverse outcomes. In a study examining the association of delays in transfer to ICU, morbidity, and mortality, 11 physiological and laboratory markers of clinical instability were observed as having high sensitivity (88%) in identifying patients who were transferred to the ICU. These markers, however, lacked specificity (13%) and had very low positive predictive value (8%). This study suggests hospital staff cannot rely on markers alone to identify patients most at risk of deterioration without using considerable resources and incurring a high cost-benefit ratio. Because of the limitations in predicting patients at highest risk of a serious event, the ability of intermittent or continuous monitoring systems to detect severe physiological abnormalities in order to provide a true estimate of risk or to determine optimum response triggering values has not been fully established.,,,, Qualitative research suggests that nurses' worry or concern often precedes deterioration in vital signs, suggesting that better characterization of “concern” might lead to detection of deterioration at an early stage when intervention to prevent adverse events may be more effective.

RATIONALE FOR CONTINUOUS VIAL SIGN MONITORING: The rationale for continuous vital sign monitoring is that suboptimal vital sign monitoring prior to an RRT referral may contribute to suboptimal patient outcomes. A more specific rationale for the EarlySense monitoring system is that alerts based on vital sign trends rather than just threshold parameters may add predictive ability to that of MEWS criteria and lead to earlier, more effective RRT calls. On busy wards, the frequency and accuracy of vital sign checks may be insufficient to detect deterioration, especially at night. Factors that may contribute to suboptimal patient monitoring include adverse working conditions, heavy workloads, lack of education and training, lack of experience and failure to recognize clinical urgency, errors in calculating EWS, communication deficits between doctors and nurses, cultural influences and intra-professional hierarchies, and lack of compliance.

WHAT ARE THE ALTERNATIVES TO EARLYSENSE?: Standard nurse-led monitoring in conjunction with EWS or MEWS is the most commonly used alternative to continuous vital sign monitoring. Other low-acuity systems are also alternatives to EarlySense. They are similar to EarlySense but require leads attached to the patient, and some require cables to connect with the display. All of these systems capture respiratory rate and heart rate, and some capture blood pressure, oxygen saturation, temperature, and ECG. Most contribute vital sign data directly to the electronic medical record. The market for low-acuity monitoring systems is growing rapidly, leading to intense technological development. Bedside monitors have sensors that are attached to the patient and connected via cables or leads to a display panel near the patient's bed and on remote displays. Manufacturers include Covidien, Masimo, Welch Allyn, and Zoe Medical. A major assumption underlying EarlySense is that these systems may be less safe than a contact-free low-acuity monitoring system because of cable management issues. Wearable monitors have sensors that attach to a small, lightweight display unit that enables monitoring even when the patient is out of bed. It is not known to what extent the need for contacts is a disadvantage for nursing staff or for patients. Few if any data are available about the use of these systems on general medical-surgical wards. For example, a search by ECRI found no clinical trials of GE Carescape or Nihon Kohden BSM-6000 bedside monitors. Philips and Sotera also manufacture wearable monitor systems. Medium-acuity telemetry systems are widely employed in the general medical and surgical wards. They are more expensive than EarlySense. An example is Intellivue (Phillips). This system uses ECG leads (wires) attached to the patient and to a small mobile device that fits into the patient's pocket. It records cardiac waveforms so that heart rate and rhythm are easily visualized. More expensive (and bulkier) models also monitor respiratory rate via the telemetry leads. Like EarlySense, these systems provide alerts if any of the parameters exceed predefined thresholds, which can be customized. Unlike EarlySense, the wearable sensors can monitor the patient in or out of bed, enabling continuous distant ECG monitoring. Continuous output can be viewed at the bedside and from a central monitoring system and text alerts are provided to nurses on mobile devices. The systems can analyze the ECG output to diagnose many cardiac arrhythmias. They are often used in conjunction with pulse oximetry (oxygen saturation monitoring) and, especially in post-operative patients, capnography.

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