Evidence review

Clinical and technical evidence

Regulatory bodies

A search of the Medicines and Healthcare Products Regulatory Agency website revealed that no manufacturer Field Safety Notices or Medical Device Alerts for this device. No reports of adverse events were identified from a search of the US Food and Drug Administration (FDA) database: Manufacturer and User Device Facility Experience (MAUDE).

Clinical evidence

Two fully published studies on the Visensia system and 4 studies that were available only as abstracts are summarised in this briefing. The fully published studies were 1 prospective, single‑centre, before‑and‑after study (Hravnak et al. 2011) and 1 randomised controlled trial that included a retrospective assessment of the Visensia alerts (Watkinson et al. 2006).

Two further studies (Tarassenko et al. 2005; Orphanidou et al. 2009) that did not report patient outcomes were excluded from further assessment, as was 1 paper (Hravnak et al. 2008) that was a phase I report of the Hravnak et al. (2011) study. Four other abstracts which presented overlapping results of the Hravnak (2008) and Hravnak et al. (2011) studies were also excluded.

The Hravnak et al. (2011) study (presented in tables 1 and 2) was a prospective, single‑centre, before‑and‑after study based in the US. It used Visensia to analyse data for 4 vital signs: heart rate, respiratory rate, blood pressure and peripheral oxygen saturation. The study assessed whether the VSI (calculated from data for the 4 vital signs) correlated with single‑parameter cardio‑respiratory instability concern criteria. Specifically, these criteria were a heart rate of <40 or >140 beats/min, a respiratory rate of <8 or >36 breaths/min, systolic blood pressure of <80 or >200 mm Hg, diastolic blood pressure of >110 mm Hg, and peripheral oxygen saturation of <85%. The study also assessed whether nurse response to VSI alerts were associated with a reduction in patient instability. The study had 3 sequential stages. In stage 1 (8 weeks), patients had continuous single‑channel monitoring and standard care; the VSI was recorded but not displayed. In stage 2 (16 weeks), the VSI was displayed on the bedside and central monitors and staff were educated on using the software. In stage 3 (8 weeks), staff responded to VSI alerts using a pre‑defined process developed for this purpose.

In order to evaluate the impact of VSI alerts, the individual vital signs data were analysed to determine the total time when variables were within the normal physiological range (no instability), and the incidence and duration of any episodes in which the cardio‑respiratory instability concern criteria were exceeded for any reason (defined as an instability episode). These instability episodes were further categorised as instability episodes that were physiologically plausible (that is, not a result of minimal exceptions to the concern criteria) and full instability episodes, which were serious, persistent and generally displayed abnormalities across multiple vital signs.

Compared with stage 1, stage 3 (in which staff responded to VSI alerts) showed a statistically significant reduction in the average duration of instability episodes per admission, average duration of physiologically plausible instability episodes per admission, and average number of full instability episodes per admission. There was no statistically significant difference in the other reported instability categories.

The randomised controlled trial by Watkinson et al. (2006; presented in table 3) assessed continuous electronic monitoring of vital signs for reducing the frequency of adverse events in high‑risk patients outside of critical care areas compared with standard ward care. BioSign (the previous name for Visensia) was used to record the vital signs of patients in the continuous electronic monitoring. The VSI of the patients in the continuous electronic monitoring group was assessed retrospectively by 2 senior clinicians once patients had completed the study. The software was not used to alert nurses.

Technical problems with the BioSign software prevented recording for the whole monitoring period in 33 (17%) patients. Out of 690 transitions from normal to abnormal physiological activity, 652 were considered true episodes. The development of an abnormal physiological episode into a major event could be predicted using BioSign's recording of vital signs, with a sensitivity of 63% and specificity 52%.

The abstracts by Sen et al. (2009 and 2010a) reported a retrospective analysis of trauma registry data. The registry included 117 patients admitted to a level 1 trauma centre over 6 months. Vital sign data were collected both pre‑hospital and from the emergency department and the VSI calculated retrospectively. The study found that, pre‑hospital, a VSI over 3 was predictive of patients who needed life‑saving interventions (odds ratio 1.8, 95% confidence interval [CI] 1.1–4.2). The VSI had statistically significant likelihood ratios for life‑saving interventions including endotracheal intubation, blood transfusion, CPR and use of resuscitation drugs.

The abstract by Sen et al. (2010b) reported a retrospective analysis of trauma registry data on 297 patients admitted to a level 1 trauma centre over 6 months. Pre‑hospital VSI data were also calculated. The study found that a pre‑hospital VSI of over 3 was predictive of patients who needed life‑saving interventions (odds ratio 1.8, 95% CI 1.3–3.4; p<0.05).

The abstract by Choukalas et al. (2011) reported a retrospective cohort study in a mixed medical‑surgical‑cardiac ICU in an urban tertiary‑care hospital. It included 20 consecutive patients that had a cardiac arrest needing advanced cardiac life support level (ACLS) care while in hospital. VSI data were calculated at 5‑minute intervals for the 20 hours before cardiac arrest. Six of the patients did not need ACLS care. For the remaining 14, the mean lead‑time of the VSI alert before cardiac arrest was 15.1 hours. Nurses documented patient instability an average of 9.3 hours before cardiac arrest.

The abstract by Choukalas et al. (2015) reported a retrospective controlled cohort study in an 18‑bed ICU in an urban hospital, including 61 patients who had a cardiac arrest while in hospital and 729 controls. VSI data were calculated at 1‑minute intervals for the 24 hours before cardiac arrest. The study found that there was no difference in VSI between the 2 groups at the beginning of the observation period, but that it became significantly higher for patients with cardiac arrest starting from 10 hours prior (p<0.05). The study used a version of the software without preset alert levels and which is not currently commercially available.

Recent and ongoing studies

No ongoing or in‑development trials on the Visensia physiological monitoring system for detection of early clinical deterioration were identified.

Costs and resource consequences

No published evidence on resource consequences was identified. If the Visensia system allowed earlier intervention for deteriorating vital signs, then resources on treatment of complications could be saved. If it were shown to be more sensitive than other alert systems, Visensia could also provide efficiencies to the NHS by reducing the number of false alarms that take up nurses' time. Visensia is used alongside existing methods of vital sign monitoring.

Strengths and limitations of the evidence

Only 2 fully published studies were identified. One (Hravnak et al. 2011) was a prospective, single‑centre, before‑and‑after study and the other (Watkinson et al. 2006) was a retrospective assessment embedded in a randomised controlled trial.

The prospective, single‑centre, before‑and‑after study was based in the USA. All potentially unstable patients who were transferred from ICUs to step‑down units for further care were included in the study. The patient population consisted of consecutive patients recruited at different time periods for the 2 phases being compared, and were not randomised. Two physicians blinded to the phases of the study independently scored data for phase 1 and phase 3, limiting potential bias. The results may have been confounded by changes in ward care implemented during phase 2 of the study (such as additional training for nurses and physicians). The improvements attributed to Visensia may also have been due to improvements in patient care introduced during phase 2 of the study.

The study by Watkinson et al. (2006) used Visensia to record vital signs but did not use the VSI to advise patient care during the study. For this reason, the results are limited to a retrospective assessment of the logged data and identification of true abnormal physiological activity. From this study it is not clear if the use of Visensia could have led to a reduction in major events.

The 4 studies published as abstracts provide limited information in terms of study setting, methods, characteristics and results. The information is insufficient to allow judgment of the quality of the evidence in these abstracts.