Feasibility of Remote Digital Monitoring Using Wireless Bluetooth Monitors, the Smart Angel™ App and an Original Web Platform for Patients Following Outpatient Surgery

A Prospective Observational Pilot Study

Thierry Chevallier; Gautier Buzancais; Bob-Valéry Occean; Pierre Rataboul; Christophe Boisson; Natacha Simon; Ariane Lannelongue; Noémie Chaniaud; Yann Gricourt; Jean-Yves Lefrant; Philippe Cuvillon


BMC Anesthesiol. 2020;20(259) 

In This Article


This was a single-cohort, open, prospective trial conducted at a French University Hospital (Hôpital Carémeau, CHU Nîmes, France). In accordance with the current French law and the Declaration of Helsinki, this study was approved by the institutional human investigation committee (Comité de Protection des Personnes, Sud Est V, Grenoble, France: 2017, A02790–53) and registered on ClinicalTrials.gov (NCT03464721; March 8, 2018) before starting.[15]

Written informed consent was obtained from all participants before inclusion.

Inclusion Criteria

All patients > 18 years (ASA 1–3) scheduled for intermediate or major ambulatory surgery, with the ability to understand spoken and written French, were eligible and approached by the surgeon or the investigators. Surgeries were as follows: orthopaedic (shoulder repair, knee ligamentoplasty, hallux), abdominal (cholecystectomy, hernia) or gynaecological (hysterectomy, mastectomy).

Exclusion Criteria Were

Age > 80 years, refusal to participate, ASA physical status > 3, emergency and inpatient surgery, psychiatric disorder.

Once included, patients were excluded if they failed to use the remote technology. The tablet and wireless Bluetooth monitor were presented by a nurse with the investigators and tested by the patient before surgery. Their ability to perform remote monitoring involved switching the tablet on, using the login, completing the self-report questionnaire, adapting the monitor (for MAP, HR and SpO2) and starting the monitor using the app (see above). Connection to a 4G network at home was also required.


  • Routine ambulatory follow-up
    After surgery and before discharge from the ambulatory centre, patients received standard information regarding postoperative recovery and all the necessary information on postoperative care at home (analgesia, changes of dressing etc.). They were instructed to contact a 24-h telephone helpline should they have any questions or concerns outside office hours. Participants were advised to contact the local hospital's emergency department should any emergency care be required.

  • Smart Angel™ monitoring:
    The Smart Angel™ device was handed over to the patient who took the first measurements in presence of the team to ensure that the system was properly working and understood. Functionalities of the Smart Angel™ system were carefully explained and clear instructions for use were given by the research nurse and investigators, including how to move from question to question, how to enter an answer, and how to use the monitors. The Smart Angel™ system is a digital application using remote technology solutions and includes:

  1. a web administration centre which collects, in real time, all the data for each patient transmitted by remote technology. These data are exported via the web (4G collection) to a secure server (Adista™, France). All data are then filtered and presented on a dashboard which summarizes them so that the nurses and/or physicians can focus on any warning signs in the patient. Each patient is depicted on the dashboard in the form of a coloured square (green: in the normal range = no problem; yellow: at the limit of range = but no sign of severity, red: warning signs = emergency action required). On the dashboard the investigators can see all patients enrolled in the study, their assessment and flags plus all the variables for each patient in a specific new window (see Figure 1a, b, c).

  2. Remote physical parameters (HR, SpO2, MAP) with ranges (min., max.) for normal values were defined before starting the study and included in the algorithm (Figure 1c). In the event of a specific pathology or treatment (e.g. patient on beta-blockers), ranges can be adapted to specific patient characteristics and/or treatment.

  3. The tablet and app technology uses a tablet (Samsung™, Korea) integrating the software (EvolucareLabs, France) which generates health questionnaires for the patient to answer with scores for pain relief, quality of recovery, nausea and vomiting (see above). This tablet communicates with a connected monitor at the patient's home to perform discontinuous measurement. The app assesses the self-report questionnaires and the wireless Bluetooth monitors record the physiological measurements (heart rate, mean arterial blood pressure and blood oxygen saturation). The monitors used were: a wireless pulse oximeter clipped to the finger (iHeathlabs, USA) and a blood pressure monitor on the wrist (iHeathlabs, USA). When the patient is ready with the monitor, the software triggers the monitors and records the values. The patient can instantly see the tablet screen. Measurement data for each item is depicted with normal and abnormal ranges. All these data are then exported via the web (4G collection) to a secure server (Adista™, France).

  • Follow-up:
    From the day of surgery to postoperative Day 5, three times a day (morning, noon and evening), the application prompts the patient to complete the health questionnaire and follow-up with the monitors. Seven variables are recorded for each assessment:

  1. Blood oxygen level (SpO2, %)

  2. Heart rate (HR, min− 1)

  3. Mean arterial blood pressure (MAP, mmHg)

  4. Vomiting (yes/no)

  5. Nausea (yes/no)

  6. Pain score (scored on an 11-point numerical pain scale; 0 = no pain, 10 = worst pain)

  7. Quality recovery score (scored on an 11-point numerical rating scale; 0 = poor condition, 10 = excellent quality of postoperative recovery)

At the end of our 5-day study, patient monitoring was stopped and the equipment was returned to the hospital by express delivery.

Outcomes and Data Collection

Surgical, anaesthetic and patient characteristics data were collected by the research nurse and investigators. Seven variables (pain, quality of recovery, nausea, vomiting, HR, MAP and SpO2) were recorded by the app for all patients before their discharge from the centre and then three times a day from Day 1 to Day 5.

In addition, the number of time-matched variables simultaneously recorded by the patients on a paper form was returned to the centre at end of the study.

On Day 5, the patient had to answer a 10-item questionnaire with five response options ranging from "Strongly agree" to "Strongly disagree" (total: 1–100 points) and the result was converted into a System Usability Scale (SUS) based on a Lickert scale. The 10 items were:

  • I think I will use the SMART ANGEL device frequently.

  • I think the SMART ANGEL is unnecessarily complex.

  • I find the SMART ANGEL easy-to-use.

  • I think I will have to call technical support to be able to use this service.

  • I find that the SMART ANGEL features are well integrated.

  • I find that there are far too many inconsistencies in its use.

  • I think most people will learn to use the SMART ANGEL device very quickly.

  • I find the SMART ANGEL really heavy to use.

  • I felt very confident using the SMART ANGEL.

  • I had to learn a lot of things before I could use SMART ANGEL.


The primary objective of this pilot study was to compare the amount of data recorded on the website using the app with the paper form. Secondary objectives were to assess patient safety (medical rescue, readmission, and surgical complications) and the usability of this medical device.

Sample-size Calculation

As this was a pilot study, we had planned to test the system on 30 patients with no justification regarding sample-size. Published data has shown that 12 patients are a minimum requirement for pilot studies.[16]

Statistical Analysis

Statistical analysis was conducted using SAS (9.4, SAS Inc., Cary NC).

Statistical results were expressed with mean (SD) or median with interquartiles [IQ] according to distribution. The numbers (with percentages, %) were given for categorical variables. The main judgment criterion was analysed in relation to a referential volume of theoretical information based on the following calculation: number of patients (n = 30) x number of data collection periods (i.e. one on Day 0 and 3 per day from Day 1 to Day 5, i.e. 16 in total) x number of parameters measured i.e. physiological parameters (heart rate, blood pressure, oxygen saturation and self-evaluation parameters (pain score, nausea, vomiting, comfort), i.e. 7 in total. Thus, the maximum reference volume of theoretical information is 30x16x7 = 3360. In addition, a referential volume of theoretical information was calculated per day and by parameter.

Comparisons of continuous variables between the app and paper questionnaire were made using a Student's T-test or Wilcoxon-Mann-Whitney test according to distribution. Categorical variables were compared between groups (paper vs app data) by X2 or Fisher's exact test. All P values were two-tailed and a P-value of less than 0.05 was required to exclude the null hypothesis. Analysis of secondary outcomes was descriptive.