The study design is a prospective method-comparison study of patients requiring invasive arterial blood pressure monitoring for major surgery to determine accuracy and precision between systolic and diastolic BP when measured by standard invasive arterial monitoring compared to the Vitalstream™ device. This study was approved by the University's Institutional Review Board (IRB-P00037138) and written informed consent was obtained from all subjects, a legal surrogate, the parents, or legal guardians for minor subjects. The trial was registered prior to patient enrollment at clinicaltrials.gov (NCT04817137), Principal investigator: Karen Boretsky MD, https://clinicaltrials.gov/ct2/show/NCT04817137, First posted date:26/03/2021. For clarification, Vitalstream information was not used to make clinical decisions and did not replace any monitor used for standard care.
Inclusion criteria were patients ages 2–17 years old with planned invasive arterial blood pressure monitoring as part of the anesthesia care plan at the Boston Children’s Hospital Longwood campus. Exclusion criteria were patients with vascular or congenital heart disease known to affect large and small arteries, and patient or guardian refusal.
The principal investigator (PI), co-investigators and/or clinical research coordinators associated with the study identified potential patients from pre-operative schedules. Patients and their guardians were approached for consent, and participation was voluntary.
Demographic data collected: Patient age, weight, surgical procedure, co-morbidities, ASA status, and gender.
Non-invasive oscillometric BPs were performed every 5 minutes before general anesthesia induction and arterial line insertion. The attending anesthesiologist inserted an arterial catheter percutaneously and connected it to a disposable pressure transducer with standard low-compliant tubing. The transducer was placed at heart level and zeroed to ambient pressure. The transducer data was automatically digitized, processed, and collected using the Datex-Ohmeda S/5 Collect system (Datex-Ohmeda Division, Instrumentarium Corporation, Helsinki, Finland). The system provides systolic and diastolic blood pressures with 1-minute resolution, averaged over 10s intervals.
The non-invasive Vitalstream™ was placed on the patient’s finger as described and the device’s self-calibration procedure, which takes about 25 seconds, was initiated. The device scanned the finger cuff’s coupling pressure from 0 to 250 mmHg while collecting the pressure-modulated arterial pressure pulse signal. Systolic and diastolic blood pressures were calculated from the processed signal envelope at the end of the pressure scan. After that, the device operated in the continuous tracking mode with the finger cuff pressure collecting pulse data at a fixed baseline cuff pressure between 20 and 45 mmHg. The coupling pressure for continuous operation was determined as part of the self-calibration procedure. A minimum of 30 consecutive, uninterrupted minutes of data was collected and saved in digital format for analysis.
Data inclusion:
The invasive arterial monitoring data was inspected by the PI, and apparent measurement artifacts were excluded. A custom signal/noise factor was similarly used to identify and exclude Vitalstream™ data with poor quality. The factor is based on the standard ratio of the variances of the physiological signal band to the noise band and obtained using Fourier spectral analysis over an 8s window with 1s overlap. The frequency range of the band associated with the physiological signal is set to 1–10 Hz, based on data by the authors and results by others, while the noise band is automatically set to the 100–250 Hz frequency range, which is subject to ambient noise but contains no signal relevant to the base band phenomena of the arterial pressure pulse or its propagation characteristics. Data sections with an SNF below 80 were identified and excluded.
All comparisons between Vitalstream data and arterial catheter data were post-processed. Time stamps in the respective systems were used to align timing. For each arterial catheter data point, with 1-minute resolution, the beat-by-beat Vitalstream readings were averaged over a time window of 20 seconds, bracketing the arterial catheter reading.
Statistical analysis:
Statistical analysis compared the accuracy of the Vitalstream™ systole and diastole values with the corresponding arterial catheter data, as well as the VitalstreamTM’s trending ability for both blood pressure components relative to the reference. The analysis was performed using the MATLAB software package (Natick, USA).
Accuracy (bias) and precision against the reference measurements were assessed via Bland–Altman analyses. In addition, standard concordance analysis of the trend values (with a 15% exclusion zone) was assessed using 4-Quadrant plots in which differences in successive measurements for each device were plotted to compare the agreement in magnitude and direction of values.7 The Bland–Altman analyses took repeated measurements per subject into account, as required by the standard ISO 81060–3:2022.8 Cohort size of 31 was driven by the ANSI/AAMI/ ISO 81060- 2:2013 standard’s7 required lower limit of 20 children less than 17 years of age when an invasive arterial line is used for comparison, as well as the 81060-3 requirements that link the number of repeated measurements per patient with the number of required patients based on an estimated intra-class correlation coefficient (Icc) that compares the between-subject and within-subject variances. Assuming conservatively an Icc in the range of 0.6 to 0.7, the corresponding required pair of (repeated measurements per patient/number of patients) is 29/30. 7