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Tracking Blood Pressure Changes in Anesthetized Patients: the Optical Blood Pressure Monitoring (oBPM) Technology

Authors:

Abstract

Routine monitoring of blood pressure during general anesthesia relies on intermittent measurements with a non-invasive brachial cuff inflated every two to five minutes. While all these patients are equipped by a fingertip pulse oximeter, the acquired optical signals currently only provide SpO2 estimates. Our running clinical trial (NCT02651558) presents the first-ever demonstration that the optical signals acquired by a fingertip pulse oximeter can also be exploited to continuously detect blood pressure changes. Results from the first 8 enrolled patients show that the Optical Blood Pressure Monitoring (oBPM) algorithms can detect rapid blood pressure changes occurring during anesthesia with 94% of accuracy. The proposed solution is expected to allow major improvements in the safety of anesthetized patient's, allowing early detection of hemodynamic changes occurring in between two routine blood pressure measurements performed with brachial cuffs.
Abstract Routine monitoring of blood pressure during
general anesthesia relies on intermittent measurements with a
non-invasive brachial cuff inflated every two to five minutes.
While all these patients are equipped by a fingertip pulse
oximeter, the acquired optical signals currently only provide
SpO2 estimates. Our running clinical trial (NCT02651558)
presents the first-ever demonstration that the optical signals
acquired by a fingertip pulse oximeter can also be exploited to
continuously detect blood pressure changes. Results from the
first 8 enrolled patients show that the Optical Blood Pressure
Monitoring (oBPM) algorithms can detect rapid blood pressure
changes occurring during anesthesia with 94% of accuracy. The
proposed solution is expected to allow major improvements in
the safety of anesthetized patient’s, allowing early detection of
hemodynamic changes occurring in between two routine blood
pressure measurements performed with brachial cuffs.
I. MATERIALS AND METHODS
Data from a running clinical trial (NCT02651558) was
analyzed [1]. The dataset included continuous optical signals
from a commercial fingertip pulse oximeter (PPG), and
continuous blood pressure measurements from an arterial
catheter inserted at the radial artery from eight patients
(Fig. 1). The goal of the analysis was to demonstrate the
performance of the oBPM algorithms [2] in detecting BP
changes induced by vasoactive anesthetic agents, compared to
naïve predictions. Naïve predictions included BP estimates
derived from HR changes (PPG-HR), and BP estimates
derived from changes in PPG signal amplitude (PPG-AMP).
Intermittent
measurements
oBPMTM
algorithm
Time (min)
SYS
(mmHg)
100
200
Figure 1. Detection of blood pressure changes during anesthesia via the
re-analysis of pulse oximeter signals. The oBPM algorithms extrapolate
intermitent measurements performed by automated oscillometric cuffs.
J. Solà, YM. Proença, F. Braun, C. Verjus, and M. Bertschi are with the
CSEM S.A. - Centre Suisse d’Electronique et de Microtechnique, Neuchâtel,
Switzerland (e-mail: Josep.Sola@csem.ch).
Y. Ghamri, N. Pierrel, and P. Schoettker with CHUV Centre Hospitalier
Universitaire Vaudois, CH-1011 Lausanne, Switzerland (email:
Patrick.Schoettker@chuv.ch)
Figure 2. Performance of oBPM algorithms to detect BP changes from
pulse oximeter signals, compared to measured invasive systolic changes.
Performance was evaluated in terms of concordance rate (the
percentage of correctly-detected changes in BP trends), ΔBP
Error (the error in predicting the amount of such BP changes),
and Accuracy ±Δ20mmHg (the accuracy in detecting
threatening changes of more than 20mmHg)
II. RESULTS
Fig. 2 illustrates a four quadrant plot analysis of the reference
and estimated blood pressure changes via the oBPM
algorithms. Table 1 compares the performance of the oBPM
algorithm and the naïve PPG predictions (N=36).
TABLE I. PERFORMANCE OF THE OBPM ALGORITHMS
BP algorithm
Performances
Concordance
Rate
ΔBP error
(mmHg)
Accuracy
Δ20mmHg
oBPM algorithm
97%
0.3 ± 7.7
94%
Benchmark 1:
PPG-HR prediction
56%
6 ± 22
58%
Benchmark 2:
PPG-AMP prediction
47%
3 ± 28
50%
REFERENCES
[1] J. Solà, “Continuous non-invasive monitoring of blood pressure in the
operating room: a cuffless optical technology at the fingertip”,
Proceedings BMT2016, Basel, Switzerland, 2016, doi:
10.1515/cdbme-2016-0060
[2] M. Proença, "Method, apparatus and computer program for
determining a blood pressure value”, WO Patent WO/2016/138965
Tracking Blood Pressure Changes in Anesthetized Patients:
the Optical Blood Pressure Monitoring (oBPM) Technology
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Conference Paper
Full-text available
Routine monitoring of blood pressure during general anaesthesia relies on intermittent measurements with a non-invasive brachial cuff every five minutes. This manuscript provides first experimental evidence that a physiology-based pulse wave analysis algorithm applied to optical data (as provided by a standard fingertip pulse oximeter) is capable of accurately estimating blood pressure changes in-between cuff readings. Combined with the routine use of oscillometric cuffs, the presented novel approach is a candidate technology to increase patient safety by providing beat-to-beat hemodynamic measurements without the need of invasive monitoring procedures.
Method, apparatus and computer program for determining a blood pressure value
  • M Proença
M. Proença, "Method, apparatus and computer program for determining a blood pressure value", WO Patent WO/2016/138965