Tracking Significant Hemodynamic Changes with a New, Continuous, Non-Invasive Blood Pressure Monitor

R. L. Marcus, M.D., Shireen Ahmad, M.D., Raymond Glassenberg, M.D., Rastogi Prathiba, M.D. Anesthesiology; (Northwestern University Feinberg School of Medicine, Chicago, IL)

Introduction:

Automated, non-invasive BP (NIBP) monitoring (via upper arm cuff) perform poorly in obese patients with large, cone-shaped upper arms. Currently, obese patients are subject to intra-arterial cannulation (A-Line) as a reliable alternative. A new non-invasive device, the TL-150 (T-Line®) Continuous Non-Invasive Blood Pressure monitor (Tensys® Medical Systems, San Diego, CA) has been demonstrated and validated to be accurate in the general surgical population (1). We have recently demonstrated the accuracy of this monitor in subjects with BMI >30Kg/m2 (2). The purpose of this study was to compare the devices ability to accurately track significant changes in systolic, diastolic and mean blood pressure measurement compared with an intra-arterial catheter in clinically obese patients (B.M.I. > 30 kg/m2) during surgery.

Methods:

The study was approved by the IRB and written informed consent was obtained in 23 subjects undergoing surgery requiring intra-arterial catheter placement for blood pressure monitoring. The T-Line® was positioned on the subject's wrist on the arm opposite the radial A-Line. Continuous, real-time BP data was recorded simultaneously from both the T-Line® and the A-Line using an L-Box signal splitter allowing both signals to be simultaneously recorded without interruption and while displayed on a standard monitor. Sampling acquisition rates for each signal were 160 Hz. Changes in either systolic, diastolic or mean blood pressure ≥ 20 mmHg lasting at least 1 min were considered significant. Each identifiable episode of blood pressure change was then extracted for analysis. Beat-to-beat values were averaged over 20 beats for both the A-Line and T-Line® and Bland Altman analysis were preformed on the averaged values.

Results:

More than 6,000 20-beat epochs were included in the analysis. The mean time for the observed BP changes was 4.0 ± 2.18 minutes. For MBP the average absolute magnitude of the change was 32.9 mmHg, for DBP it was 26.8 mmHg and for SBP it was 41.3 mmHg. Over these same blood pressure changes, the average difference between the T-Line® and the A-Line was -6.0, -2.0 and -1.4 mmHg respectively for SBP, DBP and MBP.

Discussion:

This study demonstrates the accuracy and precision of the TL-150 for measurement of blood pressure changes in periods of significant hemodynamic alterations in clinically obese patients. This data suggests this monitor could be used in place of an A-Line in this group of subjects when arterial blood sampling is not necessary.

References:

• Janelle GM, Gravenstein N. Anesth Analg 2006;102:484–90
• Marcus RL, Ahmad S, Glassenberg R, Fitzgerald PC Anesth Analg 2006: S154.[figure1][figure2]

Anesthesiology 2006; 105: A233

Figure 1	Figure 2