Use of a pressure sensing sheath: comparison with standard means of blood pressure monitoring in catheterization procedures

Abstract

Purpose: Monitoring of blood pressure (BP) during procedures is variable, depending on multiple factors. Common methods include sphygmomanometer (BP cuff), separate radial artery catheterization, and side port monitoring of an indwelling sheath. Each means of monitoring has disadvantages, including time consumption, added risk, and signal dampening due to multiple factors. We sought an alternative approach to monitoring during procedures in the catheterization laboratory.

Methods: A new technology involving a 330 µm fiberoptic sensor embedded in the wall of a sheath structure was tested against both radial artery catheter and sphygmomanometer readings obtained simultaneous with readings recorded from the pressure sensing system (PSS). Correlations and Bland-Altman analysis were used to determine whether use of the PSS could substitute for these standard techniques.

Results: The results indicated highly significant correlations in systolic, diastolic, and mean arterial pressures (MAP) when compared against radial artery catheterization (p<0.0001), and MAP means differed by <4%. Bland-Altman analysis of the data suggested that the sheath measurements can replace a separate radial artery catheter. While less striking, significant correlations were seen when PSS readings were compared against BP cuff readings.

Conclusions: The PSS has competitive functionality to that seen with a dedicated radial artery catheter for BP monitoring and is available immediately on sheath insertion without the added risk of radial catheterization. The sensor is structurally separated from the primary sheath lumen and readings are unaffected by device introduction through the primary lumen. Time delays and potential complications from radial artery catheterization are avoided.

Keywords: Angiography; Blood Pressure; Catheter; Device.

Figure 1

Pressure sensing system (PSS). The PSS contains an electronic blood pressure monitor (BPM) device mounted on an IV pole and a sheath (6 F size currently available) with a fiberoptic pressure sensor embedded in its wall (A). The sensor opens to the arterial lumen at the tip of the sheath (B). Sensor readings output to a display on the BPM that shows systolic, diastolic, and mean arterial pressures.

Figure 2

Bland–Altman plots; pressure sensing system (PSS) versus radial artery catheterization (RAC) means. Plots for the PSS–RAC comparison for mean arterial pressure (MAP). Based on the identity plots (top row), these measures appear to be in agreement—aside from the outlier—as they are wrapped tightly around the linear parent function. The Bland–Altman plots show consistent differences across the range of measures. Differences of only a few mm Hg are explainable by differences in measuring techniques between radial and femoral pressures and between fiberoptic sensors and analog chips mounted on an IV pole (see Discussion section). The RAC measurements for patient No 4 (outlier) were higher than the sheath measurements. Different symbols and colors each represent a different subject. Broken lines on Bland–Altman plots represent mean ±2SD. Similar results in the plots were shown on the systolic and diastolic values, but are not displayed due to space limitations.

Figure 3

Bland–Altman plots; sheath versus cuff. Systolic comparison (left) suggests that higher pressure sensing system (PSS) measurements tend to correspond to lower cuff measurements (note that the patients have been marked by color and shape). The Bland–Altman plots tell a similar story—when the average of the two measurements is higher, the differences tend to be negative. An additional feature from these plots is that for more central systolic measurements (ie, 115–140 mm Hg), the differences are more likely to be positive. This suggests that the difference between the methods is not constant across all systolic blood pressure measures. If the difference between the methods was constant, we would expect a random scatter of points across the plot. The clinical significance of these differences should be considered in deciding which technique to use to monitor a particular patient procedure. The identity plot for the diastolic comparison (right, top) shows that the cuff measurements were often lower than the PSS readings, as a larger percentage of the points lie underneath the linear parent function. The Bland–Altman plot (right, bottom) shows that the differences have constant variance and are similar in magnitude across the range of measures, although the majority of them are below 0. On the basis of these plots it is reasonable to conclude that the PSS and cuff measurements are similar, although perhaps not measuring the same diastolic blood pressure.

Figure 4

Fabry–Perot versus Wheatstone Bridge. (A) In the Wheatstone Bridge circuit, application of pressure alters the resistance across the circuit, and voltage change across resistors is used to calculate pressure. For more information, see: https://www.grc.nasa.gov/www/k-12/airplane/tunwheat.html. (B) In the Endophys sheath the sensor located near the tip (A–C) receives the light signal, which reflects from surfaces at the base of an air gap in the sensor and from the internal surface of the silicon diaphragm (D). The returning light contains bands of higher and lower intensity owing to the wavelength of the light and to diffraction across the air gap (interferometry), which alter as the space is altered by depression of the diaphragm by applied pressure. This allows calculation of the pressure at the diaphragm. For further information, see: https://en.wikipedia.org/wiki/Fabry–Pérot_interferometer.