Continuous non-invasive blood pressure monitoring, a validation study of Nexfin in a pregnant population.

OBJECTIVE: To assess the accuracy of a non-invasive beat-to-beat continuous blood pressure monitoring device (Nexfin) in pregnancy according to the International Protocol of the European Society of Hypertension.
METHODS: The validation was performed according to the International Protocol of the European Society of Hypertension. The test device (Nexfin, BMEYE, Amsterdam, the Netherlands) calculates beat to beat blood pressure from finger pulse wave analysis. Measurements of systolic and diastolic BP in 33 volunteers were obtained using the mercury sphygmomanometer and the Nexfin alternatingly.
RESULTS: The device passed phase 1 as 30 systolic and 32 diastolic readings fell within 5 mmHg (25 required). In addition, the device also passed phase 2.1 as 68 systolic and 67 diastolic readings fell within 5 mmHg (65 required). Finally, it failed to pass phase 2.2 as 24 subjects for systolic and 23 for diastolic had at least 2/3 of their comparisons falling within 5 mmHg (22 required) but 6 subjects for systolic and 8 for diastolic had all three comparisons more than 5 mmHg different from the mercury readings (three allowed). The mean differences were 2.3 mmHg (SD 6.8) for SBP and 0.8 mmHg (SD 6.3) for DBP.
CONCLUSION: The Nexfin device passed phase 1 and phase 2.1 but failed to pass phase 2.2. However, adaptation of the data to the more permissive AAMI (mean difference <5 +/- 8 mmHg) and BHS (systolic grade B, diastolic grade A) protocols indicated adequate accuracy for application in research settings or for longitudinal within-patient tracking of blood pressure, given the possibility for continuous monitoring.