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Non‑invasive measurement of pulse pressure variation using a finger‑cuff method (CNAP system): a validation study in patients having neurosurgery

November 12, 2022

Abstract
The finger-cuff system CNAP (CNSystems Medizintechnik, Graz, Austria) allows non-invasive automated measurement of pulse pressure variation (PPVCNAP ). We sought to validate the PPVCNAP-algorithm and investigate the agreement between PPVCNAP and arterial catheter-derived manually calculated pulse pressure variation (PPVINV). This was a prospective method comparison study in patients having neurosurgery. PPV INV was the reference method. We applied the PPVCNAP-algorithm to arterial catheter-derived blood pressure waveforms (PPV INV−CNAP ) and to CNAP finger-cuff-derived blood pressure wave- forms (PPVCNAP ). To validate the PPVCNAP-algorithm, we compared PPV INV−CNAP to PPV INV. To investigate the clinical performance of PPVCNAP, we compared PPVCNAP to PPVINV. We used Bland–Altman analysis (absolute agreement), Deming regression, concordance, and Cohen’s kappa (predictive agreement for three pulse pressure variation categories). We analyzed 360 measurements from 36 patients. The mean of the differences between PPVINV−CNAP and PPV INV was −0.1% (95% limits of agreement (95%-LoA) −2.5 to 2.3%). Deming regression showed a slope of 0.99 (95% confidence interval (95%-CI) 0.91 to 1.06) and intercept of −0.02 (95%-CI −0.52 to 0.47). The predictive agreement between PPV INV−CNAP and PPV INV was 92% and Cohen’s kappa was 0.79. The mean of the differences between PPVCNAP and PPV INV was −1.0% (95%-LoA−6.3 to 4.3%). Deming regression showed a slope of 0.85 (95%-CI 0.78 to 0.91) and intercept of 0.10 (95%-CI −0.34 to 0.55). The predictive agreement between PPVCNAP and PPV INV was 82% and Cohen’s kappa was 0.48. The PPVCNAP-algorithm reli- ably calculates pulse pressure variation compared to manual offline pulse pressure variation calculation when applied on the same arterial blood pressure waveform. The absolute and predictive agreement between PPVCNAP and PPVINV are moderate.
Keywords Hemodynamic monitoring · Fluid responsiveness · Cardiac preload · Dynamic preload variable · Volume clamp method · Vascular unloading technology.