Noninvasive continuous arterial pressure monitoring with Clearsight during awake carotid endarterectomy: A prospective observational study

BACKGROUND: Continuous noninvasive blood pressure (CNBP) measurement using the volume-clamp method is a less invasive alternative compared with invasive intra-arterial monitoring for awake patients during carotid endarterectomy (CEA) under regional anaesthesia. OBJECTIVE: We investigated the agreement of blood pressure (BP) recorded with invasive and CNBP methods during awake CEA. DESIGN: A prospective observational study for assessing agreement with Bland-Altman plots, agreement-tolerability indices (ATI), concordance and interchangeability. SETTING: Azienda Ospedaliera Universitaria G. Martino, Messina, a University tertiary referral centre in Italy. PATIENTS: In 30 consecutive patients, we recorded continuously ipsilateral invasive and noninvasive BPs, from 3 min before carotid cross-clamping to 5 min after unclamping. MAIN OUTCOME MEASURES: Primary outcome was bias, 95% limits of agreement, ATI, concordance and interchangeability for mean arterial pressure (MAP). Secondary outcomes were agreements for systolic arterial pressure and diastolic arterial pressure. Tracking of changes was assessed with four-quadrant polar plots and the trend interchangeability method. Optimal bias was defined as 5 mmHg or less. RESULTS: A total of 2672 invasive and CNBP paired measurements (93% of overall data) were analysed, with a median of 92 readings per patient [IQR 76 to 100]. Mean (SD) bias for MAP, systolic arterial pressure and DAP were -6.8 (6.7), -3.0 (9.7) and -9.0 (5.4) mmHg, respectively. The ATIs were 0.88, 0.95 and 0.71, respectively, where ATI of 1.0 or less and at least 2.0 defined acceptable, marginal and unacceptable agreements. The four-quadrant plot analysis for beat-to-beat differences showed concordance rates of 97.3%, 99.98% and 96.4%, respectively. Polar plot analysis showed 95% limits of agreement of -3 to 3, -2 to 2 and -2 to 2 mmHg respectively. Trend interchangeability method showed an interchangeability rate of 95% for MAP. CONCLUSION: During CEA performed under regional anaesthesia, CNBP offers a less invasive approach for BP monitoring. We found acceptable agreement for MAP defined by an ATI of 0.88 and an excellent 95% global interchangeability rate. A suboptimal bias of 7 mmHg was found with CNBP for MAP.