Investigation of the accuracy of a noninvasive continuous blood pressure device in different age groups and its ability in detecting hypertension and hypotension: an observational study

Background: CNAP monitor is a continuous and noninvasive blood pressure (BP) measurement device that can be used in intraoperative monitoring. But whether its accuracy changes with age and its detectability of hypertension and hypotension are still unclear. This study was to investigate the agreement of CNAP and invasive arterial pressure (IAP) in different age groups, and the ability of CNAP to detect hypertension and hypotension.

Methods: This observational study enrolled 48 Chinese patients undergoing surgery under general anaesthesia, including 25 relatively old patients (age between 50 and 70) and 23 relatively young patients (age between 18 and 49). IAP was monitored at the radial artery and CNAP was applied on the opposite arm simultaneously. Paired BP data in the entire surgery were recorded, and analyzed with Bland Altman plot and Spearman correlation. The ratio of the hypertension and hypotension episodes detected by IAP and CNAP was analyzed using chi-square test.

Results: 7990 valid paired BP data were analyzed, wherein 4186 data were from 25 relatively old patients, and the other data were from 23 relatively young patients. Bias (SD) for relatively old patients was: systolic BP (SBP): - 6.5 (18.6) mm Hg; diastolic BP (DBP): 9.3 (7.8) mmHg; and mean BP (MBP): 4.2 (9.5) mm Hg. Bias (SD) for relatively young patients was: SBP: - 6.2 (12.1) mm Hg; DBP: 10.6 (6.9) mmHg; and MBP: 4.8 (7.3) mm Hg. The correlation between CNAP and IAP was higher in MBP than those in SBP and DBP, and it decreased with the increase of age. Comparing to IAP, CNAP tended to miss reporting a high SBP, low DBP and low MBP, and misinform a low SBP, high DBP and high MBP.

Conclusion: CNAP showed acceptable agreement with IAP in MBP for all age groups, but reduced agreement with IAP in SBP and DBP, especially for relatively old patients. Ability of CNAP to detect hypertension and hypotension episodes was weaker than IAP. Therefore, CNAP monitor is suitable for young patients and hemodynamically stable surgery, but may not be recommended for old patients with arteriosclerosis and diabetes or surgeries expecting to have fluctuating blood pressure.