CNAP ® does not reliably detect minimal or maximal arterial blood pressures during induction of anaesthesia and tracheal intubation

BACKGROUND: CNAP(®) provides continuous non-invasive arterial pressure (AP) monitoring. We assessed its ability to detect minimal and maximal APs during induction of general anaesthesia and tracheal intubation. METHODS: Fifty-two patients undergoing surgery under general anaesthesia were enrolled. Invasive pressure monitoring was established at the radial artery, and CNAP monitoring using a finger sensor recording was begun before induction. Statistical analysis was conducted with the Bland-Altman method for comparison of repeated measures and intraclass correlation coefficient (ICC). RESULTS: Patients' median age was 67 years [interquartile range (59-76)], median American Society of Anesthesiologists score was 3 [interquartile range (2-3)]. Bias was 5 and -7 mmHg for peak and nadir systolic AP (SAP), with upper and lower limits of agreement of (42:-32) and (27;-42), respectively. The corresponding ICC values were 0.74 [95% confidence interval (CI) = 0.57-0.84] and 0.60 (95% CI = 0.44-0.73). Time lags to reach these values were 7.5 s (95% CI = -10.0 to 60.0) for the highest SAP and 10 s (95% CI = -12.5 to 72.5) for the lowest SAP. Bias, lower and upper limits of agreement for diastolic, and mean AP were -14 (-36 to 9) and -12 (-37 to 13) for the nadir value and -7 (-29 to 15) and -2 (-28 to 25) for the peak value. CONCLUSIONS: The CNAP monitor could detect acute change in AP within a reasonable time lag. Precision of its measurements is not satisfactory, and therefore, it could only serve as a clue to the occurrence of changes in AP.