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

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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.


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).


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.


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.

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