Reply from the authors: Are we ready for non-invasive blood pressure monitoring?—reply

Abstract

Editor—As pointed out by Karnwal and colleagues, our report1Vos JJ Poterman M Mooyaart AQ et al.Comparison of continuous non-invasive finger arterial pressure monitoring with conventional intermittent automated arm arterial pressure measurement in patients under general anaesthesia.Br J Anaesth. 2014; 113: 67-74Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar demonstrates a bias of Nexfin with the arterial line and an accuracy that is for many clinical indications insufficient to replace invasive monitoring. Our main research question however was to assess the accuracy of Nexfin compared with conventional non-invasive blood pressure (NIBP) monitoring (upper arm BP cuff), and we must strongly disagree that ‘our article truly shows’ that anaesthesia providers should refrain from using these continuous non-invasive devices. Our research demonstrates that within the clinical context of the study population, the accuracy of Nexfin tends to be better than that of conventional NIBP monitoring (in addition to its advantage of being continuous). While conventional NIBP monitoring may be the clinical standard, it is certainly not a gold standard for arterial BP monitoring. Therefore, when using Nexfin as an NIBP monitor, we would advise to also use conventional NIBP monitoring, but take advantage of the continuous nature of continuous NIBP monitoring and be aware of the generally higher accuracy of continuous NIBP compared with intermittent NIBP monitoring. Just as with any monitoring device used in anaesthesia, the reliability of the monitor is highly dependent on the signal quality, whether it is heart rate calculation from ECG, end-tidal carbon dioxide (CO2) from the capnogram, or any other derived variable. Signal quality is difficult to quantify and requires some experience to be able to judge these waveforms in routine clinical practice. Therefore a clinician aspiring to use continuous NIBP measurement should get acquainted with appraising signal quality in order to assess the reliability of measured pressures. Whereas any clinician can to a comfortable degree assess the reliability of the oxygen saturation number based on the quality of the pulse oximetry waveform, or the reliability of the end-tidal CO2 value based on the capnogram, equivalently most cases of unreliable continuous NIBP can be appreciated based on the waveform. Consequently, the clinical reliability of continuous NIBP systems such as Nexfin or CNAP is arguably determined by the ability of the clinician to appreciate the quality of the pressure waveform. We would therefore advise any clinician who has access to a continuous NIBP monitoring system to use it several times in patients along with invasive and NIBP monitoring in order to learn to appreciate the quality of the signal and the additional information obtained by the non-invasive technology. We expect they will observe the same results as we demonstrated in our report, namely, sometimes a considerable bias with the IBP, to a degree unacceptable in many patients, but with a bias that is considerably smaller than conventional intermittent NIBP. None declared.