The impact of sensor application site on continuous noninvasive haemoglobin trends

This prospective observational clinical study investigated discrepancy between noninvasive continuous haemoglobin (SpHb, Masimo Corp., Irvine, CA) measurements with sensors placed on three fingertips during elective cardiac surgery.

The study included 12 adult patients who underwent elective coronary artery bypass grafting (CABG) under cardiopulmonary bypass (CPB). Three identical versions of SpHb sensors were placed on the fingers of the same hand and connected to dedicated Masimo Radical-7 monitors. Data were continuously recorded throughout the surgery. Multiple group comparison tests-Kruskal-Wallis and Alexander-Govern tests-were used to compare three sets of SpHb data (trends). Bland-Altman and Giavarina plots were used to compare the SpHb data with invasive arterial haemoglobin (Lab-Hb) data obtained at clinically relevant time points chosen at the discretion of the cardiac anaesthesiologist, who was blinded to the study protocol.

There was a good correlation between the time-matched SpHb data from the three sensors at 253 time points (r = 0.86-0.95), but there was a significant difference between the SpHb values obtained from each sensor and the average SpHb value of all 3 sensors (p < 0.05) at each time point. The absolute difference between the SpHb value obtained from each sensor and the average SpHb value was 0.69 g/dl g/dl (SD 1.49 g/dl). The accuracy and precision of the average SpHb for estimating Lab-Hb was higher compared to the SpHb values obtained from two out of three individual sensors (sn1 and sn3) and very similar compared to values obtained from sensor sn2.

The sensor placement site can impact the SpHb measurement causing discrepancy between SpHb measured in different fingers. The average SpHb from three fingertips appears to be more accurate and precise in estimating Lab-Hb. However, more advanced sensors are needed.