Investigation of Noninvasive in vivo Blood Hematocrit Measurement Using NIR Reflectance Spectroscopy and Partial Least-Squares Regression

Abstract

Hematocrit (Hct), the volume percent of red cells in blood, is monitored routinely for blood donors, surgical patients, and trauma victims and requires blood to be removed from the patient. An accurate, noninvasive method for directly measuring hematocrit on patients is desired for these applications. The feasibility of noninvasive hematocrit measurement by using near-infrared (NIR) spectroscopy and partial least-squares (PLS) techniques was investigated, and methods of in vivo calibration were examined. Twenty Caucasian patients undergoing cardiac surgery on cardiopulmonary bypass were randomly selected to form two study groups. A fiber-optic probe was attached to the patient's forearm, and NIR spectra were continuously collected during surgery. Blood samples were simultaneously collected and reference Hct measurements were made with the spun capillary method. PLS multivariate calibration techniques were applied to investigate the relationship between spectral and Hct changes. Single patient calibration models were developed with good cross-validated estimation of accuracy (∼ 1 Hct%) and trending capability for most patients. Time-dependent system drift, patient temperature, and venous oxygen saturation were not correlated with the hematocrit measurements. Multi-subject models were developed for prediction of independent subjects. These models demonstrated a significant patient-specific offset that was shown to be partially related to spectrometer drift. The remaining offset is attributed to the large spectral variability of patient tissue, and a significantly larger set of patients would be required to adequately model this variability. After the removal of the offset, the cross-validated estimation of accuracy is 2 Hct%.

Noninvasive monitoring of tissue hemoglobin using UV-VIS diffuse reflectance spectroscopy: a pilot study

“…With PLS, the sensitivity and specificity were 86% and 91%, while the discrete region model yielded 57% and 100%, respectively, indicating the importance of exploring these models further. While most of the studies described here exhibited good in vivo correlations of optical or acoustic parameters to total Hb and hematocrit, they typically are only useful for measurements of arterial saturations [4,5,8], require sophisticated algorithms [8,9,14] or have shown significant inter-patient variability due to skin pigmentation in the cases where measurements were made through the intact skin [12,13]. This presents an opportunity to explore new approaches that can address all three of these issues.…”

“…In that study, the one anemic donor out of 19 donors was identified, but the estimates of Hb were affected by the skin pigmentation of the calibration population. In a different study utilizing NIR reflectance measurements from the forearm of cardiac bypass patients with hematocrit ranging from 14.3 to 44.2%, a correlation coefficient of r=0.71 was achieved when compared to arterial Hb [13]. However, skin pigmentation was again found to be a largely contributing factor to the predictive ability of this technique.…”

“…Several studies have used visible (VIS) or VIS-near-infrared (NIR) diffuse reflectance spectroscopy to measure Hb concentration [11][12][13][14]. The Spectros T-Stat® is an FDAapproved VIS light spectroscopy device sensitive to ischemia [11].…”

Noninvasive Optical, Electrical, and Acoustic Methods of Total Hemoglobin Determination

“…Zhang et al reported on the utility of a similar visible/NIR diffuse reflectance spectroscopy technique (33 ). A fiber optic probe was attached against the patient's forearm (34 ), and NIR reflectance spectra were collected during cardiopulmonary bypass surgery.…”

Noninvasive Determination of Hemoglobin and Hematocrit Using a Temperature-Controlled Localized Reflectance Tissue Photometer

“…The data presented suggest the feasibility of measuring Hb and Hct noninvasively using steady-state reflectance measurements in a limited population of different skin colors. This type of steadystate determination of Hb and Hct, as well as the cardiac-pulse-based signal processing techniques, has been described in the literature (5)(6)(7)(8). The steady-state methods have a potential advantage for the determination of analytes in weak cardiac pulse situations.…”