Evaluation of a noninvasive hemoglobin and hematocrit monitoring device

Introduction

Optimal monitoring of critically ill patients remains a challenge. A noninvasive point-of-care test of blood hemoglobin and hematocrit (Hb/Hct) levels may provide rapid patient assessment, including the need for transfusion, less iatrogenic blood loss and cost savings. A new, noninvasive device, the OrSense NBM-100, was tested for continuous monitoring (CM) of Hb/Hct in an ICU and postanesthesia care unit (PACU).

Objective

The aim of this study was to evaluate the accuracy of a new noninvasive Hb/Hct continuous monitor, compared with the traditional laboratory technique in critically ill and postsurgery patients.

Materials and methods

The NBM-100 device utilizes a finger-base ring-like sensor using red–near infrared occlusion spectroscopy to detect and analyze the Hb/Hct concentrations and blood glucose level.

Study design

Ten patients were enrolled (four females, six males, ages 24–83): four in the PACU, and six in the ICU. The NBM-100 probe was placed on patients' thumbs and assessed for 2–12 hours of CM. NBM-100 output was provided every 10–15 min. Results of the device were compared with arterial blood samples taken every 30–60 min and analyzed by blood gas machine (Nova Biomedical).

Results

The NBM-100 showed Hb trend tracking for 54 hours of CM (see for example Fig. 1). The mean absolute error was 1.0 g/dl (84 points, Hb range: 8.5–12.6 g/dl). An average bias of 0.3 g/dl was found between the two methods. When calibrated with the input of the first in vitro measurement, the mean absolute error was 0.95 g/dl.

Figure 1

NBM-100 hemoglobin (Hb) tracking versus spot Hb values in one patient when calibrated with the first in vitro measurement.

Conclusions

The OrSense monitor can provide accurate, noninvasive Hb CM in critically ill patients. This may be useful for diagnosis and treatment of patients with significant Hb changes. The device and sensor provided the capability of long-term CM and early-trend information at the point of care. Particularly, the device could be valuable in patients with wide Hb dynamic ranges resulting from blood dilution and hemorrhaging.

Preliminary results of ongoing trials evaluating the NBM-100 in other settings (e.g. intermittent Hb/Hct measurements in hematology clinics and in blood banks) show a good agreement between NBM-100 and standard invasive Hb/Hct measurement methods. Further developments may enable noninvasive measurement of glucose as well.