Blood volume measurement at the bedside using ICG pulse spectrophotometry

Background: In the treatment of critically ill patients, blood volume (BV) measurement requires injection of some tracer substance and subsequent bloo d sampling to analyze the tracer concentration. To obviate both the samplin g and laboratory analysis, techniques of pulse oximetry have been adapted t o the noninvasive optical measurement in the patient's nose or finger of th e arterial concentration of an injectable dye. Methods: The authors report the clinical accuracy of a new noninvasive beds ide BV measurement test that uses pulse spectrophotometry (the pulse method ). The device detects pulsatile changes of tissue optical density of a nost ril or a finger spanned by a probe emitting two infrared wavelengths (805 a nd 890 nn). After a peripheral or central intravenous injection of indocyan ine green, the arterial dye concentration is continuously computed by refer ence to the previously measured blood hemoglobin concentration. Three types of tests of its accuracy are described here. Results: In 10 healthy volunteers, the authors compared BV determined by th e pulse method with an I-131-labeled human serum albumin method. Three subj ect data sets were excluded because of motion artifact, a low signal:noise ratio, or both. For the other seven volunteers, the bias +/- SD of pulse sp ectrophotometric RV values were 0.20 +/- 0.24 1(or 4.2 +/- 4.9%) for the no se probe and 0.34 +/- 0.31 I (or 7.3 +/- 6.9%) for the finger probe, with a mean BV of 5 1, In 30 patients who underwent cardiac surgery, the pulse me thod was compared with a standard indocyanine green method using intcfinitt ent blood sampling. In three patients, the BV could not be determined by th e pulse method because of motion artifact, low signal:noise ratio, or both. In 27 patients, the bias +/- SD of the BV by the pulse method was -0.23 +/ - 0.37 1(-5.3 +/- 8.7%) for the nose and -0.25 +/- 0.51(-4.2 +/- 8.4%) for the finger, Patient BV ranged from 2.51 to 7.13 1 (mean, 4.48 1). In 10 add itional patients before cardiac surgery, BV was measured by the pulse metho d before and shortly after removal of 400 ml blood. The pulse method record ed a decrease of By of 480 +/- 114 ml. Three days after venesection, the me an RV was 117 +/- 159 ml less than the predonation control. Conclusions: In most patients, the pulse method provides bedside measuremen t of BV without blood sampling (except for hemoglobin determination), with an estimated error less than 10%. In 10-30% of tests the method failed beca use of motion distortion of the record during the 10-min data collection pe riod or because of insufficient pulse amplitude in the test tissue.