Blood Volume: Not one Single Volume but the Sum of Two Volumes with Various Mixing in Different Parts of the Circulation

Dr. med. Mathias Haller, Prof. Dr. med. Udilo Finsterer, Institut für Anaesthesíologie, Ludwig-Maximilians-Universität, Klinilkum Großhadern, D-81366 München(FRG) The earliest attempts to determine blood volume date from the 18th century. The tracer dilution method was introduced in 1915 by Keith et al. [1]. Since then, circulating volume has been repeatedly claimed to be an important clinical parameter, with potential relevance in the monitoring of critically ill patients. Up to now, however, there has been no method available which is both easy to use and accurate. Furthermore, there is still considerable debate as to whether plasma or red cell markers should be used as determinants of blood volume. Various studies have attempted to establish standardized values for blood, plasma or red cell volumes. The volumes are mostly standardized to body weight or body surface area but nevertheless there remain considerable interindividual variations. As with many new or not widely used diagnostic parameters it is not clear whether this standardized ‘normal’ volume represents the optimal volume in the individual clinical situation in the critically ill patient. In intensive care medicine and during anesthesia the intravascular volume is mostly estimated using blood pressure and heart rate, the central venous pressure or the pulmonary occlusion pressure. These pressures may reflect cardiac function rather than the actual volume state of the patient [2]. Tracers for volume determinations are either markers of the plasma or of red cells. In recent years, radioactive isotopes were most commonly used with radioactively labeled human serum albumin for plasma volume and radiochromate tagged red cells for red cell volume determinations [3]. These tracers are difficult to handle in clinical routine and are contraindicated for repeated measurements because of radioactive contamination. Dyes used as tracers in plasma volume estimation are Evans blue [4-7] and indocyanine green [8-12]. These dyes seem to combine accuracy with lack of toxicity. But for repeated measurements, the half-life of Evans blue is too long (corresponding to the half-life of serum albumin) and, as an azo dye, Evans blue may possess a mutagenic potential as indicated in a few in vitro studies [13, 14]. A suitable nonradioactive tracer for red cells is still lacking. In this issue of INFUSIONSTHERAPIE und TRANSFU-SIONSMEDIZIN Lauermann et al. [pp 138] report a new method of labeling red cells with sodium fluorescein, a substance widely used in opthalmology. After the first report of red cell volume measurements with fluorescein (using fluoreceiniso-thiocyanate which is more stable than sodium fluorescein) in animals by Hansen [15] and a preliminary study by Lauermann [16] the method is compared with radiochromate labeled red cell volume determination as a criterion standard in Lauer-manns’ study. The results demonstrate good correlation between the two methods. The applicability of the method in the