Blood volume and extracellular fluid volume in anesthesia.

From every day experience we find that the accepted standards and indices for the quantitative adequacy of the circulating blood, such as hemoglobin-gms and hematocrit percents, are not adequate and do not reflect volume or mass. The laboratory tests that we have habitually adopted as guidelines denote percentage concentration per unit volume and not absolute amounts. There is all the difference in the world between an actual available volume and just a concentration. A patient may bleed to death, and yet, the hematocrit will show no changes; in fact, in some instances, it may rise, which would normally indicate improvement.