Hemodilution, Tonicity, and Blood Viscosity Peter W. Rand, Eleanor Lacombe J Clin Invest. 1964;43(11):2214-2226. https://doi.org/10.1172/JCI105095. Research Article Find the latest version: https://jci.me/105095/pdf Journal of Clinical Investigation Vol. 43, No. 11, 1964 Hemodilution, Tonicity, and Blood Viscosity * PETER W. RAND AND ELEANOR LACOMBE (From the Cardiovascular Research Laboratory, Maine Medical Center, Portland, Mlaine) Since the introduction of intravenous therapy, Methods fluids containing glucose or saline in relatively The principal experiments were designed to measure isotonic concentrations have far exceeded others changes in the viscosity of blood after its in vitro dilu- in use. Within the last decade new techniques tion by solutes that alter either plasma tonicity or plasma in many areas of diagnosis and treatment have viscosity. To study the effects of tonicity, compounds were selected that vary in their ability to permeate the required that fluids of various tonicity and vis- red cell membrane and hence in their ability to produce cosity be introduced into the blood stream with cell distention or creation by osmotic gradients; all such rapidity or in such great volume as to pre- are components of common intravenous fluids. Wide clude adequate dilution with the circulating cells ranges of dilution and concentration were explored. and plasma. The parameters measured, in addition to blood and plasma viscosity, included osmolality, water content, Several in vivo studies (1-4) have demonstrated and hematocrit. Since the initial number of red cells the effect of hypertonic solutions on blood flow. remained constant in each case, variations in hemato- Some authors (5-7) have noted circulatory crit from the level predicted on the basis of equivalent changes, especially in the pulmonary vascular isotonic dilution indicated changes in cell size. Similar bed, secondary to the injection of angiographic methods were used to study the response of blood vis- cosity to changes in plasma viscosity, except that iso- contrast media, which are both hypertonic and tonic solutions of high and low molecular weight dex- highly viscous. Others (8-11) have commented trans were the diluents. on the benefits of gross dilution of perfused blood Specifically, to compare hypotonic and isotonic dilu- tions, deionized water or isotonic saline (0.9 mg per 100 during extracorporeal support for open-heart ml, 287 mOsm per kg) was added to samples of f resh surgery, and some data have been presented con- human blood with hematocrit adjusted to 45. The fol- cerning the flow properties of blood diluted with lowing proportions were used: 1 ml diluent to 19 ml solutions of dextrose (12) or dextran (13, 14). blood (1:20), 2 ml diluent to 18 ml blood (1:10), and 4 ml diluent to 16 ml blood (1: 5). Measurements were At any given shear rate or temperature it is made on the original (control) and diluted samples after the concentration of red cells which primarily 30 minutes. These experiments were performed in affects the viscosity of whole blood. Viscosity quadruplicate on blood from different normal donors. To evaluate the effect of cell distention or creation rises with an increasing hematocrit. While in- on blood viscosity, 1: 20, 1: 10, and 1: 5 dilutions were vestigating the effects of various intravenous made as described above with multiple concentrations solutions on the hematocrit and viscosity of whole of saline (0.5, 0.85, 3.0, 5.0%), mannitol (5.0, 12.5, in we have noted that under 25%o), dextrose (5.0, 10.0, 20.0, 50.0%), and urea blood vitro, certain (0.85, 1.7, 4.2, 10.0%). The control sample for each conditions a drop in hematocrit has been accom- dilution of each compound tested was blood to which panied by a rise in viscosity, whereas under other an equivalent amount of plasma had been added. The circumstances an increase in hematocrit has been hematocrit of donor blood was adjusted before the addition of plasma so that each control sample would accompanied by a fall in viscosity. The sig- have a hematocrit of 40 (42.1, 44.4, and 50 for 1: 20, nificance of these findings in respect to the flow 1: 10, and 1: 5 dilutions, respectively). This portion of of blood exposed to diluents of varying osmolality the study included 54 separate dilutions representing triplicate determinations for each solute in the hypo- and viscosity appears to be of sufficient importance tonic and isotonic ranges and at least 6 determinations to warrant reporting at this time. for each in the hypertonic concentrations. For each compound the responses to increasing concentrations * Submitted for publication May 1, 1964; accepted were the same at all dilutions, but the magnitude of July 21, 1964. response varied in proportion to the degree of dilution. Supported by grant HE 07984 from the National In- To avoid duplication, we have selected data from the stitutes of Health and bv the Maine Heart Association. 1: 10 dilutions for detailed analysis. 2214 HEMODILUTION, TONICITY, AND BLOOD VISCOSITY 2215 TABLE I Osmolality and viscosity of test solutions Solution Concentration Osmolality Viscosity g/100 ml mOsm/kg H20 centistokes Dextrose in water 5.0 285 0.77 10.0 580 0.85 20.0 1,300 1.08 50.0 >2,000 2.96 Mannitol in water 2.5 150 0.75 5.0 300 0.78 12.5 775 0.94 25.0 1,766 1.35 Sodium chloride in water 0.3 100 0.70 0.5 163 0.70 0.85 272 0.71 3.0 910 0.72 5.0 1,570 0.73 10.0 >2,000 0.77 20.0 >2,000 0.90 Urea in water .85 140 0.70 1.70 280 0.71 4.25 690 0.71 10.0 1,617 0.73 Dextran, 10,000 mol wt in 5.0 300 1.04 0.85% saline 10.0 337 1.55 20.0 430 3.50 Dextran, 40,000 mol wt in 5.0 285 1.52 0.85% saline 10.0 310 3.00 20.0 378 9.79 Dextran, 150,000 mol wt in 5.0 280 2.70 0.85% saline 10.0 307 7.36 20.0 368 30.97 The same procedure was employed to investigate the poise) 1 was measured at shear rates from 212 seconds-1 effects of the dextrans, except that the diluents con- to 5 seconds-1 at 37.00 C with a Brookfield micro cone- sisted of 5, 10, and 20% solutions of dextrans of 10,000, plate viscometer after the method of Rand, Lacombe, 40,000, and 150,000 mol wt made up in isotonic saline. Hunt, and Austin (15). Although complete information Osmolality and hematocrit thus remained essentially regarding the response of viscosity at all shear rates has constant throughout each study. Dilutions of 1:20, been presented in some instances, values at 106 seconds-1 1: 10, and 1: 5 were studied, providing triplicate deter- have been used to demonstrate viscosity changes between minations at each concentration. For each dextran the samples. This particular shear rate was selected be- response varied in magnitude only, in proportion to the cause it is slow enough to reflect the shear-rate-dependent degree of dilution. Data from the 1: 10 dilutions are character of whole blood yet rapid enough to provide reported. The osmolality and viscosity of each concentration of 1 Viscosity, by definition, is shear stress/shear rate diluent appear in Table I. Note the wide range of os- (dyne-sec-cm- , or poise). 1/100 poise = 1 centipoise molality in the electrolyte and crystalloid solutions and (cp). Since blood viscosity varies with shear rate, it the high viscosities of the dextran solutions. For each must be measured with a variable-speed rotational vis- experiment, fresh venous blood was drawn with 50-ml cometer such as used here. These instruments measure siliconized syringes containing 0.37 ml heparin, 1: 1,000. shear stress, from which viscosity, in centipoise, is cal- To avoid variations caused by duration of the red cells' culated. Plasma viscosity is most practically measured exposure to the test solutions, studies were initiated on in a capillary tube viscometer. Viscosity is calculated each sample 30 minutes after initial mixing. from the rate of fall of a fixed volume of test liquid, Samples were measured for whole blood viscosity and which is related to density, other factors remaining con- hematocrit, for plasma viscosity, osmolality, water con- stant. The units are centistokes (cs). 1 centistoke = 1 tent, and specific gravity. Whole blood viscosity (centi- centipoise/density. 2216 PETER W. RAND AND ELEANOR LACOMBE excellent reproducibility throughout the hematocrit hematocrit were derived from data previously obtained range involved. Normal values at this shear rate (Ta- in this laboratory (15). ble II) and normal viscosity-shear-rate curves for each Plasma viscosity (centistokes) was measured at 370 C . 8 40 to 40 .0- 35 5.0 to 0 ao toW '~ _ 4.0 3.0 300 ° " 250 2 c E to 200 0 1:20 1:10 1:5 0 1:20 1:10 1:5 FIG. 1. A COMPARISON OF THE EFFECTS OF ISOTONIC AND HYPOTONIC DILUTIONS ON HEMATO- CRIT AND BLOOD VISCOSITY. The shaded areas represent 1 SD of the normal blood viscosity at the hematocrits produced. Vertical lines indicate the range of values from all experiments. Although hematocrits remain elevated with increasing hypotonic dilution due to increased red cell size, blood viscosity falls to the same extent as in equally diluted isotonic samples. HEMODILUTION, TONICITY, AND BLOOD VISCOSITY 2217 44 urea I:..................... 42 1 0@C°e %%s 401 38 1 36 t \_ ,, Hematocrit vs.