SummaryWe have studied, over a wide range of dilutions using techniques of clot weight, thrombelastography and scanning electron microscopy, the physical properties of a blood clot formed in vitro when fresh blood was diluted with gelatinbased colloid solutions compared with crystalloid controls. The colloid solutions tested (3.5% polygeline (Haemaccel) and 4% succinylated gelatin (Gelofusine)) produced clots that had reduced median weight (P:0.001 and P:0.018, respectively) and reduced mean shear modulus (P:0.001) compared with crystalloid controls. Scanning electron microscopy showed that the fibrin formed a less extensive mesh in the presence of the gelatin-based colloids compared with crystalloid. Reduction in clot quality with gelatin-based colloids has not been noted previously and further work is needed to ascertain if this occurs in vivo as these solutions are used frequently in patients who require full haemostatic competence. (Br. J. Anaesth. 1998; 80: 204-207) Keywords: blood, coagulation; blood, colloids; fluids, i.v.; blood, haemostasis; blood, replacement; measurement techniques, thrombelastography Plasma substitutes containing degraded and modified gelatin are being used increasingly in prehospital, resuscitation, perioperative and intensive care situations. Often they are the fluid of choice in patients with uncontrolled haemorrhage both before blood transfusion and in conjunction with transfusion of packed cells. Unlike the dextran and starch solutions, so far they have been considered as having no significant effect on clotting mechanisms following studies based principally on clotting times. [1][2][3][4] While measuring whole blood coagulation times after in vitro dilution with colloids we noted a striking difference in clot quality compared with that seen with dilution using crystalloid. Our preliminary findings have been reported previously.5 In this article we describe more detailed investigations using clot weights, haematological analysis, thrombelastography and scanning electron microscopy, and include a description of the dose-response effect of varying degrees of dilution using regression analysis. Materials and methodsWherever fresh whole blood was used, care was taken to avoid prolonged venous stasis, venepuncture from the same site or delays in pipetting, and experiments were conducted under strict temperature control.CLOT WEIGHTS A total of 35 fresh whole blood samples were diluted to 15%, 30%, 45%, 60% and 75% with 0.9% sodium chloride and Ringer's solution (controls) or the test substances, 4% succinylated gelatin (Gelofusine, B. Braun (Medical) Ltd) and 3.5% polygeline solution (Haemaccel, Hoescht UK Ltd). After dividing each sample into test and control, the total volume of each sample after dilution was 5 ml. Clot weights were measured using the method described by Macfarlane.6 Because the clots would not adhere to a glass rod the test was modified by separating the clot from plasma on gauze in a funnel. Clots were weighed on an electronic balance and then examined physica...

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The use of magnetic resonance imaging (MRI) for monitoring multiphase displacement experiments for quantitative characterization of fluid saturations is demonstrated. Displacements are conducted with one fluid phase in a porous medium being immiscibly displaced by another. Our objective is to accurately measure porosity and saturation distributions corresponding to one spatial dimension. Measures for the accuracy and resolution, with which the properties are identified, are developed. IntroductionNoninvasive imaging methods, such as X-ray CT scanning and magnetic resonance imaging (MRI), are providing exciting new opportunities for determining accurate rock characterizations and fluid-phase distributions corresponding to local regions within porous media. While much of the work reported for imaging methods have centered around the use of X-ray C T scanning (Potter and Groves, 1989;Vinegar, 1986), the versatility of MRI provides some unique opportunities for even more accurate and complete characterization of many properties associated with fluid-solid systems. Most of the work to date has dealt with static or nonflowing situations. When the porous media contain a single fluid phase, the void volume of the media can be characterized by imaging (Edelstein et al., 1988). MRI can also be used to characterize the distribution of one or more fluid phases in multiphase situations (Hall and Rajanayagam, 1987;Chen et al., 1988;Baldwin and Yamanashi, 1986;. In previous studies, fluid distributions have typically been expressed by a quantity proportional to the intensity of the signal. While these experiments demonstrate the use of imaging, they provide at best only a semiquantitative measure of rock properties and fluid-phase distributions. Porosity and fluid saturations, which are desired for quantitative analysis of fluid transport and storage in porous media, have been reported only as averages for whole samples (Edelstein et al., 1988), rather than resolved spatially in one or more dimensions.Several studies that deal with experiments involving transient multiphase flow in porous media have been reported (Baldwin and Yamanashi, 1986;Chen et al., 1988). Standard twodimensional (slice) imaging procedures were typically used. In some cases, such as the absorption of water by nylon (Blackband and Mansfield, 1986), the flow process is sufficiently slow so that the time required for imaging is not a critical issue. In other cases, the flow has been disrupted to perform the imaging under static conditions (Chen et al., 1988;Baldwin and Yamanashi, 1986). This generally is not desired for quantitative work since some redistribution of fluid phases is to be expected.In this work, we investigate the use of MRI for monitoring multiphase displacement experiments. In our experiments, one fluid phase is immiscibly displaced from a porous medium by a second fluid phase. Our objective is to accurately measure quantities that may be used to characterize the porous media and transport processes-specifically, the porosity and saturation p...

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