Effects of Hemorrhagic and Catecholamine Shock on Canine Forelimb Transcapillary Fluid Fluxes and Segmental Vascular Resistances

Abstract

Although the literature on transvascular fluid movement in shock is conflicting, considerable evidence suggests that filtration of fluid from blood to tissue in hemorrhagic and catecholamine shock may be an important determinant in the development of irreversibility [Haddy, Overbeck, and Daugherty (1968); Bloch, Pierce, and Lillehei (1966); Chien (1967)]. This conclusion regarding filtration of intravascular fluid is based largely on measurements of blood volume with dilution techniques and/or hematocrit, and plasma protein determinations in dogs. However, in primates including man the available evidence, while sparse, suggests that hypovolemic shock is associated with hemodilution due to continuous fluid reabsorption [Chien (1967)]. If this apparent discrepancy between dog and man is true it would appear that the dog is a poor shock model. It is generally agreed that in the dog filtration of fluid does occur in the intestine. However, Porciuncula and Crowell (1963) and Smith, Crowell, Moran, and Smith (1967) reported that the volume of fluid lost via the intestinal route in dogs is relatively small, and that atropine administration prevents the hemorrhagic enteritis but has little effect on survival rate or time and on the hemodynamics of the shock state. This intestinal fluid loss appears to be a pecularity to dogs only for it does not occur in primates. Dilution measurements of blood volume may be misleading in states associated with profound vasoconstriction because of inadequate mixing of tracer substances. While the changes in hematocrit and plasma protein concentrations in dogs are compatable with transvascular fluid loss, no light is shed on the mechanism of their occurrence. For example, the dog has a large spleen and contraction of this organ will itself increase hematocrit significantly. Finally other investigators employing dilution techniques in dogs have failed to observe progressive blood volume loss [Chien (1967)]. Mellander and Lewis (1963) and Lundgren, Lundwall, and Mellander (1964) reported that in cats (utilizing organ volume as an index of transvascular fluid fluxes), hemorrhage is associated with fluid filtration in skeletal muscle. However, the question arises as to whether this is simply another species peculiarity. With this is mind we began a systemic study of the direction and possible mechanism of transcapillary fluid movement in the dog utilizing a gravimetric technique. The forelimb was selected as the test organ because it contains skin and skeletal muscle which compromises over 60 percent of body weight. Hence, transvascular fluid movement in these tissues, if representative of all skin and skeletal muscle, must be of paramount importance in shock states initially as a compensatory attempt to restore blood volume (reabsorption) and possibly later in the development of the irreversible shock state (filtration). This paper summarizes our work on transvascular fluid movement and segmental vascular resistances in hemorrhagic and catecholamine shock.