Correlation of blood rheology with vascular resistance in critically ill patients

Blood rheologic measurements together with peripheral resistance determinations in vivo were made in 27 critically ill patients. Eighteen of these patients (group I) suffered from violent trauma or operative injury and the other 9 (group II) were patients with generalized sepsis. As a result of fluid therapy all patients underwent hemodilution, resulting in a decrease in blood viscosity. This drop in blood viscosity was counteracted to some extent by an increased plasma viscosity due to elevated fibrinogen levels and a decreased red cell deformability associated with massive transfusions of stored blood. The correlation of vivo hemodynamics with blood rheological data made it possible to separate the relative roles of vascular dimensions and blood viscosity in affecting the total peripheral resistance. This approach permitted us to distinguish varying degrees of vasoconstriction in nonseptic patients in low flow states (group I) and varying degrees of vasodilation in septic patients (group II). This type of analysis serves to elucidate the pathophysiology of hemodynamic alterations in disease and provides a rational basis for devising an effective therapeutic program.