Intravascular blood volume estimation during fluid resuscitation

Hemorrhagic shock, caused by a massive loss of blood, remains the leading cause of death in the battlefield and in other trauma events when advanced medical care is not immediately available. Fluid resuscitation of the trauma victim is the common practice following hemorrhage in the pre-hospital setting. Since whole blood as well as plasma transfusions are not available in field conditions, various plasma substitutes are mostly used. However, a major disadvantage of these solutions is that they distribute into all the fluid compartments (intravascular and extravascular) usually causing edema. Another disadvantage is the lack of monitoring methods that will allow assessment of intravascular fluid volume to prevent overloading. A method to determine intravascular fluid volume during the fluid therapy procedure is therefore needed. Recently, noninvasive methods for estimation of hematocrit had been introduced. This allows the development of a system based on blood dilution. To study a dilution algorithm based on infusion rate and hematocrit assessment, a lumped model of the cardiovascular system including an interstitium compartment was developed. Based on the model, an algorithm was developed to estimate intravascular blood volume based on known infused volume and hematocrit changes. Model predictions were compared with animal experiments. A good match was found, however, more animal experiments are required to obtain statistical significance.