The volume allowance formula as a guide to non-haemic solution administration. 1990.

-----------------We have developed a formula sequence which calculates the predicted blood volume, hemodilutional hematocrit and conjectively figures the amount of non-haemic solution margin allowable before reaching a minimally acceptable or 'target' hematocrit in the adult patient. Another application of the formula calculates the value for the amount of prime reduction to prevent the addition of blood to the ECC priming volume. The formula also provides the figures for the amount of blood to add to the prime of the extracorporeal circuit in order to maintain a target hematocrit. Introduction-----------------Many institutions have escalating concerns toward the administration of blood products. Complications such as hepatitis, AIDS, antibody-antigen reactions, etc. could be contained with a conservative blood product administration program and would mean savings in medical supply and administrative costs. The practice of blood conservation, especially in the field of extracorporeal circulatory technology, necessitates the need for various computations, which include predicted blood volume and approximate hematocrit adjusted for hemodilution with known amounts of non-haemic solutions. We have enhanced the application of these formulas to include a volume allowance calculation which allows the perfusionist to quantitate the amount of non-haemic solution that may be administered before reaching a target or minimally acceptable hematocrit. Methodology---------------It is our practice that all patients subjected to extracorporeal circulation during open heart surgery, as a routine, are evaluated for predicted blood volume, red cell mass, adjusted hematocrit values influenced by hemodilution, and blood product requirements, if necessary. As a rule, unless contraindicated, an average adult patient is usually allowed to hemodilute to 20-21% HCT before there is a concern to hemotransfuse. More debilitated patients may Address correspondence to: MichaelS. Vinas, CCP, c/o Vinas and Associates, 3508 Belmont Blvd.,Nashville, TN 37215 70 The Journal of Extra-Corporeal Technology require 25-30% hematocrits. As an addendum to these calculations, we developed a volume allowance formula. This formula provides us with valuable information as it pertains to the conduct of perfusion, the priming volume of the extracorporeal circuit, non-haemic solution and/or blood product administration requirements, if indicated. In example I, we present a hypothetical 70 kg adult male with no pathological disorders other than mild to moderate atherosclerotic plaque formation in the coronary arteries, a prebypass hematocrit of 38% and a prime volume of 1800 mi. For our example, we will employ the Texas Heart Institute predicted blood volume formula of 70 ml/kg (1), which correlates favorably with our own hemodilutional survey. We will also employ a revision of Edward C. Berger's anticipated hematocrit calculations (2). The volume allowance calculation assumes reasonable pathophysiology, systemic and pulmonary vascular resistance, colloidal oncotic pressure, osmotic pressure, and electrolyte values within a reasonable range. It is assumed that rehydration from the NPO status will have been achieved via anesthesiology during the pre-bypass phase as is generally our experience and an updated hematocrit prior to extracorporeal circulation. Example 1 Step 1: Calculate the predicted blood volume. 70kg. x 70 mllkg 4900 mi.-predicted blood volume (PBV) Step 2: Compute the patients red cell mass (RCM1). 4900 ml.-PBV K..3..8_(Fractional Hematocrit (HCT1) 1862 mi. RCM1 Step 3: Figure the hemodilutional hematocrit (HCT2).