Biological responses to exchange transfusion with liposome-encapsulated hemoglobin.

The present study evaluates the biological responses to 10% blood volume infusion ("top-loading," n = 7) or 50% blood volume exchange transfusion (n = 8) with a new preparation of liposome-encapsulated hemoglobin (LEH) in the conscious rat. Top-loading did not affect systemic hemodynamic variables but induced transient thrombocytopenia (-36% +/- 7%; P less than 0.05) and elevation of plasma thromboxane B2 (12.4 +/- 3.8 pg/100 microliters vs. undetectable levels at the control; P less than 0.05). Rats exchanged with LEH maintained mean arterial pressure (MAP) during the 3 hr observation period, whereas control (0.9% NaCl or lactated Ringer's solution) animals developed hypotension (-23 +/- 5 mm Hg, P less than 0.05). The maintenance of MAP in the LEH group resulted from the opposing effects of LEH-induced increase in total peripheral resistance index (TPRI; +0.06 +/- 0.01 mm Hg/ml/min/kg; P less than 0.05), and decreased cardiac index, (Cl, -25 +/- 6 ml/min/kg, P less than 0.05). In contrast, the decline in MAP in the control groups could be attributed to the lower Cl (-65 +/- 8 ml/min/kg; P less than 0.05). All rats developed metabolic acidosis (base excess of -9.7 +/- 0.6 mmol/liter; P less than 0.05), which was transient in the LEH group but progressive in the control groups. These data support the possible use of LEH as a blood substitute when massive transfusions are needed.