CRITICAL POINT IN PROGRESSIVE HEMODILUTION WITH HYDROXYETHYL STARCH
Anesthetized dogs were hemodiluted by serial blood withdrawals (10 ml/kg) and immediate infusion of equal volumes of hydroxyethyl starch solution every ten minutes until death. Serial determinations of circulatory and metabolic parameters were performed at approximately 20, 12, 8 and 5％ hematocrit values. “Complete compensation” was observed until Hb value reached approximately 5.5 g/100 ml. “Partial compensation” was observed at 5.5-4.0 g/100 ml Hb, where oxygen consumption started to decline. “Reversible decompensation” occurred at emoglobin values of 4.0-3.0 g/100 ml for the following reasons: cardiac output declined from its maximal compensatory increase; heart rate and arterial pressure decreased; right ventricular end-diastolic pressure increased; venous hemogloblin oxygen saturation decreased sharply; pH declined and arterial lactate values rose; and reversibility of hemodilution proven by survival of 80％ of 43 animals in the previous studies. “Irreversible decompensation ” occurred below 3.0 g/100 ml Hb. This is characterized by a dramatic decrease in cardiac output and venous hemoglobin oxygen saturation; and an increase in arteriovenous oxygen content difference. The lowest hemoglobin values measured (1.5-2.0 g/100 ml) were followed by another 3-7 blood exchanges before cardiac arrest occurred suddenly.