Plasma Volume Prior to and Following Volume Loading During Shock Complicating Acute Myocardial Infarction

Blood volume was measured following onset of shock in 19 patients who had sustained acute myocardial infarction. The plasma volume was measured by dilution technique utilizing R125ISA and the red cell mass by (51Cr) red cell tag, at the time of admission.The plasma volume in six survivors was 41.1 ± 3.3 ml/kg; in 13 fatal cases it was 44.7 ± 4.0 ml/kg; this difference was not significant. The red cell mass in four survivors was 27.2 ± 1.75 ml/kg and in four fatal cases, 24.7 ± 1.60 ml/kg. Since these measurements are within normal ranges, we excluded absolute hypovolemia as a significant factor in accounting for the circulatory failure. Infusion of fluids in amounts which maintained a positive fluid balance selectively increased the plasma volume (57.1 ± 4.4 ml/kg), cardiac index, stroke volume and central blood volume in survivors, and reversed arterial vasoconstriction and lactic acidosis. However, the plasma volume was unaffected in the fatal cases (44.4 ± 4.0 ml/kg) and this was associated with progressive hemodynamic and metabolic deterioration.These observations support the hypothesis that recovery from shock is associated with expansion of plasma volume. To the contrary, during fatal progression of shock, plasma volume expansion does not occur despite volume loading.