Relation of Arterial Blood Lactate to Oxygen Delivery and Hemodynamic Variables in Human Shock States

A retrospective study of 50 patients with circulatory shock and serial hemodynamic and metabolic measurements was undertaken. From the patient records, values for first measured cardiac index (CI) (t = 1) and highest CI (t = 2) with concomitantly obtained hemodynamic and metabolic variables and with arterial blood lactate levels (ABL), measured within 1.5 hours of t = 1 and t = 2 were taken. Nineteen patients had nonseptic shock (NSS), and 31 had septic shock (SS). Mortality rates were equivalent. At both t = 1 and t = 2, CI and O2 delivery (DO2) were higher and systemic vascular resistance index (SVRI) was lower in SS than in NSS. Although increases in DO2 were significant and not different between the groups and initial ABL values were similar, ABL had declined 50% in NSS but had not changed in SS (p less than 0.0001). From the hemodynamic and metabolic variables investigated in NSS, changes in ABL only correlated with changes in arterial oxygen content (CaO2; r = -0.65; p less than 0.01). Changes in ABL did not correlate with changes in DO2 in both groups. In SS, changes in ABL best correlated with changes in SVRI (r = -0.54; p less than 0.01). Our data suggest that anaerobic metabolism, reflected by ABL, decreases in response to an increase in CaO2, CI, and thus DO2 in NSS but not in hyperdynamic SS. Anaerobic metabolism in the latter may relate to peripheral vasodilation, associated with peripheral "functional" shunting of blood transported oxygen, rather than to insufficient DO2.