Relationship between oxygen delivery and metabolic acidosis during sepsis in piglets.

OBJECTIVE

To determine if the preservation of oxygen delivery (DO2) ameliorates the development of metabolic acidosis during group B streptococcal infusion.

METHODS

We examined 22 piglets (2 to 4 wks of age) that were anesthetized, intubated, and mechanically ventilated. Three groups of piglets were studied: group 1 (n = 6), in which DO2 was reduced progressively over 4 hrs by infusion of group B streptococci; group 2 piglets (n = 6) received a similar infusion of streptococci, but DO2 was preserved at presepsis levels by the infusion of dextran and exogenous porcine RBCs; group 3 piglets (n = 6) received no bacteria, but did receive a continuous infusion of 0.9% sodium chloride to maintain cardiac output, and thus, DO2, at baseline levels. To correlate arterial lactate concentrations with metabolic acidosis, four additional piglets received the continuous infusion of streptococci.

RESULTS

DO2 decreased significantly in group 1 (14.2 to 5.7 mL oxygen/kg/min) but not in either group 2 or 3. The arterial pH decreased significantly in both septic groups, groups 1 and 2 (7.47 to 7.20; 7.45 to 7.36, respectively), but not in the uninfected group 3. The pH was significantly lower for group 1 vs. group 2 piglets at 210 and 240 mins of streptococcal infusion. Base excess decreased significantly for group 1 and group 2 piglets (+1.5 to -13.9; -0.1 to -5.8 mM/L, respectively) but not in group 3. Base excess was significantly lower for group 1 vs. group 2 piglets at 210 and 240 mins of streptococcal infusion. Oxygen extraction increased significantly for only the low DO2 group 1 piglets (32% to 73%), and did not differ comparing group 2 vs. group 3. In both groups of septic piglets, metabolic acidosis developed before any detectable reduction in oxygen consumption. The increase in circulating lactate concentration (1.0 to 4.6 mM/L) was correlated with the decrease in base excess (-1.0 to -9.7 mM/L) in the four additional piglets that received an infusion of streptococci.

CONCLUSIONS

Maintaining DO2 at presepsis levels ameliorated the development of metabolic acidosis during streptococcal infusion. Nevertheless, a significant degree of metabolic acidosis developed despite the preservation of DO2.