SERIAL MEASURES OF TOTAL-BODY OXYGEN-CONSUMPTION IN AN AWAKE CANINE MODEL OF SEPTIC SHOCK

We examined serial changes in total body oxygen consumption (Vo(2)) in a permanently tracheotomized canine sepsis model. On Day 0, beagles h ad an Escherichia coli-infected (septic) or sterile (control) clot sur gically placed in the peritoneum. During the 21-d study, 10 of the 16 septic animals and none of the six control animals died (p = 0.02). Af ter clot placement septic versus control animals had decreased mean ar terial blood pressure (mm Hg; Day 1: 106 versus 128, p = 0.055; Day 2: 95 versus 125, p = 0.004, respectively) and left ventricular ejection fraction (Day 1 : 0.44 versus 0.69, p = 0.0006; Day 2: 0.33 versus 0. 57, p = 0.0001, respectively). Despite significant lethality and cardi ovascular dysfunction, in the septic group on Days 1 and 2, septic ver sus control animals had no significant differences in mean metabolic c art measured (Vo(2)DIR, ml/kg/min; Day 1: 11.9 versus 12.4, p = 0.81; Day 2: 14.2 versus 13.5, p = 0.72, respectively) and intravascular cat heter calculated (Vo(2)INDIR, ml/kg/min; Day 1: 11.2 versus 11.2, p = 0.99; Day 2: 12.8 versus 15.4, p = 0.49, respectively). On Day 1 in se ptic and control animals, volume infusion produced increases (p < 0.00 1) in oxygen delivery (Do(2)). In septic and control animals these cha nges in Do(2) were similar and were associated with similar increases in Vo(2)DIR (p = 0.001), and Vo(2)INDIR (p = 0.001). In fact, at all t ime points studied (baseline, Day 1, 2, and 21), both before and after volume infusion, levels of Do(2), Vo(2)DIR, and Vo(2)INDIR did not di ffer between septic and control animals, nor did they differ between s eptic survivors and nonsurvivors. Because levels of Vo(2)DIR and Vo(2) INDIR were similar in both groups, we pooled data from septic and cont rol animals. Throughout the study, Vo(2) showed a moderate association with Vo(2)INDIR (r = 0.55, p = 0.003), but mean Vo(2)DIR was lower at baseline (p = 0.001) and on Day 21 (p = 0.07) and greater on Day 2 (p < 0.01). In summary, our techniques, which detected small changes in both Vo(2)DIR and Vo(2)INDIR occurring with volume infusion, did not d emonstrate differences in these parameters comparing control and septi c animals. These results in euvolemic septic animals suggest that tota l body Vo(2) may not reflect pathogenetic mechanisms during sepsis and septic shock. Furthermore, these results suggest that although the le vel of total body Vo(2) may reflect the effects of therapeutic interve ntions such as volume loading, it should not itself serve as a therape utic target. 7