Hematocrit modifies the circulatory control of systemic and myocardial oxygen utilization in septic sheep.

OBJECTIVE

To describe the relationship between hematocrit and oxygen utilization before and after the onset of a hyperdynamic septic state.

DESIGN

Prospective, observational study.

SETTING

Laboratory of a large university-affiliated medical school.

SUBJECTS

Thirty mature sheep, each weighing 30 to 40 kg (0.9 to 1.1 m2 body surface area).

INTERVENTIONS

After baseline measurements, cecal ligation and perforation were used to establish an intra-abdominal source of infection. The abdominal wound was closed and animals were studied on the second postoperative day. An increase in cardiac output of > or = 30% was used to arbitrarily define the onset of sepsis. Repeat measurements were performed and the animal was killed.

RESULTS

The circulatory response to this septic insult included an increase in both cardiac index (change, baseline to sepsis, delta +2.24 +/- 0.75 L/min/m2; p < .01) and myocardial blood flows (delta +76.4 +/- 56 mL/100 g/min; p < .01). We found a negative correlation between the hematocrit and cardiac index (r2 = .21; p < .01) during the septic study, and noted that the amount (p < .01) of this correlation was significantly greater in the septic than the nonseptic study. Concurrently, the negative correlation observed between hematocrit and whole-body oxygen extraction (r2 = .21; p < .01) was significantly lower (p < .01) across the range of hematocrit values examined during the septic study vs. the similar relationship in the nonseptic study (r2 = .27; p < .01). The increase in myocardial oxygen consumption paralleled the relationship between cardiac work and hematocrit in the septic study, and was accompanied by increases in both myocardial blood flows (r2 = .25; p < .01) and myocardial oxygen extraction (r2 = .35; p < .01).

CONCLUSIONS

The normal circulatory compensation to anemia in hyperdynamic sepsis includes increases in cardiac index and whole-body oxygen extraction, although greater reliance is likely placed on the use of systemic flow reserve to maintain tissue oxygen uptake in septic vs. healthy study conditions. Furthermore, increased reliance on myocardial oxygen extraction in sepsis suggests that the normal flow-reserve supporting myocardial oxygen availability may be limited in this syndrome.