Endotoxin-induced ileal Vo2-Do2 alterations do not correlate with the severity of ileal injury

Perioperative Fluid Accumulation Impairs Intestinal Contractility to a Similar Extent as Peritonitis and Endotoxemia

BACKGROUND

Perioperative resuscitation with large amounts of fluid may cause tissue edema, especially in the gut, and thereby impairing its functions. This is especially relevant in sepsis where capillaries become leaky and fluid rapidly escapes to the pericapillary tissue. We assessed the effects of endotoxemia and peritonitis, and the use of high and moderate volume fluid resuscitation on jejunal contractility. We hypothesized that both endotoxemia and peritonitis impair jejunum contractility and relaxation, and that this effect is aggravated in peritonitis and with high fluid administration.

METHODS

Pigs were randomized to endotoxin (n = 16), peritonitis (n = 16), or sham operation (n = 16), and either high (20 mL/kg/h) or moderate volume (10 mL/kg/h) fluid resuscitation for 24 h or until death. At the end of the experiment, jejunal contractility and relaxation were measured in vitro using acetylcholine and sodium nitroprusside reactivity, and the effect of nitric oxide synthase inhibition (NOS-I) was assessed.

RESULTS

Mortality in the respective groups was 88% (peritonitis high), 75% (endotoxemia high), 50% (peritonitis moderate), 13% (endotoxemia moderate and sham operation high), and 0% (sham operation moderate volume resuscitation). Although gut perfusion was preserved in all groups, jejunal contractility was impaired in the two peritonitis and two endotoxemia groups, and similarly also in the sham operation group treated with high but not with moderate volume fluid resuscitation (model-fluid-contraction-interaction, P = 0.036; maximal contractility 136 ± 28% [average of both peritonitis, both endotoxemia and sham operation high-volume groups) vs. 170 ± 74% of baseline [sham operation moderate-volume group]). NOS-I reduced contractility (contraction-inhibition-interaction, P = 0.011) without significant differences between groups and relaxation was affected neither by peritonitis and endotoxemia nor by the fluid regimen.

CONCLUSIONS

Intestinal contractility is similarly impaired during peritonitis and during endotoxemia. Moreover, perioperative high-volume fluid resuscitation in sham-operated animals also decreases intestinal contractility. This may have consequences for postoperative recovery.

Endotoxin-induced ileal mucosal injury and nitric oxide dysregulation are temporally dissociated

Despite recent investigations, the mechanisms responsible for intestinal epithelial injury during endotoxemia remain unclear. The present study tests the hypothesis that epithelial necrosis and/or apoptosis correlate with nitric oxide (NO) dysregulation in a nonischemic model of sepsis-induced ileal injury. To test this hypothesis, a well-established in situ, autoperfused, feline ileal preparation was employed. After endotoxin (lipopolysaccharide [LPS], 3 mg/ kg, intravenously; n = 9) or vehicle (control; n = 5) treatment, ileal segments were obtained at baseline, 2 and 4 h for simultaneous evaluations of cellular and mitochondrial ultrastructure, immunoprevalence of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (a stable biomarker of peroxynitrite), and histochemical evidence of apoptosis. Epithelial necrosis was prominent by 2 h post-LPS, despite unaltered global ileal tissue oxygen content, blood volume, and blood flow. Significant evidence of apoptosis and increases in the immunoprevalence of iNOS and 3-nitrotyrosine were not evident until 4 h post-LPS. These results suggest that the early ileal mucosal necrosis may be due to LPS-induced activation of inflammatory pathways and/or microcirculatory disturbances, whereas NO dysregulation may participate in later events, including protein nitration and epithelial apoptosis.

Ileal VO(2)-O(2) alterations induced by endotoxin correlate with severity of mitochondrial injury

Sepsis is usually associated with altered O(2) metabolism in systemic organs. Until recently, inadequate O(2) delivery was thought to be the putative mechanism underlying these metabolic alterations. However, current investigations suggest that impaired O(2) consumption due to disrupted O(2) use by mitochondria may be the culprit. Therefore, we hypothesized that endotoxin (LPS)-induced V O(2)- O(2) alterations would correlate with the severity of mitochondrial injury in a systemic organ (i.e., the ileum). Using an in situ autoperfused feline ileum preparation, we assessed V O(2)- O(2) relationships and mitochondrial ultrastructure after 2 h in LPS-treated (3 mg/kg, intravenous; n = 11) and time-matched control (n = 5) animals. Mitochondrial injury was graded in a blinded fashion on the basis of characteristics associated with established stages of cell injury. LPS-treated animals developed severe mitochondrial injury in the ileal mucosa despite unchanged regional tissue perfusion and ileal oxyhemoglobin levels compared with controls. Worsening of mitochondrial injury correlated with increases in the critical O(2) delivery (r = 0.85; p < 0.002) and decreases in the maximum O(2) extraction (r = -0.61; p < 0.02) in the ileum. These results suggest that mitochondrial injury, leading to impaired O(2) utilization, may be primarily responsible for altered V O(2)- O(2) relationships in systemic organs during sepsis.

Ischemia/reperfusion injury to the ileum does not account for the ileal VO2-DO2 alterations induced by endotoxin

PURPOSE

Endotoxin (lipopolysaccharide [LPS])-induced systemic organ injury leads to disruption of normal systemic organ metabolic processes, which are manifest clinically by signs of accelerated anaerobic metabolism (e.g., tissue acidosis and hyperlactatemia) and altered VO2-DO2 relationships. The association of increased anaerobic metabolism with VO2-DO2 alterations has led to the notion that ischemia/ reperfusion (I/R) injury may be a prerequisite for the development of VO2-DO2 alterations during endotoxemia. However, in contrast to sepsis, in which oxygen consumption is often increased, oxygen consumption is severely decreased after I/R injury. Based on these observations, we hypothesized that I/R injury would result in systemic organ VO2-DO2 alterations, which are distinct from those that occur in sepsis.

MATERIALS AND METHODS

We used the in situ autoperfused feline ileal preparation to simultaneously examine microvascular permeability, reflected as the ileal lymph to plasma protein concentration ratio (CL/CP), and ileal VO2-DO2 relationships after either intravenous LPS (2.0 mg/kg; n = 5) or I/R injury (n = 5), and in matching controls (n = 5).

RESULTS

As expected, all LPS-treated and I/R-injured animals were found to have extensive ileal histological damage and marked increases in the CL/CP compared with controls (0.315 +/- 0.009 and 0.329 +/- 0.034, respectively, v 0.097 +/- 0.009; P < .001, both comparisons). In addition, the critical DO2 (DO2c) was elevated, and the critical oxygen extraction was decreased in both the I/R and LPS groups relative to controls. However, as initially hypothesized, the VO2 at the critical DO2 was markedly decreased in the I/R group compared with that of the LPS group.

CONCLUSIONS

These data indicate that I/R injury is insufficient to account for the systemic organ VO2-DO2 alterations that occur with LPS injury.