Is redistribution of microcirculatory blood flow within the small intestinal wall the cause of prolonged paralytic ileus in the critically ill?

Full text

Autoregulation of microcirculatory blood flow (MBF) and redistribution of flow within the intestinal wall (from the muscularis to the mucosa) are known mechanisms to maintain O₂ delivery in the gut during hypovolemia. During sepsis, however, autoregulation of blood flow is impaired [1]. The aim of this study as to monitor the distribution of MBF within the intestinal wall in different parts of the gastrointestinal tract during the development of septic shock.

Materials and methods

We measured systemic (CI), regional (mesenteric artery; SMA) and microcirculatory blood flow (MBF) in 11 sedated and ventilated pigs. MBF was measured with multichannel laser Doppler flowmetry in the gastric, jejunal, and colonic mucosa and the corresponding muscularis layers. Septic shock was induced by faecal peritonitis. After 240 min, i.v. fluids were administered to alter hypodynamic shock to hyperdynamic septic shock.

Results and discussion

During the first 240 min (hypodynamic shock) CI, SMA and MBF in the stomach mucosa decreased by 50% (Figs 1 and 2), while MBF in the jejunal and colonic mucosa remained virtually unchanged (Figs 3 and 4). In the muscularis of the jejunum and colon, on the other hand, MBF decreased significantly more than CI and SMA (Figs 2 and 4). Administration of i.v. fluids at 240 min resulted in a significant increase (above baseline) in CI and SMA (Fig. 1) as well as in MBF in the mucosa of the stomach, jejunum and colon. The `overshooting' increase in MBF in the jejunal and colonic mucosa, indicates that there was some hypoperfusion present in the mucosa during the hypodynamic phase despite maintained blood flow. This is supported by a significant decrease in jejunal pHi (Fig. 5) during the same time period. There was virtually no increase in MBF in the jejunal and colonic muscularis after fluid administration indicating a prolonged, perhaps endothelin induced, hypoperfusion.

Conclusion

It was concluded that MBF in the mucosa of the jejunum and colon remained unchanged, despite a 50% decrease in systemic and regional flows, suggesting a largely intact autoregulation during septic shock. MBF in the jejunal and colonic muscularis decreased significantly more than systemic and regional flows, suggesting that there is an active mechanism to maintain adequate blood flow to the mucosa during septic shock. Redistribution of blood flow from the muscularis to the mucosa causes severe hypoperfusion of the muscularis which contributes to intestinal atony frequently observed in critically ill patients.

Figure 1-5

Onset of peritonitis at 0 min and i.v. fluid administration at 240 min. Data is presented as mean ± SEM. Statistics: ANOVA for repeated mesurements. P <0.05 was considered statistically significant.