Evaluation of intestinal perfusion monitoring techniques

Introduction

Persistent hypoperfusion of the intestinal mucosal is considered important for the development of systemic complications during critical illness. The mucosal circulation is however not readily accessible to quantitative measurements of perfusion. Measurements of systemic perfusion are often extrapolated clinically to reflect regional perfusion, including the gastrointestinal organs. This extrapolation may introduce errors in the evaluation of hemodynamic status. Furthermore, the complex variable of person involves movement of blood and erythrocytes as well as the exchange of carbon dioxide and oxygen.

Aims

To investigate the relationship between clinically available techniques of measuring mucosal perfusion in relation to mesenteric and central blood flow during acute circulatory failure.

Materials and method

Thirteen fasted, anesthetized (pentobarbital) mechanically ventilated, normovolemic pigs (28–35 kg) were instrumented to monitor cardiac output (CO), portal blood flow (QPV, Transonic Systems), jejunal, mucosal laser-Doppler flowmetry (LDF, Perimed AB), jejunal CO₂-tonometry (TONO, Tonocap, Datex Instr) and jejunal, mucosal oxygen tension (tO₂, Licox, GMS). Acute reduction of CO by 40% from baseline was established by intrapericardial infusion of dextran and maintained for 90 minutes. Correlations between monitored variables were analysed by ANOVA and linear regression (*P < 0.05) and differences were analyzed by Wilcoxon's test (^§ P < 0.05).

Results

The best regressions coefficients were found between variables relating to measurements of movement of volume (QPV) or erythrocytes (LDF). Second to best regressions were obtained for TONO (measuring the exchange of CO₂). Notably, tPO₂ (measuring the exchange of O₂) did not correlate to variables of flow or CO₂ exchange.

Conclusion

In the setting of acute circulatory failure in pigs, cardiac output approximates mesenteric as well as intestinal mucosal perfusion. Importantly, the mucosal oxygen tension might vary independent from flow, which probably reflects the complexity of the counter current circulation within the mucosa. Oxygenation, being the pivotal variable determining tissue function, is thus not assessed even by techniques specifically directed towards the mucosal circulation.

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