Interpreting measures of splanchnic blood flow

Several techniques have been developed to measure the adequacy of splanchnic and gut mucosal blood flow. Gastrointestinal tonometry measures intralumenal Pco2 from which intracellular pH (pH) can be derived. Laser Doppler probes and Clark electrodes have been used to measure flow and Po2 directly. In human and animal studies, gut intramucosal acidosis occurs both in low-flow non-septic states and sepsis, and this is associated with increased gut permeability and a poor clinical outcome. However, in animal models of sepsis a low pHi occurs despite normal or increased mucosal blood flow and oxygenation. Therefore the low pH i of sepsis may represent failure of cellular oxygen utilization rather than inadequate oxygen supply, again explaining why maximizing systemic oxygen delivery has not improved outcome from septic shock. The fact that a low pHi is associated with an increase in mortality in both septic and non-septic patients does not imply a common pathophysiology. In the early phase of critical illness a low pH i is caused by an inadequate splanchnic oxygen supply, but the associated increase in mortality cannot be attributed to translocation. An alternative explanation is that the ischemic gut releases or activates some other mediator of remote organ injury. One possible mediator is the activated neutrophil.

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