Detecting gastrointestinal hypoperfusion during cardiac tamponade in pigs: A role for nitric oxide tonometry?

Objective: To evaluate different techniques and regional approaches for detecting critical reductions in gastrointestinal (GI) perfusion. Design: Laboratory, animal, controlled study. Setting: University animal research laboratory. Subjects: Thirteen anesthetized, ventilated, juvenile domestic pigs. Interventions: Dextran was infused into the pericardial sac to achieve cardiac tamponade that reduced cardiac output to 25% of baseline value Hemodynamics were invasively monitored, and blood gases were sampled in the systemic and portal circulations. Tonometers were placed in the corpus of the stomach and in the jejunum, 50 cm aboral to the ligament of Treitz. Measurements and Main Results: We measured cardiac output, portal venous blood flow, mesenteric oxygen delivery and consumption, systemic and portal venous blood gases and acid-base balance, stomach and jejunal transepithelial potential difference, stomach and jejunal intramucosal pH, arterial plasma concentrations of asymmetric dimethylarginine, and jejunal, intraluminal nitric oxide. One hour of cardiac tamponade decreased mesenteric oxygen delivery and consumption in a linear fashion and resulted in mesenteric acidosis, as evidenced by decreases in pH, standard bicarbonate, oxygen saturation, and PO₂ and increases in PCO₂. The potential difference in the jejunum decreased earlier than in the stomach, whereas stomach intramucosal pH decreased before jejunal intramucosal pH. Intraluminal nitric oxide in the jejunum was markedly reduced soon after cardiac tamponade. This reduction was accompanied by an increase in arterial plasma concentrations of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine. Investigated variables were unchanged in control animals. Conclusions: Both intramucosal pH and potential difference measurements may be used to detect critical reduction in GI perfusion. Regional and temporal differences may reduce the accuracy of these methods. Jejunal tonometry can yield an early nitric oxide measurement that indicates mesenteric low-flow conditions Jejunal tonometry also yields quantitative information about this modulator of hemodynamic and mucosal barrier function, information that is relevant to GI failure during shock.