Measurements of subcutaneous tissue PO2 reflect oxygen metabolism of the small intestinal mucosa during hemorrhage and resuscitation. An experimental study in pigs

Abstract

Background: The first tissues to be deprived of perfusion and oxygenation in a hypovolemic situation and the last ones to be reperfused are the subcutaneous tissue and the gastrointestinal mucosa. We hypothesized that measurements of subcutaneous tissue gases and pH might reflect simultaneous changes in oxygenation of the intestinal mucosa. The aim of this study was to evaluate tissue gases and pH as measures of tissue oxygenation and tissue oxygen metabolism in subcutaneous and intestinal tissues simultaneously.

Material and methods: Five out of 17 domestic pigs (weight 21-25 kg) were used as controls without bleeding. Twelve animals were bled in 3 steps, 10% of their calculated blood volume at each step. The removed blood, crystalloid and colloid were thereafter infused, and animals were stabilized for 30 min. Measurements were made after each step of bleeding, retransfusion and stabilization. Before bleeding, all animals had a sensor (Paratrend 7) implanted subcutaneously in the left groin for measurements of tissue gases and pH (P(sc)O(2), P(sc)CO(2) and pH(sc)). Catheters were positioned in the jugular vein, portal vein, carotid artery, pulmonary artery and femoral artery for infusion, bleeding and oxygen monitoring. Via a midline laparotomy, 2 silicon tonometers (TRIP sigmoid catheters) were positioned in the ileum and sigmoid colon for measurements of PCO(2) and pH (P(iI)CO(2), P(si)CO(2), pH(iI) and pH(si)). Blood flow in the portal vein was measured by an ultrasound probe (H6SB) and a Clark electrode (Cardiff tissue oxymeter) was used for serosal PO(2) measurements of the ileum (P(iI)O(2)) and sigmoid colon (P(si)O(2)).

Results: After the first step of bleeding, P(sc)O(2) decreased from 64 +/- 17 to 56 +/- 22 mm Hg (SD; p < 0.05). P(sc)CO(2) and pH(sc) did not change. P(iI)CO(2) increased from 64 +/- 14 to 79 +/- 14 mm Hg (p < 0.05), P(si)CO(2) increased from 77 +/- 16 to 90 +/- 18 mm Hg (p < 0.05). pH(iI) decreased from 7.15 +/- 0.09 to 7.03 +/- 0.09 (p < 0.05). P(iI)O(2) and P(si)O(2) decreased, but not significantly until steps of further bleeding. After re-transfusion and stabilization, P(sc)O(2) and P(iI)CO(2) returned to baseline.

Conclusion: Measurements of subcutaneous PO(2) are sensitive to bleeding and resuscitation and reflect oxygen metabolism in the small intestinal mucosa as measured by PCO(2) and pH.