Microvascular oxygen pressure in the pig intestine during haemorrhagic shock and resuscitation.

1. The aim of this study was to investigate the relation between microvascular and venous oxygen pressures during haemorrhagic shock and resuscitation in the pig intestine. To this end microvascular PO2 (microPO2) was measured by quenching of Pd-porphyrin phosphorescence by oxygen and validated for the intestines. In addition, mesenteric venous blood gasses, blood flow, ilial CO2 production and global haemodynamics were also measured. 2. In one group (n = 11), moderate shock was induced by withdrawal of 40% of the circulating blood volume. Seven of these animals were resuscitated with a crystalloid solution and four with the withdrawn blood. In a second group of three animals, a more severe shock was induced by withdrawal of 50% of the circulating blood volume; these animals were not resuscitated. 3. Baseline mesenteric venous PO2 and microPO2 values were similar (60 +/- 9 and 60 +/- 11 mmHg, respectively). During moderate shock, microPO2 dropped significantly below mesenteric venous PO2 (26 +/- 10 versus 35 +/- 8 mmHg). After resuscitation with crystalloid solution, microPO2 and mesenteric venous PO2 rose to 44 +/- 9 and 44 +/- 6 mmHg, respectively. In the group that received the withdrawn blood, values were 41 +/- 9 and 53 +/- 12 mmHg, respectively. Severe shock resulted in a drop in the mesenteric venous PO2 (n = 3) to a value similar to that seen in the moderate shock group, but the gut microPO2 dropped to a much lower value than that of the moderate shock group (15 +/- 5 versus 26 +/- 10 mmHg). 4. The results indicate that the oxygenation of the microcirculation of the gut can become lower than the venous PO2 under conditions of haemorrhagic shock.