Subcutaneous oxygen tensions provide similar information to ileal luminal CO2 tensions in an animal model of haemorrhage shock

Objectives: The cutaneous and splanchnic circulations undergo early vasoconstriction in shock. Methodological problems and insufficient information on subcutaneous carbon dioxide partial pressures limit the usefulness of previous studies on splanchnic and subcutaneous gas tensions in shock. Little comparative data exist on the responses of these tissues to shock and resuscitation. We therefore compared continuous subcutaneous PO2 (PO2sc) and PCO2 (PCO2sc) with simultaneous continuous gut luminal PCO2 (PCO2gi) in an animal model of haemorrhagic shock and resuscitation. Design: Prospective observational study. Setting: Intensive care laboratory in a teaching hospital. Subjects: Five anaesthetised rats. Interventions: Electrochemical-fiberoptic gas sensors inserted into Silastic tubing placed in the subcutaneous tissue and in the ileal lumen measured PCO2sc, PO2sc and PCO2gi continuously in five anaesthetised rats. After steady state conditions, hypotension [mean arterial blood pressure (MAP) 40 mmHg] was induced by controlled haemorrhage. The rats were allowed to remain hypotensive for 15 min and then resuscitated with shed blood and crystalloids. Arterial plasma lactate concentrations were measured at defined periods during the study. Measurements and main results: Hypovolaemia resulted in a significant decrease in PO2sc (P < 0.01) and a significant increase in PCO2gi and PCO2sc (P < 0.05). These values returned to baseline with resuscitation. PO2sc appeared to respond to haemorrhage earlier than PCO2gi and PCO2sc (P = 0.02). PO2sc was inversely correlated with PCO2gi (r(2) 0.7, P < 0.001). There were no significant changes in arterial plasma lactate concentrations. Conclusions: In our rat model, subcutaneous oxygen tension provided similar information to ileal luminal PCO2 and was more rapidly responsive than subcutaneous carbon dioxide tensions and arterial lactate during evolving haemorrhagic shock and resuscitation.