Central mixed and splanchnic venous oxygen saturation monitoring

Abstract

Central mixed venous oxygen saturation (S$\mathop v\limits^ -$O₂) monitoring in critically ill patients to estimate adequacy of peripheral perfusion is gaining increasing popularity. However, a number of unexpected responses, one of which is marked depression of regional (splanchnic) venous oxygen saturation which may coexist with normal or high S$\mathop v\limits^ -$O₂, makes interpretation pretation of this parameter difficult. The S$\mathop v\limits^ -$O₂ and hepatic venous oxygen saturation levels in seven injured (postoperative) and 15 septic patients were measured. No substantial differences between central and hepatic venous oxygen saturation were noted in nonseptic patients, however, septic subjects exhibited a normal S$\mathop v\limits^ -$O₂ of 70.5%±8.7% at a time when the hepatic venous saturation was 55.6%±14.4% which is a significant (p<0.05) reduction. This reduced oxygen saturation was noted to arise from an increased regional metabolic rate rather than reduced perfusion. Nevertheless, we conclude that a flow limited regional oxygen consumption may potentially exist despite the presence of a normal S$\mathop v\limits^ -$O₂ in certain patient subgroups such as septic subjects. Therefore, a normal S$\mathop v\limits^ -$O₂ should not be considered as sole criteria to insure optimal oxygen delivery in critically ill patients.