The monitoring of venous saturations of oxygen in children with congenitally malformed hearts

Mixed venous saturation of oxygen has for some time been used as a tool to assess the adequacy of systemic delivery of oxygen in intensive care. In the post-operative child with cardiac disease, it is increasingly being used to assess adequacy of cardiac output. In many of these patients, true sampling of mixed venous saturation of oxygen is not possible due to the infrequent use of pulmonary arterial catheters, or the presence of intra-cardiac left to right shunting leading to mixing of systemic and pulmonary venous blood. The use of saturation of oxygen in the central venous blood as a surrogate for mixed venous saturation of oxygen has been widely investigated in adults, but its use remains controversial. In this review, we discuss the theory behind the use of mixed venous saturation of oxygen in evaluating cardiac output, the problems pertinent to those patients with congenitally malformed hearts, and explore the evidence for central venous saturation of oxygen as a surrogate for mixed venous saturation of oxygen, and its use as a therapeutic target to improve outcomes in this population of patients