High mixed venous oxygen saturation levels do not exclude fluid responsiveness in critically ill septic patients

This observational study was conducted in a 32-bed university hospital medicosurgical ICU. The hemodynamic response to a fluid challenge was evaluated in 65 critically ill patients with severe sepsis. Patients were divided into two groups (responders and nonresponders) according to their cardiac index (CI) response to the challenge (>10% or <10%).Of the 65 patients, 34 (52%) were fluid responders. Baseline SvO2, CI, heart rate (HR) and mean arterial pressure (MAP) were not statistically different between groups. The responders had lower pulmonary artery occlusion pressure (PAOP) and central venous pressure (CVP) at baseline than the nonresponders. After the fluid challenge, there were no differences between the two groups in MAP, CVP, PAOP or HR. There was no correlation between changes in CI or stroke volume index and baseline SvO2. Receiver operating characteristic analysis showed that SvO2 was not a predictor of fluid responsiveness.The response of septic patients to a fluid challenge is independent of baseline SvO2. The presence of a high SvO2 does not necessarily exclude the need for further fluid administration.Patients with severe sepsis and septic shock typically have decreased vascular tone, with a high cardiac index (CI), low systemic vascular resistance and elevated mixed venous oxygen saturation (SvO2). Fluid resuscitation is essential for the restoration and maintenance of adequate intravascular volume to improve and maintain organ perfusion [1-4]. Natural or artificial colloids or crystalloids may be used for this purpose, as no differences in outcome have been reported related to the type of fluid [5]. As fluid requirements are not easily determined, a fluid challenge technique should be used on a repeated basis according to the patient's response (for example, an increase in blood pressure) and tolerance (for example, excessive increase in cardiac filling pressure) [6-8].By rearranging the Fick equation, SvO2 can be defined as the balance between fou