Can changes in arterial pressure be used to detect changes in cardiac index during fluid challenge in patients with septic shock?

Response to fluid challenge is often defined as an increase in cardiac index (CI) of more than 10-15%. However, in clinical practice CI values are often not available. We evaluated whether changes in mean arterial pressure (MAP) correlate with changes in CI after fluid challenge in patients with septic shock. This was an observational study in which we reviewed prospectively collected data from 51 septic shock patients in whom complete hemodynamic measurements had been obtained before and after a fluid challenge with 1,000 ml crystalloid (Hartman's solution) or 500 ml colloid (hydroxyethyl starch 6%). CI was measured using thermodilution. Patients were divided into two groups (responders and non-responders) according to their change in CI (responders: %CI > 10%) after the fluid challenge. Statistical analysis was performed using a two-way analysis of variance test followed by a Student's t test with adjustment for multiple comparisons. Pearson's correlation and receiver operating characteristic curve analysis were also used. Mean patient age was 67 +/- A 17 years and mean Sequential Organ Failure Assessment (SOFA) upon admittance to the intensive care unit was 10 +/- A 3. In the 25 responders, MAP increased from 69 +/- A 9 to 77 +/- A 9 mmHg, pulse pressure (PP) increased from 59 +/- A 15 to 67 +/- A 16, and CI increased from 2.8 +/- A 0.8 to 3.4 +/- A 0.9 L/min/m(2) (all p < 0.001). There were no significant correlations between the changes in MAP, PP, and CI. Changes in MAP do not reliably track changes in CI after fluid challenge in patients with septic shock and, consequently, should be interpreted carefully when evaluating the response to fluid challenge in such patients.