Incoherence between Systemic Hemodynamic and Microcirculatory Response to Fluid Challenge in Critically Ill Patients

The aim of the study was to assess the coherence between systemic hemodynamic and microcirculatory response to a fluid challenge (FC) in critically ill patients.

We prospectively collected data in patients requiring a FC whilst cardiac index (CI) and microcirculation were monitored. The sublingual microcirculation was assessed using the incident dark field (IDF) CytoCam device (Braedius Medical, Huizen, The Netherlands). The proportion of small perfused vessels (PPV) was calculated. Fluid responders were defined by at least a 10% increase in CI during FC. Responders according to changes in microcirculation were defined by at least 10% increase in PPV at the end of FC. Cohen's kappa coefficient was measured to assess the agreement to categorize patients as "responders" to FC according to CI and PPV.

A total of 41 FC were performed in 38 patients, after a median time of 1 (0-1) days after ICU admission. Most of the fluid challenges (39/41, 95%) were performed using crystalloids and the median total amount of fluid was 500 (500-500) mL. The main reasons for fluid challenge were oliguria (n = 22) and hypotension (n = 10). After FC, CI significantly increased in 24 (58%) cases; a total of 19 (46%) FCs resulted in an increase in PPV. Both CI and PPV increased in 13 responders and neither in 11; the coefficient of agreement was only 0.21. We found no correlation between absolute changes in CI and PPV after fluid challenge.

The results of this heterogenous population of critically ill patients suggest incoherence in fluid responsiveness between systemic and microvascular hemodynamics; larger cohort prospective studies with adequate a priori sample size calculations are needed to confirm these findings.