Changes in the mean systemic filling pressure during a fluid challenge in postsurgical intensive care patients

The difference between mean systemic filling (Pmsf) and central venous pressure (CVP) is the venous return gradient (dVR). The aim of this study is to assess the significance of the Pmsf analogue (Pmsa) and the dVR during a fluid challenge.

We performed a prospective observational study in postsurgical patients. Patients were monitored with a central venous catheter, a LiDCO™plus and the Navigator™. A 250-ml intravenous fluid challenge was given over 5 min. A positive response to the fluid challenge was defined as either a stroke volume (SV) or cardiac output increase of greater than 10 %.

A total of 101 fluid challenges were observed in 39 patients. In 43 events (42.6 %) the SV and CO increased by more than 10 %. Pmsa increased similarly during a fluid challenge in responders and non-responders (3.1 ± 1.9 vs. 3.1 ± 1.8, p = 0.9), whereas the dVR increased in responders (1.16 ± 0.8 vs. 0.2 ± 1, p < 0.001) as among non-responders CVP increased along with Pmsa (2.9 ± 1.7 vs. 3.1 ± 1.8, p = 0.15). Resistance to venous return did not change immediately after a fluid challenge. Heart performance (Eh) decreased significantly among non-responders (0.41 ± 0.15 vs. 0.34 ± 0.13, p < 0.001) whereas among responders it did not change when compared with baseline value (0.35 ± 0.15 vs. 0.34 ± 0.12, p = 0.15).

The changes in Pmsa and dVR measured at the bedside during a fluid challenge are consistent with the cardiovascular model described by Guyton.