Right ventricular end-diastolic volume as a predictor of the hemodynamic response to a fluid challenge

Objective: To compare thermodilution right ventricular end-diastolic volume index (RVEDVI) and pulmonary artery occlusion pressure (Ppao) as predictors of the hemodynamic response to a fluid challenge. Design: Prospective cohort study. Setting: Medical ICU of a university-affiliated county hospital and medical-surgical ICU of a community hospital. Patients: Twenty-five critically ill patients who had one or more clinical conditions that suggested the possibility of inadequate preload. Interventions: Thirty- six fluid challenges. Fluid (saline or colloid) was administered rapidly until the Ppao rose by at least 3 mm Hg. When a patient underwent more than one fluid challenge, these were given on separate days and for different clinical indications. Measurements and Results: Responders (n=20; ≤10% increase in stroke volume [SV]) and nonresponders (n= 16; < 10% increase in SV) differed with respect to baseline Ppao (10.0 ± 3.4 vs 14.2 ± 3.6 mm Hg; p=0.001), but not with respect to baseline RVEDVI (105 ± 31 vs 119 ± 33 mL/m²; p=0.22). There was a moderate correlation between RVEDVI and fluid- induced change in SV (r=0.44); the relationship between Ppao and change in SV was stronger (r=0.58). A positive response to fluid was observed in 4 of 9 cases in which RVEDVI exceeded 138 mL/m², a threshold value that has been suggested to reliably predict a poor response to fluid. Conclusion: RVEDVI was not a reliable predictor of the response to fluid. As a predictor of fluid responsiveness, Ppao was superior to RVEDVI. In an individual patient, adequacy of preload is best assessed by an empiric fluid challenge.