• Hollmann D Aya, Andrew Rhodes, Chis SterIrinaI, Nick Fletcher, R Michael Grounds, and Maurizio Cecconi.
• 1Adult Critical Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, London, United Kingdom. 2Institute of Infection and Immunity, St George's University of London, London, United Kingdom.
• Crit. Care Med. 2017 Feb 1; 45 (2): e161-e168.

ObjectiveThe objectives of this study are to determine what is the minimal volume required to perform an effective fluid challenge and to investigate how different doses of IV fluids in an fluid challenge affect the changes in cardiac output and the proportion of responders and nonresponders.DesignQuasi-randomized controlled trial.SettingCardiothoracic ICU, tertiary university hospital.PatientsEighty postcardiac surgery patients.InterventionIV infusion of 1, 2, 3, or 4 mL/Kg (body weight) of crystalloid over 5 minutes.Measurements And Main ResultsMean systemic filling pressure measured using the transient stop-flow arm arterial-venous equilibrium pressure, arterial and central venous pressure, cardiac output (LiDCOplus; LiDCO, Cambridge, United Kingdom), and heart rate. The groups were well matched with respect to demographic and baseline physiologic variables. The proportion of responders increased from 20% in the group of 1 mL/kg to 65% in the group of 4 mL/kg (p = 0.04). The predicted minimal volume required for an fluid challenge was between 321 and 509 mL. Only 4 mL/Kg increases transient stop-flow arm arterial-venous equilibrium pressure beyond the limits of precision and was significantly associated with a positive response (odds ratio, 7.73; 95% CI, 1.78-31.04).ConclusionThe doses of fluids used for an fluid challenge modify the proportions of responders in postoperative patients. A dose of 4 mL/Kg increases transient stop-flow arm arterial-venous equilibrium pressure and reliably detects responders and nonresponders.

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