In this single-center observational study, we identified that 1/ CCO measured immediately before CO recalibration after a FC demonstrated a small negative bias; 2/ ∆%CCO demonstrated intermediate trending capacity with potentially large bias between methods; and 3/ ∆%CCO had acceptable classifying performance to identify fluid responsiveness, with a risk of false negative results.

Our findings suggest that, while performing a FC monitored by calibrated CCO, cautious interpretation of the FC’s results should be made, due to potential bias impacting its relative change from baseline. The pharmacokinetics of a FC show that the infusion of 500 ml of crystalloid at 20 °C may not only improve venous return and potentially CO, but could also alter arterial or venous compliance and resistance [2]. These modifications will eventually modify the arterial root signal of CCO, and lead to misclassification [3].

FC’s hemodynamic effect dissipation occurring between the end of the FC and the end of recalibration (∽5 min) may not be retained, as the bias between method was negative (i.e. CCO was lower than COTPTD), and no cases showed a ∆%CCO > 15% in non-responders [4]. Finally, COTPTD measured by triplicate injection demonstrates a precision of ∽7% and least significant change (LSC) of ∽10%, which implies potentially inaccurate adjudication of fluid responsiveness using this technique [5].

To conclude, using CCO to evaluate fluid responsiveness in patients receiving a FC has the advantage of being efficient, but goes with the risk of misclassification and misleading clinical conclusions.