Background: An individualized fluid optimization strategy, based on maximization of cardiac stroke volume (SV) with colloid boluses (goal-directed therapy), improves outcome after surgery. Oesophageal Doppler (OD) is used for SV maximization in most randomized studies, but evidence-based guidelines for the SV maximization procedure are lacking and variation in SV may influence the indication for fluid administration. We measured beat-to-beat OD SV before and after fluid optimization in order to estimate the number of heartbeats for which SV needs to be averaged to provide an acceptable accuracy for goal-directed therapy with this technology.
Methods: Twenty patients scheduled for surgery were anaesthetized, followed by OD SV assessment. Thirty seconds of beat-to-beat data were recorded before and after volume optimization performed by successive boluses of 200 ml colloid until SV did not increase ≥10%. SV variability was assessed before and after the volume optimization when SV was measured beat to beat and when it was averaged over 2–10 heartbeats.
Results: Nineteen (95%) and 17 (85%) patients demonstrated an SV variability ≥10% before and after volume optimization, respectively, when SV was measured beat to beat. However, when SV was averaged over 10 heartbeats, only two (10%) and one (5%) of the patients demonstrated an SV variability ≥10% before and after optimization, respectively (P<0.0001).
Conclusion: OD SV variability is significantly reduced and reaches an acceptable level when SV is averaged over 10 heartbeats. The use of a shorter averaging period for SV may lead to incorrect volume administration in goal-directed fluid management.