Preload response in patients after cardiac surgery: a comparison of systolic blood pressure and systolic area variability and initial volume of distribution of glucose.

Objective: Estimation of stroke volume variation (e.g. systolic blood pressure and systolic area variability) and central extracellular compartment volume (e.g. initial volume of distribution of glucose, IVDG) may be useful in guiding fluid therapy in mechanically ventilated patients. The reliability of systolic blood pressure (SBP) variability has been well validated, but little is known about systolic area (SA) variability or IVDG. Our aim was to investigate SBP and SA variability and IVDG as predictors of preload responsive hypovolaemia in post-cardiac surgery patients.

Methods: Thirty-four mechanically ventilated patients undergoing preload enhancement post elective cardiac surgery were studied. The maximum-minimum difference and power spectral measurement of SBP and SA variability were derived from the arterial waveform trace and examined before and after rapid volume infusion. IVDG was determined prior to volume infusion from three-minute incremental glucose estimation and (with SBP and SA variability) correlated with subjects classified as hypotensive and preload responsive.

Results: Neither IVDG or SA and SBP variability were found to correlate with subjects identified as hypotensive and preload responsive. However, the power spectral measures of SBP and SA variability were significantly reduced (p = 0.007 and p = 0.026, respectively) following preload enhancement in fluid responsive subjects.

Conclusions: Our results indicate that neither IVDG, nor SBP and SA variability are predictive of preload responsive hypotension in post-cardiac surgery patients. Spectral analysis of SBP and SA may be more sensitive at assessing preload responsiveness in this patient group than traditional maximum-minimum measures.