Dynamic filling index: a novel parameter to monitor circulatory filling during minimized extracorporeal bypass.
OBJECTIVE
To evaluate the dynamic filling index, a novel parameter to monitor changes in venous return and drainable volume, in circulatory assisted patients. Minimized extracorporeal bypass systems lack volume buffering capacity, demanding tight control of drainable volume to maintain bypass flow. Therefore, with patients on minimized bypass quantitative assessment of venous drainable volume is crucial.


METHODS
In seven patients undergoing coronary artery bypass grafting using minimized extracorporeal bypass we utilized luxation of the heart to induce a reduction in venous return. The speed of the centrifugal pump was transiently and periodically reduced to monitor resultant changes in bypass flow. The dynamic filling index, a measure of drainable volume, was calculated as Deltaflow/Deltaspeed.


RESULTS
With luxation, the dynamic filling index was significantly reduced (from 2.4 +/- 0.2 to 2.0 +/- 0.2 ml/rotation, p = 0.001; 95% confidence interval of mean difference: 0.23-0.46 ml/rotation), whereas routinely recorded parameters, like bypass flow, pump inlet and arterial line pressure, did not change significantly. The intra-measurement reproducibility for the dynamic filling index was 0.5 ml/rotation (20% of the mean), suggesting good potential for this parameter to monitor on-pump venous return in patients.


CONCLUSIONS
The dynamic filling index can detect small changes in venous return and drainable volume which remain unrevealed by routinely recorded parameters. This index could be a valuable tool to monitor and control circulatory filling in individual patients supported by minimized extracorporeal bypass.
Simons
Antoine P
AP
Department of Cardiothoracic Surgery, Cardiovascular Research Institute Maastricht-CARIM, Maastricht University Medical Center-MUMC, Maastricht, The Netherlands. antoinepsimons@ctc.unimaas.nl
Reesink
Koen D
KD
Lancé
Marcus D
MD
van der Veen
Frederik H
FH
de Jong
Dick S
DS
Weerwind
Patrick W
PW
Maessen
Jos G
JG
D000368:Aged; D001810:Blood Volume; D001026:Coronary Artery Bypass / Q000379:methods*; D003326:Coronary Circulation; D017548:Echocardiography, Transesophageal; D005112:Extracorporeal Circulation / Q000379:methods*; D006439:Hemodynamics; D006801:Humans; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*