Prediction and monitoring of cardiac response to intravenous fluid administration by non-invasive measurement of the initial systolic time interval after cardiac surgery

Intravenous fluid administration is universally accepted as a treatment for
hypotension after cardiac surgery. The accuracy of indexes, used to assess
preload and predict fluid responsiveness, has been questioned, however.
Parameters, able to unmask preload deficiency and to predict an improvement in
cardiac function with volume expansion, are actively searched.

The objective of the study is to develop a non-invasive method to optimize the
assessment of cardiac preload and therapeutic fluid administration after
coronary artery bypass surgery.

The study concerns the evaluation of a method of measurement by comparison with
other methods. Thirty-five patients who are administered to the Intensive Care
Unit after coronary artery bypass surgery and who are presumably hypovolaemic
will be measured during administration of 2x250 ml of an isosmotic colloidal
fluid solution, which is part of their standard treatment. From the
electro-cardiogram (ECG), arterial pressure Pa and impedance cardiogram (ICG)
the parameters preejection period (PEP) and the respiratory change (delta) in
PEP (delta-PEP), the initial systolic time interval (ISTI) and the respiratory
change (delta-ISTI) will be determined before and after each administration of
250 ml of the fluid solution. These measures will be compared with the
simultaneous cardiac output (CO), obtained by a standard thermodillution
technique.

An additional number of four electrodes, similar to ECG-electrodes, will be
attached to the patient. A small electrical current of 0.3 mArms will be
transmitted through the thorax applied by the two outer electrodes, having a
frequency of 64 kHz. The frequency of this current is well above the range of
biological excitation and the amplitude is well below the range of biological
excitation or sensing. The method is safe to be used on the intensive care unit.
The method is non-invasive. Participating in the study contains no burden and
no risk for the subjects. The nature or duration of the treatment will not
change.