Assessing fluid responses after coronary surgery: role of mathematical coupling of global end-diastolic volume to cardiac output measured by transpulmonary thermodilution

Background Mathematical coupling may explain in part why cardiac filling volumes obtained by transpulmonary thermodilution may better predict and monitor responses of cardiac output to fluid loading than pressures obtained by pulmonary artery catheters (PACs). Methods Eleven consecutive patients with hypovolaemia after coronary surgery and a PAC, allowing central venous pressure (CVP) and continuous cardiac index (CCIp) measurements, received a femoral artery catheter for transpulmonary thermodilution measurements of global end-diastolic blood volume index (GEDVI) and cardiac index (CItp). One to five colloid fluid-loading steps of 250 ml were done in each patient (n=48 total). Results Fluid responses were predicted and monitored similarly by CItp and CCIp, whereas CItp and CCIp correlated at r=0.70 (P<0.001) with a biasof 0.40 l min