Hybrid measurement to achieve satisfactory precision in perioperative cardiac output monitoring.

Advanced haemodynamic monitoring employing minimally invasive cardiac output measurement may lead to significant improvements in patient outcomes in major surgery. However, the precision (scatter) of measurement of available generic technologies has been shown to be unsatisfactory with percentage error of agreement with bolus thermodilution (% error) of 40% to 50%. Simultaneous measurement and averaging by two or more technologies may reduce random measurement scatter and improve precision. This concept, called the hybrid method, was tested by comparing accuracy and precision of measurement relative to bolus thermodilution using combinations of three component methods. Thirty patients scheduled for either elective cardiac surgery or liver transplantation were studied. Agreement with simultaneous bolus thermodilution of hybrid combinations of continuous thermodilution (QtCCO) or Vigeleo™/FloTrac™ pulse contour measurement (QtFT) with pulmonary Capnotracking (QtCO2) was assessed pre- and post-cardiopulmonary bypass or pre- and post-reperfusion of the donor liver and compared with that of the component methods alone. Hybridisation of QtCO2 (% error 42.2) and QtCCO (% error 51.3) achieved significantly better precision (% error 31.3) than the component methods (P=0.0004) and (P=0.0195). Due to poor inherent precision of QtFT (% error 82.8), hybrid combination of QtFT with QtCO2 did not result in better precision than QtCO2 alone. Hybrid measurement can approach a 30% error, which is recommended as the upper limit for acceptability. This is a practical option where at least one component method, such as Capnotracking, is automated and does not increase the cost or complexity of the measurement process.