Measurement of cardiac output: a comparison between transpulmonary thermodilution and uncalibrated pulse contour analysis

Background. Recently, continuous monitoring of cardiac output (CO) based on pulse contour analysis (Vigileo((R))) has been introduced into practice. In this clinical study, we evaluated the accuracy of this system by comparing it with the transpulmonary thermodilution technique (TPID) in septic patients. Methods. We studied 24 mechanically ventilated patients with septic shock (16 male, 8 female, age 26-77 yr) receiving treatment with norepinephrine who for clinical indication underwent haemodynamic monitoring by the transpulmonary thermodilution technique using a PiCCO((R)) plus system (Pulsion Medical Systems, Munich, Germany). In parallel, arterial pulse contour was applied using the femoral arterial pressure curve (FloTrac((R)) pressure sensor, Vigileo((R)) monitor, Edwards Lifesciences, Irvine, USA). After baseline measurement, mean arterial pressure was elevated by increasing norepinephrine dosage, and CO was measured again before mean arterial pressure was reduced back to baseline levels. Fluid status and ventilator settings remained unchanged throughout. At each time point, CO by transpulmonary thermodilution was calculated from three central venous bolus injections of 15 ml of saline (< 8 degrees C). Linear regression and the Bland-Altman method were used for statistical analysis. Results. Overall, CO was 6.7 (SD 1.8) (3.2- 10.1) litre min(-1) for CO(TPID) and 6.2 (2.4) (3.0-17.6) litre min(-1) for CO(Vigileo((R))). Linear regression revealed: CO(Vigileo((R)))= 2 1.54+0.72xCO(TPID) litre min(-1), r(2) =0.26 (P < 0.0001). Mean bias between techniques [CO(TPID)-CO(Vigileo((R)))] was 0.5 litre min(-1) (SD 2.3 litre min(-1)). Correlation coefficients at the three time points were not significantly different from each other. Conclusions. Pulse contour analysis-derived CO (Vigileo((R)) system) underestimates CO(TPID) and is not as reliable as transpulmonary thermodilution in septic patients.