New Advances in Monitoring Cardiac Output in Circulatory Mechanical Assistance Devices. A Validation Study in a Porcine Model

Oxygen Consumption Predicts Long-Term Outcome of Patients with Left Ventricular Assist Devices

Reduced oxygen consumption (VO₂), either due to insufficient oxygen delivery (DO₂), microcirculatory hypoperfusion and/or mitochondrial dysfunction, has an impact on the adverse short- and long-term survival of patients after cardiac surgery. However, it is still unclear whether VO₂ remains an efficient predictive marker in a population in which cardiac output (CO) and consequently DO₂ is determined by a left ventricular assist device (LVAD). We enrolled 93 consecutive patients who received an LVAD with a pulmonary artery catheter in place to monitor CO and venous oxygen saturation. VO₂ and DO₂ of in-hospital survivors and non-survivors were calculated over the first 4 days. Furthermore, we plotted receiver-operating curves (ROC) and performed a cox-regression analysis. VO₂ predicted in-hospital, 1- and 6-year survival with the highest area under the curve of 0.77 (95%CI: 0.6-0.9; p = 0.0004). A cut-off value of 210 mL/min VO₂ stratified patients regarding mortality with a sensitivity of 70% and a specificity of 81%. Reduced VO₂ was an independent predictor for in-hospital, 1- and 6-year mortality with a hazard ratio of 5.1 (p = 0.006), 3.2 (p = 0.003) and 1.9 (p = 0.0021). In non-survivors, VO₂ was significantly lower within the first 3 days (p = 0.010, p < 0.001, p < 0.001 and p = 0.015); DO₂ was reduced on days 2 and 3 (p = 0.007 and p = 0.003). In LVAD patients, impaired VO₂ impacts short- and long-term outcomes. Perioperative and intensive care medicine must, therefore, shift their focus from solely guaranteeing sufficient oxygen supply to restoring microcirculatory perfusion and mitochondrial functioning.

Cardiac output monitoring with pulmonary versus trans-cardiopulmonary thermodilution in left ventricular assist devices: Interchangeable methods?

Cardiac output (CO) measurement is mandatory in patients with left ventricular assist devices (LVADs). Thermodilution with pulmonary artery catheter (PAC) remains the clinical gold standard to measure CO in these patients, however it is associated with several complications. Therefore, the agreement between PAC and new, minimally invasive monitoring methods in LVAD needs to be further investigated. The aim of this study was to assess the accuracy and reliability of transpulmonary thermodilution with a PiCCO2 monitor compared with pulmonary artery thermodilution with PAC in a LVAD. Continuous-flow LVADs were implanted in six mini-pigs to assist the left ventricle. We studied two methods of measuring CO—intermittent transpulmonary thermodilution (CO_TPTD) by PiCCO2 and intermittent pulmonary artery thermodilution by CAP, standard technique (CO_PTD)—obtained in four consecutive moments of the study: before starting the LVAD (basal moment), and with the LVAD started in normovolemia, hypervolemia (fluid overloading) and hypovolemia (shock hemorrhage). A total of 72 paired measurements were analysed. At the basal moment, CO_TPTD and CO_PTD were closely correlated (r² = 0.89), with a mean bias of −0.085 ± 0.245 L/min and percentage error of 16%. After 15 min of partial support LVAD, CO_TPTD and CO_PTD were closely correlated (r² = 0.79), with a mean bias of −0.040 ± 0.417 L/min and percentage error of 26%. After inducing hypervolemia, CO_TPTD and CO_PTD were closely correlated (r² = 0.78), with a mean bias of −0.093 ± 0.339 L/min and percentage error of 13%. After inducing hypovolemia, CO_TPTD and CO_PTD were closely correlated (r² = 0.76), with a mean bias of −0.045 ± 0.281 L/min and percentage error of 28%. This study demonstrates a good agreement between transpulmonary thermodilution by PiCCO monitor and pulmonary thermodilution by PAC in the intermittent measurement of CO in a porcine model with a continuous-flow LVAD.