TLV offers clear theorical advantages over gas ventilation (GV); however, hemodynamic effects of TLV are still controversial. Accuracy of transpulmonary thermodilution, a relatively non-invasive method, applicable in a clinical setting, to assess hemodynamic parameters including extravascular lung water volume has not yet been described in TLV. The aim of this study was to evaluate the influence of TLV on hemodynamic parameters using transpulmonary thermodilution via a femoral artery in a prospective, controlled animal experimental trial. 16 anesthetised, paralysed healthy newborn lambs were conventionally gas ventilated via a tracheotomy and instrumented for continuous monitoring and recording of: (1) Pulmonary artery (PAP) and central venous pressure (CVP) via a 4 Fr Swan-Ganz catheter; (2) Hemodynamic parameters including cardiac index (CI), arterial blood pressure (AP), as well as indexed stroke volume (SVI), systemic vascular resistance (SVRI), intrathoracic blood volume (ITBI) and extravascular lung water (EVLWI) using a transpulmonary thermodilution method via the femoral artery (PC 8000 PICCO monitor, Pulsion Medical System, München, Ge). After baseline recording, the lambs were divided into 2 groups: 1: GV group (n= 8) who remained pressure-limited GV at: Fr 40/min, PiP 15 cm H2O, Peep 5 cm H2O and FiO2 1.0; 2: TLV group (n=8), whose lungs were filled with 30 ml/kg (= FRC) pre-oxygenated PFOB (F2 chemicals, UK) and then ventilated with a volume-controlled tidal liquid ventilator using independent piston pumps (INOLIVENT) at Fr 3–4/min, Vt 25 ml/kg, I/E 1:3, FiO 1.0. Gas exchanges, arterial Lactate/Pyruvate (L/P) ratio and hemodynamic parameters were recorded at 30 min intervals during a 120 min experimental period. The animals were then euthanized and their lungs examined for the presence of perfluorothorax and sampled for subsequent histology. As compared to GV group overall and to baseline GV, TLV animals demonstrated a slight significant increase in PaCO2, and a decrease in PaO2 (Kylstra effect), but gas exchanges were maintained in the targeted range. A slight significant decrease in arterial pH was also observed, with no difference in L/P ratio, however. AP was significantly decreased but maintained in the targeted range. There was no change in PAP or CVP. CI was significantly increased as well as SVI, and SVRI was decreased. In addition, ITBI and EVLWI were significantly increased. However, due to the high thermal conductibility of PFOB, the accuracy of transpulmonary thermodilution leading to an overestimation of CI during TLV is questionable. Nonetheless, this method could be considered to monitor liquid functional residual capacity during TLV.
The team is supported in part by the Foundation for Research into Children's Diseases, the Fonds Québécois pour la Recherche sur la Nature et les Technologies and Pulsion Medical Systems AG, Munich, Germany.