ObjectiveTo investigate the influence of misplaced subclavian vein (SCV) catheter into the ipsilateral internal jugular vein (IJV) on transpulmonary thermodilution (TPTD) measurements and explore the possible mechanisms preliminarily.MethodsIn this prospective study, 408 patients in whom an SCV catheterization was indicated for TPTD monitoring were enrolled. A first set of TPTD measurements was collected at baseline in all patients (group 1, SCV catheters were correctly placed; group 2, SCV catheters were misplaced into the ipsilateral IJV). The parameters included mean transit time (MTt), downslope time (DSt), cardiac index (CI), global end-diastolic volume index (GEDVI) and extra-vascular lung water index (EVLWI). A second set of TPTD measurements was performed only in those with catheter misplacement immediately after the misplaced SCV catheters being corrected (Group 3). The differences in MTt, DSt, GEDVI and EVLWI between group 2 and 3 were recorded as ΔMTt, ΔDSt, ΔGEDVI and ΔEVLWI, respectively.ResultsGEDVI and EVLWI were significantly higher (all P<0.001) in group 2 than those in group 1, while CI was not significantly different (P>0.05) between these two groups. Multivariate logistic regression identified PaO2/FiO2 [adjusted odds ratio (OR) 1.492/10 mm Hg; 95% confidence interval (CI), 1.180 - 1.884; P<0.001], GEDVI (OR=1.307/10 mL/m2, 95% CI 1.131 - 1.511; P<0.001) and EVLWI (OR=3.05; 95%CI 1.593 - 5.840; P<0.001) as the 3 independent factors associated with the misplacement of SCV catheter into the ipsilateral IJV. In group 2, GEDVI [(1041±122)mL/m2 vs. (790±102)mL/m2, P<0.001], EVLWI [(20.3±4.0)mL/kg vs. (10.3±2.3)mL/kg, P<0.001], CI [(3.6±1.2)L·min–1·m–2 vs. (2.9±1.0)L·min–1·m–2, P<0.001], MTt [(38.2±13.3)s vs. (30.8±9.4)s, P<0.001] and DSt [(18.9±7.2)s vs. (13.2±4.9)s, P<0.001)] were significantly higher than those in Group 3. Multiple regression analysis demonstrated that ΔEVLWI (R2=0.86, P<0.001) was negatively correlated with ΔMTt (coefficient±SE, –0.52±0.12; P<0.001) and positively correlated with ΔDSt (coefficient±SE, 1.45±0.17; P<0.001).ConclusionsDuring TPTD measurements, indicator injection through an SCV catheter misplaced into the ipsilateral IJV results in an overestimation of CI, GEDVI and EVLWI. The increase in DSt might be a key factor in explaining the overestimation of EVLWI in patients with misplaced SCV catheters. Given that the accurate measurements of GEDVI and EVLWI are of utmost importance for guiding resuscitation and decision-making regarding fluids administration, immediate repositioning is required if a misplacement is suspected and confirmed by the chest X-ray.