Lack of correlation between left ventricular outflow tract velocity time integral and stroke volume index in mechanically ventilated patients

Abstract

Objective: To assess the correlation between left ventricular outflow tract velocity time integral (LVOT VTI) and stroke volume index (SVI) calculated by thermodilution methods in ventilated critically ill patients.

Design: A prospective, descriptive, multicenter study was performed.

Setting: Five intensive care units from university hospitals.

Patients: Patients older than 17 years needing mechanical ventilation and invasive hemodynamic monitoring were included.

Interventions: LVOT VTI was measured by pulsatile Doppler echocardiography. Calculations of SVI were performed through a floating pulmonary artery catheter (PAC) or a Pulse index Contour Cardiac Output (PiCCO^®) thermodilution methods.

Main variables: The relation between LVOT VTI and SVI was tested by linear regression analysis.

Results: One hundred and fifty-six paired measurements were compared. Mean LVOT VTI was 20.83±4.86cm and mean SVI was 41.55±9.55mL/m². Pearson correlation index for these variables was r=0.644, p<0.001; ICC was 0.52 (CI 95% 0.4-0.63). When maximum LVOT VTI was correlated with SVI, Pearson correlation index was r=0.62, p<0.001. Correlation worsened for extreme values, especially for those with higher LVOT VTI.

Conclusions: LVOT VTI could be a complementary hemodynamic evaluation in selected patients, but does not eliminate the need for invasive monitoring at the present time. The weak correlation between LVOT VTI and invasive monitoring deserves additional assessment to identify the factors affecting this disagreement.

Keywords: Cuidados intensivos; Echocardiography; Ecocardiografía; Hemodynamic monitoring; Intensive care; Mechanical ventilation; Monitorización hemodinámica; Ventilación mecánica.