Introduction: Left ventricular stroke volume variation (SVV) has been shown to be superior compared to static preload indicators in predicting fluid responsiveness . However, the assessment of SVV depends on both cardiac filling status and changes in intrathoracic pressure associated with mechanical ventilation . The reliability and validity of SVV has therefore been questioned in patients ventilated with low tidal volumes.
Method: 16 patients after coronary artery bypass grafting (CABG) participated in the study. Patients were mechanically ventilated in a pressurecontrolled mode (tidal volume: 7.5 ± 1.2 mL kg−1). SVV was assessed by pulse contour analysis. Left ventricular end-diastolic area index (LVEDAI) was determined by transoesophageal echocardiography. The thermodilution technique was used for measurements of cardiac index (CI), stroke volume index (SVI) and intrathoracic blood volume index (ITBI). All parameters were assessed before and after volume challenge induced by tilting the patients from anti-Trendelenburg (30° head-up) to Trendelenburg position (30° head-down).
Results: After change to the Trendelenburg position, SVV decreased significantly, while CI, SVI, ITBI, LVEDAI, central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) increased significantly. Changes in SVI were significantly correlated to changes in SVV (r = −0.60; P < 0.0005) and to changes in LVEDAI (r = 0.92; P < 0.0001), ITBI (r = 0.87; P < 0.0001), CVP (r = 0.71; P < 0.0001) and PAOP (r = 0.58; P < 0.001). Linear regression analysis of the dynamic relationship between changes in SVI induced by volume challenge and baseline values of SVV, CI, ITBI, LVEDAI, CVP and PAOP showed that only baseline values of SVV correlated with concomitant changes in SVI (r = 0.62; P < 0.005).
Discussion: The results strengthen the importance of functional haemodynamic monitoring. Assessment of hypovolaemia in the anti-Trendelenburg position by static preload parameters (CVP, PAOP, ITBI, LVEDAI) were not indicative to predict the dynamic response to volume challenge. Only baseline values of SVV correlated with the increase of SVI after the induced change in cardiac preload. The dynamic preload indicator SVV proved to be a reliable parameter in cardiac surgical patients ventilated with low tidal volumes.
1 Bendjelid K, Romand JA. Fluid responsiveness in mechanically ventilated patients: a review of indices used in intensive care. Intensive Care Med