Introduction: Assessment of heart-lung interactions under positive pressure ventilation by measurement of left ventricular stroke volume variations (SVV) is useful to optimize preload in patients following cardiac surgery . The aim of the present study was to investigate the ability of SVV measured by arterial pulse contour analysis to detect volume responsiveness in patients undergoing coronary artery bypass grafting under open thorax conditions.
Method: With approval of the ethics committee and written informed consent we studied 22 patients immediately following sternotomy. SVV, central venous pressure (CVP), left ventricular end-diastolic area index (LVEDAI) by transoesophageal echocardiography, global end-diastolic area index (GEDVI) and cardiac index (CI) by thermodilution were measured after removal of 500mL blood and after subsequent volume substitution with 500mL hydroxyethyl starch 6%. The saved blood was retransfused after termination of cardiopulmonary bypass. Isovolaemic haemodilution is performed in our service routinely to minimize the need of autologous blood transfusions.
Results: All data are expressed as mean ± SD. One way ANOVA for repeated measurements with Bonferroni adjustment and Pearson product moment correlations were performed. Blood removal led to a significant increase of SVV from 6.7 ± 2.2% to 12.7 ± 3.8%. CI (from 2.9 ± 0.6 to 2.3 ± 0.5Lmin−1 m−2) and GEDVI (from 650 ± 98 to 565 ± 98mLm−2) decreased (all P < 0.025). LVEDAI and CVP did not change significantly. After volume loading SVV decreased significantly to 6.8 ± 2.2%. Concomitantly, CI (to 3.3 ± 0.5L min−1 m−2), GEDVI (to 663 ± 104mL m−2), and CVP (to 3 ± 4 mmHg) increased significantly (all P < 0.025), whereas the increase in LVEDAI (to 11.3 ± 4.8cm2 m−2) was not significant. We found a significant correlation between the increase in CI caused by volume loading (ΔCI) and SVV before volume loading (R = 0.80; P < 0.001). Modest correlations were found between ΔCI and GEDVI (R = −0.44; P < 0.05) and LVEDAI (R = −0.52; P < 0.05) before volume loading, whereas no correlation was found for CVP.
Discussion: These findings demonstrate that changes in CI caused by volume loading can be predicted by measurement of SVV under open thorax conditions. Thus, assessing heart lung interactions may improve hemodynamic management during surgical procedures requiring thoracotomy.
1 Reuter DA, Felbinger TW, Schmidt C, et al. Stroke volume variations for assessment of cardiac responsiveness to volume loading in mechanically ventilated patients after cardiac surgery. Intensive Care Med