EFFECT OF CERTAIN MODES OF MECHANICAL VENTILATION ON HEMODYNAMICS AND OXYGEN TRANSPORT IN POST OPERATIVE CARDIAC PATIENTS WITH VALVE REPLACEMENT
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This study was conducted at the National Heart Institute and included 40 patients with valve replacement. The effects of certain modes of mechanical ventilation on hemodynarnic parameters and oxygen transport were studied postoperatively to detect the best mode with favorable effects on the patients. These included: controlled mandatory ventilation (CMV). synchronized intermittent mandatory ventilation with pressure support ventilation (SIMV+PSV) and synchronized intermittent mandatory ventilation (SEW). By comparing the hemodynarnic variables using CMV mode and S/MV + PSV mode, the latter showed significant reduction of cardiac index ( CD. stroke volume index (S/) and significant elevation in left ventricular systolic work index (LVSWI). When oxygenation and ventilation parameters were compared, the SIMV + PSV mode showed significant elevation of static compliance (Cst), alveolo arterial oxygen difference (AaD02) and shunt fraction (Qs/ Qt) and significant reduction in dynamic compliance (Cdyn), oxygen availability index. (02AVI) and oxygen consumption index (V02)). S/MV made showed a significant elevation in hemodynamic parameters including CI, Si. mean pulmonary artery pressure (mPAP). pulmonary artery wedge pressure ( PAWP ). right cardiac work index (RCI1,7) and right ventricular systolic work index (RVSWI ) with significant decrease in left cardiac work index (LCWI) when compared to CIVIV mode and it showed a significant elevation in CI SL RCWI and RVSWI with a significant reduction in LCWI, left ventricular systolic work index (LVSWI) and systemic vascular resistance index (SVRI) when compared with SIMV + PSV mode. As regards oxygenation and ventilation parameters. SIMV showed a significant elevation in oxygen availability index (02AVI) and 02 transport with signcant reduction in mixed venous oxygen content (CV02), AaD02 and Qs/Qt when compared to CMV mode and it showed a significant elevation in 02AVI and 02 trans. and a significant reduction in AaD02 and Qs/Qt when compared to SIMV + PSV mode. Allowing negative pressure ventilation by SIMV gave the best hemodynamic and oxygenation profile. Thus SIMV mode may be considered the best mode of weaning of critically ill patients. Application of positive pressure support ventilation expressed by CMV & SIMV + PSV alters circulatory hemodynamics. Thus PSV should be used with caution in patients with unstable circulatory status.