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. |
