DK2985_C000 1..28 - AlSharqia Echo Club

294 Transesophageal Echocardiography(A)(B)TLTLFLTIP OFGUIDEWIRE(C)(D)AORTICCANNULAAoTLFLFigure 13.12 A 59-year-old woman with sudden onset of severe chest pain while swimming was transferred to the hospital after thediagnosis of aortic dissection was made by a computed tomography scan. The aortic dissection involved the proximal ascending aorta(Ao) and all the remaining distal Ao (A, B) down to the iliac arteries. (C, D) Cannulation of the proximal aortic arch for cardiopulmonarybypass was performed under transesophageal echocardiography guidance to secure true lumen (TL) perfusion (FL, false lumen).(Courtesy of Drs. Nicolas Noiseux and Raymond Cartier.) [Adapted from Noiseux et al. (21).]in tricuspid inflow VTI, thus confirming an increase inright ventricular outflow impedance. This reduction inVTI occurred without concomitant decrease in rightatrial or right ventricular diastolic dimensions and withincreased right ventricular systolic dimensions, causing adrop in inspiratory right ventricular ejection fraction consistentwith right ventricular systolic function impairment.Tidal volume was the main determining factor of rightventricular afterloading during mechanical ventilation inthat study. According to the authors, in normovolemicpatients, left atrial filling improved with increased LAdimensions, which indicates that blood might be squeezedfrom the capillary bed, as suggested by other authors (24).Moreover, Vieillard-Baron et al. (23) also reported thatcyclic changes in right ventricular outflow were greaterin patients with partial collapse of the SVC during IPPV(at a tidal volume of 6–8 mL/kg) and positive endexpiratory pressure (PEEP) of 5 cmH 2 O.Patients with a SVC caval collapsibility index (definedas the difference of SVC maximal expiratory diameter andminimal inspiratory diameter over the maximal diameter).60% had greater inspiratory decrease in right ventricularoutflow velocity (70%) compared with patients with anindex ,30% (30%) (23). Partial collapse of SVCoccurred when the transmural pressure was 9 mmHg.Thus, a specific preload limitation is added to the increasein outflow impedance in these patients and results in suboptimalfilling of the LV (see Fig. 9.7). The effect ofpositive-pressure ventilation on right ventricular afterloadcan also be demonstrated using a four-chamber view andmeasuring caval diameter changes (Fig. 13.15). Jet ventilationwhich uses small tidal volume and can improveoxygenation in certain patients can also reduce the effectof IPPV on right ventricular function (Fig. 13.16).The negative impact of mechanical ventilation on theloading condition of both the RV and LV is worsened bythe application of PEEP which reduces preload through adecrease in systemic venous return and an increase inright ventricular afterload (Fig. 13.17) (25). Lower levelsof PEEP (,8 cmH 2 O) have minimal hemodynamiceffects (26) while higher levels (16 cmH 2 O) have beenreported to cause concomitant reduction in right and leftventricular dimensions with displacement of the interventricularseptum (IVS) towards the right (26). In contrast,following uncomplicated coronary artery bypass graft(CABG) surgery, Poelaert et al. (27) observed that