DK2985_C000 1..28 - AlSharqia Echo Club

304 Transesophageal Echocardiography(A)(B)LIVERPERITONEALFLUIDFigure 13.22 Presence of a new echo-free space (blood) around the liver consistent with peritoneal bleeding from arterial dissectionduring the insertion of a femoral arterial cannula.dissection have been described with femoral CPB (seeChapter 12) (45): layering of blood with crystalloidpump-prime produces a fluid interface simulating anintimal flap, with the stasis of aortic blood flow mimickingslow flow in a false lumen. This phenomenon may bepresent in up to 50% of femoral bypass cases and occursas soon as 30–40 s after initiation of the CPB. Retrogradearterial dissection may also result in retroperitoneal surgicaldissection. This presents as an echo-free space underthe liver and around the kidneys (46) (Fig. 13.22).IV. CARDIAC PHYSIOLOGY ANDPROCEDURES DURINGCARDIOPULMONARY BYPASSA. Hypothermia, Hemodilution, andNonpulsatile FlowThe period on CPB can indirectly affect cardiac physiologythrough general effects including hypothermia,hemodilution, and nonpulsatile flow.The adverse effects of hypothermia on myocardialperformance are illustrated by studies demonstrating adecreased incidence of low-output syndrome and lowercardiac isoenzyme fractions elevation in the groupkept warm. (Pathophysiology and management of cardiopulmonarybypass. In: Estafanous FG, ed. CardiacAnesthesia: Principles and Clinical Practice. 2nd ed.Chapter 14. Lippincott Williams & Wilkins, 2001.)To decrease viscosity and increase tissue perfusion,hemodilution is used during CPB, particularly duringthose using hypothermia. In patients with a normal heart,Bak et al. (47) found that acute normovolemic hemodilution(ANH) down to 80 g/L of hemoglobin caused adecrease in SVR and an increase in CO proportional tothe hemodilution, whereas systemic pressure and HRremained unchanged. Using TEE, they also observedthat the FAC increased from 44 + 7% to 60 + 9% as aresult of increased LVEDA and reduced left ventricularend systolic area (LVESA) while diastolic function wasunchanged.Finally, although organ perfusion seems better maintainedwith pulsatile than nonpulsatile perfusion, in factlittle is known about its real effect on cardiac function.B. Myocardial Perfusion and CardioplegiaFor a detailed review of myocardial intraoperative perfusionechocardiography, the reader is referred to a comprehensivereview by Aronson and Wiencek (48). Oneapplication of contrast echocardiography is the evaluationof the cardioplegia delivery. Homogenous delivery of cardioplegiais an important component of myocardial protection.Poorly protected myocardial segments may havedecreased contractility following ischemia. Cardioplegicsolutions can be delivered via the aortic root (antegrade)or through the coronary sinus (CS) (retrograde). Althoughcoronary stenosis may impede the uniform distribution ofcardioplegic solutions, myocardial protection may also beimpaired by noncoronary causes. For instance, antegradecardioplegia administered through the aortic root may beincompletely delivered to the coronary arteries duringtransient aortic regurgitation (AR) inadvertently inducedby aortic cross-clamping (Fig. 13.23). Using intraoperativecontrast TEE, Voci et al. (49) observed in patients withnormal AoV, that antegrade administration of cardioplegiawas associated with AR in 25% of the cases. Significantaortic regurgitation during antegrade cardioplegia iseasily identified by the surgeon. In this situation theheart will distend. Gentle cardiac compression can be performedto avoid ventricular overdistension and myocardialischemia. The delivery of cardioplegia as assessed bymyocardial opacification with concomitant contrast injectionwas decreased in patients with severe AR comparedwith patients without regurgitation (49). Regurgitation ofcardioplegic solution into the LV may also lead to left ventriculardilatation and mitral regurgitation (MR) easilydiagnosed with TEE and the pulmonary artery catheter(Fig. 13.23). Because antegrade delivery of cardioplegia