THE IMPORTANCE OF CARDIOPLEGIC INFUSION PRESSURE IN NEONATAL MYOCARDIAL PROTECTION

Background. Cardioplegia infusion pressure is usually not directly mon itored during neonatal heart operations. We hypothesize that the immat ure newborn heart may be damaged by even moderate elevation of cardiop legic infusion pressure, which in the absence of direct aortic monitor ing may occur without the surgeon's knowledge. Methods. Twenty neonata l piglets received cardiopulmonary bypass and the heart was protected for 70 minutes with multidose blood cardioplegia infused at an aortic root pressure of 30 to 50 mm Hg (low pressure) or 80 to 100 mm Hg thig h pressure). Group 1 (n = 5, low pressure), and group 2 (n = 5, high p ressure) were uninjured (nonhypoxic) hearts. Group 3 (n = 5, low press ure) and group 4 (n = 5, high pressure) first underwent 60 minutes of ventilator hypoxia (FiO(2) 8% to 10%) before initiating cardiopulmonar y bypass to produce a clinically relevant hypoxic stress before cardia c arrest. Function was assessed using pressure volume loops (expressed as a percentage of control), and coronary vascular resistance was mea sured with each cardioplegic infusion. Results. In nonhypoxic (uninjur ed) hearts (groups 1 and 2) cardioplegic infusion pressure did not sig nificantly affect systolic function tend systolic elastance, 104% vers us 96%), preload recruitable stroke work (102% versus 96%) diastolic c ompliance (152% versus 156%), or coronary vascular resistance but did raise myocardial water (78.9% versus 80.1%; p < 0.01). Conversely, if the cardioplegic solution was infused at even a slightly higher pressu re in hypoxic hearts (group 4), there was deterioration of systolic fu nction tend systolic elastance, k28% versus 106%) (p < 0.001) and prel oad recruitable stroke work (31% versus 103%; p < 0.001), rise in dias tolic stiffness (274% versus 153%; p < 0.001), greater myocardial edem a (80.5% versus 79.6%), and marked increase in coronary vascular resis tance (p < 0.001) compared to hypoxic hearts given cardioplegia at low infusion pressures (group 3), which preserved function. Conclusions. Hypoxic neonatal hearts are very sensitive to cardioplegic infusion pr essures, such that even moderate elevations cause significant damage r esulting in myocardial depression and vascular dysfunction. This damag e is avoided by using low infusion pressures. Because small difference s in infusion pressure may be difficult to determine without a direct aortic measurement, we believe it is imperative that surgeons directly monitor cardioplegia infusion pressure, especially in cyanotic patien ts. (Ann Thorac Surg 1998;66:1358-64) (C) 1998 by The Society of Thora cic Surgeons