EFFECTS OF HYPERTONIC SALINE ON MYOCARDIAL-CONTRACTILITY IN ANESTHETIZED PIGS

The cardiac effects of hypertonic saline (HS, 7.5% NaCl) were evaluate d using a number of indices derived from the left ventricular (LV) pre ssure-volume relationship. Left ventricular end-systolic elastance (el astance), the slope of the end-systolic pressure-volume relationship, end-systolic elastance normalized for end-diastolic volume (elastance( norm)), the rate of rise of LV pressure (dP/dt(max)), and dP/dt(max)/e nd-diastolic volume were used to assess myocardial contractility. Pigs were anaesthetized with isoflurane and instrumented for haemodynamic measurements, LV pressure, and volume (conductance catheter) determina tions. Elastance was determined during transient (8-10 s) caudal vena caval balloon occlusion. Following instrumentation, the end-tidal isof lurane concentration was reduced and maintained at 1 minimum alveolar concentration (1.5%). Pigs were randomly administered either 0.9% NaCl (n = 7) or HS (n = 9) at a dose of 4 ml/kg, over 3 min into the right atrium. There were no signiFicant differences in LV or haemodynamic m easurements between isotonic saline and HS treated pigs at any time po int. Elastance, elastance(norm) and dP/dt(max)/end-diastolic volume di d not change in either treatment group. In contrast, dP/dt(max) increa sed significantly (P < 0.015) at 5 min compared to baseline after trea tment with HS. End-diastolic volume increased significantly from 5 to 30 min following treatment with HS. Left ventricular end-diastolic pre ssure increased significantly at 5 and 60 min in HS treated pigs. Cent ral venous and pulmonary arterial wedge pressures, and cardiac index i ncreased significantly at 5 min after treatment with HS. Total periphe ral resistance decreased significantly at 5 min, followed by a return to baseline in the HS group. These results suggest that HS is not a po sitive inotrope in the anaesthetized pig and that increases in cardiac index are primarily due to an increased preload.