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Myocardial depression occurs in 40% of patients presenting with sepsis. In critically ill patients, the peak first derivative of aortic pressure (Ao_dP/dtmax) derived from a fluid-filled catheter has been commonly used by clinicians for decades to assess directional change in left ventricular (LV) contractility. However, this parameter remains questionable because of its preload sensitivity. The aim of this study was to test whether Ao_dP/dtmax represents an accurate method for assessing LV contractility when preload independence, based on dynamic indices, is achieved.
LV pressure-volume data obtained with a conductance catheter and invasive aortic pressure obtained with a fluid-filled catheter were continuously recorded in six anaesthetized and mechanically ventilated pigs. After a stabilization period, endotoxin was infused to induce septic shock. Fluid administration was continuously controlled by preload responsiveness by holding pulse pressure variation (PPV) <13%. Catecholamines were transiently administrated during shock. Ao_dP/dtmax was compared with end-systolic elastance (Ees), the gold standard method for assessing LV contractility.
Endotoxin-induced septic shock and catecholamine infusion lead to significant variations in LV contractility. The best correlation (r2 = 0.76) and agreement between Ao_dP/dTmax and Ees were obtained when PPV <11% (Figure (Figure11).
Ao_dP/dTmax is a minimally invasive and accurate method for assessing LV contractility when effective preload independence, defined as PPV <11%, is achieved.