Abstract
Objectives: The objectives of the present study were to evaluate, in patients with persistent arterial hypotension in the immediate postcardiac surgery period, the effects of norepinephrine infusion on ventriculo-arterial coupling, its determinants: arterial elastance and end-systolic ventricular elastance, and to test the ability of arterial elastance to end-systolic ventricular elastance ratio to predict stroke volume increases. Design: Prospective observational study. Setting: Cardiac-vascular surgical ICU. Patients: Twenty-eight postoperative cardiac surgery patients, in whom physicians decided to administer norepinephrine infusion, were included. Measurements and Main Results: Arterial pressure, stroke volume index, cardiac index, indexed total peripheral resistance, arterial compliance, arterial elastance, and end-systolic ventricular elastance, were measured before and after norepinephrine infusion. We estimated ventriculo-arterial coupling by the arterial elastance to end-systolic ventricular elastance ratio and defined stroke volume responders by a stroke volume increase greater than or equal to 15%. Twenty-two of the 28 subjects had altered ventriculo-arterial coupling (1.87 [1.57-2.51] vs 1.1 [1-1.18]). Fifteen of the 28 subjects (54%) were stroke volume responders. At baseline, stroke volume responders had similar arterial pressure, higher indexed total peripheral resistance, arterial elastance, arterial elastance to end-systolic ventricular elastance ratio (2.21 [1.69-2.89] vs 1.33 [1.1-1.56]; p < 0.05), and lower arterial compliance, indexed total peripheral resistance and cardiac index. Norepinephrine significantly increased arterial pressure in all subjects. In stroke volume responders, norepinephrine increased arterial elastance, end-systolic ventricular elastance, cardiac index, and improved arterial elastance/end-systolic ventricular elastance coupling. The baseline arterial elastance to end-systolic ventricular elastance ratio predicted stroke volume responsiveness (area under the curve [95% CI], 0.87 [0.71-1]; p < 0.0001). Conclusions: In patients with arterial hypotension norepinephrine increased end-systolic ventricular elastance and arterial elastance. The effects of norepinephrine on stroke volume depend on baseline ventriculo-arterial coupling. Although norepinephrine infusion corrects arterial hypotension in all subjects, increase of stroke volume occurred only in subjects with altered ventriculo-arterial coupling.