The Impact of Noradrenaline on Ventriculo-arterial Coupling and Central Cardiovascular Energy Delivery

After being informed about the study 40 elective CABG patients with written informed consent will undergo assessment of their arterio-ventricular coupling postoperatively after coronary bypass graft surgery. Whilst still in deep general anesthesia on the CT ICU the study population will be assessed by echocardiographic examination (transthoracic and transesophageal), blood pressure tracing by arterial line, respiratory data and ECG in 4 different situations.

Initially the individual patient is either considered fluid responsive (SVV >13%) og non- responsive (SVV<13%) by using stroke volume variation assessed by echocardiography.

In case of fluid responsiveness a fluid bolus of 4ml/kg of crystalloid fluid is given until SVV drops below 13% and the patient can be considered as fluid NON responder.

Right afterwards the study patient is stabilized with a baseline dose of noradrenaline (NA) intravenously in a supine position (situation 1). Situation 2 will be a slight increase in NA dose stabilizing mean arterial pressure in a "baseline + 20mmHg" state. After reversing the NA dose back to base line level the patient is allowed a short period of rest to wean of drug effect (4-5 x t1/2, appr. 12min). Subsequently the patient is to be placed in a 20% semi upright position (Anti-Trendelenburg) causing an increase in fluid responsiveness (situation 3). Following a phase of equilibration the dose of NA is again titrated up to obtain a 20mmHg increase in mean arterial pressure (situation 4).

There will be logging of arterial pressure curve and VTI-tracing I LVOT simultaneously (ultrapower, uPWR) as well as calculation of energy delivery, cardiac power, oscillatory power and -fraction and both arterial and ventricular elastance in every of those 4 situations.