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The primary goal of the study is to determine Eadyn ( = PPV/SVV) as a functional measure of arterial load, in conjunction with other actual afterload indices, systemic vascular resistance and arterial elastance. A secondary aim is the assessment of the influences of vasopressors and inotropic drugs on Eadyn, as a parameter of ventriculo-arterial coupling.

Assessment of the cardiovascular status and haemodynamics comprise directly or indirectly cardiac output, which is determined by left ventricular preload, contractility, afterload and heart rate. Various haemodynamic monitors have been introduced in anaesthesia and ICU practice, providing cardiac output either non-invasively or invasively. The combined use of arterial pressure monitoring with these devices provides insight not only in cardiac output but offers bedside assessment of most determinants of cardiovascular function. Both pulse pressure variation (PPV) and stroke volume variation (SVV) have been described as dynamic descriptors of fluid responsiveness, a measure allowing optimization of preloading conditions if haemodynamics show signals of insufficient perfusion.

Arterial load can be assessed based on a two-element Windkessel model with a static and dynamic component. The static part consists of a resistive element (systemic vascular resistance: SVR = (MAP/C0)*80, with MAP, mean arterial pressure; CO, cardiac output) and a pulsatile component (net arterial compliance C = SV/arterial pulse pressure with SV, stroke volume). Arterial elastance is considered being an integrative variable, associating both steady elements and heart rate (Ea = .9*SAP/SV with EA, arterial elastance; SAP, systolic arterial pressure). The dynamic component Eadyn is the ratio of PPV and SVV during a mechanical ventilator cycle, providing a functional assessment of ventriculo-arterial coupling.

Combined use of arterial pressure tracing (or its non-invasive surrogate) and (non-) invasive stroke volume actually may provide an interesting framework for haemodynamic monitoring and subsequent optimization in many surgical, postoperative or ICU patients. This study aims to copy as good as possible the handling and the way of management as in a clinical setting.

Inclusion Criteria:

- ICU patients, treated/supported with noradrenalin or dobutamine.

Exclusion Criteria:

• Septic shock
• Aortic valve regurgitation and defect of septum
• Severe aortic sclerosis, aortic prosthesis
• Severe hypertension (MAP > 130 mmHg)
• Cardiac arrhythmia
• Tachycardia with a heart rate higher than 150 bpm
• Age below 18 or above 75 y
• Patient height below 120 cm (48") or above 230 cm (90")
• Patient weight less than 30 kg (67 lbs.) or greater than 155 kg (341 lbs.)
• Intra-aortic balloon pump