Postoperative haemodynamic management, with particular emphasis on adequate volume status, is essential for patient outcome, as is optimised intraoperative management. Postoperative monitoring is usually performed in the PACU by non-invasive, continuous and intermittent monitoring. ECG and oxygen saturation are monitored continuously, blood pressure and laboratory analyses intermittently. The assessment of adequate oxygen supply (cardiac output - haemoglobin concentration - oxygen saturation) in the PACU is traditionally approximated only by surrogate parameters such as blood pressure and heart rate, in the sense of an empirical approach. The aim should be to transfer the available data on the benefit of early, goal-oriented haemodynamic optimisation by means of extended haemodynamic monitoring to the sensitive area of the PACU. An important prerequisite for the implementation of such haemodynamic optimisation protocols is the use of non-invasive monitoring methods, which ideally provide continuous flow and pressure-based parameters in combination with the use of intermittent transthoracic echocardiography. The necessity to continue extended haemodynamic monitoring in selected patients in the PACU on the basis of non-invasive procedures is under discussion and is not part of a defined standard today (Gruenewald et al. Anaesthesia 2015). A number of non-invasive haemodynamic monitoring methods have become available over the last few years, with a large number of scientific evaluation studies investigating the methods in various clinical settings in comparison to invasive systems. Of interest for routine clinical use are the so-called volume clamp procedures, which allow non-invasive, continuous recording of haemodynamic parameters such as stroke volume, cardiac output, blood pressure and plus pressure variation. Thus, in combination with oxygen saturation and intermittent haemoglobin determinations, they enable a punctual determination of oxygen supply (Meidert et al. Front Med (Lausanne) 2017 and Renner et al. Br J Anaesth 2017).

It is of interest whether the volume clamp method in particular provides the aforementioned parameters such as blood pressure, stroke volume, cardiac output and the pulse pressure variation continuously and without interference in the awake patient in the PACU. Another aspect is the assessment of the volume status and cardiac performance that patients show on admission to the PACU. Here, special attention is paid to the volume status after the patients have been haemodynamically optimised intraoperatively with an invasive procedure. Furthermore, we will compare how the cardiac output determined by echocardiography on admission differs from the cardiac output of the volume clamp method on admission. The differences between invasive blood pressure measurement and non-invasive pressure measurement will also be assessed.

In addition, the investigators analyse the frequencies of decreased blood pressures in comparison to a patient collective that was monitored according to standard-of-care in the PACU. Also, the comparative observation of the number of interventions performed, such as volume administration and/or catecholamine administration, between the groups.