Con: we should fully utilise the preload reserve in high-risk patients undergoing noncardiac surgery

In the German guidelines on intra-operative haemodynamic management, we emphasise that ‘even in fluid-responsive patients, the indication for fluid administration should be determined individually based on haemodynamics and clinical context’. Being ‘fluid responsive’ is a normal physiological state and does not necessarily indicate that a patient requires fluids. The Frank–Starling mechanism does not illustrate a causal relationship where an increase in cardiac preload (as an independent variable) leads to a subsequent increase in cardiac output (as a dependent variable). Rather, the evolutionary purpose of the Frank–Starling mechanism is to match cardiac output to variations in venous return caused by exercise or changes in posture. Clinicians should not routinely attempt to maximise stroke volume or cardiac output by giving fluids in patients having surgery because it is unlikely that surgical patients require their maximal cardiac output, as energy expenditure during major surgery with general anaesthesia is roughly one quarter lower than resting awake energy expenditure. In summary, clinicians should not routinely give repeated fluid boluses simply to use the full preload reserve in patients having major noncardiac surgery. Decisions to give – or not give – fluids must incorporate considerations that extend far beyond the physiological condition of ‘fluid responsiveness’.