Continuous monitoring of cardiac output (CO) and maintenance of normovolaemia are the primary aims of haemodynamic (HD) optimization in every critical care patient. Previously, invasive monitoring and intermittent thermodilution with pulmonary artery catheterization were the main methods for determining CO. However, the methods more commonly used today are either minimally invasive or non-invasive. Minimally invasive methods of transpulmonary thermodilution (TD) in CO monitoring analyze the pulse pressure curve and are divided into older, calibrated and newer, non-calibrated systems. Dynamic parameters such as stroke volume variation (SVV) and pulse pressure variation (PPV) which can be continuously monitored, are far more precise in determining the optimal goal-directed volume therapy (GDVT) in comparison to the traditional static parameters such as CVP and PCWP. Modern non-invasive continuous methods, that are still not fully validated in clinical circumstances are: applanation tonometry, plethysmography, partial CO2 rebreathing technique, and pulse wave transit time measurements of CO. Thoracic electrical bioimpedance and bioreactance uses a weak alternating current, and through the phasic variations in the charge of the current during a systolic cycle, enables continuous analysis of the stroke volume (SV) curve. It is known that volume administration will not increase SV in roughly 50% of critically ill patients (fluid non-responders), therefore, prior to volume administration, through continuous SV/CO monitoring, it is important to assess whether a patient will have an adequate haemodynamic response to fluid administration (responders). There are some methods available for predicting the response to fluid administration, like measurement of variation in the diameter of the superior and inferior vena cava, the end-expiratory occlusion test, respiratory systolic variation test, SVV and PPV. The passive leg raising (PLR) test has the highest predictive score in dynamic assessment of the volume status in a haemodynamically unstable patient.