Estimated Oxygen Extraction Versus Dynamic Parameters for Perioperative Hemodynamic Optimization

Any surgical intervention is a trauma for the organism and a stress response is activated to cope the external insult. This stress response is responsible of an increase in oxygen consumption. If patient is not able to overcome the deficit in oxygen consumption (VO2) during the first hours postoperatively, he/she will go toward complications (in case of delay to meet metabolic demand) or death (in case of persistent VO2 deficit). Therefore, several protocols have been developed to optimise haemodynamic parameters with the aim to reduce tissue hypoperfusion coming from maldistribution or inadequate perfusion and meet the increased metabolic need as soon as possible. Every patient that probably will not be able to face the surgical stress himself might benefit from modulation of haemodynamic parameters. Actually, goal directed therapy (GDT) is able to improve survival only in high-risk surgical patients. Instead, the reduction of complications rate has been shown also in intermediate-risk population. Originally, hemodynamic optimisation protocols were developed to reach supranormal value for cardiac output (CO), oxygen delivery (DO2) and VO2. Based on the concept that oxygen extraction rate (O2ER) reflects the balance between DO2 and VO2, a GDT protocol based on O2ER estimation (O2ERe) calculated as (SaO2-ScvO2)/SaO2 has been proposed showing a significantly lower number of organ failure postoperatively compared with control group. The major determinants of DO2 are cardiac output (CO), haemoglobin level (Hb) and arterial oxygen saturation (SaO2). An inadequate CO may be optimised using fluids as first line therapy and then inotropes. In mechanically ventilated patients, heart-lung interaction is useful to recognise in which portion of the Frank-Starling curve the heart of the patient is working and then if CO is able to rise after fluid administration aimed to increase preload. Several parameters based on mini-invasive monitor systems are available to assess fluid responsiveness such as pulse pressure variation (PPV) and stroke volume variation (SVV).