Effect of Targeted Fluid Therapy on Postoperative Cognitive Dysfunction.

Postoperative cognitive dysfunction (POCD) is cognitive dysfunction defined as a decline in cognitive function from baseline performance as measured by neuropsychological tests before and after surgery. Perioperative neurocognitive impairment includes preoperative neurocognitive impairment, POCD and postoperative delirium (POD). It is extremely common after cardiac surgery and affects 25% to 70% of patients. The underlying pathophysiological mechanisms leading to cognitive impairment are unclear, but many factors have been implicated in the aetiology. Pathophysiological mechanisms leading to cognitive dysfunction following cardiac surgery such as cerebral hypoperfusion, cerebral microemboli, glycaemic control and possible neurotoxic effects of anaesthetic agents have been demonstrated in the literature. The increase in the frequency of neurocognitive impairments leads to prolonged hospitalisation and increased healthcare costs. Although there are many clinical differences between POD and POCD, both lead to blood-brain barrier dysfunction and promote neuroinflammation through a systemic inflammatory response triggered by surgical trauma.

It has been shown that NOD-LRR- and pyrin domain-containing protein 3 (NLRP3) increased in the hippocampus of mice after cardiac surgery, causing hippocampal inflammation and cognitive dysfunction. In another study, it was reported that microglia in the hippocampus of rats were activated, the amount of inflammatory factors such as IL-1β, IL-6 and TNF-α increased and the permeability of the blood-brain barrier increased. POD and POCD were also found to be closely related with the concentration of peripheral inflammatory markers (such as CRP, IL-6).

Targeted fluid therapy (TFT) in cardiac surgery is the use of various haemodynamic parameters (e.g. stroke volume, cardiac output, systemic vascular resistance and stroke volume variation) and optimisation of fluids, inotropes and vasopressors to ensure adequate tissue perfusion. Because administration of more or less fluid and blood products than needed will cause many undesirable clinical conditions in patients (in case of over administration; pulmonary oedema, tissue oedema, connective and mucosal oedema or in case of under administration; perfusion failure in peripheral tissue and brain, hypotension). The aim of targeted fluid therapy is to use haemodynamic parameters that allow us to monitor the amount of fluid, inotrope requirement, tissue blood flow and oxygenation. This optimization reduces mortality by providing normal tissue perfusion, preventing inflammatory response and possible fatal complications. There are many monitors on the market that have developed rapidly in recent years and are now used in many anaesthesia clinics for perioperative volume management. When choosing this, the aim should be to select the technology that provides the most accurate and relevant haemodynamic data, taking into account the safety, comfort and general care of the patient.

For targeted fluid therapy, techniques/monitors routinely used in clinics that have them include PiCCO plus, FloTrac/EV1000, oesophageal doppler and pulmonary artery catheter. In a study conducted in major abdominal surgeries, patients followed up with Vigileo/FloTrac, which uses the principle of oesophageal doppler and pulse contour analysis for targeted fluid therapy, were compared and it was shown that major complications and mortality decreased and it was reported that the monitors were cost effective . The fact that the sternum is open in cardiac surgery is an important limitation of monitors working on the principle of pulse contour analysis. Therefore, in this study, we planned to perform advanced haemodynamic monitoring with oesophageal Doppler and to decide on fluid/blood/inotrope support by using many parameters such as stroke volume, cardiac index, oxygen delivery, and stroke volume variation (SVV) on this monitor.