Volume Optimisation and Cognitive Function in Major Abdominal Surgery

Overview

In the last 25 years, there has been a lot of attention directed on reducing perioperative morbidity and mortality by improving intraoperative monitoring and hemodynamic optimisation of patients. Advanced monitoring devices and new parameters have shifted the focus of anaesthesia management from macro- to micro circulation with the emphasis on the determinants of oxygen delivery and tissue oxygenation. There is increasing evidence that long-term outcome is improved by goal-directed optimisation of hemodynamic parameters (optimisation of stroke volume and cardiac output by fluids and inotropic and vasoactive drugs). Besides, new monitoring possibilities (depth of anaesthesia and cerebral and tissue oxygenation monitors) and adherence to protocols have proved beneficial in reducing morbidity cognitive dysfunction. However, questions are raised what the optimal goals (healthy population derived normal values, preoperative values, maximal values, restrictive fluid management) should be. Secondly, all new methods were used separately and there is a lack of studies to show the effect of combined (multimodal) monitoring on occurrence of cognitive dysfunction. All gathered data indicate that the combined use of new methods with adherence to an appropriate protocol might radically improve the perioperative management and outcome of high-risk surgical patients. The present study tests the hypothesis that intraoperative multimodal monitoring with hemodynamic optimisation, BIS-guided anaesthesia and maintenance of optimal cerebral oxygen saturation will reduce cognitive dysfunction.

BACKGROUND There is increasing evidence that intraoperative aesthetic management influences outcomes. (5). Besides this the occurrence of low MAP, low minimum alveolar concentration (MAC) and low bispectral index (BIS) increased hospital stay and mortality. Conventional intraoperative monitoring can result in occult low levels of blood flow and oxygen delivery that lead to complications that only occur days or weeks following surgery and give false re-assurance to the anaesthetist that he or she is doing a "good job". Advanced monitoring devices and new parameters have shifted the focus of anaesthesia management from macro- to microcirculation with the emphasis on the determinants of oxygen delivery and tissue oxygenation. There are more and more trials showing that introduction of new monitors and treatment protocols with predefined treatment limits or targets (goal-directed optimisation of hemodynamic parameters) improves long-term patient outcome and reduces morbidity and mortality by over 50%. Several studies have shown benefit when individualised; targeted oxygen delivery algorithms incorporating both fluid resuscitation and vasoactive drugs were used with high-risk surgical patients. The measurement of regional cerebral oxygen saturation can predict cognitive dysfunction after cardiac surgery. BIS monitoring facilitates anaesthetic titration, and reduced anaesthetic exposure and decreased the risk of postoperative cognitive dysfunction. There is reduction in strokes, less mechanical ventilation and shorter length of stay (LOS) with the use of INVOS. However, all new methods have been studied separately and there is a lack of studies to show the effect of combined (multimodal) monitoring on mortality and occurrence of complications, including cognitive decline. All gathered data indicate that the combined use of new methods (assessment of fluid status, depth of anaesthesia and tissue oxygenation) with adherence to appropriate protocol might radically improve perioperative management and outcome of high-risk surgical patients. Besides, questions are raised what the optimal goals (healthy population derived normal values, preoperative values, maximal values) should be. Lately, studies have shown that optimising cardiac output and oxygen delivery to higher (supra-normal) values intra- and postoperatively did not affect post-operative complications rate, intensive care unit stay or hospital length of stay. Probably the target should be maintaining patient's blood flow and oxygen delivery at preinduction levels. The question was also raised in fluid management. Liberal approach can lead to oedema of the intestines and other tissues, which may be responsible for poor tissue healing and other complications. In abdominal surgery, protocol-based fluid restriction reduced the incidence of perioperative complications such as cardiopulmonary events and disturbances of bowel motility while improving wound and anastomotic healing and reducing hospital stay in comparison to liberal fluid management. One of the trials has shown 52% lower rate of major postoperative complications in restrictive group than in the conventional group. HYPOTHESIS The present study tests the hypothesis that intraoperative multimodal monitoring with hemodynamic optimisation, BIS-guided anaesthesia and maintenance of optimal cerebral oxygen saturation will reduce cognitive decline.