Prediction of the Effect of Fluid Administration Using Arterial Pressure and Ventilator Data During Abdominal Surgery

It is well known, that patients with circulatory impairment sometimes, but not always, benefit from intravenous fluids. Predicting if a fluid administration will improve circulation is therefore of substantial clinical interest. Ventilator treatment induces cyclic variation in blood pressure due to interaction between the lungs and the heart. This variation is minor, but its amplitude may be used for guiding fluid administration. However, this method of using ventilator-induced variation in blood pressure to predict the effect of fluid administration was developed when different settings for ventilator treatment was recommended, compared with today. With today's recommend ventilator treatment, the method is, unfortunately, less reliable. The investigators will investigate how different ventilator settings influence variation in blood pressure, and the investigators will test if this knowledge allows us to better predict the effect of a fluid administration, by taking the ventilator settings into account.