Kinetics of the Sublingual Microcirculation During Fluid Bolus

Fluid therapy is one of the cornerstones of the treatment of organ failure. The investigators assume that fluid bolus will increase the delivery of oxygen to the cells and resolve the shock. The purpose of this study is to asses kinetics of the sublingual microcirculation in one place during a fluid bolus. It is expected that fluid therapy after normalization of the red blood cell flow velocity in the microcirculation will result in a decrease in capillary density through the formation of edema in the tissues. This can be considered to be the tipping of potentially beneficial to deleterious effects of fluid therapy. After cardiac surgery patient will be transferred to the ICU for further stabilisation. Within specific indications the patient will receive a fluid bolus, these indications are hypotension, hyperlactataemia, tachycardia or decreased urine production. The fluid bolus will be 250 ml crystalloids in 15 minutes. The investigators will observe the sublingual microcirculation during this fluid bolus. To asses the red blood cell velocity and capillary vessel density on one spot during this fluid bolus.