The purpose of this experimental study was to find out whether central haemodynamic activity influences the precision of the ethanol method used to monitor fluid absorption during endoscopic surgery. Today, the nomograms used together with this monitoring method indicate that increasing breath ethanol values reflect progressively larger absorption volumes regardless of the haemodynamic situation. Cardiac output was measured by ultrasound-Doppler and compared with the concentrations and pharmacokinetics of ethanol in the breath during and after 13 intravenous (i.v.) infusions of 15 mL kg−1 of irrigating fluid containing 1% of ethanol in nine healthy male volunteers. The results show that the peak ethanol concentration increases with cardiac output. This can probably be explained by the shorter time needed for the blood to reach and to return from well perfused tissues, thereby prolonging the apparent rate of distribution to poorly perfused tissues. It is concluded that a hyperkinetic circulation causes the ethanol monitoring method to indicate larger absorption volumes.