Standard anaesthetic practice in the high-risk surgical patient is to insert invasive arterial and central venous catheters and then to use ΔCVP and ΔMAP to guide fluid therapy, despite an accumulation of evidence to suggest that filling pressures are inadequate predictors of fluid status and responsiveness. Recent interest has been directed towards dynamic measures of cardiac filling such as SVV, SPV, PPV and Δdown and ΔVpeak. A number of large multicentre trials are underway using the LiDCOrapid. There is, however, little information about the utility of this device or, indeed, any other minimally-invasive cardiac output monitor in the prediction of fluid responsiveness.