 The ClearsightTM non invasive cardiac output device measures blood pressure using the volume clamp method developed by the Czech physiologist Jan Penaz. Using a simple non-invasive finger cuff, the volume of an artery is kept clamped at a constant diameter. Changes in diameter are measured by a photo-plethysmograph within the finger cuff, and a servo controller applies counter pressure to keep the diameter of the artery constant. This allows the measurement of beat to beat blood pressure and hence cardiac output can also be calculated. The simple and non invasive nature of this device makes it suitable to use in patients undergoing repair of fractured neck of femur regardless of the type of anaesthetic. It requires no calibration, and would make goal directed therapy accessible to this group. The Clearsight has been shown to be a valid measure of cardiac output. 