Basic principles and limitations of electrocardiographic and haemodynamic bedside monitoring

Patient management decisions in the perioperative period are often based upon pressures and electrocardiograms (ECG) obtained from bedside monitors. To interpret such data, one must be cognizant of its limitations. The requisite accuracy and precision of such data requires both knowledge of the way these data are acquired and displayed, and the reasons for making the measurements. For example, for the ECG, the differences between monitor and diagnostic modes and the effects of calibration must be understood. For invasively measured pressures, the static and dynamic properties of electronic transducing systems and displays should be known, as well as the reasons for measuring systolic, diastolic and mean pressures. This chapter provides the background to understanding how such devices obtain and process data, as well as some basic principles of data interpretation.