Processing, storage and display of physiological measurements

The key to the successful and safe management of patients is regular and accurate recording of their ‘vital signs’ as indicators of well-being. Some physiological parameters can be measured and processed manually (blood pressure, pulse rate and respiratory rate), whereas others (pH, partial pressure of oxygen (Pao2) and partial pressure of carbon dioxide in arterial blood (Paco2)) rely on electronic interpretation. In modern operating theatre and critical care settings, fully integrated, electronic, multiparameter monitoring systems based on microprocessors are standard. It is important that anaesthetists, as well as other healthcare professionals, understand the basic principles behind patient monitoring, including data processing, storage and display. Most physiological measurement systems include a sensor, transmission pathway, signal- processing stage and a display and storage device. This system may be simplified by regarding the different elements as a series of black boxes with the output from one box forming the input to the subsequent box. The initial input is a biological signal that results from the natural physiological processes occurring within the body. This signal may be chemical, electrical or mechanical in origin and is sensed by a transducer that converts it into an electrical output. Signal processing must then occur which aims to produce a meaningful output through amplification, digitization and ‘noise’ reduction. Once data have been acquired, there is usually a requirement to retain them for both immediate and long-term reference and to display them via a visual display unit.