pressure disconnect alarms, although such threshold alarms are not failsafe, s Low-flow techniques with standing bellows 6 also assist monitoring for circuit leaks. A high-pressure monitor (e.g., Norrie popoff valve) detects and warns of airway obstruction. This is more useful than the airway pressure manometer which does not serve the warning function. The last three cat~ses of hypoxaemia can be detected only by monitoring arterial or tissue POj. Three techniques are available: 1. transcutaneous oxygen analyzers (TcPOj) 2. intra-arterial PO2 sensors 3. oximetry All three techniques have inherent limitations. TcPO2 detects capillary PO2 but has limited usefulhess in underperfusion and obese states and needs a 30-45 minute warm-up. 7 Intra-arterial PO2 sensors 8 are expensive, invasive and are altered by temperature, blood flow rate and N20 concentration. Pulse oximetry, 9 a non-invasive routine monitor of ox),haemoglobin saturation, is the most 5kely of the three techniques to be adopted routinely. In conclusion, current technology provides reliable, versatile techniques to monitor lung function. However, some factors are so vital to patient survival that they should always be monitored, i.e., inspired oxygen concentration, airway pressure and disconnect alarms.