THE CAPNOGRAPH - APPLICATIONS AND LIMITATIONS - AN ANALYSIS OF 2000 INCIDENT REPORTS

The first 2000 incidents reported to the Australian Incident Monitoring Study were analysed with respect to the role of the capnograph. One hundred and fifty-seven (8%) were first detected by a capnograph and there were a further 18 (1%) in which capnography was contributory. Of the 1256 incidents which occurred in association with general-anaesthesia 48% were ''human detected'' and 52% ''monitor detected'' The capnograph was ranked second and detected 24% of these monitor detected incidents; this figure would have been nearly 30% if a correctly checked, calibrated capnograph had always been used. The capnograph is a ''front-line'' monitor for oesophageal intubation, failure of ventilation, anaesthetic circuit faults, gas embolism, sudden circulatory collapse and malignant hyperthermia. It is a valuable ''back-up'' monitor when other monitors (eg. low pressure alarm, pulse oximeter) are not in use, are being used incorrectly or fail. Such situations, in order of frequency of detection were: circuit-leak, overpressure of the breathing circuit, bronchospasm, leak of ventilator-driving-gas into the patient circuit, aspiration and/or regurgitation and hypoventilation. There were 20 reports of ''failure'', over two-thirds of which would not have occurred with appropriate checking and calibration. Seven were due to gas sampling problems and 6 to apnoea alarm failure. Two circuit leaks and 2 faulty unidirectional valves were not detected, on 3 occasions problems occurred due to power failure, calibration problems, or misinterpretation of an alarm. In a theoretical analysis of the 1256 general anaesthesia incidents it was considered that the capnograph, used on its own, would have detected 55% of these incidents, had they been allowed to evolve (43% before any potential for organ damage). It is highly recommended that a suitable, correctly checked, calibrated capnograph be used on all intubated and/or ventilated patients from the moment of intubation until extubation, capnography is also useful in the ''apnoea'' detection mode for patients breathing spontaneously on a mask.