WHICH MONITOR - AN ANALYSIS OF 2000 INCIDENT REPORTS

The role of monitors in patients undergoing general anaesthesia was st udied by analysing the first 2000 incidents reported to the Australian Incident Monitoring Study; 1256 (63%) were considered applicable to t his study. In 52% of these a monitor detected the incident first; oxim etry (27%) and capnography (24%) detected over half of the monitor det ected incidents, the electrocardiograph 19%, bloodpressure monitors 12 %, a low pressure (circuit) alarm 8%, and the oxygen analyser 4%. Of t he other monitors used, 5 first detected 1-2% of incidents, and the re maining 8 less than 0.5% each. The oximeter would have detected over 4 0% of the monitor detected incidents had its more informative modulate d pulse tone always been relied upon instead of the ''bleep'' of the E CG. A theoretical analysis was then carried out to determine which of an array of 17 monitors would reliably have detected each incident had each monitor been used on its own and had the incident been allowed t o evolve. To facilitate ''scoring'' of monitors, the incidents were ca tegorized empirically into 60 clinical situations; 40% of applicable i ncidents were ''counted for by only 5 clinical situations, 60% by 10 a nd nearly 80% by 20. 98% were accounted for by the 60 situations. A pu lse oximeter, used on its own, would theoretically have detected 82% o f applicable incidents (nearly 60% before any potential for organ dama ge). These figures for capnography are 55% and 43% and for oximetry an d capnography combined are 88% and 65%, respectively. With the additio n of blood pressure monitoring these become 93% and 65%, and of an oxy gen analyser, 95 and 67%. Other monitors, including the ECG, each incr ease the yield by by less than 0.5%.The international monitoring recom mendations and those of the Australian and New Zealand College of Anae sthetists are thoroughly vindicated by the patterns revealed in this s tudy. The priority sequence of monitor acquisition for those with limi ted resources should be stethoscope, sphygmomanometer, oxygen analyser if nitrous oxide is to be used, pulse oximeter capnograph, high press ure alarm, and, if patients are to be mechanically ventilated, a low p ressure alarm (or spirometer with alarm); an ECG, a defibrillator, a s pirometer and a thermometer should be available.