Accuracy of Drager and Wright ventilation meters

Simple compact mechanical ventilation meters for bedside monitoring are in wide-spread use in this country. We investigated the accuracy of two such ventilation meters, the Drager Volumeter and the Wright Respirometer. Volume measurements on 16 units were made at fixed flow rates between 6 and 12 l/min. Both types of spirometer showed similar magnitudes and patterns of inaccuracy. For 14 used units, the mean deviation from the actual value was the smallest between the flow rates of 15 and 30 l/min, with a mean systematic underestimation of about 15 per cent and maximum variability among individual units (S.D. 10--12 per cent) at lower flow rates. Measurements at flow rates above 120 l/min were unsatisfactory due to locking of the ventilation meter mechanism. The single new Drager Volumeter tested was relatively accurate at all flow rates measured, whereas the single new Wright Respirometer tested showed inaccuracies comparable to the mean values of the used units. We conclude that these devices are satisfactory to monitor patients on continuous mechanical ventilation but may not be adequate for bedside spirometry.