Measurement of respiratory mechanics using the Puritan-Bennett 7200a ventilator.

This study was designed in order to validate the respiratory mechanical variables measured by the Puritan-Bennett 7200a ventilator equipped with the 30/40 module. Two ventilators were connected to a lung model and submitted to several breathing patterns by modifying the respiratory rate, the tidal volume, the inspiratory flow-rate and the model resistance. The inspiratory flow-rate (V), tidal volume (VT), peak inspiratory pressure (Pmax), plateau pressure (Pplat) and PEEP measured by the ventilators were compared with the same variables measured at the connection between the breathing circuit and the lung model. The compliance (C30/40) and the resistance (R30/40) calculated by the 30/40 module were compared with those calculated by using the variables measured by the reference equipment. Both ventilators made a constant underestimation of V by 2.8 and 3.7 L.min-1, respectively. The VT was measured with a mean error of less than 10 ml but did not reflect the preselected values in the presence of an intrinsic PEEP. The Pplat was overestimated by 7 and 10%, respectively. The same calibration error was observed with Pmax which was also affected by a pressure gradient due to the resistance of the breathing circuit. Even in the absence of intrinsic PEEP, C30/40 presented an error due to the combination of the measurement errors on VT, Pplat and PEEP. Finally, R30/40 presented a high percentage of error due to the combination of the measurement errors on V, Pmax, and Pplat, and to a sporadic aberrant selection of V. Due to these numerous sources of error, the two ventilators studied did not give reliable estimates of resistance and compliance.(ABSTRACT TRUNCATED AT 250 WORDS)