Evaluation of tube compensation in the bennett 840 ventilator - A new ventilatory mode to support spontaneous breathing

Respiratory care patients frequently require intubation with an endotracheal tube (ETT). Unfortunately, the ETT introduces a pressure drop ( PETT) that depends on the respiratory flow rate, thus increasing the work of breathing (WOB). Pressure support ventilation (PSV) cannot adequately compensate for this added WOB, because the degree of inspiratory assistance by PSV is fixed. Therefore, a technique called tube compensation (TC) has been developed to address PETT. We examined the performance of TC and compared it with PSV of 5 cmH₂O. The experimental system was constructed from a simulator, a test-lung, flow sensors, and a Bennett 840, and the respiratory parameters were studied. ETTs with IDs 6.5 and 8.0 mm were used. The quadratic approximation obtained for PETT in the 6.5-mm ETT was 2.316 × flow + 7.910 × flow², while that for the 8.0-mm ETT was 1.881 × flow + 3.353 × flow². The maximum inspiratory flow (MIF) increased significantly with increasing TC, but tidal volume and inspiratory time did not show marked changes. The MIF for TC of 100% was larger than that for PSV of 5 cmH₂O, when the 6.5-mm ID was used, but there was no significant difference between these modes when an ID of 8.0 mm was used. For both the 6.5 and 8.0-mm IDs, the PV loop corresponding to 100% TC was larger than that for PSV of 5 cmH₂O. TC only compensated for the WOB caused by the ETT, whereas PSV compensated for the WOB caused by the ETT and the demand valve system. In clinical use, the differences between TC and PSV will demand attention.-tube compensation; work of breathing; flow-dependent pressure drop