Respiratory pattern and respiratory strain in automatic tube compensation and inspiratory pressure support

Study objective: To investigate whether automatic tube compensation (ATC) o r conventional pressure support (PS) is suitable to compensate for the work of breathing imposed by the breathing circuit without altering the breathi ng pattern. Methods: Breathing pattern and work of breathing were measured in healthy v olunteers. After a 20 min period of quiet breathing through a mouth piece ( control) the volunteers were breathing through a 8.0 mm ID endotracheal tub e (ETT) with four different settings: CPAP at 0 mbar,ATC, PS 5 mbar, PS 10 mbar. Each mode was applied for a 20 min period. At the end of each period data from 10 consecutive breaths were analyzed and averaged. Tidal volume ( VT), breathing frequency (f),and minute ventilation (Ve) were determined fr om the stored gas flow tracings. Work of breathing was assessed as the pres sure time product (PTP) calculated from the trans diaphragmatic pressure (P di) using a combined esophageal and gastric balloon catheter. Results: During the control period the breathing pattern was as follows:V-T =882+/-277 mi, f=13,7+/-5/min,Ve=11,5+/-4,2 L/min. Maximal Pdi was 9,2+/-5, 4 mbar and PTP was 11,3+/-7,1 mbarxs. Breathing CPAP through the ETT result ed in a slight increase in Pdi (10,8+/-5,4 mbar) and PTP (14,8+/-10,4 mbarx s) with an unchanged breathing pattern. However, for the same amount of unl oading from respiratory workload ATC did not alter the breathing pattern,wh ereas PS 5 mbar and PS 10 mbar resulted in a clear increase in VT (1014+/-2 02 ml,1336+/-305 mi, respectively). Conclusion: From the presented data in healthy volunteers it might be concl uded that ATC and PS 5 mbar and 10 mbar are suitable modes for unloading th e respiratory system from work imposed by the breathing circuit. ATC does n ot alter the breathing pattern in contrast to PS which results in an increa sed tidal volume. Therefore, the exact compensation of the work imposed by the ETT during ATC seems to be advantageous over ATC to assess the actual b reathing pattern.