Breathing pattern and work of breathing in spontaneously breathing patients during continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) with and without automatic tube compensation (ATC)

Background and objective

ATC is a new ventilatory mode compensating for the nonlinear resistance of the endotracheal tube and the added work of breathing related to the tube.

This study investigates the influence of ATC on breathing pattern and work of breathing comparing CPAP and PSV with and without ATC in a spontaneously breathing patient failing a weaning trial.

Methods

Six critically ill patients still requiring ventilatory support via endotracheal tube or a tracheal tube were studied in a randomised order during 30 min periods of pressure support ventilation 5 mbar, positive end expiratory pressure 5 mbar with ATC (PSV5-ATC) and without ATC (PSV5-noATC) and CPAP 5 mbar with ATC (CPAP5-ATC) and without ATC (CPAP5-noATC). The flow signal and airway pressure were measured with a pneumotachograph (Fleisch) and an analogue pressure transducer, respectively. Pressure time products per breath (PTP/b) and per minute (PTP/m) were calculated measuring esophageal pressure swings in the last minutes of each period.

Results

There were no significant differences in the breathing pattern (respiratory rate [RF], inspiratory time vs total respiratory time [Ti/Ttot], tidal volume [Vt], and peak flow [PF]) in any mode. Peak inspiratory pressure (PIP) was significantly higher in PSV5-ATC (12.8 mbar ± 1.5*^$# compared with PSV5-noATC (10.3 mbar ± 0.5^$#). PIP during PSV5-noATC was significantly higher than CPAP5-ATC (8.3 mbar ± 1.5^#).

There was a significant reduction in PTP/min (mbar/s/min) during PSV5-ATC (71.6 ± 38.4*^$#) compared with all other modes. During PSV5-no ATC the PTP/min was significantly lower than in CPAP5-ATC (115.2 ± 58.2^$# vs 170.5 ± 97.7). There was no significant difference in PTP/min in CPAP5 with or without ATC.

Statistics

Values given as mean ± SD: *P < 0.05 vs PSV-no ATC; ^$P < 0.05 vs CPAP-ATC; ^#P < 0.05 vs CPAP-noATC.

Conclusions

In intubated spontaneously breathing patients, work of breathing was clearly reduced using ATC in addition to PSV. CPAP5-ATC was less effective than PSV5 without ATC.

ATC without PSV did not compensate for nonlinear resistance of the tube as there was no difference in PTP during CPAP with or without ATC.