RAPID RATE VENTILATION (RRV) POTENTIALLY REDUCES BAROTRAUMA (BT) SOURCES IN RDS:

It has been suggested that RRV with short inspiratory time reduces barotrauma. We have shown that during RRV of a normal lung the peak inspiratory (PIP) and mean airway (Paw) pressures transmitted to the trachea were reduced, however, inadvertent PEEP and alveolar overdistention (AO) were produced. We were concerned that similar phenomena would occur in RDS. Therefore we measured tracheal PIP (PIPT), PEEPT, PawT, functional residual capacity (FRC), PaO2 and PaCO2 in 13 rabbits inoculated with N-nitroso N-methylurethane (which produces alveolar epithelial necrosis, atelectasis and hyaline membranes), paralyzed with Pavulon, intubated with a 3.0 mm ID ET tube and mechanically ventilated (Baby Bird®) at 30, 60 and 90 BPM, with constant inspiration:expiration time of 1:2, constant PIP, and PEEP, and 0.5 FiO2. From 30 to 90, BPM PIPT and PawT decreased significantly from 26±2(SE) to 21±2 and 10.5±0.5 to 9.7±0.5 cm H20 (p<0.01). PEEPT increased from 4.0 to 4.8±0.2 cm H2O but FRC remained unchanged. Although PEEPT increased, this increase was offset by the decrease in PIPT such that Paw decreased. PaO2 increased significantly from 103±11 to 117±11 mm Hg even though PawT decreased. PaCO2 decreased significantly from 43±4 to 24±2 mm Hg even though driving pressures (PIPT-PEEPT) decreased. We conclude that RRV of this RDS model dies not lead to inadvertent PEEP or AO and results in the reduction of several potential sources of BT.