FAST VERSUS SLOW VENTILATION FOR NEONATES

To investigate the effect of ventilation rate on respiratory mechanics , 21 neonates ventilated in the neonatal period for various reasons we re studied while being ventilated at 30 and 80 breaths/min. Dynamic re spiratory system elasticity (ERS), dynamic respiratory system resistan ce (RRS), and alveolar pressure at end expiration (EEP) were calculate d by using multilinear regression to fit the equation of motion of a l inear single-compartment model. Technically satisfactory data were obt ained from 13 neonates. With the fast ventilation rate, tidal volume a nd RRS decreased by a mean of 41.3% (p < 0.01) and 17.5% (p < 0.01), r espectively, ERS and EEP increased by a mean of 8.3% (p < 0.05) and 22 .2% (p < 0.01), respectively. Fast ventilation produced a shorter effe ctive time constant during expiration, limiting the changes in EEP and , hence, in end-expiratory lung volume. The same changes in respirator y mechanics were also observed in neonates who did not show an increas e in EEP even at high frequency. These neonates had a high elastance a nd time constant short enough to ensure adequate lung emptying. These results suggest that the respiratory mechanics of ventilated neonates are frequency dependent and that neonates with higher ERS, such as tho se with hyaline membrane disease, can cope with fast rate ventilation without developing dynamic hyperinflation.